Introduction to SIP. What is SIP? SIP - Protocol Context

Transcription

1 Introduction to SIP Slide 1 What is SIP? Session Initiation Protocol Defined by the IETF: RFC2543 Call control (Signaling) protocol Uses TCP/UDP port 5060 SR140/TR1034-IP supports SIP over UDP Creates a session over packet networks for media Independent of lower-layer transport protocols Series of ASCII/text messages, similar to HTTP Slide 2 SIP - Protocol Context SIP Session Initiation Protocol Call Signaling Sets up connection among points SDP Session Description Protocol Media setup Describes media choices to be exchanged via payload Fax Apps T.38 (T.30) UDPTL UDP Audio/ Video Apps Audio/ Video codecs: G.711 G.729 G H.263 RTP UDP Control SIP Call Control (SDP for Media Setup) UDP Interoperates with other protocols: T.38 Fax Over IP RTP Voice Over IP IP Slide 3 1

2 SIP Call Control as It Relates to T.38 SIP call control protocol establishes session connection SDP Session Description Protocol describes the media that will be established SIP sessions use T.38 protocol to carry fax media SIP and T.38 Fax-over-IP is defined in ITU-T T.38 Annex D SIP call progress codes are mapped to standard Bfv call progress values e.g., a SIP 503 will likely be reported as Special Info Tone Slide 4 Common SIP Messages INVITE Used to set up a session OK Confirms that request was successful ACK Signal completion of an INVITE transaction SIP call is established via three-way handshake INVITE/OK/ACK ACK is a critical and necessary part of the handshake BYE Terminate a session CANCEL Terminate an INVITE transaction CANCEL, ACK and BYE are only used with an INVITE Slide 5 SIP Message Format Based on the HTTP format Contains a header and a body SIP Message Header SIP Header Line: INVITE SIP Header Fields: To, From, Content-Length, etc Payload (Optional) SIP Message Body (SDP) Slide 6 2

3 SIP Headers: Request & Response A request header contains: Method target server identification SIP version INVITE sip: @abc.com SIP/2.0 A response header contains: SIP ver. status code status phrase SIP/ Session Progress Not all SIP messages have an accompanying code e.g., 183 for Session Progress Slide 7 SIP INVITE Example - Header Header Line INVITE sip: @ SIP/2.0 Followed by one or more header fields From: <sip: @ >;tag=621e800a-13c4-e9ca- 22a3 To: <sip: @ > Call-ID: ee3ccc-621e800a-13c4-4076b4ba-91e9ca- 545d@ CSeq: 1 INVITE Via: SIP/2.0/UDP :5060;branch=z9hG4bK-4076b4ba- 19a0 Contact: <sip: > Max-Forwards: 70 Content-Type: application/sdp Content-Length: Slide 8 Example OK Response Response Header SIP/2.0 Followed by header fields From: <sip: @ >;tag=621e800a-13c4-e9ca- 22a3 To: <sip: @ > Call-ID: ee3ccc-621e800a-13c4-4076b4ba-91e9ca b4b 9 545d@ CSeq: 1 INVITE Via: SIP/2.0/UDP :5060;branch=z9hG4bK-4076b4ba- 19a0 Contact: <sip: @ :5060> Content-Type: application/sdp Content-Length: Slide 9 3

4 SIP Call Setup Basic Voice Session Call setup Intelligent Sip device (Sip phone, device, ATA) INVITE 180 Ringing ACK Media Session (audio/rtp) BYE IP 180 Ringing is Gateway example of provisional, non-final message Indicates activity is occurring before final call acceptance or failure May see various provisional messages, or not, in variety of combinations Slide 10 T.38 Re-INVITE A second INVITE message is used to modify the media channel when the IP-PSTN gateway detects a fax The INVITE replaces the audio media stream with a T.38 fax media stream Either end of the SIP call can initiate the re-invite Slide 11 Re-INVITE Message Dialogic Brooktrout TR1034 Fax Board/SR140 Fax Software Gateway Fax Machine INVITE Dial 100 Trying Ringback 180 Ringing Answered ACK Media Channel: PCM ulaw CED INVITE 183 Session Progress ACK T.38 Media Session Slide 12 4

