6 Mapping SIP Responses to SS7 Cause Codes
Establishing a Session in the IMS 125
This means that service providers can expect a significant increase in their signaling
traffic, and if they are capturing this traffic for analysis and functions such as revenue
assurance, they will see a marked increase in storage capacity requirements. This is
because within SS7, the network is only concerned with communicating about physical
connections. In the SIP network, the protocol is communicating everything about the
subscriber, including the subscriber??™s current location (address).
Messages between the SS7 and SIP domains must be mapped between the two protocols.
When a SIP INVITE is received at the MGCF, the MGCF must derive certain
parameters and headers and use these values to create the equivalent SS7 messages.
Following is a description of the SS7 parameters and how they are mapped into SIP.
?– Called party number
?– Calling party number
?– Calling party??™s category
?– Forward call indicators
?– Hop counter
?– Nature of connection indicators
?– Transit network selection
?– User service information
SIP Response SS7 Cause Code
487 Request Terminated 127 Interworking
488 Not Acceptable Here 127 Interworking
491 Request Pending No Mapping
493 Undecipherable 127 Interworking
500 Server Internal Error 127 Interworking
501 Not Implemented 127 Interworking
502 Bad Gateway 127 Interworking
503 Services Unavailable 127 Interworking
504 Server Timeout 127 Interworking
505 Version Not Supported 127 Interworking
513 Message Too Large 127 Interworking
580 Precondition Failure 127 Interworking
600 Busy Everywhere 17 User Busy
603 Decline 21 Call Rejected
604 Does Not Exist Anywhere 1 Unallocated number
606 Not Acceptable 127 Interworking
TABLE 5.
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