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Network+ Exam Cram: Wireless Networking

Jun 9, 2009

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802.11 Wireless Standards

802.11 represents the IEEE designation for wireless networking. Several wireless networking specifications exist under the 802.11 banner. The Network+ objectives focus on 802.11, 802.11a, 802.11b, 802.11g, and 802.11n. All these standards use the Ethernet protocol and the CSMA/CA access method.

The 802.11 wireless standards can differ in terms of speed, transmission ranges, and frequency used, but in terms of actual implementation they are similar. All standards can use either an infrastructure or ad hoc network design, and each can use the same security protocols. Ad hoc and infrastructure wireless topologies were discussed in Chapter 1.

IEEE 802.11: There were actually two variations on the initial 802.11 wireless standard. Both offered 1 or 2Mbps transmission speeds and the same RF of 2.4GHz. The difference between the two was in how data traveled through the RF media. One used FHSS, and the other used DSSS. The original 802.11 standards are far too slow for modern networking needs and are now no longer deployed.
IEEE 802.11a: In terms of speed, the 802.11a standard was far ahead of the original 802.11 standards. 802.11a specified speeds of up to 54Mbps in the 5GHz band, but most commonly, communication takes place at 6Mbps, 12Mbps, or 24Mbps. 802.11a is incompatible with the 802.11b and 802.11g wireless standards.
IEEE 802.11b: The 802.11b standard provides for a maximum transmission speed of 11Mbps. However, devices are designed to be backward-compatible with previous 802.11 standards that provided for speeds of 1, 2, and 5.5Mbps. 802.11b uses a 2.4GHz RF range and is compatible with 802.11g.
IEEE 802.11g: 802.11g is a popular wireless standard today. 802.11g offers wireless transmission over distances of 150 feet and speeds up to 54Mbps compared with the 11Mbps of the 802.11b standard. Like 802.11b, 802.11g operates in the 2.4GHz range and therefore is compatible with it.
IEEE 802.11n: The newest of the wireless standards listed in the Network+ objectives is 802.11n. The goal of the 802.11n standard is to significantly increase throughput in both the 2.4GHz and the 5GHz frequency range. The baseline goal of the standard was to reach speeds of 100Mbps, but given the right conditions, it is estimated that the 802.11n speeds might reach a staggering 600Mbps. In practical operation, 802.11n speeds will be much slower.

The Magic Behind 802.11n

802.11n is poised to bring about the next big change in wireless networking, promising greater distances and staggering speeds. But how is this done? 802.11n takes the best from the 802.11 standards and mixes in some new features to take wireless to the next level. First among these new technologies is multiple input multiple output (MIMO) antenna technology.

MIMO is unquestionably the biggest development for 802.11n and the key to the new speeds. Essentially, MIMO uses multiplexing to increase the range and speed of wireless networking. Multiplexing is a technique that combines multiple signals for transmission over a single line or medium. MIMO enables the transmission of multiple data streams traveling on different antennas in the same channel at the same time. A receiver reconstructs the streams, which have multiple antennas as well. By using multiple paths, MIMO provides a significant capacity gain over conventional single-antenna systems, along with more reliable communication.

In addition to all these improvements, 802.11n allows channel bonding that essentially doubles the data rate again. What is channel bonding? The 802.11b and 802.11g wireless standards use a single channel to send and receive information. With channel bonding, you can use two channels at the same time. As you might guess, the ability to use two channels at once increases performance. It is expected that bonding will help increase wireless transmission rates from the 54Mbps offered with the 802.11g standards to a theoretical maximum of 600Mbps. 802.11n uses the OFDM transmission strategy.

Summary of 802.11 Wireless Standards

Table 7.5 highlights the characteristics of the various 802.11 wireless standards.

Table 7.5. 802.11 Wireless Standards

IEEE Standard	Frequency/Medium	Speed	Topology	Transmission Range	Access Method
802.11	2.4GHz RF	1 to 2Mbps	Ad hoc/infrastructure	20 feet indoors.	CSMA/CA
802.11a	5GHz	Up to 54Mbps	Ad hoc/infrastructure	25 to 75 feet indoors; range can be affected by building materials.	CSMA/CA
802.11b	2.4GHz	Up to 11Mbps	Ad hoc/infrastructure	Up to 150 feet indoors; range can be affected by building materials.	CSMA/CA
802.11g	2.4GHz	Up to 54Mbps	Ad hoc/infrastructure	Up to 150 feet indoors; range can be affected by building materials.	CSMA/CA
802.11n	2.4GHz/5GHz	Up to 600Mbps	Ad hoc/infrastructure	175+ feet indoors; range can be affected by building materials.	CSMA/CA

FHSS, DSSS, OFDM, and 802.11 Standards

The original 802.11 standard had two variations, both offering the same speeds but differing in the RF spread spectrum used. One of the 802.11 standards used FHSS. This 802.11 variant used the 2.4GHz radio frequency band and operated at a 1 or 2Mbps data rate. Since this original standard, wireless implementations have favored DSSS.

The second 802.11 variation used DSSS and specified a 2Mbps peak data rate with optional fallback to 1Mbps in very noisy environments. 802.11, 802.11b, and 802.11g use DSSS. This means that the underlying modulation scheme is similar between each standard, allowing all DSSS systems to coexist with 2, 11, and 54Mbps 802.11 standards. As a comparison, it is like the migration from the older 10Mbps Ethernet networking to the more commonly implemented 100Mbps standard. The speed was different, but the underlying technologies were similar, allowing for an easier upgrade.

Table 7.6 compares wireless standards and the spread spectrum used.

Table 7.6. Comparison of IEEE 802.11 Standards

IEEE Standard	RF Used	Spread Spectrum	Data Rate (in Mbps)
802.11	2.4GHz	DSSS	1 or 2
802.11	2.4GHz	FHSS	1 or 2
802.11a	5GHz	OFDM	54
802.11b	2.4GHz	DSSS	11
802.11g	2.4Ghz	DSSS	54
802.11n	2.4/5GHz	OFDM	600 (theoretical)

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