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Introduction to TLVs

In Call Control, the TLV is used to send data to, and receive data from, the CSP within API messages.

A TLV is an internal data structure consisting of the following elements:

• Tag - a label identifying the format of the TLV

• Length - the length of the data to follow

• Value - the data

Generic TLV Format

The generic format of a TLV is shown below:

Byte | Description
--- | ---
1 | Tag (MSB)
2 | Tag (LSB)
3 | Length (MSB)
4 | Length (LSB)
5 | Value[0] (Data)
: | :
: | Value[n]

Nested TLVs

The Call Agent feature and the DSP/RTP feature use nested TLVs. The following provides an overview and example of nested TLVs. An API message can contain nested TLVs. These TLVs are nested into the value field of another TLV in order to capture multiple properties of a call within one TLV.

The following applies to these nested TLVs.

• The TLV Count fields in the API message accounts for the top level TLVs but not the nested TLVs.

• The same TLV can be used multiple times within the same message depending on the context of the nested TLVs.

• The Length field in any "parent" TLV counts the bytes in all of its nested TLVs.

Example:

Interworking TLVs

This chapter contains TLVs used for Interworking and are indicated as such. Some of these Interworking TLVs can also be used in Standard environments and that is indicated as well.

Refer to Interworking in the Developer’s Guide: Internet Protocol.

Interworking TLVs are used in the following API messages:

Host to CSP

• Outseize Control

• Route Control

• Inseize Control

• Connect with Data

• Release Channel with Data

• Outpulse Digits

• PPL Event Request

CSP to Host

• Request for Service with Data

• Channel Released with Data

• PPL Event Indication

• Channel Release Request

Setting up, monitoring, and tearing down calls.
Tag-Length-Value block. A standardized block that allows data to inserted in a standard way into API messages.
Most Significant Bit
Least Significant Bit
Digital Signal Processor
Real-Time Transport Protocol. Supports transport of real-time data like interactive voice and video over packet-switched networks.
Interworking is a software feature within the Excel platform call control layer that enables protocol conversion by analyzing and converting Network Signaling (NS) Layer 3 information.
A computer, attached to the Excel platform through an RS-232 or Ethernet link, from which you run the telecommunications application that controls the Excel platform.
Outgoing call setup during real-time call processing on a specific channel.
See Programmable Protocol Language.
A condition that, when met, drives a state machine from one state to another. A condition that drives a Component out of its current state by invoking an associated primitive.