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Triangle Routing in Mobile IP (Final Report)

Sohaib Mahmood

{03030003@lums.edu.pk} Lahore University of Management Sciences,

Pakistan

Abstract

Mobile IP implies a protocol that allows a mobile laptop or computer to access its home network sitting on a foreign network. It has evolved over the years and has been standardized for both IP version 4 and 6. But there are several issues need to be resolved. Triangle Routing is one of them. It refers to the situation when mobile node can send packet to any internet host directly but that node or for that matter any internet node cannot access mobile node directly and the IP datagram has to pass through the home network of mobile node before reaching its destination residing in a foreign network. Several schemes have been proposed to address this issue. This survey paper presents a study that encompasses almost all realistic solutions proposed for route optimization in Mobile IP. Each scheme has been briefly analyzed and some of the results are mentioned in the paper.

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1- INTRODUCTION There is no denying the fact that mobile computing is on an all time high and still rising. There is an ever-increasing demand for wireless network interfaces that enable a mobile device, such as a laptop, to connect to the internet anywhere, anytime. This popularity in wireless and mobile internetworking is due to two reasons. Technological advancements, for example advent of PDAs and laptops have been the major factor in the rise of mobile communications. The other factor is the ever increasing reliance on internet. As internet provides a huge source of information, it also acts a communication channel. But here comes the roaming dilemma; a mobile device will require a new point of attachment every time it moves to a new network (new point of attachment means a new IP address, for example). TCP/IP Architecture was built on a major assumption that end hosts are connected to the internet statically and IP addresses were used to identify the hosts and the subnet they are residing in. This assumption is no longer valid in case of mobile and wireless internet. If a host changes its IP address, TCP will be unable to maintain the connection status for ongoing sessions. If connections are to be maintained as the node moves from one location to other, protocol modifications are required. A working group within Internet Engineering Task Force (IETF) introduced an extension called Mobile IP for supporting mobility in the internet. [2] Most of the research into wireless internet has been carried out in the context of physical layer (Radio, CDMA etc) but the effects on network layer are a separate area of study altogether. Use of network layer protocols such as IP gives the advantage that the upper level protocols are shielded from the nature of physical layer.

2- MOBILE IP Concept of Mobile IP is simple. Any end host can change its point of attachment in the internet and still being identified by its original IP address. This is accomplished by assigning two IP addresses to the end host. One is its home IP address that serves as the identifier of the end host, second one is known as Care-of address that is used for proper functioning in the new network. Before describing the operation of Mobile IP briefly, some terminologies are needed to be explained first [2]. Mobile Node: It’s a node that frequently changes its point of attachment to the internet1.

1 In this paper, terms Mobile Host and Mobile Node will be used interchangeably.

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Home Network: Mobile Node’s original point of attachment. Foreign Network: The new network Mobile Node visits. Home Agent: Home Agent (which usually is a router), residing in Mobile Node’s Home Network forwards the packets to the Mobile Node irrespective whether Mobile Node is away from home network or not. Further operations performed by HA will be described later. Foreign Agent: Foreign agent, which again is a router usually, resides in the Mobile Node’s visited network and initially provides MH with its care-of address and later on takes on the responsibility of delivering packets to MH which are received from Home Agent. Correspondent Node: A Node with which a mobile Node is communicating. It may either be mobile itself or stationary. . Overview  There are mainly three related but separate mechanisms to Mobile IP 2[1]. 2.1.1 Service Advertisement (Discovering a Care-of Address) In order to attach to a foreign network, a Mobile Node has to discover a care of address. The Care-of address discovery procedure in Mobile IP is based on Internet Control Message Protocol (ICMP) Route Advertisement protocol [17]. These advertisements are modified and extended to carry care-of addresses. Mobility Agents broadcast these messages at regular intervals (every second or once every few seconds). Basic tasks that are performed by such advertisements are:-

Allow detection of Home and Foreign Agents. Lists all (if more than one) care-of addresses. Informs the Mobile node about special features provided by foreign agents. Let the mobile node know whether its in home network or in a foreign network by identifying whether the agent is a home one or a foreign one.

2.1.2 Registration

2 It is necessary to mention here that this overview is of common mechanisms in IPv4 and IPv6. Any differences will be pointed out when necessary.

