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12-Feb-16

IT 2404 Mobile Communication ByDr T Gnanasekaran

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Mobile IP Dynamic Host Configuration Protocol- Mobile Ad Hoc Routing ProtocolsMulticast routing- TCP over Wireless Networks Indirect TCP Snooping TCP Mobile TCP Fast Retransmit / Fast Recovery Transmission/Timeout Freezing-Selective Retransmission Transaction Oriented TCP- TCP over 2.5 / 3G wireless Networks12-Feb-162UNIT IV MOBILE NETWORK AND TRANSPORT LAYERS

Mobile IP12-Feb-163

Mobile IP UsesEnable computers to maintain Internet connectivity while moving from one Internet attachment point to anotherMobile user's point of attachment changes dynamically and all connections are automatically maintained despite the changeNomadic - user's Internet connection is terminated each time the user moves and a new connection is initiated when the user dials back inNew, temporary IP address is assigned12-Feb-164

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1.Server X transmits an IP datagram destined for mobile node A, with A's home address in the IP header. The IP datagram is routed to A's home network.2.At the home network, the incoming IP datagram is intercepted by the home agent. The home agent encapsulates the entire datagram inside a new IP datagram, which has the A's care-of address in the header, and retransmits the datagram. The use of an outer IP datagram with a different destination IP address is known as tunneling.3.The foreign agent strips off the outer IP header, encapsulates the original IP datagram in a network-level Protocol Data Unit (PDU) (for example, a LAN Logical Link Control [LLC] frame), and delivers the original datagram to A across the foreign network.4.When A sends IP traffic to X, it uses X's IP address. In our example, this is a fixed address; that is, X is not a mobile node. Each IP datagram is sent by A to a router on the foreign network for routing to X. Typically, this router is also the foreign agent.5.The IP datagram from A to X travels directly across the Internet to X, using X's IP address.To support the operations illustrated in Figure 1, Mobile IP includes three basic capabilities:Discovery: A mobile node uses a discovery procedure to identify prospective home agents and foreign agents.Registration: A mobile node uses an authenticated registration procedure to inform its home agent of its care-of address.Tunneling: Tunneling is used to forward IP datagram from a home address to a care-of address.12-Feb-167

Operation of Mobile IPMobil node is assigned to a particular network home networkIP address on home network is static home addressMobile node can move to another network foreign networkMobile node registers with network node on foreign network foreign agentMobile node gives care-of address to agent on home network home agent12-Feb-168

Capabilities of Mobile IPDiscovery mobile node uses discovery procedure to identify prospective home and foreign agentsRegistration mobile node uses an authenticated registration procedure to inform home agent of its care-of addressTunneling used to forward IP datagrams from a home address to a care-of address12-Feb-169

DiscoveryMobile node is responsible for ongoing discovery processMust determine if it is attached to its home network or a foreign networkTransition from home network to foreign network can occur at any time without notification to the network layerMobile node listens for agent advertisement messagesCompares network portion of the router's IP address with the network portion of home address12-Feb-1610

Agent SolicitationForeign agents are expected to issue agent advertisement messages periodicallyIf a mobile node needs agent information immediately, it can issue ICMP router solicitation messageAny agent receiving this message will then issue an agent advertisement12-Feb-1611

Move DetectionMobile node may move from one network to another due to some handoff mechanism without IP level being awareAgent discovery process is intended to enable the agent to detect such a moveAlgorithms to detect move:Use of lifetime field mobile node uses lifetime field as a timer for agent advertisementsUse of network prefix mobile node checks if any newly received agent advertisement messages are on the same network as the node's current care-of address12-Feb-1612

Co-Located AddressesIf mobile node moves to a network that has no foreign agents, or all foreign agents are busy, it can act as its own foreign agentMobile agent uses co-located care-of addressIP address obtained by mobile node associated with mobile node's current network interfaceMeans to acquire co-located address:Temporary IP address through an Internet service, such as DHCPMay be owned by the mobile node as a long-term address for use while visiting a given foreign network12-Feb-1613

