Introduction
Wireless technologies represent a rapidly emerging area of growth and importance for providing ubiquitous access to the network for all of the campus community. Students, faculty and staff increasingly want un-tethered network access from general-purpose classrooms, meeting rooms, auditoriums, and even the hallways of campus buildings. There is interest in creating mobile computing labs utilizing laptop computers equipped with wireless Ethernet cards. Recently, industry has made significant progress in resolving some constraints to the widespread adoption of wireless technologies. Some of the constraints have included disparate standards, low bandwidth, and high infrastructure and service cost. Wireless technologies can both support the institution mission and provide cost-effective solutions. Wireless is being adopted for many new applications: to connect computers, to allow remote monitoring and data acquisition, to provide access control and security, and to provide a solution for environments where wires may not be the best solution.
What follows is an overview of existing wireless technologies and related issues.
There are numerous applications for all the different wireless technologies. For the purposes of this paper, applications of wireless technologies are divided into the following:
Although a traditional classification, this way of categorizing wireless technologies also includes their differences in cost models, bandwidth, coverage areas, etc. Finally, a section is included on issues related to wireless technologies.
Cell phones, pagers, and commercial two-way business radios can provide voice and messaging services. These devices may be based on analog or digital standards that differ primarily in the way in which they process signals and encode information. The analog standard is the Advanced Mobile Phone Service (AMPS). Digital standards are Global System for Mobile Communications (GSM), Time Division Multiple Access (TDMA), or Code Division Multiple Access (CDMA).
Normally, devices operate within networks that provide metropolitan, statewide, or nationwide coverage. These large and costly networks are operated by carriers such as AT&T, Sprint, Verizon, local phone companies, etc. and operate in different frequency bands which are allocated by the FCC. Throughput depends on the standard being used, but presently in the U.S., these networks operate throughput rates up to 16 kilobits per second (Kbps). New digital standards, also referred to as "Third-Generation Services" or 3G, are expected by 2004, and will provide 30 times faster transfer rates and enhanced capabilities. Because of the many standards, there are interoperability issues between networks, carriers, and devices. Generally, charges are based on per minute utilization or per number of messages.
Hand-held and Internet-enabled devices
Internet-enabled cell phones and Personal Digital Assistants (PDAs) have emerged as the newest products that can connect to the Internet across a digital wireless network. New protocols, such as Wireless Application Protocol (WAP), and new languages, such as WML (Wireless Markup Language) have been developed specifically for these devices to connect to the Internet. However, the majority of current Internet content is not optimized for these devices; presently, only email, stock quotes, news, messages, and simple transaction-oriented services are available. Other limitations include low bandwidth (less than 14 Kbps), low quality of service, high cost, the need for additional equipment, and high utilization of devices' battery power. Nevertheless, this type of wireless technology is growing rapidly with better and more interoperable products.
We differentiate between pure data applications in wireless local area networks (WLANs) and data, voice, and video converged in broadband wireless. We also briefly discuss Bluetooth, an emerging wireless technology.
Wireless Local Area Networks (WLAN) are implemented as an extension to wired LANs within a building and can provide the final few meters of connectivity between a wired network and the mobile user.
WLANs are based on the IEEE 802.11 standard. There are three physical layers for WLANs: two radio frequency specifications (RF - direct sequence and frequency hopping spread spectrum) and one infrared (IR). Most WLANs operate in the 2.4 GHz license-free frequency band and have throughput rates up to 2 Mbps. The new 802.11b standard is direct sequence only, and provides throughput rates up to 11 Mbps. Currently the predominant standard, it is widely supported by vendors such as Cisco, Lucent, Apple, etc. By the middle of 2002, a new standard, 802.11a, will operate in the 5 GHz license-free frequency band and is expected to provide throughput rates up to 54 Mbps.
WLAN configurations vary from simple, independent, peer-to-peer connections between a set of PCs, to more complex, intra-building infrastructure networks. There are also point-to-point and point-to-multipoint wireless solutions. A point-to-point solution is used to bridge between two local area networks, and to provide an alternative to cable between two geographically distant locations (up to 30 miles). Point-to-multi-point solutions connect several, separate locations to one single location or building. Both point-to-point and point-to-multipoint can be based on the 802.11b standard or on more costly infrared-based solutions that can provide throughput rates up to 622 Mbps (OC-12 speed). In a typical WLAN infrastructure configuration, there are two basic components:
- Access Points - An access point/base station connects to a LAN by means of Ethernet cable. Usually installed in the ceiling, access points receive, buffer, and transmit data between the WLAN and the wired network infrastructure. A single access point supports on average twenty users and has a coverage varying from 20 meters in areas with obstacles (walls, stairways, elevators) and up to 100 meters in areas with clear line of sight. A building may require several access points to provide complete coverage and allow users to roam seamlessly between access points.
- Wireless Client Adapter - A wireless adapter connects users via an access point to the rest of the LAN. A wireless adapter can be a PC card in a laptop, an ISA or PCI adapter in a desktop computer, or can be fully integrated within a handheld device.
