Introduction to Networks_v0.2

Introduction to Networks
1
Sohail Gohir CCIE#41610
CCIE (R&S,SP,DC), CCSA,CCSE, C)PTE,
CCNP SEC, R&S, CCIP, CCDP,
CCAI(CCNA,CCNP), mile2 Instructor
https://uk.linkedin.com/in/sg41610
TechNet Easy Services
www.technetes.co.uk
info@technetes.co.uk

LAN, WAN, Internetworks
— Local Area Network (LAN) -An individual network usually spans a single
geographical area, providing services and applications to people within a common
organizational structure, such as a single business, campus or region
— Wide Area Network (WAN)- Individual organizations usually lease connections
through a telecommunications service provider network.These networks that
connect LANs in geographically separated locations are referred to asWide Area
Networks.
2

• Internetworks - A global mesh of interconnected networks for
communication. Ex: Internet
3

— The term intranet is often used to refer to a private connection
of LANs andWANs that belongs to an organization, and is
designed to be accessible only by the organization's members,
employees, or others with authorization.
4

- Network Interface Card - A NIC, or LAN adapter, provides
the physical connection to the network at the PC or other host
device.The media connecting the PC to the networking device
plugs directly into the NIC.
- Physical Port - A connector or outlet on a networking device
where the media is connected to a host or other networking
device.
- Interface - Specialized ports on an internetworking device
that connect to individual networks. Because routers are used to
interconnect networks, the ports on a router are referred to
network interfaces.
6

Rules that Govern Communications
• Communication in networks is governed by pre-defined rules called
protocols.
• A group of inter-related protocols that are necessary to perform a
communication function is called a protocol suite.These protocols are
implemented in software and hardware that is loaded on each host and
network device
• Networking protocols suites describe processes such as:
-The format or structure of the message
-The process by which networking devices share information about pathways
with other networks
- How and when error and system messages are passed between devices
-The setup and termination of data transfer sessions
• Individual protocols in a protocol suite may be vendor-specific and
proprietary.
7

Protocol Suites & Industry Standard
• Many of the protocols that comprise a protocol suite reference
other widely utilized protocols or industry standards
• Institute of Electrical and Electronics Engineers (IEEE) or the
Internet EngineeringTask Force (IETF)
• The use of standards in developing and implementing protocols
ensures that products from different manufacturers can work
together for efficient communications
8

The Interaction of Protocols
• Application protocol – HTTP. HTTP defines the content and formatting of the
requests and responses exchanged between the client and server
• Transport Protocol –TCP.TCP divides the HTTP messages into smaller segments.
It is also responsible for controlling the size and rate of message exchange.
• Internetwork Protocol – IP. It encapsulating segments into packets, assigning the
appropriate addresses, and selecting the best path to the destination host.
• NetworkAccess Protocol – Protocols for data link management and the physical
transmission of data on the media.
Will learn
more in
TCP/IP model
9

Using Layer Models
— To visualize the interaction between various protocols, it is
common to use a layered model.
— Benefits of doing so:
- Assists in protocol design, because protocols that operate at a
specific layer have defined information that they act upon and a
defined interface to the layers above and below.
- Fosters competition because products from different vendors
can work together.
- Prevents technology or capability changes in one layer from
affecting other layers above and below.
- Provides a common language to describe networking functions
and capabilities.
10

Protocol & Reference Model
• 2 types of networking models
• A protocol model provides a model that closely matches the
structure of a particular protocol suite.The hierarchical set of related
protocols in a suite typically represents all the functionality required to
interface the human network with the data network. Ex:TCP/IP
model
• A reference model provides a common reference for maintaining
consistency within all types of network protocols and services.A
reference model is not intended to be an implementation specification
or to provide a sufficient level of detail to define precisely the services
of the network architecture.The primary purpose of a reference
model is to aid in clearer understanding of the functions and process
involved
Ex: OSI model
11

The OSI Reference Model
• The OSI reference model is the
primary model for network
communications.
• Allows you to view the network
functions that occur at each
layer.
• It is a framework that you can
use to understand how
information travels throughout a
network
• 7 layers -- each of which
illustrates a particular network
function.
12

