Network Management Strategies for the CIO
According to In-Stat, draft 802.11n sales grew 340% last year. By 2009, standard 802.11n products will push legacy 802.11a/g devices onto the discount rack. The question now facing most companies is not whether to migrate to 802.11n, but where, how and when to do so. This checklist will point out critical factors that should be considered when planning your 802.11n upgrade in order to maximize benefit and minimize pain.
Assess your 802.11n needs
802.11n physical and link layer enhancements could significantly increase your WLAN's speed, capacity, reach and reliability. But realizing this potential requires proper deployment: Your 802.11n upgrade must be explicitly designed to satisfy your business needs. Before purchasing access points (APs) or allocating channels, address these questions:
Which applications must be supported? Many enterprises will use 802.11n to
support more diverse and demanding applications, but a WLAN that's perfect for email can still be
lousy for voice or streaming video. Start by identifying all applications that your upgraded WLAN
must support, and quantify what each requires in terms of throughput, latency and coverage (minimum
speed/delay when roaming).
How many users must be supported and where? Break your facility into coverage
areas, and identify the total number of users in each area, as well as the percentage online at any
time. When doing so, group users by device and required application mix (e.g., voice handsets on
the second floor, meeting room laptops using Web and IM) so that capacity can be planned
accordingly.
What client devices will be used? Upgrading a laptop fleet to standard 802.11n
can take two to three years, and some legacy clients (e.g., handsets, scanners) will linger longer.
Divvy existing devices into groups, based on protocol (a/b/g/draft n/final n) and bandwidth (2.4
GHz/5 GHz/both), and forecast how proportions will evolve over time.
 |
||||
|
|
|||
|
||||
Do you have 802.11 backhaul needs? Many companies use 802.11 as an edge access
technology, but high-throughput 5 GHz 802.11n is also useful for backhaul. Identify your existing
legacy wireless bridge links (if any) and where 802.11n backhaul could be applied to better meet
old and new business needs.
Plan for legacy coexistence
Few of us have the luxury of deploying a new 802.11n WLAN from scratch. Most will need to coexist with legacy 802.11a/g devices -- from existing APs and clients to devices owned by neighbors and guests. To accomplish this, consider these questions:
Do you need protection? The 802.11n standard defines high-throughput (greenfield),
non-high throughput (HT) (legacy),
and HT mixed operating modes. If you plan to deploy 802.11n in the same location and band now
occupied by legacy devices, you must use HT mixed-mode protection mechanisms for peaceful
cohabitation.
Where can you avoid protection? HT mixed-mode avoids legacy interference but
reduces 802.11n throughput. To get the most out of 802.11n, deploy new APs in greenfield mode,
using 20 or 40 MHz channels in the 5 GHz band. This also requires rapid deployment of new 802.11n
clients, however, since legacy clients cannot speak to greenfield APs.
Should you double up? Use business needs to determine the best coexistence
approach. If 802.11n users are spread throughout your facility, consider dual-radio APs, using one
radio for legacy a/g clients and the other for new 802.11n clients. If little overlap exists
between your old WLAN and what your new WLAN must cover, consider an independent 802.11n-only
deployment.
When will you "sunset" coexistence? Legacy clients get better range when
associated to mixed-mode 802.11n APs. But speeds over 54 Mbps require new hardware, and the sooner
legacy clients retire, the better your entire WLAN will perform. Establish target date(s) for
turning a/g off.
Identify network infrastructure impacts
802.11n speed and performance can be improved with bigger, faster APs that can carry more traffic and require more juice. Before investing in this new wireless gear, decide where and how your existing distribution network equipment must be upgraded to support 802.11n:
Will your controller be a bottleneck? Many enterprises have migrated from
autonomous APs to thin APs. But WLANs that route all traffic through one central WLAN controller
could be overwhelmed by 802.11n traffic. To avoid this, consider direct AP-to-AP traffic forwarding
and/or distributed controllers.
