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Berkeley COMPSCI 268 - Lecture Notes

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1 CS 268: Computer Networking L-12 Ad Hoc Networks Mobile Routing • Mobile IP • Ad-hoc network routing • Assigned reading • Performance Comparison of Multi-Hop Wireless Ad Hoc Routing Protocols • A High Throughput Path Metric for MultiHop Wireless Routing 22 3 Overview • Internet routing • Ad hoc routing • Ad hoc routing metrics 4 How to Handle Mobile Nodes? • Dynamic Host Configuration (DHCP) • Host gets new IP address in new locations • Problems • Host does not have constant name/address  how do others contact host • What happens to active transport connections? • Naming • Use DHCP and update name-address mapping whenever host changes address • Fixes contact problem but not broken transport connections3 5 Handling Mobile Nodes (Transport) • TCP currently uses 4 tuple to describe connection • <Src Addr, Src port, Dst addr, Dst port> • Modify TCP to allow peer’s address to be changed during connection • Security issues • Can someone easily hijack connection? • Difficult deployment  both ends must support mobility 6 Handling Mobile Node • Link layer mobility • Learning bridges can handle mobility  this is how it is handled in most campus networks • Encapsulated PPP (PPTP)  Have mobile host act like he is connected to original LAN • Works for IP AND other network protocols • Multicast • Solves similar problem  how to route packets to different sets of hosts at different times • Can’t we just reuse same solutions? • Don’t really have solution for multicast either!4 7 Handling Mobile Nodes (Routing) • Allow mobile node to keep same address and name • How do we deliver IP packets when the endpoint moves? • Why can’t we just have nodes advertise route to their address? • What about packets from the mobile host? • Routing not a problem • What source address on packet? • Key design considerations • Scale • Incremental deployment 8 Basic Solution to Mobile Routing • Same as other problems in Computer Science • Add a level of indirection • Keep some part of the network informed about current location • Need technique to route packets through this location (interception) • Need to forward packets from this location to mobile host (delivery)5 9 Interception • Somewhere along normal forwarding path • At source • Any router along path • Router to home network • Machine on home network (masquerading as mobile host) • Clever tricks to force packet to particular destination • “Mobile subnet” – assign mobiles a special address range and have special node advertise route 10 Delivery • Need to get packet to mobile’s current location • Tunnels • Tunnel endpoint = current location • Tunnel contents = original packets • Source routing • Loose source route through mobile current location • Network address translation (NAT) • What about packets from the mobile host?6 11 Mobile IP (RFC 2290) • Interception • Typically home agent – hosts on home network • Delivery • Typically IP-in-IP tunneling • Endpoint – either temporary mobile address or foreign agent • Terminology • Mobile host (MH), correspondent host (CH), home agent (HA), foreign agent (FA) • Care-of-address, home address 12 Mobile IP (MH at Home) Mobile Host (MH) Visiting Location Home Internet Correspondent Host (CH) Packet7 13 Mobile IP (MH Moving) Visiting Location Home Internet Correspondent Host (CH) Packet Home Agent (HA) Mobile Host (MH) I am here 14 Mobile IP (MH Away – Foreign Agent) Visiting Location Home Internet Correspondent Host (CH) Packet Home Agent (HA) Foreign Agent (FA) Encapsulated Mobile Host (MH)8 15 Mobile IP (MH Away - Collocated) Visiting Location Home Internet Correspondent Host (CH) Packet Home Agent (HA) Mobile Host (MH) Encapsulated 16 Other 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…9 17 Overview • Internet routing • Ad hoc routing • Ad hoc routing metrics Ad Hoc Routing • Goal: Communication between wireless nodes • No external setup (self-configuring) • Often need multiple hops to reach dst 1810 19 Ad Hoc Routing • Create multi-hop connectivity among set of wireless, possibly moving, nodes • Mobile, wireless hosts act as forwarding nodes as well 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 power limitations • Low consumption of memory, bandwidth, power • Scalable with numbers of nodes • Localized effects of link failure Challenges and Variants • Poorly-defined “links” • Probabilistic delivery, etc. Kind of n2 links • Time-varying link characteristics • No oracle for configuration (no ground truth configuration file of connectivity) • Low bandwidth (relative to wired) • Possibly mobile • Possibly power-constrained 2011 21 Problems Using DV or LS • DV protocols may form loops • Very wasteful in wireless: bandwidth, power • Loop avoidance sometimes complex • LS protocols: high storage and communication overhead • More links in wireless (e.g., clusters) - may be redundant  higher protocol overhead 22 Problems Using DV or LS • Periodic updates waste power • Tx sends portion of battery power into air • Reception requires less power, but periodic updates prevent mobile from “sleeping” • Convergence may be slower in conventional networks but must be fast in ad-hoc networks and be done without frequent updates12 23 Proposed Protocols • Destination-Sequenced Distance Vector (DSDV) • DV protocol, destinations advertise sequence number to avoid loops, not on demand • Temporally-Ordered Routing Algorithm (TORA) • On demand creation of hbh routes based on link-reversal • Dynamic


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Berkeley COMPSCI 268 - Lecture Notes

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