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:
- In IP routing, the traffic pattern is less pre-
dictable compared to that of the telephone
traffic.
- 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.
- In the Internet, network administrators in dif-
ferent domains may choose different policies,
making traffic measurement and management
policies much more difficult.
- 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.
- 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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