1. Mobility Support in Wireless LAN
CHEN Zhiming
52479H
Department of Electrical and Communications Engineering
S-72 Communications Laboratory, HUT

2. S-72 Communications Laboratory, HUT
Acknowledgement
Supervisor :
Professor Sven-Gustav Häggman
Instructor :
Lic.Tech Michael Hall
Communications Laboratory,HUT
S-72 Communications Laboratory, HUT

3. S-72 Communications Laboratory, HUT
Agenda
Thesis Introduction
IEEE WLAN overview
Base Mobile IP (v4/v6) review
Enhancements to the base Mobile IP
A new proposed protocol
Summary
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4. S-72 Communications Laboratory, HUT
Thesis Introduction
S-72 Communications Laboratory, HUT

5. S-72 Communications Laboratory, HUT
Thesis Introduction
The work of the thesis is mainly based on literature study
Standarized specifications
Drafted specifications
Research publications
Discussion with the professor and the instructor
S-72 Communications Laboratory, HUT

6. S-72 Communications Laboratory, HUT
Thesis Introduction
Main goal:
Investigate how mobility is supported in WLAN, especially in the network layer.
S-72 Communications Laboratory, HUT

7. S-72 Communications Laboratory, HUT
Thesis Introduction
Major contributions:
An in-depth study in Mobile IP and its enhancements for ’seamless’ handover
Categorization of these enhancements
A new protocol proposal
S-72 Communications Laboratory, HUT

8. S-72 Communications Laboratory, HUT
IEEE WLAN overview
S-72 Communications Laboratory, HUT

9. S-72 Communications Laboratory, HUT
IEEE WLAN overview
An Extended Service Set (ESS)
S-72 Communications Laboratory, HUT

10. S-72 Communications Laboratory, HUT
IEEE WLAN overview
IEEE defines three categories of mobility in a WLAN:
No-transition: a MN is either static or moving within a BSS.
BSS-transition: a MN moves from one BSS to another within the same ESS.
ESS-transition: a MN moves from a BSS in one ESS to a BSS in a different ESS.
S-72 Communications Laboratory, HUT

11. S-72 Communications Laboratory, HUT
IEEE WLAN overview
No-transition:
supported by the association service
BSS-transition:
supported by the association and reassociation service.
IAPP (Inter Access Point Protocol ) provides a secure handover mechanism between APs in the same ESS. (Layer-2 solution).
S-72 Communications Laboratory, HUT

12. S-72 Communications Laboratory, HUT
IEEE WLAN overview
ESS-transition:
Involves different IP subnets
Is not supported by the IEEE specifications
Mobile IP provides a solution in the network layer (L3)
S-72 Communications Laboratory, HUT

13. S-72 Communications Laboratory, HUT
IEEE WLAN overview
Session Initiation Protocol (SIP)
Mobility support in the application layer
The basic SIP supports only personal mobility
Minor chnages must be added to support terminal mobility
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14. Base Mobile IP (v4/v6) review
S-72 Communications Laboratory, HUT

15. Base Mobile IP (v4/v6) review
Mobile IP allows a Mobile Node (MN) to use two IP addresses:
Static home address
Dynamic care-of address (CoA)
S-72 Communications Laboratory, HUT

16. Base Mobile IP (v4/v6) review
Mobile IPv4 operations
Discovering the CoA
CoA assigned by a foreign agent (FA),or
CoA assigned by the Dynamic Host Configuration Protocol (DHCP)
Registering the CoA
The MN registers the acquired CoA with the HA
Tunneling to the CoA
Route optimization
S-72 Communications Laboratory, HUT

17. Base Mobile IP (v4/v6) review
Follows the basic design of Mobile IPv4
Works without a FA. A MN can configure its CoA by using Stateless Address Autoconfiguration and Neighbor Discovery
Route Optimization is a part of the standard
Ingress filtering problem can be solved by using the home address destination option
S-72 Communications Laboratory, HUT

18. Base Mobile IP (v4/v6) review
Example of WLAN with Mobile IPv4
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19. Base Mobile IP (v4/v6) review
Research results:
Mobile IPv4 can be successfully implemented in the WLAN platform
However, handover delay and data loss are too significant for real-time services like VoIP.
S-72 Communications Laboratory, HUT

20. Enhancements to the base Mobile IP
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21. Enhancements to base Mobile IP
Enhancement methods can be divided into four categories:
Hierarchical FA structure or Regional Registration
Fast IP address Acquisition
Buffering or Smooth Handover
L2 triggers
S-72 Communications Laboratory, HUT

