Lecture 2 -_understanding_networks_2013

BITS 2513
INTERNET TECHNOLOGY
LECTURE 2: UNDERSTANDING
NETWORKS
1

• Network Terminology
• Network Components
• Operating Systems on the
Network
TOPICS
Network
• The OSI Model and
Networking
• Addressing on a Network
• How Data Travels on the
Network: an Example
2

• Network Adapter
– Usually an expansion card called NIC
(Network Interface Card)
• Network Protocol
– A set of rules for network communications.
Examples:
Network Terminology
• OS protocols: TCP/IP, NetBEUI
• Hardware protocols: Ethernet, Token Ring
• Segments, Packets, Datagrams
– Small “chunks” of data that travel on
network
– In the network media, the packets travel in
frames, which carry each data packet with
a header and trailer to identify each packet
3

• Hardware:
– Network Interface Card
(NIC)
– Servers
– Workstations
• Software:
– Operating Systems
– Applications
– Middleware
Network Components
– Workstations
– Hub, MAU,
Concentrator, Switch
– Connectors (RJ-45, BNC)
– Cable(UTP, coax)
– UPS (Uninterruptable
Power Supply)
5

NIC
Hub
switch
UPS
MAU
RJ-45 and
UTP
BNC male

Operating Systems on
the Networkthe Network
7

Introduction
• Communications between computers
require network OS(es) and network
protocols.
• Functions of OS in a computer:
– manage applications, hardware, and
connection to the network.
– enabling the computers on the local area
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– enabling the computers on the local area
network (LAN) to share their resources
• Protocols specify network functionality.
– Using the same set of network protocols,
different devices can communicate.
– The selected network protocol must be
supported by every operating system on
the network.
– Example : HTTP, SMTP and FTP

Introduction (continued)
How resources are shared:
◦ peer-to-peer model: several computers using
different operating systems in a small business or
home can be connected to form a small LAN.
◦ client/server model, a.k.a. domain model, a
server is used to control which resources on the
LAN are shared, and who can access these
resources.
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Network OSes are used to manage
resource sharing through mechanisms
such as
◦ user account: a collection of all of the
information that pertains to a user on a
computer
◦ authentication, validation, or logging on:
The process of entering a correct user ID and
password to gain access to a computer

• Windows 98 and Windows Me
• Windows NT Workstation, Windows
2000 Professional, Windows XP
• Linux
• Macintosh OSes e.g. Mac OS X
Client OSes
• Macintosh OSes e.g. Mac OS X
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• can be installed on a server and used
to manage network resources,
including user accounts, printers, and
file sharing across the LAN.
• Windows NT Server, Windows NT
Network OSes
• Windows NT Server, Windows NT
Enterprise Server
• Windows 2000
• Windows Server 2003
• Novell NetWare
• UNIX, Linux
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Network Operating Systems
• Some criteria to consider when selecting a
NOS are as follows:
– Reliability – stably perform in any condition
– Performance – serve the clients in a seamless way
– Adaptability – adapt request of diff. platform
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– Adaptability – adapt request of diff. platform
– Security – ability to eliminate and repel threats
– Scalability – cont. function well when size expand
– Affordability
– Ease of use and ease of installation

The OSI Model and Networking
13

Variety – OS: Apple OS X, Windows, Linux,
Unix, Sun. Hardware: Cisco, 3Com,Huawei
In an effort to identify and standardize all
the levels of communication needed in
networking, ISO developed a networking
Understanding the OSI Model
networking, ISO developed a networking
model called the Open Systems
Interconnection (OSI) reference model.
The OSI reference model provides a
universally accepted reference illustrating
how data is transmitted on a network or
between two or more networked devices.
14

15

(Continued)
Physical Layer
Physical layer is responsible for: Passing data packets on
to the cabling or wireless media (whether the media be
cabling or wireless).
Data is in ‘bit’ form
16
Data Link Layer
Data Link layer is responsible for: Receiving packets of
data from the Network layer and presenting them to the
Physical layer for transport.
E.g: NIC (with firmware)
When software is permanently embedded on a hardware
device, it is called firmware.
Data is called ‘frame’

