Stephen Deering

Multicast routing in datagram internetworks and extended LANs

Multicasting, the transmission of a packet to a group of hosts, is an important service for improving the efficiency and robustness of distributed systems and applications. Although multicast capability is available and widely used in local area networks, when those LANs are interconnected by store-and-forward routers, the multicast service is usually not offered across the resulting internetwork. To address this limitation, we specify extensions to two common internetwork routing algorithms—distance-vector routing and link-state routing—to support low-delay datagram multicasting beyond a single LAN. We also describe modifications to the single-spanning-tree routing algorithm commonly used by link-layer bridges, to reduce the costs of multicasting in large extended LANs. Finally, we discuss how the use of multicast scope control and hierarchical multicast routing allows the multicast service to scale up to large internetworks.

The PIM architecture for wide-area multicast routing

The purpose of multicast routing is to reduce the communication costs for applications that send the same data to multiple recipients. Existing multicast routing mechanisms were intended for use within regions where a group is widely represented or bandwidth is universally plentiful. When group members, and senders to those group members, are distributed sparsely across a wide area, these schemes are not efficient; data packets or membership report information are occasionally sent over many links that do not lead to receivers or senders, respectively. We have developed a multicast routing architecture that efficiently establishes distribution trees across wide area internets, where many groups will be sparsely represented. Efficiency is measured in terms of the router state, control message processing, and data packet processing, required across the entire network in order to deliver data packets to the members of the group. Our protocol independent multicast (PIM) architecture: (a) maintains the traditional IP multicast service model of receiver-initiated membership, (b) supports both shared and source-specific (shortest-path) distribution trees, (c) is not dependent on a specific unicast routing protocol, and (d) uses soft-state mechanisms to adapt to underlying network conditions and group dynamics. The robustness, flexibility, and scaling properties of this architecture make it well-suited to large heterogeneous internetworks.

RSVP: a new resource ReSerVation Protocol

A resource reservation protocol (RSVP), a flexible and scalable receiver-oriented simplex protocol, is described. RSVP provides receiver-initiated reservations to accommodate heterogeneity among receivers as well as dynamic membership changes; separates the filters from the reservation, thus allowing channel changing behavior; supports a dynamic and robust multipoint-to-multipoint communication model by taking a soft-state approach in maintaining resource reservations; and decouples the reservation and routing functions. A simple network configuration with five hosts connected by seven point-to-point links and three switches is presented to illustrate how RSVP works. Related work and unresolved issues are discussed. >

An architecture for wide-area multicast routing

Existing multicast routing mechanisms were intended for use within regions where a group is widely represented or bandwidth is universally plentiful. When group members, and senders to those group members, are distributed sparsely across a wide area, these schemes are not efficient; data packets or membership report information are occasionally sent over many links that do not lead to receivers or senders, respectively. We have developed a multicast routing architecture that efficiently establishes distribution trees across wide area internets, where many groups will be sparsely represented. Efficiency is measured in terms of the state, control message processing, and data packet processing, required across the entire network in order to deliver data packets to the members of the group. Our Protocol Independent Multicast (PIM) architecture: (a) maintains the traditional IP multicast service model of receiver-initiated membership; (b) can be configured to adapt to different multicast group and network characteristics; (c) is not dependent on a specific unicast routing protocol; and (d) uses soft-state mechanisms to adapt to underlying network conditions and group dynamics. The robustness, flexibility, and scaling properties of this architecture make it well suited to large heterogeneous inter-networks.

Host groups: a multicast extension for datagram internetworks

The extensive use of local networks is beginning to drive requirements for internetwork facilities that connect these local networks. In particular, the availability of multicast addressing in many local networks and its use by sophisticated distributed applications motivates providing multicast across internetworks. In this paper, we propose a model of service for multicast in an internetwork, describe how this service can be used, and describe aspects of its implementation, including how it would fit into one existing internetwork architecture, namely the US DoD Internet Architecture. 1 2

Hierarchical distance-vector multicast routing for the MBone

The exponential growth of the Multicast Back-bone (MBone) has resulted in increased routing overhead and processing costs. In this paper we propose a two-level hierarchical routing model as a solution to this problem. This approach involves partitioning the MBone into non-overlapping regions using DVMRP as the inter-region routing protocol; intra-region routing may be accomplished by any of a number of existing multicast protocols. Our design is flexible enough to accommodate additional levels of hierarchy, and protocols other than DVMRP at the higher levels. The unique feature of this approach is the independence of the higher level routing protocol from the subnet addresses, which allows for easy incremental deployment with small changes to existing intra-region protocols.

RSVP: A New Resource ReSerVation Protocol: Novel design features lead to an Internet protocol that is flexible and scalable.

This chapter tries to make the general design of RSVP relatively independent of the architectural components. Clearly, a particular implementation of RSVP is tied quite closely to the flowspec and interfaces used by the routing and admission control algorithms. However, the general protocol design should be independent of these. In particular, the protocol should be capable of establishing reservations across networks that implement different routing algorithms, such as IP unicast routing, IP multicast routing, the recently proposed core based tree (CBT) multicast routing, or some future routing protocols. This design goal makes RSVP deployable in many contexts. For optimally efficient routing decisions, however, routing selection and resource reservation should be integrated—so the choice of route can depend on the quality of service requested, and the stability of the route can be maintained over the duration of the reservation. The first RSVP design is verified by a detailed simulation and preliminary implementation. Much testing remains to be done in the context of larger scale simulations, as well as in real prototype networks, such as DARTnet.

SIP: Simple Internet Protocol

Several features of the Simple Internet Protocol (SIP) are described and compared to those offered by the Internet Protocol (IP). The changes required for other protocols in the TCP/IP suite to accommodate SIP are discussed, as are the mechanisms available to allow gradual transition of the Internet from IP to SIP. Future directions for SIP development, a report on current implementation status, and a summary of the specific improvements offered by SIP over IP are presented.<<ETX>>