1. Chapter 8: Mobile Network Layer

2. Introduction of Mobile IP Background- The Problem with Old IPs: Earlier internet protocol versions do not support host mobility. These were designed such that moving hosts were not considered : a node’s point of attachment to the network remains unchanged at all times and an IP address identifies a particular network. To support a mobile host with current methods, reconfiguration is necessary any time a mobile host moves.

3. Introduction of Mobile IP This is an unacceptable solution as it is time consuming and error prone. Thus the rise of “Mobile IP”.

4. What is Mobile IP? Mobile IP is an internet protocol designed to support host mobility. Its goal is to provide the ability of an host to stay connected to the internet regardless of their location. Mobile IP is able to track a mobile host without needing to change the mobile host’s long-term IP address.

5. Mobile IP Features Transparency mobile end-systems keep their IP address. continuation of communication after interruption of link possible. point of connection to the fixed network can be changed. Compatibility no changes to current end-systems and routers required. mobile end-systems can communicate with fixed systems.

6. Mobile IP Features Security authentication of all registration messages. Efficiency and scalability only little additional messages to the mobile system required (connection typically via a low bandwidth radio link). world-wide support of a large number of mobile systems in the whole Internet.

7. Terminology Mobile Node (MN): A host or router that may change its point of attachment from one network or sub network to another through the internet. This entity is reassigned a fixed home address on a home network, which other correspondent hosts will use to address their packets to regardless of its current location.

8. Terminology Home Agent (HA): A router that maintain a list of registered mobile nodes in a visitor list. It is used to forward mobile node-address packets to the appropriate local network when the mobile nodes are away from home. After checking with the current mobility bindings for a particular mobile node. It encapsulated datagram and sends it to the mobile host’s current temporary address when the mobile node.

9. Terminology Foreign Agent (FA): A router that assists a locally reachable mobile node that is away from its home network. It delivers information between the mobile node and the home agent. Correspondent Node (CN): This node sends the packets which are addressed to the communication partner.

10. Terminology Care-of-address (COA): An address which identifies the mobile node’s current location. It can be viewed as the end of a tunnel directed towards a mobile node. It can be either assigned dynamically or associated with its foreign agent.

11. Terminology CN router HA router FA Internet router home network MN foreign network COA

12. Example network mobile end-system Internet router end-system FA HA MN home network foreign network (physical home network for the MN) (current physical network for the MN) CN

13. IP Packet Delivery CN router HA router FA Internet router 1. 2. 3. home network MN foreign network 4.

14. IP Packet Delivery Step 1: the CN wants to send an IP packet to the MN. But CN does not know about the current location of MN’s. here, MN is not a part of HA. Step 2: a new header is put in front of the old IP header showing the COA as new destination and HA as source of the encapsulated packet. Step 3:the foreign agent now decapsulates the packet i.e. removes the additional header and forwards the original packet with CN as source and MN as destination to the MN. Step 4:the MN sends the packet as usual with its own fixed IP address as source and CN’s address as destination.

15. Agent Discovery One initial problem of an MN after moving is how to find a agent. How does the MN discover that its has moved? For this purpose mobile IP describes two methods: Agent Advertisement Agent Solicitation

16. Agent Advertisement HA and FA periodically send advertisement messages into their physical subnets. MN listens to these messages and detects, if it is in the home or a foreign network (standard case for home network). MN reads a COA from the FA advertisement messages.

17. type = 16 length = 6 + 4 * #COAs R: registration required B: busy, no more registrations H: home agent F: foreign agent M: minimal encapsulation G: GRE encapsulation r: =0, ignored (former Van Jacobson compression) T: FA supports reverse tunneling reserved: =0, ignored Agent advertisement Packet preference level 1 router address 1 #addresses type addr. sizelifetime checksum COA 1 COA 2 type = 16sequence numberlength 0 781516312423 code preference level 2 router address 2... registration lifetime... RBHFMGr reserved T

18. Agent Solicitation if no agent advertisement are present or the inter- arrival time is too high and the MN has not received a COA by other reason. So, the mobile node must send the Agent Solicitations. These solicitation messages do not flood the network but basically an MN can search for an FA endlessly sending out solicitation messages.

