Manual

Cisco Packet Data Serving Node (PDSN) Release 2.0

Resource Management

12.3(11)T

• A Catalyst 6500 chassis contains up to 6 MWAM cards. The total number of local IP addresses

needed in the pool for each chassis:

–

6 MWAMs * 80,000 sessions = 480,000 IP addresses in the PDSN ODAP pool.

In order to configure an ODAP subnet pool for Mobile IP Home Agent applications, determine the

number IP addresses needed for each Home Agent. Use the following formula to determine the Mobile

IP pool size:

• Home Agent Subnet IP Pool size = (number of Home Agents x number of sessions)

Always On Feature

The PDSN supports Always On service to maintain the subscriber’s packet data session in the local

network. Always On support dictates that the PDSN will not release a subscriber’s packet data session

due to PPP idle timer expiry unless the PDSN determines the user is no longer reachable.

The Always On service maintains a subscriber’s packet data session irrespective of PPP inactivity timer

value for the user. At the same time, by making use of a finite PPP inactivity timer value, this feature

provides a way to keep a session only as long as the user is reachable. The PDSN uses LCP Echos (as

per rfc1661 and IS835B) to determine if the user is reachable.

Always On service is enabled for a user only when the F15 “Always On” attribute is received and set to

a value of 1 in the access accept message from the AAA server.

The PDSN supports the ability to configure the Echo-Reply-Timeout timer and Echo-Request-Attempts

counter. There is no extra configuration required onthe PDSN to enable the Always On feature itself;

however, you can disable the feature by configuring the Echo-Request-Attempts to 0. The PPP inactivity

timer will be started for a session entering IPCP open state, if is configured or retrieved from AAA, for

the user.

For always on users:

1. Upon expiration of the inactivity timer, Echo-Request-Attempts counter is initialized to the

configured value.

2. If the Echo-Request-Attempts counter is zero, PPP session is torn down. If the

Echo-Request-Attempts counter is nonzero, an LCP Echo-Request message will be sent,

Echo-Request-Attempts counter is decremented, and Echo-Reply-Timeout timer is started.

3. Upon receipt of corresponding LCP Echo-Reply message, Echo-Reply-Timeout timer is stopped and

PPP inactivity timer is restarted.

4. Upon expiration of Echo-Reply-Timeout timer, repeat from 2 above.

This feature is not supported for VPDN users, and is not applicable to Mobile IP users.

For Always-on users, a value of “1” will be sent for F15 attribute in the accounting start/stop/interim

records. For non-always-on users, the F15 attribute will only be sent in the accounting records if

configured.

Restrictions for the Always On Feature:

• The Always On implementation follows the IS835B standard; the IS835C specific additions are not

available in this release of PDSN.

• Echo-Reply is the only packet that will stop always-on timer.

Basically it means even if there is upstream/downstream data received, the session will be teared

down unless Echo-reply received within configured number of retries and configured time interval.