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Chapter 4: Wireless Internet

Chapter 4: Wireless Internet. Introduction What is Wireless Internet? Mobile IP. TCP in Wireless Domain WAP Optimizing Web over Wireless. What is Wireless Internet?. Wireless Internet refers to the extension of the services offered by the Internet to mobile users.

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Chapter 4: Wireless Internet

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  1. Chapter 4: Wireless Internet • Introduction • What is Wireless Internet? • Mobile IP • TCP in Wireless Domain • WAP • Optimizing Web over Wireless

  2. What is Wireless Internet? • Wireless Internet refers to the extension of the services offered by the Internet to mobile users. • Many issues need to be solved for wireless Internet: • Address mobility: Traditional IP addressing does not support address mobility. Mobile IP is a solution to these network layer issue. • Inefficiency of transport layer protocols: Traditional TCP might falsely identify that the data loss is because of congestion but in fact because of transmission errors and then reduce the transmitting rate. This would make the situation even worse. Indirect-TCP (ITCP), snoop TCP, and mobile TCP are some solutions to these transport layer issues. • Inefficiency of application layer protocols: The capabilities of and the bandwidth for the handheld devices are limited. Traditional application protocols are not efficient for wireless networks. Wireless application protocol (WAP) is some solution to these application layer issues. • This chapter is focused on the issues in network, transport, and application layers and the solutions to these problems.

  3. Motivation for Mobile IP • Problem: Routing • based on IP destination address, network prefix (e.g. 156.26.10) 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 • Solution : Changing the IP-address? • adjust the host IP address depending on the current location • almost impossible to find a mobile system, DNS updates take to long time • TCP connections break, security problems • Solution: 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

  4. Requirements to Mobile IP (RFC 3344, was: 3220, 2002) • Compatibility • Mobile IP remains compatible with all lower layers protocols • no changes to current end-systems and routers required • mobile end-systems can communicate with fixed systems • Efficiency and scalability • only little additional messages to the mobile system required (connection typically via a low bandwidth radio link in Mobile IP) • world-wide support of a large number of mobile systems in the whole Internet • 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 • Security • authentication of all messages related to Mobile IP management

  5. Terminology • Mobile Node (MN): system (node) that can change the point of connection to the network without changing its IP address • Home Agent (HA) • system in the home network of the MN, typically a router • 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 • forwards the tunneled datagrams to the MN, typically also the default router for the MN • Correspondent Node (CN): communication partner • Care-of Address (COA) • address of the current tunnel end-point for the MN (at FA or MN) • actual location of the MN from an IP point of view • can be chosen, e.g., via DHCP • Two types of addresses: • Foreign agent-based COA: The COA could be located at the FA. • Co-located COA: The COA is co-located if the MN acquired additional IP address which acts as COA.

  6. Motivation for Mobile IP Data Path for Foreign Agent Care-of Address Data Path for Co-located Care-of Address

  7. Motivation for Mobile IP • Problem: Routing • based on IP destination address, network prefix (e.g. 156.26.10) 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 • Solution : Changing the IP-address? • adjust the host IP address depending on the current location • almost impossible to find a mobile system, DNS updates take to long time • TCP connections break, security problems • Solution: 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

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

  9. Data transfer to the mobile system HA 2 MN Internet home network 3 receiver foreign network FA 1. Sender sends to the IP address of MN, HA intercepts packet (proxy ARP) 2. HA tunnels packet to COA, here FA, by encapsulation 3. FA forwards the packet to the MN 1 CN sender

  10. Data transfer from the mobile system HA 1 MN Internet home network sender FA foreignnetwork 1. Sender sends to the IP address of the receiver as usual, FA works as default router CN receiver

  11. Overview COA foreign network router FA MN home network router HA Internet CN router foreign network 3. router FA MN home network router HA 2. 4. Internet 1. CN router

  12. Mobile IP with Reverse Tunneling • Normally, the Mobile Node sends packets directly back to the Correspondent Node. But this might not work all the time. • Ingress filtering: Some routers filter those packets that don’t have the same network subnet as the network where those packets are sent. For example, Without a reverse tunnel a multicast packet sent from the MN will be filtered by the routers. • Firewalls: Most firewalls filter and drop packets that originate from outside the local network but appear has a source address that belongs to the local network. The packets sent to the home network might be dropped. • Time to live (TTL): TTL in the home network is correct, but might be too low because MN is to far away from the receiver. • Router accept often only “topological correct“ addresses (firewall!) • A packet from the MN encapsulated by the FA is not topological correct in a foreign network or home network. • Reverse tunnels are needed for the MN to participate in multicast . • TTL problems should be solved.