OSI – The Application Layer
— Provides network services to
the user's applications.
— It does not provide services
to any other OSI layer
— ***Think of any network
application you use daily
13

OSI – The Presentation Layer
— It ensures that the information
that the application layer of one
system sends out is readable by
the application layer of another
system.
— ***Think of any common file
formats (JPEG, txt etc)
14

OSI – The Session Layer
— *** After you prepare your data,
you need to establish the
communication channels to send
data
— This layer establishes, manages, and
terminates sessions between two
communicating hosts.
— It also synchronizes dialogue
between the two hosts'
presentation layers and manages
their data exchange.
15

OSI – The Transport Layer
— Data will be segmented and
send to destination device.
Transport layer of destination
device will reassemble them.
— This layer handles details of
reliable transfer. (ensures
that the data arrive
completely )
16

OSI – The Network Layer
— Many paths to the same
destination. So, which path
to follow?
— Segmented data needs
address to reach the
destination (network
address)
— This layer handle 2 above
stated issues.
17

OSI – The Data Link Layer
— It provides means for
exchanging data frames over a
common media
— To detect and possibly correct
errors that may occur in the
Physical layer
— Physical Addressing,
topologies and flow control
18

OSI – The Physical Layer
— It defines the electrical,
mechanical, procedural, and
functional specifications for
activating, maintaining, and
deactivating the physical link
between end systems.
— Voltage levels, timing of voltage
changes, physical data rates,
maximum transmission
distances, physical connectors,
and other, similar, attributes
defined by physical layer
specifications.
19

Comparison --Both have application
layers, though they include
very different services
--Both have comparable
transport and network
(Internet) layers
--TCP/IP combines the
presentation and session
layer issues into its
application layer
--TCP/IP combines the OSI
data link and physical layers
into one layer
--TCP/IP appears simpler
because it has fewer layers
21

Data Encapsulation
• Build the data
• Package the data for
end to end support
(Segments)
• The data is put into a
packet or datagram
that contains a
network header with
source and destination
logical addresses
22

Data Encapsulation
— Each network device must
put the packet into a frame.
— The frame must be converted
into a pattern of 1s and 0s
(bits)
— ***Data à Segments à
Packet à Frames à Bits
23

Addressing in the Network— There are various types of addresses that must be included to
successfully deliver the data from a source application running on
one host to the correct destination application running on
another
24

Getting Data to the End Device
— The host physical address, is contained in the header of the Layer 2 PDU,
called a frame.
— Layer 2 is concerned with the delivery of messages on a single local
network.
— The Layer 2 address is unique on the local network and represents the
address of the end device on the physical media.
— In a LAN using Ethernet, this address is called the Media Access
Control (MAC) address.
— When two end devices communicate on the local Ethernet network, the
frames that are exchanged between them contain the destination
and source MAC addresses.
— Once a frame is successfully received by the destination host, the Layer 2
address information is removed as the data is decapsulated and moved up
the protocol stack to Layer 3.
25

Getting the Data Through the Internetwork
— Layer 3 protocols are primarily designed to move data from one
local network to another local network within an
internetwork.
— Layer 3 addresses must include identifiers that enable
intermediary network devices to locate hosts on different networks
— At the boundary of each local network, an intermediary network
device, usually a router, decapsulates the frame to read the
destination host address contained in the header of the packet, the
Layer 3 PDU
— Routers use the network identifier portion of this address to
determine which path to use to reach the destination host.
26

OSI and TCP/IP Models – Application Layer
— TheApplication layer, Layer seven, is the top layer of both
the OSI andTCP/IP models.
— It provides the interface between the applications we use to
communicate and the underlying network over which our
messages are transmitted.
— Application layer protocols are used to exchange data
between programs running on the source and destination
hosts.
— There are manyApplication layer protocols and new
protocols are always being developed
27

The functionality of theTCP/IP application layer
protocols fit roughly into the framework of the top three
layers of the OSI model:Application, Presentation and
Session layers
28

