The availability of Ethernet-like data transmission of greater than 10 Mbps comes with the adoption of the IEEE 802.11b WLAN standard. Products such as wireless PC Card adapters and wireless Access Points offer Ethernet speeds and standards-based interoperability. The advantages of Wireless include:
Wireless LANs communicate on spread spectrum radio waves are less susceptible to radio noise and interference and therefore appropriate for data communications. There are two types of spread spectrum: direct sequence and frequency hopping. Direct sequence is the only one that supports 11 Megabits per second (Mbps) Ethernet type speeds
Multiple wireless networks can exist in the same physical area. A DSSS network accomplishes this by breaking up the 2.4 - 2.4835 GHz band into several sub-bands that each contains an independent DSSS network. Since the 802.11 standard requires that there must be 30MHz of distance between each of the sub-bands and there is only 83.5Mhz available, only 3 DSSS networks can co-exist in an area. A FHSS network accomplishes this by using different frequency hopping sequences. The 802.11 standard defines 79 different hops and 78 different hopping sequences that are grouped in 3 sets of 26 sequences each. Theoretically 26 networks could be co-located, but due to synchronization only 15 are possible.[i]
Originally, FHSS networks had the advantage over DSSS at the 2 Mbps standard to hop around blocked signal and multi-path interference (signal bounce off of reflective surfaces causing multiple paths). FSSS could continue to function due to a wider spread of signal although at slower speeds, but recent compensation strategies such as signal strength algorithms and dual antenna access points has given DSSS a similar reliability with the advent of the 802.11b standards.
Important improvements have been seen within the Ethernet 802.3 environment. The ratification of the 802.11b or High Rate standard provides data rates of 11 Mbps. This standard is based on DSSS technology and provides speeds up to 11 Mbps with fallback rates of 5.5 Mbps, 2 Mbps, and 1 Mbps and the physical layer uses Complementary Code Keying (CCK) technology. It uses the same bandwidth as the 2 Mbps DSSS standard and thus interoperates with legacy IEEE DSSS systems. As in the wired world, higher speeds are continuously desired for applications such as streaming video, telephony and multimedia. Also, faster peak rates will allow more nodes to effectively connect to a WLAN via a single channel. Now that the standard development has stabilized many of the industry’s leading vendors have brought out high-speed products.
Before the common use and availability of 802.11b standards, there was a good reason to use FSSS. It has a lower cost, lower power consumption and is less susceptible to frequency blocking. But the overriding factor to choose DSSS is that it supports 11mbps while FSSS goes no higher than 2 mbps. Most Wireless Vendors supply DSSS 11mbps equipment today and the prices for it recently have dramatically declined. The clear choice for speed alone is DSSS.
Wireless computing, using broadcast data through encryption, can offer a level of security comparable to a wired system. The signal is modulated to encrypt its contents very securely. Spread-spectrum technologies were initially designed for the military as a modulation technique to encrypt a signal with a spreading code so that a receiver could not decode the signal without knowing the spreading code. Both DSSS and FHSS spread the transmitted signal across a larger frequency band than necessary to transmit the signal.
Frequency hopping moves the frequency of a narrow band signal around within a broad frequency bank in a pattern based on the spreading code. Direct sequence modulation transmits across the entire broad band, but at a higher signal rate. This is accomplished by multiplying the original narrow bank signal by a spreading code. [ii]
802.11b technologies support up to 128-bit Wired Equivalent Privacy (WEP) encryption security is available to provide data security that is comparable to traditional wired LANs. The WEP keys for the wireless network must be set up exactly the same on the Access Points as they are on the wireless client adapters. The same value must be assigned to Key 1 on both the Access Point and the client adapters, the same value must be assigned to Key 2 on both the Access Point and the client adapters, and so on, for all four WEP keys. For example, if WEP Key 3 on the Access Point is set to 0987654321 and it is selected as the active key, WEP Key 3 on the client adapters must be set to the same value and selected as the active key. The WEP Key extension is equivalent to the term “chipping code” and is embedded in the wireless 802.11b packet.
