13.4.2.1 The I-TCP Protocol The I-TCP protocol uses a split connection approach to handle the characteristics of the wireless component of a TCP connection. Separate transport level connections are used between the static host and the base station, and between the base station and the mobile host. Although TCP is used for the connection between the static host and the base station, a customized transport protocol that is configured to take into consideration the vagaries of the wireless link is used between the base station and the static host. The base station thus exports an “image” of the mobile host to the static host. Through this image, the stat- ic host “thinks” that it is communicating with the mobile host and not the base station. When the mobile host undergoes a hand-off across cells, the image is transferred to the base station in the new cell. Since the connection is split at the base station, it is possible for the base station to perform the bulk of the tasks, thus relieving the mobile host of any complex responsibilities. Figure 13.2 shows a pictorial representation of the I-TCP protocol. A consequence of using the split connection approach is that I-TCP does not conform to the end-to-end se- mantics of TCP. Instead, two completely different connections are maintained over the two branches. As a result, if there were a base station failure, or if the mobile host remained disconnected from the network for a prolonged period of time, the semantics in I-TCP would be different from that of regular TCP. 13.4 APPROACHES TO IMPROVE TRANSPORT LAYER PERFORMANCE 301 Physical Path STATIC HOST MOBILE HOST WIRELINE NETWORK WIRELESS LINK TCP TCP ITCP ITCP BASESTATION Split Connection Semantics Independent 3. Congestion Control 4. Reliability 2. Flow Control 1. Connection Management Figure 13.2 The I-TCP protocol. We now elaborate on the performance of I-TCP in terms of the four functionalities: ț Connection Establishment and Flow Control. Both connection establishment and flow control are altered in I-TCP in the sense that they are split across two indepen- dent connections. When a mobile host wants to initiate a connection to a static host, it sends a connection request to its base station. The base station creates the appro- priate “image” of the mobile host and in turn sends a connection request to the stat- ic host. Thus the connection establishment is done explicitly for both the split con- nections. Similarly, flow control is done independently between the static host and the base station, and the base station and the mobile host. ț Congestion Control. Like flow control, congestion control is also done independent- ly along both branches of the split connection. Although the congestion control scheme used over the connection between the static host and the base station is the same as that in regular TCP, a custom congestion control scheme can presumably be used over the connection between the base station and the mobile host. The I-TCP approach does not stipulate the use of a particular congestion control scheme that is suitable for wireless data transfer. ț Reliability. Similar to the earlier functions, reliability is also achieved independently over the split connections. When the base station acknowledges a packet to the stat- ic host, the static host no longer attempts to send the packet since it believes that the mobile host has received the packet. Then, it is the responsibility of the base station to ensure that the packet is delivered reliably over the second half of the connection. It is because of this two-stage reliability that TCP’s end-to-end semantics can be compromised by I-TCP. For example, if there is a base station failure after an ac- knowledgment is sent back to the sender, the mobile host will never receive all packets that the base station had buffered and acknowledged. However, the sender will believe that all such packets have been delivered to the mobile host. Such an in- consistency will not arise in regular TCP. Performance results for I-TCP [2] show a marginal performance improvement when operating over a local-area wireless network. On the other hand, over wide-area wireless networks, I-TCP exceeds the performance of TCP by about 100% for different mobility scenarios, and for cases where there are prolonged blackouts (more than 1 second), I-TCP is shown to improve performance by about 200%. 