INTERNET-DRAFT X. Zhang
J. Castellanos
A. Campbell
Columbia University
K. Sawada
Fujitsu Limited, Japan
M. Barry
Broadcom, Eire
July 2000
P-MIP: Minimal Paging Extensions for Mobile IP
draft-zhang-pmip-00.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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Abstract
As the number of Mobile IP users grow so will the signaling overhead
on the core IP network in support of mobility management. In cellular
networks registration and paging techniques are used to minimize the
signaling overhead and optimize the mobility management performance.
Currently, Mobile IP supports registration but not paging. We believe
that Mobile IP support for paging is important to improve the
scalability of Mobile IP networks. Recently, a number of micro-
mobility protocols [8] have been proposed that have built-in paging
functions. These micro-mobility protocols are independent of the base
Mobile IP protocol and interwork with Mobile IP [2] through mobile
gateways. We take a different approach and propose a minimal set of
paging extensions to the base Mobile IP called P-MIP. P-MIP is
designed to reduce signaling load in the core Internet and power
consumption of mobile nodes. In this draft, P-MIP, which assumes the
use of foreign agents, is described and the construction of paging
areas, movement detection, registration, paging and data handling are
presented.
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Table of Contents
1. Introduction 2
1.1 Goals. . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Assumption . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3 Terminology. . . . . . . . . . . . . . . . . . . . . . . . 3
1.4 Protocol Overview. . . . . . . . . . . . . . . . . . . . . 4
1.5 Message Format and Protocol Extensibility. . . . . . . . . 5
1.5.1 New ICMP Router Discovery Message Extension . . . . 5
1.5.2 New Control Messages. . . . . . . . . . . . . . . . 5
1.5.3 New Extension in Mobile IP Control Message. . . . . 6
1.5.4 Modification to Registration Request Message in MIP 7
2. Protocol Description 7
2.1 Paging Areas . . . . . . . . . . . . . . . . . . . . . . . 7
2.2 Movement Detection . . . . . . . . . . . . . . . . . . . . 10
2.2.1 Movement Detection in within a Paging Area . . . . 10
2.2.2 Movemnet between paging Areas. . . . . . . . . . . 10
2.3 Registration . . . . . . . . . . . . . . . . . . . . . . . 11
2.4 Paging . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.5 Data Handling. . . . . . . . . . . . . . . . . . . . . . . 13
2.5.1 Incoming Data . . . . . . . . . . . . . . . . . . . 13
2.5.2 Outgoing Data . . . . . . . . . . . . . . . . . . . 14
3. Security Considerations . . . . . . . . . . . . . . . . . . . . 14
4. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction
We envision a wireless Internet with many hundreds of millions of
wireless subscribers. As the number of mobile subscribers grows so
does the need to provide efficient location tracking that limits the
signaling load introduced in the core IP network. The vast majority
of wireless IP subscribers will not be actively communicating most of
the time. Rather, mobile nodes will be in an idle state but passively
connected to the network infrastructure. As a result, it will be
sufficient for the wireless Internet only to know the approximate
location of its population of idle users. The exact location of idle
mobile nodes only becomes important when data needs to be forwarded
to them in which case the network protocols need to be able to
efficiently search and find these users in a scalable and timely
manner. This process is called paging. While paging minimizes the
need for mobiles to register their exact location it introduces
paging overhead in terms of new signaling and delays. It is therefore
important to balance paging and registration in order to optimize
system performance. In this draft we provide an overview of P-MIP and
discuss its implementation. For more details, see [1].
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1.1 Goals
Reducing the signaling load in the core IP network and the power
consumption of mobile nodes through the introduction a minimal set of
paging extensions to the base Mobile IP protocol [2].
1.2 Assumption
Foreign agents are present on foreign networks and mobile nodes
register through foreign agents.
1.3 Terminology
Active Mode
A mobile node is in active mode if it has recently sent or
received data. A mobile node is considered to be active for an
active time period starting from the instance the node sends or
receives data.
Active Mobile Node
The mobile node in active mode.
Active Time Period
The number of seconds a mobile node is considered as active. It is
implementation dependent.
Active Timer
The timer used to record the time when a mobile node is in active
mode. Each time the mobile node sends or receives data the timer
is reset. When the timer expires the mobile node enters idle
state.
Care of Address (CoA)
As defined in [2].
