![understanding, if we do not lay to heart the lesson which He has now
given us (Ps. cxlvi. 3). II. The pettiness of party strife. How much of
selfishness, unkindness, anger, and untruthfulness does the spirit of
party give birth to! How seldom politicians of opposite parties do each
other common justice! How fierce are their rivalries! But how mean,
how worthless, how unworthy appear the objects of their strife when
death enters the arenas and waves his skeleton arm! What a great calm
falls upon the agitated spirits of men! How noise is hushed and
excitement subdued! How like do the flushed and eager politicians
seem then to silly children quarrelling for the possession of a bubble
that has just been blown into the air, and that will disappear the
moment it is grasped![1] III. The vanity of the world, the certainty of
death, and the nearness of eternity. These lessons are taught when
a beggar dies, but are more likely to be laid to heart when a prince is
laid low.[2] IV. The supreme importance of a right moral character.
Most instructive is the interest felt by survivors in the moral character
of the departed, in the evidences of his preparation for death, in the
manner in which the great summons affected him. This is the
testimony of the human conscience, that in comparison with a fitness
to appear before the tribunal of God, everything else loses its
importance. When was the amount of a man’s possessions inscribed on
his tombstone? The bare suggestion of such a thing would be
construed as a mockery of death, under whose denuding hand the rich
man leaves the world naked as he entered it. But if, in all his life, there
was one virtue in his moral character, one trait which can afford
satisfactory evidence of God’s approval, this, be sure, you will find
sculptured in conspicuous characters on his monumental marble. One
thing alone can prepare any for their last account—the belief and
practice of the Gospel of God. Have you the great calm which is
inspired by the confidence of being prepared for the great change?—W.
Adams, American National Preacher, xv. 97–105.
FOOTNOTES:](https://image.slidesharecdn.com/2492-250625093440-8a0e233b/85/Computer-Networks-and-Internets-6th-Edition-Ebook-PDF-28-320.jpg)
![[1] Here, like a shepherd gazing from his hut,
Touching his reed, or leaning on his staff,
Eager Ambition’s fiery chase I see;
I see the circling hunt of noisy men
Burst law’s enclosure, leap the mounts of right,
Pursuing and pursued, each other’s prey;
As wolves for rapine; as the fox for wiles;
Till Death, that mighty hunter, earths them all.
Why all this toil for triumphs of an hour?
What though we wade in wealth, or soar in fame?
Earth’s highest station ends in “Here he lies”—
And “Dust to dust” concludes her noblest song.—Young.
[2] The glories of our birth and state
Are shadows, not substantial things;
There is no armour against fate:
Death lays his icy hand on kings;
Sceptre and crown
Must tumble down,
And in the dust be equal made
With the poor crooked scythe and spade.
Some men with swords may reap the field,
And plant fresh laurels where they kill;
But their strong nerves at last must yield:
They tame but one another still;
Early or late
They stoop to fate,
And must give up their murmuring breath,
When they, pale captives, creep to death.
The garlands wither on your brow;
Then boast no more your mighty deeds;
Upon death’s purple altar, now,
See where the victor victim bleeds!
All heads must come
To the cold tomb!
Only the actions of the just
Smell sweet and blossom in the dust.—Shirley.](https://image.slidesharecdn.com/2492-250625093440-8a0e233b/85/Computer-Networks-and-Internets-6th-Edition-Ebook-PDF-29-320.jpg)
![The Death of Statesmen.
(Funeral Sermon for the Right Hon. George Canning.)
iii. 1–3. For, behold, the Lord, the Lord of hosts, doth take
away from Jerusalem and from Judah . . . the
counsellor, . . . and the eloquent orator.
By the death of a great statesman at the head of a government, we are
reminded.—I. Of the weight of government in a fallen world. It is a
burden that has crushed many, and has brought them to an untimely
grave. II. Of the weakness of the shoulders of mortal men. The
government of a single country, especially in troublous times, has
proved a burden too great for the courage and the endurance of the
strongest of men. III. Of the uncertainty of all human affairs. Often
does the statesman think of the uncertainty of arriving at the object of
his ambition, but seldom of the uncertainty of his remaining there,
except when he recollects how many are struggling to replace him.
Little does he think of another foe, who lurks behind, and who in some
unexpected moment will hush his eloquent tongue, and turn his fertile
brain to dust. IV. Of our absolute dependence on the Supreme
Governor. We are apt to think that it is on the profound counsellor
and mighty orator that the nation’s welfare depends, and to think little
of Him who made them what they are, to be employed as He pleases,
laid aside when He pleases, and replaced if He pleases, by others as
richly endowed. V. Of the necessity of personal preparation for
death.[1]—J. Bennett, D.D., The British Pulpit, i. 297–304.
FOOTNOTES:
[1] So live, that, when thy summons comes to join
The innumerable caravan, that moves
To that mysterious realm where each shall take
His chamber in the silent halls of death,
Thou go not like the quarry slave at night
Scourged to his dungeon; but, sustained and soothed](https://image.slidesharecdn.com/2492-250625093440-8a0e233b/85/Computer-Networks-and-Internets-6th-Edition-Ebook-PDF-30-320.jpg)
![assumed, just as the rustic traveller when near a churchyard whistles,
not because he is courageous, but to keep his courage up. Conscience
reproaches and warns, and the sinner seeks to silence it by greater
desperation in wickedness. 4. A seared conscience. In the course just
named the sinner too often succeeds. Conscience, defied and outraged,
desists from her useless efforts, and gives herself over to an insensible
lethargy; there will come an hour of terrible awakening; but meanwhile
she is blind, deaf, dumb, and the sinner perpetrates the most
abominable iniquities without a blush.[1] 5. Infidelity. The sinner has
succeeded at last in persuading himself that what he wishes were true
is true, and that there is no God, and, consequently, no day of
judgment and no hell. As soon as men have cast off fear of God, it is
easy for them to cast off fear of men. The ordinary fruit of infidelity is
vice. What but prudence is left to restrain the infidel from partaking in
the pleasures of sin? And how weak prudence is in any real contest
with passion!
II. The Consequences of Shamelessness in Sin.
This is declared by the prophet to be woe—woe of peculiar intensity
and awfulness. “Woe unto their soul!” &c. They stand in peril of the
severest chastisements of the Divine justice—1. Because
shamelessness in sin is an aggravation of sin. It is felt to be so in
the home, in the nation. Disloyalty is an evil thing, but to break forth
into open rebellion, and to take the field against the monarch, is worse.
2. Because shamelessness in sin adds to the contagiousness of
sin. One reason why sin is so hateful in the sight of God is because it
renders every sinner a moral pestilence. Corrupt, he corrupts others
(Eccles. ix. 18). But of shameless sinners this is especially true. (1) They
lead many to imitate them in their wickedness. In every community
these shameless sinners are ringleaders in vice and recruiting-sergeants
for the devil. (2) They confirm many in wickedness. Many are “halting
between two opinions,” and these shameless offenders, by their
example, and often by their persuasions, supply that which is needed
to bring these irresolute ones to a decision for a life of iniquity. Thus
they are soul-murderers as well as soul-suicides. Justice, therefore,](https://image.slidesharecdn.com/2492-250625093440-8a0e233b/85/Computer-Networks-and-Internets-6th-Edition-Ebook-PDF-34-320.jpg)
![FOOTNOTES:
[1] Blind and ignorant consciences speak peace, or hold their peace,
because they have not skill enough to find fault; they swallow many
a fly, and digest all well enough. While the scales were upon Paul’s
eyes, he was alive and quiet; he thought concupiscence, the sin and
breeder of all sin, to be no sin. Such consciences discern sin as we do
stars in a dark night,—see only the great ones of the first
magnitude, whereas a bright even discovers millions; or as we see a
few motes in the dark houses, which sunlight shows to be infinite.
Such think good meaning will serve the turn, that all religions will
save, or a “Lord, have mercy on us,” at the last gasp. The law which
nature has engraven, they tread out with sins, as men do the
engravings of tombs they walk on with foul shoes: they dare not
look in the glass of God’s law, which makes sin abound, lest the
foolishness of their souls should affright them. A number of such
sottish souls there be, whose consciences, if God opens, as He did
the eyes of the prophet’s servant, they shall see armies and legions
of sins and devils in them.—Ward, 1577–1639.
Cheering Words and Solemn Warnings.
iii. 10, 11. Say ye to the righteous, that it shall be well with
him; for they shall eat of the fruit of their own doings.
Woe unto the wicked! it shall be ill with them; for the
reward of his hands shall be given him.
Into these two orders, the righteous and the wicked, the Bible is
accustomed to divide the whole population of the globe.—A crimson
line runs between the righteous and the wicked, the line of atoning
sacrifice: faith crosses that line, but nothing else can. There can be no
righteousness where there is no faith.—This distinction is so sharp and
definite, that no man can dwell in a borderland between the two
conditions. A clear line of demarcation exists between life and death,
and such a division is fixed by God between the righteous and the](https://image.slidesharecdn.com/2492-250625093440-8a0e233b/85/Computer-Networks-and-Internets-6th-Edition-Ebook-PDF-36-320.jpg)
![is well with the righteous in life, well when he comes to die, and well
after death. 6. The blessedness of the righteous rest upon a solid
ground. The text says, “they shall eat the fruit of their doings.” Those
are the only terms upon which the old covenant can promise that it
shall be well with us; but this is not the ground upon which you and I
stand under the gospel dispensation. Absolutely to eat the fruit of our
doings would be even to us, if judgment were brought to the line and
righteousness to the plummet, a very dreadful thing. Yet there is a
limited sense in which the righteous man will do this. “I was an
hungered, and ye gave me meat,” &c., is good gospel language; and
when the Master shall say, “Inasmuch as ye did this unto one of the
least of these my people, ye did it unto me,” the reward will not be of
debt, but still it will be a reward, and the righteous will eat the fruit of
his doings. I prefer, however, to remark, that there is One whose doings
for us is the grounds of our dependence, and we shall eat of the fruit of
His doings.
II. The misery of the wicked. To expound the woe pronounced
against him, you have only to negative all that I have already said about
the righteous. It is ill with the wicked; always ill with him; and it shall
be ill with him for ever.[1] But why is it ill with the wicked? 1. He is out
of joint with all the world. Ordinary creatures are obedient to God, but
he has set himself in opposition to the whole current of creation. 2. He
has an enemy who is omnipotent. 3. His joys all hang on a thread. Let
life’s thread be cut, and where are his merriments? 4. After these joys
are over, he has no more to come. 5. Of all the comforts and hopes of
the righteous, he is utterly destitute.—C. H. Spurgeon, Metropolitan
Tabernacle Pulpit, vol. xiii. 13–24.
FOOTNOTES:
[1] Many sinners who seem so jocund in our eyes have not such
merry lives as you think. A book may be fairly bound and gilded, yet
have but sad stories writ within it. Sinners will not tell us all the
secret rebukes that conscience gives them. If you will judge of
Herod by the jollity of his feast, you may think he wanted no joy;](https://image.slidesharecdn.com/2492-250625093440-8a0e233b/85/Computer-Networks-and-Internets-6th-Edition-Ebook-PDF-38-320.jpg)
![iii. 12. O my people, they which lead thee[1] cause thee to
err, and destroy the way of thy paths.
This is at once a lament and a condemnation—a lament over the
misfortunes of those who are misguided, a condemnation of their folly
and wickedness in permitting themselves to be led astray. I. Men need
to be led. 1. This is our need as individuals. Every day we need an
answer to the questions, What ought I to do? Which way should I go?
