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layer protocols. The L2CAP can provide both connection-oriented and connectionless
communication to the higher layers. L2CAP is needed for protocol multiplexing, since the
headers of Baseband packets does not include bits to specify what higher-layer protocol is
encapsulated in the Baseband packet. The L2CAP protocol header contains logical chan-
nel identification bits with which connection-oriented protocol multiplexing can be done,
whereas, for connection less services and control information fixed, special channel iden-
tifiers are used. Segmentation and reassembly takes care of using several of the small
Baseband packets to transmit higher-layer packets of size of up to 64 kB. Once the trans-
mission of a segmented packet starts on the ACL link, no other L2CAP ACL packets can
be interleaved with the transmission; the transmitting of the whole higher-layer PDU has
to be finished first. The L2CAP layer does not support SCO links nor does it perform in-
tegrity checks. It assumes that data integrity issues are taken care of at the Baseband layer
with automatic retransmissions or forward-error corrections.

2.3.2.5 Higher Layers and Bluetooth Profiles. The Bluetooth specification de-
fines higher-layer protocols, that is, protocols to emulate several serial connections over
ACL links, such as the RFCOMM protocol, and a protocol that defines how devices can
find out about what services other devices provide, such as the Service Discovery Proto-
col (SDP). In the second volume of the specification, called the Profiles, different ser-
vices are standardized for Bluetooth links, such as headset profiles, serial port profiles,
intercom profiles, LAN access profiles, file transfer profiles, and synchronization pro-
files. Bluetooth devices connected to each other can query the profiles the other device is
offering and, if they implement the same profiles, they can establish connections for the
given profiles, ensuring interoperability.
These protocols and profiles do not reside at the bottom two layers of the OSI-7 model
and, thus, are not an integral part of IEEE802.15.1. Since they have little significance to
ad hoc networks, their functional description is omitted in this chapter.

2.3.2.6 Further Reading. Readers interested in more details of the Bluetooth speci-
fication are referred to the freely available Bluetooth specifications [7, 8], to books sum-
marizing the Bluetooth specifications, such as [10, 28], or to the many available white pa-
pers and general resources on Bluetooth on the World-Wide-Web.
65
2.3 WIRELESS PAN TECHNOLOGIES


2.3.3 Using Bluetooth for Ad Hoc Networking
Scatternet functionality is essential for Bluetooth to be used as an enabler for ad hoc net-
works; discussions on such possibilities were ongoing as early as the first appearance of
the Bluetooth specification. Unfortunately, only few of the commercially available Blue-
tooth kits implement Scatternet functionality (most of them do not even implement the
power saving modes or point-to-multipoint operations). In order to use Bluetooth as an ad
hoc network enabler, several research problems have to be solved, including an efficient
way to discover other devices (inquiry) [45], an efficient way to switch bridge nodes be-
tween Piconets (Scatternet scheduling) [29], efficient ways to schedule the polling in mul-
tislave Piconets (Piconet scheduling) [11], selecting the best links to be activated for a Pi-
conet [27], and having distributed algorithms forming Scatterenets (Scatternet formation)
[46]. An enormous amount of research is focused on each of these areas; the cited refer-
ences to each of these research areas only show a single representative publication for the
reader who wants to get more details.
Chapter 4 of this book presents, investigates, and compares proposed Bluetooth Scat-
ternet formation algorithms in detail.
Although several research groups plan to establish Bluetooth-based ad hoc networks,
currently, no working testbed is available for study, so Bluetooth ad hoc network study re-
mains in the simulation domain. IBM research has made their Bluetooth NS-2 extension
[21] open-source available and the next release is supposed to have Scatternet functionali-
ty for simulation evaluation of Bluetooth-based ad hoc networks.


