Ólafur Ragnar Helgason – Reykjavik University - Distance learning using IP multicast Ólafur Ragnar Helgason Network Systems and Services Laboratory Department of Computer Science Reykjavík University, Reykjavík, Iceland

Ólafur Ragnar Helgason – Reykjavik University – 2 Introduction – IP is everything IP dominates in technology, services and innovation IP – primary benefits –Simple service model –Avoids complexities of telephony standardization, regulatory complexities... –Flexibility –Inexpensive, commodity equipment Need to bring the benefits of IP to group communication

Ólafur Ragnar Helgason – Reykjavik University – 3 Distance learning Especially valuable in sparsely populated areas In Iceland predominantly based on ISDN equipment –justified by QoS guarantees of ISDN –expensive and specialized equipment ISDN conferencing is centralized –All data passes through a single conference bridge –Limited scalability, single point of failure H.323 solutions can increasingly use IP as transport –Architecturally the same having a single conference bridge

Ólafur Ragnar Helgason – Reykjavik University – 4 IP Multicast Promise: Bring the benefits of IP to group communication Research dates back 20 years MBone been around for 15 years Renewed interest in research on multicast STILL: MULTICAST IS NOWHERE

Ólafur Ragnar Helgason – Reykjavik University – 5 IP Multicast today Address allocation problem –reserved address range – global address allocation - limits scalability Multicast specific routing –Complex algorithms - global infrastructure Static Virtual Multicast Network –Complex management - global infrastructure IP multicast doubles the IP infrastructure CAN ONLY AFFORD MCAST IF IT DOES NOT ADD TO THE COMPLEXITY OF THE INTERNET

Ólafur Ragnar Helgason – Reykjavik University – 6 New Paradigm for IP Multicast Simple Lightweight Internet Multicast - SLIM Primary innovation What is not there!! Role of network: Sending a packet from a single source to one or more receivers Avoid, not solve, the problems of older multicast protocols No multicast specific IP infrastructure –Leverage already existing router facilities

Ólafur Ragnar Helgason – Reykjavik University – 7 SLIM Avoids address allocation –Source specific: Channel ID is pair –C is source specific channel identifier, not neccesary a multicast address Avoids Multicast routing –Unicast Join/leave signaling creates ditribution tree –Join creates classifier forwarding state in routers –Flow based forwarding Avoid virtual multicast network –Tunnels constructed dynamically as needed –Ignores non-multicast enabled routers

Ólafur Ragnar Helgason – Reykjavik University – 8 SLIM and Distance learning Increased scalability –No centralized bottleneck Can use commodity equipment and desktop applications –reception, encoding and media streaming Multicast groups can be created on-demand –No need for central authorization or coordination –Meetings can be scheduled im-promptu –Number of participants can change over session lifetime –Beyond what can be done in a conventional distance learning system

Ólafur Ragnar Helgason – Reykjavik University – 9 Experimentation Experimented with multicast over two years –Interactive conferencing, TV/Radio, Live distribution Design of SLIM makes it possible to experiment over the open internet –Unicast forwarding, general routing facilities –No network admin collaboration –Facilitates organic growth from end-users –Can cope with firewalls and NAT’s to end users

Ólafur Ragnar Helgason – Reykjavik University – 10 Distance learning experiments 1.Content distribution Single source distribution to multiple receivers Modest delay can be tolerated 2.Live distribution Real time constraints Feedback via chatroom or messenger application 3.Fully interactive teleconference Multisource multicast – distribution tree per sender Even stronger real time constraints A very small delay can be tolerated

Ólafur Ragnar Helgason – Reykjavik University – 11 H.323 Conferencing Use SLIM to implement scalable teleconferencing for H.323 clients –H.323 end systems used unchanged –H.323 conferencing acheives the scalability of multicast Multicast Gateway (MG) interrupts session initiation and media streams –Converts a unicast flow destined for a conferencing bridge to multicast flow –A central multipoint controller used for session control No centralized media bridge

Ólafur Ragnar Helgason – Reykjavik University – 12 Contribution A multicast protocol that avoids the problems that hinder widespread Internet deployment Experiments show that multicast increases flexibility and scalability in distance learning at a reduced cost Prototype of a decentralized H.323 conferencing solution that uses SLIM as a transport Current goals: Extend experiments over RHnet in Iceland and NORDUnet in scandinavia and Europe