Deploying the Next Generation of High Performance Wireless
Introduction
In less than a decade, wireless LANs have evolved from an interesting idea to an indispensable technology for millions of businesses and consumers. This technology continues to evolve. The latest generation of high-speed wireless LAN solutions, based on the Institute of Electrical and Electronics Engineers (IEEE) Draft 802.11n standard, are now available.
The 802.11n standard will offer several advantages over previous wireless LAN technologies. The most notable advantages are substantially improved reliability and greater application data throughput. However, before deciding whether to deploy 802.11n wireless solutions, organizations need answers to several questions: What do 802.11n technologies do differently from previous wireless solutions? What is the state of the standardization effort for 802.11n? Will 802.11n be backward-compatible with currently deployed wireless clients and access points? What factors should be considered to determine when it makes sense to deploy 802.11n?
To help you make more informed decisions about 802.11n, this overview provides answers to these and other questions. The overview also provides details on the state of 802.11n technology today, and introduces the Cisco® Aironet® 1140 Series and 1250 Series access points.
The Emergence of 802.11n
Today's 802.11a/b/g wireless networks have provided a powerful tool for increasing the mobility and productivity of users, and have unlocked a new generation of wireless-enabled applications. However, as wireless applications become more pervasive, the demand for greater network reliability with additional bandwidth is increasing.
The IEEE 802.11 Task Group n (TGn) has been working for several years to create a new wireless standard that will support much greater application data throughput than existing 802.11a/b/g wireless standards. The 802.11n standard is expected to deliver data rates of up to 300 Mbps per radio. (Today's 802.11a and 802.11g solutions can achieve a maximum data rate of 54 Mbps, while older 802.11b platforms deliver a maximum data rate of 11 Mbps.)
The TGn effort has progressed steadily since its inception in September 2003, but as with most complex technologies, the process of ratifying a standard takes several years. With so much interest in boosting wireless network performance and capacity, 32 different proposals were submitted initially, and the task group has struggled to agree upon a single proposal to develop into the standard.
In October 2005, Cisco and several other companies formed the Enhanced Wireless Consortium (EWC) to help break the deadlock and accelerate the 802.11n standard development process. The EWC created a new proposal, and in January 2006, the IEEE voted to accept it as the basis for the 802.11n standard. Technology providers across the industry have raced to put 802.11n solutions into production, and devices based on the second draft of the proposed standard have now begun to enter the market.
The State of 802.11n Today
The final details of 802.11n are still under discussion, and TGn is expected to ratify the final standard in January 2010. But many businesses understand the remarkable performance improvements in the areas of throughput, link reliability, and predictability and are adopting 802.11n now. The Wi-Fi Alliance is using the interim IEEE 802.11n draft 2.0 as the baseline for the initial round of Wi-Fi certification and compatibility testing that began in June 2007. The Wi-Fi Alliance certification has become the de facto standard for 802.11n and the alliance has certified about 450 products to date. Intel has shipped over 30 million 802.11n clients. Enterprises are seeing the benefits in moving forward with the de facto standard. Cisco has taken great care to ensure a smooth migration from today's de facto standard and the version that will eventually be ratified, and we expect the differences to be minimal.
How 802.11n Technology Works
Current wireless solutions operate in the 2.4-GHz radio frequency band (802.11g and 802.11b) or the 5-GHz radio band (802.11a.). Solutions based on the 802.11n standard operate in the 2.4-GHz, the 5-GHz radio band, or both bands, offering backward compatibility with preexisting 802.11a/b/g deployments. The majority of Wi-Fi devices and access points hitting the market are dual-band - operating in both the 2.4-GHz and 5-GHz frequencies. The net result for business will be a shift to greater utilization of the 5-GHz band with 802.11n given the greater available capacity and cleaner frequency.
Wireless solutions based on the 802.11n standard employ several techniques to improve the throughput, reliability, and predictability of wireless LANs. The three primary innovations are:
• Multiple Input Multiple Output (MIMO) technology
• Packet aggregation
• Channel bonding (40MHz Channels)
Together, these techniques allow 802.11n solutions to achieve up to nine times the performance over current 802.11a/b/g networks.