  13. Mobile IP with reverse tunneling • With reverse tunneling, the Mobile Node sends packets back to the Correspondent Node through a tunnel between its Care-of Address and the Home Agent. The Home Agent then forwards the packet to the Correspondent Node. • Reverse tunneling does not solve • problems with firewalls, the reverse tunnel can be abused to circumvent security mechanisms (tunnel hijacking) • optimization of data paths, i.e. packets will be forwarded through the tunnel via the HA to a sender (double triangular routing) • The reverse tunneling standard • Define reverse tunneling as an extension to mobile IP. • Designed backwards-compatible to mobile IP • An option to mobile IP (RFC 3344) • The extensions can be implemented easily and cooperate with those implementations without these extensions.

  14. Reverse tunneling (RFC 3024, was: 2344) HA 2 MN Internet home network 1 sender FA foreignnetwork 1. MN sends to FA 2. FA tunnels packets to HA by encapsulation 3. HA forwards the packet to the receiver (standard case) 3 CN receiver

  15. Mobile IP with Reverse Tunneling Return Data Path for Reverse Tunnelling with Direct Delivery Style Return Data Path for Reverse Tunneling with Encapsulating Delivery Style

  16. Network integration • 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 • Agent solicitation • MN can search for an FA by sending out solicitation messages. • Registration (always limited lifetime!) • MN signals COA to the HA via the FA, HA acknowledges via FA to MN • these actions have to be secured by authentication • Integration • HA advertises the IP address of the MN (as for fixed systems), i.e. standard routing information • routers adjust their entries, these are stable for a longer time (HA responsible for a MN over a longer period of time) • packets to the MN are sent to the HA, • independent of changes in COA/FA

  17. Agent advertisement • Agent Advertisement • Use ICMP with mobility extension Lifetime: length of time this advertisement is valid. Preference helps a node choose the router 0 7 8 15 16 23 24 31 type code checksum #addresses addr. size lifetime router address 1 preference level 1 router address 2 preference level 2 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 (Generic Routing Encapsulation) r: =0, ignored (former Van Jacobson compression) T: FA supports reverse tunneling reserved: =0, ignored . . . type = 16 length sequence number T registration lifetime R B H F M G r reserved COA 1 . . . COA 2

  18. Registration MN FA HA MN HA registration request registration request registration request registration reply registration reply t registration reply t • The COA is at the FA • The COA is co-located in MN

  19. S B D M G r Mobile IP registration request 0 7 8 15 16 23 24 31 type = 1 T x lifetime home address home agent COA identification extensions . . . 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

  20. Mobile IP registration reply 0 7 8 15 16 31 type = 3 code lifetime home address home agent identification 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 extensions . . .

  21. Encapsulation • A tunnel establishes a virtual pipe between a tunnel entry and a tunnel endpoint. • Encapsulation is the mechanism of taking a packet consisting of packet header and data and putting it into the data part of a new packet. • Decapsulation is an operation that takes a packet out of the data part of another packet. original IP header original data new IP header new data outer header inner header original data

  22. Encapsulation (1) (IP-in-IP encapsulation) • Encapsulation of one packet into another as payload • e.g. IPv6 in IPv4 (6Bone), Multicast in Unicast (Mbone) • here: e.g. IP-in-IP-encapsulation, minimal encapsulation or GRE (Generic Record Encapsulation) • IP-in-IP-encapsulation (mandatory, RFC 2003) • tunnel between HA and COA 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

  23. Encapsulation (2) (Minimal encapsulation) • Minimal encapsulation (optional) • Avoid duplication of identical fields • e.g. TTL, IHL, version, DS (RFC 2474, old: TOS) • only applicable for unfragmented packets, no space left for fragment identification ver. IHL DS (TOS) length IP identification flags fragment offset TTL min. encap. IP checksum IP address of HA care-of address COA lay. 4 protoc. S reserved IP checksum IP address of MN original sender IP address (if S=1) TCP/UDP/ ... payload

