In current communication networks, which comprise an extensive range of network nodes connected via link lines, data is often transmitted in data packets. In this type of configuration, the data packets are transferred from an originating network node, and then from network node to network node, until they arrive at the destination network node. Well-known transmission methods of this type include the so-called ATM method (asynchronous transfer mode), the so-called MPLS method (multiprotocol label switching), and methods based on the Internet protocol (IP).
There are generally a number of alternative routes for transmitting data packets from an originating network node to a destination network node. In each case, a suitable route must be selected from these alternatives for each data packet (or each stream of related data packets) to be transferred. In particular, this selection is based on the criterion of transmitting the data packets to the destination network node with a minimum of delay and a minimum of packet losses. In order to optimize the data-transfer performance of the overall communication network, the selection should also be based on the avoidance of transfer bottlenecks, i.e. the overloading of individual network nodes or link lines, where possible. This can be achieved by distributing the data-traffic load in the communication network as appropriate, although there is the problem of coordinating route selections made by individual network nodes, when distributing the data-traffic load across all network nodes.
The IETF (Internet engineering task force) Internet draft “draft-hummel-te-oct-00.txt” by Heinrich Hummel, dated October 1999, proposes the use of a central, data-traffic routing facility to distribute the data-traffic load. With central routing, coordination between all the network nodes would not be necessary in order to achieve optimum distribution of data traffic. The data-traffic routing facility sends probability details to each network node. With reference to each destination network node, these details specify the probability of selecting a particular route leading to this destination network node for a connection that is subsequently established. When the connection is subsequently established, the actual route to be used is selected using a random-number generator in accordance with the probability details that were sent.
However, the fixed assignment of connections to routes is evidently inflexible, particularly in the case of permanent connections with data-transfer speeds that fluctuate widely. Furthermore, if connections are established and shut down frequently, the permanent assignment of connections to routes results in high administration overheads for each network node concerned. This is particularly resource-intensive in the case of large communication networks linking many subordinate communication networks, e.g. large Service Provider networks, since it involves the management of very many end-to-end connections between a potentially very high number of terminal devices.
As an alternative, data packets could be distributed to the destination network node via the alternative routes without any reference to a connection assignment. However, the problem here is that, having followed different routes, the data packets do not normally arrive at the destination network node in their original transmission sequence. Reconstructing the original, connection-specific stream of data packets involves a considerable delay, since it is necessary to wait a relatively long time for each data packet to be transferred. Such delays are often not acceptable in real-time applications.