Cellular Network Infrastructure » Core Network (CN) » osmo-sip-connector

I'm writing tests against osmo-sip-connector and getting the following:

22:19:06.190029 5 SIP_Tests.ttcn:207 Matching on port SIP .msgHeader.contact.contactBody.contactAddresses[
0 <-> 0].addressField.nameAddr.addrSpec.userInfo := omit with {
    userOrTelephoneSubscriber := "98766",
    password := omit
} unmatched.msgHeader.contact.contactBody.contactAddresses[0 <-> 0].addressField.nameAddr.addrSpec.hostPor
t.portField := omit with 5060 unmatched{
    {
        addressField := {
            nameAddr := {
                displayName := omit,
                addrSpec := {
                    scheme := "sip",
                    userInfo := omit,
                    hostPort := {
                        host := "127.0.0.1",
                        portField := omit
                    },
                    urlParameters := omit,
                    headers := omit
                }
            }
        },
        contactParams := omit
    }
} with {
    {
        addressField := {
            nameAddr := {
                displayName := *,
                addrSpec := {
                    scheme := "sip",
                    userInfo := {
                        userOrTelephoneSubscriber := "98766",
                        password := omit
                    },
                    hostPort := {
                        host := "127.0.0.1",
                        portField := 5060
                    },
                    urlParameters := omit,
                    headers := omit
                }
            }
        },
        contactParams := *
    }
} unmatched.messageBody := omit with ? unmatched: First message in the queue does not match the template:

Which basically means that the "180 Ringing" response that osmo-sip-connector sends in response to the INVITE uses a "Contact" header that differs from the "To" that was used in the INVITE in the following two ways:

• it doesn't explicitly state the port number (5060) but omits it (probably implicit default to 5060)
• it is missing the telephone number of the subscriber, i.e. the user part.

I've attached a pcap file in the attachment.

So now the question to be resolved is:

• is it wrong to assume the original "To" address in "Contact"?
• if it's wrong, what kind of assumption can we make on it?

I'll try to read up the related RFCs in order to resolve that question.