Normally we would caution enterprise users to steer clear of pre-standards, but the Wi-Fi Alliance has changed the rules of the game. Given the Alliance's track record in getting interoperable products on the market, and their assurance that products built to the Draft 2.0 certification will interoperate with those based on the final standard when it is ratified, this looks to be a case where it's safe to deploy products based on the Draft.
Me-Oh-My-Oh MIMO! The major development in 802.11n that accounts for its boost in transmission capacity is the use of an optional Multiple Input-Multiple Output (MIMO) antenna system. The basic trick of a MIMO transmitter is that it can send multiple simultaneous radio transmissions, all of which occupy the same frequency channel; the 802.11n implementation can send up to four simultaneous signals, in which case one-quarter of the bits would be carried on each.
Normally if you have four transmitters all sending on the same channel, they will interfere with each other and nobody gets through. The trick in a MIMO system is that the transmitting antennas are placed some distance apart, a technique called spatial multiplexing. As the signals are originating from different points in space, the receiver will be able to distinguish each of them by its unique arrangement of multipath images (i.e. the original signal and the delayed echoes of that signal produced by its bouncing off obstacles in the environment). The amazing thing is that the transmitters do not have to be spaced that far apart to produce recognizably different images; the minimum spacing is one-half wavelength or about 3 inches for 2.4 GHz or 1.5 inches for 5 GHz transmitters.
As well as having multiple transmitters or outputs, a MIMO system can also have multiple receivers or inputs, and the energy of each transmit signal detected at each receiver is combined to improve reception; this capability also can be used to improve the performance of legacy a/b/g transmissions. The result is that a MIMO system can increase the transmission capacity through spatial multiplexing and increase the range and the reliability by combining the receive signals from each input antenna.
Besides the inherent advantage of MIMO transmission, 802.11n incorporates some other important features. First, 802.11n can operate in either the 2.4 GHz ISM or the 5 GHz U-NII bands. It can also use the standard 20-MHz channel employed in 802.11a or g, or a 40-MHz double channel. The maximum transmission rate is 289 Mbps in a 20-MHz channel, and 600 Mbps in a 40-MHz channel. None of the existing chipsets can generate four channels, so it is important to determine the maximum rate your devices can actually achieve. The standard also reduces some of the timer intervals and adds other efficiencies to the MAC protocol. Finally, the 802.11n devices can share channels with legacy a/b/g devices, though that will result in a significant reduction in throughput for the n-devices.
So Where's The Rub? Unfortunately, moving to 802.11n will involve more than just a straight equipment swap. While we're only now getting our feet wet on 802.11n, here's the first wave of issues we have uncovered.
New Equipment: The obvious requirement is that your access points and NICs will have to be upgraded; 802.11n involves a hardware, not a software upgrade. You will get some improvement in legacy NICs if you upgrade to 802.11n-capable access points, but for the full performance impact, you have to do both (i.e. "it takes two to tango").
New Network Design: The MIMO transmission results in a different coverage pattern for 802.11n access points. Traditional access points produce a coverage pattern that is characteristically round, though it can be misshapen by thick walls or other obstructions. The use of multiple transmission channels in 802.11n results in a coverage patterns with completely different shapes, and so a new site survey, either manual or computer-assisted, will be required to optimally locate the n-access points.
Wireless Intrusion Detection/Prevention System Upgrade: If you are using a Wireless Intrusion Detection/Prevention System (WIDS/WIPS) to detect unauthorized WLANs in your facility, it too will need to be upgraded to detect 802.11n transmissions. As your users can already buy 802.11n access points in Circuit City, this is something you might want to look into right away.
1-Gbps Wired Interface: As the radio link will now be operating at a speed above 100 Mbps, the connection from the access point to the wired network will have to be increased to 1 Gbps.
Power over Ethernet (PoE): Given that we install access points on the ceiling to improve the propagation pattern, we typically use Power over Ethernet (IEEE 802.3af) to power them. Most of the first-generation 802.11n access points could not operate on the nominal 15 Watts provided, so some other alternative powering plan was needed (e.g. vendor-proprietary PoE or local AC power in the ceiling). Siemens recently announced the first 802.11n AP that could operate on standard 802.3af PoE, though you should look carefully at any other capabilities you might be giving up to use standard PoE.
