TANDBERG D14049.01 manual URI Dialing for Incoming Calls

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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.

URI Dialing for Incoming Calls

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.

As a preference, SRV records should be used, and you should provide an SRV 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. It will receive the request containing the dialled URI in the form user@xample.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).

In order for locally registered endpoints to be reached

using URI dialing, they must register using a full URI.

This applies to both SIP and H.323 endpoints. If endpoints do not register using a full URI, they will be discoverable only by the VCS to which they are registered, and any neighbor VCSs.

Several mechanisms could have been used to locate the

VCS. You may wish to enable calls placed to

user@VCS_IP_address to be routed to an existing registration for user@example.com. In this case you would configure a Local Zone Transform that would strip the

IP address of the VCS from the incoming URI and replace it with the domain name of example.com.

Introduction	Getting	System	System
	Started	Overview	Configuration

D 14049.01

07.2007

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.

H.323 &	SIP	Registration	Zones and	Call	Firewall
Configuration		Control	Neighbors	Processing	Traversal

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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:

•_ Service is _ sip

•_ Proto is one of _ udp, _ tcp, or _ tls

•Port is the port number that has been configured via VCS Configuration > Protocols > SIP as the port for that particular transport protocol.

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