From the August, 2013 Issue of Cabling Installation & Maintenance Magazine
The revision of TSB-162 will take into account the possibility that next-generation wireless LAN data rates may exceed 7 Gbits/sec.
by Patrick McLaughlin
When the Telecommunications Industry Association (TIA; www.tiaonline.org) finalized the specifications in Telecommunications Systems Bulletin TSB-162 Telecommunications Guidelines for Wireless Access Points, the year was 2005 and the Institute of Electrical and Electronics Engineers (IEEE; www.ieee.org) had not yet finalized its 802.11n wireless local area network (LAN) specifications. Today 802.11n equipment is widely deployed in enterprise networks, and its multiple-input/multiple-output (MIMO) signaling scheme generates transmission speeds that can reach hundreds of Megabits per second.
The TSB-162 document mentions other TIA cabling standards, particularly including cabling-performance specifications. At the time the bulletin was written, the TIA-568-B revision of cabling standards was current. TSB-162 states that cabling should be installed and performance tested per 568-B.2 standards. In doing so it provides references to specifications that can help ensure the cabling infrastructure connected to a wireless access point supports the throughput capacity that the access point can achieve.
But that is just one practical benefit of the TSB. Another is that it can be used in a greenfield installation project as a guideline for prewiring an enterprise environment to support its wireless LAN infrastructure. "Precabling will be more practical and more cost-effective for everyone," when it is an option, says Masood Shariff, engineering senior principal in CommScope's (www.commscope.com) system engineering group. TSB-162 includes an example of a 60-foot-by-60-foot square cell structure, including the recommended placement of telecommunications outlets within the structure and references to the maximum horizontal and patch cabling distances to reach the outlets. Considering that wireless access points (WAPs) often are placed in the midst of open-office work areas in order to maximize their reach and effectiveness, the idea of precabling to outlets earmarked for access-point plugin is preferable to adding these outlets and their supporting cabling to a working office.
Supporting high speeds
In some ways the cabling systems that support wireless LAN equipment can be seen as backhaul, akin to the wireless-carrier network infrastructure that supports communication between outdoor antennas. Telecommunications outlets installed per TSB-162 meet the TIA-568-B.2 cabling performance specifications, and therefore can support 802.11n's MIMO-based access points. As the IEEE is well into the development of its next-generation wireless LAN standards, 802.11ac and 802.11ad, so too is the TIA well into the development of TSB-162-A, the first revision of its cabling-for-access-points document.
CommScope's Shariff leads the task force that is developing TSB-162-A. I asked Shariff if the task force is considering including recommendations to install cabling that can or should support the line speeds anticipated from 802.11ac or 802.11ad. He replied, "That is a very relevant question that addresses a key aspect of the revision of TSB-162. Architecturally, the IEEE 802.11 committee has made new generations of WAPs backward compatible by allowing the WAPs to work over existing infrastructure used for the 802.11n application. This means customers can swap out 802.11n WAPs for 802.11ac WAPs relatively easily in the first phases of deployment, supporting the existing 802.11n clients.
"However, as 802.11ac clients become more widely deployed, and additional channels are made active in the WAP to increase throughput and capacity, the backhaul data rate will exceed 1 Gbit/sec and may ultimately reach up to 7.3 Gbits/sec," he continued. "Therefore, and somewhat paradoxically, wireless will be the first application to exceed the performance of Category 6 cabling. While TIA TSB-162-A recognizes that initially the backhaul requirements may be addressed with multiple cables to the WAP and link aggregation, it recommends Category 6A for WAP cabling."
It looks like 802.11ac will be the heavyweight of next-generation 802.11-based wireless LAN technologies. As Shariff pointed out, "802.11ad operates in the 60-GHz band and is generally intended for short distances—within a few meters to serve a single room, or more likely, connections between specific wireless devices."
As this article was being written, the then-current draft of TSB-162-A specified performance levels of balanced twisted-pair Category 6A or two-fiber Om3 multimode or higher.
802.11ac
Cisco (www.cisco.com) published a technical paper in 2012 titled "802.11ac: The Fifth Generation of WiFi." In the paper, Cisco addresses the drivers that led to the development of the 802.11ac specification and discusses technical details explaining the technology's ability to transmit at such high speeds. The paper, available for download from Cisco's website, says, "802.11ac achieves its raw speed increase by pushing on three different dimensions: more channel bonding, increased from the maximum of 40 MHz in 802.11n up to 80 or even 160 MHz; denser modulation … ; more MIMO. Whereas 802.11n stopped at four spatial streams, 802.11ac goes all the way to eight."
Later in the paper, Cisco explains multiple-user MIMO (MU-MIMO) as a breakthrough that will enable 802.11ac to achieve previously unreachable data rates. "With 802.11n, a device can transmit multiple spatial streams at once, but only directed to a single address," the paper says. "For individually addressed frames, this means that only a single device (or user) gets data at a time. We call this single-user MIMO (SU-MIMO). With the advent of 802.11ac, a new technology is defined, called multi-user multiple input, multiple output (MU-MIMO). Here an AP is able to use its antenna resources to transmit multiple frames to different clients, all at the same time and over the same frequency spectrum. If 802.11n is like a hub, then 802.11ac can be thought of as a wireless switch (on the downlink).
