Routing SIP and H.323 Calls Using Outseize Control Message

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VoIP applications can use the Outseize Control (0x002C) message for outbound SIP and H.323 signaling. This method is required for application developers who:

• are migrating TDM applications to the VoIP environment if the TDM applications already use the Outseize Control message

The host application is responsible for selecting the span and channel for each outbound call on a per call basis. The host application also selects the source IP address and port.

The figure below provides an overview of the routing process. Note that the inbound side of the call is the same as described in the previous section. The outbound side involves the Outseize Control message rather than the Route Control message. The differences are pointed out in the steps following the figure.

1. The host application sends the Outseize Control message to the outbound span/channel Layer 4 PPL components. (Note that the Layer 4 Router component is not used.)

The Outseize Control message includes the span/channel, source IP address and port required to route the call. (For details, refer to Sample Outseize Control message following these steps.)

2. The Layer 4 PPL components send the outbound call signal to the Layer 3 SIP User Agent Client.

3. The SIP User Agent Client initiates the outbound call using a SIP INVITE message.

In the following example, the Outseize Control message contains the AIB that specifies the span and channel used to route this call. The NPDI Universal ICB contains six TLVs that specify information about this call as indicated below. You must include the Remote Side Protocol TLV (0x277E) so the call can be handed to the appropriate Layer 3 protocol. For H.323 calls, you must include the IP Signaling Series 3 Card ID TLV (0x27C1) so the call can be delivered to one of the H.323 IP Signaling Series 3 cards in the CSP.

Important! You must use the NPDI TLVs rather than the legacy TLVs for the Outseize Control message to work with SIP and H.323 signaling because they are NPDI-only oriented.

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).

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

Session-Initiation Protocol. A signaling protocol used for establishing sessions in an IP network. A session could be a simple, two-way telephone call, or it could be a collaborative multi-media conference session.

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.

See Time Division Multiplexing.

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

Call processing layer of the CSP.

See Programmable Protocol Language.

Protocol layer of the CSP.

In SIP, an application program that sends SIP requests (See also Session Initiation Protocol). Clients may or may not interact directly with a person. Users agents and proxies contain clients (and servers).

See Address Information Block.

Network Protocol Data Intelligence. Also called “Interworking,” it is a software product that operates within Excel’s Call Control (Layer 4) and Services (Layer 5) call processing layers. NPDI is meant to enhance Excel’s call processing product offering by allowing call processing layers (specifically Layers 4 and 5) to perform advanced analysis, generation, and conversion of Network Signaling (NS) Layer 3 information.

See Information Control Block.

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

A 32-bit address, used in IP routing, which includes a Network address identifier assigned by a central authority and a Host ID (an end station identifier assigned by a LAN administrator).

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

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

PCM and companding standard used in Europe to compress and expand the amplitude range of a signal before and after transmission. See µ-Law.