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Once a mobile node discovers a care-of address, it can send the information to its home agent to enable home agent to redirect the appropriate traffic to Mobile node. The process by which the mobile Node sends its care-of address to the home agent is called registration. A mobile host/node initiates the registration process by sending a Registration Request to Foreign Agent advertising the care-of address. Foreign agent just relays the information to and from the home agent without much modification. Home Agent typically approves the Registration Request and sends a Registration Reply message back to the mobile host. The reply is also authenticated and replay protected. There are further detailed scenarios in registration which can be found in detail in [2].

Figure 1: Registration

2.1.3 Tunneling Once the registration process is completed, the problem of supporting seamless connectivity is confined to the issue of delivering all the packets from home address to the mobile host at its care off address. This problem is solved by tunneling the packet, means encapsulating the IP packet in another IP header during the time it transits the internet between home network and care-of address. Supplying the original packet then can be accomplished by removing the outer IP header and delivering the result to Mobile host. Since the Mobile node gets the packet in the same form as it would have received in home network, operations theoretically proceed as if the mobile host is indeed attached to its home network. Several tunneling techniques are offered but the one described above is the most widely used and is called as IP-within-IP and is fully described in [11]. There are some alternate mechanisms such as Minimal Encapsulation [12] and Generic Routing Encapsulation.

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Figure 2: Tunneling (courtesy [1])

. Problems and Open Issues in Mobile IP  Current Mobile IP solutions are facing several problems. Here is brief description of some glaring issues. 2.2.1 Routing Issues

Base Mobile IP specifications introduce a tunnel into the routing path between correspondent nodes to the mobile node. Packets from the mobile hand, on the other hand, can go directly to the correspondent node. This asymmetry is known as Triangle Routing [3]. This asymmetry is noticeable and annoying to the mobile users. Inefficient Direct Routing: Routing procedure in Mobile IP, measured in number of hops or end to end delay, independent of triangle routing situation, is inefficient.

2.2.3 Security Issues Security is one of the foremost issues in Mobile IP and is being paid great attention to.

o Firewalls, In particular, cause difficulty for Mobile IP because they block all the incoming packets that do not meet some specified criteria.

o Mobile IP gets complicated by the operations of Ingress Filtering. Many border routers discard packets coming from within the enterprise if the packets do not contain a source IP address configured for one of the enterprise’s internal networks. Concept of Reverse Tunneling [13] has

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been proposed to counter the restriction posed by Ingress filtering.

2.2.4 User perception of Reliability The design of Mobile IP is based on the premise that the connections based on TCP should survive cell changes. Many people believe that computer communications to laptop computers are sufficiently bursty that there is no need to increase the reliability of the connections. The analogy is made to fetching Web pages, where people are used to trying again. This is tantamount to making the users responsible for the retransmission protocol and depends on the perception that computers and internet cannot be trusted to do things right the first time. 2.2.5 Quality of Service (QoS) Mobile IP v4 does not specify usable features for the provision of QoS. It is expected that future wireless internet networks will provide services that require QoS guarantees. Therefore Mobile IP should be able to assist QoS Algorithms or mechanisms. [14].♣

3 - ROUTING IN MOBILE IP

♣ There are numerous other issues to mobile IP such as IP addressing [1] etc. Details of such issues can be found in [1] and [15]. However this paper focuses on routing inefficiencies and various proposed solutions to counter it.

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. Triangle Routing  Routing in Mobile IP suffers from a famous anomaly known as Triangle Routing[3] which is cause of annoyance to the end users. Following is a detailed description of Triangle Routing.

Figure 3: Triangle Routing In figure 3, it is clear how mobile node is able to deliver packets to a correspondent internet node along a direct path through its foreign agent. Whereas the correspondent node delivers packets to the mobile node on its home address (means home Network) where home Agent routes it to the Mobile Node. This asymmetry is known as Triangle Routing, where a single leg of the triangle goes from the mobile node to the correspondent node, and the home agent forms the third vertex controlling the path taken by correspondent node to mobile node. The disadvantage of this routing is that it is not optimal as seen by the long path that a packet will traverse going from sender to mobile node instead of the direct path from mobile node to correspondent node.  . Proposed Solutions   

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Several schemes have been proposed to minimize this routing inefficiency. In this paper, a review of selected schemes would be presented and their performances would be analyzed on a common ground.