19. Registration When the mobile node is away from home, it registers its care-of-address with its home agent so that home agent knows where to forward its packets. Depending on the network configuration the mobile node could either register directly with its home agent, or indirectly via the help of its foreign agent.

20. Registration In short, MN signals COA to the HA via the FA, HA acknowledges via FA to MN. These actions have to be secured by authentication.

21. Registration t MN HA registration request registration reply t MN FAHA registration request registration request registration reply registration reply Other Network Registration Same Network Registration

22. Mobile IP registration request home agent home address type = 1lifetime 0 781516312423 T x identification COA extensions... SBDMGr S: simultaneous bindings B: broadcast datagrams D: decapsulation by MN M mininal encapsulation G: GRE encapsulation r: =0, ignored T: reverse tunneling requested x: =0, ignored

23. Mobile IP registration reply home agent home address type = 3 lifetime 0 78151631 code identification extensions... Example codes: registration successful 0 registration accepted 1 registration accepted, but simultaneous mobility bindings unsupported registration denied by FA 65 administratively prohibited 66 insufficient resources 67 mobile node failed authentication 68 home agent failed authentication 69 requested Lifetime too long registration denied by HA 129 administratively prohibited 131 mobile node failed authentication 133 registration Identification mismatch 135 too many simultaneous mobility bindings

24. Tunneling Tunneling refers to establishing of a pipe. Pipe is a term used to specify a data stream between two connected ends. For e.g. when a mobile node is roaming in a foreign network, the home agent must be able to intercept all IP datagram packets sent to the mobile node so that these datagrams can be forwarded via tunneling.

25. Tunneling There are two type of Tunnel: Forward Tunnel: A tunnel that shuttles packets towards the mobile node. Its starts at the home agent, and ends at the mobile node’s care-of-address. Reverse Tunnel: A tunnel that start at the mobile node’s care-of- address and terminates at the home agent.

26. Forward Tunneling Internet sender FA HA MN home network foreign network receiver 1 2 3 1. Sender sends to the IP address of MN, HA intercepts packet. 2. HA tunnels packet to COA, here FA, by encapsulation. 3. FA forwards the packet to the MN. CN

27. Reverse Tunneling Internet receiver FA HA MN home network foreign network sender 3 2 1 1. MN sends to FA 2. FA tunnels packets to HA by encapsulation 3. HA forwards the packet to the receiver (standard case) CN

28. Mobile IP with reverse Tunneling Router accept often only “topological correct“ addresses (firewall!) a packet from the MN encapsulated by the FA is now topological correct furthermore multicast and TTL (Time to Live) problems solved (TTL in the home network correct, but MN is to far away from the receiver) Reverse tunneling does not solve problems with firewalls, the reverse tunnel can be abused to circumvent security mechanisms (tunnel hijacking)

29. Mobile IP with reverse Tunneling optimization of data paths, i.e. packets will be forwarded through the tunnel via the HA to a sender (double triangular routing) The standard is backwards compatible the extensions can be implemented easily and cooperate with current implementations without these extensions Agent Advertisements can carry requests for reverse tunneling

30. Encapsulation Encapsulation: The process of enclosing an IP datagram within another IP header which contains the care-of- address of the mobile node. The IP datagram itself remains intact and untouched throughout the enclosing process. Decapsulation: The process of stripping the outermost IP header of incoming packets so that the enclosed datagram can be accessed and delivered to the proper destination. Decapsulation is the reverse process of encapsulation.

31. Encapsulation Types IP in IP Encapsulation Minimal Encapsulation Generic routing Encapsulation

32. IP in IP Encapsulation To encapsulate an IP datagram using IP in IP encapsulation, an outer IP header is inserted before the datagram’s existing IP header. There is tunnel between HA to COA.

