Mobile Data Networks 2Cellular Internet In mobile IP,

IP Micro Mobility Cellular IP Rajan Shankaran ITEC851 Mobile Data Networks 1IP Micro-mobility support Micro-mobility support: Efficient local handover inside foreign domain without involving a home agent Reduces control traffic on backbone Especially needed for route optimization Example approaches: Cellular IP HAWAII Hierarchical Mobile IP (HMIP) Rajan Shankaran ITEC851 Mobile Data Networks 2Cellular Internet In mobile IP, packets addressed to a mobile host are delivered using regular IP routing –a temporary address assigned to the mobile host A simple and scalable scheme that offers global mobility Mobile IP is not appropriate, however, for fast mobility and smooth handoff. Why?? Cellular mobile telephony systems are based on a different concept from that of Mobile IP Optimized for fast/smooth handoff in a local region Employs a scalable forwarding protocol Rajan Shankaran ITEC851 Mobile Data Networks 3Cellular IP Network TheuniversalcomponentofaCellularIPnetworkisthebasestation WirelessAPwithIPforwardingengine:CellularIProuting IncludesfunctionalitiesofMobileSwitchingCenters(MSC)andBaseStationControllers(BSC) NotionofGatewayRouter MobileIP:BetweenGatewayrouters. CellularIPwithinaccessnetworksmanagedbyagatewayrouter. CoA:GatewayRouter Rajan Shankaran ITEC851 Mobile Data Networks 4Cellular IP Network Location management and handoff support are integrated with routing. Objective: Minimizing control messages through data packets. Regular data packets help maintain routing state information. Tracking current location of a node. Uplink packets and Down link packets Caching state Empty IP packets maintain downlink routing state of mobile hosts: When MN has no data to send Principle of passive connectivity: soft state routes timeout in downlink routers. Paging: To locate mobile host’s current location. Rajan Shankaran ITEC851 Mobile Data Networks 6Cellular IP: Operation Three aspects need attention Routing Handoff Paging Rajan Shankaran ITEC851 Mobile Data Networks 7Routing in Cellular IP Beacon Packet: Periodic broadcast by Gateway Stations records incoming interface details: for routing purposes towards the gateway. All data packets from hosts transmitted on these routes towards the gateway. At each hop: Each base station maintains a routing cache: IP address, incoming interface Rajan Shankaran ITEC851 Mobile Data Networks 9Routing in Cellular IP A mobile host may sometimes wish to maintain its routing cache mappings: No regular data transmission A typical example: UDP stream. Keeping routing cache mappings valid: route-update packets at regular intervals called route update time. Same effect on routing cache as normal data packets Propagation restriction. Rajan Shankaran ITEC851 Mobile Data Networks 11Handoff in Cellular IP Wireless cells may overlap facilitating seamless handoff support. Protocol must support soft handoff-Packets delivered with little disturbance. Temporary simultaneous transmission –Old and new location. In case of no overlap, the protocol should still operate efficiently. Rajan Shankaran ITEC851 Mobile Data Networks 13Handoff in Cellular IP Handoff process -a migration during an ongoing data transfer, is handled automatically. Handoff in Cellular IP is always initiated by the mobile host. Rajan Shankaran ITEC851 Mobile Data Networks 14Handoff in Cellular IP Hard Handoff?? Cellular IP Tradeoff: Simplistic: supports fast and simple handoff at the price of potentially some packet loss. Handoff initiated on the basis of beacon signal strength. Reaction of Mobile host: Tuning of radio, transmission of route update packet/Data Packet Cerates routing cache mappings on route to the gateway hence configuring the downlink route to the new base station What is Handoff Latency??” -Time between handoff and arrival of first data packet. Worst case: Round-trip time between the mobile host and the cross-over point which is the gateway in the worst case: Packets lost Mappings associated with the old base station: timeout rather than being cleared Rajan Shankaran ITEC851 Mobile Data Networks 15Cellular IP Semisoft Handoff Algorithm Goal: To reduce handoff latency: Routing cache mappings associated with the new