In the journey of life, we continually come to crossings at which we are
conscious of our need of guidance. 2. Guidance is still more necessary
for men collectively. What shall be the belief of a community? What its
action? Like the apostolic band (John xxi. 2, 3) communities remain
idle, undecided, until the born leader says, “I go a-fishing,” and
instantly they say to him, “We also go with thee.” Men are naturally
gregarious; like a flock of sheep they crowd and inconvenience each
other, not knowing which way to turn, until one bolder than the rest
breaks away from the flock, and then instantly the flock begins to
follow him. II. As a rule men are misled. Boldness and wisdom do
not always go together. Not seldom the courage which prompts men to
become the leaders of others, and which goes so far to command the
assent of others, is a compound of self-conceit and ignorance. Men are
always prone to trust in the self-confident: they will believe the
boastful quack rather than the diffident philosopher. Hence in all ages
men have been caused to err—the blind have been led by the blind.
How true this is to-day in political matters, in social, in commercial, in
religious! [Give instances.] On every hand, in all these realms of
thought and action, there are those who can only rightly be described
as leaders who cause the people to err. Yes, all men carry within them
two leaders, in whom they are disposed implicitly to trust, but by
whom in the majority of instances they are misled—reason and
conscience. How absolute is the confidence placed in these guides, and
how seldom it is justified! III. To be misled is one of the most
terrible of evils. 1. It involves the loss of all the good to which right
leadership would have conducted men. 2. It involves disappointment,
shame, sorrow, and often irretrievable ruin. 3. It plunges men into
painful perplexities, so that even when they have begun to suspect that](https://image.slidesharecdn.com/2492-250625093440-8a0e233b/85/Computer-Networks-and-Internets-6th-Edition-Ebook-PDF-43-320.jpg)
![the path they are pursuing is erroneous, they know not how to discover
the true one; it seems to them to be “destroyed;” they search for it in
vain. They are like travellers who, in the darkness following Will-of-the-
Wisp, have strayed from the highway into a morass: to stand still is
impossible, and yet to step in any direction, may plunge them into
worse perils (Matt. xv. 14). How criminal is the conduct of those who
betray their fellow-men into misery such as this!
In view of these facts, 1. We should not entrust ourselves to the first
guide who offers himself to us. Let us examine the credentials of those
who ask us to trust ourselves to their care (Matt. xxiv. 24; 1 John iv. 1–3;
Isa. viii. 20). 2. In weighing the claims of men to be our leaders, we
should have regard supremely to their moral qualifications. Their
intellectual competency is, of course, not to be disregarded, but moral
character is infinitely more important. Not all good men are fitted to be
leaders; but no bad man can be safely followed by others. He is
continually apt to be guided by policy, rather than principle, and policy
leads to perdition.[2] Policy is at the best but guess-work—steering by
the current; the man who is governed by principle steers by the stars,
and neither can be long misled, nor will he wilfully mislead others.
Practical Application.—Never vote for any candidate for a public office,
however clever he may be, if his integrity is doubtful. 3. Every man
needs guidance more close and intimate than any of his fellow-men can
afford him: he needs to be led even in choosing his leaders. Whither
shall he look for this guidance? To his reason, his conscience? These
guides themselves need instruction:[3] in the absence of it, they have
led millions to perdition. We need supernatural and sure guidance,
and we have it (1) in God’s Word, and (2) in God’s Spirit (Prov. iii. 5, 6).
The man who follows these guides will be led always in the paths of
righteousness and peace.
FOOTNOTES:
[1] The marginal reading, “they which call thee happy” (Mal. iii. 12,
15), represents vividly the method adopted by the false prophets;](https://image.slidesharecdn.com/2492-250625093440-8a0e233b/85/Computer-Networks-and-Internets-6th-Edition-Ebook-PDF-44-320.jpg)
![who, instead of warning the people against the dangers of
prosperity, were ever felicitating them upon it, saying, “Peace,
peace, when there was no peace.” But the textual rendering appears
to be the preferable one.—Kay.
[2] Men know where they are going when they follow a principle;
because principles are rays of light. If you trace a ray of light in all its
reflections, you will find that it runs back to the central sun; and
every great line of honesty, every great line of honour, runs back
towards the centre of God. And the man that follows these things
knows that he is steering right Godward. But the man that follows
policies, and worldly maxims, does not know where he is steering,
except that in general he is steering toward the devil.—Beecher.
[3] Reason is God’s candle in men. But, as a candle must first be
lighted, ere it will enlighten, so reason must be illuminated by
Divine grace, ere it can savingly discern spiritual things.—Toplady,
1740–1778.
Conscience, as an expression of the law or will and mind of God, is
not now to be implicitly depended on. It is not infallible. What was
true of its office in Eden, has been deranged and shattered by the
fall; and now lies, as I have seen a sun-dial in the neglected garden
of an old, desolate ruin, thrown down from its pedestal, prostrate on
the ground, and covered by tall, rank weeds. So far from being since
that fatal event an infallible directory of duty, conscience has often
lent its sanction to the grossest errors, and prompted to the greatest
crimes. Did not Saul of Tarsus, for instance, hale men and women
to prison; compel them to blaspheme; and imbrue his hands in
saintly blood, while conscience approved the deed—he judging the
while that he did God service? What wild and profane imaginations
has it accepted as the oracles of God? and as if fiends had taken
possession of a God-deserted shrine, have not the foulest crimes, as
well as the most shocking cruelties, been perpetrated in its name?
Read the Book of Martyrs, read the sufferings of our forefathers;
and, under the cowl of a shaven monk, or the trappings of a haughty
Churchman, you shall see conscience persecuting the saints of God,
and dragging even tender women and children to the bloody
scaffold or the burning stake. With eyes swimming in tears, or
flashing fire, we close the painful record, to apply to Conscience the
words addressed to Liberty by the French heroine, when, passing its
statue, she rose in the cart that bore her to the guillotine, and
throwing up her arms, exclaimed, “O Liberty, what crimes have
been done in thy name!” And what crimes in thine, O Conscience!](https://image.slidesharecdn.com/2492-250625093440-8a0e233b/85/Computer-Networks-and-Internets-6th-Edition-Ebook-PDF-45-320.jpg)
![subjects, people their pastors. The oppression has often been so
terrible that the oppressed have sought refuge in suicide.
“Man’s cruelty to man
Makes countless thousands mourn.”
II. Oppression of the poor is one of the most hateful of all sins.
1. It is a misuse of strength. Strength is given to men that they may be
helpful to each other; but the oppressor uses his strength as if he were
a tiger or a wolf; as if he were a wrecker who drowns the shipwrecked
mariner whom he ought to rescue. 2. It is a cowardly and shameful
advantage that is taken of human weakness. To lead a blind man into a
quagmire or over a precipice would be thought a shameful act, even by
the most degraded villains. But in what respect would it differ in
principle from oppression of the poor? The weak and needy, by reason
of their feebleness and poverty, have a claim upon our pity and help; to
oppress them is to outrage the primary laws of conscience. Yet how
often it is done!
III. Oppression of the poor is among those sins which are certain
to be most terribly punished. The oppressor proceeds on the idea,
that the man whom he oppresses has no friends to succour and avenge
him. What a mistake! All the oppressed have a friend and avenger in
God. Shall oppression go unrequited? Nay, verily! For, 1. It is an offence
against God’s laws. He has distinctly commanded us to love our
neighbour as ourselves, and how manifold are the applications of this
great commandment! 2. It is an offence against God’s feelings. In a
peculiar manner His sensibilities are outraged when His children act
cruelly towards each other. Oppression of the poor kindles within Him
mingled disgust and indignation.[1]
Application. 1. A new consideration of our text would deter men from
the sin here denounced. The question which God now addresses to
oppressors He will, with a slight difference, put to them again—when
they shall be gathered at His bar! “What meant ye that ye did beat my
people to pieces, and did grind the faces of the poor?” Bethink you, O
ye oppressors, what will ye answer then? Will it be, “Lord, we thought](https://image.slidesharecdn.com/2492-250625093440-8a0e233b/85/Computer-Networks-and-Internets-6th-Edition-Ebook-PDF-47-320.jpg)
Computer Networks and Internets 6th Edition, (Ebook PDF)
- 1. Computer Networks and Internets 6th Edition, (Ebook PDF) download pdf https://ebookmass.com/product/computer-networks-and-internets-6th- edition-ebook-pdf/ Visit ebookmass.com today to download the complete set of ebook or textbook!