33. IP in IP Encapsulation Care-of address COA IP address of HA TTL IP identification IP-in-IPIP checksum flagsfragment offset lengthDS (TOS)ver.IHL IP address of MN IP address of CN TTL IP identification lay. 4 prot.IP checksum flagsfragment offset lengthDS (TOS)ver.IHL TCP/UDP/... payload

34. Minimal Encapsulation Minimal encapsulation (optional) avoids repetition of identical fields. e.g. TTL-time to live, version, DS-distributed system (RFC (request for comment) 2474, old: TOS-type of services). only applicable for non fragmented packets, no space left for fragment identification.

35. Minimal Encapsulation care-of address COA IP address of HA TTL IP identification min. encap.IP checksum flagsfragment offset lengthDS (TOS)ver.IHL IP address of MN original sender IP address (if S=1) Slay. 4 protoc.IP checksum TCP/UDP/... payload reserved

36. Generic routing Encapsulation In the most general case, a system has a packet that needs to be encapsulated and delivered to some destination. We call this the payload packet. The payload is first encapsulated in a GRE packet. The resulting GRE packet can then be encapsulated in some other protocol and then forwarded.

37. Generic routing Encapsulation We call this outer protocol the delivery protocol. This specification is generally concerned with the structure of the GRE header.

38. Generic routing Encapsulation original header original data new datanew header outer header GRE header original data original header Care-of address COA IP address of HA TTL IP identification GREIP checksum flagsfragment offset lengthDS (TOS)ver.IHL IP address of MN IP address of CN TTL IP identification lay. 4 prot.IP checksum flagsfragment offset lengthDS (TOS)ver.IHL TCP/UDP/... payload routing (optional) sequence number (optional) key (optional) offset (optional)checksum (optional) protocolrec.rsv.ver.CRKSs RFC 1701 RFC 2784 (updated by 2890) reserved1 (=0)checksum (optional) protocolreserved0ver.C

39. Optimization of packet forwarding Problem: Triangular Routing sender sends all packets via HA to MN higher latency and network load “Solutions” sender learns the current location of MN direct tunneling to this location HA informs a sender about the location of MN big security problems!

40. Optimization of packet forwarding Change of FA packets on-the-fly during the change can be lost new FA informs old FA to avoid packet loss, old FA now forwards remaining packets to new FA this information also enables the old FA to release resources for the MN

41. Optimization of packet forwarding CN HAFA old FA new MN MN changes location t Data Update ACK Data Registration Update ACK Data Warning Request Update ACK Data

42. Mobile IPv6 Mobile IP is the internet’s network-layer protocol. Mobile IP provides best-effort, connectivity packet delivery on behalf of transport-layer and higher- layer protocols. There is different version of Internet Protocol. In that IP version 6 the successor to today’s IP version 4 protocol. IPv6 protocol expands the available address space for each packet and support of the internet security protocol.

43. Problem with Mobile IP Security authentication with FA problematic, for the FA typically belongs to another organization no protocol for key management and key distribution has been standardized in the Internet patent and export restrictions Firewalls typically mobile IP cannot be used together with firewalls, special set-ups are needed (such as reverse tunneling)

44. Problem with Mobile IP QoS many new reservations in case of RSVP tunneling makes it hard to give a flow of packets a special treatment needed for the QoS

45. IP Micro-Mobility Support Mobile IP exhibits several problems regarding the duration of handover and the scalability of the registration procedure. Assuming a large number of mobile devices changing networks quite frequently a high load on the home agents as well as on the network is generated by registration and binding update messages.

