INDEX
1 INTRODUCTION……………………………………………………………8
2 Mobile IP overview...........................................................................................9
2.1 TCP/IP protocol suite……………………………………………… 11
2.2 Brief Overview of IPV4……………………………………………….11
2.3 Motivation for Moibile IP Design……………………………………..12
2.4 Overview of protocol…………………………………………………..15
3 Terminology......................................................................................................16
4 Protocol Overview……………………………………………………………17
5 Relationship of the components of mobile IP……………………………….21
6 How Mobile IP works………………………………………………………...22
6.1 Agent Discovery……………………………………………………….22
6.2 Registration…………………………………………………………….22
6.3 Tunneling………………………………………………………………23
7 Security………………………………………………………………………..27
7.1 Route Optimization……………………………………………………28
7.2 Minimal Encapsulation Scheme……………………………………… 30
7.3 Secure Mobile IP Communication…………………………………….30
7.4 SecMIP Schenario……………………………………………………..32
7.5 IPSec in SecMIP………………………………………………………33
7.6 SecMIP Operation……………………………………………………..33
8 SecMIP Implementation……………………………………………………..37
8.1 Dynamic Mobile IP and Free S/wan IPSec……………………………37
8.2 Script Implementation…………………………………………………37
9 Performance Evaluation……………………………………………………..40
9.1 Test 1…………………………………………………………………..41
9.2 Test 2…………………………………………………………………..43
9.3 Test 3…………………………………………………………………..45
9.4 Test 4…………………………………………………………………..46
10 Inter-Domain Mobility………………………………………………………50
10.1 Introduction…………………………………………………………..50
10.2 3G wireless Data Provider Architecture……………………………..50
10.3 RAFA…….…………………………………………………………..
10.4 Mobile Internet Access………..…………………………………….
10.5 Packet to mobility Ratio……………………………………………..
10.6 Handoff Enhancement………………………………………………..
10.7 Route Optimisation…….……………………………………………..
10.8 Local Registration… ………………………………………………..
11 Intra-Domain Mobility………………………………………… ………
11.1 Introduction………………………………………………………..
11.2 Wireless Network Extension ……………………………………..
11.3 Handoff in Cellular Wireless Network …………………………..
11.4 Reducing Router-Crossings ………………..…………………….
11.5 Cellular IP……………………………………………………………..
11.6 IP Micro-Mobility Support…….…………………………………..
11.7 Architecture For QOS……………………………………………..
12 Ongoing Work and Open Questions…………………………………….
13 Changes With IP version 6………………………………………………
Route Optimization……………………………………………………
Security………………………………………………………………..
Source Routing………………………………………………………..
14 Improving The Performance……………………………………………..
The exponential growth of the Internet and the inexorable increase in native computing power of laptop computers and other digital wireless data communication devices has brought the need for mobile networking into sharp focus. As network services proliferate and become available ubiquitously, every network device will take advantage of mobile networking technology to offer maximum flexibility to the customers needing those devices.
To understand the contrast between the current realities of IP connectivity and future possibilities, consider the transition toward mobility that has occurred in telephony over the past 20 years. An analogous transition in the domain of networking, from dependence on fixed points of attachment to the flexibility afforded by mobility, has just begun.
As PDAs and the next generation of data-ready cellular phones become more widely deployed, a greater degree of connectivity is almost becoming a necessity for the business user on the go. Data connectivity solutions for this group of users are a very different requirement than it is for the fixed dialup user or the stationary wired LAN user. Solutions here need to deal with the challenge of movement during a data session or conversation. Cellular service providers and network administrators wanting to deploy wireless LAN technologies need to have a solution which will grant this greater freedom
Cisco IOS has integrated new technology into our routing platforms to meet these new networking challenges. Mobile IP is a tunneling-based solution which takes advantage of the Cisco-created GRE tunneling technology, as well as simpler IP-in-IP tunneling protocol. This tunneling enables a router on a user’s home subnet to intercept and transparently forward IP packets to users while they roam beyond traditional network boundaries. This solution is a key enabler of wireless mobility, both in the wireless LAN arena, such as the 802.11 standard, and in the cellular environment for packet-based data offerings which offer connectivity to a user’s home network and the Internet.
Mobile IP provides users the freedom to roam beyond their home subnet while consistently maintaining their home IP address. This enables transparent routing of IP data grams to mobile users during their movement, so that data sessions can be initiated to them while they roam; it also enables sessions to be maintained in spite of physical movement between points of attachment to the Internet or other networks. Cisco’s implementation of Mobile IP is fully compliant with the Internet Engineering Task Force’s (IETF’s) proposed standard defined in Request for Comments.
