3.3
Compare and contrast different wireless standards
In Chapter 2, I briefly discussed wireless standards and stated that we
would cover them in much more detail in Chapter 3. In this section, I will discuss the most common wireless
standards in use in today's networks and the main technology they use. In
particular, I will discuss the aspects of distance, speed, latency, frequency,
and channels. I will also discuss Multiple Input/Multiple Output (MIMO) and
channel bonding.
802.11 is the IEEE specification that is used for wireless LAN
technology. 802.11 specifies an over-the-air interface between a wireless client
and a base station or between two wireless clients. The IEEE accepted the
specification in 1997. The original 802.11 standard used a frequency hopping
spread spectrum radio (FHSS) signal. There have been many revisions to the
standard since then. The following are the major 802.11 standards in use today:
802.11a 802.11a uses orthogonal frequency division multiplexing (OFDM) to increase
bandwidth. This standard uses the 5GHz radio band and can transmit at up to
54Mbps. It is not widely used today.
802.11b Uses direct sequence spread
spectrum (DSSS) in the 2.4GHz radio band. This standard can transmit at up to
11Mbps with fallback rates of 5.5Mbps, 2Mbps, and 1Mbps. It is quickly being
superseded by the newer and faster standards that I'll discuss next.
802.11g Uses DSSS and OFDM and the 2.4GHz
radio band. This standard enhances the 802.11b standard and can transmit at
speeds up to 54Mbps. It is one of the most commonly used standards and is
backward compatible with 802.11b, since they both can use DSSS and the 2.4GHz
band.
802.11n Uses DSSS and OFDM and the 2.4GHz
and the 5Ghz band. This standard enhances the 802.11g standard and can transmit
at speeds up to 600Mbps, although most devices in use today support speeds only
up to about 300Mbps. This standard is backward compatible with 802.11g and
802.11b and even 802.11a.
In general, the newer wireless standards can cover greater
distances than the older standards, but there is much more to this than “meets
the eye.” The general distance (also called range) of
802.11a/b/g is about 30 meters. 802.11n is a little higher, at about 90 meters.
However, these figures should never be taken for granted because they can be
affected by the construction of a building, objects around the WAP, or other
devices causing interference. You can improve distance (range) of your wireless
networks by keeping the WAP and the computers away from large metal objects that
can absorb and reflect signals. As you may remember, I already discussed
troubleshooting common wireless network issues in Chapter 2.
In general, latency is the time that it takes for data to
travel from a transmitter to a receiver, sometimes also known as delay. In wireless communications, latency is very
unpredictable to say the least. The reason for this goes back to the fact that
wireless communications can be affected by a large number of factors around the
WAP and around the computers being used. Latency is not caused by a decrease in
the speed of the connection (radio waves always travel at the speed of light)
but rather by the fact that additional management frames are used by Carrier
Sense Multiple Access with Collision Avoidance (CSMA/CA). Also, CSMA/CA may
decide to hold or delay data transmissions.
As I mentioned in Chapter 2, you don't usually set the frequency of your wireless
devices, at least not directly. You simply choose which type of wireless
technology you will use and then select the channel that you will use, or even
just accept the default. As I discussed earlier, in general, there are two
frequency bands used by 802.11 a/b/g/n. 802.11a uses the 5GHz band. 802.11a/b/g
use 2.4GHz band. Finally, 802.11n uses both bands.
You did notice that I said band? Well, in
this case, the word band refers to a range of frequencies
that are automatically selected. Some vendors allow you to tweak the advanced
settings and select only the frequencies you want. You should, however, be
careful if you choose this option because if you set it specifically for one
device, then you will need to set it specifically for all the other devices that
you want to communicate.
As I mentioned earlier, wireless networks use many different
frequencies within a band of frequencies (typically the 2.4GHz or 5GHz band).
These frequencies are sometimes combined to provide greater bandwidth for the
user. A combination of these frequencies that can be used by the end user is
referred to as a channel. Most often, wireless networks
use channels 1, 6, and 11. This is generally selected automatically, but you can
change the channel if you are receiving interference from another network or
wireless device. For the WAP and the clients to communicate, they must be on the
same channel.
Multiple-input and multiple-output (MIMO)
is a technique of using multiple antennas at both the transmitter and receiver
to improve communication performance. It is an emerging technology that offers
significant increases in speed and distance without a need for more transmission
power. MIMO is used with 802.11n and with 4G technologies.
Understand 802.11 wireless standards There
are many 802.11 wireless standards that have been developed over the years,
including 802.11/a/b/g/n. Each of these standards has its own capabilities and
limitations. You should know the frequency, distance, and speed of each
standard. Also, 802.11a uses the 5Ghz band, which makes it incompatible with
802.11b/g but still compatible with 802.11n.
Be familiar with the use of channels
Wireless networks operate in a band of frequencies, referred to as a channel. The channels most often used are 1, 6, and 11. For
your WAP to communicate with your clients, the two must share the same
channel.
Be familiar with MIMO and channel bonding
Both MIMO and channel bonding are techniques used to improve the quality of
wireless communication. MIMO, used on 802.11n, employs multiple antennas at both
the transmitter and the receiver to improve communication performance. Channel
bonding, used on 802.11g and 802.11n, combines two or more network interfaces on
a single computer for increased data throughput.