46. IP Micro-Mobility Support IP micro-mobility protocols can complement mobile IP by offering fast and almost seamless handover control in limited geographical area. The following three approaches to the solutions of the micro-mobility problems. Cellular IP Hawaii Hierarchical Mobile IPv6 (HMIPv6)

47. Cellular IP Operation: “CIP Nodes” maintain routing entries for MNs Multiple entries possible Routing entries updated based on packets sent by MN CIP Gateway: Mobile IP tunnel endpoint Initial registration processing

48. Cellular IP Security provisions: all CIP Nodes share “network key” MN key: net key, IP addr MN gets key upon registration

49. Cellular IP CIP Gateway Internet BS MN1 data/control packets from MN 1 Mobile IP BS MN2 packets from MN2 to MN 1

50. Cellular IP Advantage: Manageability: Cellular IP is mostly self-configuring and integration of Cellular IP gateway (CIPGW) into a firewall would facilitate administration of mobility- related functionality.

51. Cellular IP Disadvantages: Efficiency: Additional network load is induced by forwarding packets on multiple paths. Transparency: Changes to MNs are required. Security: Routing table are changed based on messages sent by mobile node. Additionally all system in the network can easily obtain a copy of all packets destined for an MN.

52. Hawaii- Handoff- Aware Wireless Access Internet Infrastructure Operation: MN obtains co-located COA and registers with HA. Handover: MN keeps COA, new BS answers Reg. Request and updates routers MN views BS as foreign agent Security provisions: MN-FA authentication mandatory Challenge/Response Extensions mandatory 4 3 12

53. Hawaii BS 3 Backbone Router Internet BS MN BS MN Crossover Router DHCP Server HA DHCP Mobile IP 1 2 4

54. Hawaii Advantages: Security: Challenge-response extensions are mandatory. In contrast to cellular IP routing changes are always initiated by the foreign domain’s infrastructure. Transparency: HAWAII is mostly transparent to mobile nodes.

55. Hawaii Disadvantages: Security: There are no provision regarding the setup of IPSec (IP security) tunnels. Implementation: No private address support is possible because of co-located COAs.

56. Hierarchical Mobile IPv6 (HMIPv6) Operation: Network contains mobility anchor point (MAP) mapping of regional COA (RCOA) to link COA (LCOA) Upon handover, MN informs MAP only gets new LCOA, keeps RCOA HA is only contacted if MAP changes Security provisions: no HMIP-specific security provisions binding updates should be authenticated

57. Hierarchical Mobile IPv6 (HMIPv6) MAP-mobility anchor point AR-Access router RCOA- regional COA LCOA- link COA MAP Internet AR MN AR MN HA binding update RCOA LCOA old LCOA new

58. Hierarchical Mobile IPv6 (HMIPv6) Advantages: Security: MNs can have location privacy because LCOAs can be hidden. Efficiency: Direct routing between CNs sharing the same link is possible.

59. Hierarchical Mobile IPv6 (HMIPv6) Disadvantages: Transparency: Additional infrastructure component (MAP). security: Routing tables are changed based on messages sent by mobile nodes. This requires strong authentication and protection against denial or service attacks. Additional security function might be necessary in MAPs.

60. DHCP: Dynamic Host Configuration Protocol Application simplification of installation and maintenance of networked computers. supplies systems with all necessary information, such as IP address, DNS server address, domain name, subnet mask, default router etc. enables automatic integration of systems into an Intranet or the Internet, can be used to acquire a COA for Mobile IP.

61. DHCP: Dynamic Host Configuration Protocol Client/Server-Model the client sends via a MAC broadcast a request to the DHCP server (might be via a DHCP relay). clientrelay clientserver DHCPDISCOVER

62. DHCP - protocol mechanisms time server (not selected) client server (selected) initialization collection of replies selection of configuration initialization completed release confirmation of configuration delete context determine the configuration DHCPDISCOVER DHCPOFFER DHCPREQUEST (reject) DHCPACK DHCPRELEASE DHCPDISCOVER DHCPOFFER DHCPREQUEST (options) determine the configuration

63. DHCP characteristics Server several servers can be configured for DHCP, coordination not yet standardized (i.e., manual configuration). Renewal of configurations IP addresses have to be requested periodically, simplified protocol. Options available for routers, subnet mask, NTP (network time protocol) timeserver, SLP (service location protocol) directory, DNS (domain name system)

64. Mobile Ad-hoc Network Mobility support described in earlier section so far relies on the existence of at least some infrastructure. Mobile IP requires, e.g., a home agent, tunnels and default routers. DHCP requires servers and broadcast capabilities of the medium reaching all participants or relays to servers. Cellular phone networks require base stations, infrastructure networks etc.

