BGRP: A Tree-Based Aggregation Protocol for Inter-domain Reservations

Abstract

Resource reservation needs to accommodate the rapidly growing size and increasing service diversity of the Internet. Recently, hierarchical architectures have been proposed that provide domain-level reservation. However, it is not clear that these proposals can set up and maintain reservations in an efficient and scalable fashion. 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 only maintain the sink tree information, the total number of reservations at each router scales linearly with the number of domains in the Internet. (Even aggregated versions of the current protocol RSVP have an overhead that grows like N.) BGRP relies on Differentiated Services for data forwarding. As a result, the number of packet classifier entries is extremely small. To reduce the protocol message traffic, routers may reserve domain bandwidth beyond the current load, so that sources can join or leave the tree or change their reservation without having to send messages all the way to the tree root for every such change. We use “soft state” to maintain reservations. In contrast to RSVP, refresh messages are delivered reliably, allowing us to reduce the refresh frequency. Columbia University Computer Science Technical Report No. CUCS-029-99