13.4.3 End-to-End Protocols End-to-end protocols retain the end-to-end semantics of TCP, but require changing the protocol stack at both the sender and the receiver. However, barring the cost of upgrading the protocol stacks, such schemes can typically be much more effective than the previous classes of approaches because of the possibility of a complete revamp of the congestion control and reliability schemes used. For instance, in TCP the congestion control and reli- ability schemes are closely coupled because of the use of ACKs for both reliability and congestion control. Hence, irrespective of what intermediate scheme is used to improve 302 TRANSPORT OVER WIRELESS NETWORKS TCP’s performance, the interplay between reliability and congestion control is not desir- able and will negatively influence TCP’s performance. However, in a newly designed transport protocol that does not need to conform to TCP’s design, such anomalies (at least those that show up when operating over wireless networks) can be removed. Furthermore, since there are no intermediaries as in the case of the previous classes of approaches, there is no chance for the schemes of the end-to-end protocol to interfere with the schemes used by the intermediary. Approaches that belong to this category of approaches have the fol- lowing characteristics: (i) retention of the end-to-end semantics of TCP; (ii) sophisticated and thoroughly customized congestion control and reliability schemes; and (iii) possibili- ty of a comprehensive solution that addresses most of the problems identified in the previ- ous sections. WTCP [17] is a transport protocol that belongs to this category; we elaborate on it below. 13.4.3.1 The WTCP Protocol The WTCP protocol is an end-to-end approach to improve transport layer performance over wireless networks. Although the flow control and connection management in WTCP are similar to those in TCP, WTCP uses unique mechanisms for its congestion control and reliability schemes that in tandem enable WTCP to comprehensively overcome the char- 13.4 APPROACHES TO IMPROVE TRANSPORT LAYER PERFORMANCE 303 EndtoEnd Semantics Physical Path STATIC HOST MOBILE HOST BASESTATION WIRELINE NETWORK WIRELESS LINK WTCP WTCP 1. Ratebased 1. Interpacket separation based congestion detection 2. Distinguishing congestion and noncongestion losses. 3. Selective ACKs 4. Rate adaptation and 3. Probing on blackouts transmissions. 2. Packetpair based rate estimation 4. ACK frequency tuning. feedback. Figure 13.3 The WTCP protocol. acteristics of wireless networks discussed in Section 13.3. Briefly, WTCP uses rate-based transmissions at the source, interpacket separation at the receiver as the metric for conges- tion detection, mechanisms for distinguishing between congestion and noncongestion losses, and bandwidth estimation schemes during the start-up phase as part of its conges- tion control framework. It also uses selective ACKs, no dependence on RTTs and RTOs, and a tunable ACK frequency as part of its approach for achieving reliability. We elaborate subsequently on how each of these mechanisms contribute to improving WTCP’s perfor- mance over wireless networks. WTCP requires change of the the protocol stacks at both the sender and the receiver. This is in contrast to the earlier approaches that either require no changes at the end hosts or require changes only at the mobile host. The authors of WTCP argue that although WTCP requires changes at both the sender and the receiver, since most mobile hosts com- municate with a proxy server in the distribution network of the wireless network provider, any such changes would need to be done only at the proxy and the mobile host. We now elaborate on each of the mechanisms used in WTCP: ț Connection Management and Flow Control. WTCP uses the same connection man- agement and flow control schemes as TCP. ț Congestion Control. WTCP uses the following unique schemes for its congestion control: (i) Rate-based transmissions. Since the bursty transmissions of TCP lead to in- creasing and varying delays, WTCP uses rate-based transmissions and hence spaces out transmissions of packets. This further plays a significant role in WTCP’s congestion detection. (ii) Congestion detection based on receiver interpacket separation. Congestion is detected when the interpacket separation at the receiver is greater than the sepa- ration at the sender by more than a threshold value. Such a congestion detection