The Works of DANTE - Issue 3
The DANTE View...
The GÉANT2 network will be the first trial hybrid network on an international scale in the world. Although much of the initial usage of GÉANT2 will continue to be IP, the interesting and fundamental development is the provision of point-to-point services, where a path is guaranteed on an end-to-end basis. The portfolio of GÉANT has now evolved to the point where, for most countries, the basic subscription will be “GÉANT+”. This is a combination of 10Gbps access to IP, combined with 10Gbps access to point-to-point services. The point-to-point services will make use of a new platform of switches currently being procured.
Building a switched infrastructure is very different from building a routed one. From a connectivity point of view, although not necessarily from a user point of view, routed networks degrade gracefully; more precisely put, performance goes gradually from acceptable through to awful. In contrast the switched network requires the availability of capacity on an end-to-end basis. This requires considerably greater discipline in terms of provision, definition of quality and grade of services etc.
The fact that Erlang B1 may be difficult to understand and, for the non-mathematical among us, something of a black art, does not mean to say that it does not define how things work in practice. With a new hybrid architecture, we will relearn some of the experience which the designers of switched networks have faced for many years. There is, however, a significant difference. Previously, switched networks have been based on single services (e.g. telephony call or end-to-end 64Kbps connection). We now face the challenge of organising and managing portfolios of switched services on an end-to-end basis.
Unlike routed networks, switched networks do not degrade gracefully. They either work from a user’s perspective or they fail. In this context perception is much more binary. If you are convinced that a point-to point service does not work at all, you tend to forget the bad old days of IP packet loss and endless pings. The big challenge of GÉANT2 is to prove that it is possible to organise effective switched services. This requires attention to boring things such as dimensioning and operational discipline. It will be interesting to see if we again yearn for the happy anarchy of IP.
Dai Davies
DANTE General Manager
1 Erlang B is a method, based on queuing theory, for determining networks’ behaviour relative to the amount of traffic they are carrying. It can be used to determine the network capacity required to support a predicted level of traffic at a desired quality.
