SIP 101 Presentation

An introductory presentation on SIP (Session Initiation Protocol) given by 2600hz CEO / Co-Founder Darren Schreiber during the weekly FreeSWITCH Conference Call. A more in-depth second part is also available.

1. Learning SIP: SIP 101 Tutorial! Presented by Darren Schreiber
2. SIP  is  a  Signaling  Protocol  for  Sessions   •  Session  Ini1a1on  Protocol   –  Nego1ates  a  session,  or  a  connec1on,  between  two  par1es   –  Mostly  consists  of  connec1on  headers  (things  that  wouldn’t  prac1cally   work  or  fit  in  binary  TCP/UDP  headers)   –  Can  op1onally  offer  payloads  with  the  connec1on  headers  (SDP)   –  RFC  3261     •  Session  Descrip1on  Protocol   –  SDP  is  Separate  from  SIP   –  Offer  /  Answer  Model   –  RFC  3264   Understanding  SIP  
3. INVITE  sip:14158867900@me.com:5060  SIP/2.0        From:  ”SKANKY  HOE"  <sip:9184249378@67.231.5.6>        To:  <sip:14158867900@108.166.22.22>        Contact:  <sip:9184249378@67.231.5.6:1234>        Call-­‐ID:  490dffec2cafa2772a11eec8716e        CSeq:  102  INVITE        User-­‐Agent:  2600hz        Max-­‐Forwards:  30        Allow:  INVITE,  ACK,  CANCEL,  OPTIONS,  BYE,  REFER,  SUBSCRIBE        Content-­‐Type:  applica1on/sdp        Content-­‐Length:  180          v=0        s=session        c=IN  IP4  67.231.8.9        m=audio  35918  RTP/AVP  0  18  8  3  101        a=rtpmap:101  telephone-­‐event/8000   Sample  SIP  Packet   This is SIP (Describes Connection – i.e. how to get from point A to point B) This is SDP (Describes Content)
4. INVITE  sip:14158867900@me.com:5060  SIP/2.0        From:  ”SKANKY  HOE"  <sip:9184249378@67.231.5.6>        To:  <sip:14152222222@108.166.22.22>        Contact:  <sip:9184249378@67.231.5.6:1234>        Call-­‐ID:  490dffec2cafa2772a11eec8716e        CSeq:  102  INVITE        User-­‐Agent:  2600hz        Max-­‐Forwards:  30        Allow:  INVITE,  ACK,  CANCEL,  OPTIONS,  BYE,  REFER,  SUBSCRIBE     Here  we  INVITE  someone  “14158867900@me.com”  to  connect.   NOTE:  This  isn’t  network  rou1ng  informa1on   Sample  SIP  Packet   METHOD + ARGUMENTS Method is the action being requested Arguments are the details about the action
5. INVITE  sip:14158867900@me.com:5060  SIP/2.0        From:  ”SKANKY  HOE"  <sip:9184249378@67.231.5.6>        To:  <sip:14158867900@108.166.22.22>        Contact:  <sip:9184249378@67.231.5.6:1234>        Call-­‐ID:  490dffec2cafa2772a11eec8716e        CSeq:  102  INVITE        User-­‐Agent:  2600hz        Max-­‐Forwards:  30        Allow:  INVITE,  ACK,  CANCEL,  OPTIONS,  BYE,  REFER,  SUBSCRIBE     Caller  “Skanky  Hoe”  is  calling  1-­‐415-­‐886-­‐7900.  We  don’t  know  the   recipient  par1es  Caller-­‐ID  so  we  don’t  offer  it.   Sample  SIP  Packet   TO & FROM Identification headers Can be used for BTN, ANI, Caller-ID
6. INVITE  sip:14158867900@me.com:5060  SIP/2.0        From:  ”SKANKY  HOE"  <sip:9184249378@67.231.5.6>        To:  <sip:14158867900@108.166.22.22>        Contact:  <sip:9184249378@67.231.5.6:1234>        Call-­‐ID:  490dffec2cafa2772a11eec8716e        CSeq:  102  INVITE        User-­‐Agent:  2600hz        Max-­‐Forwards:  30        Allow:  INVITE,  ACK,  CANCEL,  OPTIONS,  BYE,  REFER,  SUBSCRIBE     Contact  says  “here’s  the  network  port/IP  to  reach  me  at”.  Can  contain   tags  used  by  the  switching  system,  like  ;transport=TCP.   Sample  SIP  Packet   CONTACT Usually matches the From: but not always. Can contain tags.