Broadband wireless (BW) is an emerging wireless technology that allows simultaneous wireless delivery of voice, data, and video. BW is considered a competing technology with Digital Subscriber Line (DSL). It is generally implemented in metropolitan areas and requires clear line of sight between the transmitter and the receiving end. BW comes in two flavors: Local multi-point distribution service (LMDS) and Multi-channel multi-point distribution service (MMDS). Both operate in FCC-licensed frequency bands.
LMDS is a high bandwidth wireless networking service in the 28-31 GHz range of the frequency spectrum and has sufficient bandwidth to broadcast all the channels of direct broadcast satellite TV, all of the local over-the-air channels, and high speed full duplex data service. Average distance between LMDS transmitters is approximately one mile apart.
MMDS operates at lower frequencies, in the 2 GHz licensed frequency bands. MMDS has wider coverage than LMDS, up to 35 miles, but has lower throughput rates. Companies such as Sprint and WorldCom own MMDS licenses in the majority of U.S. metropolitan areas. Broadband wireless still involves costly equipment and infrastructures. However, as it is more widely adopted, it is expected that the service cost will decrease.
Bluetooth is a technology specification for small form factor, low-cost, short-range wireless links between mobile PCs, mobile phones, and other portable handheld devices, and connectivity to the Internet. The Bluetooth Special Interest Group (SIG) is driving development of the technology and bringing it to market and it includes promoter companies such as 3Com, Ericsson, IBM, Intel, Lucent, Motorola, Nokia, and over 1,800 Adopter/Associate member companies. Bluetooth covers a range of up to ten meters in the unlicensed 2.4GHz band. Because 802.11 WLANs also operate in the same band, there are interference issues to consider. Bluetooth technology and products started being available in 2001, but interoperability seems to be a big problem. By the time and if Bluetooth becomes an adopted technology, current WLANs will already be migrating to the 5 GHz band (mid 2002).
As with any relatively new technology, there are many issues that affect implementation and utilization of wireless networks. There are both common and specific issues depending on the type of wireless network. Some of the common factors include electromagnetic interference and physical obstacles that limit coverage of wireless networks, while others are more specific, such as standards, data security, throughput, ease of use, etc.
A major obstacle for deployment of wireless networks is the existence of multiple standards. As it was mentioned previously, there are analog and digital standards in wireless telephony. While GSM is the only widely supported standard in Europe and Asia, multiple standards are in use in the U.S. As a result, the U.S. has lagged in wireless networks deployment.Just recently, organizations have been formed to ensure network and device interoperability. For example, the adoption of the 802.11b standard has made wireless data networks one of the hottest newcomers in the current wireless market.
Another issue is coverage. Coverage mainly depends on the output power of the transmitter (FCC regulated), its location and frequency used to transmit data. For example, lower frequencies are more forgiving when it comes to physical obstacles (walls, stairways, etc.), while high frequencies require clear line of sight. For each particular application, throughput decreases as distance from the transmitter or access point increases.
Data security is a major issue for wireless due to the nature of the transmission mechanism (electromagnetic signals passing through the air). It is commonly believed that voice applications are less secure than data applications. This is due to limited capabilities of existing technologies to protect information that is being transmitted. For example, in metropolitan areas, users are at risk that simple scanning devices can highjack cell phone numbers and be maliciously used. In WLANs, authentication and encryption provide data security. Current implementations include:
- MAC address-based access lists on access points, where only registered and recognized MAC addresses are accepted and allowed to join the network.
- A closed wireless system, where users have to know non-advertised the network name to be able to join.
- RADIUS server based authentication, where users are authenticated against a centralized RADIUS server based on their MAC address or their username and password.
- Wireless Equivalency Privacy (WEP) utilizes data encryption with 40-bit or 128-bit keys that are hidden from users. WEP provides three options, depending on the level of security needed: no encryption of data, combination of encrypted and non-encrypted data, and forced data encryption.
- High security solutions for encryption are proprietary: Cisco AP-350 and Lucent/Agere AS-2000. Both offer per user/per session encryption keys and authenticate users based on username/password scheme.
It is important to understand that in WLANs, data is encrypted only between the wireless adapter and the access point. Data travels through a wired LAN unencrypted. Therefore, data transmitted by wireless is not more secure than data transmitted through the wire, but probably not less secure. Application level encryption mechanisms, like secure web transactions (SSL), SSH, etc. are responsible for further protection of data.
Voice and messageing wireless services are provided in the Knoxville area by a number of commercial wireles providers. Wireless networking access on UT campus is provided by OIT. During 2000, DII (now OIT) has evaluated a number of products for wireless LAN access. Lucent/Agere/Orinoco/Proxim Access Server 2000 was selected. This product provides encryption with dynamic per user/per session keys by using RC4 encryption algorithm, thus preventing network sniffing. Users also have to login to the wireless network by providing their NetID username and password. This is authenticated against Radius and LDAP servers. If a user is not in LDAP or does not meet other criteria, a user is denied access to the wireless network. Since the first inception and due to limited client support and buggy software/firmware, UT has reverted to AP-2000 code in May 2002.
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