Payman Arabshahi
Neda Communications, Inc.
17005 SE 31st Place
Bellevue, WA 98008
The Internet Engineering Task Force (IETF) is the protocol engineering and development arm of the Internet. The IETF is a large open international community of network designers, operators, vendors, and researchers concerned with the evolution of the Internet architecture and the smooth operation of the Internet. It is open to any interested individual. The actual technical work of the IETF is done in its working groups, which are organized by topic into several areas (e.g., routing, network management, security, etc.). Much of the work is handled via mailing lists, however, the IETF also holds meetings three times per year.
The internal management of the IETF is handled by the area directors. Together with the Chair of the IETF, they form the Internet Engineering Steering Group (IESG). The operational management of the Internet standards process is handled by the IESG under the auspices of the Internet Society . The Internet Architecture Board (IAB) is a body of the Internet Society responsible for overall architectural considerations in the Internet. It also serves to adjudicate disputes in the standards process.
Basically, Mobile-IP extends the existing Internet Protocol to allow a portable computer to be moved from one network to another without changing its IP address and without losing existing connections. This is the working field of the IETF mobileip Working Group.
The Mobile IP Working Group of the Internet Engineering task Force (IETF) is the culmination of efforts by many individuals interested in the problem of mobile routing of hosts. The first meetings were in the form of BOF (Birds of a Feather) sessions held in Atlanta (July 1991), Santa Fe (November 1991), and San Diego (March 1992) IETF meetings. In June 1992 a proposed charter for a formal Working Group was submitted by Steve Deering (who had chaired the BOF sessions) to the IETF and at the same time a mailing list was set up for conduct of the group's business. Following a revision of the charter, the Working Group was officially formed in June 30, 1992. The group uses ftp://software.watson.ibm.com/pub/mobile-ip as its archive, where minutes of meetings, proposals, and a mail archive is kept.
The IETF Mobile IP Working Group (mobileip WG) is chartered to develop or adopt architectures and protocols to support mobility within the Internet. In the near-term, protocols for supporting transparent host ``roaming'' among different subnetworks and different media (e.g., LANs, dial-up links, and wireless communication channels) shall be developed and entered into the Internet standards track. The work is expected to consist mainly of new and/or revised protocols at the (inter)network layer, but may also include proposed modifications to higher-layer protocols (e.g., transport or directory). However, it shall be a requirement that the proposed solutions allow mobile hosts to interoperate with existing Internet systems.
In the longer term, the group may address, to the extent not covered by the mobile host solutions, other types of internet mobility, such as mobile subnets (e.g., a local network within a vehicle), or mobile clusters of subnets (e.g., a collection of hosts, routers, and subnets within a large vehicle, like a ship or spacecraft, or a collection of wireless, mobile routers that provide a dynamically changing internet topology).
There are two types of Internet documents: Internet-Drafts and Request for Comments (RFCs). Internet-Drafts have absolutely no formal status and can be changed or deleted at any time. RFCs are the official document series of the IAB, and are archived permanently (i.e., they are never deleted, and once an RFC is published, it will never change); however, it is important to note that not all RFCs are standards.
Editor: Charles Perkins, IBM
Date: 22 April 1996
Expires: 22 Ocotber 1996
This document specifies protocol enhancements that allow transparent
routing of IP datagrams to mobile nodes in the Internet. Each
mobile node is always identified by its home address, regardless of
its current point of attachment to the Internet. While situated
away from its home, a mobile node is also associated with a
care-of address, which provides information about its current
point of attachment to the Internet. The protocol provides for
registering the care-of address with a home agent. The home agent
sends datagrams destined for the mobile node through a tunnel to
the care-of address. After arriving at the end of the tunnel, each
datagram is then delivered to the mobile node.
Editor: Charles Perkins, IBM
Date: 10 May 1996
Expires: 10 November 1996
This document specifies a method by which an IP datagram may
be encapsulated (carried as payload) within an IP datagram.
Encapsulation is suggested as a means to alter the normal IP routing
for datagrams, by delivering them to an intermediate destination
which would not be otherwise selected by the (network part of the)
IP destination field. This may be done for any of a variety of
reasons, but is particular useful for adherence to the mobile-IP
specification.
Editor: Charles Perkins, IBM
Date: 25 October 1995
Expires: 25 April 1996
This document specifies a method by which an IP datagram may
be encapsulated (carried as payload) within an IP datagram,
without incurring all the overhead of using a standard IP header.
Encapsulation is suggested as a means to effect ``re-addressing"
datagrams (i.e, delivering them to an intermediate destination other
than that specified in the IP destination field) for any of a variety
of reasons, but particularly those useful for adherence to the
mobile-IP specification.
