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Whether it sends the 183 with or without SDP, or whether it even sends a 183, is controlled by the Sonus SBC 1000/2000's internal, pre-programmed translation table. The internal translation table controls the translation for ISDN Progress/Alert/Connect messages, as well as SIP 18x/200 messages for calls ISDN to SIP, SIP to ISDN, and SIP to SIP.
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How does the Message Translation Table work?
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Below a Progress with no Progress Indicator (PI=0) is shown with it's matching Incoming Message configuration. Similarly, a Progress with PI=1 (Not end to end ISDN) is shown with it's matching Incoming Message configuration.
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| 1 | Incoming Message Matching |
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Special Considerations for Incoming Matching
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| title | What is _SDP Media Negotiation_? |
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SIP uses SDP to negotiate media connections. To establish a common media framework (codec, endpoint addresses, etc), an endpoint will send an SDP Offer - a list of the media that the endpoint can support. The recipient will Answer the SDP Offer with a list of media attributes that it endpoint will support for this particular session. | Expand |
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| Click here to see an example of Media Negotiation |
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| Click here to see an example of Media Negotiation |
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| In the diagram below, an INVITE with SDP is sent to the Sonus SBC 1000/2000. This SDP is an Offer - a list of the media that the endpoint is offering to support. Later, the Sonus SBC 1000/2000 replies with a 183 with SDP, essentially Answering the Offer with a media list that is acceptable for communication. Once an SDP Offer has been Answered, the media is said to be Negotiated. Both sides are now able to send media based upon the negotiated SDP parameters. | Caption |
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| 1 | INVITE With SDP Sent To to Sonus SBC 1000/2000 |
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The Media Input Matching Type
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In the example below, the Early Media Status is set to Not Negotiated. As the SIP SDP Offer has not yet been answered, the media is indeed not yet negotiated and, therefore, the match passes. If the remaining Incoming Message matches as well, the translation entry will be used to translate the message to the SIP side.
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| 1 | Early Media Status |
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In the example below, the Early Media Status is set to Negotiated. Since the media has yet to be negotiated (no SDP Answer has been sent), the match fails. That particular translation entry fails. The next translation entry, if there is one, will be checked.
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| 1 | Early Media Status |
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In the example below, the media has been negotiated therefore Early Media Status will be matched. If the rest of the Incoming Message translation is matched, that translation will be used.
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| 1 | Early Media Status Matched |
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| The same Early Media Status configuration also works for SIP to SIP calls. Click here to see the Incoming Message configuration for SIP messages |
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| The same Early Media Status configuration also works for SIP to SIP calls. Click here to see the Incoming Message configuration for SIP messages |
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| 1 | Media Not Negotiated |
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| 1 | Not Match Early Media Status Of of Not Negotiated |
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Early 183 and Negotiated Media
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| 1 | Early 183 Enabled |
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Setting the Early Media Status to ANY causes the translation to ignore the media state. |
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- The first 183 matches the Incoming Message configuration and the corresponding Progress is sent based upon the Outgoing configuration.
- The second 183 also matches, but a Progress is not sent as the Outgoing translation configuration is set for No on Subsequent.
- The next SIP packet, 180 Ringing w/SDP, matches the Incoming Message and is translated accordingly. The SDP indicates early media is available, so the Sonus SBC 1000/2000 begins to receive/send media
- The subsequent 180 Ringing w/ SDP also matches in the Incoming configuration; however, it is not translated as the Outgoing is configured to No on Cut Through.
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The translation table above contains just two entries. Each time a packet arrives, each entry is tried sequentially in top-to-bottom order. |
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Below are some additional examples of ISDN messages and which Incoming Message configurations are matched and not matched.
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| 1 | Incoming Message Configurations Not Matched |
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If no match is found, or no table is assigned to the call route, the message is translated using the internal translation table. |
Examples of Full Translations
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| 1 | Full Translation Example 1 |
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| 1 | Full Translation Example 2 |
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| 1 | Full Translation Example 3 |
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| 1 | Full Translation Example 4 |
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| 1 | Full Translation Example 5 |
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The above translation is a commonly used to generate ringback when the inbound leg does not provide ALERT or 180. |
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Translation Tables are invoked at the Call Route level. The call route (below) is configured to use the Message Translation Table called msg xlation.
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The msg xlation table contains two translation entries (detail for the second entry is displayed).
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| 1 | msg xlation Table |
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When a route containing a message translation table is used to route a call, each reply message is checked again the entries in the selected table.
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