I need to provide SRST for 1760 IP phones

[news2010a]

Hi,

I imagine I have a branch site with 1,760 Cisco 7965 IP phones.Hub is running CUCM 8.5. I also have a branch site with 1400 IP phones to deployed.

MPLS CE router to this new branch site is yet to be designed and installed. MPLS network running SIP Trunking.

Question:

I need to provide POTS lines and survivability in case the branch office MPLS/SIP Trunking goes down.

Caveat: voice traffic over the SRST/analog lines must encrypted.

I see in the Cisco website that SRST can support up to 1500 IP phones in a Cisco 3945E.

Can someone confirm if:

a) Can I stretch this to support 1760 registererd phones? Or should I put a separate Cisco router to support the remaining 257 phones?

b) In this scenario with lot of IP Phones (over 1400 IP phones), should I plan to provide a separate 3945E to handle the SRST itself? Or is it still a good design if I provide SRST based on the MPLS CE routers?

[paolo bevilacqua]

You should have two Call Managers, one per site.

Either indipendend, or members of the same cluster.

Not SRST.

Anyway for design of that size you should involve the senior technical members of your local Cisco office.

[Gajanan Pande]

Yup, I concur with Paolo. A site with that size of phone users needs a CUCM node instead of SRST. SRST might work but that's not the best design.

You might want to register other nearby but small sized sites to this node ( located at site with 1760 phones ) as well to make optimum use of it.

GP.

Pls rate helpful posts !!

[Ayodeji Okanlawon · Accepted solution]

Hi,

This all depends on what your scenario is. If you have a deployment with CUCM servers deployed in data center and you are clustering over the WAN, then can do the ff:

1. If cost is not an issue, use a single cucm as your srst device at the local site with 1760 phones. Bear in mind that you will need a cucm node license and probably device licenses. This is by far the best approach but may be expensive

2. A 3945E can support 1500 phones. So you can use a single 3945E and a 2900 ISR to provide for the remaining phones.

2b. Dont forget to purchase your srst licenses..

2b..you will need to create Two different Device pools and assign two different srst references

2c. You will need to create dial-peers to route calls in srst to the second gateway or first gateway depends on where the call originates from if the dialed number cant be found on that gateway

2d. You will need to think of how to avoid call loops in this scenario. Eg if a user dials a number that has not registered to either of the srst router, there is a tendency that the call will keep bouncing between the two gateways, hence creating a loop

3. If your budget is really tight and you control the MPLS CE router, you can use this as your second srst router.

HTH..

[news2010a]

Thank you. It makes sense.