IT351: Mobile & Wireless Computing Mobile Network Layer Objective: – To highlight the requirements of internetworking in wireless networks as opposed to wired networks. – To detail the operation of common internetworking schemes, including , MobileIP / migration to IPv6 and CellularIP. – To understand the differences between routing in a fixed network and in a MANET Outline • The Internet Protocol (IP) mobility – Motivation and overview • Mobile IP – Components and terminology – Protocols: agent discovery, registration, tunneling & encapsulation – Optimization – Reverse tunneling – Problem • IPv6 • Micro mobility protocols • DHCP • MANET routing Overview of the main chapters Chapter 10: Support for Mobility Chapter 9: Mobile Transport Layer Chapter 8: Mobile Network Layer Chapter 4: Chapter 5: Chapter 6: Chapter 7: Telecommunication Satellite Broadcast Wireless Systems Systems Systems LAN Chapter 3: Medium Access Control Chapter 2: Wireless Transmission Internet Protocol (IP) • IP for normal fixed Internet – Network layer – Most important protocol – Packet-switched, connectionless service – Fragmentation and reassembly – Error reporting using ICMP (Internet Control Message Protocol) – Delivery of packets across an internetwork (Routing) Internet (IP) Mobility • Internet (IP) provides the host with a permanent identity in the form of an IP address • This IP address is associated with a location, i.e. the IP network domain • If the host moves within the domain it will probably be ok (depends, e.g. subnetting) • If the host moves outside the domain it will not have a different IP address • If the host moves any ‘connections’ (recall – IP is connectionless) will be lost Problems with fixed IP • Two ways of assigning IP addresses: – Statically assigned IP • Host address stays constant over all connections – Common case in PC access to LANs and some ISPs – IP addresses may be dynamically assigned by DHCP • Host addresses change with each connection – Common with Laptop access and some ISPs • Problems for mobility – With static addresses the host cannot move – With dynamic addresses partners can’t communicate Motivation for Mobile IP • Routing – based on IP destination address, network prefix (e.g. 129.13.42) determines physical subnet – change of physical subnet implies change of IP address to have a topological correct address (standard IP) or needs special entries in the routing tables • Specific routes to end-systems? – change of all routing table entries to forward packets to the right destination – does not scale with the number of mobile hosts and frequent changes in the location, security problems • Changing the IP-address? – adjust the host IP address depending on the current location – almost impossible to find a mobile system, DNS updates take long time – TCP connections break, security problems Requirements for Mobile IPv4 (RFC 3344, was: 3220, was: 2002 , updated by: 4721) • 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 – support of the same layer 2 protocols as IP – no changes to current end-systems and routers required – mobile end-systems can communicate with fixed systems • Security – authentication of all registration messages • Efficiency and scalability – only little additional messages to the mobile system required – world-wide support of a large number of mobile systems in the whole Internet Mobile IP – IP Integration • What does Mobile IP do? – Extends IP for mobility not wireless networking – Mobile IP operates between network and transport layers (i.e. on top of IP but below TCP/UDP) • Mobile IP provides two addresses: – Fixed address for identification (home address) – Dynamic address for routing (care-of address/foreign address) • Benefits: – Stable address for hosts – Enables TCP to keep track of session data – Routing based on fixed source/destination Mobile IP – Components & Terminology • Mobile Node (MN) – system (node) that can change the point of connection to the network without changing its IP address • Correspondent Node (CN) – communication partner (cam be fixed or mobile node) • Home Network – The subnet the MN belongs to with respect to its IP address. No mobile IP support is needed within the home network. • Foreign Network – The current subnet the MN visits and which is not the home network – The current location of the MN from the IP point of view is called Care- of-Address (COA) • Tunneling – Packet delivery towards the MN is done using a tunnel Mobile IP – Components & Terminology • Home Agent (HA) – system in the home network of the MN, typically a router – Provides several services to the MN – registers the location of the MN, tunnels IP datagrams to the COA • Foreign Agent (FA) – system in the current foreign network of the MN, typically a router – Provides several services to the MN during its visit to the foreign network – forwards the tunneled datagrams to the MN, typically also the default