Network Layer
• Network layer is responsible for:
Dividing a block of data into
segments that are small enough to
travel over a network.
(Continued)
travel over a network.
• Segments of data are called packets,
data packets, or datagrams and contain
data, along with special identifying
information in headers and trailers at the
beginning and end of the packet.
17

Transport Layer
Transport layer is responsible for: Error checking and
requests retransmission of data if it detects errors.
The Transport layer might or might not guarantee
successful delivery of data (depends on the transport
protocol used).
(Continued)
protocol used).
Data is called ‘segment’
Session Layer
Session layer is responsible for: Establishing and
maintaining a session between two networked
stations or hosts.
A host is any computer or other device on a
network that has been assigned an IP address.
18

Presentation Layer
• Presentation layer is responsible for: receiving
requests for files from the Application layer, and
presents the requests to the Session layer.
• The Presentation layer reformats, compresses, or
encrypts data as necessary.
(Continued)
• The Presentation layer reformats, compresses, or
encrypts data as necessary.
Application Layer
• The Application layer of the OSI model is
responsible for interfacing with application
software, such as Web browsers or Web
servers.
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TCP/IP Protocols at Each Layer
(Continued)
20

The OSI Model Applied to a TCP/IP
Network
The Web browser wants to make a request to a Web server, and
processes the request using an API (Application Program Interface
)call to the OS.
The API process packages the data using HTTP format, which
includes an HTTP header, and addresses it to an IP address and
port 80, which is the default port for a Web server.
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Fig 5-33 An application asks the OS to do something using an API call

Network (Continued)
• HTTP delivers the package to TCP, giving the
destination IP address and port.
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Network (Continued)
• TCP hands the data off to IP, which resides in
the network layer and is also managed by
the OS.
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Network (Continued)
The data with its header information is a long
stream of bytes. IP breaks it into individual
packets. IP adds its own IP header that contains
its own IP address (source) and the server’s IP
address (destination). IP passes the packets off
to the hardware (NIC).to the hardware (NIC).
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Fig 5-36 IP divides data into packets, which are then released to the network

Network (Continued)
On the NIC, each
packet is given
information at its
beginning and end
in the form of frame.
A checksum is
calculated using acalculated using a
technique called
cyclical
redundancy check
(CRC). Then each
frame is sent off to
the Ethernet cable.
At the destination,
the checksum is
verified and passed
to the IP layer to be
regrouped.
25

Network (Continued)
• IP then passes the reassembled data and
header stream on to the TCP layer who
acknowledges the TCP layer on the client.
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Network (Continued)
• The HTTP server, listening at port 80, receives
the data and passes it on to the Web server.
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(Continued)
28

• TCP/IP covers the first five layers of the OSI
model, and is included in an operating system
as a group of utilities called the TCP/IP stack.
• Figure 5-41 shows the four major
groupings of the OSI model as
applied to TCP/IP networks.
29

• The first three layers of the OSI model
are handled by the protocol specific to
the application using it and are best
treated as a single group rather than
Protocols at the Application,
Presentation, and Session
Layers
treated as a single group rather than
unique layers.
• The language or protocol each
of these applications uses is listed
at the Application, Presentation,
and Session layers.
31

• A TCP/IP network has two protocols
that work at the Transport layer; one
protocol guarantees delivery and the
other does not.
• With TCP/IP, the protocol that
guarantees delivery is TCP and the
Protocols at the Transport Layer
• With TCP/IP, the protocol that
guarantees delivery is TCP and the
protocol that does not is UDP (User
Datagram Protocol).
• TCP is used for client and server
requests and responses.
• UDP ??
32

• Because TCP establishes a connection, it is
called a connection-oriented protocol.
• UDP is a protocol that sends data
Protocols at the Transport
Layer (Continued)
• UDP is a protocol that sends data
without caring about whether the
data is received.
• It does not establish a connection
first; thus, it is called a connectionless
protocol.
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Lecture 2 -_understanding_networks_2013

