[AG-TECH] Bridge availability chances.

Christoph Willing willing at vislab.uq.edu.au
Mon Apr 9 16:06:11 CDT 2007

On 10/04/2007, at 5:38 AM, Derek Piper wrote:

> 	I'm having a (possibly) similar problem with a participant in  
> Tokyo, Japan. I'm not sure of the way that bridges are chosen, but  
> it seems that from this participant's location, no bridges are  
> available at all. I'm not sure if it's firewalling or what that  
> might prevent even the LIST of bridges appearing, or what it is.

At present, all AG3 bridges are "advertised" via a single bridge  
registry (at ANL) and collected into the VenueClient's bridge list  
when it starts up. If the bridge registry is not contactable, for  
whatever reason, at startup then the VenueClient will have an empty  
bridge list. Often, restarting the VenueClient will result in a  
usable bridge list - it depends on why the registry wasn't  
contactable; it could be that the registry was down, or maybe a local  
network problem. As long as the bridge registry isn't contactable,  
there'll be an empty bridge list.

AG3.1 (real soon now) caches bridge lists so that the cached version  
can be used when the bridge registry is not reachable at start up. It  
also has an update facility i.e. update bridge list while VenueClient  
is running.

The AG2 bridge mechanism is quite different - for a particular venue,  
a site somehwere must be running a bridge server which explicitly  
targets that particular venue in its configuration file (AG3 bridges  
bridge all venues).


> Jimmy Miklavcic wrote:
>> I'm working with Kansas University Medical Center to get a small  
>> Access  Grid node running. They most certainly don't have  
>> multicast available on their campus so we are stuck with unicast.  
>> They have a "very" stringent security policy and I'm forced to  
>> narrow down the number of bridges that they will allow through  
>> their fire wall.
>>  So the question is, if I give them a list of ten bridges, what  
>> are the chances that one or two of them will be listed in the  
>> bridge registry? Should they increase their bridge locator  
>> function from 10 to say 20 to increase their chances of seeing any  
>> of the ten? Also, if a bridge is not listed in the registry, does  
>> it mean that it is not available?
>>    -- Jimmy Miklavcic
>> Multimedia Specialist
>> Jimmy.Miklavcic at utah.edu
>> 155 SOUTH 1452 EAST RM 405
>> SALT LAKE CITY, UT 84112-0190
>> Office: 801.585.9335
>>  Fax: 801.585.5366
>> http://www.anotherlanguage.org
> -- 
> Derek Piper - dcpiper at indiana.edu - (812) 856 0111
> IRI 323, School of Informatics
> Indiana University, Bloomington, Indiana

Christoph Willing                       +61 7 3365 8350
QCIF Access Grid Manager
University of Queensland

More information about the ag-tech mailing list