- 3. Contents xxiii Preface PART I Introduction And Internet Applications 1 Chapter 1 Introduction And Overview 1.1 Growth Of Computer Networking 1 1.2 Why Networking Seems Complex 2 1.3 The Five Key Aspects Of Networking 2 1.4 Public And Private Parts Of The Internet 6 1.5 Networks, Interoperability, And Standards 8 1.6 Protocol Suites And Layering Models 9 1.7 How Data Passes Through Layers 11 1.8 Headers And Layers 12 1.9 ISO And The OSI Seven Layer Reference Model 13 1.10 Remainder Of The Text 14 1.11 Summary 14 17 Chapter 2 Internet Trends 2.1 Introduction 17 2.2 Resource Sharing 17 2.3 Growth Of The Internet 18 2.4 From Resource Sharing To Communication 21 2.5 From Text To Multimedia 21 2.6 Recent Trends 22 2.7 From Individual Computers To Cloud Computing 23 2.8 Summary 24 27 Chapter 3 Internet Applications And Network Programming 3.1 Introduction 27 3.2 Two Basic Internet Communication Paradigms 28
- 4. viii Contents 3.3 Connection-Oriented Communication 29 3.4 The Client-Server Model Of Interaction 30 3.5 Characteristics Of Clients And Servers 31 3.6 Server Programs And Server-Class Computers 31 3.7 Requests, Responses, And Direction Of Data Flow 32 3.8 Multiple Clients And Multiple Servers 32 3.9 Server Identification And Demultiplexing 33 3.10 Concurrent Servers 34 3.11 Circular Dependencies Among Servers 35 3.12 Peer-To-Peer Interactions 35 3.13 Network Programming And The Socket API 36 3.14 Sockets, Descriptors, And Network I/O 36 3.15 Parameters And The Socket API 37 3.16 Socket Calls In A Client And Server 38 3.17 Socket Functions Used By Both Client And Server 38 3.18 The Connect Function Used Only By A Client 40 3.19 Socket Functions Used Only By A Server 40 3.20 Socket Functions Used With The Message Paradigm 43 3.21 Other Socket Functions 44 3.22 Sockets, Threads, And Inheritance 45 3.23 Summary 45 49 Chapter 4 Traditional Internet Applications 4.1 Introduction 49 4.2 Application-Layer Protocols 49 4.3 Representation And Transfer 50 4.4 Web Protocols 51 4.5 Document Representation With HTML 52 4.6 Uniform Resource Locators And Hyperlinks 54 4.7 Web Document Transfer With HTTP 55 4.8 Caching In Browsers 57 4.9 Browser Architecture 59 4.10 File Transfer Protocol (FTP) 59 4.11 FTP Communication Paradigm 60 4.12 Electronic Mail 63 4.13 The Simple Mail Transfer Protocol (SMTP) 64 4.14 ISPs, Mail Servers, And Mail Access 66 4.15 Mail Access Protocols (POP, IMAP) 67 4.16 Email Representation Standards (RFC2822, MIME) 67 4.17 Domain Name System (DNS) 69 4.18 Domain Names That Begin With A Service Name 71 4.19 The DNS Hierarchy And Server Model 72 4.20 Name Resolution 72 4.21 Caching In DNS Servers 74
- 5. Contents ix 4.22 Types Of DNS Entries 75 4.23 Aliases And CNAME Resource Records 76 4.24 Abbreviations And The DNS 76 4.25 Internationalized Domain Names 77 4.26 Extensible Representations (XML) 78 4.27 Summary 79 PART II Data Communication Basics 85 Chapter 5 Overview Of Data Communications 5.1 Introduction 85 5.2 The Essence Of Data Communications 86 5.3 Motivation And Scope Of The Subject 87 5.4 The Conceptual Pieces Of A Communications System 87 5.5 The Subtopics Of Data Communications 90 5.6 Summary 91 93 Chapter 6 Information Sources And Signals 6.1 Introduction 93 6.2 Information Sources 93 6.3 Analog And Digital Signals 94 6.4 Periodic And Aperiodic Signals 94 6.5 Sine Waves And Signal Characteristics 95 6.6 Composite Signals 97 6.7 The Importance Of Composite Signals And Sine Functions 97 6.8 Time And Frequency Domain Representations 98 6.9 Bandwidth Of An Analog Signal 99 6.10 Digital Signals And Signal Levels 100 6.11 Baud And Bits Per Second 101 6.12 Converting A Digital Signal To Analog 102 6.13 The Bandwidth Of A Digital Signal 103 6.14 Synchronization And Agreement About Signals 103 6.15 Line Coding 104 6.16 Manchester Encoding Used In Computer Networks 106 6.17 Converting An Analog Signal To Digital 107 6.18 The Nyquist Theorem And Sampling Rate 108 6.19 Nyquist Theorem And Telephone System Transmission 108 6.20 Nonlinear Encoding 109 6.21 Encoding And Data Compression 109 6.22 Summary 110
- 6. x Contents 113 Chapter 7 Transmission Media 7.1 Introduction 113 7.2 Guided And Unguided Transmission 113 7.3 A Taxonomy By Forms Of Energy 114 7.4 Background Radiation And Electrical Noise 115 7.5 Twisted Pair Copper Wiring 115 7.6 Shielding: Coaxial Cable And Shielded Twisted Pair 117 7.7 Categories Of Twisted Pair Cable 118 7.8 Media Using Light Energy And Optical Fibers 119 7.9 Types Of Fiber And Light Transmission 120 7.10 Optical Fiber Compared To Copper Wiring 121 7.11 Infrared Communication Technologies 122 7.12 Point-To-Point Laser Communication 122 7.13 Electromagnetic (Radio) Communication 123 7.14 Signal Propagation 124 7.15 Types Of Satellites 125 7.16 Geostationary Earth Orbit (GEO) Satellites 126 7.17 GEO Coverage Of The Earth 127 7.18 Low Earth Orbit (LEO) Satellites And Clusters 128 7.19 Tradeoffs Among Media Types 128 7.20 Measuring Transmission Media 129 7.21 The Effect Of Noise On Communication 129 7.22 The Significance Of Channel Capacity 130 7.23 Summary 131 135 Chapter 8 Reliability And Channel Coding 8.1 Introduction 135 8.2 The Three Main Sources Of Transmission Errors 135 8.3 Effect Of Transmission Errors On Data 136 8.4 Two Strategies For Handling Channel Errors 137 8.5 Block And Convolutional Error Codes 138 8.6 An Example Block Error Code: Single Parity Checking 139 8.7 The Mathematics Of Block Error Codes And (n,k) Notation 140 8.8 Hamming Distance: A Measure Of A Code’s Strength 140 8.9 The Hamming Distance Among Strings In A Codebook 141 8.10 The Tradeoff Between Error Detection And Overhead 142 8.11 Error Correction With Row And Column (RAC) Parity 142 8.12 The 16-Bit Checksum Used In The Internet 144 8.13 Cyclic Redundancy Codes (CRCs) 145 8.14 An Efficient Hardware Implementation Of CRC 148 8.15 Automatic Repeat Request (ARQ) Mechanisms 148 8.16 Summary 149
- 7. Contents xi 153 Chapter 9 Transmission Modes 9.1 Introduction 153 9.2 A Taxonomy Of Transmission Modes 153 9.3 Parallel Transmission 154 9.4 Serial Transmission 155 9.5 Transmission Order: Bits And Bytes 156 9.6 Timing Of Serial Transmission 156 9.7 Asynchronous Transmission 157 9.8 RS-232 Asynchronous Character Transmission 157 9.9 Synchronous Transmission 158 9.10 Bytes, Blocks, And Frames 159 9.11 Isochronous Transmission 160 9.12 Simplex, Half-Duplex, And Full-Duplex Transmission 160 9.13 DCE And DTE Equipment 162 9.14 Summary 162 165 Chapter 10 Modulation And Modems 10.1 Introduction 165 10.2 Carriers, Frequency, And Propagation 165 10.3 Analog Modulation Schemes 166 10.4 Amplitude Modulation 166 10.5 Frequency Modulation 167 10.6 Phase Shift Modulation 168 10.7 Amplitude Modulation And Shannon’s Theorem 168 10.8 Modulation, Digital Input, And Shift Keying 168 10.9 Phase Shift Keying 169 10.10 Phase Shift And A Constellation Diagram 171 10.11 Quadrature Amplitude Modulation 173 10.12 Modem Hardware For Modulation And Demodulation 174 10.13 Optical And Radio Frequency Modems 174 10.14 Dialup Modems 175 10.15 QAM Applied To Dialup 175 10.16 V.32 And V.32bis Dialup Modems 176 10.17 Summary 177 181 Chapter 11 Multiplexing And Demultiplexing (Channelization) 11.1 Introduction 181 11.2 The Concept Of Multiplexing 181 11.3 The Basic Types Of Multiplexing 182 11.4 Frequency Division Multiplexing (FDM) 183
- 8. xii Contents 11.5 Using A Range Of Frequencies Per Channel 185 11.6 Hierarchical FDM 186 11.7 Wavelength Division Multiplexing (WDM) 187 11.8 Time Division Multiplexing (TDM) 187 11.9 Synchronous TDM 188 11.10 Framing Used In The Telephone System Version Of TDM 189 11.11 Hierarchical TDM 190 11.12 The Problem With Synchronous TDM: Unfilled Slots 190 11.13 Statistical TDM 191 11.14 Inverse Multiplexing 192 11.15 Code Division Multiplexing 193 11.16 Summary 195 199 Chapter 12 Access And Interconnection Technologies 12.1 Introduction 199 12.2 Internet Access Technology: Upstream And Downstream 199 12.3 Narrowband And Broadband Access Technologies 200 12.4 The Local Loop And ISDN 202 12.5 Digital Subscriber Line (DSL) Technologies 202 12.6 Local Loop Characteristics And Adaptation 203 12.7 The Data Rate Of ADSL 204 12.8 ADSL Installation And Splitters 205 12.9 Cable Modem Technologies 205 12.10 The Data Rate Of Cable Modems 206 12.11 Cable Modem Installation 206 12.12 Hybrid Fiber Coax 207 12.13 Access Technologies That Employ Optical Fiber 208 12.14 Head-End And Tail-End Modem Terminology 208 12.15 Wireless Access Technologies 209 12.16 High-Capacity Connections At The Internet Core 209 12.17 Circuit Termination, DSU / CSU, And NIU 210 12.18 Telephone Standards For Digital Circuits 211 12.19 DS Terminology And Data Rates 212 12.20 Highest Capacity Circuits (STS Standards) 212 12.21 Optical Carrier Standards 213 12.22 The C Suffix 213 12.23 Synchronous Optical Network (SONET) 214 12.24 Summary 215
- 9. Contents xiii PART III Packet Switching And Network Technologies 219 Chapter 13 Local Area Networks: Packets, Frames, And Topologies 13.1 Introduction 219 13.2 Circuit Switching And Analog Communication 220 13.3 Packet Switching 221 13.4 Local And Wide Area Packet Networks 222 13.5 Standards For Packet Format And Identification 223 13.6 IEEE 802 Model And Standards 224 13.7 Point-To-Point And Multi-Access Networks 225 13.8 LAN Topologies 227 13.9 Packet Identification, Demultiplexing, MAC Addresses 229 13.10 Unicast, Broadcast, And Multicast Addresses 230 13.11 Broadcast, Multicast, And Efficient Multi-Point Delivery 231 13.12 Frames And Framing 232 13.13 Byte And Bit Stuffing 233 13.14 Summary 234 239 Chapter 14 The IEEE MAC Sublayer 14.1 Introduction 239 14.2 A Taxonomy Of Mechanisms For Shared Access 239 14.3 Static And Dynamic Channel Allocation 240 14.4 Channelization Protocols 241 14.5 Controlled Access Protocols 242 14.6 Random Access Protocols 244 14.7 Summary 250 253 Chapter 15 Wired LAN Technology (Ethernet And 802.3) 15.1 Introduction 253 15.2 The Venerable Ethernet 253 15.3 Ethernet Frame Format 254 15.4 Ethernet Frame Type Field And Demultiplexing 254 15.5 IEEE’s Version Of Ethernet (802.3) 255 15.6 LAN Connections And Network Interface Cards 256 15.7 Ethernet Evolution And Thicknet Wiring 256 15.8 Thinnet Ethernet Wiring 257 15.9 Twisted Pair Ethernet Wiring And Hubs 258 15.10 Physical And Logical Ethernet Topology 259 15.11 Wiring In An Office Building 259
- 10. xiv Contents 15.12 Ethernet Data Rates And Cable Types 261 15.13 Twisted Pair Connectors And Cables 261 15.14 Summary 262 265 Chapter 16 Wireless Networking Technologies 16.1 Introduction 265 16.2 A Taxonomy Of Wireless Networks 265 16.3 Personal Area Networks (PANs) 266 16.4 ISM Wireless Bands Used By LANs And PANs 267 16.5 Wireless LAN Technologies And Wi-Fi 267 16.6 Spread Spectrum Techniques 268 16.7 Other Wireless LAN Standards 269 16.8 Wireless LAN Architecture 270 16.9 Overlap, Association, And 802.11 Frame Format 271 16.10 Coordination Among Access Points 272 16.11 Contention And Contention-Free Access 272 16.12 Wireless MAN Technology And WiMax 274 16.13 PAN Technologies And Standards 276 16.14 Other Short-Distance Communication Technologies 277 16.15 Wireless WAN Technologies 278 16.16 Micro Cells 280 16.17 Cell Clusters And Frequency Reuse 280 16.18 Generations Of Cellular Technologies 282 16.19 VSAT Satellite Technology 284 16.20 GPS Satellites 285 16.21 Software Defined Radio And The Future Of Wireless 286 16.22 Summary 287 291 Chapter 17 Repeaters, Bridges, And Switches 17.1 Introduction 291 17.2 Distance Limitation And LAN Design 291 17.3 Fiber Modem Extensions 292 17.4 Repeaters 293 17.5 Bridges And Bridging 293 17.6 Learning Bridges And Frame Filtering 294 17.7 Why Bridging Works Well 295 17.8 Distributed Spanning Tree 296 17.9 Switching And Layer 2 Switches 297 17.10 VLAN Switches 299 17.11 Multiple Switches And Shared VLANs 300 17.12 The Importance Of Bridging 301 17.13 Summary 302
- 11. Contents xv 305 Chapter 18 WAN Technologies And Dynamic Routing 18.1 Introduction 305 18.2 Large Spans And Wide Area Networks 305 18.3 Traditional WAN Architecture 306 18.4 Forming A WAN 308 18.5 Store And Forward Paradigm 309 18.6 Addressing In A WAN 309 18.7 Next-Hop Forwarding 310 18.8 Source Independence 313 18.9 Dynamic Routing Updates In A WAN 313 18.10 Default Routes 314 18.11 Forwarding Table Computation 315 18.12 Distributed Route Computation 316 18.13 Shortest Paths And Weights 320 18.14 Routing Problems 321 18.15 Summary 322 325 Chapter 19 Networking Technologies Past And Present 19.1 Introduction 325 19.2 Connection And Access Technologies 325 19.3 LAN Technologies 327 19.4 WAN Technologies 328 19.5 Summary 332 PART IV Internetworking 335 Chapter 20 Internetworking: Concepts, Architecture, And Protocols 20.1 Introduction 335 20.2 The Motivation For Internetworking 335 20.3 The Concept Of Universal Service 336 20.4 Universal Service In A Heterogeneous World 336 20.5 Internetworking 337 20.6 Physical Network Connection With Routers 337 20.7 Internet Architecture 338 20.8 Intranets And Internets 339 20.9 Achieving Universal Service 339 20.10 A Virtual Network 339 20.11 Protocols For Internetworking 341 20.12 Review Of TCP/IP Layering 341
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- 13. xvi Contents 20.13 Host Computers, Routers, And Protocol Layers 342 20.14 Summary 342 345 Chapter 21 IP: Internet Addressing 21.1 Introduction 345 21.2 The Move To IPv6 345 21.3 The Hourglass Model And Difficulty Of Change 346 21.4 Addresses For The Virtual Internet 346 21.5 The IP Addressing Scheme 348 21.6 The IP Address Hierarchy 348 21.7 Original Classes Of IPv4 Addresses 349 21.8 IPv4 Dotted Decimal Notation 350 21.9 Authority For Addresses 351 21.10 IPv4 Subnet And Classless Addressing 351 21.11 Address Masks 353 21.12 CIDR Notation Used With IPv4 354 21.13 A CIDR Example 354 21.14 CIDR Host Addresses 356 21.15 Special IPv4 Addresses 357 21.16 Summary Of Special IPv4 Addresses 359 21.17 IPv4 Berkeley Broadcast Address Form 359 21.18 Routers And The IPv4 Addressing Principle 360 21.19 Multihomed Hosts 361 21.20 IPv6 Multihoming And Network Renumbering 361 21.21 IPv6 Addressing 362 21.22 IPv6 Colon Hexadecimal Notation 363 21.23 Summary 364 369 Chapter 22 Datagram Forwarding 22.1 Introduction 369 22.2 Connectionless Service 369 22.3 Virtual Packets 370 22.4 The IP Datagram 370 22.5 The IPv4 Datagram Header Format 371 22.6 The IPv6 Datagram Header Format 373 22.7 IPv6 Base Header Format 373 22.8 Forwarding An IP Datagram 375 22.9 Network Prefix Extraction And Datagram Forwarding 376 22.10 Longest Prefix Match 377 22.11 Destination Address And Next-Hop Address 378 22.12 Best-Effort Delivery 378
- 14. Contents xvii 22.13 IP Encapsulation 379 22.14 Transmission Across An Internet 380 22.15 MTU And Datagram Fragmentation 381 22.16 Fragmentation Of An IPv6 Datagram 383 22.17 Reassembly Of An IP Datagram From Fragments 384 22.18 Collecting The Fragments Of A Datagram 385 22.19 The Consequence Of Fragment Loss 386 22.20 Fragmenting An IPv4 Fragment 386 22.21 Summary 387 391 Chapter 23 Support Protocols And Technologies 23.1 Introduction 391 23.2 Address Resolution 391 23.3 An Example Of IPv4 Addresses 393 23.4 The IPv4 Address Resolution Protocol (ARP) 393 23.5 ARP Message Format 394 23.6 ARP Encapsulation 395 23.7 ARP Caching And Message Processing 396 23.8 The Conceptual Address Boundary 398 23.9 Internet Control Message Protocol (ICMP) 399 23.10 ICMP Message Format And Encapsulation 400 23.11 IPv6 Address Binding With Neighbor Discovery 401 23.12 Protocol Software, Parameters, And Configuration 401 23.13 Dynamic Host Configuration Protocol (DHCP) 402 23.14 DHCP Protocol Operation And Optimizations 403 23.15 DHCP Message Format 404 23.16 Indirect DHCP Server Access Through A Relay 405 23.17 IPv6 Autoconfiguration 405 23.18 Network Address Translation (NAT) 406 23.19 NAT Operation And IPv4 Private Addresses 407 23.20 Transport-Layer NAT (NAPT) 409 23.21 NAT And Servers 410 23.22 NAT Software And Systems For Use At Home 410 23.23 Summary 411 415 Chapter 24 UDP: Datagram Transport Service 24.1 Introduction 415 24.2 Transport Protocols And End-To-End Communication 415 24.3 The User Datagram Protocol 416 24.4 The Connectionless Paradigm 417 24.5 Message-Oriented Interface 417
- 15. xviii Contents 24.6 UDP Communication Semantics 418 24.7 Modes Of Interaction And Multicast Delivery 419 24.8 Endpoint Identification With Protocol Port Numbers 419 24.9 UDP Datagram Format 420 24.10 The UDP Checksum And The Pseudo Header 421 24.11 UDP Encapsulation 421 24.12 Summary 422 425 Chapter 25 TCP: Reliable Transport Service 25.1 Introduction 425 25.2 The Transmission Control Protocol 425 25.3 The Service TCP Provides To Applications 426 25.4 End-To-End Service And Virtual Connections 427 25.5 Techniques That Transport Protocols Use 428 25.6 Techniques To Avoid Congestion 432 25.7 The Art Of Protocol Design 433 25.8 Techniques Used In TCP To Handle Packet Loss 434 25.9 Adaptive Retransmission 435 25.10 Comparison Of Retransmission Times 436 25.11 Buffers, Flow Control, And Windows 437 25.12 TCP’s Three-Way Handshake 438 25.13 TCP Congestion Control 440 25.14 Versions Of TCP Congestion Control 441 25.15 Other Variations: SACK And ECN 441 25.16 TCP Segment Format 442 25.17 Summary 443 447 Chapter 26 Internet Routing And Routing Protocols 26.1 Introduction 447 26.2 Static Vs. Dynamic Routing 447 26.3 Static Routing In Hosts And A Default Route 448 26.4 Dynamic Routing And Routers 449 26.5 Routing In The Global Internet 450 26.6 Autonomous System Concept 451 26.7 The Two Types Of Internet Routing Protocols 451 26.8 Routes And Data Traffic 454 26.9 The Border Gateway Protocol (BGP) 454 26.10 The Routing Information Protocol (RIP) 456 26.11 RIP Packet Format 457 26.12 The Open Shortest Path First Protocol (OSPF) 458 26.13 An Example OSPF Graph 459
- 16. Contents xix 26.14 OSPF Areas 459 26.15 Intermediate System - Intermediate System (IS-IS) 460 26.16 Multicast Routing 461 26.17 Summary 465 PART V Other Networking Concepts & Technologies 469 Chapter 27 Network Performance (QoS And DiffServ) 27.1 Introduction 469 27.2 Measures Of Performance 469 27.3 Latency Or Delay 470 27.4 Capacity, Throughput, And Goodput 472 27.5 Understanding Throughput And Delay 473 27.6 Jitter 474 27.7 The Relationship Between Delay And Throughput 475 27.8 Measuring Delay, Throughput, And Jitter 476 27.9 Passive Measurement, Small Packets, And NetFlow 478 27.10 Quality Of Service (QoS) 479 27.11 Fine-Grain And Coarse-Grain QoS 480 27.12 Implementation Of QoS 482 27.13 Internet QoS Technologies 484 27.14 Summary 485 489 Chapter 28 Multimedia And IP Telephony (VoIP) 28.1 Introduction 489 28.2 Real-Time Data Transmission And Best-Effort Delivery 489 28.3 Delayed Playback And Jitter Buffers 490 28.4 Real-Time Transport Protocol (RTP) 491 28.5 RTP Encapsulation 492 28.6 IP Telephony 493 28.7 Signaling And VoIP Signaling Standards 494 28.8 Components Of An IP Telephone System 495 28.9 Summary Of Protocols And Layering 498 28.10 H.323 Characteristics 499 28.11 H.323 Layering 499 28.12 SIP Characteristics And Methods 500 28.13 An Example SIP Session 501 28.14 Telephone Number Mapping And Routing 502 28.15 Summary 503
- 17. xx Contents 507 Chapter 29 Network Security 29.1 Introduction 507 29.2 Criminal Exploits And Attacks 507 29.3 Security Policy 511 29.4 Responsibility And Control 512 29.5 Security Technologies 513 29.6 Hashing: An Integrity And Authentication Mechanism 513 29.7 Access Control And Passwords 514 29.8 Encryption: A Fundamental Security Technique 514 29.9 Private Key Encryption 515 29.10 Public Key Encryption 515 29.11 Authentication With Digital Signatures 516 29.12 Key Authorities And Digital Certificates 517 29.13 Firewalls 519 29.14 Firewall Implementation With A Packet Filter 520 29.15 Intrusion Detection Systems 522 29.16 Content Scanning And Deep Packet Inspection 522 29.17 Virtual Private Networks (VPNs) 523 29.18 The Use of VPN Technology For Telecommuting 525 29.19 Packet Encryption Vs. Tunneling 526 29.20 Security Technologies 528 29.21 Summary 529 533 Chapter 30 Network Management (SNMP) 30.1 Introduction 533 30.2 Managing An Intranet 533 30.3 FCAPS: The Industry Standard Model 534 30.4 Example Network Elements 536 30.5 Network Management Tools 536 30.6 Network Management Applications 538 30.7 Simple Network Management Protocol 539 30.8 SNMP’s Fetch-Store Paradigm 539 30.9 The SNMP MIB And Object Names 540 30.10 The Variety Of MIB Variables 541 30.11 MIB Variables That Correspond To Arrays 541 30.12 Summary 542 545 Chapter 31 Software Defined Networking (SDN) 31.1 Introduction 545 31.2 Marketing Hype And Reality 545
- 18. Contents xxi 31.3 Motivation For A New Approach 546 31.4 Conceptual Organization Of A Network Element 548 31.5 Control Plane Modules And The Hardware Interface 549 31.6 A New Paradigm: Software Defined Networking 550 31.7 Unanswered Questions 551 31.8 Shared Controllers And Network Connections 552 31.9 SDN Communication 553 31.10 OpenFlow: A Controller-To-Element Protocol 554 31.11 Classification Engines In Switches 555 31.12 TCAM And High-Speed Classification 556 31.13 Classification Across Multiple Protocol Layers 557 31.14 TCAM Size And The Need For Multiple Patterns 557 31.15 Items OpenFlow Can Specify 558 31.16 Traditional And Extended IP Forwarding 559 31.17 End-To-End Path With MPLS Using Layer 2 560 31.18 Dynamic Rule Creation And Control Of Flows 561 31.19 A Pipeline Model For Flow Tables 562 31.20 SDN’s Potential Effect On Network Vendors 563 31.21 Summary 564 567 Chapter 32 The Internet Of Things 32.1 Introduction 567 32.2 Embedded Systems 567 32.3 Choosing A Network Technology 569 32.4 Energy Harvesting 570 32.5 Low Power Wireless Communication 570 32.6 Mesh Topology 571 32.7 The ZigBee Alliance 571 32.8 802.15.4 Radios And Wireless Mesh Networks 572 32.9 Internet Connectivity And Mesh Routing 573 32.10 IPv6 In A ZigBee Mesh Network 574 32.11 The ZigBee Forwarding Paradigm 575 32.12 Other Protocols In the ZigBee Stack 576 32.13 Summary 577 579 Chapter 33 Trends In Networking Technologies And Uses 33.1 Introduction 579 33.2 The Need For Scalable Internet Services 579 33.3 Content Caching (Akamai) 580 33.4 Web Load Balancers 580 33.5 Server Virtualization 581
- 19. xxii Contents 33.6 Peer-To-Peer Communication 581 33.7 Distributed Data Centers And Replication 582 33.8 Universal Representation (XML) 582 33.9 Social Networking 583 33.10 Mobility And Wireless Networking 583 33.11 Digital Video 583 33.12 Higher-Speed Access And Switching 584 33.13 Cloud Computing 584 33.14 Overlay Networks 584 33.15 Middleware 586 33.16 Widespread Deployment Of IPv6 586 33.17 Summary 587 Appendix 1 A Simplified Application Programming Interface 589 617 Index
- 20. Preface I thank the many readers who have taken the time to write to me with comments on previous editions of Computer Networks And Internets. The reviews have been in- credibly positive, and the audience is surprisingly wide. In addition to students who use the text in courses, networking professionals have written to praise its clarity and to describe how it helped them pass professional certification exams. Many enthusiastic comments have also arrived from countries around the world; some about the English language version and some about foreign translations. The success is especially satisfy- ing in a market glutted with networking books. This book stands out because of its breadth of coverage, logical organization, explanation of concepts, focus on the Internet, and appeal to both professors and students. What’s New In This Edition In response to suggestions from readers and recent changes in networking, the new edition has been completely revised and updated. As always, material on older technol- ogies has been significantly reduced and replaced by material on new technologies. The significant changes include: Updates throughout each chapter Additional figures to enchance explanations Integration of IPv4 and IPv6 in all chapters Improved coverage of MPLS and tunneling New chapter on Software Defined Networking and OpenFlow New chapter on the Internet of Things and Zigbee Approach Taken Should courses take a top-down or bottom-up approach to the subject? In a bottom-up approach, one starts with transmission of bits over a single wire, and then learns how successive layers of protocols expand the functionality. In a top-down ap- proach, one starts with high-level applications, initially learning only enough to under- stand how such applications operate. Later, one learns about the underlying details.