65. Mobile Ad-hoc Network However, there are several situations where users of a network cannot rely on an infrastructure, the infrastructure is too expensive, or there is no infrastructure at all. In these situation ad hoc networks are the only solution.

66. Solution: Wireless Ad-hoc Network Single-hop: All partners max. one hop apart Bluetooth piconet, PDAs in a room, gaming devices… Multi-hop: Cover larger distances, circumvent obstacles Bluetooth scatternet, car-to-car networks… Internet: MANET (Mobile Ad-hoc Networking) group

67. Mobile Ad-hoc Network Example for the use of ad hoc networks are: Instant infrastructure: Unplanned meetings, spontaneous interpersonal communication etc. cannot rely on any infrastructure. Infrastructures need planning and administration. It would take too long to set up this kind of infrastructure therefore, ad hoc connectivity has to be set up.

68. Mobile Ad-hoc Network Disaster relief: Infrastructures typically break down in disaster areas. Hurricanes cut phone and power lines, floods destroy base stations, fires bum servers. Thus, emergency teams can only rely on an Infrastructures they can set up themselves. No forward planning can be done and the setup must be done extremely fast and reliably.

69. Mobile Ad-hoc Network Remote area: Even if Infrastructures could be planned ahead, it is some times too expensive to set up an Infrastructures in sparsely populated area. Depending on the communication pattern ad hoc networks or satellite Infrastructures can be a solution.

70. Mobile Ad-hoc Network Effectiveness: Services of existing Infrastructures might be too expensive for certain application. If for example, only connection-oriented cellular networks exist, but an application sends only a small status information every other minute, a cheaper ad hoc packet-oriented network might be a better solution. Furthermore, registration procedures might take too long and communication overhead, so ad hoc network can offer a better solution.

71. Manet: Mobile Ad-hoc Networking Fixed Network Mobile Devices Mobile Router Manet Mobile IP, DHCP RouterEnd system

72. Routing While in wireless networks with infrastructure support a base station always reaches all mobile nodes, this is not always the case in an ad hoc network. A destination node might be out of range of a source node transmitting packets. Thus routing in needed to find a path between source and destination and to forward the packets appropriately.

73. Routing In wireless networks using infrastructure cells have been defined. Within a cell, the base station can reach all mobile nodes without routing via a broadcast. In the case of ad hoc networks each node must be able to forward data for other nodes.

74. Routing In the next slide figure show at a certain time t1 the network topology might look as illustrated on the left side of the figure. Five nodes, N1 to N5 are connected depending on current transmission characteristic between them. In this snapshot of the network, N4 can receive N1 over a good link, but N1 receives N4 only via a weak link.

75. Routing Example of ad hoc network good link weak link time = t 1 time = t 2 N1N1 N4N4 N2N2 N5N5 N3N3 N1N1 N4N4 N2N2 N5N5 N3N3

76. Routing Thus links do not necessarily have the same characteristics in both direction. Reasons for this are e.g. different antenna characteristics or transmit power. N1 cannot receive N2 at all, N2 receives a signal from N1. This situation can change in the next snapshot at t2 showns.

77. Routing This very simple example already shows some fundamental differences between wired networks and ad hoc wireless networks related to routing. Asymmetric links: If node A receives a signal from node B this does not tell anything about the quality of the connection in the reverse direction. B might receive nothing have a weak link or even have a better link than the reverse direction.

78. Routing Thus routing information collected for one direction is of almost no use for the other direction. However, many routing algorithms for wired networks rely on a symmetric scenario.