Mobile computing and networking should not be confused with the portable computing and networking we have today. In mobile networking, computing activities are not disrupted when the user changes the computer's point of attachment to the Internet. Instead, all the needed reconnection occurs automatically and non-interactively.
Truly mobile computing offers many advantages. Confident access to the Internet anytime, anywhere will help free us from the ties that bind us to our desktops. Consider how cellular phones have given people new freedom in carrying out their work. Taking along an entire computing environment has the potential not just to extend that flexibility but to fundamentally change the existing work ethic.
The evolution of mobile networking will differ from that of telephony in some important respects. The endpoints of a telephone connection are typically human; computer applications are likely to involve interactions between machines without human intervention. Obvious examples of this are mobile computing devices on airplanes, ships, and automobiles. Mobile networking may well also come to depend on position-finding devices, such as a satellite global positioning system, to work in tandem with wireless access to the Internet.
However, there are still some technical obstacles that must be overcome before mobile networking can become widespread. The most fundamental is the way the Internet Protocol, the protocol that connects the networks of today's Internet, routes packets to their destinations according to IP addresses. These addresses are associated with a fixed network location much as a non-mobile phone number is associated with a physical jack in a wall. When the packet's destination is a mobile node, this means that each new point of attachment made by the node is associated with a new network number and, hence, a new IP address, making transparent mobility impossible.
Network mobility is enabled by Mobile IP, which provides a scalable, transparent, and secure solution. It is scalable because only the participating components need to be Mobile IP aware—the Mobile Node and the endpoints of the tunnel. No other routers in the network or any hosts with which the Mobile Node is communicating need to be changed or even aware of the movement of the Mobile Node. It is transparent to any applications while providing mobility. Also, the network layer provides link-layer independence; interlink layer roaming, and link-layer transparency. Finally, it is secure because the set up of packet redirection is authenticated.
Mobile Computing is becoming increasingly important due to the rise in the number of portable computers and the desire to have continuous network connectivity to the Internet irrespective of the physical location of the node. The Internet infrastructure is built on top of a collection of protocols, called the TCP/IP protocol suite. Transmission Control Protocol (TCP) and Internet Protocol (IP) are the core protocols in this suite. IP requires the location of any host connected to the Internet to be uniquely identified by an assigned IP address. This raises one of the most important issues in mobility, because when a host moves to another physical location, it has to change its IP address. However, the higher level protocols require IP address of a host to be fixed for identifying connections. The Mobile Internet Protocol (Mobile IP) is an extension to the Internet Protocol proposed by the Internet Engineering Task Force (IETF) that addresses this issue. It enables mobile computers to stay connected to the Internet regardless of their location and without changing their IP address. More precisely, Mobile IP is a standard protocol that builds on the Internet Protocol by making mobility transparent to applications and higher level protocols like TCP. This article provides an introduction to Mobile IP and discusses its advantages and disadvantages.
In IP networks, routing is based on stationary IP addresses, similar to how a postal letter is delivered to the fixed address on the envelope. A device on a network is reachable through normal IP routing by the IP address it is assigned on the network.
The problem occurs when a device roams away from its home network and is no longer reachable using normal IP routing. This results in the active sessions of the device being terminated. Mobile IP was created to enable users to keep the same IP address while traveling to a different network (which may even be on a different wireless operator), thus ensuring that a roaming individual could continue communication without sessions or connections being dropped. Because the mobility functions of Mobile IP are performed at the network layer rather than the physical layer, the mobile device can span different types of wireless and wire line networks while maintaining connections and ongoing applications. Remote login, remote printing, and file transfers are some examples of applications where it is undesirable to interrupt communications while an individual roams across network boundaries. Also, certain network services, such as software licenses and access privileges, are based on IP addresses. Changing these IP addresses could compromise the network services.
This section discusses the main concepts and operations of the IETF Mobile IP protocol. The basic protocol procedures fall into the following areas:
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Registration
Tunneling
Mobile IP is a modification to IP that allows nodes to continue to receive datagrams no matter where they happen to be attached to the Internet. It involves some additional control messages that allow the IP nodes involved to manage their IP routing tables reliably. Scalability has been a dominant design factor during the development of Mobile IP, because in the future a high percentage of the nodes attached to the Internet will be capable of mobility.
