gateway
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... PSTN.
The popularity of gateways that interwork between the PSTN and SIP
networks has motivated the publication of a set of common practices
...
... PSTN-SIP interworking gateways might be
deployed, provides use cases and identifies the mechanisms necessary
for interworking ...
... SS7. However, it is also
essential that SS7 information be available at gateways, the points
of SS7 ...
... Using SIP-T, there are three basic models for how calls interact with
gateways. Calls that originate in the PSTN can traverse a gateway to
...
... gateways. Calls that originate in the PSTN can traverse a gateway to
terminate at a SIP endpoint, such as an IP ...
... IP phone. Conversely, an IP
phone can make a call that traverses a gateway to terminate in the
PSTN. Finally, an IP network ...
... SIP may serve as a transit
network between gateways - a call may originate and terminate in the
PSTN, but cross a SIP-based network ...
... gateway determine the ISUP
variants that that gateway supports. Whether or nor a gateway
supports a particular version ...
... ISUP
variants that that gateway supports. Whether or nor a gateway
supports a particular version of ISUP ...
... endpoints:
* Gateways: A telephony gateway provides a point of conversion
between signaling protocols ...
...
* Gateways: A telephony gateway provides a point of conversion
between signaling protocols (such as ISUP ...
... circuit-switch and packet-switched audio media. The term Media
Gateway Controller (MGC) is also used in the examples and
diagrams in this document to denote large-scale clusters ...
... diagrams in this document to denote large-scale clusters of
decomposed gateways and control logic that are frequently
deployed today. So for example, a SIP-ISUP ...
... centers). For a call originating from LEC1 and be terminating in
LEC2, the originator in SIP-T is the gateway that generates the SIP
request for a VoIP call, and the terminator is the gateway ...
... gateway that generates the SIP
request for a VoIP call, and the terminator is the gateway that is
the consumer of the SIP request; MGC1 would thus be the originator
...
... SS7 information
within SIP requests at the originating gateway and reuse this SS7
information when signaling ...
... information when signaling to the PSTN at the terminating gateway.
By encapsulating ISUP information in the SIP ...
...
That much said, if only the exchange of ISUP between gateways were
relevant here, any protocol for the transport of signaling ...
... voice calls do not always both originate
and terminate in the PSTN (via gateways); SIP phones can also be
endpoints ...
... encapsulation and translation) in the SIP messages that it
transmits towards the terminating gateway. The terminator
extracts the ISUP content from the SIP message ...
... call that is routed by one or more proxy servers to the
appropriate terminating gateway. The terminating gateway
converts to ISUP ...
... proxy servers to the
appropriate terminating gateway. The terminating gateway
converts to ISUP signaling ...
... SS7 ISUP message will eventually
be received by the gateway that is the point of interconnection with
the PSTN network. This gateway ...
... gateway that is the point of interconnection with
the PSTN network. This gateway is from the perspective of the SIP
protocol the user agent client ...
... routing is used in the IP network to determine the
appropriate point of termination (in this instance a gateway) and to
establish a SIP dialog and begin negotiation ...
... between the origination and termination endpoints. The egress
gateway then signals ISUP to the PSTN, reusing any encapsulated ...
... ISUP
encapsulation in the request - the terminating gateway therefore only
performs translation on the SIP headers ...
... SIP Call setup requests (i.e., INVITEs). When a call originates in
the PSTN, a gateway is the UAC; otherwise some native SIP endpoint is
...
... In the case of calls originating in the PSTN (see Figure 3 and Figure
5), the originating gateway takes the necessary steps to preserve the
ISUP information by encapsulating it in the SIP request ...
... SIP request it creates.
The originating gateway is entrusted with the responsibility of
identifying the version of the ISUP ...
... In case of PSTN terminations (see Figure 3 and Figure 7) the egress
gateway terminates the call to its PSTN interface. The terminator
...
... encapsulated ISUP (for gateways only), support for multipart MIME,
graceful handling of unknown MIME content ...
... proxy servers are entrusted with the task of
routing messages to one another, as well as gateways and SIP phones.
Each proxy server ...
... interfaces (SIP bridging across different gateways that don't support
any ISUP variants in common). In order to optimize for maximum
...
... variant of ISUP to another in order to facilitate the termination
of that call over a gateway interface that does not support the
ISUP ...
... point in the path of the request, it is optimal to perform it at a
point that is at the greatest proximity to the terminating
gateway. This could be accomplished by delivering the call to an
application that might perform the conversion between variants.
Feature transparency in this case is contingent on the
...
... b) An alternative would be to sacrifice ISUP transparency by handing
the call off to a gateway that does not support the version of the
originating ISUP ...
...
If the SIP-T originator is a gateway that received an ISUP request,
it must always perform both encapsulation ...
... encapsulated ISUP in
the message, the gateway should use a canonical template for the
message type ...
... message type in question (a pre-populated ISUP message configured
in the gateway) instead.
o Translate the headers ...
... SIP at the message level. In SIP-T deployments gateways are
entrusted with the task of generating a specific ISUP message for
...