Multicast: Beacons

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Multicast Beacons Bridges

• Mark Hayes
• Technical Director - Cambridge eScience Centre

Access Grid on the Desktop - Tuesday 15th June
2004
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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. 224.2.177.155. Multicast
packets are sent to this group, represented by a
special sort of IP address in the
range 224.0.0.0-239.255.255.255. (There is also
an associated port number.)
http//www.tldp.org/HOWTO/Multicast-HOWTO.html
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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...

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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.

http//dast.nlanr.net/Projects/Beacon/
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Beacon architecture
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Screenshot
http//ulcc.beacon.ja.net/
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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,
  233.3.18.1/55524)
• Start it up
• start_beacon.bat

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Interpreting the beacon display

• At its most basic
• greengood, yellowwarning, redtrouble,
• grey/whiteno 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.

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What to do when things look bad...

• Talk to your (friendly) local network support
  staff
• Contact the Access Grid support centre
• http//www.agsc.ja.net/
• support_at_agsc.ja.net
• Useful information theyll likely need IP
  address/hostnames,
• address for the multicast group youre attempting
  to join.
• Your local e-Science Centre may also be able to
  help

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Questions?
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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.
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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
http//people.man.ac.uk/zzcgumd/software/QuickBri
dge.tar.gz Documentation at http//www.accessgri
d.org/agdp/guide/network-bridging.html (also
covers the multi-session bridge for ANL virtual
venues.)
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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.
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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
• http//people.man.ac.uk/zzcgumd/software/QuickB
  ridge.tar.gz
• Uncompress in a new directory
• tar -zxvf QuickBridge.tar.gz
• Compile the C source code
• cc -o QuickBridge QuickBridge.c

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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
233.2.171.193 59756 50304 University of
Cambridge Cam v 233.2.171.193 59754 50306
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.
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Using QuickBridge
Connecting to a bridge from an Access Grid
session In command line mode cd
C\ag\agapps\bin (or similar) audio rat
ltQuickBridge hostnamegt/ltportgt video vrm
ltQuickBridge hostnamegt/ltportgt
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Questions?