Application Layer Used Protocols
• TheTransport layer uses an addressing scheme called a port
number. Port numbers identify applications and Application layer
services that are the source and destination of data
• Domain Name System (DNS) -TCP/UDP Port 53
• HypertextTransfer Protocol (HTTP) -TCP Port 80
• Simple MailTransfer Protocol (SMTP) -TCP Port 25
• Post Office Protocol (POP) - UDP Port 110
• Telnet -TCP Port 23
• Dynamic Host Configuration Protocol - UDP Port
67(Server),68(Client)
• FileTransfer Protocol (FTP) -TCP Ports 20 and 21
29

• The Presentation layer (of OSI model) has 3 primary functions:
- Coding and conversion of Application layer data to ensure that
data from the source device can be interpreted by the
appropriate application on the destination device.
- Compression of the data in a manner that can be decompressed
by the destination device.
- Encryption of the data for transmission and the decryption of
data upon receipt by the destination.
-Think of any common file formats (JPEG, txt etc)
30

— The Session Layer
- It creates and maintains dialogs between source and destination
applications.
- It handles the exchange of information to initiate dialogs, keep
them active, and to restart sessions that are disrupted or idle for
a long period of time
31

Source Port: 16 bits
Destination Port: 16 bits
Sequence Number: 32 bits
The sequence number of the first data octet in this segment (except
when SYN is present). If SYN is present the sequence number is the
initial sequence number (ISN) and the first data octet is ISN+1.
Acknowledgment Number: 32 bits
If the ACK control bit is set this field contains the value of the next
sequence number the sender of the segment is expecting to
receive. Once a connection is established this is always sent.
Header Length: Specify the length of Segment header in the bytes
The number of 32 bit words in the TCP Header. This indicates where
the data begins. The TCP header (even one including options) is an
integral number of 32 bits long.
Reserved: 6 bits
Reserved for future use. Must be zero.
33

URG: Urgent Pointer field significant
ACK: Acknowledgment field significant
PSH: Push Function
RST: Reset the connection
SYN: Synchronize sequence numbers
FIN: No more data from sender
Window: 16 bits
The number of data octets beginning with the one indicated in the
acknowledgment field which the sender of this segment is willing to
accept.
Checksum: Is the value of the dynamic window – how many octets
can be sent before waiting for acknowledgement.
34

TCP Server Processes
— Each application process running on the server is configured
to use a port number, either by default or manually by a
system administrator.
— An individual server cannot have two services assigned to the
same port number within the sameTransport layer services.
— Security measure – block ports
35

Connection establishment
— When two hosts communicate usingTCP, a connection is
established before data can be exchanged.
— To establish the connection, the hosts perform a three-way
handshake. Control bits in theTCP header indicate the progress
and status of the connection. (flags)
— URG - Urgent pointer field significant
— ACK - Acknowledgement field significant
— PSH - Push function
— RST - Reset the connection
— SYN - Synchronize sequence numbers
— FIN - No more data from sender
36

Application and Operation of TCP Mechanisms
— Describe the role of port numbers in establishingTCP sessions
and directing segments to server process
37

3 Way Handshake – role
— The 3 way handshake :
— Establishes that the destination device is present on the network
— Verifies that the destination device has an active service and is
accepting requests on the destination port number
— Informs the destination device that the source client intends to
establish a communication session on that port number
39

Confirming receipt
— The sending host is expected to send a segment that uses a sequence
number that is equal to the acknowledgement number.
42

Flow control – reducing window size
43

UDP
• UDP is a simple protocol that provides the basicTransport layer
functions.
• Application layer protocols that use UDP include:
– Domain Name System (DNS)
– Simple Network Management Protocol (SNMP)
– Dynamic Host Configuration Protocol (DHCP)
– Routing Information Protocol (RIP)
– Trivial FileTransfer Protocol (TFTP)
– Online games
44

UDP Header
— The UDP PDU is referred to as a datagram
— Because there is no session to be created with UDP, as soon as
the data is ready to be sent and the ports identified, UDP can
form the datagram and pass it to the Network layer to be
addressed and sent on the network.
46

UDP Datagram Reassembly
— Because UDP is connectionless, sessions are not established
before communication takes place as they are withTCP
— UDP does not keep track of sequence numbers
— UDP has no way to reorder the datagrams into their
transmission order
47

UDP Protocol
— Trace the steps as the UDP protocol and port numbers are
utilized in client-server communication.
48