1. Route Optimizations in Mobile IP (ROMIP) proposed by Charles Perkins and David Johnson in February 2000 and were included in Mobile IP version 6 specifications [3].

2. Reverse Routing, proposed by Peifang Zhou and Oliver W.

Yang in proceedings of 1999 IEEE conference in Electrical and Computer Engineering [5].

3. Location Registers, proposed by Thomas Raleigh, Danny Yang, Li Fung Chang, in IEEE info COM 1999 [7].

4. Bi Directional Route optimization, proposed by Chun-Hsin Wsu, Ann-Tzung Cheng, Shao-Ting Lee in Mid 2003 [6].

5. IBM’s Mobile Network System, proposed by Yakov Rekhter and Charles Perkins in 1992 [18].

6. Optimized Route, proposed by Amit Mahajan, Ben Wild in first quarter of 2003 [8].

7. Secure Short Cut Routing, proposed by Trevor Blackwell, Kee Chan, Koling Chang, Thomas Charuhas, James Gwertzman, Brad Karp, H. T. Kung, W. David Li, Dong Lin, Robert Morris, Robert Polansky, Diane Tang, Cliff Young, John Zao in USENIX Summer 1994 Technical Conference [16].

4 – DISCUSSION OF SCHEMES . Route Optimizations in Mobile IP (ROMIP)  After the routing discrepancies were found out in base specifications, Charles Perkins (now the document editor of Mobile IP working group) along with D. Johnson proposed ROMIP which consists of four steps. [3]

Binding Cache Maintenance Smooth Handoffs Registration Key Management Special Tunnels

ROMIP [3] mainly deals with correspondent nodes as these are the one who needs to be told the new care-of address of the mobile node.

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Before explaining these steps, two terms are needed to be explained: Binding: The triplet of numbers that contains the Mobile node’s home address, care-of address and registration lifetime means how long mobility agents may use the binding. Binding updates: The message that supplies a new binding to an entity that needs to know the new care-of address for a mobile node. It contains the mobile node’s home address, new care-of address and a new registration life time. A-Binding Cache Maintenance: To deliver bindings to correspondent nodes, ROMIP defines four new messages sent to the same port as the base Mobile IP protocol. These message are binding Warning (which tells correspondent nodes that it should get a new binding), binding Request (correspondent nodes asks for a new binding), binding Update (to the correspondent nodes) and binding Acknowledgement (correspondent nodes confirms that it has received the binding. These messages are handled pretty simply:-

Home agent is responsible to send Binding Updates to correspondent nodes when it sends a packet to mobile node at its home address. Mobile node is not concerned with the delivery of binding updates. A correspondent agent with an expired binding will tunnel packets to a wrong care-of address. Foreign agent at the expired care-of address is then responsible to send a binding warning to either home agent or to the corresponding node.

A binding Update could provide the opportunity for any malicious act if accepted from any unauthorized agent. Thus a correspondent node should not process any Binding Updates unless it is sure that the update was from either a mobile node or an authorized home agent. An authentication extension to the Binding Update is provided for this purpose [ROMIP]. B- Smooth Hand off: An interesting scenario occurs when a binding Update is sent to the mobile node’s previous foreign Agent and mobile node has moved to a new care-of address. In such case, previous foreign agent is responsible to deliver packets to its new care-of address.

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Figure 4: Smooth Hand off

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To affect this smooth hand-off, a Previous Foreign Agent Notification message has been proposed. A mobile node creates all the information needed by its new foreign agent to deliver a new authorized Binding Update to previous Foreign Agent. Previous Foreign Agent must send a confirmation back to new Foreign Agent. The Mobile node has to have an established security association with previous Foreign Agent before it creates an Update. C- Registration Key establishment: To enable a smooth hand-off, mobile node needs to establish a security association with its foreign agents as described earlier. This is provided in ROMIP by using appropriate messages embedded in original Registration Request message. After the conclusion of Registration process when the mobile node receives the registration reply, these key establishment messages allow the distribution of registration key to both the mobile node and foreign agent. Typically, a suitable key request is appended to the Request Message and the corresponding key reply messages are appended to the Reply. There are number of messages defined for this purpose, to allow flexibility in key management which is still an active area of research. Either mobile node or foreign agent could have a public key, and foreign agent can share associations with mobile node or with home agent. But in the case when security association is established between foreign agent and mobile node, man-in-the-middle attacks can occur which are hazardous in wireless environment where an anonymous foreign agent can mediate access. D- Special Tunnels: If the previous foreign agent has no fresh binding for the mobile node, special tunnels are used [10], which indicates to the Home Agent the need for special handling. Since mobile node’s cache binding has expired, the previous foreign Agent will not be able to find the home address in the de-capsulated packet and therefore will not be able to send an IP packet back to the Home Agent. Instead of doing that, Foreign Agent encapsulates the IP packet to be sent to the Home Agent using its care-of address as Source IP address. Home Agent, after receiving this packet, compares the source address with the care-of address known in the binding created from the last registration. In case of a match, Home agent will not tunnel the IP packet back to the care-of address. If addresses do not match, then the decapsulated packet is re-tunneled and sent to the current care-of address known from the registration. Observation