2.3.4 HomeRF”SWAP
The HomeRF Working Group [20] was launched in 1998 by Compaq, Intel, Motorola,
National Semiconductor, Proxim, and Siemens to establish an industry standard support-
ing wireless home networks. Although enjoying the support of several big industry play-
ers, HomeRF has never taken off due to the popularity of IEEE802.11b. HomeRF posi-
tioned itself in the niche market of domestic users, which is why it is listed in this chapter
under WPANs. HomeRF provides QoS-provisioned services, for example, for voice calls,
as well as packet-switched best-effort services at the 2.4 GHz ISM band, with rates simi-
lar to that of IEEE802.11b (from specification 2.0), using FH technology. HomeRF™s FH
PHY layer was designed to work around interfering sources in the home environment,
such as microwave ovens, by monitoring the channels and banning those channels from its
hopping scheme that have too much interference.
The MAC layer protocol of HomeRF is called SWAP (Shared Wireless Access Proto-
col), which provides TDMA services for isochronous data and two different priorities of
IEEE802.11, like CSMA/CA service for asynchronous data.
Although HomeRF products are available in limited supply, and nothing contradicts
using the technology for ad hoc networking, the popularity and inexpensiveness of Wi-Fi
preempts HomeRF for use as an enabler for ad hoc networking testbeds. Additionally,
HomeRF is not an open standard, making its acceptance even more difficult.


2.3.5 RFID
Radio Frequency Identification (RFID) is a technology for providing a low-bandwidth,
extremely inexpensive scheme for small integrated devices to talk wirelessly to access
66 OFF-THE-SHELF ENABLERS OF AD HOC NETWORKS


points relaying their ID (along with some optional data). RFID is used mainly for invento-
ry purposes to be able to automatically monitor large inventories that are individually
tagged with RFID tags. RFID can use active or passive tags. Passive tags do not have an
internal power source but need to be placed in an electromagnetic field to be activated and
readable, whereas active tags are battery operated and have a longer range, but are more
expensive. Unfortunately, RFID technology lacks strong standards; most of the products
available represent someone™s proprietary technology.
The authors of this chapter are unaware of any serious RFID-based ad hoc network
proposals, testbeds, or simulations, although RFID can be an extremely inexpensive basis
for large-scale, low-rate-sensor ad hoc networks. The reader interested in more details
about RFID is referred to the online resources [37, 38].


2.4 CONCLUSION

This chapter introduced several WPAN and WLAN standards. In the WLAN are, the
strongest competitor today is IEEE802.11b, also called Wi-Fi 2.4 GHz. Wi-Fi 5.2 GHz
(IEEE802.11a) is quickly emerging, providing symbol rates comparable to that of Fast-
Ethernet. Wi-Fi defines an ad hoc operational mode, which makes it the most common
off-the-shelf enabler for ad hoc network testbeds.
Bluetooth is the strongest standard in the WPAN field. Although the Bluetooth specifi-
cation allows for the establishment of ad hoc networks, referred to as Scatterenets, there
are major challenges that need to be overcome for Bluetooth to be considered a strong
contender as an off-the-shelf ad hoc networking enabler.
Although it has been shown that none of these technologies is perfect for ad hoc net-
works, they will remain the premier choices for establishing testbeds. Ad hoc research
will have to wait for dedicated ad hoc PHY and MAC technology until a killer application
is defined for wide, commercial use of ad hoc networks.
Chapters 3 and 4 further investigate the use of the IEEE802.11 and Bluetooth tech-
nologies, respectively, for ad hoc networking.


ACKNOWLEDGMENTS

Our sincere gratitude goes to Rózsa P. Záruba and Wook Choi, who helped in collecting
and compiling the references for this chapter.


REFERENCES

1. Official Homepage of The IEEE802.11 Working Group for Wireless LANs, http://
grouper.ieee.org/groups/802/11/.
2. IEEE 802, “Get IEEE 802,” http://standards.ieee.org/getieee802/.
3. 802“11 Planet Online Resource, http://www.80211-planet.com/.
4. Acticom R&D, http://www.acticom.de/1357.html.
5. Ad Hoc Protocol Evaluation Testbed, http://apetestbed.sourceforge.net/.
6. W. A. Arbaugh, “An Inductive Chosen Plaintext Attack Against WEP/WEP2,” IEEE Document
802.11-01/230, May 2001.
67
REFERENCES


