Network Working Group Stephane Antoine
Internet-Draft France Telecom
Intended status: Standards Track December 15, 2006
Expires: June 18, 2007
Using Higher Layer Triggers for Low Latency Handoffs in MIPv4
draft-antoine-mip4-lowlatency-handoff-triggers-00
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Copyright (C) The IETF Trust (2006).
Abstract
This document introduces the use of triggers coming from layers
higher than the link layer to initiate the Low Latency Handoff in
Mobile IPv4 (MIPv4) . The Low Latency Handoff for MIPv4 assumes
availability of Layer 2 (L2) triggers that contain Layer 3 (L3)
information for the Mobile Node (MN) to handoff. However, the low
latency draft does not describe the method by which the L2 trigger is
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produced neither does it explicitly describe by what mechanism the L3
information present in the L2 trigger is acquired. The Low Latency
Handoff for MIPv4 relies on availability of the L2 trigger. However
relying only on the link information to initiate a handoff does not
generally gather enough information for the MN to handoff to the most
suitable available access network. Information from higher layers
such as Higher Layer Triggers can be used to command a MN to quickly
move from one access to another one. Using Higher Layer Triggers to
initiate the handoff enables the implementation of policy based
handoff to garantee load balancing of the wireless networks and
Quality of Services to the end users.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Inadequacies of relying on Layer 2 triggers alone for Low
Latency Handoffs . . . . . . . . . . . . . . . . . . . . . . . 5
5. Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Scenario 1 . . . . . . . . . . . . . . . . . . . . . . . . 5
5.2. Scenario 2 . . . . . . . . . . . . . . . . . . . . . . . . 6
6. Using Higher Layer Triggers to initiate the Low Latency
Handoff in MIPv4 . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Pre-Registration handoff . . . . . . . . . . . . . . . . . 6
6.1.1. Network initiated: . . . . . . . . . . . . . . . . . . 6
6.1.2. Mobile initiated: . . . . . . . . . . . . . . . . . . . 7
6.2. Post-Registration Handoff . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . . 7
8. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 8
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8
10. Normative References . . . . . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 8
Intellectual Property and Copyright Statements . . . . . . . . . . 9
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1. Introduction
Low Latency Handoffs in MIPv4 [LOWLATMIP4] introduces a method that
achieves low latency for Mobile IPv4 in support of real-time
services. The two methods presented in to achieve low latency are
based on reception of various Layer 2 triggers on the MN and the
Foreign Agent (FA). The Layer 2 trigger introduced in [LOWLATMIP4]
informs L3 of a particular event before L2 handoff actually takes
place. The Low Latency Handoff in MIPv4 is only initiated just
before the L2 handoff takes place as indicated by the L2 triggers.
L2 trigger usually occurs when the signal strength reaches a critical
level that requires a handoff to take place. However, handoff may be
needed upon reception of parameters other than the ones related to
the relative signal strength received. L2 trigger indicating that
the MN has just entered the coverage area of a WLAN network is not
enough indication to handoff to the most suitable network at the most
suitable time. A Mobile Node which is simultaneously connected to
several networks, does not necessarily have enough information to
initiate the handoff from its default network to a most prefered
access network. Due to lack of additional information, the MN may
stay connected to an acces network that may turn out to be more
costly for the MN than another available one. The lack of
information, can cause the MN to stay connected to one access network
that does not offer the MN the best quality of service. This lack of
informmation, prevents the management of load sharing mechanisms on
different access networks to suit several subscribers having
different profiles. Higher Layer Triggers or Handoff Commands in
response to a policy decision can trigger the MN handoff to the most
preferable available network at the most suitable time. The Higher
Layer Trigger or Handoff Command comes from a Network Node or from
the MN itself. Higher Layer Trigger or a Handoff Command may trigger
a MIPv4 handoff even without indication of a pending L2 handoff.
Implementing the Higher Layer Handoff Trigger is compatible with
[LOWLATMIP4]. One can design a system in which a Higher Layer
Trigger or a Handoff Command is used to generate a L2 trigger that
subsequently initiates the Low Latency Handoff in MIPv4. In case
urgent handoff is needed as indicated by a pending L2 handoff, the
low latency takes place even if no Higher Layer Trigger has been
received.
2. Terminology
This section introduces the Handoff Command and the Higher Layer
Handoff Trigger.
Handoff Command - It is a message sent by an entity in the network to
instruct the MN to initiate a handoff.