MIMO Technology
802.11a/b/g wireless access points and clients communicate through a single spatial stream over a single antenna. 802.11n access points and clients transmit two or more spatial streams, and employ multiple receive antennas and advanced signal processing to recover the multiple transmitted data streams. MIMO-enabled access points use spatial multiplexing to transmit different bits of a message over separate antennas, providing much greater data throughput and allowing for more robust, resilient wireless LANs. Whereas previous wireless technologies had problems dealing with signal reflections, MIMO actually uses these reflections to increase the range and reduce "dead spots" in the wireless coverage area.
Ultimately, 802.11n networks that incorporate both MIMO-enabled access points and MIMO-enabled wireless clients will deliver dramatic gains in reliability and data throughput. However, even when MIMO is deployed only in wireless access points, the technology still delivers significant performance enhancements (up to 30 percent over conventional 802.11a/b/g networks)-even when communicating only with non-MIMO 802.11a/b/g clients.
This performance gain is a result of MIMO smart antenna technology, which allows wireless access points to receive signals more reliably over greater distances (and allows clients to operate at higher data rates) than with standard diversity antennas. For example, at the distance from the access point at which an 802.11a/g client communicating with a conventional access point might drop from 54 Mbps to 48 Mbps or 36 Mbps, the same client communicating with a MIMO access point may be able to continue operating at 54 Mbps.
Channel Bonding
The most straightforward way to increase the capacity of a network is to increase the operating bandwidth. However, conventional wireless technologies are limited to transmitting over one of several 20-MHz channels. 802.11n networks employ a technique called channel bonding to combine two adjacent 20-MHz channels into a single 40-MHz channel. The technique more than doubles the channel bandwidth. Channel bonding is most effective in the 5-GHz frequency given the far greater number of available channels. The 2.4-GHz frequency has only 3 non-overlapping 20-MHz channels. Therefore, bonding two 20-MHz channels uses two thirds of the total frequency capacity. Therefore, the IEEE has defined rules on when a device can operate in 40MHz channels in the 2.4GHz space to ensure optimal performance. Cisco expects that the greatest benefits of channel bonding will be realized in the 5-GHz frequency.
Packet Aggregation
In conventional wireless transmission methods, the amount of channel access overhead required to transmit each packet is fixed, regardless of the size of the packet itself. As data rates increase, the time required to transmit each packet shrinks, but the overhead cost remains the same, potentially becoming much greater than the packet itself at the high speeds delivered with 802.11n.
802.11n technologies increase efficiency by aggregating multiple packets of application data into a single transmission frame. In this way, 802.11n networks can send multiple data packets with the fixed overhead cost of just a single frame. Packet aggregation is more beneficial for certain types of applications such as file transfers due to the ability to aggregate packet content. However, real-time applications (e.g. voice) do not benefit specifically from packet aggregation because its packets would be interspersed at regular intervals and combining packets into a larger payload would introduce unnecessary latency. Voice and other multimedia applications still benefit from other effects of MIMO.
Advantages of 802.11n
The innovative techniques and technologies employed in 802.11n result in a wireless LAN that offers several important advantages over previous wireless solutions. These advantages include:
• Greater reliability: MIMO allows 802.11n networks to provide a more robust wireless service that supports more concurrent connections. With the ability to communicate over multiple antennas and eliminate dead spots, 802.11n networks can maintain optimal performance at greater distances (even with conventional 802.11a/b/g clients) and provide an improved user experience for high-bandwidth voice and video applications. MIMO improves the signal transmit and receive characteristics of the wireless transmission to reduce the number of packet retries resulting in a more reliable and consistent level of throughput.
• Greater throughput: The combination of MIMO, channel bonding, and packet aggregation allow 802.11n networks (employing both 802.11n clients and access points) to achieve data rates as high as 600 Mbps, which is nine times greater than the maximum available with 802.11a/g. 802.11n access points also enhance the performance of wireless clients built under previous standards.
• In mixed environments, 802.11a/g clients delay 802.11n client communications and reduce overall system performance. New Cisco ClientLink technology offers performance improvements to 802.11a/g clients in mixed-mode environments. Please see the ClientLink white paper for more details http://www.cisco.com/en/US/prod/collateral/wireless/ps5678/ps10092/white_paper_c11-516389.html
• Greater coverage predictability: Enterprises are designing wireless networks for performance and MIMO provides greater throughput resulting in more predictable coverage throughout the facility. The coverage improvements extend to 802.11a/b/g clients as well as 802.11n clients. At any given location, a client connecting to an 802.11n access point with MIMO will receive greater throughput than it would otherwise receive from a traditional 802.11a/b/g access point. As a result, 802.11n networks can support more clients using high-bandwidth applications than previous wireless solutions.