Authors: David B. Johnson, Carnegie Mellon
University; and Charles Perkins, IBM
Date: 22 February 1996
Expires: 22 August 1996
This document defines extensions to the operation of the base
Mobile IP protocol to allow for optimization of datagram routing from
a correspondent node to a mobile node. Without Route Optimization,
all datagrams destined to a mobile node are routed through that
mobile node's home agent, which then tunnels each datagram to the
mobile node's current location. The protocol extensions described
here provide a means for correspondent nodes that implement them
to cache the binding of a mobile node and to then tunnel their own
datagrams for the mobile node directly to that location, bypassing
the possibly lengthy route for each datagram to and from the mobile
node's home agent. Extensions are also provided to allow datagrams
in flight when a mobile node moves, and datagrams sent based on an
out-of-date cached binding, to be forwarded directly to the mobile
node's new binding.
Author: Jim Solomon, Motorola
Date: December 29 1995
Expires: June 29, 1996
As required by [RFC 1264], this draft report discusses the
applicability of Mobile IP to provide host mobility in the Internet.
The final form of this draft report is a prerequisite to advancing
Mobile IP on the standards track. In particular, this document
describes the key features of Mobile IP and shows how the
requirements for advancement to Proposed Standard RFC have been
satisfied.
Author: Charles Perkins, IBM; and David B. Johnson, Carnegie Mellon University
Date: 26 January 1996
Expires: 26 July 1996
This document specifies mobility messages that allow transparent
routing of IP datagrams to mobile nodes in the Internet. Each
mobile node is always identified by its home address, regardless of
its current point of attachment to the Internet. While situated
away from its home, a mobile node is also associated with a
care-of address, which provides information about its current
point of attachment to the Internet. The protocol provides for
notifying the mobile node's home agent, and any other interested IPv6
addressable entities, about the care-of address of the mobile node.
When necessary, the home agent sends packets destined for the mobile
node through a tunnel to the care-of address. After arriving at the
end of the tunnel, the packets are then delivered to the mobile node.
Authors: D. Cong and M. Hamlen, Motorola; and Charles Perkins, IBM
Date: April 1996
Expires: October 1996
This memo defines the Management Information Base (MIB) for use with
network management protocols in TCP/IP-based internets. In
particular, it describes managed objects used for managing the Mobile
Node, Foreign Agent and Home Agent of the Mobile IP Protocol.
Author: W. Simpson, Daydreamer
Date: October 1995
This document discusses implementation techniques for using IP Protocol/Payload number 4 Encapsulation for tunneling with IP Security and other protocols.
This Chapter contains abstracts of some recent papers in the area of Mobile IP.
Authors: Andrew Myles and David Skellern
Date: December 1993
Host mobility is becoming an increasingly important feature with the recent arrival of notebook and palm top computers, the development of wireless network interfaces and the implementation of the global network. This paper describes and compares three proposals from Sony, IBM and Columbia University for mobile host protocols (MHP) that are compatible with the TCP/IP protocol suite. A set of basic requirements for a MHP are also suggested and it is observed that none of the three proposals entirely satisfies these requirements. Each proposal has faults in their implementation of mobile network layer functionality. Moreover, it is noted they do not address problems that must be solved in both higher and lower layers.
Authors: Andrew Myles and David Skellern
Date: May 1993
Host mobility is becoming an increasingly important issue because of the arrival of notebook and palm top computers, the development of wireless network interfaces and the implementation of global networks. The paper compares four proposals for mobile host protocols (MHPs) that are compatible with the TCP/IP protocol suite. A set of requirements for an MHP is proposed and it is observed that while all proposals perform the basic task none of the proposals entirely satisfy the requirements.
Authors: Andrew Myles and Charles Perkins
Date: August 1994
Authors: Charles Perkins, Andrew Myles, and David Johnson
Date: June 1994
The paper describes the Internet Mobile Host Protocol (IMHP), which allows transparent routing of IP packets to mobile hosts in the Internet, while using only the mobile host's home IP address. No changes are required in stationary hosts that communicate with mobile hosts, and no changes are required in mobile hosts above the IP level. IMHP quickly converges to optimal routing following the movement of a mobile host, while maintaining the weak security model of today's Internet. Detailed examples of operation are presented.
Authors: Charles Perkins, Andrew Myles, and David Johnson
Date: December 1994
Remarks: Revised Version of INET'94 Paper (previous reference)
This paper describes a protocol that allows transparent routing of IP packets to mobile hosts in the Internet, while using only the mobile host's home IP address. The protocol, called IMHP (Internet Mobile Host Protocol), requires no changes in stationary hosts that communicate with mobile hosts, and requires no changes in mobile hosts above the IP level. IMHP quickly converges to optimal routing following the movement of a mobile host, while preserving the current level of security in the Internet. Detailed examples of operation are presented.