scheme is valid because queue buildups that occur because of congestion result in interpacket separations between packets increasing as the packets traverse the network. Further, using such a detection scheme, congestion can be detected be- fore packet losses occur, thereby optimally utilizing the scarce resources of wireless networks. (iii) Computation at the receiver. The receiver does most of the congestion control computation in WTCP. Thus, WTCP effectively removes the effect of reverse path characteristics from the congestion control. (iv) Distinguishing between congestion- and noncongestion-related losses. WTCP uses an interpacket separation-based scheme to distinguish between conges- tion- and noncongestion-related losses [19]. Thereby, the congestion control scheme in WTCP reacts only to congestion-related losses. (v) Start-up behavior. WTCP uses a packet pair-like approach to estimate the avail- able rate, and sets its initial rate to this value. When the connection experiences a blackout, WTCP uses the same estimation scheme as when it recovers from the blackout. 304 TRANSPORT OVER WIRELESS NETWORKS ț Reliability. A unique aspect of WTCP is the fact that it decouples the congestion control mechanisms cleanly from the reliability mechanisms. Hence, it uses sepa- rate congestion control sequence numbers and reliability sequence numbers in its data transfer. WTCP has the following features in its reliability scheme: (i) Use of selective acknowledgments. Unlike TCP which uses only cumulative acknowledgments, WTCP uses a combination of cumulative and selective ac- knowledgments to retransmit only those packets that are actually lost, thereby saving on unnecessary transmissions. (ii) No retransmission timeouts. Although TCP suffers from not being able to accu- rately measure RTT, and hence experiences inflated RTOs, WTCP does not use retransmission timeouts. Instead, it uses an enhanced selective acknowledgment scheme to achieve reliability. (iii) Tunable ACK frequency. The ACK frequency in WTCP is tunable by the sender, depending on the reverse path characteristics. Performance results (both real-life and simulation experiments) show that WTCP per- forms significantly better than regular TCP. For packet error rates of around 4%, WTCP shows a performance improvement of about 100% over regular TCP. As the packet error rate increases, the difference in WTCP’s performance in comparison with regular TCP keeps increasing. 13.4.4 Comparative Discussion In order to provide intuition as to how the above-discussed approaches compare with each other, we now provide a high-level discussion on their drawbacks. ț Link Layer Schemes. Link layer schemes suffer from the following drawbacks: (i) When the delay over the wireless component of the end-to-end path is a signifi- cant portion of the end-to-end delay, it is more likely that the retransmissions performed by the enhanced link layer will interfere with the retransmissions at the sender, thereby degrading throughput. (ii) When the bandwidths are very low, the delay bandwidth product on the wireless link reduces considerably. In such a scenario, it is unlikely that there will be suf- ficient number of duplication ACKs for the snoop module to detect a packet loss and perform a local retransmission. (iii) The snoop module needs to reside on the base station of the wireless network. However, upgrading the base station is in the hands of the wireless network provider and it is unlikely that a wireless network provider will allow for arbi- trary code to be injected into the base stations. ț Indirect Protocols. Indirect protocols suffer from the following drawbacks when compared with the other approaches. (i) Break in end-to-end semantics. As described earlier, it is possible for the sender and receiver in I-TCP to believe in states inconsistent with each other. This can 13.4 APPROACHES TO IMPROVE TRANSPORT LAYER PERFORMANCE 305 happen when the mobile host stays disconnected from the base station for a pro- logned period of time, or there is a failure at the base station. (ii) Processing overhead. Since I-TCP is a transport layer mechanism, all packets will have to go up to the transport layer at the point of split, and come down again through the protocol stack. This will introduce unnecessary overheads into the end-to-end data transfer. (iii) The base station needs to maintain state on a per-connection basis and it is