IPv4 Packet Header
— 6 key fields of IPv4: IP SourceAddress, IP Destination Address,
Time-to-Live (TTL),Type-of-Service (ToS), Protocol, Fragment
Offset
49

— IP Destination Address
— IP Source Address
— Time-to-Live (TTL) - an 8-bit binary value that indicates the
remaining "life" of the packet.TheTTL value is decreased by at
least one each time the packet is processed by a router (a hop).
When the value becomes zero, the router discards or drops the
packet.
— Protocol - enables the Network layer to pass the data to the
appropriate upper-layer protocol. Ex: 01 ICMP, 06TCP, 17 UDP
50

— Type-of-Service - contains an 8-bit binary value that is
used to determine the priority of each packet
— Fragment offset - identifies the order in which to place
the packet fragment in the reconstruction
— The More Fragments (MF) flag - a single bit in the Flag field
used with the Fragment Offset for the fragmentation and
reconstruction of packets
— Don't Fragment (DF) flag - a single bit in the Flag field that
indicates that fragmentation of the packet is not allowed
51

Other IPv4 Header
— Version - Contains the IP version number (4)
— Header Length (IHL) - Specifies the size of the packet header.
— Packet Length -This field gives the entire packet size, including
header and data, in bytes.
— Identification -This field is primarily used for uniquely
identifying fragments of an original IP packet
— Header Checksum -The checksum field is used for error
checking the packet header.
— Options -There is provision for additional fields in the IPv4
header to provide other services but these are rarely used.
52

Host Routing Table
— A host creates the routes used to forward the packets it
originates.
— These routes are derived from the connected network and the
configuration of the default gateway.
— Hosts automatically add all connected networks to the routes.
— Command: netstat - r
56

— Data Link layer is divided into two sublayers: an upper sublayer
and an lower sublayer.
-The upper sublayer defines the software processes that provide
services to the Network layer protocols. (LLC)
-The lower sublayer defines the media access processes
performed by the hardware. (MAC)
58
Data Link Layer

Ethernet Protocol for LAN
— Ethernet is a family of networking technologies that are defined
in the IEEE 802.2 and 802.3 standards.
— Ethernet standards define both the Layer 2 protocols and the
Layer 1 technologies.
— Ethernet is the most widely used LAN technology and supports
data bandwidths of 10, 100, 1000 Mbps.
60

Physical Layer
— The OSI Physical layer provides the means to transport
across the network media the bits that make up a Data Link
layer frame.
— The delivery of frames across the local media requires the
following Physical layer elements:
-The physical media and associated connectors
-A representation of bits on the media
- Encoding of data and control information
-Transmitter and receiver circuitry on the network devices
62

— The purpose of the Physical layer is to create the electrical,
optical, or microwave signal that represents the bits in each
frame.
— It is also the job of the Physical layer to retrieve these individual
signals from the media, restore them to their bit representations,
and pass the bits up to the Data Link layer as a complete frame.
63
Physical Layer

Type of Media – Copper Media
— Cables that use copper wires to signal data and control bits
between network devices
— Ex:Twisted pair, Coaxial cable
— Data is transmitted on copper cables as electrical pulses.
— The timing and voltage values of these signals are susceptible
to interference or "noise" from outside the communications
system.
— Cable types with shielding or twisting of the pairs of wires
are designed to minimize signal degradation due to
electronic noise.
64

Copper Media - Unshielded Twisted Pair
(UTP)
— Very common, cheap, easy to install
— It consists of 4 pairs of color-coded wires that have been
twisted together
— The twisting has the effect of canceling unwanted signals.
— This cancellation effect also helps avoid interference from
internal sources called crosstalk.
— Crosstalk is the interference caused by the magnetic field
around the adjacent pairs of wires in the cable.
65

RJ-45 Connector
The following are main cable types that are obtained by using specific wiring
conventions:
- Ethernet Straight-through,
- Ethernet Crossover &
-Rollover
66