- 21. xxiv Preface This text combines the best of top-down and bottom-up approaches. The text be- gins with a discussion of network applications and the communication paradigms that the Internet offers. It allows students to understand the facilities the Internet provides to applications before studying the underlying technologies that implement the facilities. Following the discussion of applications, the text presents networking in a logical manner so a reader understands how each new technology builds on lower layer tech- nologies. Intended Audience The text answers the basic question: how do computer networks and internets operate? It provides a comprehensive, self-contained tour through all of networking that describes applications, Internet protocols, network technologies, such as LANs and WANs, and low-level details, such as data transmission and wiring. It shows how pro- tocols use the underlying hardware and how applications use the protocol stack to pro- vide functionality for users. Intended for upper-division undergraduates or beginning graduate students who have little or no background in networking, the text does not use sophisticated mathematics, nor does it assume a detailed knowledge of operating systems. Instead, it defines concepts clearly, uses examples and figures to illustrate how the technology operates, and states results of analysis without providing mathematical proofs. Organization Of The Material The text is divided into five parts. The first part (Chapters 1–4) focuses on uses of the Internet and network applications. It describes protocol layering, the client-server model of interaction, the socket API, and gives examples of application-layer protocols used in the Internet. The second part (Chapters 5–12) explains data communications, and presents back- ground on the underlying hardware, the basic vocabulary, and fundamental concepts used throughout networking, such as bandwidth, modulation, and multiplexing. The fi- nal chapter in the second part presents access and interconnection technologies used in the Internet, and uses concepts from previous chapters to explain each technology. The third part (Chapters 13–19) focuses on packet switching and packet switching network technologies. Chapters give the motivation for using packets, introduce the IEEE model for layer 2 protocols, and consider wired and wireless networking technolo- gies, such as Ethernet and Wi-Fi. The third part also introduces the four basic categories of network technologies: LAN, MAN, PAN, and WAN, and discusses rout- ing in WANs. The final chapter presents examples of network technologies that have been used in the Internet.
- 22. Organization Of The Material xxv The fourth part (Chapters 20–26) focuses on the Internet protocols. After discuss- ing the motivation for internetworking, the text describes Internet architecture, routers, Internet addressing, address binding, and the TCP/IP protocol suite. Protocols such as IPv4, IPv6, TCP, UDP, ICMP, ICMPv6, and ARP are reviewed in detail, allowing stu- dents to understand how the concepts relate to practice. Because IPv6 has (finally) be- gun to be deployed, material on IPv6 has been integrated into the chapters. Each chapter presents general concepts, and then explains how the concepts are implemented in IPv4 and IPv6. Chapter 25 on TCP covers the important topic of reliability in trans- port protocols. The final part of the text (Chapters 27–33) considers topics that cross multiple layers of a protocol stack, including network performance, network security, network management, bootstrapping, multimedia support, and the Internet of Things. Chapter 31 presents Software Defined Networking, one of the most exciting new developments in networking. Each chapter draws on topics from previous parts of the text. The place- ment of these chapters at the end of the text follows the approach of defining concepts before they are used, and does not imply that the topics are less important. Use In Courses The text is ideally suited for a one-semester introductory course on networking taught at the junior or senior level. Designed for a comprehensive course, it covers the entire subject from wiring to applications. Although many instructors choose to skip over the material on data communications, I encourage them to extract key concepts and terminology that will be important for later chapters. No matter how courses are orga- nized, I encourage instructors to engage students with hands-on assignments. In the un- dergraduate course at Purdue, for example, students are given weekly lab assignments that span a wide range of topics: from network measurement and packet analysis to net- work programming. By the time they finish our course, each student is expected to know how an IP router uses a forwarding table to choose a next hop for an IP datagram; describe how a datagram crosses the Internet; identify and explain fields in an Ethernet frame; know how TCP identifies a connection and why a concurrent web server can handle multiple connections to port 80; compute the length of a single bit as it propa- gates across a wire at the speed of light; explain why TCP is classified as end-to-end; know why machine-to-machine communication is important for the Internet of Things; and understand the motivation for SDN. The goal of a single course is breadth, not depth — to cover the subject, one can- not focus on a few technologies or a few concepts. Thus, the key to a successful course lies in maintaining a quick pace. To cover the most important topics in a semester, the lower layer material in Part II can be condensed, and the sections on networks and inter- networking can be allocated four weeks each, leaving two weeks for the introductory material on applications and topics such as network management and security. The de- tails of socket programming can be covered in programming exercises, either in labs or as homework problems.
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- 25. the images themselves: first, natural principles, then living creatures in which these principles were supposed to be embodied, then the living creatures themselves. To have begun at the end would have been too great a shock; the absurdity as well as the wickedness of such worship would have been too obvious. Thus was the empire of the idols founded, and it continues to this day. II. The empire of the idols has been world-wide. It might have been supposed to be a folly that could be imposed only on a few barbarous tribes, and that all civilised nations would have rejected it with distain; but as a matter of fact, it is precisely among these nations (Egypt, Greece, Rome, Judæa, India) that idolatry flourished most and in its basest forms. Hence the empire of idolatry was co-extensive with the globe. In Elijah’s time even God thought it a great thing that He would assure His prophet that there were seven thousand who had not bowed the knee to Baal (1 Kings xix. 18). III. The idols have been served with passionate devotion. In almost all ages worshippers of idols have put to shame the worshippers of God, by their fidelity to their convictions, the scrupulousness of their observance of the rites which they have esteemed religious, and the greatness of the cost at which they have done honour to their gods. IV. The idols have had for their allies the most influential of social and moral forces. Their priests and dependents (Acts. xix. 25) have jealously watched every encroachment on the empire of their gods. Rulers, for political reasons, have strenuously endeavoured to uphold the national faiths. Custom and fashion have wrought in the same direction. But, above all, the idols have had their most powerful allies in the human breast—in the instinct of worship, and the craving for sensual indulgences. Idolatry has combined these most powerful of all cravings—has provided deities in whose worship the worst passions of man’s animal nature have been gratified. V. Nevertheless the empire of idolatry shall be utterly destroyed. It shall vanish as utterly as the great empire of Assyria. “The idols He shall utterly abolish.” Already that empire has been overthrown where it seemed most firmly established, and the complete fulfilment of the prediction of our text is obviously now only a question of time. Even in heathen countries, men are becoming ashamed of their idols, and are representing them as merely the media of worship.
