1. Quiz Problem – Draw Ladder Diag

2. INVITE sip:eeichen@mit.edu SIP/2.0 +++ 27-1-2009 17:19:02.589930 INFO SIP ::send_sip_udp Send to: udp:18.7.21.199:5060 <= where it’s going to (ip land) INVITE sip:eeichen@mit.edu SIP/2.0 <= the sip method Via: SIP/2.0/UDP 192.168.1.43;rport;branch=z9hG4bKfckjgqfj Max-Forwards: 70 To: <= who it’s for From: "neu voip" ;tag=nmvey <= who its (apparently) from Call-ID: kttpclsbofkgnlp@neuvoip-desktop CSeq: 849 INVITE Contact: <= where it’s coming from (ip land) Content-Type: application/sdp Allow: INVITE,ACK,BYE,CANCEL,OPTIONS,PRACK,REFER,NOTIFY,SUBSCRIBE,INFO, MESSAGE Supported: replaces,norefersub,100rel User-Agent: Twinkle/1.2

3. SIP/2.0 100 trying -- your call is important to us +++ 27-1-2009 17:19:02.603422 INFO SIP ::process_sip_msg Received from: udp:18.7.21.199:5060 SIP/2.0 100 trying -- your call is important to us Via: SIP/2.0/UDP 192.168.1.43;rport=5060;branch=z9hG4bKfckjgqfj;received=129.10.135.161 To: From: "neu voip" ;tag=nmvey Call-ID: kttpclsbofkgnlp@neuvoip-desktop CSeq: 849 INVITE Server: OpenSer (1.0.0-tls (i386/linux)) Content-Length: 0

4. SIP/2.0 302 Moved Temporarily & ACK Received from: udp:18.7.21.199:5060 SIP/2.0 302 Moved Temporarily Via: SIP/2.0/UDP 192.168.1.43;received=129.10.135.161;rport=5060;branch=z9hG4bKfckjgqfj To: ;tag=329cfeaa6ded039da25ff8cbb8668bd2.4b6e From: "neu voip" ;tag=nmvey Call-ID: kttpclsbofkgnlp@neuvoip-desktop CSeq: 849 INVITE Contact: <= where has he moved to ?? Server: OpenSer (1.0.0-tls (i386/linux)) Content-Length: 0 Send to: udp:18.7.21.199:5060 ACK sip:eeichen@mit.edu SIP/2.0 Via: SIP/2.0/UDP 192.168.1.43;rport;branch=z9hG4bKfckjgqfj Max-Forwards: 70 To: ;tag=329cfeaa6ded039da25ff8cbb8668bd2.4b6e From: "neu voip" ;tag=nmvey Call-ID: kttpclsbofkgnlp@neuvoip-desktop CSeq: 849 ACK User-Agent: Twinkle/1.2 Content-Length: 0

5. INVITE sip:4100@evophone.caltech.edu SIP/2.0 Send to: udp:131.215.116.153:5060 INVITE sip:4100@evophone.caltech.edu SIP/2.0 Via: SIP/2.0/UDP 192.168.1.43;rport;branch=z9hG4bKavvvplxa Max-Forwards: 70 To: From: "neu voip" ;tag=nmvey Call-ID: kttpclsbofkgnlp@neuvoip-desktop CSeq: 850 INVITE Contact: Content-Type: application/sdp Allow: INVITE,ACK,BYE,CANCEL,OPTIONS,PRACK,REFER,NOTIFY,SUBSCRIBE,IN FO,MESSAGE Supported: replaces,norefersub,100rel User-Agent: Twinkle/1.2 Content-Length: 308 v=0 o=twinkle 1608730462 422021922 IN IP4 192.168.1.43

6. SIP/2.0 100 Trying Received from: udp:131.215.116.153:5060 SIP/2.0 100 Trying Via: SIP/2.0/UDP 192.168.1.43;branch=z9hG4bKavvvplxa;received=129.10.135.161;rport=5060 From: "neu voip" ;tag=nmvey To: Call-ID: kttpclsbofkgnlp@neuvoip-desktop CSeq: 850 INVITE User-Agent: Asterisk PBX Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY Supported: replaces Contact: Content-Length: 0

7. OK from caltech, ACK from NEU Received from: udp:131.215.116.153:5060 SIP/2.0 200 OK Via: SIP/2.0/UDP 192.168.1.43;branch=z9hG4bKavvvplxa;received=129.10.135.161;rport=5060 From: "neu voip" ;tag=nmvey To: ;tag=as62d74d66 Call-ID: kttpclsbofkgnlp@neuvoip-desktop CSeq: 850 INVITE User-Agent: Asterisk PBX Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY Supported: replaces Contact: Send to: udp:131.215.116.153:5060 ACK sip:4100@131.215.116.153 SIP/2.0 Via: SIP/2.0/UDP 192.168.1.43;rport;branch=z9hG4bKjylgaalz Max-Forwards: 70 To: ;tag=as62d74d66 From: "neu voip" ;tag=nmvey Call-ID: kttpclsbofkgnlp@neuvoip-desktop CSeq: 850 ACK

8. After talking (presumably) BYE and ACK Send to: udp:131.215.116.153:5060 BYE sip:4100@131.215.116.153 SIP/2.0 Via: SIP/2.0/UDP 192.168.1.43;rport;branch=z9hG4bKuxipbbsd Max-Forwards: 70 To: ;tag=as62d74d66 From: "neu voip" ;tag=nmvey Call-ID: kttpclsbofkgnlp@neuvoip-desktop CSeq: 851 BYE User-Agent: Twinkle/1.2 Received from: udp:131.215.116.153:5060 SIP/2.0 200 OK Via: SIP/2.0/UDP 192.168.1.43;branch=z9hG4bKuxipbbsd;received=129.10.135.161;rport=5060 From: "neu voip" ;tag=nmvey To: ;tag=as62d74d66 Call-ID: kttpclsbofkgnlp@neuvoip-desktop CSeq: 851 BYE User-Agent: Asterisk PBX

9. Ladder Diagram

10. So – what’s happening – just call forwarding