Reflector User GuideLines

November 25, 2004

Véronique Baudin

LAAS-CNRS

How to use Reflector ?

Start from the Platine Web Page at Laas

Goal of the reflector module

A reflector module has been developed to allow videoconference sessions for users without any multicast access. This reflector encapsulates the multicast messages in point-to-point messages. It translates the multicast network addresses, authorizing the crossing of firewalls that stop the multicast service. It uses UDP protocol which is well adapted to real-time traffic.

The reflector module has been designed for multicast traffic coming from the videoconference application, but it can be easily modified to be adapted for any other application built on top of a multicast service.

Each session member using the videoconference creates four data flows, each one identified by four different ports: PA and PA+1 for the audio flow and the audio control; PV and PV+1 for the video and the video control.

The reflector encapsulates the multicast flows, identified by an IP address #1, into UDP-based messages. When received, the UDP messages are decapsulated. The initial IP #1 address is then translated into another IP #2 address that corresponds to the identification of the other multicast group (figure 1.).

Figure 1. : Reflector principle

The behavior is symmetrical: the inverse address translation is made when sending information from group #2 to group #1. Figure 2. details the four data flows handled in a bidirectional way.

Figure 2. Full duplex communications

The reflector module can be used to interconnect:

- Two multicast groups located on two different LANS connected by a WAN

- A single user with a remote multicast group

How and when do we start Reflector

Click on the Reflector link on the Platine web starting page

You must obtain the following window:

If a session using Videoconference tool or Vic and Rat is used by both participants who can access or not global multicast address group, we can use the reflector module to include all participants.

The session defines the multicast group 224.235.235.224 on port number 3200, for example.

A first set of participants can use this multicast group.

A second set of participants from a school cannot use this multicast group.

If all participants must work together, we must start 2 reflectors:

o The first one on a machine enable to join the global multicast group 224.235.235.224 with TTL=64.

o The second one on a machine of the school local network, enable to join another machine on the global Internet.

The first machine is for example on LAAS network, and it’s called machine1@laas (its IP@ is 140.93.10.10).

On this machine, the module reflector must be started with the following information:

The second machine on the local network school has a public IP address, for example machine2@school (its IP@ is 212.205.10.10)

Adresses description

The Local Address means the multicast adress group used par a visioconference tool on your local network, on global network if all yours participants can access it.

The Distant Address means the distant machine on which all your local traffic is sent to be resent to the address used by the visioconference

Ports description

The local port must be the port number defined in the session configuration file, an dit can be the same for different multicast groups

The distant group is the port number where the reflector machine receive all traffic in order to translate it to the portnumber of the visioconference tool.