Author: David Johnson
Date: October 1995
Considers the problem of providing transparent support for very large numbers of mobile hosts within a large internetwork such as the Internet. The availability of powerful mobile computing devices and wireless networking products and services is increasing dramatically, but internetworking protocols such as IP used in the Internet do not currently support host movement. To address this need, the Internet Engineering Task Force (IETF) is developing protocols for mobile hosts in the Internet. The paper analyzes the problem to be solved, reviews the current state of that effort, and discusses its scalability to very large numbers of mobile hosts in a large internetwork.
Author: David Johnson
Date: June 1994
This paper describes a new protocol for transparently routing packets to mobile hosts operating in a large internetwork. The protocol, called the Mobile Host Routing Protocol (MHRP), allows any host to become mobile at any time, yet there is no penalty for a host being ``mobile capable", since the protocol automatically uses only the standard internetwork routing mechanisms and adds no overhead when a mobile host is currently connected to its home network. The paper concentrates on the design of MHRP as it applies to the Internet using IP. Mobile hosts use only their ``home" IP addresses, regardless of their current location in the Internet. No changes are required in stationary hosts that communicate with mobile hosts, and no changes are required in mobile hosts above the IP level. MHRP introduces several new features to provide better robustness for routing to mobile hosts, and provides better scalability to very large numbers of mobile hosts than previous mobile host protocols.
Author: David Johnson
Date: October 1993
Argues that being a mobile host (or a mobile capable host) should be a standard property of all hosts in the Internet, and summarizes the design of a new protocol for transparently allowing these mobile hosts to interoperate in the Internet using IP. A mobile host may move from one network to another at any time, while always using only its ``home" IP address. Any host may be configured to be a ``mobile host" simply by running the appropriate software on it, and there is no penalty for this configuration, since the protocol automatically uses only the standard IP routing mechanisms, adding no overhead to IP, when a mobile host is currently connected to its home network. The protocol scales well to very large numbers of mobile hosts and adds little overhead for packets sent to a mobile host currently connected to a foreign network. The protocol is currently being implemented within the Berkeley networking code and is expected to be available shortly to interested groups outside Carnegie Mellon.
Authors: David B. Johnson and David A. Maltz
Date: 1996
An ad hoc network is a collection of wireless mobile hosts forming a temporary network without the aid of any centralized administration or standard support services. In such an environment, it may be necessary for one mobile host to enlist the aid of others in forwarding a packet to its destination due to the limited propagation range of each mobile host's wireless transmissions. Some previous attempts have been made to use conventional routing protocols for routing in ad hoc networks, treating each mobile host as a router. This position paper points out a number of problems with this design and suggests a new approach based on separate route discovery and route maintenance protocols.
Author: David Johnson
Date: February 1993
Authors: Andrew Myles, David Johnson, and Charles Perkins
Date: June 1995
Host mobility is becoming an important issue due to the recent proliferation of notebook and palmtop computers, the development of wireless network interfaces, and the growth in global internetworking. This paper describes the design and implementation of a mobile host protocol, called the Internet mobile host protocol (IMHP), that is compatible with the TCP/IP protocol suite, and allows a mobile host to move around the Internet without changing its identity, In particular, IMHP provides host mobility over both the local and wide area, while remaining transparent to the user and to other hosts communicating with the mobile host. IMHP features route optimization and integrated authentication of all management packets. Route optimization allows a node to cache the location of a mobile host and to send future packets directly to that mobile host. By authenticating all management packets, IMHP guards against possible attacks on packet routing to mobile hosts, including the interception or redirection of arbitrary packets within the network. A simple new authentication mechanism is introduced that preserves the level of security found in the Internet today, while accommodating the transition to stronger authentication based on public key cryptography or shared keys that may either be manually administered or provided by a future Internet key management protocol.
Author: Henry Y. Gong
Date: January 1996
This paper describes and summarizes the characteristics of the current Internet draft for Mobile IP. In addition to the current internet draft, this paper also discusses alternative Mobile IP proposals so that the reader may understand the different design issues associated with the different protocols.
Author: Mitchell P. Tasman
Date: 1994
We describe a new type of network layer address, the hybrid address, which contains a Partial Destination Identifier, a Unique ID, and a Location Sequence number. The Partial Destination Identifier, which changes as a mobile ES relocates between areas of an internetwork, allows for efficient routing, while the Unique ID is used for ES identification at the lowest layers of a routing hierarchy. Finally, the Location Sequence Number, which a mobile ES increments as it relocates between areas, is used to compare the age of multiple addresses for a given mobile ES. We present a mobility design that incorporates the hybrid address, and is based on the ISO OSI connectionless routing architecture and protocols. Each mobile ES has a home address and a current address. The home address is stored in a global database, and the ES's home area keeps track of the current address. After a mobile ES relocates to a new area, it sends Reconnect messages to the home and previous areas, each of which caches a forwarding pointer for the mobile ES. ESs that communicate with a mobile ES send datagrams directly to the mobile ES. To accomplish this, each ES maintains cache entries for its mobile correspondents. When a datagram containing an out-of-date address is forwarded by an area, a Rewrite message is sent to the source ES, which updates its cache entry for the destination. An ES also updates its cache based on the source addresses of incoming datagrams.
