Selective FA Revocation

In a 3GPP2 environment, when a subscriber roams between their service provider’s network and anotherpartner service provider’s network, the PDSN gateway sends a Resource Revocation message to theHome Agent to remove the subscriber. This causes timing problems, so Selective FA Revocation

selectively ignores these “remove subscriber” requests. Revocation is done on a Foreign Agent basis.
Thus, a given HA will statically configure a list of Foreign Agents from which to ignore the “remove
subscriber” messages.
Here is a detailed call-flow for Selective FA Revocation:
1. A dual 1x/DO handset registers with RF and establishes a data call on DO. Unlike a voice call, the
RF network does not register this data call with the VLR, as it has no knowledge of EVDO networks
(as per standards).
2. The handset goes dormant (35 seconds on Samsung, 30 seconds on RIM, 40 seconds on Sierra).
3. The handset does a physical transition from a DO coverage area to a 1x coverage area. As part of
this transition, the handset informs the 1x RF via the MTX that it has an active Data Session, but has
no data to send, as it’s dormant (DRS bit is set to 0). A new session is established to the PDSN
through the MTX PCF.
4. Based on the events in Step 3, the 1x PCF queries the VLR for this active Data Session mentioned
by the Handset, and because of Step 1, cannot find such session.
5. As part of the events in Step 3, the PCF now sends the PDSN (through the OpenRP interface) a
message with the Mobility Event Indicator (MEI) set to 0. To the PDSN, this event, as part of a
call-setup is for a brand new session, does the following check
– if MEI=0 and IMSI is a new IMSI not currently assigned to an existing session, proceed and
establish the new session.
– if MEI=0 and IMSI is currently assigned to a session, consider this session old, and tear down
the session.
6. Since MEI=0 and IMSI is currently assigned to a session (as this is a Hybrid PDSN, handling both
DO and 1X sessions at the same time), the PDSN will send a PPP TermReq to the handset and send
a Resource Revocation to the Home Agent.
7. The Mobile Node, which was dormant, does not see the TermReq. The MTX RF will buffer the
message for a while.
8. The Mobile Node becomes active and has data to send. It still acts as if it has a valid Mobile IP
session, receives the TermReq (buffered), and Acks the message, followed by an immediate RF
setup/RRQ. The RRQ contains previously assigned values such as assigned IP address for the
Handset, IP address of the HA and so on.
9. The PDSN regards this as a new session (MEI=0 and IMSI is a not currently assigned to a session)
and sends the RRQ to the HA.
10. The HA now sees a RRQ with no existing binding (as it was revoked in step (6)), and with
parameters in the RRQ and considers it a static-assigned MN.
11. The HA sends a Code-139 (administrative prohibited) back to the MN.
With Selectable FA Revocation, the Hybrid PDSN/FA will go through the above conditions and send the
revocation to the Home Agent. However, in this case the HA ignores the revocation, but sends a RR
response to the PDSN.
7-8
Cisco Mobile Wireless Home Agent Feature for IOS 12.4(15)XM
Chapter 7 Terminating IP Registrations
Mobile IPv4 Registration Revocation
As a result, the MN and Home Agent still have a binding state but the PDSN/FA no longer has a PPP
session/visitor table entry. Eventually, the mobile goes active and has Data Ready to Send, where the 1x
RF channel DRS=1 is included. In this scenario, the VLR is not queried and the OpenRP message to the
PDSN has MEI set to 1. Regardless of the MEI value, the PDSN will initiate PPP, and send a RRQ with
the previously assigned home address. In this case HA will accept the Re-registration.


Configuring Selective FA Revocation
Perform the following tasks to configure Selective FA Revocation:
Here is an example of the ip mobile home-agent revocation ignore command:
You can ignore revocation from the FA by specifying the standard access-list number or standard
access-list name.
Configuring access-list name to ignore the requests from COA 5.1.1.4
Router(config)#ip access-list standard ?
<1-99> Standard IP access-list number
<1300-1999> Standard IP access-list number (expanded range)
WORD Access-list name
Router(config)#ip access-list standard fa_acl1
Router(config-std-nacl)#permit 5.1.1.4
Configuring access-list number to ignore the requests from COA 5.1.1.5
Router(config)#ip access-list standard ?
<1-99> Standard IP access-list number
<1300-1999> Standard IP access-list number (expanded range)
WORD Access-list name
Router(config)#ip access-list standard 1
Router(config-std-nacl)#permit 5.1.1.5
Configuring access-list name to selectively ignore requests from FA 5.1.1.4 . This is to associate the
above created acl with the ip mobile home-agent revocation ignore command.
Router((config)#ip mobile home-agent revocation ignore ?
<1-99> fa Access-list number
WORD fa Access-list name
Router(config)#ip mobile home-agent revocation ignore fa_acl1
Configuring the access-list number to selectively ignore requests from FA 5.1.1.5
Router(config)#ip mobile home-agent revocation ignore 1
Note ip mobile home-agent revocation ignore currently does not support using 1300-1999 (Standard IP
access-list number (expanded range).
Command Purpose
Router(config)# ip mobile home-agent revocation ignore fa acl Enables the HA to send a revocation
acknowledgement to the PDSN/FA but not delete
the binding. fa-acl is either a acl number 1-99, or
a name.