"However," the Cisco paper then points out, "MU-MIMO is a challenging technology to implement correctly and won't be available in the first wave of AP products. And even when available, MU-MIMO does come with caveats." The paper then visually illustrates MU-MIMO with three users in an environment. "To send data to user 1, the AP forms a strong beam toward user 1. At the same time the AP minimizes the energy for user 1 in the direction of user 2 and user 3. This is called ‘null steering' … At the same time, the AP is also sending data to user 2 and forms a beam toward user 2, and forms notches toward users 1 and 3." The same principle is applied for user 3. Essentially (described in technical terms in the paper and far-less-technical terms here), the signal intended for any particular user manifests in a strong beam toward that user and a "pullback" (or "notch" as it is described in Cisco's paper) toward the other users. The paper says, "In this way, each of users 1, 2 and 3 receives a strong copy of the desired data and is only slightly degraded by interference from data for the other users.
"For all this to work properly, especially the deep nulls, the AP has to know the wireless channel from itself to all of the users very accurately. And since the channel changes over time, the AP has to keep measuring the channel, which adds overhead." The paper later summarizes the practicality of MU-MIMO as follows: "MU-MIMO allows an AP to deliver appreciably more data to its associated clients, especially for small form-factor clients (often BYOD clients) that are limited to a single antenna. If the AP is transmitting to two or three clients, the effective speed increase varies from a factor of unity (no speed increase) up to a factor of two or three times, according to wireless channel conditions."
Back to cabling
So the implementation of 802.11ac will require as much forethought and advanced planning as possible, and for many, part of that planning will be the cabling infrastructure that supports the wireless access points. In addition to the electrical or optical performance-level recommendation that will be in TSB-162-A, the revised bulletin also will address the powering of those access points. CommScope's Shariff explained, "TSB-162-A allows three options for powering: local powering, midspan powering, and switch powering. Since WAPs are generally powered remotely using IEEE 802.3af or IEEE 802.3at powering schemes to negate the need and expense of a power outlet in the vicinity of the WAP, TSB-162-A recognizes these powering schemes and includes informative illustrations for the cabling supporting them.
"Since balanced cabling can support many different powering schemes and it is the WAP equipment that is designed to use IEEE 802.3 powering schemes, TSB-162-A is not limited to only IEEE 802.3 powering schemes," he continued. "Note that since power needed by WAPs continues to increase, TSB-162-A recommends Category 6A or better cabling for remote powering of WAPs."
Additionally, the release of TSB-162-A will reinforce the idea that prewiring or precabling is the most efficient approach to building an infrastructure for a wireless LAN, when such an approach is an option. Shariff noted, "TSB-162-A continues to use the grid approach to precable WAP coverage areas in the building to improve installation speed and cost. The cell size is determined by the capacity, throughput, occupancy and RF survey information. Once the cell size is determined, the maximum length of the equipment cord used to attach the WAP to the TO [telecommunications outlet] is the fundamental metric to determine horizontal cable length to the outlet serving the access point.
"For the 18.3-meter (60-foot) square grid illustrated in TIA TSB-162-A, this maximum radial length of the equipment cord is 13 meters (42 feet). Using this length and assuming a 20-percent additional insertion loss in the equipment cord, the maximum length of the permanent link from the TO to the patch panel in the TR is limited to 80 meters (242 feet). This is less than the permanent link to work area, which is limited to a maximum of 90 meters (295 feet)."
It begins at home
Wireless networking is unlike Ethernet-based wired networking in that often, consumer- or home-based use sets the pace for technologies that later are adopted in enterprise environments such as commercial office buildings. Smartphones with 802.11ac capability built in have been available for some time, as have the first (consumer-grade) class of ac networking products. The second-generation networking products, with the capabilities described in this article and the potential to push backhaul data rates into multiple gigabits, are what the networking world is waiting for.
In late June the WiFi Alliance (www.wi-fi.org) announced its WiFi Certified ac program, aimed at consumer markets and products. When announcing the program, the alliance said, "WiFi Certified ac products deliver whole-home coverage at two or even three times the speed of older WiFi products and handle demanding applications such as Ultra HD and 4K video, multimedia and rapid file transfer with ease."
The alliance's president and chief executive officer Edgar Figueroa commented, "Consumers have an insatiable appetite for rich, connected experiences. WiFi Certified ac advanced the ability of WiFi to satisfy that appetite by increasing capacity and improving performance."
ABI Research (www.abiresearch.com) analyst Phil Solis added, "The latest generation of the technology, WiFi Certified ac, preserves interoperability, which has been the foundation for the technology's success, and will enable product manufacturers to continue to explore new avenues for wireless connectivity."
As manufacturers begin to produce enterprise-grade 802.11ac networking equipment, the specifications by which enterprise networks can be appropriately cabled for such devices forge ahead. The group writing the telecommunications systems bulletin meets again in October. Early indications suggest that if all goes smoothly with the consensus-based specification, TSB-162-A could be approved for publication in spring 2014. ::
Patrick McLaughlin is our chief editor.
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