base station must be created before the actual handoff takes place. Semisoft handoff technique takes advantage before the mappings timeout at the old BS: Aperiod when both the old and new downlink routes are valid Before handoff, in this period mobile host sends a semisoft packet to new BS: Semisoft Handoff Returns back immediately to old BS. While the host is still in contact with the old base station, Semisoft packet configures routing cache mappings associated with the new base station. Improves handoff performance: providing probabilistic guarantees instead of fully eliminating packet loss Rajan Shankaran ITEC851 Mobile Data Networks 16Cellular IP Semisoft Handoff Algorithm After a semisoft delay, the host can perform a regular handoff. Semisoft Delay: Waiting time before handoff Need for the delay Rajan Shankaran ITEC851 Mobile Data Networks 17Semisoft Handoff Algorithm: Synchronization Problems Ensures that the mobile host continues to receive packets immediately after handoff. Does notensure a smooth handoff Synchronization problems: Depending on the network topology and traffic conditions, the time to transmit packets from the cross-over point to the old and new base stations may be different New BS lags Behind: Duplicate packets New BS is ahead: Missing packets (more Problematic) Perfect synchronization not necessary. Rajan Shankaran ITEC851 Mobile Data Networks 19Semisoft Handoff Algorithm: Synchronization Problems Crossover Delay introduced -To synchronize the delay difference between the new path and the old path from the crossover node Sufficient to compensate, with high probability, the time difference between the two streams This can be best achieved at the cross-over switch Flag setting on semisoft packet Crossover switch Subsequent Route update/data packets after handoff restores normalcy. Rajan Shankaran ITEC851 Mobile Data Networks 20Cellular IP Handoff: Other Issues At handoff the mobile host remains temporarily out of radio contact while moving between two cells Some packets may get lost. Recovery initiated by upper layers. If a host reappears before the RC timeout, service continues without any further delay. If RCs have timed out, they are reconfigured by the first packet (data) transmitted by the host Rajan Shankaran ITEC851 Mobile Data Networks 21Cellular IP: Paging Process Idle mobile host Active-state-timeout: Idle mobile hosts allow their respective soft-state routing cache mappings to time out. Hosts send paging-update packets at regular intervals Paging update packets: Empty IP packets addressed to the gateway. IP type parameter: to distinguish from a route update Update sent to BS with best signal quality Paging-update packets are routed on a hop-by-hop basis to the gateway: Paging cache. Base stations may optionally maintain paging cache. Rajan Shankaran ITEC851 Mobile Data Networks 23Cellular IP: Paging Process Paging occurs when a packet is addressed to an idle mobile host and the gateway or base stations find no valid routing cache mapping for this host. Without any paging cache the first packet addressed to an idle mobile host is broadcast in the access network Paging cache present; packets sent on valid interfaces No extra delay incurred but Paging load –memory/processor overhead Rajan Shankaran ITEC851 Mobile Data Networks 24Paging Process When IP packets arrive at the gatew
ay router, addressed to a mobile host for which no up-to-date routing information is available: Paging Caches are used to find the host. Packets queued at the gateway. Gateway generates a control packet: Paging Packet: Routed in the access network using paging caches. A full hop-by-hop route may be available to the host’s current location: All BSeshave PCs. Caches simply reverse the route taken by recent paging-update packets If some nodes do not have PC, then they will forward the paging packet to all outgoing ports. Idle host moves to active state upon reception of packet. Triggers transmission of Route Update packet at the host: RC state creation Rajan Shankaran ITEC851 Mobile Data Networks 25Paging cache versus Route cache Paging cache mappings are updated by any packet sent by mobile hosts including paging-update packets. In contrast, routing cache mappings