22. Enhancements to base Mobile IP
Hierarchical FA structure or Regional Registration CN HA
RCoA
MAP
Mobility Anchor Point
AR1
AR2
LCoA2
LCoA1 MN
movement
S-72 Communications Laboratory, HUT

23. Enhancements to base Mobile IP
Hierarchical FA structure or Regional Registration
Goal: to reduce the Binding Update or Registration with the HA and CNs.
How: limiting the Registration within the foreign network as long as the MN roams within the foreign network.
S-72 Communications Laboratory, HUT

24. Enhancements to base Mobile IP
2. Fast IP address Acquisition
WLAN Frames
Current fields in the association-related frames
New proposed fields
Association Request
Capability, listen interval, SSID, supported rates
Mobile IP bit, current IP address (128 bit to support IPv6)
Association Response
Capability, Status Code,
Association ID (AID), supported rates
IP address (128 bits to support IPv6)
Reassociation Request
Capability, listen interval,
SSID, supported rates, current AP address
Reassociation Response
Capability, Status Code, AID, supported rates
S-72 Communications Laboratory, HUT

25. Enhancements to base Mobile IP
Fast IP address Acquisition
MN inserts its current IP address into a new field of 32 bits (128 bits for IPv6) and a Mobile IP bit in the Association and Reassociation messages.
In the Response to the Association and Reassociation messages, there will be an IP address field of 32 bits (128 bit for IPv6).
MN can start the Registration right after.
Router Advertisement and Movement Detection are not needed.
S-72 Communications Laboratory, HUT

26. Enhancements to base Mobile IP
Buffering or Smooth Handover
Basic idea:
Make routers or APs buffer incoming traffic for the MNs. By buffering, the packets in flight during a handover will not be lost.
S-72 Communications Laboratory, HUT

27. Enhancements to base Mobile IP
L2 triggers
In a normal handover process, usually the L3 handover will not take place until the MN finishes the L2 handover and then connects to a new link.
By using L2 triggers, L3 handover can start earlier before a L2 handover is completed.
S-72 Communications Laboratory, HUT

28. Enhancements to base Mobile IP
L2 triggers
The old FA continues to provide services (e.g. advertisement from the neighboring new FAs ) to the MN even after the MN has moved into a new FA (the new link is not fully established yet)
L2 events trigger the set-up of communications between the old and new FAs.
S-72 Communications Laboratory, HUT

29. A new proposed protocol
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30. A new proposed protocol
Follows the design scheme of category #2 ” Fast IP address Acquisition”
Speeds up L3 handover without the need of Agent Advertisement, Movement Detection and Agent Solicitation.
S-72 Communications Laboratory, HUT

31. A new proposed protocol
Improvements:
No need to modify the existing association and reassociation request frames.
Instead,utilizes the SSID information contained in the existing association and reassociation requests frames.
Thus, it appears more practical than the method used in category #2.
S-72 Communications Laboratory, HUT

32. A new proposed protocol
Basic idea:
The APs and FAs have been pre-configured so that they have knowledge of their IP domains.
The new FA will respond to the assocaition/ reassociation request with a CoA if the MN has moved into a new IP subnet (from the SSID).
The MN can start registration right after.
S-72 Communications Laboratory, HUT

33. S-72 Communications Laboratory, HUT
Summary
S-72 Communications Laboratory, HUT

34. S-72 Communications Laboratory, HUT
Summary
IEEE WLAN mobility support can be realized:
In layer 2 – IAPP
In layer 5 – SIP (with minor changes to the base protocol)
In layer 3 – Mobile IP
Problems: handover delay and data loss
Solutions: enhancements to the base Mobile IP
S-72 Communications Laboratory, HUT

35. S-72 Communications Laboratory, HUT
Summary
Categorization of the enhanvement methods:
Hierarchical FA structure or Regional Registration
Fast IP address Acquisition
Buffering or Smooth Handover
L2 triggers
S-72 Communications Laboratory, HUT

36. S-72 Communications Laboratory, HUT
Summary
The proposed protocol:
Speeds up the Mobile IP handover without modifying the existing association and reassociation request frames.
S-72 Communications Laboratory, HUT

37. S-72 Communications Laboratory, HUT
Thnak you!
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38. S-72 Communications Laboratory, HUT
Questions??
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