Network Layer Mobility Rajan Shankaran ITEC851 Mobile Data Networks 1Lecture Organization ï¬This Lecture introduces protocols and mechanisms developed for the network layer to support mobility. ï¬The most prominent example is Mobile IP-discussed in the first section of the lecture, which adds mobility support to the internet. Under Mobile IP we discuss: ï¬The operation of the protocol, ï¬Examine underlying tunneling schemes ï¬Examine Multicast techniques. ï¬We then examine Micro mobility protocol-Cellular IP. ï¬Finally the lecture discusses Mobile IP-802.11 interoperability models. Rajan Shankaran ITEC851 Mobile Data Networks 2Mobility Considerations in Network-Layer Design From the network layerâ€™s standpoint, how mobile is a user? ï¬User movement: Different challenges at the network layer. ï¬Case 1: User has a laptop with a wireless interface card ï¬User roams within a building. ï¬Same wireless link used regardless of mobility. ï¬User not mobile form network layer perspective. ï¬Case 2: User zooms along on a highway at 150km/h: wants an uninterrupted connection btoremote application. ï¬Passes through multiple access points. ï¬Definitely mobile from the network layer perspective. ï¬Case 3: MobileUser: ï¬No ongoing connection needed between different points of attachment. Rajan Shankaran ITEC851 Mobile Data Networks 3Mobility Considerations in Network-Layer Design ï¬How important is the mobile nodeâ€™s address? ï¬With mobile telephony, your phone numberâ€”essentially the network-layer address of your phone ï¬Remains static despite mobility ï¬Must a laptop similarly maintain the same IP address while moving between IP networks?-Consider the BMW passenger from case 2: previous slide ï¬Transparency from applicationâ€™s perspective needed. Rajan Shankaran ITEC851 Mobile Data Networks 5Mobility versus Portability There are two similar terms: Mobility and portability ï¬Portability: Computers can be operated at any set of points of attachment, but not during the time that the computer changes its point of attachment. ï¬Mobility: Involves continuous contact with network resources maintained: There is an uninterrupted connectivity between the application and the source. Rajan Shankaran ITEC851 Mobile Data Networks 6Mobility Problem: Internet View ï¬Need arises due to IP addressing scheme. ï¬Addressing: Routing based on IP hierarchical addressing structure. ï¬Address valid when host attaches itself to network. ï¬Routers use this association to route the packet to host. ï¬Prefix used for packet delivery. ï¬IP address; ï¬endpoint identifier ï¬Routing directive ï¬IP address â€“endpoint Identifier: Indicates Point of attachment.: Example â€“22.214.171.124/16 Rajan Shankaran ITEC851 Mobile Data Networks 8Internet Protocol (IP) Address ï¬An Internet Protocol address (IP address) is a numerical label assigned to each device (e.g., computer, printer) participating in a computer network that uses the Internet Protocol for communication. ï¬It serves two principal functions: ï¬Host or network interface identification ï¬Location addressing. ï¬A name indicates what we seek. ï¬An address indicates where it is. ï¬A route indicates how to get there. ï¬Internet Protocol Version 4 (IPv4)â€32 â€“bits for addressing still in use. ï¬A new addressing system : Internet Protocol Version 46 (IPv6) , using 128 bits for the address being deployed worldâ€wide. Rajan Shankaran ITEC851 Mobile Data Networks 9Mobility Problem: Internet View Change in network, address no longer valid. ïƒ˜Change the address in mobile device ï¬Breaks some applications: ï‚§TCP related Problems: Examine TCP tuple ï‚§Loss of packets ïƒ˜Retain the same address: Routing system limitation ïƒ˜One other option: ïƒ˜Create a route more specific to the prefix ïƒ˜Exception Route: Scalability problems ïƒ˜Let mobilitybe handled at a lower layer: Link layer ïƒ˜802.11 wireless networks ïƒ˜Degree of mobility is limited. Rajan Shankaran ITEC851 Mobile Data Networks 10Requirements of Mobility ï¬Efficient Handoff: Soft and hard ï¬Location Management: Location detection, privacy ï¬Efficient Routing: Shortest path routing, low latency ï¬Security: security critical, overheads