7. INVITE  sip:14158867900@me.com:5060  SIP/2.0        From:  ”SKANKY  HOE"  <sip:9184249378@67.231.5.6>        To:  <sip:14158867900@108.166.22.22>        Contact:  <sip:9184249378@67.231.5.6:1234>        Call-­‐ID:  490dffec2cafa2772a11eec8716e        CSeq:  102  INVITE        User-­‐Agent:  2600hz        Max-­‐Forwards:  30        Allow:  INVITE,  ACK,  CANCEL,  OPTIONS,  BYE,  REFER,  SUBSCRIBE     Call-­‐ID  iden1fies  this  unique  connec1on  /  conversa1on.  Should  never   change  during  a  call  or  registra1on.   Sample  SIP  Packet   CALL-ID Identifies this conversation / connection
8. INVITE  sip:14158867900@me.com:5060  SIP/2.0        From:  ”SKANKY  HOE"  <sip:9184249378@67.231.5.6>        To:  <sip:14158867900@108.166.22.22>        Contact:  <sip:9184249378@67.231.5.6:1234>        Call-­‐ID:  490dffec2cafa2772a11eec8716e        CSeq:  102  INVITE        User-­‐Agent:  2600hz        Max-­‐Forwards:  30        Allow:  INVITE,  ACK,  CANCEL,  OPTIONS,  BYE,  REFER,  SUBSCRIBE     Sequence  number  is  a  sequen1al  number  that  increases  for  each   packet  send  and  receive.  Keeps  things  in  order.  Used  for  removing   duplicate  packets  as  well  (IMPORTANT!  Why  do  we  have  dupes?)   Sample  SIP  Packet   CSEQ Sequence number.
9. INVITE  sip:14158867900@me.com:5060  SIP/2.0        From:  ”SKANKY  HOE"  <sip:9184249378@67.231.5.6>        To:  <sip:14158867900@108.166.22.22>        Contact:  <sip:9184249378@67.231.5.6:1234>        Call-­‐ID:  490dffec2cafa2772a11eec8716e        CSeq:  102  INVITE        User-­‐Agent:  2600hz        Max-­‐Forwards:  30        Allow:  INVITE,  ACK,  CANCEL,  OPTIONS,  BYE,  REFER,  SUBSCRIBE     User-­‐Agent  iden1fies  what  type  of  phone  or  switch  generated  this   packet.   Sample  SIP  Packet   USER-AGENT Friendly identifier.
10. INVITE  sip:14158867900@me.com:5060  SIP/2.0        From:  ”SKANKY  HOE"  <sip:9184249378@67.231.5.6>        To:  <sip:14158867900@108.166.22.22>        Contact:  <sip:9184249378@67.231.5.6:1234>        Call-­‐ID:  490dffec2cafa2772a11eec8716e        CSeq:  102  INVITE        User-­‐Agent:  2600hz        Max-­‐Forwards:  30        Allow:  INVITE,  ACK,  CANCEL,  OPTIONS,  BYE,  REFER,  SUBSCRIBE     Count-­‐down  to  death  in  a  loop!   Sample  SIP  Packet   MAX FORWARDS Loop detection
11. INVITE  sip:14158867900@me.com:5060  SIP/2.0        From:  ”SKANKY  HOE"  <sip:9184249378@67.231.5.6>        To:  <sip:14158867900@108.166.22.22>        Contact:  <sip:9184249378@67.231.5.6:1234>        Call-­‐ID:  490dffec2cafa2772a11eec8716e        CSeq:  102  INVITE        User-­‐Agent:  2600hz        Max-­‐Forwards:  30        Allow:  INVITE,  ACK,  CANCEL,  OPTIONS,  BYE,  REFER,  SUBSCRIBE        Content-­‐Type:  applica1on/sdp        Content-­‐Length:  334     Feature  list  supported  by  the  end  device   Sample  SIP  Packet   SUPPORTED FEATURES List of what this phone allows for METHODs