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ROMIP technique has solved the problem of triangle routing with an efficient but a complex way. All the entities involved share four kind of messages and also require constant updates to their binding status. Correspondent internet hosts have to be Mobility aware to participate in Route optimization message exchanges. Thus major hardware and software changes are required in each entity involved. Currently, IPv4 does not support cache bindings and thus scalability is a key issue in ROMIP. Though ROMIP has been standardized and included in IPV6 specifications. A comparison of MIP [1] and ROMIP [3] was carried out by Pang [19] with a simulated topology and it showed that with MIP, end to end delay is increased drastically due to triangle routing, especially when Mobile Host is far from Home Agent. Using ROMIP reduced that delay thrice the original one [19]. Thus end to end delay might have been reduced but cost wise it has gone up as each node and router requires special functionality. . Reverse Routing   Peifang Zhou and Oliver W. Yang presented Reverse Routing [5] as an alternative to ROMIP [3]. It took the simplicity behind MIP [1] and the techniques mentioned in ROMIP and in addition tried to reduce the complexities of ROMIP. In order to make it more effective they also introduced a new technique of updating the routing table. 4.2.1 Method

A mobile node receives and sends IP packets conventionally on its home network. As it moves to a foreign network, it obtains a care-of address in foreign subnet. After receiving it, mobile node sends a registration message to the sender. The registration message contains the mobile node’s home address and care-of address and is routed from foreign network. When the registration message reaches the network where the sender is located, the router of the network intercepts the registration message, updates its routing table and the drops the registration message. Thus, all future messages for the mobile node from the sender will be routed according to the newly updated entry. Its called reverse routing as the registration message travels along in reverse direction from mobile node to the correspondent node.

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Figure 5: Reverse Routing

Observation Reverse Routing is much simpler than the ROMIP one which can be seen from the fact that ROMIP needs four messages whereas Reverse Routing needs only one message. Thus they have reduced the cost of equipment. A simulated comparison carried out by [19] verified that end to end delay is almost similar to that of ROMIP but signaling cost is reduced. Details can be found in [19]. Though there is still a problem with reverse routing that Router in the correspondent network needs to be default router in order for this approach to work and all the routers in CN network need to be mobility aware. Thus scalability issue can still arise. . location registers  Thomas Raleigh et al introduced Mobile IP Location register [7] (MIP-LR) which eliminated tunneling [1]. They also proposed co-located care-of addresses served by a DHCP like server and separate the remaining functions into different functional entities to eliminate the use of Home agent and foreign agents. Before further explanation few terms need to be defined here. Home Location Register (HLR) The database mapping between a mobile host’s home IP address to its care-of address is maintained by Home location register (HLR).

