Showing results for 
Search instead for 
Did you mean: 

2921 (or more likely 3925) with 16 T1's - overloaded?


Hopefully some one here can give an expert opinion on this

The following configuration is ok per specs of 2921, but is this really asking for trouble?

I am concerned that perhaps the router will be overwhelmed and hover around 80% or more cpu/mem usage. when processing calls on all 8 T1's?

2921 (CISCO2921/K9) with 4 VWIC3-4MFT-T1/E1 + 2 of PVDM3-192  (A total of 16 PRI's)

(Expecting mostly G711, some fax-relay and/or g729 (medium-complexity))

Inserted later:

It looks like 2921 only supports a maximum of 240 T1/E1 channels, while 16 would need 384.

The 3925 looks to be a better fit with support for upto 480 T1/E1 (800 sip sessions).

By the way this is a gateway setup, PRI to SIP

Message was edited by: moqtadir1



It sure looks okay if I were to compare your requirements against the "Recommend WAN Access Speed (with services)"

Hope this Helps.

Nicholas Ong

Unfortunately data on this link concerns me.

It says a 2921 can only have 240 Digital Voice channels, which means a maximum of 10 T1s.

Althought it can have 400 sip sessions.

If what I interpreted is true, then the next logical step is to choose 3925.

In that case, I would like to apply my original question to the 3925 router, will it be happy with 16T1's in its stomach?


paolo bevilacqua
Hall of Fame Master Hall of Fame Master
Hall of Fame Master

The alternative would be to stay on the safe side, and use an AS5400XM that is very proven.


I understand that something in the AS5xxx can be put in place.

But the major advantages of the AS5400 is all we don't need here:

SS7 support, ability to group multiple gateways together via MLPPP

And mainly can't justify the cost of getting a new cisco 3950 with all cards (~$24000) vs the AS5400 series (> $40000).

I am just curious if anyone has done this and if not then atleast say that they have seen this configuration working somewhere.

The fact that the 3900 series is more recent makes it a little more harder.


I'm thinking.  Why not 2x 2921, load balance across the 2.  In that case, you get resiliency + handling of the load.



Yes that would work, but we have close to 50 T1's and I am trying to reduce the number of chassis to like 3, as opposed to 6.

Now costwise, 2x 2921's ~= 1x 3925, which is certainly doable, but long-term, power usage on 6 chassis vs 3 chassis is going to be a saving, plus a 4th chassis can give the needed spare/redundancy.

Converting 50 T1's to two DS3's is outside the scope of approved things on this project

While the solutions suggested here are doable and perfectly fine, I am specifically looking to see if the capacity in question is a possibility.

Getting Started

Find answers to your questions by entering keywords or phrases in the Search bar above. New here? Use these resources to familiarize yourself with the community: