BGP applies a “hop-by-hop” routing; a BGP
router only advertises the routes to its neigh-
bours (in neighbouring domains) that it uses
itself. BGP runs over TCP (see Section 3.4) and
uses TCP port 179. After establishing a transport
connection, BGP exchanges the initial data flow,
which is the entire BGP routing table. Then,
incremental updates are sent when something in
the routing table is changing. Hence, periodical
updates of the total routing table are avoided to
save transfer capacity. Periodic “keep-alive”
messages are however used to ensure that the
peer BGP process is still running.
When transit is allowed, the routing information
has to be conveyed between the border nodes.
An example is the two nodes depicted in Figure
19 c). An interior “version” of BGP may then
be used, referred to as IBGP, not treated in any
nodes on the path between the pair of border
nodes.
6.2.3 Routing and Traffic Engineering
From the routing perspective, networks are
divided into Autonomous Systems (ASs) where
each AS is divided into Interior Gateway Proto-
col (IGP) areas to allow for hiding and aggregat-
ing routing information. This way of hierarchical
routing allows for more efficient routing han-
dling, although from a traffic engineering per-
spective it may hide information, e.g. on paths
used. Related to establishment of Label Switch-
ed Paths (LSPs) such information could be re-
quested, leading to the introduction of additional
features into the routing protocols, ref. [Jens01],
e.g. to support traffic engineering.
Typical attributes identified to support traffic
engineering operations are:
- maximum bandwidth;
- maximum reservable bandwidth;
- unreserved bandwidth (could be specified per
class); - resource class/colour.
These can be exchanged by the routing protocols
in order to allow for constraint-based routing of
LSPs. When LSPs are established by signalling,
the protocols may be enhanced in order to take
into account the constraints. In particular, when
backup LSPs are to be set up, one should see to
it that the backup path does not have overlapping
hops with the primary path. This could be a chal-
lenging problem in particular when fibre optic
cables carrying multiple wavelengths are used.
Then the routing process should be informed of
the grouping (i.e. the ones passing on the same
cable). One suggestion is to use the resource
class/colour field to indicate links that belong
to the same group (goes on the same cable)
[ID_ppro]. Such a grouping could also be
utilised to reduce the amount of routing informa-
tion to be exchanged, as similar routing mea-
sures may be applicable for all links in the
group. This is also related to constraint-based
routing as described in [Feng01].7 Concluding Remarks
The main objective of this paper was to present
formats and mechanisms related to the major
protocols in Internet. These are the IP and the
TCP, although UDP is gaining stronger foothold
for traffic flows carrying timing sensitive data
(audio and video). Several of the accompanying
papers in this issue of the Telektronikkrefer to
protocol fields and procedures mentioned above.References
[Come88] Comer, D. Internetworking with
TCP/IP.Prentice-Hall, 1988.[Feng01] Feng, B et al. State-of-the-art of IP
Routing. Telektronikk, 97 (2/3), 130–144, 2001.
(This issue.)[ID_ecn] Ramakrishnan, K K et al. The addition
of Explicit Congestion Notification (ECN) to IP.
draft-ietf-tsvwg-ecn-00.txt, Nov. 2000. Work in
progress.[ID_pilc] Balakrishnan, H, Padmanabhan, V N.
TCP Performance Implications of Network
Asymmetry.draft-ietf-pilc--asym-02.txt, Nov.- Work in progress.
[ID-ppro] Dovolsky, D, Bryskin, I. 2000. Calcu-
lating protection paths and proxy interfaces in
optical networks using OSPF.draft-dovolsky-
bryskin-cspf-pathprotect-proxy-00.txt. Work in
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Friendly Rate Control (TFRC): Protocol Specifi-
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Work in progress.[Jens01] Jensen, T. Basic IP-related Mecha-
nisms. Telektronikk, 97 (2/3), 54–85, 2001. (This
issue.)[Jens01a] Jensen, T. Network Principles and
Applications. Telektronikk, 97 (2/3), 287–310,- (This issue.)
[RFC793] IETF. 1981. Postel, J. Transmission
Control Protocol. DARPA Internet Program.
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