Internet DRAFT - draft-gwon-mobileip-l3mp-mipv4
draft-gwon-mobileip-l3mp-mipv4
MOBILE-IP Working Group Youngjune L. Gwon (Editor)
INTERNET-DRAFT Atsushi Takeshita
Expires: August 23, 2001 DoCoMo USA Labs
February 23, 2001
Network Layer Triggered Mobile IPv4 Predictive Handoff
<draft-gwon-mobileip-l3mp-mipv4-00.txt>
Status of this memo
This document is an individual contribution for consideration by the
Mobile IP Working Group of the Internet Engineering Task Force.
Comments should be submitted to the mobile-
ip@standards.nortelnetworks.com mailing list.
Distribution of this memo is unlimited.
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. Internet-Drafts are working
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Abstract
This draft describes a network layer (layer 3) handoff-triggering
mechanism and associated Mobile IPv4 predictive handoff scheme that
is free of the link layer (layer 2) triggering events. By utilizing
layer 3 information only, the network layer mobility prediction
(L3MP) mechanism first predicts the future per packet latency. Then,
the L3MP selects the future access point given the predicted values
in advance. The future access point suggestion by the L3MP triggers
the Mobile IP predictive handoff. The predictive handoff scheme
described in this draft encompasses three significant steps before
switching the actual access point: L3MP handoff triggering,
pre-register, and route pre-optimization.
Table of Contents
1. Introduction
2. Terminology
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3. Scope of the Solution
4. Link Layer Independency
5. Access Network Considerations
5.1 Layer 3 Signaling from Different Nearby Base Stations
5.2 Signal Strength vs. Per Packet Latency
6. Network Layer Mobility Prediction (L3MP)
6.1 L3MP Latency Prediction (L3MP-LP)
6.2 L3MP Access Point Selection (L3MP-APS)
6.3 Compact Layer 3 Beacon Format
7. Specifying Handoff Triggering Events
8. Mobile IPv4 Predictive Handoff
8.1 Layer 3 Trigger
8.2 Pre-register
8.3 Route Pre-optimization
9. Security Considerations
10. Acknowledgement
11. References
12. Author's Addresses
1. Introduction
A number of Mobile IP fast handoff schemes currently proposed in the
IETF Mobile-IP Working Group require a handoff trigger specified by
the link layer (layer 2) events. The layer 2 triggering events are
interpreted to initiate the Mobile IP handoff at the network layer
(layer 3). Although a handoff solution should not depend on the
mobile wireless access technologies, it is an obscure task to
universally specify the layer 2 triggering events from different
access technologies. Furthermore, one cannot expect the layer 2
triggers from every wireless device. To avoid this air-interface
(physical layer or layer 1) and layer 2 diversity issues, a
generalized layer 3-contained methodology or layer 3 triggering
mechanism that is independent of the access technologies (layers 1
and 2) must be developed.
This draft considers both the layer 3 mobility prediction mechanism
(L3MP) and the L3MP triggered predictive Mobile IPv4 handoff. By
utilizing the layer 3 information only, the L3MP is an association of
two sub-functions: Latency Prediction (L3MP-LP) and Access Point
Selection (L3MP-APS). The L3MP-LP predicts the future per packet
latency based on the present and the previous latency samples
obtained at the layer 3. Thus, the L3MP-LP reflects the future layer
3 communication quality. The L3MP-APS selects the future access point
given multiple L3MP-LP values for different access points (e.g.
mobility agents and access routers) in prior to an occurrence of the
actual handoff.
The Mobile IPv4 predictive handoff scheme presented in this draft
encompasses three steps performed in advance: predictive handoff
triggering, pre-register, and route pre-optimization.
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2. Terminology
This draft uses terms defined in Mobile IPv4 and other related
documents. In addition, this document uses the following terms:
Layer 3 Triggering Events
Layer 3 contained process that initiates the Mobile IP
predictive handoff.
L3MP
An acronym for layer 3 mobility prediction or network layer
mobility prediction (See network layer mobility prediction).
L3MP-LP
An acronym for L3MP-latency prediction is a process of
predicting the future value of per packet latency using the
present and previous latency samples. Latency samples are
obtained by using ICMP timestamp option on layer 3 beacon.
Timestamp is marked by the mobility agents and the mobile node
retrieves the packet traveling time upon the reception of the
layer 3 beacon. Thus, L3MP-LP is a prediction based layer 3
link evaluation capability.
L3MP-APS
An acronym for L3MP-access point selection is a process of
choosing the access point (access routers or mobility agents)
given the L3MP-LP prediction values.
Network Layer Mobility Prediction
A mechanism that chooses the future access point for a mobile
node by encompassing two separate processes: latency prediction
(L3MP-LP) and access point selection (L3MP-APS).
Pre-register
Mobile IPv4 registration before switching the actual access
point. Pre-register can only be successful if the handoff of a
mobile node is correctly anticipated in timely manner.
Otherwise, it will only increase the layer 3 control signaling
due to unnecessary pre-register.
Route Pre-optimization
Route optimization [2] before switching the actual access
point, i.e. establishing direct routes between the mobile and
correspondent nodes before the actual handoff.
