Network system designers are constantly seeking ways to
future-proof their Ethernet infrastructure to ensure the network is robust
enough to handle their needs and accommodate future applications without costly
modifications down the road. Given the current explosion in demand for wireless
capabilities, one smart strategy in designing a new network or upgrading an
existing one is to include the wireless LAN (WLAN) in the planning process
right from the start.
Whether designing the network for an office building, a
manufacturing plant, or a college campus, WLANs can be used to provide seamless
over-the-air communications in areas where mobility and portability are needed.
But they also create new cabling requirements at the back end, often in
hard-to-access locations. Therefore, it is far less costly and labor intensive
to install the entire cabling infrastructure at once - without walls, ceilings
and other obstructions in the way - than to install WLAN cabling later as a
WLAN Cabling Topology
The most common way to deploy WLAN access points (APs) is to
mount them in ceilings and cable them directly to an Ethernet switch port.
Generally, a 15- to 20-ft piece of cable called a service loop is left in the
ceiling (see Figure) in case an AP later needs to be moved slightly
to fine-tune coverage or avoid interference
from other RF devices, such as wireless phones and microwave ovens. Planning
for those cable runs upfront, in addition to wired network cabling needs, is
both financially and operationally smart because all the necessary materials
can be purchased in bulk with a corresponding volume discount, and labor costs
Additional costs and inconvenience arise if the WLAN is
deployed later, when walls and ceilings have to be opened up again. Not only
can this potentially disrupt network operation, but it can also significantly
increase the overall cabling project cost, depending on the property size and
Network designers must also note that the
wiring closet needs to contain most of the equipment required for the
distribution network that supports the wireless APs: Ethernet switches, Power
over Ethernet (PoE) switches and power injectors, phone system elements and
uninterruptible power supplies, for example. These active devices require
heating, ventilation and air conditioning (HVAC) and ac or dc power and can
thus be more costly if installed later on.
Click here for a larger version
For these reasons, it is much more
efficient and cost-effective to plan the network design and cabling aspects of
the WLAN in tandem with the wired one, treating the two as a single cohesive
Pre-Planning the Wi-Fi Network
In the early days of wireless, many organizations installing
Wi-Fi conducted a physical site survey by walking around the premises to
determine the number and placement of APs needed. While this process may have
worked for smaller installations, it becomes unwieldy for today's larger and
more extensive WLANs.
Using automated Wi-Fi surveying and planning tools, designers
can electronically pre-design the WLAN before work begins. They can import the
blueprint into the application and indicate where to place APs and how many are
needed, based on stated wireless goals and the type of Wi-Fi equipment
To create the optimal Wi-Fi design, network designers and IT
management should determine:
Where in the building wireless connectivity is desired;
Whether to provide users with near-ubiquitous coverage
throughout the building, or whether coverage in key common areas will suffice;
- Who will have access to the network - and where they are
likely to roam throughout the† building.
Another major network design decision concerns the WLAN
applications to be supported. Wireless networks supporting Voice over IP (VoIP)
typically require denser AP deployment than those that simply provide wireless
data access. This is because data networking is far more tolerant of packet
loss, delivery delays and jitter than voice, which requires stable, ubiquitous
coverage and minimum delays when connections are handed off from AP to AP as a
For data access, installing an AP in public areas, such as
meeting rooms, cafeteria and lobby, might be sufficient for some organizations.
However, consistent voice and location service support will require coverage
nearly everywhere. That means more APs and more cabling runs to more places.
The same density consideration applies to data connections in areas where large
groups of people congregate to use the network simultaneously.† It's important that all of these factors be
considered up front to avert wireless coverage problems
Choosing a Wi-Fi Technology
Selecting the Wi-Fi technology that best suits the
organization's needs is an important early phase decision to be made by the
network designer. Whether the choice is 802.11n, 802.11g, 802.11a or some
combination, this decision will affect cabling and other downstream choices
because these WLAN types run at differing throughput speeds and coverage ranges
and offer differing capabilities and performance.
The newest technology available in WLAN equipment, 802.11n,
generally offers data-connect rates of up to 300 Mb/s per radio, which may be
the ideal choice for high-bandwidth, high-consumption applications. However,
the equipment costs for 802.11n can be higher than for earlier Wi-Fi
technologies. A good strategy is to discuss this critical decision with an
experienced and knowledgeable network system provider to ensure the correct
decision is made based upon current and potential future use.
Additional Factors to Consider
Once the range of coverage and the 802.11 technology is
determined, several other factors enter into the wired and wireless LAN design
Ali Safari is director
of business development and product management for Trapeze Networks, a Belden
brand; Paul Kish is director of systems and standards for Belden.
- APs, Placement and Channel Planning. The WLAN site-planning
tool can be used to automatically lay out the wireless network. Given the
proper input, the program will calculate the number and location of APs
required, and on what channels they should operate to avoid interference. The
program will automatically build the layout and specify at what power levels
each AP should transmit for the best overall operation, keeping in mind FCC and
other regulatory power limitations.
- Outfitting the Telecommunications Room. Taking into account
the number of APs to be installed on each floor, the network system consultant
can advise on additional equipment needed for the upgraded environment,
including: Ethernet switch ports, Ethernet or PoE switches and power injectors,
LAN/WLAN controllers and other devices.
Cable Types and Power Delivery. If the
plan is to deploy 802.11n now or in the future and procure gigabit-speed switch
ports accordingly, it is advisable to install Category 6 copper cabling from
the telecommunications room out across the floors and throughout walls and
ceilings. Category 6 twisted-pair cabling provides better noise immunity and
more signal-to-noise headroom for supporting gigabit-per-second speeds across
Ethernet's 100m standard distance.