less likely that a wireless network provider will allow for a connection-specific state to reside on the devices inside the wireless network. ț End-to-End Protocols. The drawbacks of WTCP are: (i) WTCP assumes that interpacket separation is a good metric for the detection of congestion. Although this might be true when the bottleneck link is definitely the wireless link, the same is not evident when the bottleneck link can be some- place upstream of the wireless link. (ii) Loss distinguishing mechanism. The loss detection mechanism currently used by WTCP is a heuristic. However, the heuristic can be shown to fail in several scenarios [6]. (iii) WTCP requires changes in the protocol stack at both the sender and the receiv- er. Hence, in the absence of proxy servers, static hosts will have to have a dedi- cated protocol stack for communications with the mobile hosts. 13.5 SUMMARY Wireless networks are becoming an integral part of the Internet, with the mobile user pop- ulation increasing at an astronomical rate. Conventional protocols at the different layers of the network protocol stack were designed for a primarily wireline environment, and relat- ed studies have shown that they will not suffice for a predominantly wireless environment. In this chapter, we addressed the issue of reliable transport over heterogeneous wireline/wireless networks. We provided a brief overview of the TCP transport protocol, identified the key characteristics of wireless network environments, and discussed the limitations that these characteristics impose on the performance of TCP. We then dis- cussed three broad classes of approaches to support efficient, reliable transport over wire- less networks. However, due to lack of space, we have not touched upon an abundant amount of relat- ed work besides those presented in this chapter [3]. Most of the approaches considered in this chapter focus on wireless link characteristics and do not explicitly address the issue of mobility and hand-offs. Several approaches have been proposed in related work that ad- dress the hand-off issues in a wireless environment through intelligent network layer schemes [18]. In addition, we have focused only on transport layer problems and solutions in a cellular wireless environment, and have not included the related work in the area of transport over multihop wireless networks in our discussions. For a detailed look at some of the solutions for reliable transport over multihop wireless networks, see [10, 12]. Briefly, the problem of transport over multihop wireless network is made more complicat- 306 TRANSPORT OVER WIRELESS NETWORKS ed because of the added dimension of fine-grained mobility. In [10], the authors propose an explicit link failure notification extension to TCP wherein the node upstream of a link failure (because of mobility) sends an ELFN message to the TCP source. The TCP source then freezes its operations until a new route is computed. In [12], the authors argue that in addition to an ELFN mechanism, it is essential to have a hop-by-hop rate control mecha- nism for effective congestion control over multihop wireless networks. REFERENCES 1. J. Agosta and T. Russle, CDPD: Cellular Digital Packet Data Standards and Technology, McGraw Hill, New York, NY, 1997. 2. A. Bakre and B. R. Badrinath, I-TCP: Indirect TCP for mobile hosts, in Proceedings of Interna- tional Conference on Distributed Computing Systems (ICDCS), Vancouver, Canada, May 1995. 3. H. Balakrishnan, V. N. Padmanabhan, S. Seshan, and R. Katz, A comparison of mechanisms for improving TCP performance over wireless links, in Proceedings of ACM SIGCOMM, Stanford, CA, August 1996. 4. H. Balakrishnan, S. Seshan, E. Amir, and R. Katz, Improving TCP/IP performance over wire- less networks, in Proceedings of ACM MOBICOM, Berkeley, CA, November 1995. 5. V. Bharghavan, A. Demers, S. Shenker, and L. Zhang, MACAW: A medium access protocol for wireless LANs, in Proceedings of ACM SIGCOMM, London, England, August 1994. 6. S. Biaz and N. H. Vaidya, Discriminating congestion losses from wireless losses using inter- arrival times at the receiver, in In Proceedings of IEEE Asset, Richardson, TX, March 1999. 7. H. I. Kassab, C. E. Koksal, and H. Balakrishnan, An analysis of short-term fairness in wireless media access protocols, in Proceedings of ACM SIGMETRICS, Santa Clara, CA, June 2000. 