BGRP: Sink-Tree-Based Aggregation for Inter-Domain Reservations

(Title was originally The Border Gateway Reservation Protocol (BGRP) for Tree-Based Aggregation of Inter-Domain Reservations) 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 and protocol, called the Border Gateway Reservation Protocol (BGRP), for inter-domain resource reservation that can scale in terms of state storage, message processing load 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 reservation states at each router scales, in the worst case, linearly with the number of domains in the Internet. BGRP relies on differentiated services for data forwarding. As a result, the number of packet classifier entries is equal to the number of traffic classes, not the number of flows. 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 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.