Cisco Cisco Expressway Maintenance Manual
_sip._udp
is not recommended because SIP messages for video systems are too large to be carried on a packet based
(rather than stream based) transport. UDP is often used for audio only devices. Also, UDP tends to be spammed more
than TCP or TLS.
than TCP or TLS.
Example DNS Record Configuration
A company with the domain name
example.com
wants to enable incoming H.323 and SIP calls using URI addresses in
the format
user@example.com
. The Expressway hosting the domain has the FQDN
expressway.example.com
.
Their DNS records would typically be as follows:
■
SRV record for
_h323ls._udp.example.com
returns
expressway.example.com
■
SRV record for
_h323cs._tcp.example.com
returns
expressway.example.com
■
SRV record for
_h323rs._tcp.example.com
returns
expressway.example.com
■
NAPTR record for
example.com
returns
—
_sip._tcp.example.com
and
—
_sips._tcp.example.com
■
SRV record for
_sip._tcp.example.com
returns
expressway.example.com
■
SRV record for
_sips._tcp.example.com
returns
expressway.example.com
■
A record for
expressway.example.com
returns the IPv4 address of the Expressway
■
AAAA record for
expressway.example.com
returns the IPv6 address of the Expressway
How you add the DNS records depends on the type of DNS server you are using. Instructions for setting up two
common DNS servers are given in the DNS configuration section.
common DNS servers are given in the DNS configuration section.
SIP endpoints always register with an AOR in the form of a URI, so no special configuration is required.
Several mechanisms could have been used to locate the Expressway. You may want to enable calls placed to
user@<IP_address>
to be routed to an existing registration for
user@example.com
. In this case you would configure a
that would strip the IP_address suffix from the incoming URI and replace it with the suffix of
URI Dialing and Firewall Traversal
If URI dialing via DNS is being used in conjunction with firewall traversal, DNS zones should be configured on the
Expressway-E and any Expressways on the public network only. Expressways behind the firewall should not have any
DNS zones configured. This will ensure that any outgoing URI calls made by endpoints registered with the Expressway
will be routed through the Expressway-E.
Expressway-E and any Expressways on the public network only. Expressways behind the firewall should not have any
DNS zones configured. This will ensure that any outgoing URI calls made by endpoints registered with the Expressway
will be routed through the Expressway-E.
In addition, the DNS records for incoming calls should be configured with the address of the Expressway-E as the
authoritative proxy for the enterprise (the DNS configuration section for more information). This ensures that incoming
calls placed using URI dialing enter the enterprise through the Expressway-E, allowing successful traversal of the
firewall.
authoritative proxy for the enterprise (the DNS configuration section for more information). This ensures that incoming
calls placed using URI dialing enter the enterprise through the Expressway-E, allowing successful traversal of the
firewall.
About ENUM Dialing
ENUM dialing allows an endpoint to be contacted by a caller dialing an E.164 number - a telephone number - even if
that endpoint has registered using a different format of alias.
that endpoint has registered using a different format of alias.
Using ENUM dialing, when an E.164 number is dialed it is converted into a URI using information stored in DNS. The
Expressway then attempts to find the endpoint based on the URI that has been returned.
Expressway then attempts to find the endpoint based on the URI that has been returned.
The ENUM dialing facility allows you to retain the flexibility of URI dialing while having the simplicity of being called
using just a number - particularly important if any of your callers are restricted to dialing using a numeric keypad.
using just a number - particularly important if any of your callers are restricted to dialing using a numeric keypad.
The Expressway supports outward ENUM dialing by allowing you to configure ENUM zones on the Expressway. When
an ENUM zone is queried, this triggers the Expressway to transform the E.164 number that was dialed into an ENUM
domain which is then queried for using DNS.
an ENUM zone is queried, this triggers the Expressway to transform the E.164 number that was dialed into an ENUM
domain which is then queried for using DNS.
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Cisco Expressway Administrator Guide
Dial Plan and Call Processing