REGISTER
2. REGISTER 3. Cx-Query
Cx-SELECT-PULL
4. Cx-Query response
Cx-SELECT-PULL
response
5. REGISTER
6. Cx-PUT
Cx-PULL
7. Cx-PUT response
Cx-PULL response
8. 200 OK
9. 200 OK
10. 200 OK
Visited Network Home Network
Figure 5.1 Sample call flow for registering with the IMS
116 Chapter 5
?– SECURITY-VERIFY populated with the content from the SECURITY-SERVER
header received in the response 401 Unauthorized during previous authentication
and registration
?– SUPPORTED populated with the option tag PATH
?– P-ACCESS-NETWORK-INFO identifying the type of network used to access
the IMS
After registration, if the subscriber should be assigned a new IP address (after roaming
into another network, for example), the subscriber must cancel all previous registrations
and register with the new IP address. Otherwise, the network will be attempting
to connect to the old IP address and sessions will fail.
It is purely up to the service provider whether or not to force the subscriber to authenticate
himself or herself again during the re-registration process. Some operators
may choose to reject the re-registration as a security measure, forcing the subscriber
device to authenticate itself again using the same procedures we discussed earlier.
However, this will result in additional traffic to the HSS as well as through the
network. For this reason some operators may select the latter procedure and allow
subscribers to re-register without authenticating again.
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