Frame Relay and Multiple sub-interfaces

[rkirmeier]

Can anyone tell if it is possible to setup a router with one phyical frame-relay connection and multiple logical connectioins (sub-interfaces) where the total bandwidth of all the remote Frame Relay connections add up to more then the total bandwidth of the main Frame Relay connection.

In other words..

Router 1A:
384K Bandwidth
4 sub interfaces for 4 different PVCs

Router 1B:
128K bandwidth

Router 2B:
128K Bandwidth

Router 3B:
128K Bandwidth

Router 4B:
128K Bandwidth

4 x 128K = 512K

I beleive this to be possible and practical as at any point Router 1A would not be utilizing all available bandwidth. I realize that at no point would all routers be able to utilize the full bandwidth of it's connection.

Thanks,
Robin K

 

[abovebrd]

note: for some reason I noticed that network B could not see at talk to my PIX firewall on network A

What could that mean ?

Network A 192.168.1.0
Network B 192.168.2.0
Both are connected via frame relay 192.168.4.1 thru 4.2

It seems this is the key to my problem ?
What would the answer be ?

-Danny

 

[Humby]

Yes it is possible. But there a few things to keep in mind before you overcommit a circuit. First, How much bandwidth does each circuit really need? Is the application you are running latency dependant? I would say if you think that eack link will average at 50% or lower than do it. You start to have problems after about 60% with latency. I have approximately 100 locations running over 4 t-1's. If that is any indication. we have 56k, 128k and 256 k PVC's. The application we run doesn't need alot of bandwidth but it is latency dependant. We average at approx 35% but peak at full t-1 speed at times. If you check any Frame relay book it will give you info on over commiting a circuit.
Here is a page I say that has some good info on frame relay:

http://www.alliancedatacom.com/framerelay.asp

Good luck!!!

 

[rkirmeier]

Thanks Humby (MIS)...

Just what I was looking for!!

 

[talisker]

You can configure your sub-interfaces to use more than the total fractional T1 port speed - in this case 384K. This will work in many cases because a T1 connection is full-duplex - which means you can have 384Kb/s of data going out & in at the same time.

The risk of doing this occurs when all of the sub-interfaces burst to their full (configured) CIR at the same time IN THE SAME DIRECTION. In other words, if all the sub-interfaces start sending data OUT of the router at 128K, you'll be exceeding the physical port-speed of your F-T1.

The result is lots of dropped packets until the data rate drops down to the physical port speed.

Since each sub-interface will be able to burst up to 384Kb/s anyway, there's no real advantage to doing what you're suggesting.