Registration ProcessMobile node sends registration request to foreign agent requesting forwarding serviceForeign agent relays request to home agentHome agent accepts or denies request and sends registration reply to foreign agentForeign agent relays reply to mobile node12-Feb-1614

Registration Operation MessagesRegistration request messageFields = type, S, B, D, M, V, G, lifetime, home address, home agent, care-of-address, identification, extensionsRegistration reply messageFields = type, code, lifetime, home address, home agent, identification, extensions 12-Feb-1615

Registration Procedure SecurityMobile IP designed to resist attacksNode pretending to be a foreign agent sends registration request to a home agent to divert mobile node traffic to itselfAgent replays old registration messages to cut mobile node from networkFor message authentication, registration request and reply contain authentication extensionFields = type, length, security parameter index (SPI), authenticator12-Feb-1616

Types of Authentication ExtensionsMobile-home provides for authentication of registration messages between mobile node and home agent; must be presentMobile-foreign may be present when a security association exists between mobile node and foreign agentForeign-home may be present when a security association exists between foreign agent and home agent12-Feb-1617

TunnelingHome agent intercepts IP datagrams sent to mobile node's home addressHome agent informs other nodes on home network that datagrams to mobile node should be delivered to home agentDatagrams forwarded to care-of address via tunneling Datagram encapsulated in outer IP datagram12-Feb-1618

Mobile IP Encapsulation OptionsIP-within-IP entire IP datagram becomes payload in new IP datagramOriginal, inner IP header unchanged except TTL decremented by 1Outer header is a full IP headerMinimal encapsulation new header is inserted between original IP header and original IP payloadOriginal IP header modified to form new outer IP headerGeneric routing encapsulation (GRE) developed prior to development of Mobile IP12-Feb-1619

DHCP

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Ad Hoc Routing ProtocolsAn ad hoc routing protocol is a convention, or standard, that controls how nodes decide which way to route packets between computing devices in a mobile ad hoc network12-Feb-1622

Three categories of ad hoc routing protocols Flat routing Hierarchical routing Hybrid (both proactive and reactive) routingGeographic position assisted routing

Again they are fall into two sub categoriesProactive protocolsReactive protocols 12-Feb-1623

Table-driven (proactive) routingThis type of protocols maintains fresh lists of destinationsand their routes by periodically distributing routing tablesthroughout the network.Examples of proactive algorithms are:Optimized Link State Routing Protocol (OLSR)Destination Sequence Distance Vector (DSDV)Advantage is that they can give QOS guarantees related tconnection setup, latency and other real time requirementsDisadvantage of proactive scheme are their overhead inLightly loaded networks, the algorithm generates a lot ofunnecessary traffic and drains the batteries of mobiledevice

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On-demand (reactive) routingThis type of protocols finds a route on demand by floodingThe network with Route Request packets. Advantage of scalability if there light traffic and low mobility,mobile device utilizes longer low power periods, they wake upfor data transmission or route discovery. The main disadvantages of such algorithms are:High latency time in route finding.Excessive flooding can lead to network clogging.Examples of on-demand algorithms are:Ad hoc On-demand Distance VectorDynamic Source Routing Flow State in the Dynamic Source RoutingPower-Aware DSR-based12-Feb-1625

Hybrid (both proactive and reactive) routingThis type of protocol combines the advantages of proactive andreactive routing. The routing is initially established with some proactively prospected routes and then serves the demand from additionally activated nodes through reactive flooding. The choice of one or the other method requires predetermination for typical cases. The main disadvantages of such algorithms are:Advantage depends on number of other nodes activated.Reaction to traffic demand depends on gradient of traffic volume.Examples of hybrid algorithms are:1.ZRP (Zone Routing Protocol) ZRP uses IARP as pro-active 2.IERP as reactive component.12-Feb-1626