are updated by data and route-update packets sent by mobile hosts. What do you observe? Idle versus active mobile hosts Rajan Shankaran ITEC851 Mobile Data Networks 29Mobile IP: L3 Handoff Mobile IP: allows a mobile node to migrate between different IP networks No breakdown in upper-layer communication sessions. Handoff: Movement changing point of attachments. This handoff is composed of a sequence of stages Includes the detection of a mobile node’s movement to the new network. movement detection: introduces latency Results in packet losses Not appropriate for real time traffic. Rajan Shankaran ITEC851 Mobile Data Networks 33Mobile IP Handoff Performance Due to layer independence principle: No communication between mobile IP and the lower layers Mobile IP movement detection mechanisms independent of lower layers. Movement detection algorithms: Critical to the performance of mobile IP Handoff Rajan Shankaran ITEC851 Mobile Data Networks 35Mobile IP Handoff Sequence A MIPv4 handoff may be divided into the following three stages Link-layer handoff (discussed in the previous slide) Mobile IP movement detection Mobile IP registration 802.11: hard handoff-hence the 3 stages happen in strict sequence Mobile IP at L3, 802.11 at L2: Mobile IP not link aware Heterogeneity, independence from lower layers Rajan Shankaran ITEC851 Mobile Data Networks 36Mobile IP Handoff The movement detection stage commences after a MN establishes a link/connection to a new network: 802.11 association. MN detects that it has moved to a new IP network. It receives relevant configuration information and other network settings related information. The last stage of a Mobile IP handoff is registration: MN sends a registration request containing the mobile’s new CoA back to the home agent. Rajan Shankaran ITEC851 Mobile Data Networks 37Mobile IP Handoff Latency Need an effective way of decreasing the interruption caused by a Mobile IP handoff. Requires optimizations to the movement detection process. Three approaches: Advertisement mechanisms L2 based hints L2-L3 integrated handoffs We first briefly get introduced to these schemes. Rajan Shankaran ITEC851 Mobile Data Networks 38Advertisement-Based Mechanisms Rajan Shankaran ITEC851 Mobile Data Networks 39 Mobile IP movement detection relies purely on the periodic broadcasting of agent advertisements by all mobility agents Extension of ICMP Router Advertisementmessages: Mobility-specific information such as available CoAs, network prefix part of any supplied router addresses. Key field: AdvertisementLifetime: Helps determine if current agent is unreachable. Recommended maximum rate for broadcasting advertisements: RFC 2002. RFC 3220 Heavy bandwidth consumption must be avoided Expiry triggers active search, polling cached entities. Agent solicitationAdvertisement-Based Mechanisms MN does not receive an advertisement within the specified lifetime: Current agent unreachable. Advertisement interval: 1/3 of life time Presence/absence recently cached advertisements from other agents: Solicitation process. How should the Mobile Node react: Two approaches Lazy Cell Switching/Eager Cell Switching (Eager Binding) Rajan Shankaran ITEC851 Mobile Data Networks 40Agent Selection Agent Selection is the state in which advertisements are evaluated and an appropriate agent is selected prior to registration. Based on a local Mobility Agent list List traversed-One with longest outstanding lifetime is selected. Selection process may acquire significant time periods. Rajan Shankaran ITEC851 Mobile Data Networks 41Link-Layer Hint-Based Mechanisms AllowsinformationfromthelinklayertobepasseduptoMobileIP,enablingfastermovementdetectiontobeperformed. Some movement detection mechanisms that allow link-layer hints to be gathered by Mobile IP: Advertisement caching Solicitation on link-layer handoff Hybrid Hint-Based Mechanism We will examine each of these schemes. Rajan Shankaran ITEC851 Mobile Data Networks 44Advertisement Caching A modified 802.11 access point will cache the most recent unsolicited advertisement. Completion of the 802.11association process as a “link-up” hint. Most recent advertisement can be delivered immediately: Configuration information readily available