Applications that will benefit most from the additional throughput, reliability, and predictable coverage of 802.11n wireless LANs include:
• Environments and applications that require sharing of large files, including anything from advanced design and engineering applications to users in a conference room collaborating on a large Microsoft PowerPoint presentation
• Voice and video applications that demand high-quality transmissions, such as video conferencing and IPTV services that use multiple streams of high-definition video
• Facilities with challenging RF characteristics including warehouses, manufacturing floors and retail locations
• Disaster recovery, backup, and storage applications
Backward Compatibility with Existing Platforms
For the next few years, it will be common for Wi-Fi networks to support a mix of 802.11a/g and 802.11n clients. Because they operate at lower data rates, the older clients can reduce the capacity of the entire network. Cisco ClientLink technology addresses this problem by making sure that 802.11a/g clients operate at the best possible rates. This extends the useful life of existing 802.11a/g devices and is beneficial for organizations that want all clients on their networks, regardless of type, to get the bandwidth and throughput they need.
An 802.11n network can incorporate 802.11a/g clients with minimal performance loss. However, as with today's 802.11g networks, operating in a mixed environment that includes 802.11b clients can substantially affect throughput. (The throughput of today's 802.11g networks may drop from 25 Mbps to as low as 7 Mbps when 802.11b clients enter the environment, and 802.11n networks will suffer a comparable performance decrease.) However, organizations deploying 802.11n have the option of configuring the network to exclude 802.11b clients on some channels or on all channels to ensure that throughput remains high.
Organizations that can benefit from 802.11n but still rely on 802.11b/g devices (and plan to continue using those devices for the foreseeable future) can plan to deploy 802.11n in mixed mode in both the 2.4-GHz frequency and 5-GHz frequency. Organizations will experience the greatest performance improvements in the 5-GHz frequency given the relatively fewer number of existing 802.11a clients, the greater availability of spectrum, and the fact that the 5-GHz frequency has less interference than the 2.4GHz frequency.
The Cisco Aironet 1140 Series Access Point
The Cisco Aironet 1140 Series Access Point is a business-ready 802.11n indoor access point designed for simple deployment and energy efficiency. It has a sleek design that blends into enterprise environments, and it can be powered with standard 802.3af Power over Ethernet.
The Cisco Aironet 1250 Series Access Point
The Cisco Aironet 1250 Series is an enterprise-class 802.11n rugged indoor access point designed for above-ceiling deployments or challenging RF environments such as factories, warehouses, and large retail establishments. The 1250 Series provides antenna versatility, a strong metal enclosure, a broad operating temperature range, and plenum rating.
Investment Protection
The current market momentum behind the 802.11n draft 2.0 standard is such that a significant change to the final standard requiring more than a software upgrade is unlikely. You can enhance the performance of your WLAN networks with 802.11n draft 2.0 solutions today, without worrying about incompatibility with future wireless technologies, protocols, and standards.
Cisco Services
When integrating a wireless LAN with your wired infrastructure or migrating from an autonomous solution to a centralized one, the challenge is to design, build, and operate a secure wireless network in alignment with your business requirements that can scale with the evolving business environment.
Cisco and our Wireless LAN Specialized Partners offer a broad portfolio of end-to-end services based on proven methodologies for planning, designing, implementing, operating, and optimizing the performance of a variety of secure voice and data wireless network solutions, technologies, and strategies. Cisco Wireless LAN Specialized Partners bring application expertise to help deliver a secure enterprise mobility solution with a low total cost of ownership.
Conclusion
The high-speed wireless applications of the future may change the way people work and communicate as profoundly as the advent of wireless networking itself. However, the enormous potential of these innovations may be mitigated if the next-generation wireless technologies that an organization deploys today cannot support the standards of tomorrow. Organizations that stand to realize the most benefit from emerging high-speed wireless technologies should seriously consider the advantages of 802.11n solutions.