• TCP and UDP communicate with the Network
layer, which is sometimes called the Internet
layer.
• Some of the other supporting protocols include ARP
(Address Resolution Protocol), responsible for
locating a host on a LAN; RARP (Reverse Address
Protocols at the Network Layer
locating a host on a LAN; RARP (Reverse Address
Resolution Protocol), responsible for
discovering the Internet address of
a host on a LAN; and ICMP (Internet
Control Message Protocol), responsible
for communicating problems with
transmission to devices that need to
know about these problems.
35

• PPP (Point-to-Point Protocol) is used over
telephone lines, and allows a computer to
connect to a network using a modem.
• PPP is the most popular protocol for
Protocols at the Data Link and
Physical Layers
• PPP is the most popular protocol for
managing network transmission
from one modem to another.
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• MAC addresses function at the lowest
(Data Link) networking level.
• If a host does not know the MAC address
of another host on a local area network, it
uses the operating system to discover the
MAC (Media Access Control)Addresses
uses the operating system to discover the
MAC address.
• MAC-48 addresses in human-friendly form is
six groups of two hexadecimal digits
• e.g. 01-23-45-67-89-ab or 01:23:45:67:89:ab
38

• All the protocols of the TCP/IP suite
identify a device on the Internet or an
intranet by its IP address.
• An IP address is 32 bits long, made up of
4 bytes separated by periods.
• Within an IP address, each of the four
IP Addresses
• Within an IP address, each of the four
numbers separated by periods is
called an octet.
• The first part of an IP address
identifies the network, and the last
part identifies the host.
39

• IP addresses that can be used by
companies and individuals are divided
into three classes: Class A, Class B, and
Class C, based on the number of possible
IP addresses in each network within each
class.
Classes of IP Addresses
class.
• The group of IP addresses assigned
to an organization are unique to all
other IP addresses on the Internet
and are available for use on the Internet.
• The IP addresses available to the Internet
are called public IP addresses.
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• Private IP addresses are IP addresses that
are assigned by a network administrator for
use on private intranets that are isolated
from the Internet.
• The RFC 1918 recommends that the
Private IP Addresses
• The RFC 1918 recommends that the
following IP addresses be used for private
networks:
– 10.0.0.0 through 10.255.255.255
– 172.16.0.0 through 172.31.255.255
– 192.168.0.0 through 192. 168. 255.255
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• Instead of IP addresses permanently
being assigned to computers (called
static IP addresses), an IP address is
assigned for the current session only
Dynamically Assigned IP
Addresses
assigned for the current session only
(called a dynamic IP address).
• Internet service providers (ISPs) are
organizations through which individuals
and businesses connect to the Internet.
42

• If the hosts on a network using private IP
addresses need to access the Internet, a
problem arises because the private IP
addresses are not allowed on the Internet.
Network Address Translation
• The solution is to use NAT (Network
Address Translation), which uses a
single public IP address to access the
Internet on behalf of all hosts on the
network using other IP addresses.
43

• Because of an impending shortage of IP
addresses, as well as some limitations in
the current standards for IP, a new
scheme of IP addresses called the IPv6
(IP version 6) standard is currently being
Plans for New IP Addresses
(IP version 6) standard is currently being
developed and implemented.
• Current IP addresses using the current
IPv4 (IP version 4) have 32 bits with
eight bits in each of four octets.
45

• With the new system, each address
segment can have 32 bits, for a total of
128 bits for the entire address.
• A disadvantage of IPv6 is the fact that so
much software used on the Internet would
Plans for New IP Addresses
(Continued)
much software used on the Internet would
become outdated because current
software is designed to hold 32-bit IP
addresses and, with the new system,
this number would no longer be
sufficient.
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IPv6 Status April 2013
• IPv6 address allocation has
happened and is happening
very smoothly
• More work in regional and local
transit networkstransit networks
• Content providers (especially
local content) and enterprise
customers need to keep working
on enabling IPv6 in their Internet
resources

• A port is a number used to address
software or services running on a
computer.
• A host computer might have several
services running on it.
Ports
services running on it.
• Each server running on the host is
assigned a port.
• The port is written at the end of the IP
address, separated from the IP address
with a colon—like this: 169.49.209.19:80
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Lecture 2 -_understanding_networks_2013

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