B.I.E.R. (RFC8279) – Bit-Indexed Explicit Replication – is a multicast mechanism wherein the source of a multicast data packet explicitly identifies and indicates the set of destinations by way of inserting a destination bit-string into each multicast data packet. Each bit in the destination-bit-string corresponds to a destination in the network towards which – if the bit is set – the multicast data packet will be forwarded. Upon receipt of a multicast data packet, a B.I.E.R. router consults its unicast routing table in order to identify those interfaces over which copies of the received multicast data packet are to be sent, so as to follow the shortest path to each destination. When sending the multicast data packet over an interface, the B.I.E.R. router will clear all bits in the destination bit-string, except for those destinations for which the shortest path is via this interface.
B.I.E.R. thus offers multicast as a network service, by way of using (but, not constructing) a shortest-path source-tree, rooted in the source of each multicast data packet.
This project develops extensions to B.I.E.R. for enabling efficient and reliable content distribution. Among the axioms for the project are that:
- redundant traffic is avoided,
- for reliability purposes, retransmissions from close routers (i.e., localised retransmission traffic) are prioritized,
- essential traffic is forwarded along shortest paths,
- no per-flow (or other) state-requirements are imposed on intermediate routers,
- the developed protocol extensions can operate across routers with a non-modified data/forwarding plane.
Another way of expressing the two latter points is to say, that the protocol extensions developed must “work across the internet”, i.e., must not assume that all routers participating in data forwarding are aware of the developed protocol extensions (or, are even B.I.E.R.-aware).
Reliability mechanisms require that destinations are able to detect packet losses, learn to dynamically identify good candidates for packet recovery (e.g. local peers that have received and cached the lost packet) and request retransmission from them, thus allowing the system to adapt to networking conditions that may change over time. As appropriate, the project integrates ideas from ICN, 6CN or Segment Routing, and privileges a balanced approach between analytical modelling, network simulations, and experiments.