8. D. Chiu and R. Jain, Analysis of the increase/decrease algorithms for congestion avoidance in computer networks, Journal of Computer Networks and ISDN, 17(1): 1–14, June 1989. 9. Wireless Data Forum. http://www.wirelessdata.org/. 10. G. Holland and N. Vaidya, Analysis of TCP performance over mobile ad-hoc networks, in Pro- ceedings of ACM MobiCom, Seattle, WA, August 1999. 11. H-Y. Hsieh and R. Sivakumar, Performance comparison of cellular and multi-hop wireless net- works: A quantitative study, in Proceedings of ACM SIGMETRICS, Boston, MA, 2001. 12. P. Sinha J. Monks and V. Bharghavan, Limitations of TCP-ELFN for ad hoc networks, in Pro- ceedings of IEEE International Workshop on Mobile Multimedia Communications, Tokyo, Japan, October 2000. 13. P. Karn, MACA—A new channel access method for packet radio, in ARRL/CRRL Amateur Ra- dio 9th Computer Networking Conference, London, ON, Canada, September 1990. 14. T. V. Lakshman and U. Madhow, The performance of TCP/IP for networks with high bandwidth- delay products and random loss, IEEE/ACM Trans. Networking, 5(3):336–350, 1997. 15. S. Lu, V. Bharghavan, and R. Srikant, Fair queuing in wireless packet networks, in Proceedings of ACM SIGCOMM, Cannes, France, September 1997. 16. M. Satyanarayanan, Fundamental challenges in mobile computing, in ACM Symposium on Principles of Distributed Computing, Philadelphia, PA, May 1996. 17. P. Sinha, N. Venkitaraman, R. Sivakumar, and V. Bharghavan, WTCP: A reliable transport proto- REFERENCES 307 col for wireless wide-area networks, in Proceedings of ACM MOBICOM, Seattle, WA, August 1999. 18. S. Seshan, H. Balakrishnan, and R. H. Katz, Handoffs in cellular wireless networks: The daedalus implementation and experience, Kluwer International Journal on Wireless Personal Communications, 4(2):141–162, 1997. 19. P. Sinha, T. Nandagopal, T. Kim and V. Bharghavan, Service differentiation through end-to-end rate control in low bandwidth wireless packet networks, in Proceedings of IEEE International Workshop on Mobile Multimedia Communications, San Diego, CA, November 1999. 308 TRANSPORT OVER WIRELESS NETWORKS CHAPTER 14 Security and Fraud Detection in Mobile and Wireless Networks AZZEDINE BOUKERCHE Department of Computer Sciences, University of North Texas 14.1 INTRODUCTION The fusion of computer and telecommunication technologies has heralded the age of in- formation superhighway over wireline and wireless networks. Mobile cellular communi- cation systems and wireless networking technologies are growing at an ever-faster rate, and this is likely to continue in the foreseeable future. Wireless technology is presently be- ing used to link portable computer equipment to corporate distributed computing and oth- er sources of necessary information. Wide-area cellular systems and wireless LANs promise to make integrated networks a reality and provide fully distributed and ubiquitous mobile communications, thus bringing an end to the tyranny of geography. Higher relia- bility, better coverage and services, higher capacity, mobility management, power and complexity for channel acquisition, handover decisions, security management, and wire- less multimedia are all parts of the potpourri. Further increases in network security are necessary before the promise of mobile telecommunication can be fulfilled. Safety and security management against fraud, intru- sions, and cloned mobile phones, just to mention a few, will be one of the major issues in the next wireless and mobile generations. A “safe” system provides protection against errors of trusted users, whereas a “secure” system protects against errors introduced by impostors and untrusted users [1]. Therefore, rather than ignoring the security concerns of potential users, merchants, and telecommunication companies need to acknowledge these concerns and deal with them in a straightforward manner. Indeed, in order to convince the public to use mobile and wireless technology in the next and future generations of wireless systems, telecom companies and all organizations will need to explain how they have addressed the security of their mobile/wireless systems. Manufacturers, M-business, service providers, and entrepreneurs who can visualize this monumental change and effectively leverage their experiences on both wireless and Internet will stand to benefit from it. Concerns about network security in general (mobile and wired) are growing, and so is research to match these growing concerns. Indeed, since