router for the MN – FA can also provide security service, • Care-of Address (COA) – actual location of the MN from an IP point of view – address of the current tunnel end-point for the MN (at FA or MN) – all packets sent to the MN are delivered to the COA – Foreign agent COA: located at the FA – Co-located COA: can be chosen, e.g., via DHCP if IP addresses are available. Example network HA MN router home network mobile end-system Internet (physical home network for the MN) FA foreign network router (current physical network for the MN) CN end-system router Data transfer from the mobile system HA 1 MN home network sender Internet FA foreign network 1. Sender sends to the IP address of the receiver as usual, CN FA works as default router receiver Data transfer to the mobile system HA 2 MN home network 3 receiver Internet FA foreign network 1. Sender sends to the IP address of MN, HA intercepts packet 1 2. HA tunnels packet to COA, here FA, CN by encapsulation 3. FA forwards the packet sender to the MN Overview COA router home router MN FA network HA foreign Internet network CN router 3. router home router MN 2. FA network HA 4. foreign Internet network 1. CN router Mobile IP – The Protocols • Three major problems: – Discovery of new point of attachment – Registration of new location with Home domain – Delivery of datagrams to registered locations • Agent Discovery – Mobility agents advertise availability – MN solicits agent • Registration – Updating the care-of-address with home network • Tunneling – Delivery of data to mobile node’s care-of-address, via permanent home address 1. Agent Discovery • One initial problem of an MN after moving is how to find a foreign agent – How does the MN discover that it has moved? • Mobile IP describes two methods: – Agent advertisement – Agent solicitation • Agent Advertisement – Extends the current ICMP (Internet Control Message Protocol – Router 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 Agent Discovery (cont) • Agent Solicitation – Alternatively, mobile node may solicit agent (Broadcast or Multicast) • Mobile node can now proceed to register Agent Advertisement 0 7 8 15 16 23 24 31 (ICMP – extension) type code checksum #addresses addr. size lifetime router address 1 preference level 1 router address 2 preference level 2 ... type = 16 length sequence number registration lifetime R B H F M G r T reserved COA 1 COA 2 ... 2. Registration • Mobile Node requests registration from Foreign Agent (or directly for co- located COA) • Request is forwarded to Home Agent – Includes CAO + home addresses • Home Agent replies to Foreign Agent • Security From: Perkins, C.E., “Mobile networking through Mobile IP,” IEEE Internet – Authentication between all Computing, Volume 2, Issue 1, Jan.-Feb. 1998 Page(s):58 – 69. three parties – Mobile-Home auth. is based on shared secret 3. Tunneling & Encapsulation • Communication between an IP node and a Mobile Node • Delivery of data to mobile node’s COA via permanent home address • Tunneling is achieved by encapsulation IP tunnel Home Agent Foreign Agent 2 1 3 4 (triangular routing) IP Host Mobile Node Encapsulation • Encapsulation of one packet into another as payload – e.g. IPv6 in IPv4 , Multicast in Unicast – here: e.g. IP-in-IP-encapsulation • IP-in-IP-encapsulation (mandatory, RFC 2003) – tunnel between HA and COA original IP header original data new IP header new data outer header inner header original data Mobile IP – Encapsulation • IP-within-IP encapsulation MobileIP Header IP Header IP Header IP Payload IP Payload Encapsulation ver. IHL DS (TOS) length IP identification flags fragment offset TTL IP-in-IP IP checksum IP address of HA Care-of address COA ver. IHL DS (TOS) length IP identification flags fragment offset TTL lay. 4 prot. IP checksum IP address of CN IP address of MN TCP/UDP/ ... payload Optimization of packet forwarding • Problem: Triangular Routing – sender sends all packets via HA to MN – higher latency and network load • “Solution” – Avoid routing through Home Agent – Corresponding IP host is given care-of-address – sender learns the current location of MN – direct tunneling to this location – HA informs a sender about the location of MN – big security problems! Optimization of packet forwarding (cont.) • Requires authentication (to prevent hijacking) • Process is entitled mobility-binding – Request – Update – Authorization CN HA – Acknowledgement Request Update – Warning (if needed) ACK • If a packet is sent to a wrong FA Optimization: Change of Foreign Agent • 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 Reverse Tunneling • The return path from MN to CN looks quite simple. MN can directly send its packets to CN. However, this leads to several problems: – Firewalls • Most companies have firewalls • To provide security the firewall rejects a topologically incorrect packet – Multicast • An MN in a foreign network can not transmit multi-cast