Hierarchical routing protocolsWith this type of protocol the choice of proactive and of reactive routing depends on the hierarchic level in which a node resides. The routing is initially established with some proactively prospected routes and then serves the demand from additionally activated nodes through reactive flooding on the lower levels. The choice for one or the other method requires proper attributation for respective levels. The main disadvantages of such algorithms are:Advantage depends on depth of nesting and addressing scheme.Reaction to traffic demand depends on meshing parameters.Examples of hierarchical routing algorithms are:CBRP (Cluster Based Routing Protocol)FSR (Fisheye State Routing protocol)12-Feb-1627

Geographic routingGeographic routing (also called geo routing or position-based routing) is a routing principle that relies on geographic position information. It is mainly proposed for wireless networks and based on the idea that the source sends a message to the geographic location of the destination instead of using the network address. The idea of using position information for routing was first proposed in the 1980s in the area of packet radio networks and interconnection networks.Geographic routing requires that each node can determine its own location and that the source is aware of the location of the destination. With this information a message can be routed to the destination without knowledge of the network topology or a prior route discovery.12-Feb-1628

29Multicasting And MulticastRouting Protocols12-Feb-16

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In unicast routing, the router forwards the received packet through only one of its interfaces.Introduction: Unicasting

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MulticastingIn multicast routing, the router may forward the received packet through several of itsinterfaces.12-Feb-16

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Multicasting versus multiple unicasting

Emulation of multicasting through multiple unicasting is not efficient and may create long delays, particularly with a large group.12-Feb-16

33Application of MulticastingAccess to Distributed DatabasesInformation Dissemination: e.g. multicast software updates to customersNews DeliveryTeleconferencing, Web SeminarsDistant Learning12-Feb-16

34Multicast RoutingObjectivesEvery member receives EXACTLY ONE copy of the packetNon-members receive nothingNo loops in routeOptimal path from source to each destination.

TerminologySpanning Tree: Source is the root, group members are the leaves.Shortest Path Spanning Tree: Each path from root to a leaf is the shortest according to some metric12-Feb-16

35Multicast TreesSource-Based Tree:For each combination of (source , group), there is a shortest path spanning tree.Approach 1: DVMRP; an extension of unicast distance vector routing (e.g. RIP)Approach 2: MOSPF; an extension of unicast link state routing (e.g. OSPF)Group-Share TreeOne tree for the entire groupRendezvous-Point Tree: one router is the center of the group and therefore the root of the tree.CBT and PIM-SP protocols.12-Feb-16

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Multicast routing protocols12-Feb-16

37 Distance Vector Multicast Routing Protocol - DVMRPNo pre-defined route from source to destination. Tree is gradually created by successive routers along the path.Uses shortest path (fewest hops)Prevent loops: apply Reverse Path Forwarding (RFP)Prevent Duplication: apply Reverse Path Broadcasting (RPB)Multicast with dynamic membership: apply Reverse Path Multicasting (RPM) with pruning, grafting, and lifetime.12-Feb-16

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Reverse Path ForwardingIn reverse path forwarding (RPF), the router forwards only the packets that have traveled the shortest path from the source to the router; all other copies are discarded. No Loops12-Feb-16

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Reverse Path BroadcastingPrevent Duplication in RPF12-Feb-16

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RPF versus RPBThe router with the shortest path to the source becomes the designated parent of a networkA Router forwards packets only to its designated child networks12-Feb-16

41RPB creates a shortest path broadcast tree from the source to each destination. It guarantees that each destination receives one and only one copy of the packet. 12-Feb-16

42Figure 14-8

RPF, RPB, and RPMRPM adds pruning and grafting to RPB to create a multicast shortest path tree that supports dynamic membership changes.12-Feb-16

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MOSPF12-Feb-16

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Unicast tree and multicast tree12-Feb-16

