BGRP: Sink-tree-based aggregation for inter-domain reservations

Abstract

Resource reservation must operate in an efficient and scalable fashion, to accommodate the rapid growth of the Internet. In this paper, we describe a distributed architecture for inter-domain aggregated resource reservation for unicast traffic. We also present an associated protocol, called the Border Gateway Reservation Protocol (BGRP), that scales well, in terms of message processing load, state storage and bandwidth. Each stub or transit domain may use its own intra-domain resource reservation protocol. BGRP builds a sink tree for each of the stub domains. Each sink tree aggregates bandwidth reservations from all data sources in the network. Since backbone routers maintain only the sink tree information, the total number of reservations at each router scales linearly with the number of Internet domains N. (Even aggregated versions of the current protocol RSVP have a reservation count that can grow like O(N2).) BGRP maintains these aggregated reservations using “soft state.” To further reduce the protocol message traffic, routers may reserve bandwidth beyond the current load, so that some sources can join or leave the tree without sending messages all the way to the tree root. BGRP relies on Differentiated Services for data forwarding, hence the number of packet classifier entries is extremely small.