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Ad hoc communication #3/3

Ad hoc communication #3/3. Course element content for Ad hoc. Lecture 1 (Ad hoc concept and networking overview) Ad hoc concept Ad hoc basic functionality Ad hoc possible usage areas Background of ad hoc Networking: OSI, Protocols, routing, TCP/IP Project description (briefly)

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Ad hoc communication #3/3

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  1. Ad hoc communication #3/3

  2. Course element content for Ad hoc • Lecture 1 (Ad hoc concept and networking overview) • Ad hoc concept • Ad hoc basic functionality • Ad hoc possible usage areas • Background of ad hoc • Networking: OSI, Protocols, routing, TCP/IP • Project description (briefly) • Lecture 2 (Networking and routing in depth) • TCP/IP in depth • Routing protocols: purpose, conceptual function and review • Standardization work: IETF, IEEE current protocols • Additional ad hoc routing features • Lecture 3 (Advanced concepts) • MAC layer • ARP • Quality of Service (QoS): SNR, Bandwidth constraints, Neighbor solicitation errors • IPv6 • Security considerations Ad hoc communication: Concept, OSI and TCP/IP

  3. IEEE 802.11a Data rate Modulation Coding rate 6 BPSK ½ 9 BPSK ¾ 12 4-QAM ½ 802.11 phy Defines a series of encoding and transmission schemes 18 4-QAM ¾ 24 16-QAM ½ FHHS (802.11 2Mbps) DSSS (802.11b 11Mbps) OFDM (802.11a 54Mbps) 36 16-QAM ¾ 48 64-QAM ½ 54 64-QAM ¾ OSI layer 1 802.11 PHY Sublayer Defines the physical and electrical characteristics of the network. The NIC cards in your PC and the interfaces on your routers all run at this level since, eventually, they have to pass strings of ones and zeros down the wire! Examples of modulation and data rates Examples:Ethernet/802.3   Token Ring (802.5) SNAP/802.2 X.25 FDDI ISDN Frame Relay   SMDS   ATM   Wireless (WAP, CDPD, 802.11) Fibre Channel   DDS/DS0/T-carrier/E-carrier   SONET/SDH   DWDMPPP   HDLC   SLIP/CSLIP   xDSL   Cable Modem (DOCSIS)

  4. 0-2312 FrameControl Duration/ ID Address 1 Address 2 Address 3 SequenceControl Address 4 Frame Body FCS MAC Header 4 2 6 2 6 6 6 2 2 bits 2 1 1 1 1 1 1 1 4 1 Protocol Version Type Subtype To DS From DS More Fragments Retry Power Mgt. More data WEP Order OSI layer 2 MAC 802.11 MAC Frame The 802.11 MAC frame, as shown in the following figure, consists of a MAC header, the frame body, and a frame check sequence (FCS). The numbers in the following figure represent the number of bytes for each field. 802.11 MAC Frame Format Frame Control Field

  5. 802.11 MAC Layer Overhead Network Capacity Approximations for 802.11b, 802.11g and 802.11a Source: Cisco Systems, Inc.

  6. OSI reference model ARP

  7. Address Resolution Protocol (ARP) • ARP translates Ethernet addresses (MAC) to Internet Protocol addresses (IP) • Data communication (IPv4) is initiated by ARP messages. • ARP messages are sent automatically. • Has been deprecated in IPv6 and replaced by the Neighbor Discovery Protocol (NDP) which is a pure layer 4 protocol.

