[AG-TECH] Feasibility Question

[Bronek Carr]

Hi all,

We are assessing the feasibility of constructing AG Nodes at four sites so 
that they can connect together.  We shall use the conventional  letters S, 
F, M and L to denote the locations. Our major concern is network bandwidth 
and the goal of this question is to understand whether,  given the 
available network bandwidth,  a good quality inter-site communication is 
possible. We would also like to understand what are the project 
constraints deriving from the available bandwidth constraint. Following is 
a brief description of network links:
Network Links
Location "S" - Location "F":      2x155Mbps, present utilization 30%; 
Location "S" - Location "M":     4 Mbps Committed Information Rate  [12 
Mbps theoretical], present utilization 50% 
Location "F" - Location "M":     4 Mbps Committed Information Rate  [12 
Mbps theoretical], present utilization 50% 
Location "S" - Location "L":       4 Mbps Committed Information Rate [6 
Mbps theoretical] on a IMA connection [4 ATM lines] and 2 Mbps on a 
permanent dedicated connection; both the two lines are at present utilized 
only for small FTP download traffic, but we expect a 50% utilization rate 
in the future.

We have not finalized the Access Grid node configurations, but we would 
like to have in each node four cameras, unless network bandwidth 
constraints forces us to reduce this figure. We also do not know have at 
present any use case scenario, however, we may assume that the most 
typical usage will be a two-site video conference. 

Given that high quality video and audio are required in order to make the 
Access Grid really useful, we need to understand:

Questions
1.  whether we are forced to limit the project to sites "S" and "F" having 
a large bandwidth direct connection or we can hold our original goal of 
connecting all the four sites
2. whether we can hold our goal of having four video streams or we should 
instead assume that in each video conference involving locations "M" 
and/or "L" only one video stream can be used
3. whether we should add a mixer, in the sense of RFC 1889, acting as 
gateway towards locations "M" and "L"
4. whether we can afford having a multiple-site video conference or we are 
restricted to two-site video conferences. 
5. whether Gary Refka's figures (see Building an Access Grid Node), namely 
 256 Kbps per camera/site and 128 Kbps per site, are adequate/required for 
a high quality communication or not.  If we base our analysis on these 
figures, 2,256 Kbps should be required/adequate for a 
four-cameras-per-site video conference
 

Thank you in advance to everybody helping us to figure out how to cope 
with this issue.

Best regards

Bronek Carr
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