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Higher Layer Handoff Trigger - It is a trigger that comes from a
layer higher than Layer 2. The Higher Layer Handoff Trigger can come
from Layer 3 or the application layer. The Higher Layer Handoff
Trigger may have been generated locally by the entity receiving the
trigger. It may also have been generated by a Network Node other
than the node receiving the trigger. The Higher Layer Handoff
Trigger may be received as an IP message initiated from the network
(Handoff Command). The entity receiving the Higher Layer Handoff
Trigger is either the MN or the FA or another entity in the network
such as the Access Router (AR) that could subsequently interacts
directly with the MN at layer 2. The Higher Layer Handoff Trigger
can generate the Layer 2 trigger.
3. Motivation
The Higher Layer Trigger or Handoff Command coming from the Network
or the MN serves to implement policy based network controlled
handoffs. A network operator can command a set of users to handoff
to different networks to provide load sharing on its different access
networks. The network operator can selectively command Mobile Nodes
to handoff to different access networks to provide a level of Quality
of Service to different users according to their user profiles. The
Higher Layer Trigger that comes from the MN application can initiate
handoff when the quality of the application becomes poor. For a
Voice over IP application for example, the perceived quality of the
voice can serve as a Trigger to the MN to initiate a handoff to a
better network. Figure 1 and 2 illustrate the initiation of the Low
Latency Handoff by a Higher Layer Trigger from the network or the MN
itself.
MN oFA/nFA Network Node/entity HA/GFA
| | | |
| |Higher Layer Trigger/Command | |
| |<------------------------------| |
--|----------------------------------------------------------------------
| | | | |
| | |Low Latency in MIPv4 | |
| | | | |
-------------------------------------------------------------------------
Figure 1: Network initiated, source/target triggered.
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MN oFA nFA Network Node/entity HA/GFA
| | | | |
| |Higher Layer Trigger/Command | |
|<--------------------------------------------| |
| or | | | |
|Higher Layer Trigger | | |
|<~~~~~~ | | | |
--|---------------------------------------------------------------------
| | | | | | |
| | |Low Latency in| MIPv4 | | |
| | | | | | |
------------------------------------------------------------------------
Figure 2: Mobile initiated.
4. Inadequacies of relying on Layer 2 triggers alone for Low Latency
Handoffs
The Low Latency Handoff in MIPv4 relies on L2 triggers as an
indication of a pending L2 handoff to initiate the early MIPv4
registration before the L2 handoff actually takes place. L2 triggers
although not exactly define in [LOWLATMIP4] correspondent to events
such as perception of signal noise ratio at the MN or Link Up, Link
Down, reception of an agent solicitation... Reception of L2 triggers
alone is not always sufficient information to rely upon for the
initiation of the Layer 3 handoff. Handoff Commands can be used to
force a handoff even if the signal quality is very good on all of the
MN's interfaces. In such scenarios, the handoff triggers coming from
a higher layer protocol can be used to initiate the L3 handoff
presented in [LOWLATMIP4].
5. Scenarios
A few scenarios can illustrate the application of handoff triggers
from higher layers to initiate the Low Latency Handoff in MIPv4.
5.1. Scenario 1
The handoff trigger comes locally from a Layer 3 or above of the MN
due to variations or degradation in the application for example.
Application degradation may be due to increased load in the MN's
serving network. The MN can interpret such degradation as a hint for
an eventual need to handoff to a different access network. The MN
may generate a scan to obtain the identifier of other networks
available (BSSID identifier for example of the Access Point that is a
potential handoff target). The MN resumes the actions with a Proxy
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Router Solicitation (PrRtSol) as in the Pre-Registration Low Latency
Handoff in MIPv4 case. Note that scanning of potential new access
networks may not result in finding a target access network to handoff
to as the MN may not be in an overlapping networks coverage area. In
that case, the hint received (from L3 or the application) would have
not triggered the handoff.
5.2. Scenario 2
A Mobile Node is using a WLAN connection and is simultaneously in the
coverage area of WLAN and 3G with a good signal reception in WLAN.
The Link Up on the 3G interface is not necessarily a trigger
providing sufficient information to initiate the Pre-registration
with L3 handoff towards 3G. However a network policy may require the
MN to execute a handoff due to various network conditions and
policies pre-established. To achieve policy based network control
handoff, several techniques can be designed: The MN can collect
information and send it to the network which ultimately takes the
decision to instruct the MN or the FA (by a Handoff Command) to
handoff to a preferred type of available network. The criterion
initiating the handoff is not restricted to the signal noise ratio
perceived at lower layers. Instead the set of criteria can include
other parameters such as the link characteristics of available
networks, the load on the MN serving network and neighbouring access
networks, the level of quality of service perceived...(Such a
scenario is the most appealing for network operators as it enables
the network to initiate and assist the handoff). One may design a
system in which Higher Layer Triggers are used to initiate the Low
Latency Handoff in MIP.
