A guide to wireless standards for CompTIA Network+ candidates
We’ve looked at some of the wireless networking related topics that appear on CompTIA’s Network+ certification exams (both the current N10-005 exam and the upcoming N10-006) in other articles. To finish that topic, the focus this month is on wireless standards and what you need to know about them to pass this certification exam. Much of this information is excerpted from the CompTIA Network+ Exam Cram.
802.11 represents the IEEE designation for wireless networking. Several wireless networking specifications exist under the 802.11 banner. The Network+ objectives focus on 802.11a, 802.11b, 802.11g, 802.11n, and 802.11ac. All these standards use the Ethernet protocol and the CSMA/CA access method. NOTE: Exams like to see if you know not only the characteristics of the wireless standards, but also the access method. Remember: 802.11 wireless standards use 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.
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. Devices are designed to be backward compatible, however, 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 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 most popular wireless standard today is 802.11n. The goal of the 802.11n standard was 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 can reach a staggering 600Mbps. In practical operation, 802.11n speeds are much slower.
IEEE 802.11ac: The newest of the wireless standards listed in the Network+ objectives is 802.11ac, which became an approved standard in January of 2014 and can be thought of as an extension of 802.11n. Any device using this standard must support all the mandatory modes of both 802.11n and 802.11a. The goal of the standard is 500Mbps with one link and 1Gbps with multiple links. It has support for up to 8 MIMO streams and increased channel bonding. 802.11ac is a 5 GHz-only technology.
The Magic Behind 802.11n and 802.11ac
802.11n took the best from the 802.11 standards and mixed in some new features to take wireless to the next level. First among these new technologies was multiple input multiple output (MIMO) antenna technology.
MIMO was 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.
While 802.11n can transmit more than one spatial stream at the same time, the streams are directed to a single address (MIMO). 802.11ac allows for multiple user MIMO (MUMIMO) to let an AP send multiple frames to multiple clients at the exact same time (thus allowing the AP to act like a switch instead of just a hub).
In addition to all MIMO, 802.11n enabled channel bonding that essentially doubled the data rate. 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 can 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.
802.11ac extends this by increasing the maximum from 40 MHz to 80 MHz (with hypothetical of 160 MHz). By doubling the channel bandwidth, twice as much data can be carried in the same time. NOTE: In wireless networking a single channel is 20MHz in width. When two channels are bonded, they are a total of 40MHz. 802.11n systems can use either the 20MHz channels or the 40MHz channel.
Aggregation is the other big difference, allowing data to be packaged together to increase speeds. 802.11n brought the technology to the mainstream and 802.11ac simply builds on it.
Summary of 802.11 Wireless Standards
The following table highlights the characteristics of the various 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|
|802.11ac||5GHz||Up to 1Gbps||Ad hoc/infrastructure||115+ feet indoors; range can be affected by building materials||CSMA/CA|
FHSS, DSSS, OFDM
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 noisy environments. 802.11, 802.11b, and 802.11g use DSSS. This means that the underlying modulation scheme is similar between each standard, enabling 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 1000Mbps standard. The speed was different, but the underlying technologies were similar, enabling an easier upgrade.
The following table compares wireless standards and the spread spectrum used.
|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|
Summing it Up
To prepare for the wireless networking portion of a certification exam — particularly CompTIA’s Network+ — it helps to know the basics of wireless standards. This article highlighted the characteristics of the various 802.11 wireless standards.