79. Routing Redundant links: Wired networks have redundant links to survive link failures. However, there is only some redundancy in wired networks, which additionally is controlled by a network administrator. In ad hoc networks nobody controls redundancy so there might be many redundant links up to the extreme of a completely meshed topology.

80. Routing Routing algorithms for wired networks can handle some redundancy but a high redundancy can cause a large computational overhead for routing table updates.

81. Routing Interference: In wired networks links exist only where a wire exists and connections are planned by network administrators. This is not the case for wireless ad hoc networks. Links come and go depending on transmission characteristics one transmission might interfere with another one and nodes might overhear transmissions of other nodes.

82. Routing Interference thus creates new problems by ‘unplanned’ links between nodes: if two close-by nodes forwarded two transmissions, they might interfere and destroy each other. Interference might also help routing on the other hand. A node can learn the topology with the help of packets overheard.

83. Routing Dynamic topology: The greatest problem for routing arises form the highly dynamic topology. The mobile nodes might change frequently. This result in frequent changes in topology, and valid only for a short period of time. In ad hoc networks routing tables must somehow reflect these frequent change in topology and routing algorithms have to be adapted.

84. Traditional Routing Algorithms Distance Vector periodic exchange of messages with all physical neighbors that contain information about who can be reached at what distance. selection of the shortest path if several paths available. Link State periodic notification of all routers about the current state of all physical links. router get a complete picture of the network.

85. Problems of traditional routing algorithms Dynamic of the topology frequent changes of connections, connection quality, participants. Limited performance of mobile systems periodic updates of routing tables need energy without contributing to the transmission of user data, sleep modes difficult to realize. limited bandwidth of the system is reduced even more due to the exchange of routing information. links can be asymmetric, i.e., they can have a direction dependent transmission quality.

86. Destination Sequence Distance Vector (DSDV) Destination sequence distance vector routing is an enhancement to distance vector routing for ad hoc networks. Distance vector routing is used as RIP in wired networks. It performs extremely poorly with certain network changes due to the count-to-infinity problem. Each node exchanges its neighbor table periodically with its neighbors.

87. Destination Sequence Distance Vector The strategies to avoid this problem which are used in fixed network do not help in the case of wireless ad hoc networks, due to the rapidly changing topology. Effects might be the creation of loops or unreachable regions within the network.

88. Destination Sequence Distance Vector DSDV now adds two things to the distance vector algorithm: Sequence numbers: Each rouging advertisement comes with a sequence number. Within ad hoc networks advertisements may propagate along many paths. Sequence numbers help to apply the advertisements in correct order. This avoids loops that are likely with the unchanged distance vector algorithm.

89. Destination Sequence Distance Vector Damping: Transient changes in topology that are of short duration should not destabilize the routing mechanisms. Advertisements containing changes in the topology currently stored are therefore not disseminated further. A node waits with dissemination if these changes are most likely not yet stable. Waiting time depends on the time between the first and the best announcement of a path to a certain destination.

90. Destination Sequence Distance Vector The routing table for N1 in routing topic slide figure as shown in table. DestinationNext HopMetric N1 0 N2 1 N3N22 N4 1 N5N42 Fig: Part of a routing table for DSDV

91. Dynamic Source Routing Imagine what happens in an ad hoc network where nodes exchange packets from time to time i.e. the network is only lightly loaded, and DSDV or one of the traditional distance vector or link state algorithms is used for updating routing tables. Although only some user data has to be transmitted the nodes exchange routing information to keep track of the topology.

92. Dynamic Source Routing These algorithms maintain routes between all nodes, although may be there is currently nod data exchange at all. This causes unnecessary traffic and prevents nodes from saving battery power.

93. Dynamic Source Routing Dynamic source routing therefore divides the task of routing into two separate problems. Route Discovery: A node only tries to discover a route to a destination if it has to send something to this destination and there is currently no known route.