- 26. The victory of Christianity over idolatry is already assured. The struggles that are yet to shake the world will be, not between Christianity and idolatry; not even between Christianity and atheism, for atheism is necessarily merely a brief episode in human experience; but between Christianity and other forms of monotheism. Application. 1. In the wide-spread and long-continued empire of the idols we have a conclusive proof of man’s need of a Divine revelation. The natural progress of fallen man is not to light, but to darkness (Rom. i. 21–23; 1 Cor. i. 21). 2. In the prediction of our text, we have a conclusive proof of that in the Bible we have such a revelation. Consider the circumstances of the prophet: idolatry on every hand, corrupting even His own people. It was contrary to all experience; it must have seemed to many who first heard it as the ravings of a lunatic. Such a prediction, already so marvellously fulfilled, came from God! 3. In the approaching complete fulfilment of the prediction of our text, let us rejoice. And let us labour as well as pray, that the time may be hastened when by idolatry God shall be no longer dishonoured and man degraded. Man’s Insignificance and God’s Supremacy. ii. 22. Cease ye from man, whose breath is in his nostrils: for wherein is he to be accounted of? In this verse the whole Bible is summed up. The folly of trusting in man, and the necessity of trusting in God alone, is its greatest lesson, from its commencement to its close. This is what we are taught—I. By its record of God’s providential dealings with the Jews and other nations. Continually He has accomplished His ends by very different means than man would have selected. Egypt saved from perishing by famine through the instrumentality of a young slave; Naaman delivered from his leprosy through the ministrations of a little maid; Israel rescued by Gideon and his three hundred soldiers; the boastful
- 27. Philistines defeated by a young shepherd, &c. II. By the grand scheme of human redemption which it discloses. In it God is everything, and man nothing. The only means by which man can be restored to holiness, to the Divine favour and life everlasting, were provided by God; man contributed nothing either to its completeness or efficiency. The benefit is man’s, the glory all belongs to God. Nor in appropriating it does he do anything that is meritorious. In repentance there is no merit: it is simply that state of mind which is required of us in view of the sins we have committed. Nor in faith; it is simply the recognition of the ability of another, and the consequent entrustment of ourselves to Him, to do that for us which we confess our inability to do for ourselves.—Blessed is the man, and he only, who has learned these two things. So long as a man depends on his own wisdom, power, and goodness, or on the wisdom, power and goodness of other men, he must be disquieted and unhappy. We can attain to substantial quiet and an abiding satisfying peace only when we feel that our dependence is on a Being omnipresent, independent, and supreme, as well as abundant in truth and love (Isa. xxvi. 3).—Joseph Holdech, D.D., American National Preacher, xxxvi. 255–265. Lessons from a National Bereavement. (Sermon preached on the Sunday after the death of President Harrison.) ii. 22. Cease ye from man, whose breath is in his nostrils: for wherein is he to be accounted of? The event which has just befallen us as a nation is fitted to teach— I. The vanity of human dependence. The atheism of the human heart displays itself in a disposition to confide entirely in an arm of flesh. This is so in the family, the church, the nation. In various ways God endeavours to teach nations their real dependence upon Himself —by famine, by pestilence, by commercial disasters, by the death of their rulers. What “fools” we must be, and how “brutish” must be our
- 28. understanding, if we do not lay to heart the lesson which He has now given us (Ps. cxlvi. 3). II. The pettiness of party strife. How much of selfishness, unkindness, anger, and untruthfulness does the spirit of party give birth to! How seldom politicians of opposite parties do each other common justice! How fierce are their rivalries! But how mean, how worthless, how unworthy appear the objects of their strife when death enters the arenas and waves his skeleton arm! What a great calm falls upon the agitated spirits of men! How noise is hushed and excitement subdued! How like do the flushed and eager politicians seem then to silly children quarrelling for the possession of a bubble that has just been blown into the air, and that will disappear the moment it is grasped![1] III. The vanity of the world, the certainty of death, and the nearness of eternity. These lessons are taught when a beggar dies, but are more likely to be laid to heart when a prince is laid low.[2] IV. The supreme importance of a right moral character. Most instructive is the interest felt by survivors in the moral character of the departed, in the evidences of his preparation for death, in the manner in which the great summons affected him. This is the testimony of the human conscience, that in comparison with a fitness to appear before the tribunal of God, everything else loses its importance. When was the amount of a man’s possessions inscribed on his tombstone? The bare suggestion of such a thing would be construed as a mockery of death, under whose denuding hand the rich man leaves the world naked as he entered it. But if, in all his life, there was one virtue in his moral character, one trait which can afford satisfactory evidence of God’s approval, this, be sure, you will find sculptured in conspicuous characters on his monumental marble. One thing alone can prepare any for their last account—the belief and practice of the Gospel of God. Have you the great calm which is inspired by the confidence of being prepared for the great change?—W. Adams, American National Preacher, xv. 97–105. FOOTNOTES:
- 29. [1] Here, like a shepherd gazing from his hut, Touching his reed, or leaning on his staff, Eager Ambition’s fiery chase I see; I see the circling hunt of noisy men Burst law’s enclosure, leap the mounts of right, Pursuing and pursued, each other’s prey; As wolves for rapine; as the fox for wiles; Till Death, that mighty hunter, earths them all. Why all this toil for triumphs of an hour? What though we wade in wealth, or soar in fame? Earth’s highest station ends in “Here he lies”— And “Dust to dust” concludes her noblest song.—Young. [2] The glories of our birth and state Are shadows, not substantial things; There is no armour against fate: Death lays his icy hand on kings; Sceptre and crown Must tumble down, And in the dust be equal made With the poor crooked scythe and spade. Some men with swords may reap the field, And plant fresh laurels where they kill; But their strong nerves at last must yield: They tame but one another still; Early or late They stoop to fate, And must give up their murmuring breath, When they, pale captives, creep to death. The garlands wither on your brow; Then boast no more your mighty deeds; Upon death’s purple altar, now, See where the victor victim bleeds! All heads must come To the cold tomb! Only the actions of the just Smell sweet and blossom in the dust.—Shirley.
- 30. The Death of Statesmen. (Funeral Sermon for the Right Hon. George Canning.) iii. 1–3. For, behold, the Lord, the Lord of hosts, doth take away from Jerusalem and from Judah . . . the counsellor, . . . and the eloquent orator. By the death of a great statesman at the head of a government, we are reminded.—I. Of the weight of government in a fallen world. It is a burden that has crushed many, and has brought them to an untimely grave. II. Of the weakness of the shoulders of mortal men. The government of a single country, especially in troublous times, has proved a burden too great for the courage and the endurance of the strongest of men. III. Of the uncertainty of all human affairs. Often does the statesman think of the uncertainty of arriving at the object of his ambition, but seldom of the uncertainty of his remaining there, except when he recollects how many are struggling to replace him. Little does he think of another foe, who lurks behind, and who in some unexpected moment will hush his eloquent tongue, and turn his fertile brain to dust. IV. Of our absolute dependence on the Supreme Governor. We are apt to think that it is on the profound counsellor and mighty orator that the nation’s welfare depends, and to think little of Him who made them what they are, to be employed as He pleases, laid aside when He pleases, and replaced if He pleases, by others as richly endowed. V. Of the necessity of personal preparation for death.[1]—J. Bennett, D.D., The British Pulpit, i. 297–304. FOOTNOTES: [1] So live, that, when thy summons comes to join The innumerable caravan, that moves To that mysterious realm where each shall take His chamber in the silent halls of death, Thou go not like the quarry slave at night Scourged to his dungeon; but, sustained and soothed
- 31. By an unfaltering trust, approach thy grave Like one that wraps the drapery of his couch About him, and lies down to pleasant dreams.— Bryant. National Greatness. iii. 1–8. For, behold, &c. I. The elements of national greatness are intellectual and moral, rather than material. A nation may have “the staff of bread” and “the stay of water,” but lacking the persons enumerated in ver. 2, 3, it cannot be a great nation. While, therefore, it is reasonable to put forth efforts to increase the material resources of the nation, we should be more concerned to improve the producers than the produce. II. For the supply and continuance of these supreme elements of national greatness, we are absolutely dependent upon God. Well to remember that for all material blessings we are absolutely dependent upon Him. The moral value of a bad harvest is often great; it reminds us that, do what the most skilful agriculturists may, it is “God that giveth the increase.” Nor less dependent are we upon Him for the men without whom no nation can be great. Wise statesmen, skilful inventors, eloquent orators, &c., are very special gifts of God; such men cannot be manufactured. III. These essential elements of national greatness God will take away for those nations that are regardless of His goodness and defiant of His authority (ver. 1, 8). National sins bring on national judgments. No national judgment is more severe or prolific of disasters than the removal or denial of great leaders. IV. Not only can God abase the greatest nation, but He can reduce it to the depths of humiliation which beforehand it would have regarded as inconceivable. See through what states of national sorrow and shame the prophet declared that Israel should be led. 1. The diminution of its material resources and the removal of all its leaders of society (ver. 1–3). 2. The government entrusted to weak
- 32. and childish rulers (ver. 4). 3. Social anarchy (ver. 5). 4. Social degradation so extreme, that men are solicited to rule merely because they have a little wealth (ver. 6). 5. The last state of national degradation—its supreme places of authority have become so contemptible and perilous that no one can be induced to fill them (ver. 7). These considerations concern us individually. The nation is but an aggregate of individuals; and what they are, it is. Hence it behoves us— 1. To strive after personal holiness. This seems a very small remedy for national evils. But it is only by each man adopting it that the nation can be made religious. If each drop in the ocean could eliminate the salt with which it is charged, the ocean would become fresh. Besides, by our example we may stimulate others to personal reforms, and they again others. 2. To entreat God to deal with us as a nation in the way of mercy, and not of judgment (Ps. ciii. 10). There is a mighty power in intercessory prayer. 3. Diligently to promote all moral and social reforms. We must labour as well as pray. A Christian man will assist in all political reforms, because it is the will of God that righteousness should prevail in all things. But much more interested will he be in all movements and institutions having for their end and the intellectual and moral advancement of the people: the school, the temperance society, better dwellings for the working classes, the diffusion of a pure literature, &c. 4. To put forth constant efforts to bring and keep our fellow-countrymen under the influence of the Gospel. Of all regenerative and conservative influences the Gospel is the most active and powerful. A nation composed entirely of genuine Christians would be at once the most happy, prosperous, and powerful the world has ever seen. The direct and short way to exalt Great Britain is to strive to lead all our countrymen to the knowledge and service of Christ. This is a work, not for ministers only, but for the whole Church. There would be more happy Christians if there were more working Christians. It is not the running brooks, but the standing pools, that become stagnant.
- 33. Shameless Sinners. iii. 9. They declare their sin as Sodom, they hide it not. Extremes are generally detestable: equatorial heat, arctic cold; the speaker whom we must strain to hear, the orator who roars, &c. So in morals: foolhardy rashness, cowardice; prodigality, penuriousness; hypocrites, and such shameless sinners as are spoken of here. Such persons are even more detestable than hypocrites; these at least pay this homage to virtue, that they array themselves in her outer garments. Desperate and vain is the endeavour to cloak iniquity, yet even this is better than the effrontery which leads some to flaunt it in open day. How surprising is such effrontery! When we consider what sin is—a thing horribly degrading to man as well as insufferably offensive to God—we should have expected beforehand that men would have been as anxious to hide their vices, as they are to conceal any loathsome disease with which they may be afflicted. But it is not so. There are tens of thousands of sinners as devoid of shame as were those who dwelt in Sodom; nay, they glory in their shame. Consider— I. The Causes of Shamelessness in Sin. 1. Ignorance. There are many so uninterested in moral and spiritual things; they have grown up surrounded by such evil examples, that they have no consciousness of the foulness of their vices, any more than a peasant has of the ungracefulness of his manners. This cause operates among the lower classes to an extent scarcely conceivable by the cultured and refined. 2. Habit. Many an open and shameless sinner, at the outset of his career, when he was first betrayed into transgression, was ashamed almost to walk through the street, and imagined that every one whom he met had heard of, and despised him for, his offence. But the offence was repeated; it became a habit; and in proportion as it has done so, has the offender’s sense of shame died out of him. He thinks as little of it as a soldier does of his uniform, which when it was first put on caused him to think that all eyes were fixed upon him. 3. A desire to silence conscience. The effrontery is often
- 34. assumed, just as the rustic traveller when near a churchyard whistles, not because he is courageous, but to keep his courage up. Conscience reproaches and warns, and the sinner seeks to silence it by greater desperation in wickedness. 4. A seared conscience. In the course just named the sinner too often succeeds. Conscience, defied and outraged, desists from her useless efforts, and gives herself over to an insensible lethargy; there will come an hour of terrible awakening; but meanwhile she is blind, deaf, dumb, and the sinner perpetrates the most abominable iniquities without a blush.[1] 5. Infidelity. The sinner has succeeded at last in persuading himself that what he wishes were true is true, and that there is no God, and, consequently, no day of judgment and no hell. As soon as men have cast off fear of God, it is easy for them to cast off fear of men. The ordinary fruit of infidelity is vice. What but prudence is left to restrain the infidel from partaking in the pleasures of sin? And how weak prudence is in any real contest with passion! II. The Consequences of Shamelessness in Sin. This is declared by the prophet to be woe—woe of peculiar intensity and awfulness. “Woe unto their soul!” &c. They stand in peril of the severest chastisements of the Divine justice—1. Because shamelessness in sin is an aggravation of sin. It is felt to be so in the home, in the nation. Disloyalty is an evil thing, but to break forth into open rebellion, and to take the field against the monarch, is worse. 2. Because shamelessness in sin adds to the contagiousness of sin. One reason why sin is so hateful in the sight of God is because it renders every sinner a moral pestilence. Corrupt, he corrupts others (Eccles. ix. 18). But of shameless sinners this is especially true. (1) They lead many to imitate them in their wickedness. In every community these shameless sinners are ringleaders in vice and recruiting-sergeants for the devil. (2) They confirm many in wickedness. Many are “halting between two opinions,” and these shameless offenders, by their example, and often by their persuasions, supply that which is needed to bring these irresolute ones to a decision for a life of iniquity. Thus they are soul-murderers as well as soul-suicides. Justice, therefore,
- 35. demands that their punishment shall be especially severe. Their doom will probably be as manifest as their guilt. Application. 1. Let those who have been thus shameless in sin humble themselves before Almighty God. Even for them to-day there is mercy (ch. lv. 7; i. 18). Let no sinner be deterred from seeking mercy by the greatness of his sins (Ezra ix. 6, with Ps. cviii. 4, and Rom. v. 20). Yet let no sinner presume further to transgress because God is so merciful. There is an awful warning in the gracious invitation (ch. lv. 6). 2. As ignorance is one main cause of shamelessness in sin, let Sunday-school teachers recognise the importance of the task in which they are engaged. Though they may not be able to point to individual conversions as the result of their efforts, they are not labouring in vain; by them the moral sense of the community is being raised. Evil as are our days, the testimony is conclusive that the former days were not better, but worse. 3. As habit is another main cause of shamelessness in sin, let the young be anxiously on their guard against the formation of evil habits. But habits grow from acts. A single action is consequently more important than it seems. There are certain actions which have in themselves a special decisiveness of influence. When a young man has once entered a bar parlour, he has entered upon the high way to drunkenness; he may not reach it, but he is on the high way to it. Another most decisive step towards shamelessness in sin is taken when a young person who has been trained under Christian influence joins a Sunday excursion. It is by this gate that millions have entered the path of open transgression, along which they have hastened to perdition. 4. Let the people of God be very careful to leave shameless sinners without excuse. It is by the inconsistencies of professing Christians that such persons endeavour to shield themselves from censure and to silence their consciences. Hence Eph. v. 15; Col. iv. 5; 1 Thess. v. 22.
