MTP Required or Not on SIP Trunk to CUPS SIP Proxy

Unanswered Question

Hi There,

I am battling with the situation below. I hope the details make sense. If any one has any suggestions or leads or has tried something similar please let me know.

With Thanks

Paul

MTP Required or Not on SIP Trunk to CUPS SIP Proxy?

Call manager 6.0.1

Currently we have IOS SW MTPs & IOS HW Transcoders in SiteA (2 routers) and in SiteB (1

Router)

SiteA phones are in the SiteA Device Pool and SiteA MRGL and will use SiteA MTPs

SiteB phones are in the SiteB DP and SiteB MRGL and will use SiteB MTPs

SiteA DP calls to SiteB DP are G729 and vice versa.

We have a SIP Trunk into CUPS SIP Proxy and on to CVP Call Server (SIP Proxy and CVP local to SiteA). Currently MTP required is selected on Trunk.

SIP Trunk into CCM is in TrunkC DP and SiteA MRGL and will use SiteA MTPs (Trunk C Device Pool has region settings of G711 to both SiteA and SiteB device pool regions)

This is ok for SiteA ingressing calls through the SIP Trunk. However SiteB calls also ingress to CCM through the same SIP Trunk and are routed to IP phones in SiteB and will hence use

SiteA DSPs (MTPs) instead of SiteB DSPs (MTPs).

Typically all calls to SiteA extensions through the SIP trunk will have originated from the PSTN incoming through an IOS gateway in SiteA and entering CVP system and to SIP trunk on routing to an agent

Typically all calls to SiteB extensions through the SIP trunk will have originated from the PSTN incoming through an IOS gateway in SiteB and entering CVP system and to SIP trunk on routing to an agent

Internal IP phone users to also need to be able to call to CVP via the SIP Trunk

So in the event of MTPs being used across the WAN, what is the bandwidth utilization

involved?

So if we have MTP required unchecked we run into the following issues:

1. Ext calls at G729 through the SIP trunk to CVP. The call is after playing prompts etc in CVP vxml rerouted back to an agent extension G729 through SIP Trunk. The call disconnects

2. Ext calls at G729 through the SIP trunk to CVP. Caller hears the prompts back as fuzzy noise

3. PSTN caller ingresses to CCM via SIP Trunk and routed at G729 to ext. Ext places call on hold and cant unhold

4. Same as call 3 above except call to ext is G711 but the result is the same

5. PSTN caller ingresses to CCM via H323 gateway at G711 to ext. Ext answers the call and transfers it at g711 through the SIP trunk and the call

fails after a few seconds

Basically I am firstly wondering can the 5 call issues be resolved without MTP required on SIP Trunk.

If not can I force SiteB calls to use the siteB MTPs and not traverse the WAN for MTPs (despite the SIP

trunk using the MRGL which contains the SiteA MTPs) and what is the bandwidth impact of using MTP resources over the WAN

I have this problem too.
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rbua Fri, 03/28/2008 - 05:23

Hi Charl,

this kind of scenario is truly material for a PDI case, please try that path, addressing all the different implications and design for the failing scenario goes beyond the scope of a public forum.

PDI Reference:

www.cisco.com/go/pdihelpdesk

Regards,

Riccardo

We have a similiar environment here, CCM 6.01, CVP 4.02, CUPS, however there is no G729, so we don't have exactly same call scenario as yours.

Basically inbound CVP calls, transfered to agent can be done through SIP trunks without MTP, agent consult transfer to CVP will need MTP. Single-step transfer is ok.

This was reported to TAC as GW bug, CSCsl47919

Hope this helps,

Wei

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