Current Foreign Agent
The foreign agent of the network which a mobile node is currently
visiting.
Foreign Agent
As defined in [2].
Foreign Network
As defined in [2].
Home Address
As defined in [2].
Home Agent
As defined in [2].
Home Network
As defined in [2].
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Idle Mode
A mobile node is in idle mode if it has not recently sent or
received data.
Idle Mobile Node
A mobile node in idle mode. Whenever an idle node sends or
receives data, its mode is changed to active and its active timer
started. In this case an idle mobile node becomes an active mobile
node.
Mobile Node State
Mobile node state consists of a per-node tuple (operational mode,
active timer). Operational mode can be active mode or idle mode.
Mobile node state is kept in both mobile nodes and registered
foreign agents.
Mobility Binding
As defined in [2].
Paging Area (PA)
The area on which a registered foreign agent conducts paging. A PA
consists of two or more networks. When an idle mobile node moves
within a paging area, it does not register.
Paging Request Message
A message sent by a registered foreign agent in order to locate an
idle mobile node.
Paging Reply Message
A message sent by a paged mobile node to the registered foreign
agent to inform it of the paged mobile node's current location.
Registered Foreign Agent
The foreign agent of the network through which a mobile node has
registered just before the mobile node receives a Paging Request.
That is, the foreign agent through which a mobile node made its
latest registeration with its home agent. Thus, the mobile node's
care-of-address in its home agent's mobility binding is provided
by the registered foreign agent. Note, a mobile node and its
registered foreign agent may be in different networks.
Security Parameter Index (SPI)
As defined in [2].
1.4 Protocol Overview
An active mobile node behaves in exactly the same manner as in Mobile
IP [2]. When it changes its point of attachment, it registers. For an
idle mobile, when it moves within a paging area, it does not
register. However, when an idle mobile node moves to a different
paging area, it registers.
When there are packets destined to a mobile node, its home agent
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forwards data to its registered foreign agent. The registered
foreign agent first checks if it has the mobile node's information on
record. If it has a record, then it checks if the mobile node
supports paging or not. If the mobile node supports paging, then the
registered foreign agent checks the mobile node's state. If the
mobile node is in active mode, the registered foreign agent
decapsulates packets and sends them to the mobile node, just as in
the case of Mobile IP [2]. If the mobile node is in idle mode, the
registered foreign agent sends a Paging Request message to other
foreign agents in the same paging area as well as to its own network.
When the mobile node receives a Paging Request message, it registers
through the current foreign agent to its home agent. After receiving
a Registration Reply message, the mobile node sends a Paging Reply
message back to its registered foreign agent through its current
foreign agent to inform the registerd foreign agent of its current
location.
When the registered foreign agent receives a Paging Reply message, it
forwards buffered packets to the mobile node through its current
foreign agent.
1.5 Message Format and Protocol Extensibility
1.5.1 New ICMP Router Discovery Message Extension
Paging area ID (PAI) extension:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | PAI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This PAI extension is used in non-overlapping paging area
construction (see Section 2.1). It should be added in agent
advertisement message and periocally broadcast on the network.
1.5.2 The New Control Messages
Paging Request:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | length | reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| the home address of paged mobile node 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| the home address of paged mobile node 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extensions ...
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+-+-+-+-+-+-+-+-+-+
length = 2 + 4 * N (bytes), where N is the number of mobile nodes
paged. length does not cover the type, length and extensions fields.
Paging response:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | length | reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| the home address of paged mobile node 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| the care-of address of paged mobile node 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extensions...
+-+-+-+-+-+-+-+-
length = 2 + 8 * N (bytes), where N is the number of responding
mobile nodes. length does not cover the type, length, and extensions
fields.
1.5.3 New Extension in Mobile IP Control Message
Foreign-Foreign Authentication Extension:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | length | SPI...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
... SPI (cont.) | Authenticator ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Paging Area ID Extension:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | length | reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP address of FA1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP address of FA2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP address of FA3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
+-+-+-+-+-+-+-+-
Paging Area ID extension is used for overlapping paging area
construction. This extension represents a list of foreign agent IP
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addresses in the same paging area. It should be inserted in the
Registration Reply message.
1.5.4 Modification to Registration Request Message in Mobile IP
the modified bit
|
0 1 V 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type |S|B|D|M|G|V|P|r| Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Home Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Home Agent |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Care-of Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Identification +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extensions ...