- 36. FOOTNOTES: [1] Blind and ignorant consciences speak peace, or hold their peace, because they have not skill enough to find fault; they swallow many a fly, and digest all well enough. While the scales were upon Paul’s eyes, he was alive and quiet; he thought concupiscence, the sin and breeder of all sin, to be no sin. Such consciences discern sin as we do stars in a dark night,—see only the great ones of the first magnitude, whereas a bright even discovers millions; or as we see a few motes in the dark houses, which sunlight shows to be infinite. Such think good meaning will serve the turn, that all religions will save, or a “Lord, have mercy on us,” at the last gasp. The law which nature has engraven, they tread out with sins, as men do the engravings of tombs they walk on with foul shoes: they dare not look in the glass of God’s law, which makes sin abound, lest the foolishness of their souls should affright them. A number of such sottish souls there be, whose consciences, if God opens, as He did the eyes of the prophet’s servant, they shall see armies and legions of sins and devils in them.—Ward, 1577–1639. Cheering Words and Solemn Warnings. iii. 10, 11. Say ye to the righteous, that it shall be well with him; for they shall eat of the fruit of their own doings. Woe unto the wicked! it shall be ill with them; for the reward of his hands shall be given him. Into these two orders, the righteous and the wicked, the Bible is accustomed to divide the whole population of the globe.—A crimson line runs between the righteous and the wicked, the line of atoning sacrifice: faith crosses that line, but nothing else can. There can be no righteousness where there is no faith.—This distinction is so sharp and definite, that no man can dwell in a borderland between the two conditions. A clear line of demarcation exists between life and death, and such a division is fixed by God between the righteous and the
- 37. wicked. There are no monstrous nondescripts, who are neither sinners nor saints. This text ought, therefore, to lead to great searching of heart. I. The well-being of the righteous. 1. It is a great fact that it is well with the righteous. It is well with him always: in prosperity, which is a time of peril; in persecution, which is hard to bear; in childhood, manhood, and old age; in time, and throughout eternity. 2. We are assured of this fact on Divine authority. Reason might assure us of it, but it is better to have it under the hand and seal of omniscience. If thou canst not see it, let God’s word stand thee instead of sight. 3. It is the will of God that His people should know this great fact. He would have his saints happy, and therefore He says to His prophets, “Say ye,” &c. 4. With God’s people it is emphatically “well.” When God says it is “well” with a man, it must be well indeed. 5. There are many obvious reasons why it is well with the righteous. (1.) His greatest trouble is past. His greatest trouble was the guilt of sin. (2.) His next greatest trouble is doomed. The dominion of sin over him shall speedily come to an end. (3.) His best things are safe. His treasures are in heaven. (4.) His worst things work only for his good. (5.) He is well fed, for he feeds upon Christ; well clad, for he wears the imputed righteousness of Christ; well housed, for he dwells in God who has been the dwelling-place of His people in all generations; well married, for his soul is knit in bonds of marriage union to Christ; well provided for, for the Lord is his Shepherd. (6.) God has put within him many graces, that help to make things well; faith, which laughs at difficulties; love, which accepts them; patience, which endures them; hope, which expects a rest to come. (7.) Day by day, God the Holy Ghost visits him with fresh life and power. (8.) He has a bank that never breaks—the glorious “throne of grace;” and he has only to apply on bended knee to get what he will. (9.) He has ever near him a most sweet Companion, whose loving converse is so delightful that the roughest roads grow smooth, and the darkest nights glow with brightness. (10.) He has an arm to lean upon that is never weary, never feeble, never withdrawn. (11.) He is favoured with a perpetual Comforter, who pours wine and oil into every wound, and brings to his remembrance the things which Christ has spoken. It
- 38. is well with the righteous in life, well when he comes to die, and well after death. 6. The blessedness of the righteous rest upon a solid ground. The text says, “they shall eat the fruit of their doings.” Those are the only terms upon which the old covenant can promise that it shall be well with us; but this is not the ground upon which you and I stand under the gospel dispensation. Absolutely to eat the fruit of our doings would be even to us, if judgment were brought to the line and righteousness to the plummet, a very dreadful thing. Yet there is a limited sense in which the righteous man will do this. “I was an hungered, and ye gave me meat,” &c., is good gospel language; and when the Master shall say, “Inasmuch as ye did this unto one of the least of these my people, ye did it unto me,” the reward will not be of debt, but still it will be a reward, and the righteous will eat the fruit of his doings. I prefer, however, to remark, that there is One whose doings for us is the grounds of our dependence, and we shall eat of the fruit of His doings. II. The misery of the wicked. To expound the woe pronounced against him, you have only to negative all that I have already said about the righteous. It is ill with the wicked; always ill with him; and it shall be ill with him for ever.[1] But why is it ill with the wicked? 1. He is out of joint with all the world. Ordinary creatures are obedient to God, but he has set himself in opposition to the whole current of creation. 2. He has an enemy who is omnipotent. 3. His joys all hang on a thread. Let life’s thread be cut, and where are his merriments? 4. After these joys are over, he has no more to come. 5. Of all the comforts and hopes of the righteous, he is utterly destitute.—C. H. Spurgeon, Metropolitan Tabernacle Pulpit, vol. xiii. 13–24. FOOTNOTES: [1] Many sinners who seem so jocund in our eyes have not such merry lives as you think. A book may be fairly bound and gilded, yet have but sad stories writ within it. Sinners will not tell us all the secret rebukes that conscience gives them. If you will judge of Herod by the jollity of his feast, you may think he wanted no joy;
- 39. but at another time we see that John’s ghost walked in his conscience. And so doth the Word haunt many, who appear to us to lay nothing to heart. In the midst of their laughter their heart is sad; you see the lightning in their face, but hear not the thunder that rumbles in their conscience.—Gurnall, 1617–1679. Suppose a man were in prison, committed for some great offence, and condemned to die under the displeasure of his prince or state, and his servant should come to him, saying, “Sir, be of good comfort; your wife is well at home; you have very sweet children, an excellent crop of corn; your neighbours love you dearly; your sheep and cattle thrive, and all your houses are in good repair.” Would he not answer that servant, “What is all this, so long as I am condemned to die”? Thus is it with every wicked man. He is under the displeasure of the great God, a condemned man, and God is angry with him every day; and if his heart were open to be sensible of it, he would say, “You tell me of my friends, and goods, and name, and trade; but what is all this, so long as I am a condemned person, and God is angry with me every day I rise?”—Bridge, 1600–1670. Who would think, now, that sees how quietly the multitude of the ungodly live, that they must very shortly lie roaring in everlasting flames? They lie down, and rise, and sleep so quietly; they eat and drink as quietly; they go about their work as cheerfully; they talk as pleasantly, as if nothing ailed them, or as if they were as far out of danger as an obedient believer. Like a man that hath the falling sickness, you would little think, while he is labouring as strongly and talking as heartily as another man, how he will presently fall down, lie gasping and foaming, and beating his breast in torment! so it is with these men. They are as free from the fears of hell as others, as free from any vexing sorrows, not so much as troubled with any cares of the state of their souls, nor with any sad and serious thoughts of what shall become of them in another world; yes, and for the most part, they have less doubts and disquiet of mind, than those who shall be saved. Oh, happy men, if they could be always thus; and if this peace would prove a lasting peace! But, alas, there is the misery! it will not. They are now in their own element, as the fish in the water; but little knows that silly creature when he is most fearlessly and delightfully swallowing down the bait, how suddenly he shall be snatched out, and lie dead upon the bank; and as little think these careless sinners what a change is near. The sheep or ox is driven quietly to the slaughter, because he knows not whither he goes; if he knew it were to his death, you could not
- 40. drive him so easily. How contented is the swine when the butcher’s knife is shaving his throat, little thinking that it is to prepare for his death! Why, it is even so with these sensual, careless men; they fear the mischief least, when it is nearest to them, because they see it not!—Baxter, 1615–1691. The Great Law of Recompense. iii. 10, 11. Say ye to the righteous, &c. This is the testimony of conscience; conscience testifies that that which is here predicted ought to take place—that the condition and circumstances of men ought to be conformed to their character. This is the testimony of reason: in its clearest, calmest, strongest hours, it endorses this testimony of the conscience. This is the declaration of Almighty God; He here promises that He will do that which conscience and reason agree that He ought to do. Thus we have here a conclusive concurrence of testimony, and the truths announced in our text should be recorded in our memory as absolutely certain. These declarations remind us of two things. I. That we are living now in a season of probation. These messages are much needed, because we are surrounded by much that is perplexing. Here and now fidelity to conscience often entails much loss, sorrow, and suffering. Many of the wicked are prosperous and triumphant. Iniquity pays. Moreover, the sufferings of the righteous and the successes of the wicked are often lifelong. This contrast between what ought to be and what is, has been a source of moral disquietude in all ages (Ps. lxxiii., &c). Yet it is absolutely necessary. Without this moral obscurity there could not have been any moral probation. There is no temptation in prussic acid, because its deadly qualities are indisputable, and because they operate instantaneously. If all sins had their penalties as clearly and closely tied to them, vice would be impossible. And so would virtue! Obedience to the Divine will would then be, not an act of choice, but the result of an irresistible moral compulsion, and it would have in it no morally
- 41. educational influence, and nothing to render it acceptable to God. Not by chance, then, not by mistake, not as the result of a harsh and unloving decree, but as the result of ordinance of the highest wisdom and grace, we are now living in a season of moral probation. But, II. We are hastening on to a season of rectifications and rewards. Conscience and reason attest that there ought to be such a season, and the Scriptures assure us that there shall be (Eccles. xii. 14; Rom. ii. 6–10, &c.) The great facts of which our text reminds us, 1. Should give calmness and steadiness to our faith. We should not be greatly moved either by the distresses of the righteous or the triumphs of the wicked. These are most transient. The longest life is really a most inconsiderable episode in our being. This is but the beginning of our voyage; what matters it whether we clear out of port in a storm or amid bright sunshine? What will happen to us on mid-ocean is the only thing worthy of our concern. 2. They should govern us in the decisions we have continually to make in life, between courses that are right, but involve present suffering, and those which are pleasant, but wrong. The sick man who refuses to undergo the present pain which will assure him of future health, and prefers the transient ease which will presently give place to intolerable agony, is insane. Let us not imitate him in his folly. But if the rewards of every man’s hands shall be given him, how shall any man be saved? This is precisely the difficulty which the Gospel was designed to meet. It is precisely because no man can be saved on his own merits that Christ came into the World, and died for every man, and now offers redemption to every man. This offer is made to you. For Christ’s sake, the sins of the righteous shall be forgiven them; and for His sake likewise, they shall be rewarded according to their works (Matt. x. 42, xvi. 27; Heb. vi. 10, &c.) Between the doctrine of justification by faith and the doctrine of good works there is the most perfect harmony. The Curse of a Weak Government.
