Resource classattributes can be viewed as
“colours” assigned to resources such that the
set of resources with the same colour belongs to
the same “class”. Resource class attributes are
administratively assigned parameters, and they
can be used to implement various policies. Links
are the resources of special interest, and link
colour is one of the link attributes included in
the IGP TE extensions (see 4.1).
5 Development Trends
5.1 IP Multicast Routing
Today, most Internet applications are so-called
unicastbecause they use a point-to-point trans-
mission infrastructure. The usage of point-to-
multipoint transmission was limited to local net-
work applications due to the natural broadcast
capabilities of LANs. But during the past few
years, we have observed the emergence of new
applications that use multicasttransmission to
enable efficient communication among a group
of hosts (instead of two hosts). These applica-
tions require “multicast routing” – sending an IP
packet to a “group” address so that it reaches all
the members of the group, which may be scat-
tered throughout the Internet.
There is a number of key challenges that must be
met by a multicast routing algorithm to be appli-
cable to the Internet. It must route data only to
group members, optimise routes from the source
to receivers, maintain loop-free routes, and not
concentrate all multicast traffic on a subset of
links. Furthermore, the signalling in creating and
maintaining a group must scale well with a
dynamic receiver set.
In order to provide a multicast service, one also
has to implement a complex protocol architec-
ture not limited to a single routing protocol.
Issues like address allocation, domain isolation,
access control, and security have to be provided
for multicast to become a commercial service.
Today, multicast has not yet matured enough to
be widely used. Research efforts are currently
trying to address the scalability issues by provid-
ing a simpler architecture. The future of multi-
cast routing relies on these efforts, and also on
the capacity of the network providers to define
business models that can fund the deployment
of the service.
5.2 Mobility
With the advent of portable computers, the need
to support mobility in the Internet has become
pressing in recent years. According to the IETF
mobile IP working group, the requirements for a
mobile IP solution are:
1 A mobile host should be capable of continuing
to communicate, using the same IP address,
after it has been disconnected from the Inter-
net and reconnected at a different point.2 A mobile host should be capable of interoper-
ating with existing hosts, routers, and services.The first requirement is dictated by the need to
maintain TCP/IP connections while the mobile
host is roaming from cell to cell. Keeping a sin-
gle IP address is essential because this address
identifies the TCP connection. The second re-
quirement is dictated by the need for “gradual
deployment”.A few other “soft requirements” were also listed
by the IETF mobile-IP group.
1 No weakening of IP security;
2 Multicast capability;- Location privacy.
The basic model for supporting mobility in the
Internet is presented in IETF [RFC2002]. In the
same document, the mobile-IP group also de-
fined one single routing protocol. In order to
reach an agreement they took many shortcuts.We are now only seeing the beginning of mobile
computing. IP extensions for mobility are being
standardized, and the real deployment is slowly
starting. The current protocols have been de-
signed in a very conservative fashion, so as to
work in the current Internet. Many refinements
will have to be addressed in further versions of
IP mobility. To gain the advantage of mobility,
one will probably have to update the routing pro-
tocols so that they will allow multiple home
agents and clusters of bases [HUIT00].6 Conclusion
In this paper we have given an overview of the
state-of-the-art of IP routing.In today’s Internet, there is a clear distinction
between intra-domain protocols (IGPs) and
inter-domain protocols (BGPs).Each ISP can make its own choice of IGP. The
most popular IGPs are still those defined in the
80s (and based on algorithms from the late 50s),
although we observe a shift from vector-distance
protocols (such as RIP) to link-state protocols
(such as OSPF and IS-IS). Link-state protocols
have many advantages compared to the vector-
distance ones; however, they still have some
major drawbacks. One of these is that all the
IGPs used in the Internet today offer best-effort
service, which means that they do not support
QoS requirements.