Telektronikk 2/3.2001

1 Introduction

The Internet Protocol (IP) has gained a phenom-

enal place in telecommunications in the latest

years. Even the protocol’s presence for several

decades, certain events and driving forces may

well be credited its surf on the promotion wave.

The invention of web browsing and openness of

the IP and corresponding transport protocols

allowing for easy use in education and simplicity

of implementation, may be two factors. How-

ever, when deploying an IP-based network in a

commercial environment, we are faced with sev-

eral more issues.

The ongoing work related to IP, including proto-

cols, mechanisms, applications, systems, is quite

phenomenal. This implies that there is a steady

evolution in the area, which is a challenge in

keeping track of even the ideas presented within

a fairly narrow area. However, in order to follow

any discussion going on in different fora, a

knowledge of the basic mechanisms and formats

of protocols is needed. The objective of this

paper is to introduce these formats for IP and

the transport protocols.

IP is described in Chapter 2, covering both ver-

sion 4 and version 6. The IP error and control

messages are briefly outlined in Chapter 3.

Chapter 4 and Chapter 5 present the two com-

mon transport protocols, User Datagram Proto-

col and Transmission Control Protocol, respec-

tively. Addressing and routing are discussed in

Chapter 6.

2 IP Packet Formats

The most fundamental IP service is based on an

unreliable, best-effort, connectionless packet

delivery system. The service is called unreliable

because delivery is not guaranteed. The service

is called connectionlessbecause eachpacket is

treated independently from others, e.g. packets

in a sequence may travel along different paths,

or some may be lost while others are delivered.

The service is called best-effortas no packet is

assumed to be discarded on purpose.

As explained above, when information is to be

passed between two terminals, it is divided into

a number of units where each is put into an IP

packet (datagram). A network parameter maxi-

mum transfer unit (MTU) decides how long

fragments can be carried through the network.

Commonly, the fragments are reassembled at the

destination. The IP packet header formats are

treated in this section while issues related to

transport protocols are described in the follow-

ing sections.

2.1 IP version 4

The 1988 version of the IP packet format is

depicted in Figure 1. This is also known as IP

version 4 (IPv4), where each host has a 32 bit

address.

The Versionfield (4 bit) gives the IP protocol

version (the current relevant versions are 4 and

6 – note that the format of version 6 is described

Internet Protocol and Transport Protocols

TERJE JENSEN

The Internet Protocol suite has emerged as a pivotal component during the last decade. The basic

formats and protocol mechanisms for the protocols related to the Internet Protocol and its common

transport protocols are described in this paper.

Figure 1 IP version 4 packet format

Terje Jensen (39) is Research

Manager at Telenor R&D, Kjeller

He earned his PhD degree in

1995 from the Norwegian Uni-

versity of Science and Technol-

ogy. Activities include perfor-

mance modelling and analysis,

dimensioning and network evo-

lution studies.

[email protected]

Version Length Type of Service Total length

Identity Flags Fragment offset

Protocol Header checksum

Source IP address

Destination IP address

Options

Data

Padding

Time

04 8 1619 24 31

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