TCP/IP Protocol Suite Networks and Protocols Prepared by: TGK First Prepared on: Last Modified on: Quality checked by: Copyright 2009 Asia Pacific Institute

TCP/IP Protocol Suite

Networks and Protocols

Prepared by: TGK First Prepared on: Last Modified on:

Quality checked by: Copyright 2009 Asia Pacific Institute of Information Technology



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Topic & Structure of the lesson

Introduction to TCP/IPAddress Resolution Protocol (ARP)Internet Control Message Protocol (ICMP)Internet Protocol (IP)User Datagram Protocol (UDP)Transmission Control Protocol (TCP)



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Learning Outcomes

At the end of this module, YOU should be able to:

• Discuss the operations and implementations of different protocols under the TCP/IP suite.

• Discuss the benefits and considerations for choosing the appropriate TCP/IP protocol for use in a network.



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Key Terms you must be able to use

If you have mastered this topic, you should be able to use the following terms correctly in your assignments and exams:

• Regenerate signals



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Main Teaching Points

• Repeater



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Introduction to TCP/IP

• Developed for the Advanced Projects Research Agency

(ARPA)

• Designed to network a wide variety of computing

platforms, allowing expensive resources to be shared

across the USA

• Designed to be fault tolerant in case of nuclear or other

war

• Originally heavily based on UNIX systems



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• The purpose of TCP/IP

• Provides a common communication standard for

network devices (e.g. mainframes, PCs, remote

devices, telephones, etc.)

• Provides a framework for interconnection and

interoperation regardless of platform or physical

network medium

• Where is TCP/IP used?

• Basic applications:

• Telnet (23) : Remote terminal session




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• FTP (21/20) : File Transfer

• SMTP/POP (25/110) : Electronic mail

• NFS (uses RPC) : Network File System

• More advanced applications:

• HTTP (WWW port 80)

• A transport for just about everything

• TCP/IP overview

• The term TCP/IP is used generically to refer to

anything and everything related to the specific

network (IP) and transport (TCP) layer protocols:




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• TCP

• UDP

• IP

• ARP

• TELNET

• FTP

• Layered protocols

• Early communication software was one big

program which did everything




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• Early communication software was one big

program which did everything

• Difficult to modify and add new functionality

• The program was broken down into parts or

layers, each layer with very specific functionality

• ISO 7 – layer model




• TCP/IP stack

• TCP/IP in relation to the OSI 7 – layer model

• Data flow through stack

• Data from the application flows down through the

layers

• Each layer ads its own header information

• Each layer multiplexes data from one or more

higher places




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• Data from the network flows upward through the

layer

• Each layer strips off the corresponding layer’s

header information

• Each layer de-multiplexes information to one or

more higher layers

• An Ethernet card recognises an Ethernet frame

which has its own address in the destination

address field

• The link layer passes the data to the correct

network layer protocol based




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• The link layer passes the data to the correct

network layer protocol based on the contents of

the TYPE field

• The IP layer passes data up to the next layer

based on the contents of the protocol field in the

IP header

• The next layer passes data up to the specific

application based on the contents of the Port field

in the TCP/UDP header




Address Resolution Protocol (ARP)

• Addressing issues

• TCP/IP is designed for many different types of

physical network:

• Ethernet

• Token Ring

• Leased lines

• Each has its own format for physical addressing

• To run successfully on all existing and future physical

networks, IP addressing must be independent of the

physical layer



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• You have no control over the address assigned to

your network interface

• The manufacturer encodes the address onto the

interface (i.e. physical address)

• If the card fails and is replaced, the machine’s physical

address changes

• Addressing problems:

• Machines send data to each other using the physical

address

• We want to send data to another computer’s IP

address




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• The ARP protocol is used to do this

• Example of ARP process:

• machine A wants to send data to machine B whose

IP address is aaa.bb.ccc.ddd

• sends a broadcast packet, with 0806 in the type

field

• Who has IP address aaa.bbb.ccc.ddd?

• machine B recognises its own IP address and

responds, ‘Hello, that’s me! Here is my hardware

address’



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• machine A now has B’s physical address

• The IP frame can now be coded into a properly

addressed Ethernet frame




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• The answer is held in a cache so that the next time

A has data for B, it can simply look in the cache for

its physical address

• Frequently used addresses stay in the cache

• Others time-out so as not to waste memory space




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Internet Control Message Protocol (ICMP)

• IP provides best-effort delivery

• Delivery problems can be ignored; datagrams can be

“thrown away”

• ICMP provides error-reporting mechanism

• Error detection

• Internet layer can detect a variety of errors:

• Checksum (header)

• Time-To-Live (TTL) expired

• No route to destination network

• Can’t deliver to destination host (e.g no ARP reply)