  8. ARP Illustrated by Ping Example Node: 1IP Address: 192.168.0.1MAC Address: 00-0D-56-3C-DE-C0 Node: 2IP Address: 192.168.0.2MAC Address: 00-0D-56-3C-DB-9D Who has 192.168.0.2? Tell 00-0D-56-3C-DE-C0 192.168.0.2 is at 00-0D-56-3C-DB-9D ICMP Request to 192.168.0.2 Who has 192.168.0.1? Tell 00-0D-56-3C-DE-C0 192.168.0.1 is at 00-0D-56-3C-DE-C0 ICMP Reply to 192.168.0.1 ICMP Request to 192.168.0.2 ICMP Reply to 192.168.0.1 ICMP Request to 192.168.0.2 ICMP Reply to 192.168.0.1 ICMP Request to 192.168.0.2 ICMP Reply to 192.168.0.1

  9. Standard Internet ARP Message The operation code defines what type of message that is transmitted / received.

  10. Concept of Multi-hop Enabled ARP (MEARP) • Reuses existing data traffic • Introduced resending of ARP requests • Introduced forwarding of ARP replies • Mechanisms to treat the new ARP messages • Flood avoidance • Pending request list • Cross-layer issues • Link quality observations • Traffic observations • Multi-hop gateway support

  11. Node: 1IP Address: 192.168.0.1MAC Address: 00-0D-56-3C-DE-C0 Node: 2IP Address: 192.168.0.2MAC Address: 00-0D-56-3C-DB-9D Node: 3IP Address: 192.168.0.3MAC Address: 00-0D-56-3C-E2-4C ARP Enabled Ad Hoc Routing Who has 192.168.0.3? Tell 00-0D-56-3C-DE-C0 Who has 192.168.0.3? Tell 00-0D-56-3C-DB-9D 192.168.0.3 is at 00-0D-56-3C-E2-4C Use 192.168.0.2 to reach 192.168.0.3 ICMP Request 192.168.0.3 ICMP Request 192.168.0.3 Who has 192.168.0.1? Tell 00-0D-56-3C-E2-4C Who has 192.168.0.1? Tell 00-0D-56-3C-DB-9D 192.168.0.1 is at 00-0D-56-3C-DE-C0 Use 192.168.0.2 to reach 192.168.0.1 ICMP Reply 192.168.0.1 ICMP Reply 192.168.0.1

  12. Security considerations in ad hoc networks Issues: • Information integrity – Unauthorized should not be able to read our data. • Transmission security – Unauthorized should not be able to eavesdrop on out transmitted information. • Denial of Service (DoS) – No one should be able to report unusable routes, drown the network with bogus data in order to cause congestions etc.

  13. Solution: Solution: Solution: OSI layer 6 cryptography, e.g. the Secure Socket Layer (SSL). OSI layer 2 cryptography, e.g. WEP or WPA for IEEE 802.11x. Frequency hopping etc. OSI layer 3 cryptography, e.g. IP Security (IPSec, AH, ESP). Issues: Distribution of new authentication keys. Security considerations in ad hoc networks Information is relayed by someone you do not trust. How do you protect your information? An unauthorized person eavesdrops on our transmitted data packets.

  14. Solution: A node must be authenticated before it can be trusted in the ad hoc network. Nodes that are not authenticated should not be trusted and their information should not be forwarded. Issues: Distribution of new authentication keys. Security considerations in ad hoc networks An unauthorized person is injecting invalid routes, to much data traffic etc. into the ad hoc network.

  15. Security summary • Secure communication and information integrity can be performed at different OSI layers. • Ad hoc routing algorithms have to be able to authenticate other nodes. • Difficulties to distribute authentication keys to all ad hoc nodes, since all nodes may not be in reach of radio transmission.

  16. How an ordinary router works – 1 of 2 Definition: • A device that connects multiple networks together and forwards packets (of data) between them. • Uses multiple network interfaces. • Routing is preformed at the network layer (layer 3), i.e. a router does not care about higher layers. • A router has a routing table, specifying which IP address (or group of addresses) should belonging to which interface. • The Internet is hierarchy designed, which allows routers to group similar addresses to the same interface.

  17. HTTP HTTP TCP TCP IP IP IP Ethernet Ethernet Ethernet 100BASE-TX 100BASE-TX 100BASE-TX SOURCE ROUTER(S) DESTINATION How an ordinary router works – 2 of 2 • An inbound packet is received on one interface. • The MAC Header is removed. (It is only valid for one link) • The destination of the IP packet is examined to find out on which interface the packet should be transmitted. If no route is found, the packet is dropped and an Internet Control Message (ICMP) is sent to the source of the IP packet. • The Data Link Layer adds a MAC Header on the packet. • The Physical Layer transmits the packet.

