Inter-Subnet Mobile IP Handoffs in 802.11b Wireless LANs

Albert Hasson

Presentation Overview

Introduction Mobile IP overview (v4 and v6) IEEE 802.11 Mobile IP handoff mechanisms MIP handoff optimizations from literature Project focus

Introduction

WLAN technology spreading 802.11 roaming within a network Mobile IP handoff to another network How can handoff be improved? Latency during MIP handoffs in 802.11

WLANs

Introduction

Internet

Router A Router B

AP AP AP

10.64.x.x 10.128.x.x

?

10.64.1.37

Corresponding Node

Mobile IP

Allows transparent migration through different networks

Overview Mobile IPv4 Mobile IPv6 extensions to MIPv4 IP mobility entities IP mobility mechanisms

Mobile IP

Assign mobile node (MN) 2 addresses Home address

PermanentDefine transport connections

Care-of address (CoA)Corresponds to MN current locationGlobally routable

Mobile IPv4 Entities

Mobility Agents

Home AgentOn home networkMaintains CoA-home address mapping Binding CacheEncapsulate and tunnel packets to CoA

Mobile IPv4 Entities

Foreign AgentOn foreign (visited) networkDe-encapsulate tunneled packetsDeliver to MNAllow MN to configure CoA

Mobile IPv4 Mechanisms

Agent Discovery Periodic agent advertisements

Extension to ICMP Router DiscoveryAdvertise presence Include mobility-specific information (CoA)

MN may send Router solicitations

Mobile IPv4 Operation

Internet

Home Agent

Corresponding Node

Foreign Agent

HAddr1 – CoA1

HAddr2 – CoA2

Tunnel

Mobile Node

Mobile IPv6

CN maintains Binding CachePackets sent directly to MNMay be sent to Home Agent and tunneled

IPv6 Routing header instead of encapsulation

Mobile IPv6

No foreign agentsFunctionality built into IPv6 routers IPv6 Neighbor DiscoveryStateless address autoconfigurationAccess Router

Mobile IPv6 Operation

Internet

Home Agent

Corresponding Node

Access Router

HAddr1 – CoA1

HAddr2 – CoA2

Mobile Node

HAddr1 – CoA1

HAddr2 – CoA2

802.11 Wireless LANs

Basic Service Set (BSS)Set of communicating stations using WMSmallest unit of a WLAN

Form an Independent Basic Service Set (IBSS)

Ad-hoc network

802.11 Wireless LANs

Extended Service Set (ESS) Interconnection of BSSsDistribution System (DS) provides

interconnectionAccess Point (AP) bridge between wireless

and distribution media

802.11 Wireless LANs

Extended Service Set Identifier (ESSID)

Infrastructure Network

802.11 Wireless LANs

Infrastructure Mode Network

ESS

802.11 (Link-layer) Handoff

L2 handoff significant to MIP handoff Service interruption Contributes to total handoff latency

Significant variations 300-400 ms

802.11 Handoff

Decrease in SNR initiates handoff Scan

Find available APs with same ESSIDRecord signal strengthUse Probe Request & Probe ResponseSweep through channelsSelect “best” AP

802.11 Handoff

AuthenticationEstablish identity of stationOpen System – always acceptedWireless Equivalent Privacy (WEP)

802.11 Handoff

AssociationStation registered at APAP handles station trafficRe-association – transfer association from old

AP

Probe delay 90% of L2 handoff latency

802.11 Handoff

Mobile IP Handoff

Link-layer handoff Movement detection Registration

Handoff Latency is sum of these delays MN can’t receive IP packets – latency

Mobile IP Movement Detection

MIP operates independently of link-layerCDMA, wireless LAN

Agent/Router DiscoverySolicitation/advertisement messagesAdvertisements broadcastPeriod > 1/sBandwidth efficiency – detection delay

Movement Detection

Eager Cell Switching (ECS)Handoff on first new advertisementFrequent movement

Lazy Cell Switching (LCS)Wait until current access router unreachable Infrequent movementLatency up to 3 sec

Mobile IP Registration

After handoff and detection of new foreign agent/access router

Update bindings at CN & home agent Binding update message

MN home addressNew CoALifetime

Mobile IP Handoff

Internet

Router A Router B

AP AP AP

10.64.x.x 10.128.x.x

?

10.64.1.37

Corresponding Node

Home Agent

Mobile IP Optimizations

Most systems focus on one aspect of MIP handoff

Difficult to modify 802.11 handoff Micromobility Improved movement detection techniques

Micromobility

Defined domain Macro/micro-mobility Segregate access network from Internet Use hierarchal structure Different approaches

Hierarchal Mobile IPCellular IP

Micromobility

Gateway manages location informationPer-mobile routesHandoff managed locallyBounded Registration delayE.g. Hierarchal Mobile IPv6

Micromobility

Movement Detection

Establish communication between MIP and link-layer

Use “hints” or triggersHandover startLink upLink down

Communicate additional information

Movement Detection

Hinted Cell Switching (HCS)Hint after L2 handoffSend solicitation

ProblemsRouters wait random time before reply Increased signaling

Movement Detection

Fast Hinted Cell Switching (FHCS)Get identity of agent/router from link-layerBypass solicitationL2 provide IP and hardware address of routerUse SSID to contain informationNo need for movement detection

Movement Detection

FHCS problems802.11 handoff between different ESSIDs

Application specific information object Include AR or MN information on Probe

messages

Fast Hinted Cell Switching

Fast Hinted Cell Switching

Project Focus

Movement detection enhancements within micromobility framework

Investigate performing handoff processes in parallel

Network-assisted handoffs Evaluate different mechanisms wrt handoff

latency and packet loss

Project Focus

Design/implement test bed Many implementations

MIPLMonashHierarchal MIPCellular IP

Linux wireless tools

Handover to Questions…