Version 6.8 321 Mediant 2600 E-SBC
User's Manual 20. SBC Overview
20.2 SIP Dialog Initiation Process
The device's SIP dialog initiation process concerns all incoming SIP dialog initiation
requests. This includes SIP methods such as INVITE, SUBSCRIBE, OPTIONS, REFER,
INFO, UNSOLICITED NOTIFY, MESSAGE, and REGISTER.
The SIP dialog initiation process consists of the following stages:
1. Determining source and destination URL: The SIP protocol has more than one
URL in a dialog-establishing request that may represent the source and destination
URLs. When handling an incoming request, the device uses specific SIP headers for
obtaining the source and destination URLs. Once these URLs are determined, their
user and host parts are used as input for the classification process, message
manipulation, and call routing.
• All SIP requests (e.g., INVITE) except REGISTER dialogs:
♦ Source URL: The source URL is obtained from the SIP header according to
the following logic:
 The source URL is obtained from the From header.
 If the From header contains the value 'Anonymous', the source URL is
obtained from the P-Preferred-Identity header.
 If the P-Preferred-Identity header does not exist, the source URL is
obtained from the P-Asserted-Identity header.
♦ Destination URL: The destination URL is obtained from the Request-URI.
• REGISTER dialogs:
♦ Source URL: The source URL is obtained from the To header.
♦ Destination URL: The destination URL is obtained from the Request-URI.
Note: You can determine the SIP header from where the device obtains the source
URL in the incoming SIP request. This is done in the IP Group table using the 'Source
URI Input' parameter.
2. Classifying incoming SIP dialog-initiating requests to a source IP Group: The
classification identifies the incoming SIP dialog request as belonging to a specific IP
Group (from where the SIP dialog request originated). For more information, see
''Configuring Classification Rules'' on page 361.
3. SBC IP-to-IP routing: The device routes the call to a destination that can be
configured to one of the following:
• Registered user Contact listed in the device's database (only for User-type IP
Groups).
• IP Group - the destination is the address configured for the Proxy Set associated
with the IP Group (allows redundancy/load balancing).
• Specified destination address (can be based on IP address, host name, port,
transport type, and/or SRD). Routing to a host name can be resolved using
NAPTR/SRV/A-Record.
• Request-URI of incoming SIP dialog initiating requests.
• ENUM query.
• Hunt Group - used for call survivability.
• IP address (in dotted-decimal notation or FQDN - NAPTR/SRV/A-Record
resolutions) according to a specified Dial Plan index listed in the loaded Dial Plan
file.
• LDAP server or LDAP query result.
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