94. Dynamic Source Routing Route Maintenance: If a node is continuously sending packets via a route, it has to make sure that the route is held upright. As soon as a node detects problems with the current route, it has to find an alternative route.

95. Dynamic Source Routing The basic principle of source routing is also used in fixed networks, e.g. token rings. Dynamic source routing eliminates all periodic routing updates and works as follows. If a node needs to discover a route, if broadcast a route request with a unique identifier and the destination address as parameters.

96. Dynamic Source Routing Any node that receives a rout request does the following: if the station is the receiver (i.e., has the correct destination address) then return the packet to the sender (path was collected in the packet). if the packet has already been received earlier (identified via ID) then discard the packet. otherwise, append own address and broadcast packet.

97. DSR: Route Discovery B A C G I D K L E H FJ Q P M N O R Sending from C to O

98. DSR: Route Discovery Broadcast B A C G I D K L E H FJ Q P M N O R [O,C,4711]

99. DSR: Route Discovery B A C G I D K L E H FJ Q P M N O R [O,C/G,4711] [O,C/B,4711] [O,C/E,4711]

100. DSR: Route Discovery B A C G I D K L E H FJ Q P M N O R [O,C/G/I,4711] [O,C/B/A,4711] [O,C/B/D,4711] [O,C/E/H,4711] (alternatively: [O,C/E/D,4711])

101. DSR: Route Discovery B A C G I D K L E H FJ Q P M N O R [O,C/B/D/F,4711] [O,C/G/I/K,4711] [O,C/E/H/J,4711]

102. DSR: Route Discovery B A C G I D K L E H FJ Q P M N O R [O,C/E/H/J/L,4711] (alternatively: [O,C/G/I/K/L,4711]) [O,C/G/I/K/M,4711]

103. DSR: Route Discovery B A C G I D K L E H FJ Q P M N O R [O,C/E/H/J/L/N,4711]

104. DSR: Route Discovery B A C G I D K L E H FJ Q P M N O R Path: M, K, I, G

105. Dynamic Source Routing Maintaining paths after sending a packet wait for a layer 2 acknowledgement (if applicable). listen into the medium to detect if other stations forward the packet (if possible). request an explicit acknowledgement. if a station encounters problems it can inform the sender of a packet or look-up a new path locally.

106. Alternative Metrics The examples shown in this chapter always use the number of hops as routing metric. Although very simple, especially in wireless ad hoc network, this is not always the best choice. Even for fixed networks, e.g bandwidth can also be factor for the routing metric. Due to the varying link quality and the fact that different transmissions can interfere, other metrics can be more useful.

107. Alternative Metrics Routing based on assumptions about interference between signals. S1S1 N5N5 N3N3 N4N4 N1N1 N2N2 R1R1 R2R2 N6N6 N8N8 S2S2 N9N9 N7N7 neighbors (i.e. within radio range)

108. Alternative Metrics Examples for interference based routing Least Interference Routing (LIR) calculate the cost of a path based on the number of stations that can receive a transmission Max-Min Residual Capacity Routing (MMRCR) calculate the cost of a path based on a probability function of successful transmissions and interference Least Resistance Routing (LRR) calculate the cost of a path based on interference, jamming and other transmissions

109. Alternative Metrics LIR is very simple to implement, only information from direct neighbors is necessary. Previous slide figure shows an ad hoc network topology. Sender S1 wants to send a packet to receiver R1. Using the hop count as metric, S1 could choose three different paths with three hops which is also the minimum. Here mention the cost of each nodes: S1=3,N1=3,N2=4,N3=6,N4=5,R1=2

110. Dynamic Source Routing C1=cost(S1,N3,N4,R1)=16, C2=cost(S1,N3,N2,R1)=15, C3=cost(S1,N1,N2,R1)=12 All three paths have the same number of hops, but the last path has the lowest cost due to interference. Thus S1 chooses (S1,N1,N2,R1).