to be avoided ï¬Scalability: Performance vs number of mobile nodes ï¬Fault Tolerance ï¬Simultaneous Mobility: Both ends move ï¬Link Layer Independence: movement over heterogeneous networks ï¬Compatibility with IP Routing: Always acquiring/using topologically correct addresses. ï¬Transparency: Transparent to applications ï¬Quality of Service: Just as in fixed networks. Rajan Shankaran ITEC851 Mobile Data Networks 11Mobility of IP-based Wireless Networks Categories of Mobility Host Mobility and Network Mobility. Macro-mobility and Micro-mobility ï¬Macro: Inter-domain ï¬Low rate packet loss ï¬Efficient handoff and efficient routing ï¬High overheads: Cannot be used in micro mobility scenarios. ï¬Micro ï¬Localized mobility within a domain ï¬Reduced handoff latency ï¬IP Mobile Multicasting Rajan Shankaran ITEC851 Mobile Data Networks 12Mobility of IP-based Wireless Networks We will discuss the following protocols: ï¬Mobile IP with IP v4. ï¬With IPv6 is left as a reading exercise. ï¬Cellular IP ï¬Note: Session Initiation Protocol (SIP) is a signaling protocol that can used to provide mobility related services. ï¬Application layer protocol ï¬Not discussed Rajan Shankaran ITEC851 Mobile Data Networks 13Introduction to Mobile IP ï¬Mobile IP: an Internet Engineering Task Force (IETF) standard protocol which allows users to keep their own IP addresses even though they move from one network to the other. ï¬(RFC 2002): Charles Perkins ï¬Nodes to continue to receive datagrams no matter where they happen to be attached to the Internet. ï¬Goals: ï¬Host to stay connected to the Internet regardless of its location. ï¬Track a host without needing to change the mobile hostâ€™s long-term IP address. ï¬Additional control messages for managing routing tables. 16 Rajan Shankaran ITEC851 Mobile Data NetworksMobile IP -Characteristics ï¬Mobile Host communicates with other nodes after changing its link-layer point of attachment yet without changing its IP address. ï¬Mobile host communicates with other nodes that do not implement mobile IP. ï¬All messages exchanged in this framework are authenticated. ï¬Number of administrative messages minimized. ï¬Low Bandwidth factor. ï¬No geographical limitation: A user can take a palmtop or laptop computer anywhere without losing connection to home network. Rajan Shankaran ITEC851 Mobile Data Networks 17Mobile IP -Characteristics Impact ï¬Network access is assured at all times and from all locations. Home and local resources would be accessed continuously. ï¬There would no longer be an excuse for lack of productivity due to lack of connectivity. Rajan Shankaran ITEC851 Mobile Data Networks 18IETF Mobile IP: Terminology ï¬Mobile host/node ï¬Correspondent Node ï¬Mobility Agent(MA) ï¬Home agent(HA) ï¬Foreign agent(FA) ï¬Care-of Address(COA) ï¬Foreign agent-based COA(FCOA) ï¬Co-located COA(CCOA) ï¬Home Address ï¬Mobility Binding Rajan Shankaran ITEC851 Mobile Data Networks 20HA/FA Placement ï¬HA attracts and intercepts datagrams for MN using proxy ARP. ï¬MN uses gratuitous ARP to update the binding upon return ï¬What does this tell you about the location of HA? ï¬HA location options ï¬Included in router at Home Network ï¬As a separate system on the home network ï¬A virtual home network. Rajan Shankaran ITEC851 Mobile Data Networks 23HA/FA Placement ï¬MH â€“FA: bypass normal routing mechanisms and send datagrams to each other using link layer addresses. ï¬What does this tell you about the location of FA? Rajan Shankaran ITEC85
1 Mobile Data Networks 24More on Mobile IP Mobile IP protocol defines the following: ï¬an authenticated registration procedure by which a mobile node informs its home agent of its care-of-address ï¬an extension to ICMP Router Discovery (agent advertisement), which allows mobile nodes to discover prospective home agents and foreign agents ï¬the rules for routing packets to and from mobile nodes, including the specification of one mandatory tunneling mechanism and several optional tunneling mechanisms. Rajan Shankaran ITEC851 Mobile Data Networks 26Mobile IP Operation: Overview ï¬Mobile IP is a way of doing three relatively separate functions ï¬Location Discovery/Registration ï¬In service (Tunneling) ï¬Deregistration Rajan Shankaran ITEC851 Mobile Data Networks 28Location Discovery ï¬The MH is responsible for discovering whether the MH is in a home or foreign network.