ZD.net (PC Week and PC Magazine) recently did a product comparison of currently available 802.11b Wireless Products on the market. The vendors included Apple AirPort, Cisco/Aironet Wireless 340 Series, Compaq WL Series, Lucent Orinoco Wireless Network, RadioLAN Wireless Mobilink, 3Com AirConnect. The Editor’s Choice was Cisco/Aironet Wireless 340 Series. The evaluation was based on deployment, management, convenience, and performance. The Aironet product was superior in every category except performance. The RadioLAN Wireless was the fastest with shear throughput of data, but is not 802.11b compliant and is proprietary.[iii]
Cisco/Aironet wireless bridges also allow multiple sites to share a single, high-speed connection to the Internet and provide up to 128-bit Wired Equivalent Privacy (WEP). WEP’s integrated with standard authentication features providing a level of data security equal to traditional wired networks. The wireless bridges are flexible, supporting high data rates over medium and short ranges or lower data rates for long-range support. They are compact and unobtrusive and can be redeployed quickly as network requirements or company locations change. They are not affected by bad weather and require no FCC (or applicable agency) license. Configuration and management options include direct console or remote configuration via Telnet, File Transfer Protocol (FTP), Simple Network Management Protocol (SNMP) or browser graphical user interface (GUI). An enhanced Management Information Base (MIB) allows network managers to choose from a variety of SNMP-compliant network management packages. The Cisco/Aironet 340 series bridge also supports configuration and management via generally available scripting tools. Other features include support for 802.1 Spanning-Tree protocol and advanced diagnostics to simplify troubleshooting.
If the choice of Wireless product is Cisco/Aironet, there are other advantages to its implementation at Johns Hopkins University/Hospital. The Cisco/Aironet product line is due to be included in the Cisco Element Management Framework (CEMF). CEMF serves as the foundation for the Cisco Service Management System used in the management of service provider and carrier-class networks. It is based on object-oriented, open systems architecture, enabling flexibility and adaptability to network changes such as equipment models, transmission protocols, and changing standards.
The framework is made up of a set of integrated software modules and GUIs that create an internetworking structure for cohesive element management. A single CEMF server can support multiple element managers encompassing several different technologies such as routers, switches, Digital Subscriber Line access concentrator (DSLAMs), Digital Subscriber Line (xDSL), Voice over IP (VoIP), cable modems, and Wireless.
The Directory-Enabled Network (DEN) initiative now under the supervision of the Desktop Management Task Force (DMTF), consists of housing information on users, network devices of all kinds, applications, and business and security policies. Directories tie together the various system components, application-specific requirements and data, and network management. They also serve as the means to integrate these functions for an entire network.
A policy server can provides information that can be used by Dynamic Host Configuration Protocol (DHCP) servers, authentication, authorization, and account (AAA) servers (security servers), and service provisioning servers. DEN specifications were defined so that all networking and directory vendors could agree on a common baseline directory schema and information model.
Cisco Networking Services for Active Directory (CNS/AD) enables Microsoft’s Active Directory to securely and efficiently propagate directory events. It also adds DEN-compliant Cisco extensions to the core directory schema to represent Cisco network elements and services. CNS/AD will have the ability to gather and act on changing information as well. CNS/AD serves as the rendezvous point among networks, applications, routers, switches, and network access servers, and they can employ their intelligence to prioritize how the network traffic is being used to determine which application or user should get priority for available bandwidth.
CNS/AD acts as a repository of metadata (global resource information) about the entire network environment. Core activities and business-critical traffic must be protected and given priority. CNS/AD is able to segment static data from dynamic data, and continually synchronized so that changes to dynamic data are replicated in near real time. In a DEN environment, the status of all network devices, regardless of location or ownership, can be collected in the directory using a standard information model. DEN provides management control over complex data-intensive applications across a dispersed network. The ubiquity of the directory services saves money because it promotes more efficient use of valuable network resources while ensuring the customer gets the right level of service.[iv]
The Bluetooth communications device is a small, low-powered radio in a chip that will “talk” to other Bluetooth-enabled products, eliminating the need for cables or infrared beams to connect portable computers, cellular phones, printers, fax machines, etc. It will be possible to connect enabled devices on a one-to-one or one-to-many basis. For the future, this will be the prevalent way for PDAs, Mobile Computers, and phones to connect.
The computer and radio combination could then be optimized to minimize interference. A task made easier for computer engineers with only one radio. With a single-radio solution, computer vendors are no longer faced with having to make a network choice or supporting multiple networks. Since the chip supports both voice and data communications, applications will range from something as simple as replacing the cable between a mobile computer and cellular phone, to more complex connections involving multiple computers, and extending into hands-free voice communications for wireless phones in vehicles.
The Bluetooth solution eliminates the need for a wide-area network decision. This can be left to the makers of phones and modems and other wide-area network devices. The radio, which is inexpensive to build in, can be used to connect any two or more devices that are equipped with the radio module. The Bluetooth solution provides a short-range ad hoc network, enabling users to send and receive e-mail without a phone and synchronize their calendar and phone book automatically whenever the two devices detect each other’s presence.