5 The SIP Gateway: IP to PSTN IP network PSTN network Dialogic Brooktrout TR1034 Fax Board/SR140 Fax Software-based Fax Server INVITE 100 Trying 180 Ringing Gateway Dial Ringback Answered Legacy Fax Machine ACK T.38 Media Session T.30 Fax Media BYE Disconnect Slide 13 SIP Re-INVITE Re-INVITE is term used here to differentiate point at which INVITE is sent No SIP protocol message called Re-INVITE, it is an INVITE Critical for one side to send second INVITE when doing T.38 FoIP; otherwise, the call will be set up but the faxing will fail On inbound faxes, the fax server needs to send Re-INVITE to alert gateway/call Mgr that the call is a fax call On outbound faxes, the fax server should wait for the network side to send the re-invite media_renegotiate_delay_outbound=-1 Slide 14 SDP Describing the Media SDP = Session Description Protocol Describe media session attributes Payload of a SIP INVITE or other message (e.g., OK, ACK) SIP Message Session Level Information Protocol Version Originator and Session ID Media Description 1 Media name and transport Connection Information Media Description 2 Media name and transport Connection Information Slide 15 5

6 SIP Request With SDP Fields SIP Message: INVITE headers v=0 o=dialogicipfax 0 0 IN IP s=sipfax t=0 0 c=in IP m=audio RTP/AVP 0 a=rtpmap:0 pcmu/8000 m=image UDPTL t38 a=t38faxversion:0 a=t38maxbitrate:14400 a=t38faxratemanagement:transferredtcf a=t38faxmaxbuffer:200 a=t38faxmaxdatagram:72 a=t38faxudpec:t38udpredundancy Session Level Information Media Description 1 Media Description 2 Slide 16 SIP Response Classes 1xx Provisional Non-final, more than one can be sent before a final response 2xx Success Request was successful 3xx Redirection Not an error condition, returns new target(s) to try 4xx Request Failure Busy, bad request format, unknown content encoding 5xx Server Failure Internal server error 6xx Global Failure Domain level service rejection Slide 17 Typical Provisional Responses 100 Trying: request being processed Typically sent immediately after side receives INVITE Indication that the INVITE itself is OK 180 Ringing: alerting user Side that received INVITE is letting the calling party know that the intended recipient is being alerted that a call is coming in 181 Forwarding: call is being forwarded 183 Session Progress: User Agent is processing the INVITE Hold on, still working on putting call through Slide 18 6

7 SIP - 2xx 6xx Example Final Responses : request completed successfully 302 Moved Temporarily: List of alternate targets 305 Use Proxy: List of alternate proxies 404 Not Found: User or extension does not exist Most often seen if no dial peer or route pattern on gateway/cm 481 Transaction Cancelled 486 Busy Here: Subscriber busy or distinctive busy. 488 Not Acceptable Here: No acceptable media in SDP offer 503 Service Unavailable SIT tones 600 Busy Everywhere Congestion busy Slide 19 IP Flows on Dialogic Brooktrout TR1034 Fax Board and NIC 1. Application places outbound call; Dialogic layer uses IP Call Control stack, which uses the NIC Ethernet port SIP Trace shows INVITE from NIC IP, UDP port Application sends fax; Dialogic layer uses T.38 Fax engine which uses Brooktrout TR1034 Ethernet port T.38 Trace shows media stream bound to Brooktrout TR1034 IP, UDP port Network hub When you configure the gateway, which IP address are you going to put in the gateway configuration? IP Call Control TR1034 Fax Server Application T.30 T NIC Dialogic layer UDP Slide 20 Why Network Hub? Let us say Ethernet cable from Dialogic Brooktrout TR1034 Fax Board IP port and Ethernet cable from server NIC are each run to separate switch ports If Wireshark network trace program is run on server NIC, it will only see SIP packets T.38 packets go to IP port on Brooktrout TR1034 Fax Board ; Wireshark can not view Insert network hub to view all packets---sip and T.38 Connect Ethernet cable from server NIC and Ethernet cable from Brooktrout t TR1034 Fax Board IP port to separate ports on hub Connect Ethernet cable from another hub port to network switch Packets are broadcast on all ports Wireshark would then see the T.38 as well as SIP packets Will see SIP between media gateway/call Manager and server NIC IP, T.38 between Brooktrout TR1034 Fax Board and media gateway IP Slide 21 7