The mobility algorithm has been implemented and tested in a simulation environment, and performs quite well. We also present the results of a study on strategies for caching mobile ES forwarding pointers at Intermediate Systems in the interior of an internetwork, based on the type and contents of transit control messages. Caching at interior Intermediate Systems based on Reconnect messages yields the greatest benefit, for both tree-shaped and general topology internetworks, while caching based on transit Rewrite messages is not recommended.
Authors: T. Blackwell, Chan Kee, Chang Koling, T. Charuhas,
J. Gwertzman, B. Karp, H.T. Kung, W.D. Li, Lin Dong, R. Morris.
Date: June 1994
Describes the architecture and implementation of a mobile IP (Internet Protocol) system. It allows mobile hosts to roam between cells implemented with 2-Mbps radio base stations, while maintaining Internet connectivity. The system is being developed as part of a course on wireless networks at Harvard and has been operational since March 1994.
The architecture scales well, both geographically and in the number of mobile hosts supported. It supports secure short-cut routing to mobile hosts using the existing Internet routing system without change. The implementation demonstrates a robust, low-complexity realization of the architecture, and provides trade-off opportunities between efficiency and cost.
Measured performance of the mobile system is generally excellent. The system can handle a high rate of location updates, and routes packets almost as efficiently for mobile hosts as the Internet does for stationary hosts. We observe reasonable TCP (Transmission Control Protocol) behavior during hand-offs.
Authors: R. Hager, A. Klemets, G.Q. Maguire, M.T. Smith, and F. Reichert
Date: May 1993
The mobility of portable computers and workstations is not transparent to users. They adjust to reduced services as long as they have no connection to a supporting infrastructure. The goal of the Walkstation project is to realize a user transparent mobile IP router (MINT) for wireless links (infrared and radio) operating at 1-10 Mbit/sec. For the study of user behavior and system characteristics, a campuswide testbed (ERIC) with 50-100 stations is planned to demonstrate the new solutions found in the Walkstation II project.
Authors: A. Klemets, G.Q. Maguire, F. Reichert, and M.T. Smith
Date: December 1993
Today, mobility of portable computers and workstations is not transparent to users. They adjust to reduced services as long as they have no connection to a supporting infrastructure. The goal of the Walkstation project is to realize a user transparent mobile IP router (MINT) for wireless links (infrared and radio) operating at 1-10 Mbit/sec. For the study of user behavior and system characteristics a campus wide testbed (ERIC) with 50-100 stations is planned to demonstrate the new solutions found in the Walkstation II project.
Authors: A. Bakre, and B.R. Badrinath
Date: June 1995
IP based solutions to accommodate mobile hosts within existing internetworks do not address the distinctive features of wireless mobile computing. IP-based transport protocols thus suffer from poor performance when a mobile host communicates with a host on the fixed network. This is caused by frequent disruptions in network layer connectivity due to i) mobility and ii) unreliable nature of the wireless link. We describe I-TCP, which is an indirect transport layer protocol for mobile hosts. I-TCP utilizes the resources of Mobility Support Routers (MSRs) to provide transport layer communication between mobile hosts and hosts on the fixed network. With I-TCP, the problems related to mobility and unreliability of wireless link are handled entirely within the wireless link; the TCP/IP software on the fixed hosts is not modified. Using I-TCP on our testbed, the throughput between a fixed host and a mobile host improved substantially in comparison to regular TCP.
Authors: Ben Lancki, Abhijit Dixit, and Vipul Gupta
Date: May 1996
A short article which motivates the need for Mobile-IP and describes its basic operation.
Authors: Vipul Gupta, Abhijit Dixit, and Ben Lancki, SUNY Binghamton
Date: May 1996
Among other topics, these transparencies include a description of the ARP and nonce-related problems (w/ solutions) in Draft-15 of the IETF Mobile-IP proposal (pages 33-34). These problems have been fixed in Draft-16. Also included are route manipulations (pp. 18-19) on Linux machines required to support mobility without foreign agents.
Authors: H. Balakrishnan, S. Seshan, and R.H. Katz
Date: 1995
TCP is a reliable transport protocol tuned to perform well in
traditional networks where congestion is the primary cause of
packet loss. However, networks with wireless links and mobile
hosts incur significant losses due to bit-errors and handoffs.