Communications companies will no longer have to build external cables for PC Cards to enable their wireless phones and network cards to interface to computers. A Bluetooth module built into the phone or wireless network connection points will enable it to send and receive information to and from any computer so equipped. Since Bluetooth is capable of short-range voice communications as well, it will also be used as a hands-free voice interface for cellular phones, a speakerphone link, and a link between the phone and other electronics in an automobile. Bluetooth technology enables multiple devices to communicate with each other using a common set of standards when they are within range.
The compelling reasons for incorporating Bluetooth are to wirelessly connect mobile computers to cellular phones, and to establish small workgroups quickly and easily. As the number of Bluetooth-equipped devices grows, so will their uses. Printers fax machines, LANs, and more will be able to communicate with each other. On the communications side, cellular phones, two-way pagers, wireless data-only terminals, and most other two-way wireless-capable devices will be Bluetooth-equipped. Bluetooth will provide the “glue” for the merger of wireless and computers.
The low-power radio module can and will be built into mobile computers, mobile phones, printers, fax machines, and network connection points. While its primary focus is to be the wireless connection between mobile computers and/or between computers and wireless network devices such as cellular phones, Bluetooth supports data speeds of up to 721 Kbps (including a 56 Kbps back channel) as well as three voice channels. Originally the price of the Bluetooth equipment should be fifteen to twenty dollars. The cost should drop to about $5 by 2001 when the devices will be ubiquitous.
The Bluetooth design is a collaborative effort between communications and computing companies. Ericsson and Nokia independently were working on similar radio concepts. They understood the need for a partner on the computer side and independently approached Intel with the idea. Intel has been instrumental in driving the concept to reality. Microsoft, IBM, Toshiba, Motorola, 3COM, and Palm are all working on Bluetooth implementation.
Bluetooth has been designed to operate in a multi-user environment. Devices can be enabled to communicate with each other by the computer or communications device end user. Up to eight users or devices can make up a piconet, and ten piconets can co-exist in the same coverage range sometimes referred to as a cell. Since each link is encoded and protected against both eavesdropping and interference. Bluetooth can be considered a secure short-range wireless network.[v]
The balance of the specifications is as follows:
Frequency Band: 2.4 GHz (unlicensed ISM Band)
Transmitter Power: 1 milliWatt (0 dBm)
Technology: Spread Spectrum
Hybrid Direct sequence and frequency hopping
Maximum Voice Channels: 3 per piconet
Maximum Data Channels: 7 per piconet
Data speed: 721 Kbps per piconet
Expected System Range: 10 meters (40 feet)
Number of Devices Supported: 8 per piconet, 10 piconets in a coverage area
Security: Yes, link layer
Power Requirement: 2.7 volts
Power Consumption: 30 uA sleep, 60 uA hold, 300 uA standby
8-30 mA transmitting
Module size: 0.5 square inches [vi]
There is a graceful degradation of the symbol rate for more than 10 piconets in a given coverage area. To secure the transmission, Bluetooth wireless technology has built-in encryption and authentication. Bluetooth minimizes potential interference and eavesdropping by employing fast frequency hopping at1600 hops/sec. Also, an automatic output power adaptation reduces the range exactly to the required specification, which makes the system difficult to eavesdrop.
The primary advantage to this system is that computer vendors can build it in. They don’t have to worry about choosing a wide-area network to support, or stocking an assortment of modules for several networks, and engineers need only minimize interference for one radio on one frequency band. Further, enabling their computers for wireless data communications will not require a PC Card slot or option bay cavity for these will remain available for other uses.
The primary disadvantage of Bluetooth is interference. Bluetooth supporters say they don’t compete with the HomeRF and 802.11B standards vying for wireless networking dominance, but a pending FCC ruling allowing HomeRF to operate at a faster speed could cause interference with Bluetooth devices. Also, there are concerns with the 802.11b crowd about Bluetooth using the ISM (Instrument, Scientific, Medical) bandwidth. There are published studies available on http://www.wirelessethernet.org done by Bluetooth and Wireless vendors on the interference in the 2.45 GHz bandwidth. It seems the farther away the Bluetooth devices are from the sending unit; there is more chance of interference in the presence of a Wireless Access Point. Another disadvantage is that Bluetooth-enabled devices at the range of 100 feet get seriously compromised when walls go up between devices. Also, the standard speed for wireless Ethernet connections is now approaching 10 Mbps and Bluetooth’s top speed is about 721 Kbps.
[i]
Wireless LAN Technology Summary and
Technical Recommendation
Weinberg Comprehensive Cancer Center Johns Hopkins Medicine
Ben Reynolds Monday, April 26, 1999