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Mobility Binding: Mobile node’s COA with its remaining registration lifetime is called mobility binding. A-Registration: The location of a mobile host is always registered at the HLR. When the mobile node is at home the HLR simply maintains the identity mapping. When the mobile host moves to a foreign network it obtains a COA for that subnet; the mobile host registers the COA with the HLR using a Registration message, as for MIP. The HLR returns a registration reply containing the allowed Lifetime for this registration (similar to MIP). B-Packet Delivery: When a correspondent node wishes to send packets to Mobile node at its care-of address, it first discovers the HLR and then queries it to get the mobility binding. Then it is able to send packets directly to the mobile node’s care-of address. It caches the binding and uses it for future packets for mobile node. Correspondent node needs to update its binding by querying the HLR again before the remaining registration lifetime expires. C-Eager Caching: Mobile node maintains a list of active correspondent nodes that have sent messages during the current registration lifetime. When it moves to a new subnet, it sends a binding update messages to these active nodes. This is similar to binding updates in ROMIP [3]. D-Obtaining the HLR address: How the correspondent host obtains the address of the mobile host’s HLR is related to the issues of HLR survivability. If the HLR serving the mobile host was located in the mobile’s network, the correspondent host could issue the query for the COA to the mobile host’s permanent IP address; if the mobile host were at home, it would respond, and if not, the HLR would trap the query (using proxy ARP) and respond. However, for survivability the HLR

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Figure 6: Packet delivery in MIP-LR with a single HLR. Light arrows: control packets, heavy

arrows: data (courtesy [7]) may not be located in the mobile’s home network. In that case, two possibilities arise: that a single HLR suffices, or multiple HLRs are required. In a small system it might be possible that a single HLR suffices to support all the mobile hosts in the system. In that case every correspondent host may be configured with the address of the HLR; to improve survivability, the HLR can be implemented on a commercial hot-standby fault-tolerant platform. In general, however, multiple HLRs may be required to distribute the workload, to reduce the network communication cost of contacting the HLR, and to obtain survivability, by scattering the HLRs throughout the network. In case of multiple HLRs, issues like consistency and replication arise which are addressed in detail in [7] and can be found there. Observation MIP-LR has reduced the cost drastically as it does not require any Foreign agents or Home Agents as location register deals with the mobility. But it puts the extra burden on correspondent nodes

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as they need to be mobility aware and should be able to query the Location register in order to get MN’s care-of address. But on the other hand this scheme also suggests that HLRs can also be multiple in numbers and can be located outside the home network of mobile node. This also adds to the load of CN as it should know the addresses of HLRs of mobile nodes to query them. This highlights two factors i) scalability is still an issue and ii) this scheme will be hard pressed to work in environments other than campus and small enterprise ones. Authors have maintained the position that real cost of the scheme comes when there are multiple Location registers and when consistency needs to be observed in all of them in order to get latest information. . optimized route   In this scheme, some modifications were proposed in mobility agents in MIP i.e. home agents and foreign agents. As these agents are routers, they will perform regular router functionalities like forwarding normal packets. Additionally they will have a wireless link to be able to communicate to mobile hosts. This scheme also requires the mobility agents to be able to cache bindings of a mobile host and thus act as caching agents too. After the addition of all these functionalities these agents are called mobile routers. [8]. 4.4.1 Method When Home agent receives the packet, it will send back a message to correspondent node notifying it of mobile node’s current position. This message will be in the form of an ICMP message which is meant for only those nodes (routers and hosts) which support Mobile IP. CN will ignore this ICMP packet since its protocol does not support binding caches. But there is a possibility that one or more mobile routers [8] will be on the route from Home Agent (HA) to correspondent node (CN) and also on the route from CN to HA. There is also this strong possibility that some of mobile routers on these routes will be same. In such case, a mobile router on the path from HA to CN will put a binding in its cache whose entry is the home address of mobile node and corresponding care-of address. Next time when CN sends a packet to mobile node on its home network, if a mobile router that has the binding is on the packets path, it will intercepts the packet and routes it directly to the mobile node’s foreign network. Even if there are more than one mobile routers with the binding, the first one to intercept the packet will

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route the packet. There will be binding lifetime associated with the

Figure 7: Optimized Route

binding entries in order to decrease the probability of forwarding packets to a foreign network. In the case it happens, a smooth hand-off, similar to the one described in section 3.2 and [3], is proposed. Also, when HA receives a binding update from mobile node notifying it that it has moved to a new foreign network, HA will send back a message to CN to notify mobile routers on the downstream path about this change. In cases when the packets destined for home network did not pass through any mobile routers, the HA will just forward the packet to foreign agent as in MIP [1]. Also, just before the binding for mobile node is about to expire, HA will send another binding update towards CN. If same mobile router receives this binding and is still receiving packets from the CN destined for mobile node, it proceeds as before. Mobile router will send warning to HA if it does not receive packets for some time (to be decided by delays etc) telling HA that the connection between CN and mobile node might be terminated. HA will stop sending binding updates to this Correspondent node unless it receives an indication that all the connections were not terminated. For example, if HA receives packets for mobile nodes from same correspondent node. Observation As evident from the above, authors of this scheme have proposed structural change in mobility agents. i.e. new wireless links, caching capabilities etc. But on the other hand, they have taken away the cost of major software changes correspondent nodes or in any other node for that matter. It is also noteworthy that it puts lesser burden on Correspondent network router as compared to reverse routing as mobility routers can reside anywhere in the topology. Thus scalability has improved. Simulation results