  24. original header original data outer header GRE header originalheader original data new header new data Generic Routing Encapsulation • Generic routing encapsulation (GRE) supports other network layer protocols in addition to IP. • GRE allows the encapsulation of packets of one protocol suite into the payload portion of a packet of another protocol suite. RFC 1701 ver. IHL DS (TOS) length IP identification flags fragment offset TTL GRE IP checksum IP address of HA Care-of address COA C R K S s rec. rsv. ver. protocol checksum (optional) offset (optional) key (optional) sequence number (optional) routing (optional) ver. IHL DS (TOS) length RFC 2784 IP identification flags fragment offset TTL lay. 4 prot. IP checksum IP address of CN C reserved0 ver. protocol IP address of MN checksum (optional) reserved1 (=0) TCP/UDP/ ... payload

  25. Optimization of packet forwarding • Triangular Routing • sender sends all packets via HA to MN • higher latency and network load • Solutions: the optimized mobile IP protocol • Sender (CN) learns the current location of MN • direct tunneling to this location • HA informs a sender about the location of MN • big security problems! Tunnel hijacking, location exposed • Route optimization • Binding cache: The CN can keep the mapping of MN’s IP address and COA in a cache. • Binding request and binding update: The CN can find the binding using a binding request message, to which the HA responds with a binding update message. • Binding acknowledgement: Conformation of binding. • Binding warning: In some cases, a handoff may occur, but CN may continue to use the old mapping.

  26. Optimization of packet forwarding • Any optimization scheme should try to ensure guaranteed delivery, low latency, and low overhead. • Simultaneous bindings is a feature of Mobile IP that allows an MN to register more than one COA at the same time, that is the HA allows MN to register more than one COA. • The mobile IP variations include four options for packets directed from the MN to the CN and four more options for packets from the CN to the MN. See Table 4.1 and 4.2.

  27. Change of foreign agent CN HA FAold FAnew MN Data Data Data Update ACK Data Data MN changeslocation Registration Update ACK Data Data Data Warning Request Update ACK Data Data t

  28. Handoffs • A handoff is required when the MN changes its FA because the signal of the current FA becomes weak. • The typical phases involved in handoff are: • Measure the signal strength • Decide where and when to hand off • Establish a new connection • Classification of Handoffs: • Mobile initiated handoff: The MN measures the signal strength and decides the handoff. • Mobile evaluated handoff: The MN measures the signal strength but BS decides the handoff. • Network initiated handoff: the network (BS) measures the signal strength and decides where the MN should be handed over. • Mobile assisted handoff: The MN assists the network in the network initiated scenario by measuring the downlink signal strength.

  29. Handoffs • Classification of Handoffs: • Hard handoff: only one active connection at a time. • Soft handoff: two active connections during the handoff. • Signaling procedure-based handoffs: • Forward handoff: MN decides the target BS and requests the target BS for the handoff. • Backward handoff: MN decides the target BS and requests the current BS for the handoff. • Fast handoffs are required to reduce the delay. • Pre-registration handoffs: the registration with the HA takes place before the handoff while the MN is still attached to the old FA. • Post-registration handoffs: registration takes place after the MN is connected to the new FA.

  30. Mobility Support • The mobility management can be categorized into two types: • Macro-mobility protocols such as the Mobile IP deal with the inter-domain movement. • Micro-mobility protocols aim to handle local movement (intra-domain) of mobile hosts without interaction with the Mobile IP enabled Internet. • Micro-mobility is required to 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 • Micro-mobility approaches: • Handoff Aware Wireless Access Internet Architecture (HAWAII) • Cellular IP • Terminal Independent Mobility for IP (TIMIP) • Hierarchical Mobile IP (HMIP) • Hierarchical Mobile IPv6 (HMIPv6) • Important criteria: Security Efficiency, Scalability, Transparency, Manageability

  31. Home Agent Macro mobility by Mobile IP Home Network INTERNET FA Gateway as FA Macro-mobility handover Micro mobility domain Micro-mobility handover Handovers in Micro Mobility transparent outside the domain Macro and Micro mobility

