End users in a new site report being unable to hear the remote party when calling or being called by users at headquarters. Calls to and from the PSTN work as expected. To investigate the SIP signalin

The correct answer is D. c= line of SDP content. The c= (connection data) line in the SDP body of a SIP message contains the IP address to which RTP media should be sent. One-way audio between sites is a classic symptom of an incorrect or unreachable IP address in the SDP - for example, a private/NAT address being advertised ac

Signaling and Media Protocols

Question

End users in a new site report being unable to hear the remote party when calling or being called by users at headquarters. Calls to and from the PSTN work as expected. To investigate the SIP signaling to troubleshoot the problem, which field can provide a hint for troubleshooting?

Options

AContact: header of the 200 OK response
BAllow: header if the 200 OK response
Co= line of SDP content
Dc= line of SDP content

How the community answered

(46 responses)

A
7% (3)
B
2% (1)
C
13% (6)
D
78% (36)

Explanation

The c= (connection data) line in the SDP body of a SIP message contains the IP address to which RTP media should be sent. One-way audio between sites is a classic symptom of an incorrect or unreachable IP address in the SDP - for example, a private/NAT address being advertised across a routed WAN, or the wrong interface IP being used. Checking the c= line in the 200 OK (or INVITE) lets you verify whether the IP address being advertised is correct and reachable from the remote site. The Contact header is used for signaling routing, the Allow header lists supported methods, and the o= line is the session origin identifier - none of these directly affect RTP media delivery.

Topics

#SIP Troubleshooting#SDP#One-way Audio#Media Negotiation

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