MobilityENEE 426 | Communication Networks | Spring 2008 Lecture 18Mobile Users• Seamless connectivity as users move around the network– Wired– Wireless• Properties– Applications unaware user is moving between L2/L3 networks– L4 sessions remain active as user movesENEE 426 | Communication Networks | Spring 2008 Lecture 18Home NetworkMobile IP• Allows user to maintain the same IP address no matter where they connect to the Internet• In home networkInternetENEE 426 | Communication Networks | Spring 2008 Lecture 18Visited NetworkMobile IP• In visited network, actual IP address changes• Need “agent” in each network to broker connectionHome NetworkInternetHome AgentForeign AgentENEE 426 | Communication Networks | Spring 2008 Lecture 18Triangular Routing• Mobile has two IP addresses– Care-of address on visited network– Permanent address on home network• Home agent – Maintains mappings of care-of to permanent address– Encapsulates inbound traffic with an additional IP headerPayloadIPMACPayloadIPMAC IPENEE 426 | Communication Networks | Spring 2008 Lecture 18Triangular Routing• Mobile node decapsulates tunneled data• To transmit, mobile node can simply send data to the server with home network IP address as source• Can cause security problems if routers check source addressesENEE 426 | Communication Networks | Spring 2008 Lecture 18Reverse Tunneling• All data travels through the home agent• Added latency over traditional Mobile IPVisited NetworkHome NetworkInternetHome AgentForeign AgentENEE 426 | Communication Networks | Spring 2008 Lecture 18Mobile Infrastructure• Mobile IP good for Infrastructure networks• What about when your entire infrastructure is mobile?InternetHome NetworkVisitedNetworkInternetENEE 426 | Communication Networks | Spring 2008 Lecture 18Many types of Mesh Routing• Pro-active– Pre-establish routing information• Re-active– On-demand routes• Pro/Re hybrid• Adaptive routing– Tables updated based on node mobility• Hierarchical– Super-nodes organize flows• Geographical– GPS-aware• Power-AwareENEE 426 | Communication Networks | Spring 2008 Lecture 18On-Demand Routing• If the mesh network is stationary, you can run standard algorithms like RIP or OSPF• If network is dynamically changing, RIP/OSPF not appropriate• On-Demand Routing– End-hosts requests routing information on a per-transaction basis– Determine routing information in real timeENEE 426 | Communication Networks | Spring 2008 Lecture 18Dynamic Source Routing (DSR)• Flood network with route request• Each hop maintains route information• When destination receives message, reverses route and sends it back to the source• Source then has full routing information14576382(6,1)(6,1,2)(6,1,2,3)(6,1,2,3,8)ENEE 426 | Communication Networks | Spring 2008 Lecture 18Adhoc On-Demand Distance Vector Routing (AODV)• Improvement to DSR• On-path nodes remember routing information as it propagates, build transient routing tables• Source node does not need to include all the addressing informationENEE 426 | Communication Networks | Spring 2008 Lecture 18Disconnected Networks• Delay-Tolerant Networks• Disruption-Tolerant NetworksENEE 426 | Communication Networks | Spring 2008 Lecture 18Delay-Tolerant Networks (DTNs)• Rely on node mobility to deliver messages• Store and forward networks• If node is completely disconnected, how does it know to whom it should give a message?ENEE 426 | Communication Networks | Spring 2008 Lecture 18Epidemic Routing• Easy solution: give the message to everyone you see– Message spreads like a disease• Inefficient, wastes storage space on devices who are not on the path between the source and destination• Improvement:– When the destination receives the message, it sends out an ACK, so devices can delete the buffered message– Spreads like a vaccineENEE 426 | Communication Networks | Spring 2008 Lecture 18Gradient Decent• Each node broadcasts distance, incremented each hop– Much like distance-vector routing• Only pass messages to nodes with smaller value than you• Topology changes– Distance number inaccurate– Solution• Each node gradually increments values• If you receive a message with lower value, updateENEE 426 | Communication Networks | Spring 2008 Lecture 18Analyzing DTNs• Analysis depends on mobility model– Random appearance– Random walk– Random way-point– Localized random