That's the easy stuff. The real decisions will center around how you plan and manage your wireless LAN network going forward. We noted that 802.11n can operate in either the 2.4 GHz or 5 GHz bands, so which will you use? Fundamental to that decision will be whether you intend to support legacy a/b/g devices on the same network with your n-devices.
The knee-jerk response from many consultants has been to leave your existing b/g devices where they are in the increasingly congested 2.4 GHz band, and use the 5 GHz band with its 23 available 20 MHz channels for n-devices. Unfortunately, many customers were looking at deploying WLAN voice services in the 5 GHz band using 802.11a handsets; we don't expect 802.11n-capable voice handsets for a few years at least. Should we change our voice deployment plan to use 2.4 GHz for voice and migrate our legacy data devices to 802.11n in the 5 GHz band, or should we divide our 5 GHz channels between 802.11a voice devices and high-capacity 802.11n devices?
Conclusion Wireless LANs have been one of the great technology success stories for the past decade, and that success has been driven by progressive advances in interoperable products. With the introduction of 802.11n, we are starting to feel the outside edges of the envelope, and can clearly see the limitations created by the requirement to maintain backwards compatibility with transmission rates that can go as low as 1 Mbps.
While public Hot Spot operators must continue to support every Wi-Fi device ever made, enterprise customers have greater flexibility in defining company-wide standards. I always tell my clients to set all of their access points to g-only and then hang around the Help Desk to see who calls; when someone calls, give them a 802.11g-card! We might wind up doing something similar with 802.11n, but if we plan the migration correctly, we shouldn't have to cut our legacy users off at the knees.
New Network Design: The MIMO transmission results in a different coverage pattern for 802.11n access points. Traditional access points produce a coverage pattern that is characteristically round, though it can be misshapen by thick walls or other obstructions. The use of multiple transmission channels in 802.11n results in a coverage patterns with completely different shapes, and so a new site survey, either manual or computer-assisted, will be required to optimally locate the n-access points.
Wireless Intrusion Detection/Prevention System Upgrade: If you are using a Wireless Intrusion Detection/Prevention System (WIDS/WIPS) to detect unauthorized WLANs in your facility, it too will need to be upgraded to detect 802.11n transmissions. As your users can already buy 802.11n access points in Circuit City, this is something you might want to look into right away.
1-Gbps Wired Interface: As the radio link will now be operating at a speed above 100 Mbps, the connection from the access point to the wired network will have to be increased to 1 Gbps.
Power over Ethernet (PoE): Given that we install access points on the ceiling to improve the propagation pattern, we typically use Power over Ethernet (IEEE 802.3af) to power them. Most of the first-generation 802.11n access points could not operate on the nominal 15 Watts provided, so some other alternative powering plan was needed (e.g. vendor-proprietary PoE or local AC power in the ceiling). Siemens recently announced the first 802.11n AP that could operate on standard 802.3af PoE, though you should look carefully at any other capabilities you might be giving up to use standard PoE.
That's the easy stuff. The real decisions will center around how you plan and manage your wireless LAN network going forward. We noted that 802.11n can operate in either the 2.4 GHz or 5 GHz bands, so which will you use? Fundamental to that decision will be whether you intend to support legacy a/b/g devices on the same network with your n-devices.
The knee-jerk response from many consultants has been to leave your existing b/g devices where they are in the increasingly congested 2.4 GHz band, and use the 5 GHz band with its 23 available 20 MHz channels for n-devices. Unfortunately, many customers were looking at deploying WLAN voice services in the 5 GHz band using 802.11a handsets; we don't expect 802.11n-capable voice handsets for a few years at least. Should we change our voice deployment plan to use 2.4 GHz for voice and migrate our legacy data devices to 802.11n in the 5 GHz band, or should we divide our 5 GHz channels between 802.11a voice devices and high-capacity 802.11n devices?
Conclusion Wireless LANs have been one of the great technology success stories for the past decade, and that success has been driven by progressive advances in interoperable products. With the introduction of 802.11n, we are starting to feel the outside edges of the envelope, and can clearly see the limitations created by the requirement to maintain backwards compatibility with transmission rates that can go as low as 1 Mbps.
While public Hot Spot operators must continue to support every Wi-Fi device ever made, enterprise customers have greater flexibility in defining company-wide standards. I always tell my clients to set all of their access points to g-only and then hang around the Help Desk to see who calls; when someone calls, give them a 802.11g-card! We might wind up doing something similar with 802.11n, but if we plan the migration correctly, we shouldn't have to cut our legacy users off at the knees.