As explained in the previous section, IP assumes that a node’s network address uniquely identifies the node’s point of attachment to the Internet. Therefore, a node must be located on the network indicated by its IP address to receive datagrams destined to it; otherwise, datagrams destined to the node would be undeliverable. Without Mobile IP, one of the two following mechanisms must be typically employed for a node to change its point of attachment without losing the ability to communicate:
The node must change its IP address whenever it changes its point of attachment.
Host-specific routes must be propagated throughout the relevant portion of the Internet
routing infrastructure.
Both these alternatives are plainly unacceptable in the general case. The first makes it impossible for a node to maintain transport and higher layer connections when the node changes location. The second has obvious and severe scaling problems that are especially relevant considering the explosive growth in sales of notebook (mobile) computers.
Mobile IP was devised to meet the following goals for mobile nodes that move (that is, change their point of attachment to the Internet) more frequently than once per second. The following five characteristics should be considered baseline requirements to be satisfied be any candidate for a mobile IP protocol:
A mobile node must be able to communicate with other nodes after changing its link-layer point of attachment to the Internet, yet without changing its IP address.
A mobile node must be able to communicate with other nodes that do not implement
Mobile IP.
All messages used to transmit information to another node about the location of a mobile node must be authenticated to protect against remote redirection attacks.
The link by which a mobile node is directly attached to the Internet may often be a
wireless link. This link may thus have a substantially lower bandwidth and higher error rate than the traditional wired networks. Moreover, mobile nodes are likely to be battery powered, and minimizing power consumption is important. Therefore, the number of administrative messages sent over the link by which a mobile node is directly connected to the Internet should be minimized, and the size of these messages should be kept as small as possible.
Mobile IP must place no additional constraints on the assignment of IP addresses.
2.1 The TCP/IP Protocol Suite
TCP/IP protocol suite, the cornerstone of Internet networking, is a four-layer system. Each layer is responsible for a specific task. The four layers, from top to bottom, are application layer, transport layer, network layer, and link layer. The application layer handles the details of the particular application (e.g., FTP, TELNET, HTTP etc.). The transport layer provides a flow of data between two Internet nodes. There are two widely used transport layer protocols on the Internet: TCP (Transmission Control Protocol) and UDP (User Datagram Protocol). TCP provides a reliable flow of data between two nodes by maintaining a connection-oriented environment. On the other hand, UDP provides an unreliable and connectionless datagram service. The network layer handles the movement of packets around the network by implementing efficient routing algorithms. IP (Internet Protocol), the default network layer protocol on the Internet, is described in detail in the next section. The link layer provides interfaces to the network hardware devices in the form of device drivers. Examples include IEEE 802.2 (LANs), X.25, packet radio etc. The physical layer, which is often tightly-coupled with the datalink, is responsible for transmitting raw bits across the network through network interface cards and cables.
The overall protocol stack is also a tightly-coupled system. Each layer provides some services that the upper layers use. Thus, support for mobility is likely to affect all the layers. For example, the link layer needs to make provisions to accomodate the distinguishing characteristics of wireless media like low bandwidth and difference in power levels of end-to-end nodes. The network layer that routes data to a destination host based on its location, needs to be modified so that it can handle routing when the physical location of the host changes. Similarly, at the transport layer, it is neccessary to provide a better end-to-end delivery service, especially in the case of dropped packets; packets may be lost during mobility and need to be delivered immediately to the new location. Finally, the application layer requires additional support in terms of automatic configuration, service discovery, and link awareness. As an example of an application layer change, if an FTP session is in progress during mobility, the FTP application needs to configure itself being aware of the location changes.
Mobile IP extends IP to support mobile computing. The next section gives an overview of IP, as a preamble to Mobile IP.
2.2 Brief Overview of IPv4
At the network layer, the Internet is viewed as a set of networks or autonomous systems connected together in a hierarchical manner. IP is the mechanism that connects these networks together. Its basic function is to deliver data from a source to a destination independent of the physical location of the two.
IP identifies each node uniquely, using an IP address that designates its physical attachment to the Internet. IP addresses are 32-bit long integers and are represented in a dotted decimal format (e.g., 128.55.44.1), for ease of use. Every IP packet consists of an IP header and an IP payload. The header contains the IP addresses of the sending node and the receiving node along with some other information.