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carried out by the authors indeed showed that end to end delay is almost halved the delay incurred in base ROMIP [3]. But the bottleneck in this scheme is the density of mobile router which can decrease performance as mobile router will have to exchange lots of messages in order to keep itself updated. Further simulation results can be found in [8].  . bidirectional route optimization  Before describing the details, few definitions that are introduced in this design are as follows: Correspondent Agent (CA): Correspondent agent [6] maintains a binding cache introduced in [3] and intercepts all the packets coming to and from the correspondent nodes. It is used to retain the transparency to correspondent nodes and to serve multiple CNs of the same subnet. Tunneling cache: A foreign agent maintains a tunneling cache [6] for bidirectional route optimization. An entry in the tunneling cache indicates that a correspondent network supports route optimization and direct tunneling so a FA can directly tunnel a packet received from a mobile node to the correspondent node that matches a tunneling cache entry. A-Bi Directional Direct Tunneling: A Correspondent Agent (CA) Router in the correspondent node (CN) network will intercept all packets involving CN. When it intercepts a packet from a correspondent node and it does not have the a binding cache entry for the receiver of the packet, packet will be forwarded like a normal IP datagram. According to [3], this normal packet may cause home agent to send a binding update message (discussed in section 3.2) to the sender CN. While intercepting this message, CA will create a new binding cache entry. When a CA intercepts a packet sent from a CN and it has the binding cache entry, it will encapsulate and tunnel the packet to responsible Foreign Agent (FA). Upon the receipt of this tunneled packet, FA will de-tunnel and forward the packet to mobile node. It will also realize that the network from where the packet was sent supports route optimization so it will create or update its tunneling cache. When a FA receives a packet from a visiting mobile node and it does not have the tunneling cache entry for the destination node, it will reverse tunnel the packet to Mobile node’s home agent.

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Correspondent agent will intercept the packet tunneled from the FA, it will de-tunnels it and forwards it to the destination CN. B-Subnet-based Route Optimization: A correspondent Agent will put the subnet mask of the correspondent network in an encapsulated packet from a correspondent node to mobile node and the recipient foreign agent will keep this subnet information in its tunneling cache. From then on, foreign agent will use the subnet information to decide whether a CN is behind a CA that supports direct tunneling.

Figure 8: Bidirectional Route Optimization

C-Binding Optimization: In ROMIP [3], when a mobile node moves and an IP smooth hand off occurs, it relies on the home agent which keeps the binding update list to send binding update messages to all CNs. In this proposed scheme, as foreign agent can transmit packet directly to mobility aware correspondent agents, the foreign agent can also send binding updates to CAs when the mobile node moves away [6]. However, to support backward compatibility with the base mobile IP [1] and ROMIP [3], this foreign agent still needs to send a binding warning message to home agent notifying it that mobility binding is being updated. Observation This scheme was mainly designed for wireless LANs but authors maintained that this scheme can generally be applied to all LANs as well where Triangle routing is an issue in MIP. This scheme has tried to reduce the end to end delay dramatically by

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employing bi directional optimizations. Their main target, smooth handoff latency is minimized through their simulation results found in [6]. This scheme also proposes a reduced size in binding caches at each Mobility agent. Though it gets rid of caches in existing nodes and subsequent compatibility with existing nodes, it puts greater load on mobility agents by introducing the concepts of tunneling cache in FA and binding cache in correspondent agent. Thus economic factor can be an issue while employing this scheme in practical.