the seminal work by D. Denning [9] in 1981, many intrusion-detection prototypes, for instance, have been created. Intru- sion-detection systems aim at detecting attacks against computer systems and wired net- 309 Handbook of Wireless Networks and Mobile Computing, Edited by Ivan Stojmenovic´ Copyright © 2002 John Wiley & Sons, Inc. ISBNs: 0-471-41902-8 (Paper); 0-471-22456-1 (Electronic) works, or against information systems in general. However, intrusion detection in mobile telecommunication networks has received very little attention. It is our belief that this is- sue will play a major role in future generations of wireless systems. Several telecom carri- ers are already complaining about the loss due to impostors and malicious intruders. In this chapter, we will identify and describe several aspects of wireless and mobile net- work security. We will discuss the intrusion detection systems in wired and wireless net- works and identify the new challenges and opportunities posed by the ad hoc network, a new wireless paradigm for mobile hosts. Unlike traditional mobile wireless networks, ad hoc networks do not rely on any fixed infrastructure. Instead, they rely on each other to keep the network connected. Next, we will examine the authentication problem of mobile users. Finally, we discuss the problems of cloning and fraud detection in mobile phone operations 14.2 NETWORK SECURITY PROBLEMS Security is an essential part of wired and wireless network communications. Interestingly enough, these systems are designed to provide open access across vast networked environ- ments. Today’s technologies are usually network-operation-intrusive, i.e., they often limit the connectivity and inhibit easier access to data and services. With the increasing popu- larity of wireless networks, the security issue for mobile users could be even more serious than we expect. The traditional analogue cellular phones are very insecure. The 32-bit ser- ial number, the 34-bit phone number, and the conversation in a cell can be scanned easily by an all-band receiver. The widely used advanced mobile phone system (AMPS) is an analogue phone system. Therefore, sending a password or a host name through this system can be a serious security issue. Other security issues in wireless networks that have been studied extensively are anonymity and location privacy in mobile networks; these have re- ceived a great deal of interest recently [23]. A typical situation is one in which a mobile user registered in a certain home domain requests services while visiting a foreign do- main. Concerned about security and privacy, the user would prefer to remain anonymous with respect to the foreign domain. That is, only the home domain authority should be in- formed as to the mobile user’s real identity, itinerary, whereabouts, etc. Another important issue, namely cloning phones, raises a number of concerns to many telecom carriers. In- deed, many telecommunication companies are losing money due to the use of clones or genuine mobile phones by impostors. One might argue that although it is rather easy to clone an AMPS phone, it is much trickier to clone a D-AMPS, a GSM, or an IS-95 phone. However, the security issue remains, and needs to be resolved in the next wireless network generation. Consequently, there has been a great deal of interest recently in designing mo- bile phones using new technologies, such as Boot Block flash technology used by Intel Corporation, that will make it much more difficult to clone cellular phones. However, to the best of our knowledge there is very little work being done at the software level. To combat cloning, cellular operators analyze usage to check for unusual patterns. Most obvi- ously, they know that genuine phone cannot be in two places at once. If a phone is making more than one call at a time, it has definitely been cloned. Furthermore, to verify if a call is out of the client patterns, current software (i) does not have an efficient automatic process to warn clients about the impostors using their mobile phones; in most of these 310 SECURITY AND FRAUD DETECTION IN MOBILE AND WIRELESS NETWORKS [...]