This environment violates many of the assumptions made by TCP,
causing degraded end-to-end performance. The authors describe
the additions and modifications to the standard Internet
protocol stack (TCP/IP) to improve end-to-end reliable
transport performance in mobile environments. The protocol
changes are made to network-layer software at the base station
and mobile host, and preserve the end-to-end semantics of TCP.
One part of the modifications, called the snoop module, caches
packets at the base station and performs local retransmissions
across the wireless link to alleviate the problems caused by
high bit-error rates. The second part is a routing protocol
that enables low-latency handoff to occur with negligible data
loss. The authors have implemented this new protocol stack on
a wireless testbed. The experiments show that this system is
significantly more robust at dealing with unreliable wireless
links than normal TCP; the authors have achieved throughput
speedups of up to 20 times over regular TCP and handoff
latencies over 10 times shorter than other mobile routing
protocols.
Authors: A. Fasbender, D. Kesdogan, and O. Kubitz
Date: March 1996
In this paper we present a possible extension of the proposed Mobile IP and route optimization protocols, the Non-Disclosure Method (NDM). It prevents the tracking of user movements by third parties and gives mobile users control over the revelation of their location information, according to their personal security demands.
We give an overview on Mobile IP protocols and briefly discuss these protocols in terms of security issues. We show that confidential location management in Mobile IP is an unsolved problem. Then we propose our method for providing untraceable communications in packet-oriented mobile networks. NDM is based on the idea of mixes, which has been suggested by Chaum for hiding the originator addresses of electronic mails. Our algorithm prevents the linkability of sender and recipient addresses in Mobile IP, can be easily adopted to other mobility supporting networks as well. We conclude our paper with performance aspects, discussing the trade-off between the level of security provided and the costs of NDM in terms of increased packet transmission delays. For this purpose, we present a new modelling approach for Internet connections, which is based on empirically derived packet delay distributions and their analytical description. Our results show that the overhead for confidential location management is not as critical as might be expected, and that a considerable delay reduction compared to mixes can be achieved.
Authors: A. Fasbender, D. Kesdogan, and O. Kubitz
Date: March 1996
The amount of mobile and nomadic computing is expected to increase dramatically in the near future. Hand in hand with this ubiquitous mobile computing security and privacy problems show up, which have not been dealt with sufficently up to now. The main problems are traffic analysis and the easy access to location information, for example in the popular Internet just by looking at the address headers of messages. In this paper the need for security and privacy supporting networks is discussed.
We present the Non-Disclosure Method (NDM) as a way to provide the user with variable and scalable security and privacy. We exemplarily demonstrate the applicability of NDM in an existing network by presenting an upward compatible protocol extension to the Internet Protocol (IP), the Secure IP in IP Protocol. Its main design goal is the untraceability of network connections in mobile environments.
Author: Anders Klemets, klemets@it.kth.se
Date: July 1995
Authors: Fredrik Tarberg and Fredrik Broman
Date: January 1996
Date: February 8 1994
RoamAbout Mobile IP mobile client/server networking software from Digital Equipment Corporation enables mobile users with portable computers to connect to their company's network wherever they are working. These portable computers keep their permanent IP network address independently of their physical location, so mobile users have the same environment and level of service both in the workplace and away from it.
When applications are permanently bound to an IP address, mobile workers can access them from their portable computers no matter where they are connected to the network - within the building or campus or at company sites reachable via a corporate network infrastructure. Moreover, they can have access to the same network services without reconfiguring their hosts. For sites with many in-building wireless networks on different subnets, RoamAbout Mobile IP lets users roam across subnets without losing ongoing network connections.
Date: September 25 1995
Telxon Corporation today announced it has joined forces with FTP Software, Inc. and Aironet Wireless Communications Inc. to deliver the first integrated mobile Internet Protocol (IP) solution that allows mobile workers to take notebook, portable or pen-based computers anywhere they go in a corporate facility and maintain continuous wireless connections to an enterprise computing network. The initiative extends wired, in-building network environments by supporting a virtual office where mobile computer users can stay in touch with associates and manage business as if they were at their desks.
The new mobile IP solution combines FTP Software's DOS and Windows network software, Aironet's wireless LAN access points and Telxon's portable and pen-based computers to enable the TCP/IP networking protocol to better meet the full needs of mobile users. It allows users to roam across multiple segments of TCP/IP enterprise networks, without disrupting wireless network connections, and access applications and information, send and receive electronic mail, and update and query databases.
Slide Presentation is available at http://www.ini.cmu.edu/ãe26/mip/
Authors: John F. Drum and Adam S. Epstein
Date: December 14, 1995
Authors: Y.Z. Li, K.C. Chua, and Y.C. Tay, National University of Singapore
Date: December 1995
This document describes an implementation of mobile IP within the Linux kernel. The implementation conforms to mobile IP Internet Draft 13, but leaves some modules to be implemented in the future. The system supplies an interface to user programs through the existing TCP/IP socket. Some problems are also stated. The source code with the implementation is free software and can be redistributed and modified under the terms of GNU General Public License.
