Short answer: yes.
Slightly longer: I have seen the same behavior. Without lr|lr=on the UA will (correctly) go over to strict routing and use contact in r-uri for the ACK. As long as only your record-route disappeared (i.e. you are the only hop in-between the UAS and UAC) this works.  As your external proxy is B2BUA (at least for signalling), your fine if you relay the ACK.
I'm not sure exactly when this happens and why, I seem to remember I posted something on this behavior for sjphone a while back, but I'm not capable of finding it.
g-)

Cesc wrote:
Hello everyone!

I have my system based on ser 0.9.6. Internal calls work just fine.
I am now trying to interop with another system. It has a sort of
asterisk functionality, but it is not asterisk, it is a private
software company product.

my.phone --------->   my.ser.proxy  ------------->   external.proxy
------------->  external phone
10.111.0.119           10.111.0.50                   10.111.0.20
                10.111.0.144

There is no firewall or nat in the way.

The problem, i think, is that the external.proxy is buggy. I told
that to the company, but who knows when they will fix this.

* Look at the OK (message #9 and #10). My.ser.proxy record-routes all
invites. The Record-route headers reach the external.phone, which
copies them in the OK
message, sends the OK to the external.proxy ... and when this forwards
it to my.ser.proxy, they are gone! The OK reaches my.phone, but then
it generates my
problem: the ACK. It contains NO ROUTE headers and the r-uri is also
simply pointing to the external.proxy.
If the ACK had the ROUTE headers, my.ser.proxy would loose_route the
message and voila!
But as loose_route() returns false, my (maybe bad) config file gets
confused and treats it like a "new" call ... so it lookup("location")
of the ACK r-ruri fails,
and the ACK is dropped.
Should i modify the config file so that ACK, if not loose_route'd, are
simply t_relay'd?

* They also modify the contact field. The reason is because behind the
external.proxy could be H323 or SIP phones, so they sort of want to be
a termination as far as signalling is concerned.

I attach the message flow, hope it helps ... Thanks!

Cesc 


No.     Time           Source                Destination           Protocol Info
      1 0.000000000    10.111.0.119          10.111.0.50           SIP/SDP  Request: INVITE sip:6007@10.111.0.20, with session description
Session Initiation Protocol
    Request-Line: INVITE sip:6007@10.111.0.20 SIP/2.0
    Message Header
        Via: SIP/2.0/UDP 10.111.0.119;rport;branch=z9hG4bK0a6f0077000004b2452bb819000009f00000191e
        Content-Length: 337
        Contact: <sip:7005@10.111.0.119:5060>
        Call-ID: D95A2208-3031-44E8-862E-2877A042900D@10.111.0.119
        Content-Type: application/sdp
        CSeq: 1 INVITE
        From: "7005"<sip:7005@10.111.0.50:5060>;tag=12083790462495
        Max-Forwards: 70
        To: <sip:6007@10.111.0.20>
        User-Agent: SJphone/1.60.289a (SJ Labs)
    Message body
        Session Description Protocol
            Session Description Protocol Version (v): 0
            Owner/Creator, Session Id (o): - 3369481881 3369481881 IN IP4 10.111.0.119
            Session Name (s): SJphone
            Connection Information (c): IN IP4 10.111.0.119
            Time Description, active time (t): 0 0
            Session Attribute (a): direction:active
            Media Description, name and address (m): audio 49248 RTP/AVP 3 97 98 8 0 101
            Media Attribute (a): rtpmap:3 GSM/8000
            Media Attribute (a): rtpmap:97 iLBC/8000
            Media Attribute (a): rtpmap:98 iLBC/8000
            Media Attribute (a): fmtp:98 mode=20
            Media Attribute (a): rtpmap:8 PCMA/8000
            Media Attribute (a): rtpmap:0 PCMU/8000
            Media Attribute (a): rtpmap:101 telephone-event/8000
            Media Attribute (a): fmtp:101 0-11,16