7. Bluetooth SIG, “Specification of the Bluetooth System”Core,” vol. 1, version 1.1, http://
www.bluetooth.com/dev/specifications.asp, February 2001.
8. Bluetooth SIG, “Specification of the Bluetooth System”Profiles,” vol. 2, version 1.1, http://
www.bluetooth.com/dev/specifications.asp, February 2001.
9. N. Borisov, I. Goldberg, and D. Wagner, “Intercepting Mobile Communications: The Insecurity
of 802.11,” in Proceedings of the Seventh Annual International Conference on Mobile Comput-
ing and Networking (MOBICOM2001), pp. 180“189, Rome, Italy, July 2001.
10. J. Bray, C. F. Sturman, and J. Mendolia, Bluetooth 1.1: Connect Without Cables, 2nd ed., Pren-
tice-Hall, 2001.
11. A. Capone, M. Gerla, and R. Kapoor, “Efficient Polling Schemes for Bluetooth Picocells,” in
Proceeding of the IEEE International Conference on Communications (ICC2001), vol. 7, pp.
1990“1994, Helsinki, Finland, June 2001.
12. I. Chen, “Wireless Ad Hoc Messenger,” a Virginia Tech and Microsoft project, http://people.
cs.vt.edu/˜irchen/microsoft-grant/description.html.
13. J. C. Chen and J. M. Gilbert, “Measured Performance of 5GHz 802.11a Wireless LAN Sys-
tems,” Atheros Communications White Paper, http://www.atheros.com/pt, 2001.
14. T. Clausen, P. Jacquet, A. Laouiti, P. Minet, P. Mulethaler, A. Qayyum, and L. Viennot, “Opti-
mized Link State Routing Protocol,” IETF DRAFT, draft-ietf-manet-olsr-02.txt, http://hiper-
com.inria.fr/olsr/, July 2002.
15. The DAWN project, http://ntrg.cs.tcd.ie/dawn.php.
16. ETSI”BRAN, “ETSI HIPERLAN 1 Standards,” http://www.etsi.org/frameset/home.htm?/
technicalactiv/Hiperlan/hiperlan1.htm.
17. ETSI”BRAN, “ETSI HiperLAN 2 Standards,” http://www.etsi.org/frameset/home.htm?/tech-
nicalactiv/Hiperlan/hiperlan2.htm.
18. Global Mobile Information Systems Simulation Library (GloMoSim), http://pcl.cs.ucla.edu/
projects/glomosim/.
19. J. Habetha and M. Nadler, “Concept of Wireless Centralized Multihop Ad Hoc Network,” in
Proceedings of the European Wireless Conference, Dresden, September 2002.
20. HomeRF Working Group, http://www.homerf.org.
21. IBM Research, BlueHoc: Open-Source Bluetooth Simulator, http://www“124.ibm.com/devel-
operworks/opensource/bluehoc/.
22. IBM Zurich Research Laboratory, “Wireless Infrared Multipoint Network”Alr,” http://www.
zurich.ibm.com/cs/wireless/usermodel.html.
23. D. B. Johnson, “Routing in Ad Hoc Networks of Mobile Hosts,” in Proceedings of the. ACM
MOBICOM ˜94, December 1994.
24. M. Johnsson, “HiperLAN/2”The Broadband Radio Transmission Technology Operating in the
5GHz Frequency Band,” White Paper in HiperLAN 2 Global Forum, http://www.hiperlan2.com/
technology.asp, 1999.
25. P. Karn, “MACA”A New Channel Access Protocol for Wireless LANs,” in Proceedings of the
ARRL/CRRL Amateur Radio 9th Computer Networking Conference, pp.134“140, 1990.
26. A. McCormick, “OFDM Tutorial,” http://oldeee.see.ed.ac.uk/˜acmc/OFDMTut.html.
27. Gy. Miklós, A. Rácz, Z. Turányi, A. Valkó, and P. Johansson, “Performance Aspects of Blue-
tooth Scatternet Formation,” in poster section of MobiHoc 2000, Boston, MA, August 2002.
28. B. A. Miller and C. Bisdikian, Bluetooth Revealed: The Insider™s Guide to an Open Specifica-
tion for Global Wireless Communications, Prentice-Hall, 2000.
29. V. B. Misic and J. Misic. “Performance of Bluetooth Bridges in Scatternets With Limited Ser-
vice Scheduling,” ACM/Kluwer Journal of Mobile Networks and Applications (MONET), spe-
cial issue on Advances in Research of Wireless Personal Area Networking and Bluetooth En-
abled Networks, 2002.
68 OFF-THE-SHELF ENABLERS OF AD HOC NETWORKS