- 42. iii. 12. As for my people, children are their oppressors, and women rule over them. “Children,” “women,” are not to be taken literally. In interpreting the second of these figures, we must remember the status of women in ancient times in the East. I. A weak government is a curse. 1. By such a government the affairs of a nation are mismanaged, its resources squandered, and its great possibilities unrealised. 2. A weak government always becomes in the end an oppressive government. By it the national burdens are caused to press most heavily on those least able to bear them. 3. Under such a government, privileged classes and monopolies multiply and grow strong, to the hurt of the nation at large. 4. Worst of all, and as the source of countless evils, government itself comes to be despised, and the national respect for law destroyed. In short, under a weak government a nation makes rapid progress towards anarchy. II. The curse of a weak government is not long in overtaking a nation that gives itself up to luxury and loses its regard for moral considerations. 1. It is only by such a nation that such a government would be tolerated. 2. By such a nation such a government is likely to be for a time most popular (Jer. v. 31). The cures for political evils are not political but moral. Political remedies will but modify the symptoms. Political evils are really due to moral causes, and can only be removed by moral reformations. Hence, while good men will never neglect their political duties (no good man will neglect any duty), they will be especially in earnest to uplift the nation morally, and therefore will do their utmost to strengthen those agencies which have this for their aim—the church, the school, and those societies which exist for the diffusion of the Scriptures and of religious liberty. Wherever the Bible becomes the book of the people, oppression by “children” becomes impossible, and the government of “women” is set aside. Blind Leaders.
- 43. iii. 12. O my people, they which lead thee[1] cause thee to err, and destroy the way of thy paths. This is at once a lament and a condemnation—a lament over the misfortunes of those who are misguided, a condemnation of their folly and wickedness in permitting themselves to be led astray. I. Men need to be led. 1. This is our need as individuals. Every day we need an answer to the questions, What ought I to do? Which way should I go? In the journey of life, we continually come to crossings at which we are conscious of our need of guidance. 2. Guidance is still more necessary for men collectively. What shall be the belief of a community? What its action? Like the apostolic band (John xxi. 2, 3) communities remain idle, undecided, until the born leader says, “I go a-fishing,” and instantly they say to him, “We also go with thee.” Men are naturally gregarious; like a flock of sheep they crowd and inconvenience each other, not knowing which way to turn, until one bolder than the rest breaks away from the flock, and then instantly the flock begins to follow him. II. As a rule men are misled. Boldness and wisdom do not always go together. Not seldom the courage which prompts men to become the leaders of others, and which goes so far to command the assent of others, is a compound of self-conceit and ignorance. Men are always prone to trust in the self-confident: they will believe the boastful quack rather than the diffident philosopher. Hence in all ages men have been caused to err—the blind have been led by the blind. How true this is to-day in political matters, in social, in commercial, in religious! [Give instances.] On every hand, in all these realms of thought and action, there are those who can only rightly be described as leaders who cause the people to err. Yes, all men carry within them two leaders, in whom they are disposed implicitly to trust, but by whom in the majority of instances they are misled—reason and conscience. How absolute is the confidence placed in these guides, and how seldom it is justified! III. To be misled is one of the most terrible of evils. 1. It involves the loss of all the good to which right leadership would have conducted men. 2. It involves disappointment, shame, sorrow, and often irretrievable ruin. 3. It plunges men into painful perplexities, so that even when they have begun to suspect that
- 44. the path they are pursuing is erroneous, they know not how to discover the true one; it seems to them to be “destroyed;” they search for it in vain. They are like travellers who, in the darkness following Will-of-the- Wisp, have strayed from the highway into a morass: to stand still is impossible, and yet to step in any direction, may plunge them into worse perils (Matt. xv. 14). How criminal is the conduct of those who betray their fellow-men into misery such as this! In view of these facts, 1. We should not entrust ourselves to the first guide who offers himself to us. Let us examine the credentials of those who ask us to trust ourselves to their care (Matt. xxiv. 24; 1 John iv. 1–3; Isa. viii. 20). 2. In weighing the claims of men to be our leaders, we should have regard supremely to their moral qualifications. Their intellectual competency is, of course, not to be disregarded, but moral character is infinitely more important. Not all good men are fitted to be leaders; but no bad man can be safely followed by others. He is continually apt to be guided by policy, rather than principle, and policy leads to perdition.[2] Policy is at the best but guess-work—steering by the current; the man who is governed by principle steers by the stars, and neither can be long misled, nor will he wilfully mislead others. Practical Application.—Never vote for any candidate for a public office, however clever he may be, if his integrity is doubtful. 3. Every man needs guidance more close and intimate than any of his fellow-men can afford him: he needs to be led even in choosing his leaders. Whither shall he look for this guidance? To his reason, his conscience? These guides themselves need instruction:[3] in the absence of it, they have led millions to perdition. We need supernatural and sure guidance, and we have it (1) in God’s Word, and (2) in God’s Spirit (Prov. iii. 5, 6). The man who follows these guides will be led always in the paths of righteousness and peace. FOOTNOTES: [1] The marginal reading, “they which call thee happy” (Mal. iii. 12, 15), represents vividly the method adopted by the false prophets;
- 45. who, instead of warning the people against the dangers of prosperity, were ever felicitating them upon it, saying, “Peace, peace, when there was no peace.” But the textual rendering appears to be the preferable one.—Kay. [2] Men know where they are going when they follow a principle; because principles are rays of light. If you trace a ray of light in all its reflections, you will find that it runs back to the central sun; and every great line of honesty, every great line of honour, runs back towards the centre of God. And the man that follows these things knows that he is steering right Godward. But the man that follows policies, and worldly maxims, does not know where he is steering, except that in general he is steering toward the devil.—Beecher. [3] Reason is God’s candle in men. But, as a candle must first be lighted, ere it will enlighten, so reason must be illuminated by Divine grace, ere it can savingly discern spiritual things.—Toplady, 1740–1778. Conscience, as an expression of the law or will and mind of God, is not now to be implicitly depended on. It is not infallible. What was true of its office in Eden, has been deranged and shattered by the fall; and now lies, as I have seen a sun-dial in the neglected garden of an old, desolate ruin, thrown down from its pedestal, prostrate on the ground, and covered by tall, rank weeds. So far from being since that fatal event an infallible directory of duty, conscience has often lent its sanction to the grossest errors, and prompted to the greatest crimes. Did not Saul of Tarsus, for instance, hale men and women to prison; compel them to blaspheme; and imbrue his hands in saintly blood, while conscience approved the deed—he judging the while that he did God service? What wild and profane imaginations has it accepted as the oracles of God? and as if fiends had taken possession of a God-deserted shrine, have not the foulest crimes, as well as the most shocking cruelties, been perpetrated in its name? Read the Book of Martyrs, read the sufferings of our forefathers; and, under the cowl of a shaven monk, or the trappings of a haughty Churchman, you shall see conscience persecuting the saints of God, and dragging even tender women and children to the bloody scaffold or the burning stake. With eyes swimming in tears, or flashing fire, we close the painful record, to apply to Conscience the words addressed to Liberty by the French heroine, when, passing its statue, she rose in the cart that bore her to the guillotine, and throwing up her arms, exclaimed, “O Liberty, what crimes have been done in thy name!” And what crimes in thine, O Conscience!
- 46. deeds from which even humanity shrinks; against which religion lifts her loudest protest; and which furnish the best explanation of these awful words, “If the light that is in you be darkness, how great is that darkness!” (Matt. vi. 23). So far as doctrines and duties are concerned, not conscience, but the revealed Word of God, is our one, only sure and safe directory.— Guthrie. Oppression of the Poor. iii. 15. What mean ye that ye beat my people to pieces, and grind the faces of the poor? saith the Lord God of hosts. That infidelity should progress among the labouring classes is one of the most surprising and unreasonable things imaginable. For there is no book so emphatically on the side of the poor as is the Bible. Were the Bible obeyed, the miseries of the poor would vanish. The truth, however, is, that the Bible has suffered from its professed friends. The upper classes who have patronised it have not put its precepts into practice, and the victims of their greed and oppression have foolishly accepted their conduct as an exposition of the teaching of the book which they have professed to venerate. Hence the wrongs which the poor have suffered have prepared them to listen to the blasphemies and to accept the sophisms of infidel lecturers. The employer of labour who oppresses his men during the six days of the week, and goes to church twice on the Sunday, is more dangerous to society than a score of Tom Paines or Bradlaughs. Hence also it is the duty of God’s “prophets” in all ages to confront such men with the question of our text. I. Oppression of the poor is one of the most common of all sins. It has been practised in all ages, in all countries, by all classes, in most varied forms. “Poor” is a relative term. Masters have oppressed their servants, debtors their creditors, officers their soldiers, kings their
- 47. subjects, people their pastors. The oppression has often been so terrible that the oppressed have sought refuge in suicide. “Man’s cruelty to man Makes countless thousands mourn.” II. Oppression of the poor is one of the most hateful of all sins. 1. It is a misuse of strength. Strength is given to men that they may be helpful to each other; but the oppressor uses his strength as if he were a tiger or a wolf; as if he were a wrecker who drowns the shipwrecked mariner whom he ought to rescue. 2. It is a cowardly and shameful advantage that is taken of human weakness. To lead a blind man into a quagmire or over a precipice would be thought a shameful act, even by the most degraded villains. But in what respect would it differ in principle from oppression of the poor? The weak and needy, by reason of their feebleness and poverty, have a claim upon our pity and help; to oppress them is to outrage the primary laws of conscience. Yet how often it is done! III. Oppression of the poor is among those sins which are certain to be most terribly punished. The oppressor proceeds on the idea, that the man whom he oppresses has no friends to succour and avenge him. What a mistake! All the oppressed have a friend and avenger in God. Shall oppression go unrequited? Nay, verily! For, 1. It is an offence against God’s laws. He has distinctly commanded us to love our neighbour as ourselves, and how manifold are the applications of this great commandment! 2. It is an offence against God’s feelings. In a peculiar manner His sensibilities are outraged when His children act cruelly towards each other. Oppression of the poor kindles within Him mingled disgust and indignation.[1] Application. 1. A new consideration of our text would deter men from the sin here denounced. The question which God now addresses to oppressors He will, with a slight difference, put to them again—when they shall be gathered at His bar! “What meant ye that ye did beat my people to pieces, and did grind the faces of the poor?” Bethink you, O ye oppressors, what will ye answer then? Will it be, “Lord, we thought
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