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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 Excel platform delivers carrier-class voice quality over H.323.
The Excel H.323 offering on the Excel platform 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.
Seamless PSTN-IP Signaling Interworking: SIP/H.323/SS7/ISDN
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 Excel platform 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 Excel platform 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.
See the following PPL Component in this chapter.
PPL Component for H.225 - 0x00A1
The following data ICBs support the User Input Indication message. See the following in the ICB Chapter in the API Reference:
0x5B IP Signaling Series 3 Card ID
0x5C H.323 Hookflash Received (no data)
0x5D H.323 DTMF Signal Input Received
0x5E H.323 Signal Update Input Received
0x5F H.323 Alphanumeric Input Received
0x62 Remote Endpoints UII Capabilities
The Excel platform 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 following TLVs support alias addressing:
0x02C1 Vendor ID
0x02C4 Gateway E164
0x02C6 Gateway URL ID
0x02C7 Gateway E-mail ID
0x27C4 Source IP
0x27C5 Source Port
0x27D8 Source H.323 ID
0x27D9 Source URL
0x27DA Source E-mail
0x27DC Remote H.323 ID
0x27DD Remote URL
0x27DE Remote E-mail
Gatekeeper Support
The Excel platform interfaces to gatekeepers from leading companies. This feature requires the Excel platform 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 the send the prefix.
0x02D3 Gateway Technology Prefix
In this Excel H.323 implementation, the following specifications are supported:
H.225.0 (RAS, Q.931, RTP/RTCP)
H.245 and audio codecs
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.
Call Progress and Alerting Messages
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 Excel platform will establish a voice path when required.
The Excel platform does the following:
Processes an optional Progress message on an outgoing call.
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 Excel platform 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 a Progress message to network.
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.
This functionality works in gateway or normal (non-gateway) mode.
Dual Ethernet Port
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. The host-to-Excel platform traffic is carried on Ethernet port A and the signaling traffic is carried on the Ethernet port B. Excel recommends this configuration.
The BOOTP server is required to configure 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, Excel 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.
Codec List in H.323-Initiated Offers
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 following applies to this feature:
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.
The IP Network Interface card must use Profile 2.
The VDAC-ONE card must use Profile 0.
Without this feature, the call might not get established because the CSP could include a codec type that endpoint will not accept.
The figure below provides an overview of this process.
Figure 8-1 Codec List in Offer
Outseize Control messages
The host application provides the codec list and sends the list in the Outseize Control message as shown in Host Provides Codec List:
Figure 8-2 Host Provides Codec List
TLVs Used
Use the following TLVs in the Outseize Control message to include the codec types:
0x29FF - Local End-Point Media Info
0x2A0E - Media Connection Address
0x2A01 - Per Media Stream Information
0x2A03 - Media Type
0x2A07 - Media Port
0x2A02 - Per Codec Info
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.
Important! DO NOT use the following TLVs for these codec types:
0x0100 - RTP Payload Type
0x0101 - RTP Payload Size
0x27B0 - RTP Payload Type
0x27B1 - RTP Payload Size
Outseize Control Message Trace
The following trace for the Outseize Control message shows the nested TLVs containing the codec information.