Voice Attributes

You can configure the following voice attributes with the Resource Attribute Configure (0x00E3) message:

The RTP payload type indicates the algorithm used for compressing the data or payload portion of the packet.

RTP payload sizes can be changed in multiples of the specified RTP Payload Type's base packetization rate. On the IP Network Interface Series 2 card, the RTP payload size is tightly coupled with RTP payload type. Changing the default RTP payload type also changes the default RTP payload size to its applicable value (unless a new default RTP payload size is also specified). Using the non-default RTP Payload Type during call establishment results in the default RTP Payload Size not being used. If the RTP Payload Size is not provided, the default for the specific payload type is used.

For the IP Network Interface Series 2 card, refer to VDAC-ONE Resource Profile Terminal Capabilities for each payload type's base packetization rate (for example,1 x payload size), its default payload size and maximum payload size.

During a normal voice conversation, much of the time is wasted on silence from one or both ends. Ethernet bandwidth can be conserved if, during these periods of silence, RTP packets are sent with silence-encoded, compressed payloads.

TLV: 0x0102 RTP Silence Suppression
(Do not send to an active call that is in fax/modem mode.)

A voice activity detection (VAD) algorithm determines which portions of the input signal contain active speech. At the beginning of silence periods (the end of active periods), a special silence insertion descriptor (SID) packet is generated that describes the background noise. The SID packets are generated at the onset of the silence period and whenever the characteristics of the background noise change. The speech decoder that receives the SID packet uses a comfort noise generation (CNG) algorithm to reproduce the background noise from the information in the packet and possibly information contained in past active voice packets. The average bit rate required for voice transmission is lowered considerably when using silence suppression.

In compliance with ITU G.168, this feature eliminates echo introduced by impedance mismatched hybrids. You can enable and disable Echo Cancellation on an established connection.

You can set the redundancy level for RTP using the RTP Payload Redundancy TLV. See RFC 2198.

During call setup, the Connection Mode is automatically determined according to the presence of destination and source addresses in the Route Control (0x00E8) or Outseize Control (0x002C) message.

To change the Connection Mode after a call is established using Resource Attribute Configure (0x00E3) message, send the Connection Mode (0x01DB) TLV with the appropriate mode set.

Example: After a two-way call has been established to a Call Center, the caller is put on hold and connected to music. The Connection Mode of the Call Center line is changed to Transmit Only. If callers enable the mute feature on their phone, the Connection Mode on their line is changed to Receive Only.

There is no default Connection mode. If you query the Module Connection Mode, it is reported as 0xFF. This is a generic value and does not indicate a specific mode. You cannot set the Connection Mode to this value.

Important! Source Address (IP/RTP Port) is always required in Route Control or Outseize Control messages.

This TLV allows DTMF signals to be relayed within the VoIP media stream, using a special RFC 2833-compliant packet format. Low bit-rate audio codecs (such as G.729 or G.723.1) can compromise the signal integrity of DTMF digits (and other telephony tones and signals), causing inaccurate detection and recognition of the DTMF digits on the recipient side. When this feature is enabled, the detected incoming DTMF digits (PSTN side) are removed from the audio stream by the IP Network Interface Series 2 card. The information for the detected and removed DTMF digits is embedded within the RTP stream, using a special RFC 2833-compliant packet format. The IP Network Interface Series 2 card on the receiving side decodes this special RTP payload carrying DTMF information, and regenerates the DTMF digits toward the receiving PSTN side. This TLV cannot be set for an active call. It can be configured only before or during the setup of the IP Network Interface Series 2 card call.

Because the VDAC-ONE card allows up to 30 milliseconds of a digit through before blocking it, the distant end might hear a very short audible sound.

The EXS API has been updated to allow you to configure how DTMF digits are transmitted to the IP network.

• The new value 0x02 removes the digit from the voice stream and drops the digit.

• If you are using the VDAC card, this TLV can be configured only before or during the call establishment. It cannot be set during an active call. If you are using the IP Networking Series 2 card, this TLV can be configure on the fly while the call is active.

This TLV is used to specify the local RTCP port number. If this port is not specified by the host during the IP Network Interface Series 2 card call setup, the source RTCP port is set one higher than the source RTP port, per RFC 1889. This TLV can be set during an active call.

This TLV is used to specify the remote RTCP port number. If this port is not specified by the host during the IP Network Interface Series 2 card call setup, the destination RTCP port is set to one higher than the destination RTP port, per RFC 1889. This TLV can be set during an active call.

You configure the Minimum Jitter Buffer Delay by using the Minimum Jitter Buffer Delay TLV in the Resource Attribute Configure (0x00E3) message. The range of valid values is 0 - 150 milliseconds.

Important! You cannot configure the Minimum Jitter Buffer Delay on an established connection.

You configure the Maximum Jitter Buffer Delay by using the Maximum Jitter Buffer Delay TLV in the Resource Attribute Configure (0x00E3) message. The range of valid values is 150-300 milliseconds.

Important! You cannot configure the Maximum Jitter Buffer Delay on an established connection.

The VDAC-ONE card and the IP Network Interface Series 2 card allows RFC 2198 dynamic payload negotiation for clear channel calls only.

You first must enable RFC 2198 with the RTP Payload Redundancy TLV (0x01D1) in the Resource Attribute Configuration (0x00E3) message.

You can configure the default value at configuration time or change this value per call as follows:

• To configure the default RFC 2198 Payload Type, use the RFC 2198 Dynamic Payload Type TLV (0x01F2) in the Resource Attribute Configuration (0x00E3) message.

• To change the default RFC 2198 payload type per call, use the TLV above within the Generic PPL ICB (0x1E) in the Route Control (0x00E8) or Outseize Control (0x002C) messages.

Real-Time Transport Protocol. Supports transport of real-time data like interactive voice and video over packet-switched networks.

Tag-Length-Value block. A standardized block that allows data to inserted in a standard way into API messages.

Internet Protocol. Part of the TCP/IP family of protocols used to route messages and tracks the addresses of nodes.

The protocol used in most local area PC networks. Typically, most Ethernet networks support data transmission speeds up to 10 Mbps, but 100 Mbps is also possible.

International Telecommunications Union (UN)

Outgoing call setup during real-time call processing on a specific channel.

The point in the Excel platform where a DS0 connects to a network. Also known as a "socket."

Voice over Internet Protocol. The delivery of voice information in digital form in discrete packets rather than in the traditional circuit-committed protocols of the public-switched telephone network (PSTN).

Public Switched Telephone Network

ITU-T standard defines a set of call control, channel setup, and codec specifications for transmitting real-time voice and video over networks that do not offer guaranteed service or quality of service.

Signaling technique where the full channel bandwidth is used for data transmission, while the framing and control bits (signaling) use a separate channel. No control or signaling is performed on this path. See B8ZS and ZBTSI.