Wireless Intrusion Detection/Prevention System Upgrade: If you are using a Wireless Intrusion Detection/Prevention System (WIDS/WIPS) to detect unauthorized WLANs in your facility, it too will need to be upgraded to detect 802.11n transmissions. As your users can already buy 802.11n access points in Circuit City, this is something you might want to look into right away.
1-Gbps Wired Interface: As the radio link will now be operating at a speed above 100 Mbps, the connection from the access point to the wired network will have to be increased to 1 Gbps.
Power over Ethernet (PoE): Given that we install access points on the ceiling to improve the propagation pattern, we typically use Power over Ethernet (IEEE 802.3af) to power them. Most of the first-generation 802.11n access points could not operate on the nominal 15 Watts provided, so some other alternative powering plan was needed (e.g. vendor-proprietary PoE or local AC power in the ceiling). Siemens recently announced the first 802.11n AP that could operate on standard 802.3af PoE, though you should look carefully at any other capabilities you might be giving up to use standard PoE.
That's the easy stuff. The real decisions will center around how you plan and manage your wireless LAN network going forward. We noted that 802.11n can operate in either the 2.4 GHz or 5 GHz bands, so which will you use? Fundamental to that decision will be whether you intend to support legacy a/b/g devices on the same network with your n-devices.
The knee-jerk response from many consultants has been to leave your existing b/g devices where they are in the increasingly congested 2.4 GHz band, and use the 5 GHz band with its 23 available 20 MHz channels for n-devices. Unfortunately, many customers were looking at deploying WLAN voice services in the 5 GHz band using 802.11a handsets; we don't expect 802.11n-capable voice handsets for a few years at least. Should we change our voice deployment plan to use 2.4 GHz for voice and migrate our legacy data devices to 802.11n in the 5 GHz band, or should we divide our 5 GHz channels between 802.11a voice devices and high-capacity 802.11n devices?
Conclusion Wireless LANs have been one of the great technology success stories for the past decade, and that success has been driven by progressive advances in interoperable products. With the introduction of 802.11n, we are starting to feel the outside edges of the envelope, and can clearly see the limitations created by the requirement to maintain backwards compatibility with transmission rates that can go as low as 1 Mbps.
While public Hot Spot operators must continue to support every Wi-Fi device ever made, enterprise customers have greater flexibility in defining company-wide standards. I always tell my clients to set all of their access points to g-only and then hang around the Help Desk to see who calls; when someone calls, give them a 802.11g-card! We might wind up doing something similar with 802.11n, but if we plan the migration correctly, we shouldn't have to cut our legacy users off at the knees.
1-Gbps Wired Interface: As the radio link will now be operating at a speed above 100 Mbps, the connection from the access point to the wired network will have to be increased to 1 Gbps.
Power over Ethernet (PoE): Given that we install access points on the ceiling to improve the propagation pattern, we typically use Power over Ethernet (IEEE 802.3af) to power them. Most of the first-generation 802.11n access points could not operate on the nominal 15 Watts provided, so some other alternative powering plan was needed (e.g. vendor-proprietary PoE or local AC power in the ceiling). Siemens recently announced the first 802.11n AP that could operate on standard 802.3af PoE, though you should look carefully at any other capabilities you might be giving up to use standard PoE.
That's the easy stuff. The real decisions will center around how you plan and manage your wireless LAN network going forward. We noted that 802.11n can operate in either the 2.4 GHz or 5 GHz bands, so which will you use? Fundamental to that decision will be whether you intend to support legacy a/b/g devices on the same network with your n-devices.
The knee-jerk response from many consultants has been to leave your existing b/g devices where they are in the increasingly congested 2.4 GHz band, and use the 5 GHz band with its 23 available 20 MHz channels for n-devices. Unfortunately, many customers were looking at deploying WLAN voice services in the 5 GHz band using 802.11a handsets; we don't expect 802.11n-capable voice handsets for a few years at least. Should we change our voice deployment plan to use 2.4 GHz for voice and migrate our legacy data devices to 802.11n in the 5 GHz band, or should we divide our 5 GHz channels between 802.11a voice devices and high-capacity 802.11n devices?