No.     Time           Source                Destination           Protocol Info
      3 0.001209000    10.111.0.50           10.111.0.20           SIP/SDP  Request: INVITE sip:6007@10.111.0.20:5060, with session description
Session Initiation Protocol
    Request-Line: INVITE sip:6007@10.111.0.20:5060 SIP/2.0
    Message Header
        Record-Route: <sip:10.111.0.50;ftag=12083790462495;lr=on>
        Via: SIP/2.0/UDP 10.111.0.50;branch=z9hG4bK2eff.75fbc652.0
        Via: SIP/2.0/UDP 10.111.0.119;rport=5060;branch=z9hG4bK0a6f0077000004b2452bb819000009f00000191e
        Content-Length: 337
        Contact: <sip:7005@10.111.0.119:5060>
        Call-ID: D95A2208-3031-44E8-862E-2877A042900D@10.111.0.119
        Content-Type: application/sdp
        CSeq: 1 INVITE
        From: "7005"<sip:7005@10.111.0.50:5060>;tag=12083790462495
        Max-Forwards: 16
        To: <sip:6007@10.111.0.20>
        User-Agent: SJphone/1.60.289a (SJ Labs)
    Message body
        Session Description Protocol
            Session Description Protocol Version (v): 0
            Owner/Creator, Session Id (o): - 3369481881 3369481881 IN IP4 10.111.0.119
            Session Name (s): SJphone
            Connection Information (c): IN IP4 10.111.0.119
            Time Description, active time (t): 0 0
            Session Attribute (a): direction:active
            Media Description, name and address (m): audio 49248 RTP/AVP 3 97 98 8 0 101
            Media Attribute (a): rtpmap:3 GSM/8000
            Media Attribute (a): rtpmap:97 iLBC/8000
            Media Attribute (a): rtpmap:98 iLBC/8000
            Media Attribute (a): fmtp:98 mode=20
            Media Attribute (a): rtpmap:8 PCMA/8000
            Media Attribute (a): rtpmap:0 PCMU/8000
            Media Attribute (a): rtpmap:101 telephone-event/8000
            Media Attribute (a): fmtp:101 0-11,16

No.     Time           Source                Destination           Protocol Info
      5 0.040629000    10.111.0.20           10.111.0.144          SIP/SDP  Request: INVITE sip:6007@10.111.0.144:5060;transport=UDP, with session description
Session Initiation Protocol
    Request-Line: INVITE sip:6007@10.111.0.144:5060;transport=UDP SIP/2.0
    Message Header
        Via: SIP/2.0/UDP 10.111.0.20:5060;branch=z9hG4bKm27749469
        Via: SIP/2.0/UDP 10.111.0.50;branch=z9hG4bK2eff.75fbc652.0
        Via: SIP/2.0/UDP 10.111.0.119;rport=5060;branch=z9hG4bK0a6f0077000004b2452bb819000009f00000191e
        RECORD-ROUTE: <sip:10.111.0.50;ftag=12083790462495;lr=on>
        From: "7005"<sip:7005@10.111.0.50:5060>;tag=12083790462495
        To: <sip:6007@10.111.0.20>
        Call-ID: D95A2208-3031-44E8-862E-2877A042900D@10.111.0.119
        CSeq: 1 INVITE
        Max-Forwards: 16
        Contact: <sip:10.111.0.20>
        User-Agent: SJphone/1.60.289a (SJ Labs)
        Content-Type: application/sdp
        Content-Length: 337
    Message body
        Session Description Protocol
            Session Description Protocol Version (v): 0
            Owner/Creator, Session Id (o): - 3369481881 3369481881 IN IP4 10.111.0.119
            Session Name (s): SJphone
            Connection Information (c): IN IP4 10.111.0.119
            Time Description, active time (t): 0 0
            Session Attribute (a): direction:active
            Media Description, name and address (m): audio 49248 RTP/AVP 3 97 98 8 0 101
            Media Attribute (a): rtpmap:3 gsm/8000
            Media Attribute (a): rtpmap:97 ilbc/8000
            Media Attribute (a): rtpmap:98 ilbc/8000
            Media Attribute (a): fmtp:98 mode=20
            Media Attribute (a): rtpmap:8 pcma/8000
            Media Attribute (a): rtpmap:0 pcmu/8000
            Media Attribute (a): rtpmap:101 telephone-event/8000
            Media Attribute (a): fmtp:101 0-11,16

