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URI Dialing
TANDBERG VIDEO COMMUNICATIONS SERVER ADMINISTRATOR GUIDE
URI Dialing for Incoming Calls
Types of DNS Records Required
The ability of the VCS to receive incoming calls made via URI dialing relies on the presence of DNS records for each domain the VCS is hosting.
These records can be of various types including:
• A records, which provide the IPv4 address of the VCS |
• AAAA records, which provide the IPv6 address of the VCS |
• Service (SRV) records, which specify the FQDN of the VCS |
and the port on it to be queried for a particular protocol and |
transport type. |
SRV Record Format
The format of SRV records is defined by RFC 2782 [3] as:
_Service. _ Proto.Name TTL Class SRV Priority Weight Port Target
For the VCS, these will be as follows:
•_ Service and _ Proto will be different for H.323 and SIP, and will depend on the protocol and transport type being used.
•Name is the domain in the URI that the VCS is hosting (e.g. example.com)
•Port is the port on the VCS that has been configured to listen for that particular service and protocol combination
•Target is the FQDN of the VCS.
• NAPTR records, which specify SRV record and transport |
preferences for a SIP domain. |
You should provide an SRV or NAPTR record for each combination of domain hosted and protocol and transport type enabled on the VCS.
Process
When an incoming call has been placed using URI dialing, the VCS will have been located by the calling system via one of the DNS record lookups described above. The VCS will receive the request containing the dialled URI in the form user@example. com. The VCS will then check its local registrations and FindMe names and if any are an exact match, the call will be routed to the appropriate device(s).
Configuring H.323 SRV Records
Annex O of H.323 [15] defines the procedures for using DNS to locate gatekeepers and endpoints and for resolving H.323 URL aliases. It also defines parameters for use with the H.323 URL.
The VCS supports two types of SRV record as defined by this Annex. These are Location and Call, with _ Service set to _ h323ls and _ h323cs respectively. If you wish the VCS to be contactable via H.323 URI dialing, you should provide at least a Location SRV record, as it provides the most flexibility and the simplest configuration.
Location SRV Records
For each domain hosted by the VCS, you should configure a Location SRV record as follows:
•_ Service is _ h323ls
•_ Proto is _ udp
•Port is the port number that has been configured via VCS Configuration >
Protocols > H.323 as the Registration UDP port.
Call SRV Records
Call SRV records (and A/AAAA records) are intended primarily for use by endpoints which cannot participate in a location transaction, exchanging LRQ and LCF. The configuration of a Call SRV record should be as follows:
•_ Service is _ h323cs
•_ Proto is _ tcp
•Port is the port number that has been configured via VCS Configuration >
Protocols > H.323 as the Call signaling TCP port.
Configuring SIP SRV Records
RFC 3263 [16] describes the DNS procedures used to resolve a SIP URI into the IP address, port, and transport protocol of the next hop to contact.
If you wish the VCS to be contactable via SIP URI dialing, you should configure an SRV record for each SIP transport protocol enabled on the VCS (i.e. UDP, TCP or TLS) as follows:
•Valid combinations of _ Service and
_ Proto are:
•_ sips. _ tcp
•_ sip. _ tcp
•_ sip. _ udp
•Port is the port number that has been configured via VCS Configuration > Protocols
> SIP as the port for that particular transport protocol.
Introduction | Getting Started |
| Overview and |
| System |
| VCS |
| Zones and | Call | Bandwidth |
| Firewall |
| Maintenance |
| Appendices |
| Status |
| Configuration |
| Configuration |
| Neighbors | Processing | Control |
| Traversal |
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D14049.03 |
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MAY 2008 |
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