3 Call flow between the SIP and SS7 domains
TABLE 5.2 SIP Response to an Address Complete (ACM) Message
Backward Call Indicator/Called Party??™s
Status Indicator Parameters SIP Response
00 No indication 183 Session Progress
01 Subscriber free 180 Ringing
122 Chapter 5
183 Session Progress. If a response 183 Session Progress has already been sent, then
the EXM is encapsulated within an INFO message.
There is no mapping for Pass Along Message (PAM) or Suspend (SUS). If encapsulation
is being used then these messages are simply encapsulated within a SIP INFO
message. The purpose of these two SS7 messages differ dependent on implementation,
but are typically used to support features such as three way calling (the switches hold
the call connection when the subscriber does a hook flash to initiate these features).
There is no need for these in the SIP domain.
There is also mapping of cause code values contained within an SS7 Release (REL).
These cause codes are mapped to a SIP REASON header within a SIP BYE or CANCEL.
Likewise, there is mapping between specific cause codes and SIP responses. Tables 5.4
and 5.5 provide the mapping between SS7 cause codes and SIP responses.
TABLE 5.3 SIP Response to a Call Progress (CPG) Message
Event Information/Event Indicator Parameters SIP Response
000 0001 Alerting 180 Ringing
000 0010 Progress 183 Session Progress
000 0011 In-band info 183 Session Progress
SS7 Cause Code SIP Response
1 Unallocated number 404 Not Found
2 No route to network 500 Server Internal Error
3 No route to destination 500 Server Internal Error
4 Send special information tone 500 Server Internal Error
8 Preemption 500 Server Internal Error
9 Preemption circuit reserved for re-use 500 Server Internal Error
17 User busy 486 Busy Here
18 No user responding 480 Temporarily Unavailable
19 No answer from the user 480 Temporarily Unavailable
20 Subscriber absent 480 Temporarily Unavailable
21 Call rejected 480 Temporarily Unavailable
22 Number changed 410 Gone
27 Destination out of order 502 Bad Gateway
28 Invalid number format (address incomplete) 484 Address Incomplete
29 Facility rejected 500 Server Internal Error
31 Normal unspecified 480 Temporarily Unavailable
TABLE 5.
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