... encryption and password management, maintenance of security equipment and services, and informing users of their responsibilities 14.4 INTRUSION DETECTION SYSTEMS (IDS) Intrusion is most probably one of the key issues that wireless and mobile systems will have to deal with The nature of wireless ad hoc networks makes them very vulnerable to 312 SECURITY AND FRAUD DETECTION IN MOBILE AND WIRELESS NETWORKS. .. industry and the increasing popularity of wireless networks, there has been a great deal of concern about security in wireless and mobile telecommunication systems TABLE 14.1 Number of neurons in the hidden layer and respective error rate Number of neurons (hidden layer) Error rate 50 107 100 110 111 127 5.0185 4.3758 4.4252 4.2027 4.2027 4.3511 322 SECURITY AND FRAUD DETECTION IN MOBILE AND WIRELESS NETWORKS. .. 15.4 MOBILE AD HOC NETWORKS AND THE INTERNET The wide acceptance of Internet standards and technologies was and is one of the key steps for building global computer networks capable of connecting everything and reaching everyone In the near future, with the advent of inexpensive wireless technologies, a large number of users will be mobile Extending IP internetworking for seamless operation over wireless. .. A Boukerche and M S M A Notare, Neural fraud detection in mobile phone operations, 4th IEEE BioSP3, Bio-Inspired Solutions to Parallel Processing, May 2000, pp 63 6 64 4 5 A Boukerche, M Sechi Moretti, and A Notare, Applications of neural networks to mobile and wireless networks, In Biologically Inspired Solutions to Parallel and Distributed Computing, A Zomaya (Ed.), New York: Wiley, 2001 6 E Brinksma... 16, 35–50, 2001 31 Y Zhang and W Lee, Intrusion detection in wireless ad hoc networks, IEEE/ACM MobiCom Proc., 2000, pp 275–283 32 R Rivest, The MDS message-digest algorithm, RFC2 86, Internet Engineering Task Force, Symbolic, Inc., 1982 33 A Boukerche and M S M A Notara, Behavior based intrusion detection in mobile phone systems, Journal of Parallel and Distributed Computing, in press Handbook of Wireless. .. application for ad hoc networks, commercial interest in this type of networks continues to grow Applications such as rescue missions in times of natural disasters, law enforcement operations, commercial and educational use, and sensor networks are just a few possible commercial examples Ad hoc wireless networks inherit the traditional problems of wireless and mobile communications, such as bandwidth optimization,... confidentiality, integrity, authentication, and nonrepudiation but also new types of threats that are extended even to 314 SECURITY AND FRAUD DETECTION IN MOBILE AND WIRELESS NETWORKS the basic structure of the networks The salient characteristics of ad hoc networks pose both challenges and opportunities in achieving these security goals Since ad hoc networks use wireless links, they are susceptible to... Recognition and Neural Networks, Cambridge University Press, 19 96 26 M S M A Notare, A Boukerche, F Cruz, B Risco, and C Westphal security management against cloning mobile phones, IEEE Globecom’99, pp 969 –973 Dec 1999 27 S P Shieh, C T Lin, and J T Hsueh, Secure communication in global systems for mobile telecommunication, in Proceedings of the First IEEE Workshop on Mobile Computing, 1994, pp 1 36 142 28... wireless technology [49, 50, 56] Traditional cellular and mobile networks are still, in some sense, limited by their need for infrastructure (i.e., base stations, routers) For mobile ad hoc networks, this final limitation is eliminated Ad hoc networks are key to the evolution of wireless networks [48] Ad hoc networks are typically composed of equal nodes that communicate over wireless links without any... of network protocols and applications, especially if wireless technologies evolve to become a significant part of the infrastructure [ 46] The Internet Engineering Task Force (IETF) Working Group on Mobile Ad Hoc NETworks (MANET) is standardizing routing in ad hoc networks The group studies routing specifications, with the goal of supporting networks scaling up to hundreds of routers [40] The work of . systems and wired net- 309 Handbook of Wireless Networks and Mobile Computing, Edited by Ivan Stojmenovic´ Copyright © 2002 John Wiley & Sons, Inc. ISBNs: 0-471-41902-8 (Paper); 0-471-224 56- 1. http://www.wirelessdata.org/. 10. G. Holland and N. Vaidya, Analysis of TCP performance over mobile ad-hoc networks, in Pro- ceedings of ACM MobiCom, Seattle, WA, August 1999. 11. H-Y. Hsieh and R Lakshman and U. Madhow, The performance of TCP/IP for networks with high bandwidth- delay products and random loss, IEEE/ACM Trans. Networking, 5(3):3 36 350, 1997. 15. S. Lu, V. Bharghavan, and R.