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Core-Based TreeCBT12-Feb-16

46Figure 14-10

Shared-group tree with rendezvous router12-Feb-16

47Figure 14-11

Sending a multicast packet to the rendezvous router12-Feb-16

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In CBT, the source sends the multicast packet (encapsulated in a unicast packet) to the core router. The core router decapsulates the packet and forwards it to all interested hosts. 12-Feb-16

TCP for Wireless Networks12-Feb-1649

Outline Motivation TCP mechanisms Indirect TCP Snooping TCP Mobile TCP Fast retransmit/recovery Transmission freezing Selective retransmission Transaction oriented TCP

Adapted from J. Schiller, Mobile Communications, Chapter 1012-Feb-1650

Motivation Transport protocols typically designed forFixed end-systemsFixed, wired networksTCP congestion controlPacket loss in fixed networks typically due to (temporary) overload situations Routers discard packets as soon as the buffers are full TCP recognizes congestion only indirectly via missing acknowledgements Retransmissions unwise, they would only contribute to the congestion and make it even worseSlow-start algorithm as reaction12-Feb-1651

51How does TCP start: he doesnt know the sustainable rate of the network: slow start, mult decr./add incr.,

TCP Slow StartSender calculates a congestion window for a receiverStart with a congestion window size equal to one segmentExponential increase of the congestion window up to the congestion threshold, then linear increaseMissing acknowledgement causes the reduction of the congestion threshold to one half of the current congestion window Congestion window starts again with one segment

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TCP Fast Retransmit/RecoveryTCP sends an acknowledgement only after receiving a packetIf a sender receives several acknowledgements for the same packet, this is due to a gap in received packets at the receiverHowever, the receiver got all packets up to the gap and is actually receiving packetsTherefore, packet loss is not due to congestion, continue with current congestion window (do not use slow-start)12-Feb-1653

Influences of mobility on TCPTCP assumes congestion if packets are droppedtypically wrong in wireless networks, here we often have packet loss due to transmission errorsfurthermore, mobility itself can cause packet loss, if e.g. a mobile node roams from one access point (e.g. foreign agent in Mobile IP) to another while there are still packets in transit to the wrong access point and forwarding is not possibleThe performance of an unchanged TCP degrades severelyhowever, TCP cannot be changed fundamentally due to the large base of installation in the fixed network, TCP for mobility has to remain compatiblethe basic TCP mechanisms keep the whole Internet together12-Feb-1654

Indirect TCP IIndirect TCP or I-TCP segments the connectionno changes to the TCP protocol for hosts connected to the wired Internet, millions of computers use (variants of) this protocoloptimized TCP protocol for mobile hostssplitting of the TCP connection at, e.g., the foreign agent into 2 TCP connections, no real end-to-end connection any longerhosts in the fixed part of the net do not notice the characteristics of the wireless part

mobile hostaccess point (foreign agent)wired Internet

wireless TCP

standard TCP12-Feb-1655

I-TCP socket and state migration

mobile hostaccess point2 Internet

access point1

socket migrationand state transfer

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Indirect TCP IIAdvantagesno changes in the fixed network necessary, no changes for the hosts (TCP protocol) necessary, all current optimizations to TCP still worktransmission errors on the wireless link do not propagate into the fixed networksimple to control, mobile TCP is used only for one hop between, e.g., a foreign agent and mobile hosttherefore, a very fast retransmission of packets is possible, the short delay on the mobile hop is knownDisadvantagesloss of end-to-end semantics, an acknowledgement to a sender does not any longer mean that a receiver really got a packet, foreign agents might crashhigher latency possible due to buffering of data within the foreign agent and forwarding to a new foreign agent12-Feb-1657

