Telektronikk 2/3.2001

1 Introduction

As the Internet is growing from a playground for

an elite group of computer scientists in the early

80s to a huge network connecting tens (or hun-

dreds) of millions of users, the importance of

routing has become more and more obvious.

Routing, which is the process of finding a path

from a source to every destination in the net-

work, is the underlying structure that glues the

world-wide Internet together.

The concept of routing was introduced with the

telephone network. Over the past hundred years,

many different routing policies have been used

in the telephone network. As computerised

switching systems have been introduced, the

routing policies have become increasingly

sophisticated. However, all telephone routing

policies have their special features that differ

from the IP (or Internet) routing, so we cannot

simply adopt these policies to IP networks.

Some of the special characteristics of IP routing

compared to routing in telephone networks are

listed below:

1. In IP routing, the traffic pattern is less pre-
   dictable compared to that of the telephone
   traffic.


2. Routers and links in IP networks are not as
   reliable as switches and links in the telephone
   network, so maintaining connectivity is an
   important task of IP routing.


3. In the Internet, network administrators in dif-
   ferent domains may choose different policies,
   making traffic measurement and management
   policies much more difficult.


4. Since voice calls require the same, simple
   quality of service, the admission control deci-
   sion is trivial. In the Internet, however, con-
   nectivity is not sufficient to complete a call:

the path must also have sufficient resources

available.

5. IP routing is performed on a packet level,
   while the telephone network routing problem
   is performed in a circuit switched network.

In this document, we start with an overview of

the routing protocols that are currently in use in

the Internet (Chapter 2). The increasing traffic

demand and new requirements (such as QoS)

call for more sophisticated routing protocols.

Therefore, in Chapter 3 we discuss a new con-

cept of routing, namely Constraint-based rout-

ing. It refers to a class of routing systems that

compute routes through a network subject to sat-

isfaction of a set of constraints (e.g. resource

availability, policy) and requirements (such as

QoS). In the most general setting, constraint-

based routing may also seek to optimise overall

network performance while minimising costs.

Multi-Protocol Label Switching (MPLS) is a

technique promoted by the IETF that integrates

the label swapping paradigm with network layer

routing. The MPLS ability to support constraint-

based routing makes it highly relevant for this

study. Therefore, routing in MPLS is discussed

in Chapter 4.

In Chapter 5 we give a brief overview of the

status and trends of routing research and devel-

opment activities. Finally some concluding re-

marks are given in Chapter 6.

2 Current IP Routing

Protocols

In this chapter we make an overview of currently

deployed routing protocols. We start with a gen-

eral introduction of routing functionalities, pro-

tocol requirements, and choices in the design of

routing protocols. Next follows a description of

routing in IP networks. We shall discuss the

most popular routing protocols that are in use

State-of-the-art of IP Routing

BONING FENG, ANNE-GRETHE KÅRÅSEN,

PER THOMAS HUTH AND BJØRN SLAGSVOLD

This paper summarises the state-of-the-art of IP routing. Starting with an overview of the currently used

routing strategies and protocols in IP networks, it identifies the problems and challenges introduced by

the explosive growth of the Internet and the introduction of newer applications and services.

The routing problems in future IP networks are not trivial, with many complex problems yet to be identi-

fied and solved. In this paper, a class of routing systems that compute routes subject to satisfaction of

a set of constraints and requirements (called “constraint-based routing”, CBR) is presented.

Also included in this paper is a discussion of requirements for developing new routing protocols that

support new types of services, such as multicast and mobility.

Anne-Grethe Kåråsen (42) is

Research Scientist at Telenor

R&D, Kjeller. She is working in

the Internet Network Architec-

ture group with special interest

in layer 1-3 network manage-

ment and control.

anne-grethe.karasen

@telenor.com

Boning Feng (41) is Research

Scientist at Telenor R&D, Kjeller.

He is working in the Internet

Network Architecture group with

special interests in traffic engi-

neering, IP, routing, and simula-

tion. Before he joined Telenor in

1998, he was working as Asso-

ciate Professor at the Norwegian

University of Science and Tech-

nology, where he also received

his Master and PhD degrees in

Telematics with special focus on

traffic modelling and analysis.

[email protected]

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