(Agent Discovery) ï¬Agent Advertisement: Internet Router Discovery Protocol (IRDP) message (RFC 1991) ï¬Agent Solicitation ï¬Time to Live (TTL) set to 1, multicast address, 126.96.36.199, broadcast address, 255.255.255.255 ï¬In the absence of advertisement and solicitation failure, DHCP can be used. Rajan Shankaran ITEC851 Mobile Data Networks 30Agent Advertisement ï¬An extension to ICMP router advertisement. ï¬Mobility agents transmits advertisements to advertise its services on the link. ï¬Includes a list of CoAs ï¬Helps MN locate their current point of attachment. ï¬Advertisements are sent out one third of the lifetime given in the header. ï¬MN can miss 3 consecutive advertisements before deleting the agent ï¬Foreign networks can enforce visiting policy. ï¬Detect returning to home network Rajan Shankaran ITEC851 Mobile Data Networks 31Agent Solicitation ï¬Agent solicitations should only be sent in the absence of agent advertisements and when the care-of address can not be determined through a link-layer protocol or other means ï¬MN should limit the rate at which its sends solicitations. ï¬Limiting Signalling Overhead Rajan Shankaran ITEC851 Mobile Data Networks 33Registration ï¬It is a method by which a MN: ï¬Request forwarding services when visiting a foreign network ï¬Inform the HA of their current COA. ï¬Renewal ï¬Deregistering ï¬Creates/modifies mobility binding at HA ï¬Registration Lifetime ï¬Other services ï¬HA discovery ï¬Selection of tunneling protocols ï¬request for compression ï¬Maintain simultaneous registration: Datagram sent to each active CoA. ï¬Deregistration: Of a specific or all CoAs Rajan Shankaran ITEC851 Mobile Data Networks 35Registration Process Registration:Registration consists of the following steps: ï¬If a mobile node discovers that it is on the home network, it operates without any mobility services. ï¬If the mobile node is on a new network: sends a Registration Request message (which includes the permanent IP address of the mobile host and the IP address of its home agent) ï¬The foreign agent sends a Registration Request (containing the permanent IP address of the mobile node and the IP address of the foreign agent to the home agent). ï¬Home Agent updates the mobility binding by associating the care-of address of the mobile node with its home address. ï¬The home agent then sends an acknowledgement to the foreign agent. ï¬The foreign agent in turn updates its visitor list by inserting the entry for the mobile node and relays the reply to the mobile node. Rajan Shankaran ITEC851 Mobile Data Networks 36Two Types of Registration ï¬HA can deny registration ï¬Mobile IP defines two different registration procedures ï¬Via Foreign Agent (FA) â€“FA CoA ï¬Directly with Home Agent (HA) â€“Co-located CoA ï¬Using a co-located CoA on a link where FA advertisement was not heard from ï¬Deregistration at home network. ï¬Registration Request/Reply messages Rajan Shankaran ITEC851 Mobile Data Networks 37Mobile Node Move Detection ï¬Lifetime based The mobile node records the Lifetime of advertisement message. If it fails to receive another advertisement from the same agent until the Lifetime expires, it considers to find a new agent. ï¬Network prefixes based The Prefix-length extension is used to determine if the newly received advertisement is in the same subnet as the mobile nodeâ€™s current care-of-address. Rajan Shankaran ITEC851 Mobile Data Networks 42In-Service In Service:This stage can be subdivided into the following steps: ï¬When a correspondent node wants to communicate with the mobile node, it sends an IP packet addressed to the permanent IP address of the mobile node. ï¬The home agent intercepts this packet, consults the mobility binding table to find out if the mobile node is currently visiting any other network. ï¬Determine CoA ï¬Performs encapsulation, tunnels the datagram to MNâ€™s current location. ï¬The home agent will iterate the procedure until the service