Authors: Vipul Gupta, Abhijit Dixit, and Ben Lancki, SUNY Binghamton
Date: May 1996
Linux Mobile-IP is an implementation of Mobile-IP for the Linux operating system Among other features, this release supports operation of a mobile host on a foreign network even in the absence of foreign agents, e.g. we are able to remove a portable computer from an ethernet LAN in our Lab, drive home (several miles away) and reattach to the Internet using PPP without disturbing any existing TCP connections. To the best of the authors' knowledge, it is the first IETF compliant Mobile-IP implementation for Linux with such support.
The Cellular Digital Packet Data (CDPD) Network is a peer multi-protocol, connectionless network, proposed by the CDPD Forum, a trade association of carriers, equipment suppliers, and application developers. It is based on early IETF Mobile-IP work so the two proposals have many similarities but also some differences. The idea behind CDPD is that it may share unused channels in existing Advanced Mobile Phone Systems (AMPS) to provide a 19.2 kbps data channel. The CDPD describes in detail the three lower network layers.
The terminologies of CDPD and Mobile-IP are different. CDPD is following the OSI model terminology. The mobile node is called a mobile end-system (M-ES), the home and foreign agents are called mobile home and mobile serving functions (MHF and MSF respectively) and reside in a mobile data intermediate system (MD-IS). A mobile data base station (MDBS) is also defined which deals with the airlink communications and acts as a data link layer relay between the M-ES and the serving MD-IS. Two protocols, the Mobile Node Registration Protocol (MNRP) and the Mobile Node Location Protocol (MNLP) are responsible for registration of the M-ES with its home MD-IS and the proper routing of packets destined for the M-ES.
How do Mobile IP and CDPD compare? We can compare these mobile data systems from a variety of perspectives including:
The final topic in our comparison is a prediction and a discussion of issues surrounding co-existence and convergence between these standards.
Obviously, the goal is to objectively compare Mobile IP and CDPD. In particular,
Mobile IP is contained strictly within Layer 3. Mobile IP recognizes that the link by which a mobile node is attached to the Internet may often be a precious wireless link, which should be optimized where possible by the Layer 3 protocol (in this case Mobile IP).
The terminologies of CDPD and Mobile IP are different. CDPD is following the OSI reference model terminology. Mobile IP adheres to conventional IP terminology with some extensions. Table 1 maps the key concepts of Mobile IP to their corresponding terms in CDPD.
Even though, securing the network layer of the CDPD network is not required in the CDPD specifications, the CDPD specification team recognized that providing data confidentiality and authentication for the mobility tunnel was important. Network Layer Security Protocol (NLSP), which can be considered an adjunct to CLNP, provides comprehensive security services. Unfortunately, it is a lot more theoretical than real.
Mobile IP specifications are the product of one of IETF's Working Groups. The standardization process is completely open and based on volunteers' effort. This process is also complex and dynamic. ``Rough Consensus and Running Code" best expresses the general flavor of Mobile IP's standardization process. Sometimes, IETF Working Groups are highly efficient and produce high quality specifications in short time frames. That has not been the case with the Mobile IP Working Group. The CDPD specification effort was funded by a group of cellular service providers. The specification was developed by a small team of paid consultants under the direction of cellular service provider representatives. There was significant schedule pressure in the CDPD specification development process. The CDPD Release 1.0 specification was developed in less than a year, and the following Release 1.1 was developed in about one year.
The value of coupling mobility with Internet access is significant. Any solution that provides mobile connectivity to the Internet is likely to be in high demand and heavily used. From this perspective, the opportunity for widespread deployment of both CDPD and Mobile IP technologies is immense. However, in some ways these technologies are in competition with one other. Unless CDPD services are widely deployed soon and unless the subnetwork-independent characteristic of CDPD mobility is further developed and adopted by users of other than cellular-based media, it is unlikely that CDPD mobility will become the mainstream solution to Internet mobility. The Mobile IP standardization process has been quite slow and the base specification for Mobile IP has not yet reached RFC status as of this writing. However, Mobile IP enjoys certain characteristics which seem to ensure its survival until it becomes widely adopted. These characteristics include complete openness, subnetwork independence, user orientation, and proven correct specifications. Another key factor in the widespread deployment of any network is the fitness of the network operators and equipment manufacturers for the job at hand. CDPD network operators are cellular service providers and CDPD equipment manufacturers are typically tele-communication equipment suppliers. Mobile IP network operators are likely to be Internet Service Providers and Mobile IP equipment manufacturers are typically data-communication equipment suppliers. We note that the entire Internet phenomenon was essentially independent of the public telecommunications providers. It is important to recognize that even though CDPD mobility has the potential to become a generalized mobility solution and compete with Mobile IP, it was not designed as such. Since CDPD's mobility management scheme is similar to that of Mobile IP, either could be adapted to interoperate with the other. Depending on the degree of integration gration desired, this could be a relatively easy or a significant job. Finally, CDPD devices are native IP hosts which can communicate with Mobile IP hosts without any modifications. The whole point of the Internet is that the local subnetwork connection is largely irrelevant to communications with the rest of the IP-based world. This is the foundation tion and the benefit of layered communications protocols. It is the communication itself and not the protocol used that is important.
