Software Overview

The H.323 VoIP Gateway complies with H.323 Version 2.0, and therefore supports all gateway Registration, Admission, and Status (RAS) functions.

The H.323 VoIP Gateway provides an interface between the PSTN and IP network for voice calls. IP-to-IP calls are also supported on the gateway. The H.323 stack is implemented on the specially-configured IP Signaling Series 3 card. The IP Signaling Series 3 card has a special software load that includes IP Signaling interface support and the H.323 stack.

Assuming adequate network conditions, the CSP delivers carrier-class voice quality over H.323.

The CSP H.323 offering on the CSP provides both signaling and media capability, so application developers do not need to add these features separately. The H.323 signaling is provided by the IP Signaling Series 3 card and media is provided by the VDAC-ONE or IP Network Interface Series 2 card.

This H.323 implementation uses Universal Protocol Data Format (UPDF) to provide seamless protocol interworking, with no need for protocol-specific messages. This interworking includes calls from PSTN-to-PSTN, IP-to-IP, PSTN-to-IP, and IP-to-PSTN.

The User Input Indication (UII) message is available in the CSP to transmit inputs from the user interface to the receiver. The inputs could be a button that the user presses on the PSTN side of the call such as a DTMF keypad or hookswitch information. The UII message transmits the hookflash and DTMF signal information on the IP side of the call.

The hookflash is a common input indicating a brief on-hook condition that occurs during a call. For example, during a call, the phone user quickly depresses and then releases the hook on their telephone. It is not long enough in duration to be interpreted as a signal to disconnect the call; however, telephone switches and PBXs are frequently programmed to intercept hookflash indications and use them to allow a user to invoke supplemental services. For example, your local service provider may allow users to enter a hookflash to switch between calls if the user subscribes to a call waiting service.

To enable the CSP to transmit the PPL Event Indication message to the host, you must set Configuration Byte 1 for PPL Component L3P H.225 (0xA1) to 0x01. To disable, set the configuration byte to 0x00.

The following data ICBs support the User Input Indication message. See the following in the ICB Chapter in the API Reference:

The CSP supports multiple alias addresses such as E.164, H.323Id, URL, and e-mail for the IP Signaling Series 3 card and remote H.323 endpoints.

The CSP interfaces to gatekeepers from leading companies. This feature requires the CSP to send a gateway technology prefix in the registration request (RRQ). Use this prefix to configure the gateway's routing table or database in the gatekeeper. Include the new TLV below in the VoIP Protocol Configure message to create and send the prefix.

The VDAC-ONE or IP Network Interface Series 2 card provides the RTP stream for the H.323 call.

The H.323 software gets the RTP Payload Type and Payload size from the Route Table or Route Control message. If the type and size are not specified in either of those, the H.323 software uses the defaults.

The Progress message is an optional Q.931 call setup message. It can be sent by an H.323 gateway to indicate the progress of a call when interworking with a Switched Circuit Network (SCN). This message can also be sent by an H.323 endpoint before the Connect message is sent, depending on the supplementary service interaction.

On an H.323 call, Call Alerting and Progress messages can contain a Progress Indicator Information Element (IE) to describe an event that occurred during the life of the call. The CSP will establish a voice path when required.

• Determines if the Q.931 Progress Indicator IE is present in the Alerting or Progress messages on a call.

• Sends a PPL event indication to the host when the CSP receives an Alerting or Progress message. A message is sent to the
VDAC-ONE (or IP Network Interface Series 2) card to establish the voice path.

• Receives a PPL Event Request of Alerting or Progress from the host with the progress indicator.

• Transmits the appropriate Release Complete Reason in Release Complete message to the network. The new Release Cause Codes are listed in the Release Cause Code TLV (0x27E3) in the Tag Length Value Blocks chapter in the API Reference.

You can configure the second Ethernet port on the
IP Signaling Series 3 card to separate the H.323 signaling traffic from the host control traffic. Cantata recommends having the host-to-CSP traffic carried on Ethernet port A and the H.323 signaling traffic carried on the Ethernet port B.

The additional information is carried in the vendor specific area of the BOOTP response. You modify the BOOTP configuration to include new entries to carry the IP Address, Gateway IP Address, and Subnet Mask for the second physical Ethernet port.

Configuring the second Ethernet port is optional but if you enter an IP Address for Ethernet port B you must enter an associated Subnet Mask.

Important! Although a gateway IP Address may be configured for both Port A and Port B, only one is utilized. If two gateway IP addresses are configured, one for Port A and one for Port B the one specified for Port A will be used. Therefore, Cantata recommends that you configure only one gateway IP Address and that it be on Port B.

If you do not configure the second ethernet port, it is internally set to the same values configured for the first ethernet port.

For the associated procedure, refer to Configuring Dual Ethernet Ports on IP Signaling Card in the Application Development chapter in the Developer Guide: Overview.

The CSP can send a list of up to five supported codecs in an H.323 offer to an endpoint when establishing a media session. The receiving endpoint selects one codec from that list and reports the selection back in the answer message to the CSP.

• The codec list is applicable for calls that use SIP or H.323 signaling and is not for clear-channel VoIP calls. For SIP signaling refer to Codec List in SIP-Initiated Offer.