6. Using Higher Layer Triggers to initiate the Low Latency Handoff in
MIPv4
6.1. Pre-Registration handoff
The MN MAY perform regular scans to obtain information about its
available networks. The MN MAY report regularly to a network entity
such information. The network entity might then take the decision to
instruct the MN to handoff. The handoff trigger from higher layer
protocol could be received at the FA (Network initiated) or at the MN
(Mobile initiated).
6.1.1. Network initiated:
The MN reports to a central entity (Policy Decision Point) the IP
addresses of its available FAs obtained through scanning. Upon
decision to instruct the MN to handoff to a particular access
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network, the network entity will send a Handoff Command to a FA to
initiate handoff to the target access network. The termination of
the Handoff Command can be the oFA (for the source trigger handoff)
or the nFA (for the target trigger handoff). The Handoff Command
could contain the IP address of the nFA it is instructed the MN to
move to. The Handoff Command in turn generates the Layer 2 source or
target trigger in use in the Low Latency Handoff in MIPv4. The
Handoff Command when implemented provides a means to pass the IP
address of the new FA (nFA) or the old FA (oFA) for use in the L2
trigger. A method by which the Handoff Command from layer 3
generates a Layer 2 trigger at the FA is not described in this
document.
6.1.2. Mobile initiated:
The Mobile Initiated Pre-registration handoff can result from a
Higher Layer Handoff Trigger that originated locally on the MN or
from a Handoff Command sent from another node in the network. The
Handoff Command may contain limited information such as the type of
the preferred network to move to (i.e 3G or WLAN or WiMAX, the load
on each network, the QoS ...). When the MN receives an instruction
to handoff it can then issue a new scan to obtain the BSSID
identifier of the Access Point that is a potential handoff target.
The reception of the BSSID of the target AP can be the layer 2
trigger that then initiates the Mobile Initiated Pre-registration
Handoff as in [LOWLATMIP4].
6.2. Post-Registration Handoff
The application of Handoff Command towards the Post registration
handoff is restricted. As the Post Registration Handoff effectively
starts with the loss of L2 connectivity with the oFA L2-Link Down
(L2-LD) it makes it more difficult to initiate it with Higher Layer
Triggers.
7. Security Considerations
This document introduces a framework describing the use of triggers
coming from layers higher than the link layer to initiate the Low
Latency Handoff in Mobile IPv4. The Handoff Layer Triggers MUST be
secured to provide reliable information to the Low Latency for MIPv4.
The mechanism causing the delivery of the Triggers MUST also be
secured and MUST not introduce any vulnerability to the low Latency
handoff for MIPv4. Securing the delivery of Higher Layer Triggers
prevents an attacker in the network to send bogus messages causing
the MN undesired handoffs. A Security Association SHOULD exist
between the Network Node sending the Command and the recipient (the
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FA or the MN) of the Higher Layer Trigger. The establishment of
these Security Associations are out of the scope of this document.
8. Conclusion
This document introduces the use of triggers from layers higher than
layer 2 to initiate the Low Latency Handoff in MIPv4. The trigger
issued from the application or the network layer may in turn generate
the Layer 2 trigger. Layer 2 trigger is not necessarily received as
an indication of a stronger or lower signal received at the MN from
the access network. The Higher Layer Trigger coming from the network
is a Handoff Command which makes it possible to implement policy
decision based handoff. According to a policy decision the system
may command the MN to handoff to the most preferable Access Network.
The policy based handoff decision may be taken locally on the MN or
may be implemented on a different node in the network.
9. Acknowledgements
The author wish to thank Karim El Malki for reviewing this document
and for providing useful comments.
10. Normative References
[LOWLATMIP4]
K. El Malki, Editor., "Low Latency Handoffs in Mobile
IPv4", October 2005.
Author's Address
Stephane Antoine
France Telecom
Chiswick Park
London, Chiswick W4 5XS
United Kingdom
Phone: + 44 (0)208 849 5821
Fax: +44 (0)208 849 0991
Email: stephane.antoine@orange-ft.com
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