packets in a way that emanate from its home network • The foreign network might not even provide the technical infrastructure for multicast communication – TTL (time to live) • TTL might be low to reach the destination • Adjusting the TTL results in non transparent mobile IP • To solve these problems, reverse tunneling has been defined as an optional extension to mobile IP. Reverse tunneling (RFC 3024, was: 2344) HA 2 MN home network sender 1 Internet FA foreign network 1. MN sends to FA 3 2. FA tunnels packets to HA CN by encapsulation 3. HA forwards the packet to the receiver (standard case) receiver Problems with Mobile IP • Inefficient routing – Indirect routing via Home Agent may be slow – Home Agent may get overloaded with traffic • Firewalls What happens when Firewalls are operating? – typically mobile IP cannot be used together with firewalls, special set-ups are needed (such as reverse tunneling) – Internal addresses appear to enter a network – Mobile IP cannot handover connections Problems 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 • QoS – many new reservations in case of RSVP (resource reservation) – tunneling makes it hard to give a flow of packets a special treatment needed for the QoS • Security, firewalls, QoS etc. are topics of research and discussions Mobile IP and IPv6 (RFC 3775) • Mobile IP was developed for IPv4, but IPv6 simplifies the protocols – security is integrated and not an add-on, authentication of registration is included -Protocols for registration, discovery etc. are available as standard, not layered above IP – COA can be assigned via auto-configuration (DHCPv6 is one candidate), every node has address auto-configuration – no need for a separate FA, all routers perform router advertisement which can be used instead of the special agent advertisement; addresses are always co-located – MN can signal a sender directly the COA, sending via HA not needed in this case (automatic path optimization) – „soft“ hand-over, i.e. without packet loss, between two subnets is supported • MN sends the new COA to its old router • the old router encapsulates all incoming packets for the MN and forwards them to the new COA • authentication is always granted IP Micro-mobility support • Mobile IP (and MIPv6) problems – Designed to Internetwork mobile nodes across wide areas – Concentrates on address migration issues – Not suitable for fast migration and handoff within a defined geographical area • Micro mobility protocols: Keep the frequent updates generated by local changes away from the home network IP Micro-mobility support • Micro-mobility support: – Efficient local handover inside a foreign domain without involving a home agent – Reduces control traffic on backbone – Especially needed in case of route optimization • Example approaches (research, not products): – Cellular IP – HAWAII – Hierarchical Mobile IP (HMIP) • Important criteria: Security Efficiency, Scalability, Transparency, Manageability 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 Mobile ad hoc networks • Standard Mobile IP needs an infrastructure – Home Agent/Foreign Agent in the fixed network – DNS, routing etc. are not designed for mobility • Sometimes there is no infrastructure! – remote areas, ad-hoc meetings, disaster areas – cost can also be an argument against an infrastructure! • Main topic: routing – no default router available – every node should be able to forward A B C Solution: Wireless ad-hoc networks • Network without infrastructure – Use components of participants for networking • Examples – 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, TETRA police network, car-to-car networks… • Internet: MANET (Mobile Ad-hoc Networking) group Manet: Mobile Ad-hoc Networking Mobile Router Manet Mobile Devices Mobile IP, DHCP Fixed Network Router End system Problem No. 1: Routing • Highly dynamic network topology – Device mobility plus varying channel quality – Separation and merging of networks possible – Asymmetric connections possible – Redundant links, interference N7 N6 N6 N7 N1 N1 N2 N3 N3 N2 N4 N4 N5 N5 time = t1 time = t2 good link weak link 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 Routing in ad-hoc networks • THE big topic in many research projects – Far more than 50 different proposals exist – The most simplest one: Flooding! • Reasons – Classical approaches from fixed networks fail • Very slow convergence, large overhead – High dynamicity, low bandwidth, low computing power • Metrics for routing – Minimal • Number of nodes, loss rate, delay, congestion, interference … – Maximal • Stability of the logical network, battery run-time, time of connectivity … 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 (TCP RTT) Dynamic source routing • Split routing into discovering a path and maintaining a path • Discover a path – only if a path for sending packets to a certain destination is needed and no path is