In Chapter 2, I briefly discussed wireless standards and stated that we
would cover them in much more detail in Chapter 3. In this section, I will discuss the most common wireless
standards in use in today's networks and the main technology they use. In
particular, I will discuss the aspects of distance, speed, latency, frequency,
and channels. I will also discuss Multiple Input/Multiple Output (MIMO) and
channel bonding.
802.11 a/b/g/n standards
802.11 is the IEEE specification that is used for wireless LAN
technology. 802.11 specifies an over-the-air interface between a wireless client
and a base station or between two wireless clients. The IEEE accepted the
specification in 1997. The original 802.11 standard used a frequency hopping
spread spectrum radio (FHSS) signal. There have been many revisions to the
standard since then. The following are the major 802.11 standards in use today:
802.11a 802.11a uses orthogonal frequency division multiplexing (OFDM) to increase
bandwidth. This standard uses the 5GHz radio band and can transmit at up to
54Mbps. It is not widely used today.802.11b Uses direct sequence spread
spectrum (DSSS) in the 2.4GHz radio band. This standard can transmit at up to
11Mbps with fallback rates of 5.5Mbps, 2Mbps, and 1Mbps. It is quickly being
superseded by the newer and faster standards that I'll discuss next.802.11g Uses DSSS and OFDM and the 2.4GHz
radio band. This standard enhances the 802.11b standard and can transmit at
speeds up to 54Mbps. It is one of the most commonly used standards and is
backward compatible with 802.11b, since they both can use DSSS and the 2.4GHz
band.802.11n Uses DSSS and OFDM and the 2.4GHz
and the 5Ghz band. This standard enhances the 802.11g standard and can transmit
at speeds up to 600Mbps, although most devices in use today support speeds only
up to about 300Mbps. This standard is backward compatible with 802.11g and
802.11b and even 802.11a.Distance
In general, the newer wireless standards can cover greater
distances than the older standards, but there is much more to this than “meets
the eye.” The general distance (also called range) of
802.11a/b/g is about 30 meters. 802.11n is a little higher, at about 90 meters.
However, these figures should never be taken for granted because they can be
affected by the construction of a building, objects around the WAP, or other
devices causing interference. You can improve distance (range) of your wireless
networks by keeping the WAP and the computers away from large metal objects that
can absorb and reflect signals. As you may remember, I already discussed
troubleshooting common wireless network issues in Chapter 2.Latency
In general, latency is the time that it takes for data to
travel from a transmitter to a receiver, sometimes also known as delay. In wireless communications, latency is very
unpredictable to say the least. The reason for this goes back to the fact that
wireless communications can be affected by a large number of factors around the
WAP and around the computers being used. Latency is not caused by a decrease in
the speed of the connection (radio waves always travel at the speed of light)
but rather by the fact that additional management frames are used by Carrier
Sense Multiple Access with Collision Avoidance (CSMA/CA). Also, CSMA/CA may
decide to hold or delay data transmissions.Frequency
As I mentioned in Chapter 2, you don't usually set the frequency of your wireless
devices, at least not directly. You simply choose which type of wireless
technology you will use and then select the channel that you will use, or even
just accept the default. As I discussed earlier, in general, there are two
frequency bands used by 802.11 a/b/g/n. 802.11a uses the 5GHz band. 802.11a/b/g
use 2.4GHz band. Finally, 802.11n uses both bands.You did notice that I said band? Well, in
this case, the word band refers to a range of frequencies
that are automatically selected. Some vendors allow you to tweak the advanced
settings and select only the frequencies you want. You should, however, be
careful if you choose this option because if you set it specifically for one
device, then you will need to set it specifically for all the other devices that
you want to communicate.Channels
As I mentioned earlier, wireless networks use many different
frequencies within a band of frequencies (typically the 2.4GHz or 5GHz band).
These frequencies are sometimes combined to provide greater bandwidth for the
user. A combination of these frequencies that can be used by the end user is
referred to as a channel. Most often, wireless networks
use channels 1, 6, and 11. This is generally selected automatically, but you can
change the channel if you are receiving interference from another network or
wireless device. For the WAP and the clients to communicate, they must be on the
same channel.MIMO
Multiple-input and multiple-output (MIMO)
is a technique of using multiple antennas at both the transmitter and receiver
to improve communication performance. It is an emerging technology that offers
significant increases in speed and distance without a need for more transmission
power. MIMO is used with 802.11n and with 4G technologies.
Exam Essentials
Understand 802.11 wireless standards There
are many 802.11 wireless standards that have been developed over the years,
including 802.11/a/b/g/n. Each of these standards has its own capabilities and
limitations. You should know the frequency, distance, and speed of each
standard. Also, 802.11a uses the 5Ghz band, which makes it incompatible with
802.11b/g but still compatible with 802.11n.Be familiar with the use of channels
Wireless networks operate in a band of frequencies, referred to as a channel. The channels most often used are 1, 6, and 11. For
your WAP to communicate with your clients, the two must share the same
channel.Be familiar with MIMO and channel bonding
Both MIMO and channel bonding are techniques used to improve the quality of
wireless communication. MIMO, used on 802.11n, employs multiple antennas at both
the transmitter and the receiver to improve communication performance. Channel
bonding, used on 802.11g and 802.11n, combines two or more network interfaces on
a single computer for increased data throughput.