Mobility Support in Wireless
LAN
CHEN Zhiming
52479H
Department of Electrical and Communications
Engineering
24.7.2016
S-72 Communications Laboratory,
HUT
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Acknowledgement
• Supervisor :
Professor Sven-Gustav Häggman
• Instructor :
Lic.Tech Michael Hall
• Communications Laboratory,HUT
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Agenda
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Thesis Introduction
IEEE802.11 WLAN overview
Base Mobile IP (v4/v6) review
Enhancements to the base Mobile IP
A new proposed protocol
Summary
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Thesis Introduction
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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
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Thesis Introduction
• Main goal:
– Investigate how mobility is supported in
WLAN, especially in the network layer.
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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
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IEEE802.11 WLAN overview
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IEEE802.11 WLAN overview
• An Extended Service Set (ESS)
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IEEE802.11 WLAN overview
• IEEE802.11 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.
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IEEE802.11 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).
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IEEE802.11 WLAN overview
• ESS-transition:
– Involves different IP subnets
– Is not supported by the IEEE802.11
specifications
– Mobile IP provides a solution in the network
layer (L3)
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IEEE802.11 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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Base Mobile IP (v4/v6) review
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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)
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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
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Base Mobile IP (v4/v6) review
• Mobile IPv6
– 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
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Base Mobile IP (v4/v6) review
• Example of WLAN with Mobile IPv4
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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.
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Enhancements to the base
Mobile IP
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Enhancements to base Mobile IP
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Enhancement methods can be divided
into four categories:
1. Hierarchical FA structure or Regional
Registration
2. Fast IP address Acquisition
3. Buffering or Smooth Handover
4. L2 triggers
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Enhancements to base Mobile IP
1. Hierarchical FA structure or Regional
Registration
CN
HA
RCoA
MAP
LCoA1
AR1
AR2
MN
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Mobility Anchor Point
LCoA2
movement
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Enhancements to base Mobile IP
1. 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.
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Enhancements to base Mobile IP
2. Fast IP address Acquisition
WLAN Frames
Current fields in the associationrelated 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
Mobile IP bit, current
IP address (128 bit
to support IPv6)
Reassociation
Response
Capability, Status Code, AID,
supported rates
IP address (128 bits to
support IPv6)
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Enhancements to base Mobile IP
2. 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.
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Enhancements to base Mobile IP
3. 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.
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Enhancements to base Mobile IP
4. 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.
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Enhancements to base Mobile IP
4. 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.
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A new proposed protocol
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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.
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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.
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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.
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Summary
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Summary
• IEEE802.11 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
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Summary
•
Categorization of the enhanvement
methods:
1. Hierarchical FA structure or Regional
Registration
2. Fast IP address Acquisition
3. Buffering or Smooth Handover
4. L2 triggers
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Summary
• The proposed protocol:
– Speeds up the Mobile IP handover without
modifying the existing association and
reassociation request frames.
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Thnak you!
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Questions??
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