One document matched: draft-mun-mobileip-layer2-handoff-mipv4-00.txt
Youngsong Mun
INTERNET-DRAFT Jongjin Park
Expires April 2003 Soongsil University
October 2002
Layer 2 Handoff for Mobile-IPv4 with 802.11
<draft-mun-mobileip-layer2-handoff-mipv4-00.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering Task
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Abstract
Mobile-IPv4 describes how a Mobile Node can perform layer 3 handoff between
subnets served by different Foreign Agents. Sometimes the delay during
handoffs can exceed the threshold of delay sensitive applications. So low
delay must be considered.
This document describes a method to perform fast handoff on the Layer 2 for
Mobile-IPv4 with 802.11's Access Point. Mobile-IPv4 Registration messages
are carried in the Information Elements of 802.11 frames. According to this
method, Mobile-IPv4 can perform handoff at the same time as 802.11 handoff.
But some modifications bust be adopted in the existing Mobile-IPv4 and
802.11's entities such as Mobile Node and Access Point.
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1. Introduction
Mobile-IPv4 describes how a Mobile Node (MN) can perform Layer 3 handoff
between subnets served by different Foreign Agents (FAs). Sometimes the
delay during handoffs can exceed the threshold of delay sensitive
applications. So low delay must be carefully considered. The aim of this
document is to achieve low delay Mobile-IPv4 handoff during movement between
FAs. The proposed method is base on the Layer 2 handoff (802.11's
Association/Reassociation procedure).
In the Mobile-IPv4, when a Mobile-IPv4 (MIP4) MN moves from subnet to
another subnet, MN seeks a Foreign Agent (FA) situated in the subnet and
registers with the FA. The IP packet sent in Registration Message has the
Home IP address as the source, and the destination address can be the FA's
IP address. The FA then responds with Registration Reply Message. The
Registration Message also includes Authentication Extensions.
In the 802.11 wireless LAN network, an 802.11 client connects to an 802.11
Access Point (AP) on the Layer 2. The 802.11 provides a mechanism to achieve
Association/Reassociation procedure between AP's and the client. A 802.11
client first authenticates and then associates with selected AP. When the
802.11 client decides that it is better to move to anotherd AP, it can
carry out a pre-authentication and re-association with that AP.
2. Terminology
The following terminology and abbreviations are used in this document. The
reference network architecture and handover scenario is illustrated in Figure 1.
AR: Access Router
MN: Mobile Node
FA: Foreign Agent
HA: Home Agent
BU: Binding Update
HoA: Home of Address
CoA: Care of Address
AP: Access Point
BSS: Basic Service Set
ESS: Extended Service Set
SSID: Service Set ID
IE: Information Element
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[FA1]
|
V ....... [AP1]---- |
[MN]... | |------[AR1]--|
V ....... [AP2]---- |---------> [HA]
V |
V ....... [AP3]----------[AR3]--|
|
[FA3]
... - 802.11 link
--- - 802.3 link
Figure 1. Reference Network Architecture
3. Protocol Overview
3.1 Technique
The Figure 1 shows the scenario when MN moves from AP1 to AP2 (movement
from one BSS to another BSS within the same ESS) and continously move from
AP2 to AP3 (movement from a BSS in one ESS to a BSS within another ESS).
Because the same ESS means same subnet, the transition from AP1 to AP2
handoff means that the MN is in the same subnet, hence MIPv4 registration
is not required. But the MN only knows that here is different BSS. Hence
this document present that if any transitions between BSSs are occurred
then MN always sends Registration Request Message within 802.11 Association
/Reassociation Request Message. It is achieved by substitute 802.11
Information Element with MIPv4 Registration Request Message.
When the AP acquires MIPv4 Registration Request Message from the 802.11
Association/Reassociation Request Message, the AP rearrange this information
to the 802.3 frame and then send to the assigned FA. If FA knows that MN has
been already registered then FA responds with MIPv4 Registration Reply
Message to the MN directly (bypass AP) which can be generated without
exchange message sequence from FA to HA. Else if FA knows that MN is unknown
then FA responds with MIPv4 Registration Reply Message to the MN directly
(bypass AP) which can be generated with exchange message sequence from FA
to HA.
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3.2 Handoff Message Timing
MN AP1 AP2 AP3 FA1 HA
----- 802.11 Authentication Request------------>
<---- 802.11 Authentication Response------------
.