+-+-+-+-+-+-+-+-
Change one of the reserved bits in the Registration Request message
used in Mobile IP to the P bit which indicates if the mobile node
supports the paging function or not. A P bit of '1' means that the
mobile node supports paging and a P bit of '0' means that the mobile
node does not support paging.
2. Protocol Description
2.1 Paging Areas
A paging area consists of two or more networks and has a unique
paging area ID (PAI). Paging areas can be configured based on a
number of criteria (e.g., node mobility, traffic patterns, mobile
density, etc.) so that most mobile nodes move within the same paging
area. Paging areas can be configured manually by administrators
setting parameters at each foreign agent or more automatically by
having foreign agents interact with paging servers. The benefit of
paging servers is that the administrator only needs to configure the
server. In this case, each foreign agent acquires its paging area
information directly orom the server. Foreign agents and mobile nodes
are aware of their paging area based on the PAI.
There are two types of paging area construction in P-MIP called non-
overlapping and overlapping paging areas. In the case of non-
overlapping paging areas, a network can only be associated with one
paging area, as shown Figure 1.
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Internet
| | | |
+ --- | ------- | --+ +-- | ------- | ---+
| | | | | | | |
| +--+--+ +--+--+| |+--+--+ +--+--+ |
| | FA1 | | FA2 || || FA3 | | FA4 | |
| +-----+ +-----+| |+-----+ +-----+ |
| | | |
+-------- PA1 ------+ +------ PA2 -------+
Figure 1: Non-overlapping Pagin Areas
In the non-overlapping scheme, each paging area has a unique paging
area ID. Paging area IDs can be reused in the same sense as spatial
reuse, with adjacent paging areas having different IDs. Paging area
ID assignment could follow the same lines as IP addresses, with
authorized organizations managing their allocation and assignment.
A paging table is maintained by each foreign agent and can be
manually set or configured by a paging server or an administrator. In
P-MIP, the agent advertisement message is extended to carry the
paging area ID, as shown in the Section 1.5. The agent advertisement
message must be broadcast periodically so that the paging area ID can
be periodically distributed. Paging tables for the non-overlapping
scheme have the following format:
-------------------------
PAI | xxxx xxxx
-----+-------------------
FA1 | FA1's IP address
FA2 | FA2's IP address
FA3 | FA3's IP address
. | .
. | .
. | .
In the case of non-overlapping paging only the PAI value (0000-FFFFH)
is transmitted in agent advertisement messages and not the list of FA
IP addresses.
In the case of overlapping paging areas, the paging area ID is made
up of the entire list of foreign agent IP addresses in a paging area.
This is different to the PAI for non-overlapping paging area where
PAI is a two-byte value. The paging area ID in the overlapping scheme
does not need to be broadcast periodically as is the case in non-
overlapping paging IDs. Rather, the paging area ID is sent to mobile
nodes using an extended registration reply message, as shown in
Section 1.5. Each foreign agent maintains a paging table which is
also the paging area ID in the case of the overlapping scheme. A
paging table in the overlapping scheme can be manually configured and
has the following format:
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-------------------------
FA1 | FA1's IP address
FA2 | FA2's IP address
FA3 | FA3's IP address
. | .
. | .
. | .
Each paging scheme has a number of advantages and disadvantages. In
the case of non-overlapping paging areas, a paging ID (i.e. two-
octets value) is much shorter than overlapping paging IDs (i.e.
multiple IP addresses). Therefore, the bandwidth and power consumed
to manage paging IDs will be more efficient in the case of non-
overlapping areas. However, this scheme can not take advantage of
overlapping paging areas. As a result, there will be a
disproportionate amount of registration traffic generated at paging
area borders. With overlapping paging areas, the paging area ID could
be rather large when there is a large number of foreign agents in a
paging area. In this case, each mobile node must be aware of all the
foreign agent IP addresses in the paging area. Mobile nodes need to
be capable of maintaining this state information in order to detect
if they have moved to a different paging area. Overlapping paging
area information is not transmitted periodically so that the impact
on radio resources and mobile node resources is limited.