Without this feature, the call might not get established because the CSP could include a codec type that endpoint will not accept.

The host application provides the codec list and sends the list in the Outseize Control message as shown in Host Provides Codec List:

Use the following TLVs in the Outseize Control message to include the codec types:

The Outseize Control Message Trace shows how to use these TLVs in the Outseize Control message. Note that the Outseize Control message cannot exceed 260 bytes.

The following trace for the Outseize Control message shows the nested TLVs containing the codec information.

The H.323 protocol resident in the IP Signaling Series 3 card enables the CSP (gateway) to communicate with other H.323 gateways and gatekeepers in the call server network architecture.

Prior to this feature, the Gateway (CSP) supported either gateway (direct calls) or gatekeeper routed calls at any one time. When the Gateway (CSP) was registered with a gatekeeper it would process all the calls as Gatekeeper routed calls.

Starting with Release 8.4.0, if the CSP is registered with a Gatekeeper the CSP may send an ARQ (Admission Request) message to the Gatekeeper to request information about a remote endpoint. If the CSP chooses to send an ARQ to the gatekeeper, when the gatekeeper responds with the ACF (Access Confirmed), the response will determine if the CSP sends the call to the gatekeeper or directly to the remote endpoint.

If the remote endpoint IP address TLV 0x27C2 is included in the Route Control/Outseize message, then the CSP will send the call to the remote endpoint IP address that is specified in the TLV 0x27C2. The CSP will not send the ARQ to the gatekeeper.

If the remote endpoint IP Address TLV 0x27C2 is omitted from the Route Control or Outseize Control message, then the CSP sends the ARQ message to the Gatekeeper. When the ACF is returned, the CSP looks in the message to determine where to send the call. The CSP will send the call either to the remote endpoint IP address provided by the gatekeeper or to the gatekeeper as specified in the ACF message.

The end result is the CSP does not actually modify the gatekeepers’ behavior. The CSP acts differently based upon data included in the Route Control/ Outseize Control message.

To invoke this feature use the Route Control (0x00E8) message with the Remote End Signaling IP Address (Q.931) (0x 27C2) TLV. This TLV provides the remote endpoint IP address for the call. This TLV will be used for each call to determine whether the ARQ and ACF message exchanged is implemented for that call.

Important! The Remote End Signaling Port (Q.931) (0x27C3) TLV specifies the remote signaling port. The defaults are: port number 1719 for gatekeeper routed calls and port number 1720 for gateway routed calls. This TLV is only necessary when using non-standard values.

The H.245 is a control signaling protocol in the H.323 multimedia communication architecture used to exchange end-to-end H.245 messages such as:

This configurable CSP H.245 Tunneling feature permits the encapsulation of H.245 messages within H.225 message between H.323 endpoints.

To enable H.245 Tunneling for the IP Signaling card, use the H.245 Tunneling Configure TLV (0x02D5) in the VoIP Protocol Configure message (0x00EE). Refer to the TLV chapter in the API Reference.

The IP Signaling cards can then accept incoming calls with H.245 tunneling. With this feature enabled on the IP Signaling card, H.245 tunneling can be used on a per outbound call basis by using the H.245 Outbound Tunneling TLV (0x27E4) in Route Control or Outseize Control messages.

Note that if tunneling is not enabled on the IP Signaling card using the H.245 Tunneling Configure TLV (0x02D5) in the VoIP Protocol Configure message, then the CSP cannot offer outbound tunneling calls.

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).

A device that translates calls between an IP network and another network, typically the PSTN.

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.

The Registration, Admission, and Status messages communicated between two H.323 entities for example between an Endpoint and a Gatekeeper.

Public Switched Telephone Network

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

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.

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.

See Signaling System Number Seven.

See Integrated Services Digital Network.

Universal Protocol Data Format. A predefined data format set used by a line card to communicate to the Layer 4 and above to represent information of the network-side of the line card. This set is independent of the network-side protocol.UPDF offers a "super scale" protocol format for signaling.

See Universal Protocol Data Format.

See Programmable Protocol Language.

A programmable software component that uses PPL state machines that can be modified with the PPL Tool.

See Information Control Block.

Address format for ISDN networks. The international public telecom-munications numbering plan. A standard set by ITU-T for addressing telephone numbers. See ITU Recommendation E.164 (1991).

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

An H.323 entity on the network that provides address translation and controls access to the network for H.323 terminals and other end points. The gatekeeper may also provide other services to the endpoints such as bandwidth management and locating gateways.

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

Call signaling protocol for setup and termination of calls.

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

Real-Time Transport Control Protocol.

SCN. A public or private switched telecommunications network such as GSTN or ISDN. TCP: transmission control protocol, reliable network-ing layer on top of IP.

See Switched Circuit Network.

In PPL, a condition that, when met, drives a state machine (PPL Component) from one state to another, by invoking an associated Primitive. In PPL files, an Event is marked by an arrow and text.

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.

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.

Boot protocol for TCP/IP

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 bits of an Internet Protocol (IP) address used for a subnetwork.

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

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.

See Converged Services Administrator.

CSA. GUI-based tool used to configure, provision and monitor a Excel platform related to, for example, SIP, H.323, and VDAC Resouce Attributes.