SIP 102 Presentation

A follow up to the first introduction to SIP presentation. An in-depth look into SIP:
- Understanding Headers
- Sticky proxies
- BLF (Busy Lamp Field)
- Troubleshooting

Presentation given during the weekly FreeSWITCH Conference Call.

1. Learning SIP: SIP 102 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. More  Advanced  Topics   •  Via:,  Record-­‐Route,  Route  and  Path   –  How  these  work  with  proxies   –  How  proxies  are  supposed  to  behave   –  How  FreeSWITCH  uses  these  headers   –  RFC  3261     •  No1fy,  Subscribe,  BLF,  MWI   –  SDP  is  Separate  from  SIP   –  Offer  /  Answer  Model   –  RFC  3265   Understanding  SIP  
5. Via  headers  contain  path  traversed  by  a  request   •  Sample        Via:  SIP/2.0/UDP  57.230.8.195;branch=z9hG4f        Via:  SIP/2.0/UDP  57.230.8.89;branch=z9hG42        Via:  SIP/2.0/UDP  57.230.0.81:5060;branch=z9hG49     •  Notes   –  Via  Headers  are  manipulated  (added/removed)  as  they  go   –  Request  URI  is  not  manipulated  (nor  is  rest  of  packet)   –  The  response  is  sent  back  using  the  top  Via:   –  Each  server  removes  itself  from  the  Via:  header  on  a  match   –  When  any  UA  gets  a  SIP  response,  there  should  only  be  1  Via   Via  
6. Via  header  collec1on      Phone    -­‐-­‐-­‐>Proxy1  -­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐>  Proxy  2    -­‐-­‐-­‐-­‐-­‐>  Server    Via:  Phone      Via:Proxy1        Via:Proxy2                Via:Phone        Via:Proxy1                            Via:Phone     As  the  packet  traverses  from  the  phone  to  the  server  it  traverses   two  proxies   •  Phone  adds  itself  as  a  Via:   •  Each  proxy  adds  itself  to  the  Via:  header   Via  
7. Via  header  collec1on      Phone    <-­‐-­‐-­‐Proxy1  <-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐-­‐  Proxy  2    <-­‐-­‐-­‐-­‐-­‐  Server    Via:  Phone      Via:Proxy1        Via:Proxy2                Via:Phone        Via:Proxy1                            Via:Phone     Packet  traverses  from  server  to  phone  via  same  two  proxies   •  Each  proxy  REMOVES  itself  from  Via:   Via:  headers  are  required  for  each  hop,  by  all  devices   Via  
8. Via’s  allow  direct  routes  taken  later     Via   Phone   Server   Proxy  1   Proxy  2   Proxy  A   Proxy  B   OK REGISTER FUTURE
9.       What  if  you  WANT  to  guarantee  the  same   proxy  be  used?       S1cky  Proxies  
10. Record-­‐Route  Headers  tell  endpoints  to   “remember”  them  and  always  use  them   Record-­‐Route:  <sip:57.230.8.89:5060;lr;oag=19QNr566rKH3B>   Record-­‐Route:  <sip:57.230.8.195:5060;lr;oag=19QNr566rKH3B>     •  These  proxies  want  to  stay  in  the  path  for  all  future  signaling   •  Will  be  kept  by  each  user  agent  for  the  dura1on  of  this  dialog   •  Will  be  converted  into  “Route:”  headers  for  new  requests   –  Flipped  Order!   Record-­‐Route  
11. Record-­‐Routes  Ensure  Same  Path     Record-­‐Route   Phone   Server   Proxy  1   Proxy  2   Proxy  A   Proxy  B   ACK RINGING INVITE OK