currently available • Maintaining a path – only while the path is in use one has to make sure that it can be used continuously • No periodic updates needed! Dynamic source routing • Path discovery – broadcast a packet with destination address and unique ID – if a station receives a broadcast packet • 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 – sender receives packet with the current path (address list) • Optimizations – limit broadcasting if maximum diameter of the network is known – caching of address lists (i.e. paths) with help of passing packets • stations can use the cached information for path discovery (own paths or paths for other hosts) DSR: Route Discovery Sending from C to O P R C G Q B I E K M O A H D L F J N DSR: Route Discovery Broadcast P R [O,C,4711] C [O,C,4711] G Q B I E K M O A H D L F J N DSR: Route Discovery P R [O,C/G,4711] C G [O,C/G,4711] Q [O,C/B,4711] B I E K M O A [O,C/E,4711] H D L F J N DSR: Route Discovery P R C G Q [O,C/G/I,4711] B I E K M O A H [O,C/E/H,4711] [O,C/B/A,4711] D L F J N [O,C/B/D,4711] (alternatively: [O,C/E/D,4711]) DSR: Route Discovery P R C G Q [O,C/G/I/K,4711] B I E K M O A H D L F J N [O,C/E/H/J,4711] [O,C/B/D/F,4711] DSR: Route Discovery P R C G Q [O,C/G/I/K/M,4711] B I E K M O A H D L F J N [O,C/E/H/J/L,4711] (alternatively: [O,C/G/I/K/L,4711]) DSR: Route Discovery P R C G Q B I E K M O A H D L F J N [O,C/E/H/J/L/N,4711] DSR: Route Discovery P R C G Q Path: M, K, I, G B I E K M O A H D L F J N Dynamic Source Routing III • 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 A plethora of ad hoc routing protocols • Flat – Proactive : set up routing tables regardless of any traffic • FSLS – Fuzzy Sighted Link State • FSR – Fisheye State Routing • OLSR – Optimized Link State Routing Protocol (RFC 3626) • TBRPF – Topology Broadcast Based on Reverse Path Forwarding – Reactive: Set up a path between sender and receiver if a communication is needed • AODV – Ad hoc On demand Distance Vector (RFC 3561) • DSR – Dynamic Source Routing (RFC 4728) • DYMO – Dynamic MANET On-demand • Hierarchical – CGSR – Clusterhead-Gateway Switch Routing – HSR – Hierarchical State Routing – LANMAR – Landmark Ad Hoc Routing – ZRP – Zone Routing Protocol • Geographic position assisted – DREAM – Distance Routing Effect Algorithm for Mobility – GeoCast – Geographic Addressing and Routing – GPSR – Greedy Perimeter Stateless Routing – LAR – Location-Aided Routing Clustering of ad-hoc networks Internet Cluster head Base station Cluster Super cluster Further difficulties and research areas • Auto-Configuration – Assignment of addresses, function, profile, program, … • Service discovery – Discovery of services and service providers • Multicast – Transmission to a selected group of receivers • Quality-of-Service – Maintenance of a certain transmission quality • Power control – Minimizing interference, energy conservation mechanisms • Security – Data integrity, protection from attacks (e.g. Denial of Service) • Scalability – 10 nodes? 100 nodes? 1000 nodes? 10000 nodes? • Integration with fixed networks The next step: Wireless Sensor Networks (WSN) • Commonalities with MANETs – Self-organization, multi-hop – Typically wireless, should be energy efficient • Differences to MANETs Example: www.scatterweb.net – Applications: MANET more powerful, more general WSN more specific – Devices: MANET more powerful, higher data rates, more resources WSN rather limited, embedded, interacting with environment – Scale: MANET rather small (some dozen devices) WSN can be large (thousands) – Basic paradigms: MANET individual node important, ID centric WSN network important, individual node may be dispensable, data centric – Mobility patterns, Quality-of Service, Energy, Cost per node … Properties of wireless sensor networks • Sensor nodes (SN) monitor and control the environment • Nodes process data and forward data via radio • Integration into the environment, typically attached to other networks over a gateway (GW) • Network is self-organizing and energy efficient • Potentially high number of nodes at very low cost per node GW Bluetooth, TETRA, … SN SN SN SN SN SN GW SN SN SN SN GW SN GW SN Promising applications for WSNs • Machine and vehicle monitoring – Sensor nodes in moveable parts – Monitoring of hub temperatures, fluid levels … • Health & medicine – Long-term monitoring of patients with minimal restrictions – Intensive care with relative great freedom of movement • Intelligent buildings, building monitoring – Intrusion detection, mechanical stress detection – Precision HVAC with individual climate • Environmental monitoring, person tracking – Monitoring of wildlife and national parks – Cheap and (almost) invisible person monitoring – Monitoring waste dumps, demilitarized zones • … and many more: military, RFID, telematics … – WSNs are quite often complimentary to fixed networks!
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