\section{Examples}
\label{sec:examples}

The SDP message body and the {\BYE} and {\ACK} exchanges are the same as
in \citenorm{draft-ietf-sipping-basic-call-flows} and omitted for
brevity.

\subsection{Simple Call}

\begin{verbatim}
   User A                  User B
     |                        |
     |       INVITE F1        |
     |----------------------->|
     |    180 Ringing F2      |
     |<-----------------------|
     |                        |
     |       200 OK F3        |
     |<-----------------------|
     |         ACK F4         |
     |----------------------->|
     |   Both Way RTP Media   |
     |<======================>|
     |                        |
\end{verbatim}

In this scenario, User A completes a call to User B directly. The call
from A to B is marked with a resource priority indication. 

\begin{verbatim}
   F1 INVITE User A -> User B  
     
   INVITE sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bf9
   Max-Forwards: 70
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 3848276298220188511@atlanta.com
   CSeq: 1 INVITE
   Resource-Priority: dsn.flash
   Contact: <sip:UserA@client.atlanta.com;transport=tcp>
   
   Content-Type: application/sdp
   Content-Length: ...

   ...

   F2 180 Ringing User B -> User A

   SIP/2.0 180 Ringing
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=8321234356
   Call-ID: 3848276298220188511@atlanta.com
   CSeq: 1 INVITE
   Contact: <sip:UserB@client.biloxi.com;transport=tcp>
   Content-Length: 0
      
   
   F3 200 OK User B -> User A
   
   SIP/2.0 200 OK
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=8321234356
   Call-ID: 3848276298220188511@atlanta.com
   CSeq: 1 INVITE
   Resource-Priority: dsn.flash
   Contact: <sip:UserB@client.biloxi.com;transport=tcp>
   Content-Type: application/sdp
   Content-Length: ...

   ...
\end{verbatim}

\subsection{Receiver Does Not Understand Namespace}

In this example, the receiving UA does not understand the ``dsn''
namespace and thus returns a 417 (Unknown Resource-Priority) status
code.  We omit the message details for messages F5 through F7 since they
are essentially the same as in the first example.

\begin{verbatim}
   User A                  User B
     |                        |
     |       INVITE F1        |
     |----------------------->|
     | 417 R-P failed F2      |
     |<-----------------------|
     |         ACK F3         |
     |----------------------->|
     |                        |
     |       INVITE F4        |
     |----------------------->|
     |    180 Ringing F5      |
     |<-----------------------|
     |       200 OK F6        |
     |<-----------------------|
     |         ACK F7         |
     |----------------------->|
     |                        |
     |   Both Way RTP Media   |
     |<======================>|
\end{verbatim}

\begin{verbatim}
   F1 INVITE User A -> User B  
     
   INVITE sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bf9
   Max-Forwards: 70
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 3848276298220188511@atlanta.com
   CSeq: 1 INVITE
   Resource-Priority: dsn.flash
   Contact: <sip:UserA@client.atlanta.com;transport=tcp>
   
   Content-Type: application/sdp
   Content-Length: ...

   ...

   F2 417 Resource-Priority failed  User B -> User A
   
   SIP/2.0 417 Resource-Priority failed
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>;tag=8321234356
   Call-ID: 3848276298220188511@atlanta.com
   CSeq: 1 INVITE
   Accept-Resource-Priority: q735.0, q735.1, q735.2, q735.3, q735.4
   Contact: <sip:UserB@client.biloxi.com;transport=tcp>
   Content-Type: application/sdp
   Content-Length: 0

   F3 ACK User A -> User B
   
   ACK sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bd5
   Max-Forwards: 70
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl   
   To: LittleGuy <sip:UserB@biloxi.com>;tag=8321234356
   Call-ID: 3848276298220188511@atlanta.com
   CSeq: 1 ACK
   Content-Length: 0

   F4 INVITE User A -> User B  
     
   INVITE sip:UserB@biloxi.com SIP/2.0
   Via: SIP/2.0/TCP client.atlanta.com:5060;branch=z9hG4bK74bf9
   Max-Forwards: 70
   From: BigGuy <sip:UserA@atlanta.com>;tag=9fxced76sl
   To: LittleGuy <sip:UserB@biloxi.com>
   Call-ID: 3848276298220188511@atlanta.com
   CSeq: 2 INVITE
   Resource-Priority: q735.3
   Contact: <sip:UserA@client.atlanta.com;transport=tcp>
   
   Content-Type: application/sdp
   Content-Length: ...
   ...
\end{verbatim}