111. Overview of ah-hoc Routing protocols: Flat ad-hoc routing Flat ad-hoc routing protocol comprise those protocols that do not set up hierarchies with clusters of nodes. Special nodes acting as the head of a cluster or different routing algorithms inside or outside certain regions. All nodes in this approach play an equal role in routing. The addressing scheme is flat.

112. Overview of ah-hoc Routing protocols: Flat ad-hoc routing This category again falls into subcategories: Proactive protocols: it is set up tables required for routing regardless of any traffic that would require routing functionality. The following protocols supported to this group: Fisheye state routing & Fuzzy sighted link state: They making the update period dependent on the distance to a certain hop.

113. Overview of ah-hoc Routing protocols: Flat ad-hoc routing Topology broadcast based on reverse path forwarding &Optimized link state routing: They try to reduce the traffic caused by link state information dissemination.

114. Overview of ah-hoc Routing protocols: Flat ad-hoc routing Advantages: They can give QOS guarantees related to connection set-up, latency or other real time requirements. Disadvantages: Their overheads in lightly loaded networks.

115. Overview of ah-hoc Routing protocols: Flat ad-hoc routing Reactive protocols: It is try to avoid this problem by setting up a path between sender and receiver only if a communication is waiting. The following protocols supported to this group: Dynamic source routing (DSR) & ad-hoc on- demand distance vector (AODV): AODA acquires and maintains routes only on demand link DSR nodes.

116. Overview of ah-hoc Routing protocols: Flat ad-hoc routing Advantages: A clear advantage of on-demand protocols is scalability as long as there is only light traffic and low mobility. Disadvantages: These protocols also exhibit disadvatages.

117. Overview of ah-hoc Routing protocols: Hierarchical ad-hoc routing Algorithms such as DSDV,AODV and DSR only work for a smaller number of nodes and depend heavily on the mobility of nodes. For larger networks, clustering of nodes and using different routing algorithms between and within clusters can be a scalable and efficient solution. The motivation behind this approach is the locality property meaning that if a cluster can be established nodes typically remain within a cluster, only some change clusters.

118. Overview of ah-hoc Routing protocols: Hierarchical ad-hoc routing If the topology within a cluster changes, only nodes of the cluster have to be informed. Nodes of other clusters only need to know how to reach the cluster. Clusters can be combined to form super clusters etc, building up a larger hierarchy. Using this approach one or more nodes can act as cluster heads, representing a router for all traffic to/from the cluster.

119. Overview of ah-hoc Routing protocols: Hierarchical ad-hoc routing All nodes within the cluster and all other cluster heads use these as gateway for the cluster. Different routing protocols may be used inside and outside clusters: Cluster head-Gateway Switch routing (CGSR): it is a typical representative of hierarchical routing algorithm based on distance vector (DV) routing. Hierarchical state routing: it is base on link-state principle. This applies the principle of clustering recursively, creating multiple levels of clusters and cluster of clusters etc.

120. Overview of ah-hoc Routing protocols: Hierarchical ad-hoc routing Zone routing protocol (ZRP): it is a hybrid hierarchical routing protocol. Each node using ZRP has predefined zone with the node as the center. The zone comprises all other nodes within a certain hop-limit. Proactive routing is applied within the zone while no-demand routing is used outside the zone.

121. Overview of ah-hoc Routing protocols: Geographic-position-assisted ad-hoc routing If mobile nodes know their geographical position this can be used for routing purposes. This improves the overall performance of routing algorithms if geographical proximity also means radio proximity. The following protocols supported to Geographic- position-assisted: GeoCast: It allows messages to be sent to all nodes in a specific region. It is based on geographic information instead of logical number.

122. Overview of ah-hoc Routing protocols: Geographic-position-assisted ad-hoc routing Location-aided routing: this protocol is similar to Dynamic source routing (DSR) but limits rout discovery to certain geographical regions. Greedy perimeter stateless routing: It is based on location information. This used only the location information of neighbors that are exchanged via periodic beacon messages or via piggybacking in data packets.