Convergence time in VPNs

Abstract: Convergence time for a network is the time it needs to adapt to a new
situation. This new situation can appear in a number of way but in this
thesis only two possible changes are looked upon, when a link in the network
fails and when a link recovers again.

Today, convergence time is an important issue for network service providers
since they want to give their customers access to the best network available.
This means that the network convergence should be as fast as possible. For
the Virtual Private Network (VPN) service, it is crucial that the convergence
time is low since the VPN service gives the customer the impression that he
is working on a Local Area Network between the company's offices and not
through a service provider backbone. The VPN services looked upon in this
thesis use an Multi Protocol Label Switched (MPLS) core network which uses
label switching to forward the packets. To make this possible, a few
protocols are used. Border Gateway Protocol (BGP) is used on the access links
between the core network and the customers and between different autonomous
systems in the core network for distributing and receiving reachability
information about the VPN. Label Distribution Protocol (LDP) or sometimes
even ReSource reserVation Protocol - Traffic Extension (RSVP-TE) is used for
distributing labels and enabling label switching in the core.

In this thesis, these protocols are looked upon and the relevant parameters
are extracted. These parameters are theoretically looked upon and
optimizations are then proved by practical testing. From the results it is
concluded that BGP has the worst convergence time, both in access and peering
links. LDP and RSVP-TE could both be improved from their default
configuration.