Cisco VoIP and Collaboration Trainer's Blog (Dmytro Benda, CCSI#33268): April 2022

Welcome Message

Hello my dear reader,

Welcome to my blog, which is dedicated to Cisco technologies. On its pages we will talk about the limitless world of telephony and networking.

We will focus mostly on Cisco collaboration solutions and technologies. These are IP PBX based on Cisco Unified Communications Manager and Cisco Unified Communications Manager Express, Cisco contact centers, Cisco Voice Gateways, etc. Also, I will introduce you the education news: Cisco authorized courses, my own developed training programs, our upcoming events, online learning.

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Sincerely, Dmytro Benda

Wednesday, April 13, 2022

Soure Port 5060 on Cisco CUBE for your SIP trunk connection to an ITSP

Recently, one of our students encountered a problem when connecting his CUCM to a telephony provider (ITSP) via a SIP trunk. Between the CUCM and the ITSP, a CUBE gateway was installed, as expected. The problem was the following: when making an outgoing call to the ITSP, CUBE sent a SIP INVITE, however, the provider did not respond to this request in any way, and no response messages were received from it.

Of course, the first thing to do in such a situation is to check which transport layer protocol (TCP or UDP) is configured on the gateway. However, in this case, the ITSP requested SIP messages to be sent with UDP transport, but Cisco gateways by default send all SIP messages with UDP, i.e. this was not the cause of the problem (you can control it with debug ccsip messages command). After talking with the provider's engineer, it was found out that they expect communication to the SIP gateway with the Destination Port = 5060, but they would also like to see Source Port as 5060 as well.