Xcast – a new scheme for

Zhang Ying Overview

„ 1. Introduction „ 2. Xcast Overview „ 3. The cost of the traditional multicast scheme „ 4. Motivation „ 5. Application „ 6. Xcast Flexibility 1.Introduction

„ Multicast „ sends data to a group of destinations efficiently „ Xcast – Explicit Multicast „ complements the existing scheme „ eliminates the per session signaling and per session state information „ supports a very large number of small multicast sessions 2. Xcast Overview

„ Terminology used here: „ Session

„ ‘multicast session’ used instead of ‘multicast group’ „ Channel

„ In a session with multiple senders, the flow sourced by one send will be called a channel. How does Xcast work?(1)

„ The source node keeps track of the destinations in the multicast channel that it wants to send packets to. „ The source node encodes the list of destinations in the Xcast header and sends the packet to a „ Each router along the way parses the header, partitions the destinations based on each destination’s next hop, and forwards a packet with an appropriate Xcast header to each of the next hops How does Xcast work?(2)

„ When there is only one destinations left, the Xcast packet can be converted into a normal unicast packet, which can be unicasted along the remainder of the router. How does Xcast work?—example(1) How does Xcast work?—example(2)

„ Perform a router lookup table to determine the next hop for each of the destinations listed in the packet „ Partition the set of destinations based on their next hop „ Replicate the packet so that there‘s one copy of the packet for each of the next hops found in the previous steps. How does Xcast work?—example(3)

„ Modify the list of destinations in each of the copies so that the list in the copy for a given next hop includes just the destinations that ought to be routed through that next hop „ Send the modified copies of the packet on to the next hop „ If there is only one destination for a particular next hop, the packet can be sent as a standard unicast packet to the destination 3. The cost of Traditional Multicast Scheme „ Traditional multicast were designed to handle very large multicast group. Scalability problems will occur when there is a very large number of groups. „ Two components of traditional IP multicast model „ The Host Group model „ A Multicast Routing Protocol The Host Group Model

„ A group of hosts is identified by a multicast group address, which is used both for subscriptions and forwarding. „ Two main costs „ Multicast address allocation „ Destination unawareness A Routing Algorithm

„ Maintains the member state and delivery tree „ Can be done by either a broadcast algorithm or a multicast algorithm „ Costs of multicast routing protocol „ Connection state „ Source advertisement mechanism „ Interdomain routing

4. Motivation – Advantages(1)

„ 1. Routers do not have to maintain state per session „ 2. No multicast address allocation required „ 3. No need for multicast routing protocols „ 4. No core node, so no single point of failure „ 5. Symmetric paths are not required „ 6. Automatic reaction to unicast resources „ 7. Easy security and accounting 4. Motivation – Advantages(2)

„ 8. Heterogeneous receiver „ 9. Xcast packets can make use of traffic engineered unicast path „ 10. Simple implementation of reliable protocols on the top of Xcast „ 11. Flexibility „ 12. Easy transition mechanisms 4. Motivation – Disadvantages(1)

„ 1. Overhead: each packet contains all remaining destinations „ 2. More complex header processing: each destination in the packet needs a routing lookup table „ 3. Xcast only works with a limited number of receivers 5. Application

„ IP telephony, video conferencing, multi-player games, collaborative e-meetings etc. „ Bridging the access link 6. Xcast Flexibility Reference

„ Draft „ ftp://ftp.rfc-editor.org/in-notes/internet- drafts/draft-ooms-xcast-basic-spec-07.txt „ R. Boivie, N. Feldman, Y. Imai, W. Livens, D. Ooms, O. Paridaens, E. Muramoto