Cisco Systems H.323 Codec Selection, Quick Reference for Important Parameters, Parameter Value

Chapter 3 Provisioning the Cisco HSI

H.323 Stack Configuration

Codec Selection

The Cisco HSI negotiates the media stream codec to establish a match between the PSTN MGCP media gateway (for example, the Cisco AS5xxx series or Cisco MGX series) and the H.323 endpoint or gateway. To match codecs, the MGCP gateway must be configured to match what is expected at the H.323 end. Similarly, the Cisco HSI also must be configured with the same codecs.

The Cisco HSI receives a list of codecs from the MGCP gateway and matches the listed codecs to the codecs that are configured on the HSI. The HSI advertises all of the successful matches in the H.245 terminalCapabilitySet messaging with the H.323 endpoint.

It is important to determine and configure the “frames-per-packet” value correctly on the Cisco HSI per codec. If “frames-per-packet” value is incorrect, the codec may not be negotiated successfully between the HSI and the H.323 endpoint.

It is also important to configure the MGCP gateway correctly. The gateway should be configured to provide “static payload” values for the required codecs, rather than dynamic payload types (see Table 4 in RFC 3551, Schulzrinne and Casner).

Quick Reference for Important Parameters

Table 3-13, Table 3-14, Table 3-15, and Table 3-16can be used in initial HSI configuration. The tables present parameters that you might use frequently to align the Cisco HSI with an existing PSTN or Voice over IP network.

Table 3-13presents important call control parameters.

Table 3-13 Common Call Control Parameters

Parameter Name		Parameter Value	Description
A_CC_oLinecall		0—Unknown	Calling party's category
		10—Ordinary
A_CC_Clir		0—No indication	Address presentation restricted indicator
		1—Presentation allowed
		2—Presentation restricted
		3—Address not available
A_CC_ANumDataSI		0—None	Screening indicator
		1—User provided not verified
		2—User provided verified passed
		3—User provided verified failed
		4—Network provided
A_CC_oIsdnAllTheWay		0—ISDN user part not used all the way	Forward call indicator, ISUP indicator
		1—ISDN user part used all the way
A_CC_oIsdnPref		0—ISDN user part preferred all the way	Forward call indicator, ISUP preference
		1—ISDN user part not required all the
		way
		2—ISDN user part required all the way
	Cisco H.323 Signaling Interface User Guide
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