No.     Time           Source                Destination           Protocol Info
      9 3.736665000    10.111.0.144          10.111.0.20           SIP/SDP  Status: 200 OK, with session description
Session Initiation Protocol
    Status-Line: SIP/2.0 200 OK
    Message Header
        Via: SIP/2.0/UDP 10.111.0.20:5060;branch=z9hG4bKm27749469
        Via: SIP/2.0/UDP 10.111.0.50;branch=z9hG4bK2eff.75fbc652.0
        Via: SIP/2.0/UDP 10.111.0.119;rport=5060;branch=z9hG4bK0a6f0077000004b2452bb819000009f00000191e
        Record-Route: <sip:10.111.0.50;ftag=12083790462495;lr=on>
        Call-ID: D95A2208-3031-44E8-862E-2877A042900D@10.111.0.119
        CSeq: 1 INVITE
        From: "7005"<sip:7005@10.111.0.50:5060>;tag=12083790462495
        To: <sip:6007@10.111.0.20>;tag=0rxFXxkiza46soF7
        Contact: <sip:6007@10.111.0.144:5060>
        Allow: INVITE, ACK, OPTIONS, BYE, CANCEL, REGISTER, REFER, NOTIFY, INFO, PRACK, UPDATE
        Supported: 100rel, replaces
        Content-Type: application/sdp
        Content-Length: 140
    Message body
        Session Description Protocol
            Session Description Protocol Version (v): 0
            Owner/Creator, Session Id (o): 6007 14194531 23224216 IN IP4 10.111.0.144
            Session Name (s): SIP CALL
            Connection Information (c): IN IP4 10.111.0.144
            Time Description, active time (t): 0 0
            Media Description, name and address (m): audio 10000 RTP/AVP 8
            Media Attribute (a): rtpmap:8 PCMA/8000

No.     Time           Source                Destination           Protocol Info
     10 3.751306000    10.111.0.20           10.111.0.50           SIP/SDP  Status: 200 OK, with session description
Session Initiation Protocol
    Status-Line: SIP/2.0 200 OK
    Message Header
        Via: SIP/2.0/UDP 10.111.0.50;branch=z9hG4bK2eff.75fbc652.0
        Via: SIP/2.0/UDP 10.111.0.119;rport=5060;branch=z9hG4bK0a6f0077000004b2452bb819000009f00000191e
        From: "7005"<sip:7005@10.111.0.50:5060>;tag=12083790462495
        To: <sip:6007@10.111.0.20>;tag=0rxFXxkiza46soF7
        Call-ID: D95A2208-3031-44E8-862E-2877A042900D@10.111.0.119
        CSeq: 1 INVITE
        Contact: <sip:10.111.0.20:5060>
        Content-Type: application/sdp
        Content-Length: 140
    Message body
        Session Description Protocol
            Session Description Protocol Version (v): 0
            Owner/Creator, Session Id (o): 6007 14194531 23224216 IN IP4 10.111.0.144
            Session Name (s): SIP CALL
            Connection Information (c): IN IP4 10.111.0.144
            Time Description, active time (t): 0 0
            Media Description, name and address (m): audio 10000 RTP/AVP 8
            Media Attribute (a): rtpmap:8 pcma/8000

No.     Time           Source                Destination           Protocol Info
     11 3.751589000    10.111.0.50           10.111.0.119          SIP/SDP  Status: 200 OK, with session description
Session Initiation Protocol
    Status-Line: SIP/2.0 200 OK
    Message Header
        Via: SIP/2.0/UDP 10.111.0.119;rport=5060;branch=z9hG4bK0a6f0077000004b2452bb819000009f00000191e
        From: "7005"<sip:7005@10.111.0.50:5060>;tag=12083790462495
        To: <sip:6007@10.111.0.20>;tag=0rxFXxkiza46soF7
        Call-ID: D95A2208-3031-44E8-862E-2877A042900D@10.111.0.119
        CSeq: 1 INVITE
        Contact: <sip:10.111.0.20:5060>
        Content-Type: application/sdp
        Content-Length: 140
    Message body
        Session Description Protocol
            Session Description Protocol Version (v): 0
            Owner/Creator, Session Id (o): 6007 14194531 23224216 IN IP4 10.111.0.144
            Session Name (s): SIP CALL
            Connection Information (c): IN IP4 10.111.0.144
            Time Description, active time (t): 0 0
            Media Description, name and address (m): audio 10000 RTP/AVP 8
            Media Attribute (a): rtpmap:8 pcma/8000

No.     Time           Source                Destination           Protocol Info
     12 3.756127000    10.111.0.119          10.111.0.50           SIP      Request: ACK sip:10.111.0.20:5060
Session Initiation Protocol
    Request-Line: ACK sip:10.111.0.20:5060 SIP/2.0
    Message Header
        Via: SIP/2.0/UDP 10.111.0.119;rport;branch=z9hG4bK0a6f0077000004b2452bb81d00000c5f00001922
        Content-Length: 0
        Call-ID: D95A2208-3031-44E8-862E-2877A042900D@10.111.0.119
        CSeq: 1 ACK
        From: "7005"<sip:7005@10.111.0.50:5060>;tag=12083790462495
        Max-Forwards: 70
        To: <sip:6007@10.111.0.20>;tag=0rxFXxkiza46soF7
        User-Agent: SJphone/1.60.289a (SJ Labs)
  

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