8 IP Flows with Dialogic Brooktrout SR140 Fax Software on the NIC 1. Application places outbound call; Dialogic layer uses IP Call Control stack, which uses the NIC Ethernet port SIP trace shows INVITE from NIC, UDP port Application sends fax; Dialogic layer hands fax to T.30 and then T.38 Fax engine which uses the NIC Ethernet port T.38 trace shows media stream from NIC Brooktrout SR140 LICENSE IP Call Control NIC Fax Server Application T.30 T.38 Dialogic layer Network switch-gateway Slide 22 No Network Hub? No Problem. With Dialogic Brooktrout SR140 Fax Software, all packets flow to same IP---the server NIC Wireshark can see all packets---sip and T.38 Slide 23 SIP Entities User Agent Endpoint Entity which issues/accepts SIP commands Two logical parts: Client (UAC) and Server (UAS) Examples: Dialogic Brooktrout TR1034 Fax Board, Dialogic Brooktrout SR140 Fax Software, IP Gateway Optional: Proxy Server Makes requests on behalf of client Address lookup Registrar Accepts REGISTER requests Updates location database with the contact information of the user Redirect Server Accepts a SIP request, maps the SIP address of the called party to a new address and returns it to the client SIP registration/proxy/redirect servers can be co-located Slide 24 8

9 SIP Proxy Server Example Dialogic Brooktrout TR1034 Fax Board/ Dialogic Brooktrout SR140 Fax Software Dialogic.com SIP proxy server SIP User Agent 1. INVITE 2. INVITE Ringing Ringing ACK 8. RTP Media Stream 9. BYE Slide 25 SIP Registrar Server Example Dialogic Brooktrout TR1034 Fax Board/SR140 Fax Software Dialogic.com SIP registrar server 1. REGISTER 2. ACK Slide 26 SIP Redirect Server Example Dialogic Brooktrout TR1034 Fax Board/SR140 Fax Softwarebased Fax Server redirect server Dialogic.com 1. INVITE Dialogic Brooktrout TR1034 Fax Board/SR140 Fax Softwarebased Fax Server Moved Temporarily 3. ACK 4. INVITE Ringing ACK 8. RTP Media Stream 9. BYE Slide 27 9

10 Books About SIP and Fax SIP Demystified Gonzalo Camarillo Carrier Grade Voice Over IP Daniel Collins SIP: Understanding the Session Initiation Protocol, 2nd Edition Alan B. Johnston Internet Communications Using SIP Henry Sinnreich, Alan B. Johnston Fax, Modem, and Text for IP Telephony David Hanes, Gonzalo Salgueiro Slide 28 Online SIP References IETF documents and RFCs: RFC2543: SIP: Session Initiation Protocol RFC2327: SDP: Session Description Protocol Great source for experienced SIP people and laypeople Good comparison of SIP, H.323 and MGCP protocols Slide 29 SIP Lab Exercise 1. Configure Dialogic Brooktrout SR140 Fax Software for SIP using FaxVoiceDiag tool 2. Input Cisco Gateway address 3. Change sip_from: field to your name 4. Test to: fax machine phone Instructor s Dialogic Brooktrout SR140 Fax Software on screen 5. Run packet sniffer & capture trace Slide 30 10