12. INVITE  sip:14158867900@me.com:5060  SIP/2.0        From:  ”SKANKY  HOE"  <sip:9184249378@67.231.5.6>        To:  <sip:14158867900@108.166.22.22>        Contact:  <sip:9184249378@67.231.5.6:1234>        Call-­‐ID:  490dffec2cafa2772a11eec8716e        CSeq:  102  INVITE        User-­‐Agent:  2600hz        Max-­‐Forwards:  30        Allow:  INVITE,  ACK,  CANCEL,  OPTIONS,  BYE,  REFER,  SUBSCRIBE        Content-­‐Type:  applica1on/sdp        Content-­‐Length:  334     Feature  list  supported  by  the  end  device   Sample  SIP  Packet   WHAT KIND OF AUDIO/VIDEO/ STREAM/ MESSAGE Content Type of the communication after it’s setup
13.  v=0        o=root  7626  7626  IN  IP4  72.249.1.111        t=0  0        s=session        c=IN  IP4  72.249.1.111        m=audio  22222  RTP/AVP  0  18  8  3  101        a=rtpmap:0  PCMU/8000        a=rtpmap:18  G729/8000        a=fmtp:18  annexb=no        a=rtpmap:8  PCMA/8000        a=rtpmap:3  GSM/8000        a=rtpmap:101  telephone-­‐event/8000        a=fmtp:101  0-­‐16        a=silenceSupp:off  -­‐  -­‐  -­‐  -­‐        a=p1me:20        a=sendrecv   Sample  SDP  Packet   DESCRIPTION TAG Can be anything. Often contains a copy of the SDP IP
14.  v=0        o=root  7626  7626  IN  IP4  72.249.1.111        t=0  0        s=session        c=IN  IP4  72.249.1.111        m=audio  22222  RTP/AVP  0  18  8  3  101        a=rtpmap:0  PCMU/8000        a=rtpmap:18  G729/8000        a=fmtp:18  annexb=no        a=rtpmap:8  PCMA/8000        a=rtpmap:3  GSM/8000        a=rtpmap:101  telephone-­‐event/8000        a=fmtp:101  0-­‐16        a=silenceSupp:off  -­‐  -­‐  -­‐  -­‐        a=p1me:20        a=sendrecv   Sample  SDP  Packet   TIME TAG Usually 0 0 because this is actually part of SIP, not SDP
15.  v=0        o=root  7626  7626  IN  IP4  72.249.1.111        t=0  0        s=session        c=IN  IP4  72.249.1.111        m=audio  22222  RTP/AVP  0  18  8  3  101        a=rtpmap:0  PCMU/8000        a=rtpmap:18  G729/8000        a=fmtp:18  annexb=no        a=rtpmap:8  PCMA/8000        a=rtpmap:3  GSM/8000        a=rtpmap:101  telephone-­‐event/8000        a=fmtp:101  0-­‐16        a=silenceSupp:off  -­‐  -­‐  -­‐  -­‐        a=p1me:20        a=sendrecv   Sample  SDP  Packet   TYPE OF SESSION Can be unicast or multicast. Unicast can be indicated by a space or – sign.
16.  v=0        o=root  7626  7626  IN  IP4  72.249.1.111        t=0  0        s=session        c=IN  IP4  72.249.1.111        m=audio  22222  RTP/AVP  0  18  8  3  101        a=rtpmap:0  PCMU/8000        a=rtpmap:18  G729/8000        a=fmtp:18  annexb=no        a=rtpmap:8  PCMA/8000        a=rtpmap:3  GSM/8000        a=rtpmap:101  telephone-­‐event/8000        a=fmtp:101  0-­‐16        a=silenceSupp:off  -­‐  -­‐  -­‐  -­‐        a=p1me:20        a=sendrecv   Sample  SDP  Packet   IP ADDRESS FOR RTP RECEIPT Very important, often misunderstood. This is the IP you want to RECEIVE audio on.