  32. Hierarchical Architecture • Elements in different levels • Access router (AR) • A number of access routers organize access network • Each router incorporates mobility management functions • Access point (AP) • An AR that directly communicates with the mobile terminals at the radio interface • Access Network Gateway (ANG) • The root AR, interfacing with the core IP network • Perform mobility management functions to support MobileIP-based macromobility • Mobile terminal (MT) • Runs the user applications • Roaming between different APs

  33. Mobile IP and IPv6 • Mobile IP was developed for IPv4, but IPv6 simplifies the protocols • security is integrated and not an add-on, authentication of registration is included • 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

  34. Internet HA Backbone Router Crossover Router 2 Mobile IP 4 BS BS DHCP Server Mobile IP MN MN DHCP 1 HAWAII • Operation: • MN obtains co-located COAand registers with HA • Handover: MN keeps COA,new BS answers Reg. Requestand updates routers • MN views BS as foreign agent • Security provisions: • MN-FA authentication mandatory • Challenge/Response Extensions mandatory 1 2 3 4 BS 3

  35. HAWAII: Security • Advantages: • Mutual authentication and Challenge/Response extensions mandatory • Only infrastructure components can influence routing entries • Potential problems: • Co-located COA raises DHCP security issues (DHCP has no strong authentication) • Decentralized security-critical functionality(Mobile IP registration processing during handover) in base stations • Authentication of HAWAII protocol messages unspecified(potential attackers: stationary nodes in foreign network) • MN authentication requires PKI (Public Key Infrastructure) or AAA (Authentication, Authorization, and Accounting) infrastructure

  36. HAWAII: Other issues • Advantages: • Transparency: Mostly transparent to MNs(MN sends/receives standard Mobile IP messages) • Explicit support for dynamically assigned home addresses • Disadvantages: • Mixture of co-located COA and FA concepts may not be supported by some MN implementations • No private address support possible because of co-located COA

  37. Internet Mobile IP CIP Gateway data/control packets from MN 1 BS BS BS packets from MN2 to MN 1 MN1 MN2 Cellular IP • Operation: • CIP node (gateway) maintains routing entries (soft state) for MNs • Multiple entries possible • Routing entries updated based on packets sent by MN • CIP (Cellular IP) Gateway: • Mobile IP tunnel endpoint • Initial registration processing • Security provisions: • all CIP Nodes share“network key“ • MN key: MD5(net key, IP addr) • MN gets key upon registration

  38. Cellular IP: Security • Advantages: • Initial registration involves authentication of MNs and is processed centrally by CIP Gateway • All control messages by MNs are authenticated • Replay-protection (using timestamps) • Potential problems: • MNs can directly influence routing entries • Network key known to many entities (increases risk of compromise) • No re-keying mechanisms for network key • No choice of algorithm (always MD5, prefix+suffix mode) • Proprietary mechanisms (not, e.g., IPSec AH)

  39. Cellular IP: Other issues • Advantages: Manageability • Simple and elegant architecture • Mostly self-configuring (little management needed) • Integration with firewalls / private address support possible • Disadvantages: • Efficiency: Multiple-path forwarding may cause inefficient use of available bandwidth • Transparency: Not transparent to MNs (additional control messages) • Security: Public-key encryption of MN keys may be a problemfor resource-constrained MNs

  40. TIMIP • Terminal Independent Mobility for IP (TIMIP) • An Architecture for IP mobility in wireless access networks • Based on principles similar to those in the HAWAII and Cellular IP architectures • Suited for micro-mobility scenarios • using Mobile IP for macro-mobility • TIMIP can be implemented in the network nodes and work transparently to the IP layer of the terminals • Micro-mobility: Whenever the MN moves within the same TIMIP domain, the route updates and the corresponding acknowledgements will propagate up the hierarchy until the crossover AR is reached. • Macro-mobility: Similar to Cellular IP and HAWAII, TIMIP relies solely on Mobile IP to support macro-mobility.