http://www.raleigh.ibm.com/tr2/tr292003.ps
The popularity of wireless communications has underscored the need for a standardized set of Network layer protocols that allow mobile computers to access the Internet from various points of attachment without the need for user intervention or system reconfiguration: that is, support for mobility must be provided. This paper discusses two protocols being developed to address this need:
The CDPD Forum, a trade association of carrier, equipment suppliers, and application developers, has specified a set of mobility-enabling protocols for use in the Cellular Digital Packet Data networks that are now being deployed nationwide by cellular carriers. The CDPD Forum recently published their revised specification: CDPD Specification, Version 1.1; January 1, 1995.
The Mobile-IP Working Group of the Internet Engineering Task Force has also developed a set of mobility-enabling protocols. Currently, this work is at the level of an Internet Draft, with plans to have it accepted as an RFC by year end 1995. The most recent version of this specification is: IP Mobility Support; Internet Draft; January 4, 1995, C. Perkins (editor).
Mobility support is provided by new protocols that complement the existing IP protocol and its associated intra- and inter-domain routing protocols. This paper describes the constituent functions of each approach, outling their strengths and weaknesses. It discusses basic methods, network management support, and conformance issues. It briefly touches on additional mobility support functions offered by the respective protocols. Finally, it discusses unification between the CDPD and Mobile-IP approaches.
Triangular routing is the basic approach used in both CDPD and Mobile-IP. Since this has been the subject of much discussion and debate, Appendix A presents the author's views on the topic.
The Mobile IP Working Group of the Internet Engineering Task Force (IETF) is addressing the requirement of mobility in today's Internet. Mobile IP enables a mobile node to send and receive packets over the Internet using its home address regardless of its point of attachment. In essence, Mobile IP extends the existing Internet Protocol to allow a portable computer to be moved from one network to another without changing its IP address and without losing existing connections. In this section we will discuss:
The current base specification for Mobile IP is an ``Internet Draft". Internet Drafts are draft documents that may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet Drafts as reference material or to cite them other than as ``work in progress."
The Mobile IP Working Group of the Internet Engineering Task Force (IETF) is the culmination of efforts by many individuals interested in the problem of mobile routing of hosts. The first meetings were in the form of BOF (Birds of a Feather) sessions held at the Atlanta (July, 1991), Santa Fe (November, 1991), and San Diego (March, 1992) IETF meetings. In June, 1992, a proposed charter for a formal Working Group was submitted to the IETF and at the same time a mailing list was set up for conduct of the group's business. Following a revision of the charter, the Working Group was officially formed in June 30, 1992.
The IETF Mobile IP Working Group (mobileip WG) is chartered to develop or adopt architectures and protocols to support mobility within the Internet. In the near-term, protocols for supporting transparent host ``roaming" among different subnetworks and different media (e.g., LANs, dial-up links, and wireless communication channels) are to be developed and entered into the Internet standards track. The work is expected to consist mainly of new and/or revised protocols at the (inter)network layer, but may also include proposed modifications to higher-layer protocols (e.g., transport or directory). However, it is a requirement that the proposed solutions allow mobile hosts to interoperate with existing Internet systems. In the longer term, the group may address, to the extent not covered by the mobile host solutions, other types of internet mobility, such as mobile subnets (e.g., a local network within a vehicle), or mobile clusters of subnets (e.g., a collection of hosts, routers, and subnets within a large vehicle, like a ship or spacecraft, or a collection of wireless, mobile routers that provide a dynamically changing internet topology).
In this section we provide an overview of the current base specification for Mobile IP. The terminology is similar to CDPD and is summarized in Table 1. The Mobile IP approach is analogous to postal service delivery: whenever you move to a new location, you ask your home post office to forward your mail to your new address via the local post office there. Thus, a mobile node first leaves its home network and connects to a foreign network. An agent on the home network then intercepts packets sent to the mobile node and forwards them to an agent on the foreign agent. This agent then delivers packets locally to the mobile node visiting that network.
Mobile nodes are supported by two service entities.