Snooping TCP ITransparent extension of TCP within the foreign agentbuffering of packets sent to the mobile hostlost packets on the wireless link (both directions!) will be retransmitted immediately by the mobile host or foreign agent, respectively (so called local retransmission)the foreign agent therefore snoops the packet flow and recognizes acknowledgements in both directions, it also filters ACKschanges of TCP only within the foreign agent (+min. MH change)

wired Internet

buffering of dataend-to-end TCP connection

local retransmissioncorrespondenthostforeignagentmobilehost

snooping of ACKs12-Feb-1658

Snooping TCP IIData transfer to the mobile hostFA buffers data until it receives ACK of the MH, FA detects packet loss via duplicated ACKs or time-outfast retransmission possible, transparent for the fixed networkData transfer from the mobile hostFA detects packet loss on the wireless link via sequence numbers, FA answers directly with a NACK to the MHMH can now retransmit data with only a very short delayAdvantages:Maintain end-to-end semanticsNo change to correspondent nodeNo major state transfer during handoverProblemsSnooping TCP does not isolate the wireless link wellMay need change to MH to handle NACKsSnooping might be useless depending on encryption schemes12-Feb-1659

Mobile TCPSpecial handling of lengthy and/or frequent disconnectionsM-TCP splits as I-TCP doesunmodified TCP fixed network to supervisory host (SH)optimized TCP SH to MHSupervisory hostno caching, no retransmissionmonitors all packets, if disconnection detectedset sender window size to 0sender automatically goes into persistent modeold or new SH reopen the windowAdvantagesmaintains semantics, supports disconnection, no buffer forwardingDisadvantagesloss on wireless link propagated into fixed networkadapted TCP on wireless link

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60Problems with timer that can grow to 1min even if the connection comes back

How is the timer computed in TCP

Fast retransmit/fast recoveryChange of foreign agent often results in packet loss TCP reacts with slow-start although there is no congestionForced fast retransmitas soon as the mobile host has registered with a new foreign agent, the MH sends duplicated acknowledgements on purposethis forces the fast retransmit mode at the communication partnersadditionally, the TCP on the MH is forced to continue sending with the actual window size and not to go into slow-start after registrationAdvantagesimple changes result in significant higher performance Disadvantagefurther mix of IP and TCP (to know when there is a new registration), no transparent approach12-Feb-1661

Transmission/time-out freezingMobile hosts can be disconnected for a longer timeno packet exchange possible, e.g., in a tunnel, disconnection due to overloaded cells or mux. with higher priority trafficTCP disconnects after time-out completelyTCP freezingMAC layer is often able to detect interruption in advanceMAC can inform TCP layer of upcoming loss of connectionTCP stops sending, but does not assume a congested link MAC layer signals again if reconnected Advantagescheme is independent of data and TCP mechanisms (Ack,SN) => works even with IPsecDisadvantageTCP on mobile host has to be changed, mechanism depends on MAC layer12-Feb-1662

Selective retransmissionTCP acknowledgements are often cumulativeACK n acknowledges correct and in-sequence receipt of packets up to nif single packets are missing quite often a whole packet sequence beginning at the gap has to be retransmitted (go-back-n), thus wasting bandwidthSelective retransmission as one solutionRFC2018 allows for acknowledgements of single packets, not only acknowledgements of in-sequence packet streams without gapssender can now retransmit only the missing packetsAdvantage: much higher efficiencyDisadvantagemore complex software in a receiver, more buffer needed at the receiver12-Feb-1663

63Check RFC2018

Transaction oriented TCPTCP phasesconnection setup, data transmission, connection release using 3-way-handshake needs 3 packets for setup and release, respectivelythus, even short messages need a minimum of 7 packets!Transaction oriented TCPRFC1644, T-TCP, describes a TCP version to avoid this overheadconnection setup, data transfer and connection release can be combinedthus, only 2 or 3 packets are neededAdvantageefficiencyDisadvantagerequires changed TCPmobility no longer transparent 12-Feb-1664

ReferencesBook: Wireless Communications and Networks by William Stallings PPT: WilliamStalling.com/StudentsSupport.html.http://www.wirelesscommunication.nl/reference/about.htm

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THANK YOU12-Feb-1612-Feb-1666