The maximum benefit of the overlapping scheme is achieved when each
foreign agent is located at the center of its paging area. As shown
in Figure 2, foreign agent FA2 is located at the center of paging
area PA2, FA3 is located at the center of PA3, and so on. Whenever a
mobile node registers, it will get a new paging area ID (i.e., the
list of foreign agent IP addresses in the paging area). This allows
the mobile node to position itself at the center of the new paging
area when it has to register. In this case, registration initiated by
crossing new paging area borders is reduced and it allows for an even
distribution of registration traffic. This approach would further
reduce the signaling associated with mobile nodes that move around
paging area borders particularly in the case of non-overlapped paging
areas.
Internet
| | | |
| +--- | ------- | ------- | ---+
+ --- | ---|--- | ------- | -- + | |
| | | | | | | |
| +--+--+ | +--+--+ +--+--+ | +--+--+ |
| | FA1 | | | FA2 | | FA3 | | | FA4 | |
| +-----+ | +-----+ +-----+ | +-----+ |
| | | |
+----------|---PA2-------------+ |
+-------------PA3-------------+
Figure 2: Overlapping Paging Areas
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Based on the paging area scheme selected, P-MIP operates differently
such as in the case of movement detection. In this draft, we
highlight these operational differences by referring to the two
paging schemes discussed above.
2.2 Movement Detection
2.2.1 Movement within a Paging Area
The algorithms used to detect if a mobile node has moved to a
different network are the same for P-MIP as Mobile IP [2]. Two
algorithms are used for movement detection in Mobile IP.
In the first approach, mobile nodes detect movement using agent
advertisement messages and the advertisement lifetime. When a mobile
node receives an agent advertisement the lifetime of the
advertisement is included in the message. If a mobile node does not
receive another advertisement before the advertisement lifetime
expires then the mobile node assumes that it has moved to a different
network. In the second approach, a mobile node compares the network
prefix obtained from newly received agent advertisement message with
the current CoA. If they are different, the mobile will assume it has
moved to a different network.
If a mobile node is in active mode when it detects it has moved then
a handoff is initiated which invokes the registration procedure. In
this case, the mobile node's location will be updated at both the
foreign and home agents. In contrast, if a mobile nodes is in idle
state and it detects it has moved to a new network within the same
paging area then no registration is necessary. However, if an idle
mobile node does not have a valid foreign agent on record then it
should locate one for further movement detection and registration.
2.2.2 Movement between Paging Areas
The algorithms used to detect movement between paging areas are
different based on the paging area scheme.
In the case of non-overlapping paging areas, a mobile node records
the lifetime received in agent advertisements until the lifetime
expires. If a mobile node fails to receive another advertisement from
the same agent within the specified lifetime then the mobile node
assumes that is has lost contact with the foreign agent. If the
mobile node has previously received an agent advertisement from
another foreign agent for which the lifetime field has not yet
expired then the mobile node should check if the paging area ID from
the new agent is the same as its current paging ID. If the IDs are
the same then the mobile node will do nothing except keep tracking
the foreign agents identified in the advertisements. If the paging
IDs are different then idle mobile nodes should immediately register
with the new foreign agent. If the mobile node is not in contact with
any foreign agent then it should send out an agent solicitation
message. Upon reception of an agent advertisement message, the mobile
node should check if the new paging area ID is the same as the old
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one. It uses this test to determine whether it has moved to a
different paging area.
In the case of overlapping paging areas, a mobile node should record
the lifetime received in agent advertisements until that lifetime
expires. If a mobile node fails to receive another advertisement from
the same agent within the specified lifetime then the mobile node
assumes that it has lost contact with the agent. If the mobile node
has previously received an agent advertisement from another foreign
agent for which the lifetime field has not yet expired then the
mobile node should check if the source IP address of the agent
advertisement sent by the new foreign agent is in the current paging
ID's foreign agent list. The current foreign agent list is obtained
in the registration reply message. If the new foreign agent's IP
address is not in the current foreign agent list then idle mobile
node registers with the new foreign agent. If the mobile node is not
in contact with a foreign agent then it should send out an agent
solicitation message. Upon reception of a advertisement message, the
mobile node should check if the new foreign agent's IP address is in
the current foreign agent list or not. It uses this test to determine
whether it has moved to a new paging area or not.
2.3 Registration
Registration follows the same procedure as Mobile IP [2]. However,
after receiving a registration reply message both the foreign agent
and the mobile node update the mobile node state by setting the the
operational mode to active state and starting the active timer. In
the case of the overlapping paging areas scheme, the registration
reply message includes the paging area ID. The mobile node records
the paging area ID. The list of foreign agents in the paging area
that represents the paging ID is inserted by the foreign agent in the
registration reply message returned to the mobile node.