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. other works  A- IBM’s Mobile network system  An MH in IBM’s system [RePe 92] [BhPe 93] has a permanent IP address. Each MH has an HA, and the HA tells the IP routing system that it is the gateway for its MHs. Thus when a CH sends a packet to the MH, it ends up at the HA, which will forward it to the MH. When an MH moves to a new location, it finds a nearby FA, and sends the FA’s address to the MH’s HA. The HA tells the MH’s previous FA to forget about the MH. When an MH sends a packet to a CH, it includes an IP Loose Source Route option [Br 89]. This option records the address of the MH’s FA. The CH caches the FA address, and sends any further packets for the MH via that FA. If the MH moves, its old FA will forward packets from the CH to the MH’s HA. Any reply from the MH will carry the MH’s new location, allowing the CH to update its location cache. If all Internet hosts implemented Loose Source Route correctly, IBM’s system would provide efficient routing with no changes to either CHs or routers. Sadly, a dearth of correct Loose Source Route implementations thwarts this elegant system. Few systems actually remember and use the latest source route for TCP, and possibly none do so for UDP; Source routes are not authenticated, so if implemented correctly they could be used to redirect packets arbitrarily. B- Secure shortcut routing for Mobile IP This work was carried out by Blackwell et al in 1994 [16]. It is, though carried independently and simultaneously, is very much identical to the ROMIP [3] with the additional address to the security concerns. 5 – CONCLUSION The issue of triangle routing is far from resolved at this stage. As we can observe, almost all the schemes proposed for the solution suffers from various problems. Either significant software and hardware changes are required at the correspondent internet hosts or at infrastructure routers need to be smarter and more mobility aware. MIP was developed with much enthusiasm in early nineties but work going on in countering triangle

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routing has fallen below in that aspect. Slow growth of wireless networks and the under utilization of already deployed mobile IP protocol has further decreased the amount of work carried out for route optimization. However, Route optimization techniques are inevitably going to be a major area of focus again when the mobile IP deployment speeds up. There is a need to strike the right balance between different parameters such as end to end delay; cost and manufacturing of the equipment etc and most of these proposed schemes suffer from decreased performance in one or the other parameter. Though it would have been ultra nice to monitor the behavior of all such schemes in a simulated environment but lack of simulation setup has resulted on the reliance on respective authors’ results and deduction of main points from those results.

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References  [1] Perkins, C. Mobile Networking through Mobile IP, Sun Microsystems, February 1998. [2] Perkins, C. IP Mobility Support for IP v4, RFC 3344, Nokia Research Center, August 2002. [3] Perkins, C. Route Optimization in Mobile IP (ROMIP), Internet Draft draft-ietf-mobileip-optim-11, work in progress, August 2002. [4] Perkins, C. and Johnson, David. Mobility support in IPv6, IEEE 1996. [5] Zhou P et al. Reverse Routing: An alternative to ROMIP Protocol, University of Ottawa, May 9, 1999. [6] Wu Chun-Hsin et al. Bi-directional Route Optimizations in Mobile IP over wireless LAN, Academia sinica, May 2003. [7] Chang et al. Enhancing Survivability of Mobile Internet Access Using Mobile IP with Location Registers, IEEE 6/99. [8] Mahajan, A et al. Route Optimizations in Mobile IP, University of Berkeley, April 2003. [9] Pink, Stephen and Lin Tan,Cheng. A Fast Handoff Scheme for Wireless Netorks, IEEE 8/99. [10] Perkins, C. Special tunneling, draft-ietf-mobileip-spectun-00, work in progress, Dec 2000. [11] Perkins, C. IP Encapsulation within IP, RFC 2003, May 1996. [12] Perkins, C. Minimal Encapsulation within IP, RFC 2004, May 1996. [13] Montenergo G. Reverse Tunneling for Mobile IP, RFC 2344, May 1998. [14] Mahadevan,Indu and Sivalingam, Krishna. Quality of Service Architecture for Wireless Networks: Intserv and Diffserv Models, IEEE 8/99. [15] Hinden R et al. IP Version 6 Addressing Architecture, RFC 1884, Dec 1995. [16] Blackwell T et al. Secure short cut Routing for Mobile IP, Usenix summer conference, Jun 1994. [17] Conta A et al. Internet Control Message Protocol (ICMPv6), RC 1885, Dec, 1995 [18] Rekhter et al. Optimal Routing for Mobile Hosts using IP’s Loose Source Route Option, Internet Draft, Oct 1992.

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[19] Pang et al. Comparison of Route Optimization and Reverse Routing, Final Report, Fall 2003