Conclusion Wireless LANs have been one of the great technology success stories for the past decade, and that success has been driven by progressive advances in interoperable products. With the introduction of 802.11n, we are starting to feel the outside edges of the envelope, and can clearly see the limitations created by the requirement to maintain backwards compatibility with transmission rates that can go as low as 1 Mbps.
While public Hot Spot operators must continue to support every Wi-Fi device ever made, enterprise customers have greater flexibility in defining company-wide standards. I always tell my clients to set all of their access points to g-only and then hang around the Help Desk to see who calls; when someone calls, give them a 802.11g-card! We might wind up doing something similar with 802.11n, but if we plan the migration correctly, we shouldn't have to cut our legacy users off at the knees.
Power over Ethernet (PoE): Given that we install access points on the ceiling to improve the propagation pattern, we typically use Power over Ethernet (IEEE 802.3af) to power them. Most of the first-generation 802.11n access points could not operate on the nominal 15 Watts provided, so some other alternative powering plan was needed (e.g. vendor-proprietary PoE or local AC power in the ceiling). Siemens recently announced the first 802.11n AP that could operate on standard 802.3af PoE, though you should look carefully at any other capabilities you might be giving up to use standard PoE.
That's the easy stuff. The real decisions will center around how you plan and manage your wireless LAN network going forward. We noted that 802.11n can operate in either the 2.4 GHz or 5 GHz bands, so which will you use? Fundamental to that decision will be whether you intend to support legacy a/b/g devices on the same network with your n-devices.
The knee-jerk response from many consultants has been to leave your existing b/g devices where they are in the increasingly congested 2.4 GHz band, and use the 5 GHz band with its 23 available 20 MHz channels for n-devices. Unfortunately, many customers were looking at deploying WLAN voice services in the 5 GHz band using 802.11a handsets; we don't expect 802.11n-capable voice handsets for a few years at least. Should we change our voice deployment plan to use 2.4 GHz for voice and migrate our legacy data devices to 802.11n in the 5 GHz band, or should we divide our 5 GHz channels between 802.11a voice devices and high-capacity 802.11n devices?
Conclusion Wireless LANs have been one of the great technology success stories for the past decade, and that success has been driven by progressive advances in interoperable products. With the introduction of 802.11n, we are starting to feel the outside edges of the envelope, and can clearly see the limitations created by the requirement to maintain backwards compatibility with transmission rates that can go as low as 1 Mbps.
While public Hot Spot operators must continue to support every Wi-Fi device ever made, enterprise customers have greater flexibility in defining company-wide standards. I always tell my clients to set all of their access points to g-only and then hang around the Help Desk to see who calls; when someone calls, give them a 802.11g-card! We might wind up doing something similar with 802.11n, but if we plan the migration correctly, we shouldn't have to cut our legacy users off at the knees.
That's the easy stuff. The real decisions will center around how you plan and manage your wireless LAN network going forward. We noted that 802.11n can operate in either the 2.4 GHz or 5 GHz bands, so which will you use? Fundamental to that decision will be whether you intend to support legacy a/b/g devices on the same network with your n-devices.
The knee-jerk response from many consultants has been to leave your existing b/g devices where they are in the increasingly congested 2.4 GHz band, and use the 5 GHz band with its 23 available 20 MHz channels for n-devices. Unfortunately, many customers were looking at deploying WLAN voice services in the 5 GHz band using 802.11a handsets; we don't expect 802.11n-capable voice handsets for a few years at least. Should we change our voice deployment plan to use 2.4 GHz for voice and migrate our legacy data devices to 802.11n in the 5 GHz band, or should we divide our 5 GHz channels between 802.11a voice devices and high-capacity 802.11n devices?
Conclusion Wireless LANs have been one of the great technology success stories for the past decade, and that success has been driven by progressive advances in interoperable products. With the introduction of 802.11n, we are starting to feel the outside edges of the envelope, and can clearly see the limitations created by the requirement to maintain backwards compatibility with transmission rates that can go as low as 1 Mbps.
While public Hot Spot operators must continue to support every Wi-Fi device ever made, enterprise customers have greater flexibility in defining company-wide standards. I always tell my clients to set all of their access points to g-only and then hang around the Help Desk to see who calls; when someone calls, give them a 802.11g-card! We might wind up doing something similar with 802.11n, but if we plan the migration correctly, we shouldn't have to cut our legacy users off at the knees.