  18. C B A Wireless routing • The Physical Layer receives all wireless communication. All filtering, i.e. packets that are not destined for the local device, is performed at the Data Link Layer. • Power is consumed when receiving and computing data. • Most ad hoc routing algorithms performs routing at the Network Layer. • Routes are set by saying:To reach C, send to B.

  19. Dynamic Source Routing (DSR) TCPHEADER TCP PAYLOAD • Reactive routing protocol. • Modifies every IP packet with an additional header, DSR Header.Example: IPHEADER DSRHEADER

  20. Dynamic Source Routing (DSR) DSR Header TCPHEADER TCP PAYLOAD IPHEADER DSRHEADER Next Header F Reserved Payload Length (Option1) (…) (Option N)

  21. Dynamic Source Routing (DSR) DSR Header options Next Header F Reserved Payload Length (Option1) (…) Options: • Variable-length field; • The length of the Options field is specified by the Payload Length field in this DSR Options header. • Contains one or more pieces of optional information (DSR options).

  22. Dynamic Source Routing (DSR) DSR Header options Next Header F Reserved Payload Length (Option1) (…) • Route Request option • Route Reply option • Route Error option • Acknowledgement Request option • Acknowledgement option • DSR Source Route option • Pad1 option • PadN option • Route Request option • Route Reply option • Route Error option • Acknowledgement Request option • Acknowledgement option • DSR Source Route option • Pad1 option • PadN option

  23. Dynamic Source Routing (DSR) DSR options example ROUTE REQUEST • Opt Data Len 8-bit unsigned integer. Length of the option, in octets, excluding the Option Type and Opt Data Len fields. • Identification A unique value generated by the initiator (original sender) of the Route Request. • Target Address The address of the node that is the target of the Route Request. Option Type Opt Data length Identification Target Address Address[1] Address[2] … Address[N]

  24. Dynamic Source Routing (DSR) DSR options example ROUTE REPLY Opt Data length Reserved Option Type L TargetAddress Address[1] Address[2] … Address[N] L: Set to indicate that the last hop given by the Route Reply (the link from Address[n-1] to Address[n]) is actually an arbitrary path in a network external to the DSR network. Addresses: The source route being returned by the Route Reply.

  25. DSR Considerations • DSR packets can not be traversed on the Internet. • If the DSR network is interconnected with another network, e.g. the Internet, all DSR information, i.e. the DSR Header, has to be removed in the packet!

  26. Why have QoS techniques? – 1 of 2 • Ideal QoS = unlimited throughput + no delay + no drops • But… • Links have limited bandwidth. • Applications/nodes compete for bandwidth. • Some applications try to take all available bandwidth. • Transmissions takes time and packets get queued. • Different applications have different QoS requirements.

  27. R1 R2 R3 R4 news server 2 news server 1 file server 1 Why have QoS techniques? – 2 of 2 1.0 2.0 1.5 0.064 2.0 voip A voip B 2.0 0.064 1.0 1.5 unit: Mbps

  28. Issues in QoS-aware MANETs Quality of Service metrics • Delay, bandwidth, probability of packet loss, and delay variance (jitter). • Power consumption and service coverage area. • QoS metrics could be defined in terms of one of the parameters or set of parameters in varied proportions.

  29. QoS in MANETs: Issues and difficulties • Unpredictable link properties. • Node mobility. • Limited battery life. • Hidden and exposed terminal problems. • Route maintenance. • Security.