An important performance difference between Mobile IP and P-MIP
relates to the number of registration generated. P-MIP reduces
signaling in comparison to the base Mobile IP protocol because idle
mobile nodes do not register when moving between networks in the same
paging area. For an evaluation Of P-MIP see [1].
In Mobile IP, a mobile node registers when:
o a mobile node changes its point of attachment;
o a mobile node's registration lifetime is near expiration (we call this
registration refresh); and
o a mobile node detects that its current foreign agent has rebooted.
In P-MIP, a mobile node registers when:
o a mobile detects it has moved to a new paging area;
o a mobile node's registration lifetime is near expiration;
o a mobile nodes detects that its current foreign agent has rebooted;
o a mobile node is paged and is not on the same network as the paging
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foreign agent; and
o an idle mobile node is about to transmit data.
2.4 Paging
When a foreign agent needs to locate an idle mobile node, it
broadcasts a paging request message in its network, and at the same
time, unicasts the message to all other foreign agents in its paging
area. These foreign agents then broadcast the page within their own
wireless networks. The paging request message lists the home
addresses of all paged mobile nodes, as shown in the Section 1.5. P-
MIP supports the optimization that a foreign agent may have a number
of paging request to make at any one moment. In this case P-MIP can
aggregate all mobile nodes paging requests into a single paging
request message. This helps to minimize the paging overhead as the
number of paged mobile nodes grow.
When a foreign agent receives a paging request, it first conducts an
authentication check if the foreign agents share a mobility security
association. If authentication is passed, the foreign agent
broadcasts the paging message on its own network. When a mobile node
finds its home address in the paging request and the message is
directly from its registered foreign agent then the mobile node is
still located in the same network. In this case, the mobile node
sends a paging reply back to its registered foreign agent without
registering, and then sets its operational mode to active and
restarts its active timer. Otherwise, the mobile node will first
start the registration procedure to make sure that the binding
between its home address and new CoA from its current foreign agent
is valid. Following this the mobile node responds to the paging
request by sending a paging reply. The mobile node will insert its
CoA in the paging reply. To avoid potential collisions between
signaling messages (i.e., registrations and paging reply messages)
from multiple paged mobiles in the same network, the transmission
time for each registration and paging reply (to a foreign agent) is
randomized.
A foreign agent conducts authentication checks on paging reply
messages received from paged mobile nodes if the foreign agent and
the mobile nodes share a secure association. If a foreign agent is
not the registered foreign agent, then it will forward the paging
reply message to the registered foreign agent which initiated paging.
It does this after appending the foreign agent to foreign agent
authentication extension in the message. If the foreign agent is the
mobile node's registered foreign agent, then it updates the mobile
node state by setting the operational mode to active and starting the
active timer.
The registered foreign agent originating paging removes the mobile
node ``record'' associated with all paged mobile nodes that are not
located in its network after receiving a paging reply. The registered
foreign agent takes this action because it assumes that these mobile
nodes have initiated new registrations. The term ``record'' used in
this draft refers to Mobile IP mobility management related
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information maintained by a home agent, foreign agent and mobile
node. A record comprises transient state information that includes
the mobile nodes home address, home agent address, CoA and various
timer related information associated with control messages (e.g.,
registration lifetime, etc.).
The registered foreign agent will retransmit the paging request after
a paging period if no response is received to an earlier paging
request. The paging period is implementation dependent. If a mobile
node's registration lifetime expires during paging then the
registered foreign agent stops paging the mobile node. Each
successive paging period should be at least twice the previous
duration. After sending three successive paging request the foreign
agent assumes that the mobile is not in the paging area and removes
the record associated with this mobile.
Once a paging reply is received by the registered foreign agent then
any buffered data for the paged mobile node is forwarded toward the
mobile node.
2.5 Data Handling
When a mobile node is on a foreign network incoming and outgoing data
to and from the mobile, respectively, are handled as follows.
2.5.1 Incoming Data
When there are incoming packets destined to a mobile node, the mobile
node's home agent forwards data to its CoA which belongs to the
mobile node's registered foreign agent. When the registered foreign
agent receives the data, it first determines whether it has a record
for the mobile node. If it has a record, then it checks if the mobile
node supports a paging function which is determined based on the P
bit in Registration Request message (see Section 1.5). If P bit is
set to '1', then it means the mobile node supports paging function.