30. Mobile Ad Hoc Network Testbed (MART), http://www.cs.hut.fi/˜mart/index.html.
31. The MOMENT Ad Hoc Network Testbed Project, http://moment.cs.ucsb.edu/projects.html.
32. The Monarch Project, http://www.monarch.cs.rice.edu/.
33. The Network Simulator”NS-2, http://www.isi.edu/nsnam/ns/.
34. The OFDM Forum, http://www.ofdm-forum.com.
35. OPNET modeler, http://www.opnet.com.
36. C. E. Perkins and P. Bhagwat, “Highly Dynamic Destination Sequenced Distance Vector Rout-
ing (DSDV) for Mobile Computers,” in Proceeding of the ACM SIGCOMM ˜94, vol. 24, no. 4,
p. 234, October 1994.
37. RFID Technologies, http://www.aimglobal.org/technologies/rfid/.
38. RFID Journal, www.rfidjournal.com.
39. B. Sklar, “Rayleigh Fading Channels in Mobile Digital Communications Systems Part I: Char-
acterization,” IEEE Communications Magazine, pp. 90“100, July 1997.
40. B. Sklar, “Rayleigh Fading Channels in Mobile Digital Communications Systems Part II: Miti-
gation,” IEEE Communications Magazine, 102“109, July 1997.
41. Ultra-wideband Networking Group, http://www.uwb.org.
42. The Wireless Network Testbed, http://www.ee.surrey.ac.uk/CCSR/Mobile/Projects/Testbed/.
43. S. Xu and T. Saadawi, “Does the IEEE802.11 MAC Protocol Work Well in Multihop Wireless
Ad Hoc Networks?,” IEEE Communications Magazine, 39, 6, 130“137, June 2001.
44. O-C. Yue, “Design Trade-Offs in Cellular/PCS Systems,” IEEE Communications Magazine,
146“152, September 1996.
45. G. V. Záruba, “Accelerated Neighbor Discovery in Bluetooth Based Personal Area Networks,”
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CHAPTER 3




IEEE 802.11 AD HOC NETWORKS:
PROTOCOLS, PERFORMANCE,
AND OPEN ISSUES

GIUSEPPE ANASTASI, MARCO CONTI, and ENRICO GREGORI




3.1 INTRODUCTION

The previous chapter has presented the activities of the different task groups within the
IEEE 802.11 project [14], and has highlighted that the IEEE 802.11 is currently the most
mature technology for infrastructure-based wireless LANs (WLANs). The IEEE 802.11
standard defines two operational modes for WLANs: infrastructure-based and infrastruc-
tureless or ad hoc. Network interface cards can be set to work in either of these modes but
not in both simultaneously. The infrastructure-based is the mode commonly used to con-
struct the so-called Wi-Fi hotspots, i.e., to provide wireless access to the Internet. The
drawbacks of an infrastructure-based WLAN are the costs associated with purchasing and
installing the infrastructure. These costs may not be acceptable for dynamic environments
in which people and/or vehicles need to be temporarily interconnected in areas without a
preexisting communication infrastructure (e.g., intervehicular and disaster networks), or
where the infrastructure cost is not justified (e.g., in-building networks, specific residen-
tial community networks, etc.). In these cases, a more efficient solution can be provided
by the infrastructureless or ad hoc mode.
When operating in this mode, stations are said to form an Independent Basic Service
Set (IBSS) or, more simply, an ad hoc network. Any station that is within the transmission
range of any other, after a synchronization phase, can start communicating. No Access
Point (AP) is required, but if one of the stations operating in the ad hoc mode also has a

69
Mobile Ad Hoc Networking. Edited by Basagni, Conti, Giordano, and Stojmenovic.
ISBN 0-471-37313-3 © 2004 Institute of Electrical and Electronics Engineers, Inc.
70 IEEE 802.11 AD HOC NETWORKS: PROTOCOLS, PERFORMANCE, AND OPEN ISSUES


connection to the wired network, stations forming the ad hoc network have a wireless ac-
cess to the Internet.
The IEEE 802.11 technology is a good platform to implement single-hop ad hoc net-
works because of its extreme simplicity. Single-hop means that stations must be within
the same transmission radius (say, 100“200 meters) to be able to communicate. This limi-
tation can be overcome by multihop ad hoc networking. This requires the addition of rout-
ing mechanisms at stations so that they can forward packets toward the intended destina-
tion, thus extending the range of the ad hoc network beyond the transmission radius of the
source station. Routing solutions designed for wired networks (e.g., the Internet) are not
suitable for the ad hoc environment, primarily due to the dynamic topology of ad hoc net-
works.
In a pure ad hoc networking environment, the users™ mobile devices are the net-

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