Alias for SIP user
Original Publication Date: 2001-Feb-28
Included in the Prior Art Database: 2001-Feb-28
Alias for SIP user
IETF draft-schulzrinne-sip-register-00 describes how a SIP user can have a name and multiple aliases by performing multiple SIP registrations. The user does one registration for its normal name and an additional registration for each of its aliases. If the user is connected via a high bandwidth connection this may not be a problem. But when a user registers from a mobile phone (MS) a more efficient procedure may be required.
To enable mobility, the user's SIP registrar keeps track of the user's current location. It stores the user's location(s), as 'contact(s)' in a database keyed by the user's SIP URL. Each time the user moves to a new host, the MS must do a SIP registration (Figure 1).
Figure 1. SIP mobility is enabled by SIP registrations. At terminal 1 the user registers (step 1). When the user later moves to a new host, the user again sends a REGISTER message to its SIP registrar server. The message contains the URL of the user and contact information for the current host.
SIP call setup
A caller sets up a SIP session with a callee by sending a SIP INVITE message. The INVITE contains the SIP URL of the callee. The INVITE is first sent to the SIP registrar server of the callee. The registrar will forward the message to the host of the callee or return a redirection contact to the caller.
New SIP alias method
We propose a new method for a user to establish an alias SIP URL. With an alias SIP URL the user can be invited on multiple publicly known URLs. The method has two steps (Figure 2):
1. The user establishes a SIP registrar server that will accept the user's alias SIP URL.
2. The user sends a single SIP REGISTER message to the established server. The message contains 'To' information equal to the alias SIP URL and 'Contact' information equal to the users existing SIP URL.
What is new is that a SIP contact normally points to a physical host. Here it points to an abstract name.
Figure 2. To define an alias, a user with an existing SIP identity has to establish a SIP registrar server for the alias and send a single REGISTER message for the alias. The contact in this message specifies the already existing user URL (step 1).
The new method has a number of nice properties: The registrar server, the caller's and the callee's host terminal can be standard SIP, and when the user with the alias moves to another host, the user only needs to send a single REGISTER message, namely the one the user normally sends (step 2 in Figure 2). The alias does not need to register. Mobility for the alias is automatically taken care of.
Figure 3. The existing URL and the alias URL can be in different SIP registrar servers. The servers can be in the same or in different domains.
The existing URL and the alias URL can be in the same or different registrars. For exam...