These entities interact in the following ways: 1. Agent Discovery Home agents and foreign agents may advertise their availability via broadcast on each link for which they provide service. A newly arrived mobile node can likewise broadcast a solicitation on the link to learn if any prospective agents are present. The advertisement is an extension of router advertisement (RFC 1256). It allows a mobile node to determine its point of attachment (moved to a new foreign network, or returned to its home network). Advertisements contain:
2. Registration When the mobile node is away from home, it registers its care-of address with its home agent. Depending on its method of attachment, the mobile node will register either directly with its home agent, or through a foreign agent which forwards the registration to the home agent. Home and foreign agents may reject registration requests; this option is necessary to combat registration attacks by the ``bad guys." Registration attacks can be of at least three types: Forgery, whereby bogus mobile node location is sent to the home agent; Modification, whereby a valid registration request is altered to send the mobile node's traffic elsewhere; and Replay which involves storing a valid registration request for later malicious diversion of mobile node traffic. To prevent an attacker from changing a mobility binding the following precautions are taken:
3. Tunneling/Encapsulation Tunneling is used for transportation of mobile node packets from the home network to the foreign network. There are two endpoints: The home agent which encapsulates and transmits; and the care-of address entity which receives and decapsulates. The original packet becomes a payload in the new packet sent to the care-of address.There are various options for implementing this: IP-in-IP (draft), GRE, and Minimal Encapsulation are among the encapsulation options.
The following steps outline the operation of the Mobile IP protocol:
When away from home, Mobile IP uses protocol tunneling to hide a mobile node's home address from intervening routers between its home network and its current location. The tunnel terminates at the mobile node's care-of address. The care-of address must be an address to which datagrams can be delivered via conventional IP routing. At the care-of address, the original datagram is removed from the tunnel and delivered to the mobile node. Mobile IP provides two alternative modes for the acquisition of a care-of address:
The mode of using a co-located care-of address has the advantage that it allows a mobile node to function without a foreign agent, for example, in networks that have not yet deployed a foreign agent. It does, however, place additional burden on the IPv4 address space because it requires a pool of addresses within the foreign network to be made available to visiting mobile nodes. It is difficult to efficiently maintain pools of addresses for each subnet that may permit mobile nodes to visit. It is important to understand the distinction between the care-of address and the foreign agent functions. The care-of address is simply the endpoint of the tunnel. It might indeed be an address of a foreign agent (a foreign agent care-of address), but it might instead be an address temporarily acquired by the mobile node (a co-located care-of address). A foreign agent, on the other hand, is a mobility agent that provides services to mobile nodes.
[c]../gif/fig1.gif In Figure 2, the visiting mobile node transmits a packet to the corre- spondent node. Routing of this packet is done in the conventional way, with no need to involve either the home or foreign agent.
[c]../gif/fig2.gif
The Mobile IP protocol is outlined in steps below, under four basic procedural categories. In our discussions MN denotes ``Mobile Node," HA denotes ``Home Agent," and FA denotes ``Foreign Agent". 1. Network Attachment During this phase, foreign and home agents advertise their presence via agent advertisement messages. The mobile node may also optionally solicit an agent advertisement message from them. 1. MN - attaches to a new foreign network. 2. MN - solicits an agent advertisement (if necessary). 3. FA - sends advertisement. 2. Registration Now that the mobile node is on a foreign network, it obtains a care-of address on this network, and registers its new care-of address with its home agent, possibly via the foreign agent. 4. MN - requests registration from FA. 5. FA - forwards registration request to HA. 6. HA - sends registration reply to FA. 7. FA - forwards registration reply to MN. 8. HA - proxy ARPs for MN. 3. Data Transfer to the Mobile Node Data sent to the mobile node's home address are now intercepted and tunneled by the home agent to the mobile node's care-of address. These are then received at the tunnel endpoint (foreign agent for example) and delivered to the mobile node. 9. HA - intercepts, encapsulates, and forwards packets to FA (arrow 2 in Figure 1). 10. FA - decapsulates and forwards to MN (arrow 3 in Figure 2). 4. Data Transfer From the Mobile Node Data from the mobile node are delivered to their destination using stan- dard IP routing mechanisms, not necessarily passing through the home agent. 11. MN - Encapsulates and forwards packets to Destination (Figure 2).
A new version of the Internet Protocol, IPv6, is being developed with 128-bit addresses. IPv6 remedies perceived flaws in the existing version of IP (that is, IPv4). Mobile computers are likely to account for a substantial fraction of the population of the Internet during the lifetime of IPv6. The development of IPv6 presents a rare opportunity, in that there is no existing installed base of IPv6 hosts or routers with which compatibility must be maintained. All IPv6 nodes may be assumed to perform the few operations needed to support Internet-wide mobility. The most important function needed to support mobility is the reliable and timely notification of a mobile node's current location to those other nodes that need it. The home agent needs this location information in order to redirect packets from the home network to the mobile node. Correspondent nodes need this information in order to send their own packets directly to the mobile node.