time expires for the mobile node. ï¬Proxy ARP: For HA to intercept packets destined to a mobile host. Rajan Shankaran ITEC851 Mobile Data Networks 44In-Service ï¬Foreignagentdecapsulatesthepacketandfindsoutthemobilenode’shomeaddress.Itthenconsultsthevisitorlisttoseeifithasanentryforthatmobilenode. ï¬Ifthereisanentryforthemobilenodeonthevisitorlist,theforeignagentretrievesthecorrespondinglinkaddressandrelaysittothemobilenode. ï¬Mobilenodewantstosendamessagetoacorrespondentnode ï¬PacketsforwardedtoFA ï¬FAusesnormalroutingtodeliverpacketstotheCN_FAactsasanormalrouter. ï¬TheFAcontinuesservingthemobilenodeuntilthegrantedlifetimeexpires.Ifthemobilenodewantstocontinuetheservice,ithastoreissuetheregistrationRequest. Rajan Shankaran ITEC851 Mobile Data Networks 45In-Service Delivering Datagrams ï¬Several methods of encapsulation (tunneling) are available ï¬IP-in-IP encapsulation. ï¬Minimal Encapsulation. ï¬Generic record Encapsulation Rajan Shankaran ITEC851 Mobile Data Networks 46IP in IP Encapsulation ï¬Simply encapsulates the original IP packet within the new IP header ï¬Decrements TTL by 1, and ï¬Sets the outer protocol field to 4 (IP-in-IP) ï¬No support for IP fragmentation (path MTU discovery) ï¬Doubles IP packet sizes Rajan Shankaran ITEC851 Mobile Data Networks 47Generic Routing Encapsulation ï¬Tunneling protocol designed to encapsulate a wide variety of network layer packets inside IP tunneling packets. ï¬Designed to be stateless: The tunnel end-points do not monitor the state or availability of other tunnel end-points. Rajan Shankaran ITEC851 Mobile Data Networks 50Tunnel Management ï¬ICMP used to to send error messages indicating, for example, that a requested service is not available or that a host or router could not be reached. ï¬Returns 8 octets of original datagram beyond the header. ï¬May not cover inner (original) header of the tunneled packet. ï¬Encapsulatercannot relay ICMP from interior of the tunnel to the original sender. ï¬Solution: Tunnel Management. Rajan Shankaran ITEC851 Mobile Data Networks 55Tunnel Management ï¬Tunnel management involves maintaining Tunnel Soft StateInformationabout a tunnel to enable more timely use of the tunnel, especially, including management of transient tunnel error conditions. ï¬Idea: To return accurate ICMP messages to the sender. ï¬ICMP messages: ï¬Datagram too big. ï¬Time exceeded. ï¬Destination Unreachable. ï¬Source Quench. Rajan Shankaran ITEC851 Mobile Data Networks 56Tunnel Soft State ï¬Soft state information: ï¬MTU of tunnel ï¬TTL (path length) of tunnel. ï¬Ability to reach end of tunnel. ï¬ICMP messages received from the interior of tunnel updates the soft state of the tunnel at the encapsulator. ï¬Encapsulatormight send ICMP for subsequent datagrams. ï¬Example: MTU case. Rajan Shankaran ITEC851 Mobile Data Networks 57Tunnel Soft State ï¬Path MTU Discovery. ï¬Tunnel MTU Discovery: ICMP datagram too big message. ï¬Donâ€™t Fragment (DF) option.
ï¬Case 1: Source of the un-encapsulated datagram is doing MTU discovery. ï¬MTU: MTU of tunnel -size of outer header ï¬Case 2: Source of the un-encapsulated datagram is not doing MTU discovery. ï¬Fragmentation and Encapsulation Rajan Shankaran ITEC851 Mobile Data Networks 58Deregistration ï¬Deregistration involves MN dropping its COA after returning back to its home network. ï¬Request sent to HA. ï¬Use of gratuitous ARP ï¬There is no need to deregister with the foreign agent because the service expires automatically when the service time expires. ï¬Movement from one Foreign network to another Foreign network: Lost datagrams Rajan Shankaran ITEC851 Mobile Data Networks 61Problems with Mobile IP 1. Routing Inefficiencies: Triangle Routing ï¬Fix: Route Optimization ï¬Provides Binding Cache keeping track of MN ï¬Supports Previous FA’s Notification of MN’s New Location 2. Handoff Delay: Higher layer protocols may drop the packets. Rajan Shankaran ITEC851 Mobile Data Networks 63Problems with Mobile IP 3.Problem of Intra-Domain Movement 4.Single Home Agent Model:The dependence in Mobile IP on a fixed HA reduces fault tolerance. III.Even though Simple and Easy, it is fragile IV.Fix: Supports Multiple Home Agents