17.  v=0        o=root  7626  7626  IN  IP4  72.249.1.111        t=0  0        s=session        c=IN  IP4  72.249.1.111        m=audio  22222  RTP/AVP  0  18  8  3  101        a=rtpmap:0  PCMU/8000        a=rtpmap:18  G729/8000        a=fmtp:18  annexb=no        a=rtpmap:8  PCMA/8000        a=rtpmap:3  GSM/8000        a=rtpmap:101  telephone-­‐event/8000        a=fmtp:101  0-­‐16        a=silenceSupp:off  -­‐  -­‐  -­‐  -­‐        a=p1me:20        a=sendrecv   Sample  SDP  Packet   MEDIA TYPE, PORT AND PREFERENCES Very important, often misunderstood. This is the PORT you want to RECEIVE audio on. Also includes a codec preference list.
18.  v=0        o=root  7626  7626  IN  IP4  72.249.1.111        t=0  0        s=session        c=IN  IP4  72.249.1.111        m=audio  22222  RTP/AVP  0  18  8  3  101        a=rtpmap:0  PCMU/8000        a=rtpmap:18  G729/8000        a=fmtp:18  annexb=no        a=rtpmap:8  PCMA/8000        a=rtpmap:3  GSM/8000        a=rtpmap:101  telephone-­‐event/8000        a=fmtp:101  0-­‐16        a=silenceSupp:off  -­‐  -­‐  -­‐  -­‐        a=p1me:20        a=sendrecv   Sample  SDP  Packet   NOTE THE PREFERENCE LIST! Matches the codecs defined below in the attribute section. Common codecs aren’t listed.
19.  v=0        o=root  7626  7626  IN  IP4  72.249.1.111        t=0  0        s=session        c=IN  IP4  72.249.1.111        m=audio  22222  RTP/AVP  0  18  8  3  101        a=rtpmap:0  PCMU/8000        a=rtpmap:18  G729/8000        a=fmtp:18  annexb=no        a=rtpmap:8  PCMA/8000        a=rtpmap:3  GSM/8000        a=rtpmap:101  telephone-­‐event/8000        a=fmtp:101  0-­‐16        a=silenceSupp:off  -­‐  -­‐  -­‐  -­‐        a=p1me:20        a=sendrecv   Sample  SDP  Packet   CODEC DESCRIPTIONS AND ATTRIBUTES Default codecs not actually required
20.  v=0        o=root  7626  7626  IN  IP4  72.249.1.111        t=0  0        s=session        c=IN  IP4  72.249.1.111        m=audio  22222  RTP/AVP  0  18  8  3  101        a=rtpmap:0  PCMU/8000        a=rtpmap:18  G729/8000        a=fmtp:18  annexb=no        a=rtpmap:8  PCMA/8000        a=rtpmap:3  GSM/8000        a=rtpmap:101  telephone-­‐event/8000        a=fmtp:101  0-­‐16        a=silenceSupp:off  -­‐  -­‐  -­‐  -­‐        a=p1me:20        a=sendrecv   Sample  SDP  Packet   RTP ATTRIBUTES More general attributes
21. Yup,  I  heard  ya!      SIP/2.0  100  Trying        From:  ”SKANKY  HOE"  <sip:9184249378@67.231.5.6>        To:  <sip:14158867900@108.166.22.22>        Call-­‐ID:  490dffec2cafa2772a11eec8716e        CSeq:  102  INVITE        User-­‐Agent:  2600hz        Max-­‐Forwards:  30        Allow:  INVITE,  ACK,  CANCEL,  OPTIONS,  BYE,  REFER,  SUBSCRIBE   Sample  Response  -­‐  Transi1onal  
22. Yup,  I  heard  ya!      SIP/2.0  100  Trying        From:  ”SKANKY  HOE"  <sip:9184249378@67.231.5.6>        To:  <sip:14158867900@108.166.22.22>        Call-­‐ID:  490dffec2cafa2772a11eec8716e        CSeq:  102  INVITE        User-­‐Agent:  2600hz        Max-­‐Forwards:  30        Allow:  INVITE,  ACK,  CANCEL,  OPTIONS,  BYE,  REFER,  SUBSCRIBE   Sample  Response  -­‐  Transi1onal  