  30. Hidden and exposed terminal problems currently transmitting wants to transmit Range of terminal A Range of terminal C Range of terminal B Range of terminal C A B C D A B C will collide with transmission from A at B cannot send to D due to carrier sense Hidden Terminal Problem Exposed Terminal Problem

  31. QoS Support in the Physical Layer • Channel estimation • Signal-to-noise ratio in channels fluctuates  adaptive modulation • Accurate channel estimation at the receiver and then reliable feedback of the estimation to the transmitter. • Joint source-channel coding • Takes both source characteristics and channel conditions into account

  32. QoS Provisioning at the MAC Layer • Fully distributed scheme is needed that should first solve the hidden and exposed terminal problems. • Multihop access collision avoidance (MACA) • Request-to-send/clear-to-send (RTS/CTS) dialogs • Does not completely eliminate the hidden terminal problem • MACA for Wireless (MACAW) • Extension to MACA to provide faster recovery from hidden terminal collisions • IEEE 802.11 • Collision avoidance feature of MACA and MACAW by its distributed control function (DCF) • Carrier sense multiple access with collision avoidance (CSMA/CA)

  33. QoS-aware routing at the Network Layer • Types of MANET routing protocols: • Proactive, table-driven routing schemes. • Reactive, on-demand routing schemes. • These algorithms are based on the discovery of shortest paths. • QoS-aware routing protocol should find a path that satisfies the QoS requirements in the path from source to the destination.

  34. Transport Layer issues for QoS TCP performs poorly in terms of end-to-end throughput in MANETs • The assumption used in Internet that packet losses are due to congestion is not valid in MANET environments TCP performance improvement in wireless networks • Local retransmissions • Split-TCP connections (Use of multi-path) Explicit feedback mechanisms to distinguish between losses due to errors and congestion is necessary for QoS provisioning in MANETs.

  35. QoS Summary • Quality of Service is the idea that transmission rates, error rates, and other characteristics can be measured, improved, and, to some extent, guaranteed in advance. • Cross-layer, OSI layers that is, issues needs to be examined. (Interaction between layers that is)

  36. IPv6 overview IPv6 Motivation for developing IPv6: • Header fields simplification, including removal of fields. • Revision of fields. • New fields were added. • Fixed header size. (Improves routing efficiency) • Increased amount of addresses. • Scalability. (Introduction of extension headers) IPv6 Note! IPv6 only affect layer 3 and 7 in the OSI model.

  37. Version IHL Type of Service Total Length Identification Flags Fragment offset Time To Live Protocol Header Checksum Source Address Destination Address (Option line 1) (Option 1) (Option line 10) (Option 10) IP header overview From IPv4 toIPv6 Payload length Version IHL Type of Service Total Length Version IHL Type of Service Total Length Identification Flags Fragment offset Identification Flags Fragment offset Header Checksum Next Header Time To Live Protocol Hop Limit Time To Live Protocol Header Checksum IP header Source Address Source Address Destination Address Destination Address Transport Layer Data….

  38. IP header overview IPv6 Hop-by-hop options Version Flow Label Version Traffic Class Destination options Payload length Next Header Hop Limit Source Address Routing header Base Header ESP ……. Destination Address TCP header Application payload ( Extension Headers) Extension headers ( Extension Header) ( Extension Header)

  39. Solution: Only use Global addresses! A neighbor (point-to-point) could move, i.e. the node is no longer our neighbor. If the Link Local address is used, it should not be routed! Issue: IPv6 effect on ad hoc routings • IPv6 currently uses two different types of addresses: • Link Local addresses (Used for point-to-point communication – not routable!) • Global addresses (Used on the Internet – Routable!)

  40. Solution: IPv6 header compression! IPv6 addresses are large (128 bits), which reduces the amount of available space for IP payload. Issue: IPv6 effect on ad hoc routings IPv6 Routing Header • Similar to the DSR Header. • Allows the source of an IP packet to choose the packets path. • Ad hoc routing algorithms could take an advantage of this additional header.

  41. Ad hoc communication References • Internet Protocol version 6:http://www.ipv6.org • How 802.x Wireless Works: http://www.microsoft.com/technet/prodtechnol/windowsserver2003/library/TechRef/370b019f-711f-4d5a-8b1e-4289db0bcafd.mspx

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