MPLS diffusion - Multicast IP and traffic engineering

IP broadcast services are based on "1-to-N" group communication schemes, where a content source broadcasts to n receivers, or "N-to-P", where N transmitters have the capacity to broadcast to P receivers (as in the case of a videoconferencing service, for example). These group communication modes are mainly based on the use of IP multicast transmission for real-time TV broadcasting services, for example.

IP multicast transmission is characterized by the establishment and maintenance of receiver-initiated distribution trees, along which traffic is routed.

However, the IP multicast transmission mode has limitations intrinsic to the protocol mechanisms involved: for example, at no time does a source have any information about the location and distribution density of receivers, which can affect the level of quality associated with content delivery, as perceived by end-users.

Similarly, the IP multicast transmission mode provides no strict guarantee as to the bandwidth required to convey the various multicast streams without significant degradation such that it is not perceptible to the end user (image pixelation, for example).

Furthermore, it is not possible to take account of an end-user's network access capabilities to influence the way in which the multicast tree will be constructed and, for example, allow the source to decide whether to broadcast a TV program in Standard Definition (SD) or High Definition (HD).

These limitations have led the Internet Engineering Task Force (IETF) to begin work a few years ago on exploiting MPLS (Multi-Protocol Label Switching) traffic engineering functions, capable of establishing point-to-multipoint tree structures, whose characteristics - in terms of guaranteed bandwidth and robustness - are likely to overcome the shortcomings of IP multicast transmission.

However, the specifications published by the IETF are very rarely applied, if at all, by operators and other IPTV service providers. There are many reasons for this factual reluctance:

• the state of the art shows that few router manufacturers today support the functions described in these standards, and more often than not impose a static configuration on the various routers likely to participate in the establishment and maintenance of MPLS point-to-multipoint (P2MP) trees;

• current standards impose engineering such that the router directly connected to the content source will be the root of the P2MP tree, to which the various branches will be grafted according to a priori knowledge of the "leaf" trees...and the receivers to which these leaves are connected.

The aim...