Eager binding exhibited by the mobile node. Rajan Shankaran ITEC851 Mobile Data Networks 45Solicitation on link-layer handoff MN’s Mobile IP layer made aware of link layer handoff events Hand-off Hint should be communicated to the Mobile IP sublayer every time that a link layer hand-off takes place The receipt of a link layer hint causes a mobile node to broadcast agent solicitation. Overrules layer independence Hint: Link layer information on handoff: 802.11 association completion 802.11 Association completion as an indication that link-layer handoff Triggers solicitations -agents will respond with an advertisement. Rajan Shankaran ITEC851 Mobile Data Networks 46Solicitation on link-layer handoff Refer to the figure (Next slide) Receipt of a link-layer hint -mobile node broadcasts an agent solicitation. Forces all adjacent mobility agents to respond with a unicast agent advertisement. MN exhibits eager binding. Advantage: Mobile node promptly determines identity of local agents regardless of advertisement period. Rajan Shankaran ITEC851 Mobile Data Networks 47Hint Based Mechanism: Issues Solicitation flooding: Overheads in the presence of large number of roaming nodes. Broadcast storm with every location change DrawbackofECSalgorithm:Oscillatorybehaviour. ContinuouslyperformingIPhandoffsbetweenthetwoforeignagents. Rajan Shankaran ITEC851 Mobile Data Networks 49Fast Hinted Cell Switching Address the problem of: Flooding of solicitation messages Extend the amount of information communicated from the link-layer to MIP: E.g.: Identity of the local mobility agent. IP and hardware address Triggers immediate registration and adapting fast at new location. How does link layer determine this information? It is Bearer specific. For example, existing implementation over IEEE 802.11 network: Use of network’s Service Set Identifier (SSID) field to convey information: Why? Mobile node directly proceeds to Registration: Skips Agent Selection phase. Rajan Shankaran ITEC851 Mobile Data Networks 50Addressing the ECS Algorithm drawback Drawback of ECS algorithm MNcontinuouslymonitors802,11linkqualityparameters. MobileIPinformedwhensignalqualityreachesacertainthreshold. Strongsignalstrength:LCSmode Weaksignalstrength(belowthethreshold):ECSmode-handoffcompletion,receiptofadvertisement:RevertbacktoLCS Rajan Shankaran ITEC851 Mobile Data Networks 52L2-L3 Integrated handoffs Schemetominimizehandoffdelaythataccomplishesthelayer2handoff(IEEE802
.11)andthelayer3handoff(MobileIPv4)atthesametime. L3informationencapsulatedinL2messages. Thereare2approaches SimultaneousHandoffScheme:L2-L3integrationwithouttheuseofIAPP L2-L3integrationwiththeuseofIAPP(notdiscussed) Rajan Shankaran ITEC851 Mobile Data Networks 53Issues with Simultaneous handoff scheme Complexity in AP. Delay in the completion of layer 2 handoff. Rajan Shankaran ITEC851 Mobile Data Networks 57Mobile IP Availability Solaris Mobile IP Linux OS. MosquitoNetResearch Group (Stanford University) Linux OS. Monarch Research Project(CMU) Free Mobile IP implementation. Portland State Secure Mobile Networking Project Use if IPSecfor Mobile IP. Hierarchical Mobile IP Rajan Shankaran ITEC851 Mobile Data Networks 59Mobile IP Availability Most commercial vendors support Mobile IP. Cisco, Nokia, Siemens, HP. Mobile IP client services, providers Birdstep Intelligent Mobile IP Client v2.0, Universal Edition Internet Mobility Management with Secgo Mobile IP ipUnplugged Rajan Shankaran ITEC851 Mobile Data Networks 60Other Mobile IP Schemes Several schemes have been proposed: Columbia Proposal (Ioannidis and Maguire from Columbia University) IBM Proposal Sony’s virtual IP Proposal Hierarchical Mobile IP. Rajan Shankaran ITEC851 Mobile Data Networks 61Core Topics/Examination All topics covered are important from Exam Perspective. In particular, pay attention to: Overall operation of Mobile IP Tunnel management Multicast Mobile IP-802 Handoff. Exam Explain how tunnelling works in general and especially for mobile IP using IP-in-IP, minimal, and generic routing encapsulation, respectively. Discuss the advantages and disadvantages of these three methods. Rajan Shankaran ITEC851 Mobile Data Networks 62

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