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New Member

SIP 181 support on IOS

Does Cisco IOS supports SIP 181 messages?

When we make outbound calls to some PSTN numbers and they are call forwarded some times we get SIP 181 messages back that our Cisco 2400 series with 12.4(4)T8 doesn't respond and the calls get killed by the carrier.


Re: SIP 181 support on IOS

According to this cisco doc they do not:

Cisco IOS gateway does not support SIP 181 message (call being forwarded) which causes SDP establishment failure during a call forward

between PSTN phone and Avaya stations. PSTN user does not get ringback. This applies to Call Forwarding (all and busy) calls.


Re: SIP 181 support on IOS

This guide will give you a more detailed explanation of which messages are accepted:

The Cisco Voice Configuration library is a good summary link for voice configuration/troubleshooting:

Here is the excerpt from the SIP configuration guide about SIP responses (including 181).

SIP Responses

Table 5 through Table 10 show SIP responses that are supported by Cisco SIP gateways in compliance

with RFC 3261.

Cisco SIP gateways do not initiate the use of keepalive messages for calls that they originate or terminate. If the remote gateway uses a keepalive message, the SIP gateway complies.

INVITE Yes. SIP gateways support midcall Invite requests with the same call-ID

but different Session Description Protocols (SDP) session parameters(to change the transport address).

Midcall INVITE requests can also change the port number, codec, or refresh the session timer value.

INFO Yes. SIP gateways can accept and generate INFO messages.

NOTIFY Yes. Used in implementation of the Refer requests. Notify messages let the initiator of the Refer request know the outcome of the transfer.

Notify messages also let a subscriber know of any changes occurring in selected events, such as dual tone multifrequency events (DTMF) or

message waiting indication (MWI) events.

OPTIONS Yes. SIP gateways receive this method only.

PRACK Yes. Enable or Disable Provisional Reliable Acknowledgements


REFER Yes. The SIP gateway responds to a Refer request and also generates a Refer request for attended and blind call transfers.

REGISTER Yes. The SIP gateway can send and receive SIP REGISTER requests.

SUBSCRIBE Yes. The SIP gateway can generate and accept SUBSCRIBE requests.

The gateway processes SUBSCRIBE requests for selected applications such as DTMF telephony events and for MWI.

UPDATE Yes. The SIP gateway can accept UPDATEs for media changes, target

refreshes, and QoS scenarios. The gateway will send UPDATEs only for QoS scenarios.

Table 4 SIP Methods (continued)

Method Supported by Cisco Gateways?

Table 5 1xx Responses

1xx Responses Comments

100 Trying Action is being taken on behalf of the caller, but that the called party has

not yet been located. The SIP gateway generates this response for an

incoming Invite request. Upon receiving this response, a gateway stops

retransmitting Invite requests and waits for a 180 Ringing or 200 OK


180 Ringing The called party has been located and is being notified of the call. The

SIP gateway generates a 180 Ringing response when the called party has been located and is being alerted. Upon receiving this response, the gateway generates local ringback, then it waits for a 200 OK response.

Achieving SIP RFC Compliance

Information About SIP RFC Compliance 8

181 Call is being forwarded The call is being rerouted to another destination.

The SIP gateway does not generate these responses.

Upon receiving these responses, the gateway processes the responses in

the same way it processes a 100 Trying response.

182 Queued The called party is not currently available, but has elected to queue the

call rather than reject it.

The SIP gateway does not generate these responses.

Upon receiving these responses, the gateway processes the responses in

the same way it processes a 100 Trying response.

183 Session progress Performs inband alerting for the caller.

The SIP gateway generates a 183 Session progress response when it

receives an ISDN Progress message with an appropriate media indication

from the PSTN.

Re: SIP 181 support on IOS

181 Messages may not need a response since they are 1xx series messages. You would need to check whether or not reliable 1xx messaging (rel1xx) is in the supported/required field of the response or request from the other endpoint. As well, you would probably want to try newer code like 12.4(20)T for better SIP support.



New Member

Re: SIP 181 support on IOS

So is there a way to fix this? Who's not following the SIP standard, the carrier or Cisco?

Sent from Cisco Technical Support iPhone App

Hall of Fame Super Gold

SIP 181 support on IOS

Post the complete trace and relevant config.

New Member

SIP 181 support on IOS


The router is IOS 15.0(1r)M1 - at this point all I know from my client is that their provider Paetech/Windstream shows that our end does not respond to the 181 message when transfering or forwarding a call from a cell phone to it's VM do to a RNA.  We are fairly certain that it's only specific cell phone carriers that insist on a response.  AT&T and T-mobile seem to have the issue while Spring and Verizon do not.

At this point I'm just trying to figure out if there is a way to force the gateway to respond to the 181 so that the calls will stop failing.

If there are specific traces you migh find helpful in the situation let me know.



Hall of Fame Super Gold

SIP 181 support on IOS

You posted rommon version,not IOS version.

The trace to take is "debug ccsip message" one for a working, and one for a non-working call.

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