When will you need more backhaul? In theory, an 802.11n AP could send 600 Mbps
onto your wired network. In practice, mixed mode will start under 200 Mbps and grow over time.
Predict when your 10/100 Ethernet edge switches will require upgrade to gigabit backhaul.
|
||||
|
|
|||
|
||||
How will you slake 802.11n's thirst for power? 802.3af PoE cannot deliver enough
wattage to drive most 802.11n APs at full capacity. Possible solutions include using fewer MIMO
antennas or radios, proprietary PoE, two PoE ports per AP, midspan PoE injectors, or AC power.
Engineer your new radio network
802.11n APs are not simply faster. They use MIMO antennas, wider channels to make better use of the air and listen more effectively, and signal processing techniques like spatial multiplexing, space-time block coding and transmit beam forming. These capabilities change what an optimal WLAN looks like, and results can vary across buildings due to multi-path. To avoid expensive mistakes and post-install revisions, take the time to formally plan your new WLAN:
Where will you place 802.11n APs? Some vendors recommend swapping legacy APs for
802.11n APs. That is simple, but may or may not be most effective. With 802.11n, cell shape and
size is far less intuitive. For best results, use a predictive planner to model 802.11n and suggest
AP locations that create the coverage areas and capacities needed by your users and
applications.
Does your plan really work? Models are helpful but are no substitute for
reality. Use a site survey to visualize actual RF coverage, based on measurements taken when people
and other obstacles are present, using representative clients (a/b/g and n). Because a strong
signal may not mean good user experience with MIMO, measure application performance in both
directions.
What bands and channels will you use? 802.11n can use 20 or 40 MHz channels in
the 2.4 or 5 GHz bands. The 2.4 GHz band used by most clients is overcrowded, though. Stick to 20
MHz channels there, saving 40 MHz for high-throughput applications in the 5 GHz band, and utilize
automatic channel selection and power adjustment to simplify planning.
Should you prioritize traffic? Most business-grade 802.11n APs also support
802.11e Wi-Fi multimedia prioritization. If your WLAN must support voice, video and data using
shared APs, map your applications onto WMM access categories and 802.1p LAN
classes of service.
Anticipate management and security upgrades
After 802.11n installation, the maintenance, monitoring and security practices used with your old WLAN still apply, but tools used to support these tasks must be upgraded to deal with the complexities and threats associated with the new standard.
Is your WLAN manager up to the job? Large enterprises can leverage existing WLAN
managers, but others may find that the time has come to invest in new tools. 802.11n is more
dynamic, and capabilities like automated tuning and client locationing become more important.
Is your wireless intrusion
prevention system (WIPS) ready for 802.11n? Protocol extensions and 40 MHz channels create
something of a blind spot for intrusion prevention systems that use a/b/g sensors to monitor the
air. Upgrade your WIPS sensors (or APs used as sensors) to listen and respond to 802.11n threats in
both bands.
Can you troubleshoot 802.11n problems? WLAN analyzers, spectrum analyzers, and
performance monitoring systems must also be upgraded -- from new 802.11n adapters and protocol
decoders to analysis engines that understand 802.11n options and coexistence impacts. Training on
802.11n may also be a worthwhile investment.
Conclusion
Moving to 802.11n is a major network upgrade. Many will take this opportunity to expand how wireless is used, moving from casual Internet access in isolated locations to more comprehensive coverage and mission-critical business applications. Making this change cost-effectively and efficiently, with minimal disruption, requires careful planning and network engineering. We hope this checklist provides a starting point for making your own next-generation WLAN bigger, faster and better.
|
|
 |
|
|
|
About the author:
Lisa A. Phifer is vice president of Core Competence Inc. She has been involved in the design,
implementation and evaluation of data communications, internetworking, security and network
management products for more than 20 years and has advised companies large and small regarding
security needs, product assessment and the use of emerging technologies and best practices.
This was first published in April 2008
Join the conversationComment
Share
Comments
Results
Contribute to the conversation