  41. Tunneling Tunneling TIMIP architecture Accessrouter(level 2) Corenetwork Accesspoint(level 1) Accessrouter(level n-x) Accessnetworkgateway (level n) Accessrouter(level 2) Accesspoint(level 1)

  42. Internet 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 HA RCOA MAP binding update AR AR LCOAold LCOAnew MN MN

  43. Hierarchical Mobile IP: Security • Advantages: • Local COAs can be hidden, which provides some location privacy • Direct routing between CNs sharing the same link is possible (but might be dangerous) • Potential problems: • Decentralized security-critical functionality (handover processing) in mobility anchor points • MNs can (must!) directly influence routing entries via binding updates (authentication necessary)

  44. Hierarchical Mobile IP: Other issues • Advantages: • Handover requires minimum number of overall changes to routing tables • Integration with firewalls / private address support possible • Potential problems: • Not transparent to MNs • Handover efficiency in wireless mobile scenarios: • Complex MN operations • All routing reconfiguration messages sent over wireless link

  45. Problems with mobile IP • Security Problems • Registration request by a malicious node • Replay attacks • Tunnel hijacking • A FA can itself be a malicious node. • Authentication with FA problematic, for the FA typically belongs to another organization • Patent and export restrictions • IETF is working on the protocol for key management and key distribution has been standardized in the Internet. • Firewalls • typically mobile IP cannot be used together with firewalls, special set-ups are needed (such as reverse tunneling) • QoS • many new reservations in case of RSVP (Resource reSerVation Protocol) • tunneling makes it hard to give a flow of packets a special treatment needed for the QoS • Security, firewalls, QoS etc. are topics of current research and discussions!

  46. Security in Mobile IP • Security requirements (Security Architecture for the Internet Protocol, RFC 1825) • Integrityany changes to data between sender and receiver can be detected by the receiver • Authenticationsender address is really the address of the sender and all data received is really data sent by this sender • Confidentialityonly sender and receiver can read the data • Non-Repudiation (Non-Denial of the message previously sent) • sender cannot deny sending of data (The sender can prove that the message was in fact received by the alleged receiver.) • The receiver can prove that the message was in fact sent by the alleged sender. • Traffic Analysiscreation of traffic and user profiles should not be possible • Replay Protectionreceivers can detect replay of messages

  47. IP-Header IP header Authentification-Header authentication header UDP/TCP-Paket UDP/TCP data not encrypted encrypted IP security architecture (1) • Two or more partners have to negotiate security mechanisms to setup a security association • typically, all partners choose the same parameters and mechanisms • Two headers have been defined for securing IP packets: • Authentication-Header • guarantees integrity and authenticity of IP packets • if asymmetric encryption schemes are used, non-repudiation can also be guaranteed • Encapsulation Security Payload • protects confidentiality between communication partners IP header ESP header encrypted data

  48. IP security architecture (2) • Mobile Security Association for registrations • parameters for the mobile host (MH), home agent (HA), and foreign agent (FA) • Extensions of the IP security architecture • extended authentication of registration • prevention of replays of registrations • time stamps: 32 bit time stamps + 32 bit random number • nonces: 32 bit random number (MH) + 32 bit random number (HA) MH-FA authentication FA-HA authentication MH-HA authentication registration request MH FA registration request HA registration reply registration reply

  49. Key distribution • Home agent distributes session keys • foreign agent has a security association with the home agent • mobile host registers a new binding at the home agent • home agent answers with a new session key for foreign agent and mobile node FA MH response: EHA-FA {session key} EHA-MH {session key} HA

  50. MRSVP – Resource Reservation • The current Resource reSerVation Protocol (RSVP) is not adequate for mobile and wireless networks. • Mobility-aware RSVP protocols: • Require that an MN must be able to make advance reservations along data flow paths. • Have information on the set of locations from which the MN requires reservations, mobility specification (MSPEC). • Two types of reservations: • Active: an active reservation is a normal RSVP-like reservation that is on the data flow path from the current location of the MN. • Passive: A passive reservation is made along all paths to and from other locations in MSPEC of the MN. • Components in MRSVP: • Proxy agents (PAs) make reservations on behalf of mobile senders and receivers. • A local proxy agent (LPA) is that to which the MN is currently attached. • Every other agent in the MSPEC will be a remote proxy agent (RPA).

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