.
.
-------802.11 Reassociation Request ---------->
(MIPv4 Registration IE included)
<------802.11 Reassociation Response-----------
---MIPv4 Registration--->
<--------------------------------------------------MIPv4 Reply-----------
---802.11 Dissociation Request--->
.
.
.
------ 802.11 Reassociation Request---------------------->
(MIPv4 Registration IE included)
<------802.11 Reassociation Response----------------------
(MIPv4 Reply IE included)
MIPv4 Registration
------------->
MIPv6 BU
<------>
<--------------------------------------------------MIPv4 Reply-----------
---802.11 Dissociation Request----------------->
Figure 2. Handoff Message Timing Diagram
When the MN moves from AP2 to AP3 there is a change of the serving FA,
hence FA3 now needs to execute a FA-HA message exchange.
4. MIPv4 BU Message in 802.11 Management Frames
The 802.11 Association/Reassociation frames are shown in the Figure 3.
The Association/Reassociation frames carry an optional MIPv4 Registration Request
Message as information element. The MIPv4 Registration Request Message is
contained in the 802.11 Association/Reassociation Request Messages. The MIPv4
Registration Reply Message is sent to the MN directly and is independent with
the 802.11 Association/Reassociation Response messages.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Frame Control | Duration |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Address | Source Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Transmitter Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Transmitter Address | Sequence Control |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
+ MIPv4 Registration Request IE +
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Frame Check Sequence |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3. 802.11 (Re) Association Request Frame
The MIPv4 Registration Request IE with a unique Element ID. The 802.11
Information Element consists of the following fields: Element ID, Length ID, and
Information. The length field is 1 octet long and specifies the length of the
information field in number of octets. The information field is consited with
MIPv4 Registration Request Message.
In the Figure 4, the Home Address is the IP address of the MN. The Home Agent is
the IP address of the MN's HA. The Care of Address is the IP address for the tunnel
endpoint. The Identification is a 64-bit number constructed by the MN and used for
matching registration requests with registration replies, as well as for protecting
against replay attacks of registration messages.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Element ID | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type |S|B|D|M|G|V|rsv| Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Home Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Home Agent |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Care-of Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Identification +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extensions ...
+-+-+-+-+-+-+-+-
Figure 4. MIPv4 Registration Request IE of 802.11
The FA determines the Layer 2 address of the Request message that came from and
after receiving a reply message from the HA, the FA sends the reply message to this
Layer 2 address. The FA must not use the ARP response for this Layer 2 address.
5. Considerations
There are some considerations for the mobile entities.
5.1 Considerations for MN
The MN should have capability of passing the MIPv4 informations to the 802.11
driver and vice-versa. At the instant the MN is ready to send an Association/
Reassociation Request it should be able to access the MN's MIPv4 attributes.
But, when the MN receives an MIPv4 Registration Reply Message independently
with 802.11 Association/Reassociation Response Message.
5.2 Considerations for 802.11 AP
The 802.11 AP must have FA's MAC address information and be able to extract/
rearrange the MIPv4 Registration Request IE.
When the FA is an inpendent entity (seperate with AP) with its own IP address,
the situation is more difficult. Because the AP behaves only Layer 2 device,
so they do not understand FA's Advertisement Message.
The simple method to overcome this problem is to use intall program of AP.
This program acquires FA's information throug FA's Advertisement Message or
manual input.
After registration is complete, the MN would send periodic ICMP Registration
Request directly to the FA which would be carried by regular 802.11 Data Frames.
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6. Acknowledgments
All the RFCs, IDs, freely available 802.11 standards, and web-sites.
Specially thanks for Goswani's ID for simulataneous handoff of MIPv4.
7. References
[1] IEEE, "Part 11: Wireless LAN Medium Access Control (MAC) and
Physical Layer (PHY) Specifications", 1999.
[2] Mustafa Ergen, "IEEE 802.11 Tutorial," June 2002.
[3] Bob Conner, "IEEE 802.11 and HIPERLAN WIRELESS LANs: An Overview and
Comparison," April 2000.
[4] Perkins, C., "IP Mobility Support", RFC 3220, January 2002.
8. Contact Informations
Jongjin Park Youngsong Mun
Soongsil University Soongsil University
Seoul Korea Seoul Korea
spel@sunny.soongsil.ac.kr mun@computing.ssu.ac.kr
This document expires April 2003.
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