• Internet layer discards datagrams with problems

• Error reporting

• Some errors can be reported

• Router sends message back to source in datagram

• Message contains information about problem

• Encapsulation in IP datagram

• Types of messages

• ICMP defines error and informational messages




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• Error messages:

• Source quench

• Time exceeded

• Destination unreachable

• Redirect

• Fragmentation required

• Informational messages:

• Echo request/reply

• Address mask request/reply

• Router discovery



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• Message Transport

• ICMP encapsulated in IP

• ICMP messages sent in response to incoming

datagrams with problems

• ICMP message not sent for ICMP message




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• ICMP and Reachability

• An Internet host A, is reachable from another host B,

if datagrams can be delivered from A to B

• ping program tests reachability – sends datagram

from B to A that A echoes back to B

• Use ICMP echo request and echo reply messages

• Internet layer includes code to reply to incoming ICMP

echo request messages




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• Ping sample output (Windows)



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Internet Protocol (IP)

• IP module is central to Internet technology

• Routes IP packets between intermediate systems

• Fragmentation and re-assembly

• Unreliable datagram service

• IP address: 32 bit value

• Usually written as four octets in dotted decimal notation

• Consists of two parts: network number and host number

• Three classes of IP address: class A, B, and C

• Twenty + RFCs specifying IP



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• Ver – format of IP header (e.g. 4 or 6)

• IHL – IP header length in 32 bit words

• TOS – Type of Service

• Total length – bytes in the datagram

• Identification – IP packet ID number

• Flags – may/don’t/last/more fragment(s)

• Fragment Offset – for fragment reassembly

• TTL – packet time to live (hops)

• Protocol – protocol to give data to



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• Header Checksum – checksum on header only

• Source Address – IP address of packet originator

• Destination Address – IP address of destination

• IP Address Classes




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• Subnet Mask

• You have no control over the network address

• Assigned by e.g. RIPE, RIR, etc.

• Subnet mask allows you to assign part of the host

field of the address to be network number

• Allows your network to be divided into interior

networks; externally only one network address is

sufficient to access your site

• Keeps size of external routing tables to a minimum



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• The effect of the Netmask



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• As the number of subnets increases, the number of

hosts possible on each subnet decreases

• The node number of a host on a given subnet is

added to the subnet address to give the complete IP

number for the node

• E.g. With a subnet mask of 255.255.255.128 and a

network number of 193.77.140.128, Host 1 on this

network would have the IP number – 193.77.140.129



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• Best-effort Delivery

• IP is designed to work over all types of network

hardware, which may malfunction

• So IP datagrams may get lost, may be duplicated, may

be delayed, may be delivered out of order, or may be

delivered in a corrupt state

• We need higher layers of protocol software to deal

with these errors




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User Datagram Protocol (UDP)

• Connectionless unreliable datagram delivery service

• Adds only port number for multiplexing and delivery to

application and checksum

• If checksum fails on receipt, packet is simply discarded

• If application can’t accept data, packet is discarded]

• Low overhead: only 8 bytes of header added

• Used for broadcasts

• NFS

• DNS



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• UDP datagram:

• Source port – sending process (reply to this port)

• Destination port – receiving process

• Length – length of UDP header + data

• Checksum – pseudo header + UDP header + data

User Datagram Protocol (UDP)



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Transmission Control Protocol (TCP)

• The transport layer

• has no concept of routing

• does not know about any intermediate nodes

• Reliable delivery

• TCP works on top of IP

• TCP is connection-oriented. It corrects lost,

corrupted, out-of-order and delayed packets

• Guaranteed delivery service

• Positive acknowledgement with timeout and re-

transmission



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• Sliding window protocol

• Full-duplex connection

• Used for:

• Telnet

• FTP

• SMTP

• There are Twenty RFCs describing TCP

• How TCP ensures reliability

• Every message has a sequence number. The receiver

can tell if a message is missing or out of order




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• Corrupted messages are detected by means of

checksums

• TCP acknowledges all correctly received messages

(sends ACK to the sender)

• TCP header:




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• Initial sequence numbers are chosen randomly and

sent to the other side when the connection is set up

• Source port – the sending process

• Destination port – the receiving process

• Sequence number – sequence number of first byte of

data in the segment

• Acknowledgement number

• Valid if ACK bit is set

• Gives sequence number of next data expected to

be received



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• Data offset (or HLEN) – number of 32-bit words in

TCP header

• Flags (or Code Bits)

• Window – number of bytes sender will accept

• Checksum – pseudo header + TCP header + data

• Urgent – points to byte in segment that follows

urgent data



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Quick Review Question



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Follow Up Assignment



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Summary of Main Teaching Points



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Q & A

Question and Answer Session



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Topic and Structure of next session

•

Next Session

Documents

TCP/IP Protocol Suite Networks and Protocols Prepared by: TGK First Prepared on: Last Modified on: Quality checked by: Copyright 2009 Asia Pacific Institute