3. Scope of the Solution
This draft specifies both the layer 3 handoff-triggering mechanism,
namely the L3MP, and the Mobile IPv4 predictive handoff scheme
that is triggered by the L3MP. This draft specifies the layer 3
triggering events and the methodology of obtaining such events. This
draft also speficies the predictive handoff extentions to the base
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Mobile IPv4 specification [1] and the route optimization extention
[2].
4. Link Layer Independency
This draft describes yet another approach that utilizes the
information available at the layer 3 only for the Mobile IP handoff
trigger. It is necessary to develop the layer 3-contained handoff
triggering events for the following reasons:
a) It is difficult to specify layer 2 triggering events if the
access technologies (layers 1 and 2) differ.
b) If changes in access technology should not affect layer 3,
faster deployment of new access technology is possible.
c) Broader concept of handoff such as inter-access technology
handoff can be implemented easily, e.g. WLAN to cellular
handoff.
d) One cannot expect and specify all possible layer 2 triggers
from every type of wireless devices.
5. Access Network Considerations
This draft generally considers fully IP-based network technologies
and therefore possibly beyond the third generation networks. However,
the scope of this draft should not be restricted to the fully
IP-based or beyond the third generation network technologies.
5.1 Layer 3 Signaling from Different Nearby Base Stations
A mobile node is in charge of detecting the layer 3 beacons that are
used for layer 3 prediction. This draft considers that the mobile
node may simultaneously listen to multiple layer 3 signaling beacons
transmitted by different nearby base stations. For the current or the
third generation systems, layer 3 beacon may have to be transmitted
over either the signaling channel or common shared channels to
resolve the situation.
5.2 Signal Strength vs. Per Packet Latency
Obtaining per packet latency is a layer 3 analogous process that is
similar to the periodic beacon pilot strength measurement occurred at
lower layers (layers 1 and 2). Beacon pilot strength measurement is
reflected in terms of SIR (CDMA), SNR (TDMA), or raw signal power
depending on wireless access technologies. To accomplish the layer 2
like measurement at layer 3, a compact layer 3 beacon packet should
be introduced.
Furthermore, per packet latency should be predicted. A successful
prediction creates a time gap that can be used for preparing the
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Mobile IP handoff in advance.
6. Network Layer Mobility Prediction (L3MP)
The L3MP is a mechanism that resides within a mobile node. The mobile
node is responsible to carry out the L3MP operation by capturing the
layer 3 beacons periodically transmitted by the nearby base stations.
The compact layer 3 beacon format is described in 6.3.
The L3MP consists of two parts: latency prediction (L3MP-LP) and
access point selection (L3MP-APS). L3MP-LP is the layer 3 link
evaluation capability by predicting the future value of per packet
latencies with respect to the different foreign agents or access
routers. Then, the foreign agent that is predicted for the best
future performance, i.e. giving the smallest L3MP-LP value, is
selected by the L3MP-APS.
Figure 1 depicts an overall diagram of the L3MP operation in the
access network.
____ _____ L3 Beacon ____ L3 Beacon _____ ____
|AR1 |-|BTS1 | ==========> | MN | <========== |BTS2 |-|AR2 |
---- ----- ---- ----- ----
Figure 1: Mobile Node Operating L3MP in the Access Network
6.1 L3MP Latency Prediction (L3MP-LP)
There are a number of ways to predict the future value given the
present and past per packet latency samples that are obtained by ICMP
timestamp on layer 3 beacons. There are some important observations:
a) The variation of per packet latency over time, T(t), is a
stochastic process.
b) The obtained present and past per packet latency samples are
samples of T(t).
c) More recent latency samples are more correlated to the future
outcome of the latency.
d) It may be necessary that distorted samples should be sampled
out for the prediction accuracy.
Estimation theory may be applied to compute the future expected
value of the per packet latency given the present and past samples.
However, unless the first and the second order distribution of the
latency samples are known or properly modeled, estimating the future
expected value of a stochastic process involves the complex
computation of auto-and-cross correlation matrices. Although relying
on estimation theory is a solution, its applicability remains
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questionable in reality.
On the other hand, adaptive approach is a practical solution that
involves less computational complexity. Adaptive L3MP-LP is depicted
in Figure 2. The present and previous latency samples and error are
inputs for the adaptive predictor. Adaptive prediction is iterative
process that the prediction error is also fed back for computation.
^
/
/
------------------
T_present ====> | |
| |
T_previous_1 ====> | |
| Adaptive |==========> T_predicted
T_previous_2 ====> | Predictor | |
| | |
.... | | |
------------------ |
/ | -
/ T_future + =====> error
/ |
/_____________________|
Figure 2: Adaptive L3MP-LP
The adaptive prediction accuracy is related with the number of
previous samples as its inputs. It can also be modeled in terms of
the differences of consecutive samples.
A popular algorithm such as least mean square (LMS) method [3] can be
applied to efficiently compute adaptive prediction. Gauss-Markov
approximation of the user mobility may further reduce the
computational burden by using a couple of the previous samples.