12. Route  Headers  tell  endpoints  to  route  via   specific  paths   Route:  <sip:57.230.8.195:5060;lr;oag=19QNr566rKH3B>   Route:  <sip:57.230.8.89:5060;lr;oag=19QNr566rKH3B>     •  Usually  in  response  to  new  requests  and  old  Request-­‐Route   •  This  strategy  allows  for  stateless  rou1ng  of  many  many  calls   –  Most  of  the  rou1ng  informa1on  is  kept  in  the  packet   –  Only  first  and  last  endpoint  must  “remember”  things   –  Offloads  work  to  calling  devices   –  Can  be  manipulated   Route  
13. Path  Headers  are  very  similar  to  Route   –  Allow  rou1ng  via  specific  proxies   –  Used  by  3GPP  implementa1on   Path  solves  the  problem  of  differing  routes  inbound/outbound     From  the  RFC:   1)  Path  applies  to  REGISTER  and  responses  to  REGISTER.   Record-­‐Route  doesn't.   2)  Path  is  direc1onal  and  starts  at  the  node  origina1ng  the  Path   header  and  is  "learned"  by  the  node  receiving  the  Path   header.   3)  The  Path  header  is  a  unidirec1onal  opera1on.   Path  
14. Path  allows  different  routes  in  and  out     Path   Phone   Server   Proxy  1   Proxy  2   Proxy  A   Proxy  B   REGISTER OK
15. Many  different  mechanisms   –  Can  be  difficult  to  understand   –  Can  be  difficult  to  troubleshoot   –  Tags  and  parsing  is  done  differently  by  different  devices   –  See  lots  of  failures  due  to  unknown  chars  or  tags     Packet  Size!   –  We  see  this  the  most  as  carriers  interop  more  and  more   –  Packets  can  become  too  large   –  People  then  try  to  1nker  with  them  without  knowledge   •  Break  them     Problems  w/  Rou1ng  
16.   Subscribe   NoGfy   and   Busy  Lamp  Field  (BLF)  
17. User  wishes  to  receive  informa1on  about  the   status  of  a  service   –  Can  be  MWI   –  Can  be  Presence  (BLF)   –  Can  be  Fax   –  Can  be  anything,  really   •  Different  defini1ons  of  services:    hup://www.iana.org/assignments/sip-­‐  events/sip-­‐events.xml   SUBSCRIBE  
18. We’re  going  to  look  at  an  Aastra  which  is  the  most  complex      SUBSCRIBE  sip:301@somecustomer.com:5060  SIP/2.0        From:  "201"  <sip:201@somecustomer.com>        To:  <sip:301@somecustomer.com>        Call-­‐ID:  28981ade3fc3c117        CSeq:  14683  SUBSCRIBE        Event:  dialog        Expires:  3611        Accept:  applica1on/dialog-­‐info+xml     BLF  Subscribe  
19. We’re  going  to  look  at  an  Aastra  which  is  the  most  complex      SIP/2.0  202  Accepted        From:  "201"  <sip:201@somecustomer.com>        To:  <sip:301@somecustomer.com>        Call-­‐ID:  28981ade3fc3c117        CSeq:  14683  SUBSCRIBE        Contact:  <sip:301@somecustomer.com:5060  >        Expires:  3611   BLF  Subscribe  
20.  NOTIFY  sip:201@somecustomer.com        From:  “301”  <sip:301@somecustomer.com>        To:  "201"  <sip:201@somecustomer.com>        Call-­‐ID:  28981ade3fc3c117        CSeq:  295539543  NOTIFY        Content-­‐Type:  applica1on/dialog-­‐info+xml          <?xml  version="1.0"?>        <dialog-­‐info  xmlns="urn:iex:params:xml:ns:dialog-­‐info"   version="839"  state="par1al"  en1ty=”301@somecustomer.com">        <dialog  id="da0d7773-­‐b030-­‐4a6b-­‐8235-­‐b3780aab1d23"   direc1on="recipient">        <state>early</state>        </dialog>        </dialog-­‐info>   BLF  Dialog  (info+xml)  -­‐  Ringing  