23. I’m  Ringing  The  Handset      SIP/2.0  180  Ringing    From:  ”SKANKY  HOE"  <sip:9184249378@67.231.5.6>        To:  <sip:14158867900@108.166.22.22>        Call-­‐ID:  490dffec2cafa2772a11eec8716e        CSeq:  102  INVITE        User-­‐Agent:  2600hz        Max-­‐Forwards:  30        Allow:  INVITE,  ACK,  CANCEL,  OPTIONS,  BYE,  REFER,  SUBSCRIBE         Sample  Response  -­‐  Transi1onal  
24. They  Answered!      SIP/2.0  200  OK    From:  ”SKANKY  HOE"  <sip:9184249378@67.231.5.6>        To:  <sip:14158867900@108.166.22.22>        Call-­‐ID:  490dffec2cafa2772a11eec8716e        [  …  ]          o=FreeSWITCH  1340177972  1340177973  IN  IP4  108.166.87.71        s=FreeSWITCH        c=IN  IP4  108.166.87.71        t=0  0        m=audio  24036  RTP/AVP  0  101        a=rtpmap:0  PCMU/8000        a=rtpmap:101  telephone-­‐event/8000        a=fmtp:101  0-­‐16        a=silenceSupp:off  -­‐  -­‐  -­‐  -­‐        a=p1me:20       Sample  Response  -­‐  Transi1onal  
25. They  Answered!      SIP/2.0  200  OK    From:  ”SKANKY  HOE"  <sip:9184249378@67.231.5.6>        To:  <sip:14158867900@108.166.22.22>        Call-­‐ID:  490dffec2cafa2772a11eec8716e        [  …  ]          o=FreeSWITCH  1340177972  1340177973  IN  IP4  108.166.87.71        s=FreeSWITCH        c=IN  IP4  108.166.87.71        t=0  0        m=audio  24036  RTP/AVP  0  101        a=rtpmap:0  PCMU/8000        a=rtpmap:101  telephone-­‐event/8000        a=fmtp:101  0-­‐16        a=silenceSupp:off  -­‐  -­‐  -­‐  -­‐        a=p1me:20       Sample  Response  -­‐  Connect  
26. Sequence  Number   -­‐  Unique  for  each  transac1on   -­‐  Transac1ons  make  up  a  dialog   -­‐  No  duplicates  in  the  en1re  dialog   -­‐  Retries  can  be  discarded   -­‐  SIP  Retries!     Call-­‐ID  iden1fies  conversa1on   -­‐  Includes  REGISTER,  INVITE,  NOTIFY   SIP  Headers  Analyzed  
27. General  Thoughts   -­‐  Call-­‐IDs  oren  represent  a  device’s  en1re  registra1on  history  if  the  IP  or   other  info  hasn’t  changed  and  there’s  been  no  denials/rejects   -­‐  Useful  for  debugging   -­‐  Call  Forwarding  Fun  with  To/From  and  Method  URIs   -­‐  The  device  crea1ng  the  packet  ALWAYS  has  full  control  over  what  port   and  IP  to  send  media  to     SIP  Headers  Anaylzed  
28. Retries   -­‐  Same  Call-­‐ID  &  Sequence  number  from  the  sending  device     Timeouts   -­‐  Cancels  from  FreeSWITCH  (note  the  defaults  in  FS)   -­‐  Who  cancelled  first?  Stop  blaming  FreeSWITCH  J   -­‐  RECOVERY_ON_TIMER_EXPIRE!!!   -­‐  PROGRESS_TIMEOUT  in  some  cases   Errors!   -­‐  Wrong  Contact:  string  or  missing  proxy/transport  tags   -­‐  OK,  blame  FreeSWITCH   SIP  Headers  Debugging  
29. Can  Cover  If  People  Want   -­‐  T.38  Setup  (not  actual  protocol)   -­‐  BLF  No1fies  (two  forms)          ß  my  knowledge  is  s1ll  light  here  but  growing   -­‐  REGISTER  /  AUTH   -­‐  Video  Codecs   -­‐  Codec  Preferences   -­‐  Security  /  TLS/SSL  /  ZRTP   -­‐  darren@2600hz.com    -­‐    SEND  ME  TOPICS  FOR  TRAINING!   SIP  Headers  Debugging  
30. THANKS!! ?