6.2 L3MP Access Point Selection (L3MP-APS)
Mapping from the predicted future latency value to the future access
point selection is performed by a simple method. Among all
communicable mobility agents or access points, one that gives the
smallest latency prediction value is chosen, e.g. there may be 6
possible nearby base stations connected to different mobility agents
in optimal hexagonal cellular network configuration.
6.3 Compact Layer 3 Beacon Format
Although there is no definite requirement of layer 3 beaconing
period, the layer 3 beacon format must be as compact as possible.
Access point entities are required to send this layer 3 beacon so
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that any mobile node capable of listening can measure the per packet
latency for L3MP. Figure 3 shows a compact layer 3 beacon format for
this purpose. ICMP timestamp is included for layer 3 detection and
measurement purposes.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ IP Header with Agent's IP address (20 Bytes) +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Authentication (Optional) +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ ICMP Timestamp (20 Bytes) +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Compact Layer 3 Beacon Format
7. Specifying Handoff Triggering Events
Layer 3 handoff triggering events are specified by the output of the
L3MP, i.e. in the form of mobility agent's or access router's IP
addresses, so that a mobile node can actively contact them to carry
out the predictive handoff in timely manner. It is noteworthy that
the L3MP operates on the basis of optimizing the future latency
performance of the mobile node. If multiple agent
addresses are available, the preference for each agent also has to be
specified.
Once the addresses of the mobility agents or access routers are
available, the mobile node may start contacting the candidate
agent by sending pre-register request.
8. Mobile IPv4 Predictive Handoff
The Mobile IPv4 predictive handoff is really a temporary
simultaneous binding of a mobile node to two or more
care-of-addresses.
8.1 Layer 3 Trigger
As specified in Section 7, a layer 3 triggering event causes the
predictive handoff to be initiated. The layer 3 trigger is created by
the L3MP to provide the candidate mobility agent's IP addresses used
for pre-register and route pre-optimization.
8.2 Pre-register
Then, the mobile node sends pre-register request to the nFA via oFA
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while maintaining the connection with the oFA. This is illustrated
in Figure 3. If other secure (not via oFA) way to pre-register is
possible, then the mobile node may do it so. It is also necessary
if regional registration is not supported, the mobile node should
pre-register with its home agent.
Pre-register request via oFA
------ ------- ------
| MN |=======>| oFA |=======>| nFA |
| |<=======| |<=======| |
------ ------- ------
Pre-register reply via oFA
Figure 3: Pre-register to nFA via oFA
It should be noted that pre-register has relatively shorter
lifetime compared to the registration. The mobile node is
responsible for renewing the pre-register to the (regular) Mobile
IP registration after actually switching the access point.
Pre-regsiter request and reply packet formats are identical to
the registration request and reply formats except for the different
type numbers (TBD) and the shorter lifetimes.
8.3 Route Pre-optimization
Route pre-optimization sets up the direct and optimized routes
between the mobile node and its correspondent nodes in prior to the
actual handoff. This draft adds two new messages to the route
optimization draft [2]: Pre-binding update and route pre-optimization
completion messages. These two new messages are very similar to
the existing binding update and binding acknowledge messages except
for the different type numbers (TBD) and the shorter lifetime.
9. Security Considerations
Any mobile node with proper wireless transceiver is capable of
capturing the layer 3 beacon in the access network. Therefore, the
L3MP operation can create possible security attacks in the access
network. It is generally recommended that authentication header
should be included in the layer 3 beacon format.
Since the nature of the L3MP is to provide the predictive handoff
trigger at the layer 3 by predicting the future access point in
timely manner, unnecessary compuation regarding the authentication
that may cause an extra L3MP operational overhead should be avoided.
Security considerations regarding the predictive handoff extention
described in this draft conforms with those of the base Mobile
IPv4 specification [1].
10. Acknowledgements
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The authors of this draft appreciates advisors from the DoCoMo
Communications Laboratories USA's Advisory Board for their
valuable comments and inputs. The authors are also in gratitude to
our colleagues at Multimedia and Wireless Laboratories of NTT DoCoMo.
11. References
[1] Charles Perkins, "IP Mobility Support," RFC 2002, October 1996
[2] C. Perkins and D. Johnson, "Route Optimization in Mobile IP,"
draft-ietf-mobileip-optim-10.txt (work in progress), November
2000
[3] B. Widrow and S. Stearns, "Adaptive Signal Processing," 1985 by
Prentice Hall
12. Authors' Addresses
Questions about this memo can be directed to:
Youngjune Gwon
DoCoMo Communications Laboratories USA, Inc.
181 Metro Drive, Suite 300
San Jose, CA 95110
USA
Phone: +1 408 451 4734
Email: gyj@dcl.docomo-usa.com
Fax: +1 408 573 1090
Atsushi Takeshita
DoCoMo Communications Laboratories USA, Inc.
181 Metro Drive, Suite 300
San Jose, CA 95110
USA
Phone: +1 408 451 4705
Email: takeshita@dcl.docomo-usa.com
Fax: +1 408 573 1090
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