21.  NOTIFY  sip:201@somecustomer.com        From:  “301”  <sip:301@somecustomer.com>        To:  "201"  <sip:201@somecustomer.com>        Call-­‐ID:  28981ade3fc3c117        CSeq:  295539543  NOTIFY        Content-­‐Type:  applica1on/dialog-­‐info+xml          <?xml  version="1.0"?>        <dialog-­‐info  xmlns="urn:iex:params:xml:ns:dialog-­‐info"   version="839"  state="par1al"  en1ty=”301@somecustomer.com">        <dialog  id="da0d7773-­‐b030-­‐4a6b-­‐8235-­‐b3780aab1d23"   direc1on="recipient">        <state>completed</state>        </dialog>        </dialog-­‐info>   BLF  Dialog  (info+xml)  -­‐  Answered  
22.  NOTIFY  sip:201@somecustomer.com        From:  “301”  <sip:301@somecustomer.com>        To:  "201"  <sip:201@somecustomer.com>        Call-­‐ID:  28981ade3fc3c117        CSeq:  295539543  NOTIFY        Content-­‐Type:  applica1on/dialog-­‐info+xml          <?xml  version="1.0"?>        <dialog-­‐info  xmlns="urn:iex:params:xml:ns:dialog-­‐info"   version="839"  state="par1al"  en1ty=”301@somecustomer.com">        <dialog  id="da0d7773-­‐b030-­‐4a6b-­‐8235-­‐b3780aab1d23"   direc1on="recipient">        <state>terminated</state>        </dialog>        </dialog-­‐info>   BLF  Dialog  (info+xml)  -­‐  Hungup  
23. You  can  tell  the  phone  how  to  use  features  for  this  call     <local>        <iden1ty  display="301">sip:301@somecustomer.com</iden1ty>        <target  uri="sip:301@somecustomer.com">        <param  pname="+sip.rendering"  pvalue="yes"/>        </target>        </local>        <remote>        <iden1ty  display=”12223334444">sip: 12223334444@somecustomer.com</iden1ty>        <target  uri="sip:**301@somecustomer.com"/>        </remote>        </dialog>   BLF  Dialog  (info+xml)  -­‐  Other  
24.  NOTIFY  sip:503@somecustomer.com:17003  SIP/2.0        From:  <sip:2600hz@2600hz.com>        To:  <sip:503@somecustomer.com:17003>        Call-­‐ID:  b4d7e053-­‐4b8e-­‐1230-­‐8a9f-­‐40408f53e0fd        CSeq:  30976298  NOTIFY        Event:  message-­‐summary        Content-­‐Type:  applica1on/simple-­‐message-­‐summary        Content-­‐Length:  94          Messages-­‐Wai1ng:  no        Message-­‐Account:  sip:503@somecustomer.com        Voice-­‐Message:  0/0  (0/0)   Simple  SIP  Dialog  -­‐  MWI  
25. SIP/2.0  200  OK        From:  <sip:2600hz@2600hz.com>;tag=gX01N9908S7Fg        To:  <sip:503@somecustomer.com:17003>        CSeq:  30976298  NOTIFY        Call-­‐ID:  b4d7e053-­‐4b8e-­‐1230-­‐8a9f-­‐40408f53e0fd        Contact:  <sip:503@somecustomer.com:17003>        Event:  message-­‐summary        User-­‐Agent:  PolycomSoundPointIP-­‐SPIP_501-­‐UA/2.2.2.0084        Content-­‐Length:  0   Simple  SIP  Dialog  -­‐  MWI  
26. Tips  in  troubleshoo1ng  MWI,  BLF,  etc.   •  Make  sure  you’re  sending  the  right  stuff   •  You  can  trace  by  Call-­‐ID!   •  Oversized  packets!   •  Lost  Packets!   Hint:  TCP  can  be  handy  for  problema1c  clients  here   Troubleshoo1ng  
27. Learning  more  is  easy!     But  there  is  only  one  way  to  learn  more…   How  To  Learn  More…  
28. GO            TO                  CLUECON   How  To  Learn  More…  
29. THANKS!! ?