“Multicast: Beacons & Bridges” Mark Hayes Technical Director - Cambridge eScience Centre Access Grid on the Desktop - Tuesday 15th June 2004

Multicast: an overview Multicast is a one-to-many distribution model for network traffic, especially used for video conferencing and other forms of data distribution. Machines express an interest in receiving multicast traffic by joining a “multicast group”, e.g Multicast packets are sent to this group, represented by a special sort of IP address in the range (There is also an associated port number.)

How do I know if I have working multicast? Ask your local network admin Try the ‘mtrace’ tool - a multicast version of ‘traceroute’ ftp://limestone.uoregon.edu/pub/multicast/kddlabs-mirror/mtrace/ Install the NLANR multicast beacon client...

The NLANR beacon Application developed by The National Laboratory for Applied Network Research (NLANR), USA v0.8 written in Java - OS/platform independent (latest v0.9 in Perl. We will only consider v0.8 here.) client-server architecture - clients exchange multicast packets (with time stamps) and calculate % packet loss, delay, etc. - server collects these parameters from the clients and presents them to the user via a web interface. Open source (BSD-type license) allows modification, unlimited distribution provided you acknowledge NLANR.

Beacon architecture

Screenshot

Installing the beacon client Prerequisites: a working Java run-time environment, and an accurate system clock! (use NTP/Win XP time sync.) Download the source (v0.8 available from NIEeS) Install in a new directory mkdir beacon; unzip ukbeacon-v0.8.zip Edit the configuration file to point to a beacon server and a multicast group + port number (e.g. ulcc.beacon.ja.net/19997, /55524 ) Start it up start_beacon.bat

Interpreting the beacon display At its most basic: green=good, yellow=warning, red=trouble, grey/white=no information available (usually indicates no working multicast, also bad!) The beacon webpage usually indicates how much % packet loss/time delay etc. corresponds to which colour The columns indicate statistics for multicast senders, the rows for receivers. Note that multicast traffic is not necessarily symmetric.

What to do when things look bad... Talk to your (friendly) local network support staff Contact the Access Grid support centre: Useful information they’ll likely need: IP address/hostnames, address for the multicast group you’re attempting to join. Your local e-Science Centre may also be able to help

Questions?

Multicast-Unicast bridge Luckily for the multicast-deprived, it is possible to “bridge” to a multicast capable network. Usually considered a temporary solution until multicast can be enabled, or as a workaround during a multicast outage.

QuickBridge Runs on a multicast capable machine. Clients connect to the bridge and it forwards all multicast traffic to/from a specific multicast group on behalf of the client. Developed by Mike Daw (Manchester) and Stephen Booth (EPCC) Available for download at Documentation at (also covers the multi-session bridge for ANL virtual venues.)

Usage scenarios 1. Local network does not support multicast at all May require the co-operation of a friendly remote site with multicast to run the bridge for you. 2. AG node behind a firewall that will not forward multicast (but the local network beyond the firewall does), therefore run a bridge yourself on a machine just outside the firewall.

Installing QuickBridge Choose a machine to run the bridge software. (Linux) N.B. this should not be running other AG software Download the source from Uncompress in a new directory tar -zxvf QuickBridge.tar.gz Compile the C source code cc -o QuickBridge QuickBridge.c

Using QuickBridge Starting the server on a multicast-capable machine: Multicast groups and port numbers are defined for each AG virtual venue in the vv.dat file. e.g. the entry for the University of Cambridge virtual venue reads: Cam a University of Cambridge Cam v University of Cambridge./QuickBridge.ksh -s -r Cam This will output the unicast port numbers for audio and video. The remote user connecting to the bridge will need these port numbers and the hostname of the machine running the bridge.

Using QuickBridge Connecting to a bridge from an Access Grid session: In command line mode: cd C:\ag\agapps\bin (or similar) audio: rat / video: vrm /

Questions?