Rajan Shankaran ITEC851 Mobile Data Networks 64Route Optimization ï¬Problem: Triangular Routing ï¬sender sends all packets via HA to MN: Longer path than optimal. ï¬Significant delay in delivery and unnecessary burden on networks ï¬Route Optimization: Solves the above mentioned problem. Rajan Shankaran ITEC851 Mobile Data Networks 66Route Optimization ï¬Route Optimization has 4 parts: ï¬Updating Binding caches ï¬Managing Smooth handoffs between FAs ï¬Acquiring registration keys for smooth handoffs ï¬Using Special Tunnels Rajan Shankaran ITEC851 Mobile Data Networks 67Binding Caches ï¬Provides a means for any node to maintain a binding cache containing CoA of one or more mobile nodes. ï¬The home agent maintains a binding cache containing all the bindings for all those mobile nodes that are using its services while they are away from the home network. ï¬Enables a CN to discover MNâ€™s current CoA, maintain the binding for tunneling packets. ï¬Binding Update message ï¬A CN tunnels the packet directly to the COA of the mobile node if it has an entry in the binding cache ï¬Binding Update: Lifetime, authentication Rajan Shankaran ITEC851 Mobile Data Networks 68Location Management ï¬To identify the current location of a mobile node and keep track of its changes as it moves on. ï¬For call setup process. Key Questions ï¬How does network know where intended recipient of a message is currently located? ï¬Where should information about current location of a mobile node be stored? ï¬Who should be responsible for determining mobile nodeâ€™s location? Rajan Shankaran ITEC851 Mobile Data Networks 70Location Management ï¬Solutions based on Push or Pull based strategies. ï¬In Mobile IPv4, Home Agent (HA) and Foreign Agent (FA) are employed for location management. ï¬HA address. ï¬FA address. ï¬The HA maintains the Mobility binding. ï¬Itâ€™s a push based strategy. Rajan Shankaran ITEC851 Mobile Data Networks 71Location Management ï¬Location management involves Handoff Management. ï¬Handoff Management: To provide mobile nodes for seamless handover, whenever they move into different IP network regions during a session. ï¬Service disruption issues ï¬Was not supported in the initial base Mobile IP specification. Rajan Shankaran ITEC851 Mobile Data Networks 72Location Management ï¬After a fresh registration event, datagram tunnelled to the new location. ï¬But in flight datagrams destined to MH at old location are lost. ï¬Retransmission initiated by higher layer protocols. Rajan Shankaran ITEC851 Mobile Data Networks 73Smooth FA Handoff Rajan Shankaran ITEC851 Mobile Data Networks 74 ï¬Route optimization: Provides a means for MNâ€™s previous FA to be reliably notified of MNâ€™s new mobility binding ï¬Inflight datagrams forwarded to new CoA ï¬Registration with new FA: MN requests for old FA notification. ï¬New FA-Old FA: Binding Update message. ï¬OLD FA maintains a forwarding pointer. ï¬Old FA forwards packets to new FA. ï¬This notification mechanism will be much more effective than a method involving the home agent: Proximity of Foreign networks. ï¬Security: Registration keySmooth FA Handoff ï¬Smooth FA Handoff needs four additional messages (Refer to next slide) ï¬Binding request ï¬Binding update ï¬Binding acknowledgement ï¬Binding warning Rajan Shankaran ITEC851 Mobile Data Networks 75Acquiring registration keys for smooth handoffs Registration Key: ï¬Provides the means to create the needed authentication and replay protection so that the recipient of a binding update message can believe it. ï¬Allowing the mobile node and foreign agent to create a registration key for later use in making smooth transition to a new point of attachment. ï¬Registration Key: Between FA and MN ï¬Obtaining Registration Keys ï¬Using MNâ€™s Public key-FA supplies Registration key. ï¬Using FAâ€™s public key: HA supplies the registration key. ï¬Using a existing security association between HA-FA: HA supplies the registration key. ï¬Diffe-Hellman Key exchange between FA-MN. Rajan Shankaran ITEC851 Mobile Data Networks 77Out of Date Binding Entry ï¬FA receives a tunnelled datagram ï¬no visitor list entry ï¬No binding cache entry ï¬Conclusion: Node sending the tunneleddatagram has an out-of-date binding cache entry for the mobile node. ï¬What to do with this datagram? Rajan Shankaran ITEC851 Mobile Data Networks 7880 Some Security Issues and possible Solutions ï¬Firewalls and Ingress filtering: ï¬Firewalls:Basic mechanism used by firewalls is filtering out any datagrams that do not meet specified criteria. For example, Enterprise firewalls are typically configured to block packets that appear to be emanating from local computers. This would prevent mobile nodes from communicating with nodes in their home network while they are away because the mobile nodes always use their home address. ï¬Ingress filtering: (Ingress filtering was proposed to combat denial of service attacks) Many boarder routers discard packets that seem to emanate from an address that is external to the administrative domain. This will prevent a mobile node from sending packets from a foreign network.Reverse Tunneling (Bi-directional Tunneling) ï¬Used to address the firewall traversal problem. ï¬Typically, a firewall does not allow an outgoing packet whose source address is different from its network addresses. ï¬It is unusual to have outgoing and incoming packets in different paths. ï¬Solution is reverse tunneling: Instead of sending the packets directly to the CN, the MN sends the packets back to the HA, and then the HA forwards them to the CN ï¬Advantage: Packets emanate from home network ï¬Issue: Triangle routing reduced to quadrilateral routing ï¬Other routing inefficiency Rajan Shankaran ITEC851 Mobile Data Networks 81Reverse Tunneling: TTL Problem ï¬Consider an MN sending packets with a certain TTL while still in its home network. ï¬TTL kept low: To avoid packets spilling over. ï¬MN now moves to a foreign network: This TTL still low as before: Packets may get dropped ï¬Reverse tunnel is needed that represents only one hop: FA-HA Rajan Shankaran ITEC851 Mobile Data Networks 83Mobile IP â€“Multicast Support ï¬Necessity ï¬What is multicasting? ï¬sender sends a single datagram to the multicast address, and the routers take care of making copies and sending them to all receivers that have registered their interest in data from that sender. ï¬One way streaming media ï¬Mobile IP!!!! Rajan Shankaran ITEC851 Mobile Data Networks 85Mobile IP -Multicast Datagram Routing ï¬When it is at home, a mobile node functions identically
to other multicast senders and receivers. ï¬In foreign network: mobile node MUST join the multicast group in one of two ways. Rajan Shankaran ITEC851 Mobile Data Networks 86Mobile IP -Multicast Datagram Routing ï¬Two types of multicasting ï¬Remote Subscription ï¬Bidirectional Tunneling Rajan Shankaran ITEC851 Mobile Data Networks 87Remote Subscription ï¬MH moves to a foreign network, it subscribes to the multicast group on the foreign network. Rajan Shankaran ITEC851 Mobile Data Networks 88Remote Subscription ï¬Advantages:- ï¬option is simple and provides optimal routing efficiency ï¬Disadvantages:- ï¬Will overload the multicast routers for multicast tree management ï¬Suffer from packet losses at roaming, owing to the set-up time associated with multicast subscription (later it was rectified) Rajan Shankaran ITEC851 Mobile Data Networks 89Reverse Tunneling (Bi directional Tunneling) ï¬When MH is away from its home network, a bi-directional tunnel between its HA and FA is set up. Rajan Shankaran ITEC851 Mobile Data Networks 90Bi directional Tunneling ï¬Advantages:- ï¬Guarantees multicast packet delivery against roaming ï¬Handles the mobility of both the source and recipients ï¬Disadvantages:- ï¬The routing path for packet delivery may be far from optimality ï¬Tunnel convergence problem can occur Rajan Shankaran ITEC851 Mobile Data Networks 91Mobile IPv6 Some advantages of Mobile IPv6 over Mobile IPv4 are: ï¬Unlike Mobile IPv4 -Route Optimization is built as a fundamental part of Mobile IPv6. ï¬Foreign Agents are not needed in Mobile IPv6. ï¬Enhanced features address auto-configuration and neighbour discovery may the node independent of any router. ï¬Solves Ingress Filtering Router based problems. Rajan Shankaran ITEC851 Mobile Data Networks 92