In contrast, if the P bit is set to '0', then it means the mobile
node does not support a paging function or does not need a paging
function (e.g., when the mobile node stays in a network for a long
period of time). If the mobile node supports paging then the
registered foreign agent checks the mobile node state.
If the mobile node is in an active state then it is likely that the
mobile node is located on the same network. In this case, the foreign
agent decapsulates packets and forwards them to the mobile node. As
discussed above, the originating foreign agent sends a paging request
if the mobile node is in idle state, and at the same time, buffers
the data for the mobile node. When the originating foreign agent
receives a paging reply it forwards any buffered data to the mobile
node. If the mobile node is not in the registered foreign agent's
network any more then the registered foreign agent removes the mobile
node's record.
In the case that a mobile node does not respond to multiple page
requests the registered foreign agent removes the mobile node's
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INTERNET-DRAFT P-MIP July 2000
record and send an ICMP message ``node not found'' to the home agent.
2.5.2 Outgoing Data
In active mode a mobile node can simply send data. If the mobile node
is idle it first determines if it is still located on the same
network where it is currently registered by checking agent
advertisement lifetime or by sending an agent solicitation message.
If the mobile node resides on the same network then it sets the
operational mode to active and starts the active timer before
transmitting data. If a mobile node is on a different network then it
initiates a registration procedure to update its location record in
its home agent and foreign agent. It is very likely that a mobile
that is sending out going data will also receive data in return.
Therefore, the home agent and foreign agent bindings need to be
updated to facilitate the delivery of incoming data to the mobile
node.
In order for a foreign agent to track a mobile node's operational
state, both outgoing and incoming data should be routed through the
current foreign agent. Therefore, the foreign agent should act as a
routing point for outgoing data as well as decapsulating and
forwarding incoming data.
3. Security Considerations
The authentication method used in P-MIP is the same as in Mobile IP
[2]. If a mobility security associations exist among foreign agents
in a paging area then the foreign agent to foreign agent
authentication extension should be attached at the end of the paging
request and reply messages. If a mobility security association exists
between a foreign agent and a mobile node then the mobile node to
foreign agent authentication extension should be attached at the end
of the paging request and reply messages.
4. References
[1] X. Zhang, K. Sawada, J. Castellanos, A. Campbell, "P-MIP:
Minimal Paging Extensions for Mobile IP," In submission to
WMCSA 2000 - Third IEEE workshop on Mobile Computing Systems
and Application, June, 2000. http://comet.columbia.edu/pmip.
[2] C. Perkins, "IP Mobility Support," RFC 2002, IETF, Oct. 1996.
[3] A. Campbell, J. Gomez, C-Y. Wan, Z. Turanyi, and A. Valko,
"Cellular IP," Internet Draft, IETF, 1999.
[4] R. Ramjee, T. La Porta, S. Thuel, K. Varadhan, and L.
Salgarelli, "IP Micro-mobility support using HAWAII," Internet
Draft, IETF, Dec. 1999.
[5] R. Ramjee, T. La Porta, and L. Li, "Paging support for IP
mobility using HAWAII," Internet Draft, IETF, Mar. 2000.
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INTERNET-DRAFT P-MIP July 2000
[6] E. Gustafsson, A. Jonsson, and C. Perkins, "Mobile IP Regional
Registration," Internet Draft, IETF, Mar. 2000
[7] C. Castelluccia, "Extending Mobile IP with Adaptive Individual
Paging: A Performance Analysis," INRIA, Nov. 1999.
http://www.inrialpes.fr/planete/people/ccastel/Welcome.html#PUB
[8] A. Campbell, J. Gomez, S. Kim, C-Y Wan, Z. Turanyi, and A.
Valko, "Comparison of Micro-mobility Protocols," Internet
Draft, IETF, July 2000.
Authors' Addresses
Xiaowei Zhang, Javier Castellanos, Andrew Campbell,
Kentaro Sawada, Micheal Barry
Department of Electrical Engineering, Columbia University
Rm. 807 Schapiro Research Building
530 W. 120th Street, New York, NY 10027
Phone: (212) 939-7157
email: {xzhang, sawaken, javierg, campbell}@comet.columbia.edU
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