CS 268: Computer NetworkingL-11 Ad Hoc NetworksMobile Routing• Mobile IP• Ad-hoc network routing• Assigned reading• Performance Comparison of Multi-Hop WirelessAd Hoc Routing Protocols• A High Throughput Path Metric for MultiHopWireless Routing23Overview• Internet routing• Ad hoc routing• Ad hoc routing metrics4How to Handle Mobile Nodes?• Dynamic Host Configuration (DHCP)• Host gets new IP address in new locations• Problems• Host does not have constant name/address howdo others contact host• What happens to active transport connections?• Naming• Use DHCP and update name-address mappingwhenever host changes address• Fixes contact problem but not broken transportconnections5Handling Mobile Nodes (Transport)• TCP currently uses 4 tuple to describeconnection• <Src Addr, Src port, Dst addr, Dst port>• Modify TCP to allow peer’s address to bechanged during connection• Security issues• Can someone easily hijack connection?• Difficult deployment both ends mustsupport mobility6Handling Mobile Node• Link layer mobility• Learning bridges can handle mobility this is how it ishandled in most campus networks• Encapsulated PPP (PPTP) Have mobile host act likehe is connected to original LAN• Works for IP AND other network protocols• Multicast• Solves similar problem how to route packets todifferent sets of hosts at different times• Can’t we just reuse same solutions?• Don’t really have solution for multicast either!7Handling Mobile Nodes (Routing)• Allow mobile node to keep same address andname• How do we deliver IP packets when the endpointmoves?• Why can’t we just have nodes advertise route to theiraddress?• What about packets from the mobile host?• Routing not a problem• What source address on packet?• Key design considerations• Scale• Incremental deployment8Basic Solution to Mobile Routing• Same as other problems in ComputerScience• Add a level of indirection• Keep some part of the network informedabout current location• Need technique to route packets through thislocation (interception)• Need to forward packets from this locationto mobile host (delivery)9Interception• Somewhere along normal forwarding path• At source• Any router along path• Router to home network• Machine on home network (masquerading as mobilehost)• Clever tricks to force packet to particulardestination• “Mobile subnet” – assign mobiles a special addressrange and have special node advertise route10Delivery• Need to get packet to mobile’s currentlocation• Tunnels• Tunnel endpoint = current location• Tunnel contents = original packets• Source routing• Loose source route through mobile currentlocation• Network address translation (NAT)• What about packets from the mobile host?11Mobile IP (RFC 2290)• Interception• Typically home agent – hosts on home network• Delivery• Typically IP-in-IP tunneling• Endpoint – either temporary mobile address orforeign agent• Terminology• Mobile host (MH), correspondent host (CH),home agent (HA), foreign agent (FA)• Care-of-address, home address12Mobile IP (MH at Home)Mobile Host (MH)VisitingLocationHomeInternetCorrespondent Host (CH)Packet13Mobile IP (MH Moving)VisitingLocationHomeInternetCorrespondent Host (CH)PacketHome Agent (HA)Mobile Host (MH)I am here14Mobile IP (MH Away – Foreign Agent)VisitingLocationHomeInternetCorrespondent Host (CH)PacketHome Agent (HA)Foreign Agent (FA)EncapsulatedMobile Host (MH)15Mobile IP (MH Away - Collocated)VisitingLocationHomeInternetCorrespondent Host (CH)PacketHome Agent (HA)Mobile Host (MH)Encapsulated16Other Mobile IP Issues• Route optimality• Triangle routing• Can be improved with route optimization• Unsolicited binding cache update to sender• Authentication• Registration messages• Binding cache updates• Must send updates across network• Handoffs can be slow• Problems with basic solution• Reverse path check for security• Do we really need it…17Overview• Internet routing• Ad hoc routing• Ad hoc routing metricsAd Hoc Routing• Goal: Communication between wirelessnodes• No external setup (self-configuring)• Often need multiple hops to reach dst1819Ad Hoc Routing• Create multi-hop connectivity among set ofwireless, possibly moving, nodes• Mobile, wireless hosts act as forwarding nodes aswell as end systems• Need routing protocol to find multi-hop paths• Needs to be dynamic to adapt to new routes,movement• Interesting challenges related to interference and powerlimitations• Low consumption of memory, bandwidth, power• Scalable with numbers of nodes• Localized effects of link failureChallenges and Variants• Poorly-defined “links”• Probabilistic delivery, etc. Kind of n2 links• Time-varying link characteristics• No oracle for configuration (no groundtruth configuration file of connectivity)• Low bandwidth (relative to wired)• Possibly mobile• Possibly power-constrained2021Problems Using DV or LS• DV protocols may form loops• Very wasteful in wireless: bandwidth, power• Loop avoidance sometimes complex• LS protocols: high storage andcommunication overhead• More links in wireless (e.g., clusters) - maybe redundant higher protocol overhead22Problems Using DV or LS• Periodic updates waste power• Tx sends portion of battery power into air• Reception requires less power, but periodicupdates prevent mobile from “sleeping”• Convergence may be slower inconventional networks but must be fast inad-hoc networks and be done withoutfrequent updates23Proposed Protocols• Destination-Sequenced Distance Vector (DSDV)• DV protocol, destinations advertise sequence numberto avoid loops, not on demand• Temporally-Ordered Routing Algorithm (TORA)• On demand creation of hbh routes based on link-reversal• Dynamic Source Routing (DSR)• On demand source route discovery• Ad Hoc On-Demand Distance Vector (AODV)• Combination of DSR and DSDV: on demand routediscovery with hbh routing24DSR Concepts• Source routing• No need to maintain up-to-date info atintermediate nodes• On-demand route discovery• No need for periodic route advertisements25DSR Components• Route discovery• The mechanism by which a sending nodeobtains a route to destination• Route maintenance• The mechanism by which a sending nodedetects that the network topology has changedand its route to destination is no longer
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