Type Use
Category 1 (1Mhz) Voice Only (Telephone Wire)
Category 2 (4Mhz) Data to 4 Mbps (LocalTalk)
Category 3 (16Mhz) Data to 10 Mbps (Ethernet)
Category 4
(20Mhz)
Data to 20 Mbps (16 Mbps Token Ring)
Category 5
(100Mhz)
Data to 100 Mbps (Fast Ethernet)
Category 5e
(100Mhz)
Data to 1000Mbps (Full Duplex Fast Ethernet
and Gigabit Ethernet)
Category 6
(250Mhz)
Data to 1000Mbps (more stringent specifications
for crosstalk and system noise)
75

Copper Media – Shielded Twisted Pair (STP)
— STP uses two pairs of wires that are wrapped in an overall
metallic braid or foil.
— STP provides better noise protection than UTP cabling,
however at a significantly higher price
76

— STP was the cabling structure specified for use inToken Ring.
— Demand become less asToken Ring becomes less popular
— Might revive as the new 10 GB standard for Ethernet has a
provision for the use of STP cabling
77

Copper Media - Coaxial Cable
— Coaxial cable consists of a copper conductor surrounded by a
layer of flexible insulation.
— Over this insulating material is a woven copper braid, or metallic
foil, that acts as the second wire in the circuit and as a shield for
the inner conductor.
— The second layer reduces the amount of outside electromagnetic
interference.
— Covering the shield is the cable jacket.
78

• Coax is an important type of cable that is used in wireless
and cable access technologies.
• In the past, coaxial cable was used in Ethernet
installations.
• Coax cables are used to attach antennas to wireless
devices.The coaxial cable carries radio frequency (RF)
energy between the antennas and the radio equipment.
• Hybrid Fiber Coax (HFC) –A network which
incorporates optic fiber along with coaxial cable to create
broadband networks. Commonly used by cableTV
companies
80

Fiber Media
• Fiber-optic cabling uses either glass or plastic fibers to guide light
impulses from source to destination.
• The bits are encoded on the fiber as light impulses .
• Optical fiber cabling is capable of very large raw data bandwidth
rates.
• Most current transmission standards have yet to approach the
potential bandwidth of this media.
81

Fiber Compared to Copper Cabling
• Fiber media is immune to electromagnetic interference
• Optical fibers are thin and have relatively low signal loss, they
can be operated at much greater lengths than copper media,
• More expensive (usually) than copper media over the same
distance (but for a higher capacity)
• Different skills and equipment required to terminate and splice
the cable infrastructure
• More careful handling than copper media
83

700 nanometers 400 nanometers
The wavelength of the light in optical fiber is either 1550
nm, 1310 nm, or 850 nm.
85

Two fibers are required to support full duplex operation
85

Wireless Media
— Wireless media carry electromagnetic signals at radio and
microwave frequencies that represent the binary digits of data
communications.
— 4 common data communications standards that apply to wireless
media are:
- IEEE 802.11, (Wi-Fi) –Wireless LAN technology that uses
CSMA/CA media access process.
- IEEE 802.15,Wireless Personal Area Network (WPAN) or
Bluetooth that uses a device pairing process to communicate over
distances from 1 to 100 meters.
86

— IEEE 802.16 - Commonly known asWiMAX (Worldwide
Interoperability for MicrowaveAccess), uses a point-to-
multipoint topology to provide wireless broadband access.
— Global System for Mobile Communications (GSM) -
Includes Physical layer specifications that enable the
implementation of the Layer 2 General Packet Radio Service
(GPRS) protocol to provide data transfer over mobile cellular
telephony networks.
87

• In general, a wireless LAN requires the following network
devices:
-Wireless Access Point (AP)
-Wireless NIC
• SomeWLAN Ethernet-based standards
- IEEE 802.11a, 5 GHz frequency band, speeds of up to 54 Mbps
- IEEE 802.11b, 2.4 GHz, 11 Mbps
- IEEE 802.11g, 2.4 GHz, 54 Mbps (operate at the same radio
frequency and range as 802.11b but with the bandwidth of
802.11a)
- IEEE 802.11n, 2.4 GHz or 5 GHz, 100 Mbps to 210 Mbps
with a distance range of up to 70 meters
88

Media Connector – RJ-45 for UTP
90

End ofWeek one
Don’t forget to read at
home & labs
The end…
91

Introduction to Networks_v0.2

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