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In this section: Table of Contents maxLevel 3

Whenever a

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 (SBC) receives Each time a Sonus SBC 1000/2000 receives an ISDN Progress/Alert/Connect or a SIP 183/180/200 message, it is translated to the outgoing leg of the call. Although it may appear that incoming messages are simply copied from incomging to outgoing leg, in fact, they are run through an internal translation table to determine precisely what to send (on the outgoing leg).

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This article outlines the various configuration parameters of the Message Translation functionality, how the parameters are used, and how to configure them to override the pre-programmed translations.

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Basic Message Translation

Looking at the diagram below:

Below is a description of a basic message translation:

• We can see an SIP INVITE to the Sonus SBC 1000/2000.
• Which results in the Sonus SBC 1000/2000 generating an ISDN Setup.
• As the ISDN network routes the call, it returns a PROGRESS to the Sonus SBC 1000/2000.
• In turn, the Sonus SBC 1000/2000 sends a 183 to the SIP endpoint.

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

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Does the Message Translation Table work?

Although the internal translation table works for the majority of installations, it may be necessary to customize a translation. This is accomplished by creating an entry in the Message Translation table that

1. Identifies specific incoming messages and.
2. Converts them to the desired output.

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The first phase of the the Message Translation table works on the incoming message. When a message arrives, it is checked against all of the translations entries in the table, specifically the Incoming Message configuration.

Below For a Progress with no Progress Indicator (PI=0) is shown with it's , it requres a matching Incoming Message configuration. Similarly, a Progress with PI=1 (Not end to end ISDN) is shown with it's requires matching Incoming Message configuration. Both Progress messages match the incoming (translation) message. Since they match, the outgoing message will be eventually translation via the Outgoing Translation configuration.

Special Considerations for Incoming Matching

In the diagram below

For example, 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.

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title What is _SDP Media Negotiation_?
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 its endpoint will support for this particular session.
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Click here to see an example of Media Negotiation	Click here to see an example of Media Negotiation

The Media Input Matching Type

Some applications cannot accept additional SDPs once the media has been negotiated, so the Sonus SBC 1000/2000 includes an additional Incoming Message criteria that permits a translation to be matched based on whether media negotiation has been completed.

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Configuring the Early Media Status to Negotiated means that the incoming message will only be translated if the media is already negotiated Configuring the Early Media Status to Not Negotiated means that an incoming message will only be translated if the media has not yet been negotiated.

 

Early Media Status set to Not Negotiated. For exampleIn 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.

In the example belowEarly Media Status is set to Negotiated. For example, 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.

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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The same Early Media Status configuration also works for SIP to SIP calls. Click here to see the Incoming Message configuration for SIP messages	The same Early Media Status configuration also works for SIP to SIP calls. Click here to see the Incoming Message configuration for SIP messages

 

Early 183 and Negotiated Media

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Early 183 and Negotiated Media

If Early 183 is Enabled in the SIP Signaling Group, the SBC will immediately reply to the INVITE with a 183 w/SDP. The SDP Answer fulfills the negotiated media requirements.

 

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Setting the Early Media Status to ANY causes the translation to ignore the media state.

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When a incoming message matches in the Incoming Message configuration, the second phase of the process is to send an outgoing message that conforms to the corresponding Outgoing configuration.
In
For example, see the call setup below:

• 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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You might notice that the The Incoming Message format remains the same, even when the incoming message is SIP. The Message and IE Types do not change to SIP references because any given translation maybe used for either SIP or ISDN. A ISDN to SIP conversion table (below) will assist in selecting the appropriate desired parameters. Message Type SIP Message Progress 183 Session Progress Alert 180 Ringing Connect 200 OK

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The Media Cut Through parameter controls how the Sonus SBC 1000/2000 handles early media for calls that have:

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Because the Media Cut Through is part of Message Translation (which is applied at the call route), it is possible to override the Signal Group-level Play Ringback setting. In the table below, note how the Media Cut Through configuration interacts with Sonus SBC 1000/2000's Ringback setting.

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Remember that the Play Ringback function is only activated when the Sonus SBC 1000/2000 receives either ALERT or 180.

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For ISDN-originated calls, configure the Media Cut Through to Yes on Early Media if you want the caller to hear inband ringing associated with 183w/SDP.

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Mismatching Input Translation Criteria

Below are some additional examples of ISDN messages and which Incoming Message configurations are matched and or not matched.

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• The incoming Progress may not match the Input Message Parameters, which will then proceed to the next entry in the message translation table. Outgoing messages will be translated per the Outgoing configuring table. 

 

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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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The above translation is a commonly used to generate ringback when the inbound leg does not provide ALERT or 180.

Invoking a Translation Table

Translation Tables are invoked at the Call Route level. The For example, the call route (below) is configured to use the Message Translation Table called (i.e., msg xlation).

The msg xlation table contains two translation entries (detail for the second entry is displayed).

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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.

For details on Call Routing, refer to Creating and Modifying Entries to Call Routing Tables.

For details on Message Translation, refer to Creating and Modifying Entries to Message Translation Tables.

Message Translation Reference

For a listing of the pre-programmed Message Translations on the Sonus SBC 1000/2000, see Message Translation Reference.

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