To correctly deliver these packets, IP executes two major steps: packet routing and packet forwarding. Packet routing involves use of protocols like BGP, RIP, and OSPF to decide the route that each packet has to travel. The route is decided using a routing table of <> pairs at each router. Destination addresses are paired with a pair contained in the routing table. Packet forwarding involves use of protocols like ARP, proxy ARP etc. to deliver the packet to the end node once it has arrived at the destination network. This is typically done by discovering the hardware address of the host corresponding to its IP address.
2.3 Motivation for the Mobile IP design
The IP address of a host consists of two parts
1) The higher order bits of the address determine the network on which the host resides;
2) The remaining low-order bits determine the host number.
IP decides the next-hop by determining the network information from the destination IP address of the packet. On the other hand, higher level layers like TCP maintain information about connections that are indexed by a quadruplet containing the IP addresses of both the endpoints and the port numbers. Thus, while trying to support mobility on the Internet under the existing protocol suite, we are faced with two mutually conflicting requirements:
(1) a mobile node has to change its IP address whenever it changes its point of attachment, so that packets destined to the node are routed correctly.
(2) to maintain existing TCP connections, the mobile node has to keep its IP address the same. Changing the IP address will cause the connection to be disrupted and lost.
Mobile IP, the standard proposed by IETF, is designed to solve the problem by allowing each mobile node to have two IP addresses and by transparently maintaining the binding between the two addresses. One of the IP addresses is the permanent home address that is assigned at the home network and is used to identify communication endpoints. The other is a temporary care-of address that represents the current location of the host. The main goals of Mobile IP are to make mobility transparent to the higher level protocols and to make minimum changes to the existing Internet infrastructure.
In a typical scenario, the care-of address of a mobile node is the foreign agent's IP address. There can be another kind of care-of address, known as colocated care-of address, which is usually obtained by some external address assignment mechanism.
The basic Mobile IP protocol has four distinct stages. These are:
- Agent Discovery: Agent Discovery consists of the following steps:
- Mobility agents advertise their presence by periodically broadcasting Agent Advertisement messages. An Agent Advertisement message lists one or more care-of addresses and a flag indicating whether it is a home agent or a foreign agent.
- The mobile node receiving the Agent Advertisement message observes whether the message is from its own home agent and determines whether it is on the home network or a foreign network.
- If a mobile node does not wish to wait for the periodic advertisement, it can send out Agent Solicitation messages that will be responded by a mobility agent.
- Registration: Registration consists of the following steps:
- If a mobile node discovers that it is on the home network, it operates without any mobility services.
- If the mobile node is on a new network, it registers with the foreign agent by sending a Registration Request message which includes the permanent IP address of the mobile host and the IP address of its home agent.
- The foreign agent in turn performs the registration process on behalf of the mobile host by sending a Registration Request containing the permanent IP address of the mobile node and the IP address of the foreign agent to the home agent.
- When the home agent receives the Registration Request, it updates the mobility binding by associating the care-of address of the mobile node with its home address.
- The home agent then sends an acknowledgement to the foreign agent.
- 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.
- In Service: This stage can be subdivided into the following steps:
- 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.
- The home agent intercepts this packet and consults the mobility binding table to find out if the mobile node is currently visiting any other network.
- The home agent finds out the mobile node's care-of address and constructs a new IP header that contains the mobile node's care-of address as the destination IP address. The original IP packet is put into the payload of this IP packet. It then sends the packet. This process of encapsulating one IP packet into the payload of another is known as IP-within-IP encapsulation or tunneling.
- When the encapsulated packet reaches the mobile node's current network, the foreign agent decapsulates the packet and finds out the mobile node's home address. It then consults the visitor list to see if it has an entry for that mobile node.
- If there is an entry for the mobile node on the visitor list, the foreign agent retrieves the corresponding media address and relays it to the mobile node.
- When the mobile node wants to send a message to a correspondent node, it forwards the packet to the foreign agent, which in turn relays the packet to the correspondent node using normal IP routing.
- The foreign agent continues serving the mobile node until the granted lifetime expires. If the mobile node wants to continue the service, it has to reissue the Registration Request.
Deregistration
If a mobile node wants to drop its care-of address, it has to deregister with its home agent. It achieves this by sending a Registration Request with the lifetime set to zero. There is no need for deregistering with the foreign agent as registration automatically expires when lifetime becomes zero. However if the mobile node visits a new network, the old foreign network does not know the new care-of address of the mobile node. Thus datagrams already forwarded by the home agent to the old foreign agent of the mobile node are lost.
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