Integrated Wired and Wireless Network Infrastructure Design

DN Staff

October 22, 2010

6 Min Read
Integrated Wired and Wireless Network Infrastructure Design

Network system designers are constantly seeking ways tofuture-proof their Ethernet infrastructure to ensure the network is robustenough to handle their needs and accommodate future applications without costlymodifications down the road. Given the current explosion in demand for wirelesscapabilities, one smart strategy in designing a new network or upgrading anexisting one is to include the wireless LAN (WLAN) in the planning processright from the start.

Whether designing the network for an office building, amanufacturing plant, or a college campus, WLANs can be used to provide seamlessover-the-air communications in areas where mobility and portability are needed.But they also create new cabling requirements at the back end, often inhard-to-access locations. Therefore, it is far less costly and labor intensiveto install the entire cabling infrastructure at once - without walls, ceilingsand other obstructions in the way - than to install WLAN cabling later as aseparate project.

WLAN Cabling Topology

The most common way to deploy WLAN access points (APs) is tomount 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 theceiling (see Figure) in case an AP later needs to be moved slightlyto fine-tune coverage or avoid interferencefrom other RF devices, such as wireless phones and microwave ovens. Planningfor those cable runs upfront, in addition to wired network cabling needs, isboth financially and operationally smart because all the necessary materialscan be purchased in bulk with a corresponding volume discount, and labor costsare reduced.

Additional costs and inconvenience arise if the WLAN isdeployed later, when walls and ceilings have to be opened up again. Not onlycan this potentially disrupt network operation, but it can also significantlyincrease the overall cabling project cost, depending on the property size andcomplexity.

Network designers must also note that thewiring closet needs to contain most of the equipment required for thedistribution network that supports the wireless APs: Ethernet switches, Powerover Ethernet (PoE) switches and power injectors, phone system elements anduninterruptible power supplies, for example. These active devices requireheating, ventilation and air conditioning (HVAC) and ac or dc power and canthus be more costly if installed later on.

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For these reasons, it is much moreefficient and cost-effective to plan the network design and cabling aspects ofthe WLAN in tandem with the wired one, treating the two as a single cohesiveproject.

Pre-Planning the Wi-Fi Network

In the early days of wireless, many organizations installingWi-Fi conducted a physical site survey by walking around the premises todetermine the number and placement of APs needed. While this process may haveworked for smaller installations, it becomes unwieldy for today's larger andmore extensive WLANs.

Using automated Wi-Fi surveying and planning tools, designerscan electronically pre-design the WLAN before work begins. They can import theblueprint into the application and indicate where to place APs and how many areneeded, based on stated wireless goals and the type of Wi-Fi equipmentselected.

To create the optimal Wi-Fi design, network designers and ITmanagement should determine:

  • Where in the building wireless connectivity is desired;

  • Whether to provide users with near-ubiquitous coveragethroughout the building, or whether coverage in key common areas will suffice;and

  • Who will have access to the network - and where they arelikely to roam throughout the building.

Another major network design decision concerns the WLANapplications to be supported. Wireless networks supporting Voice over IP (VoIP)typically require denser AP deployment than those that simply provide wirelessdata access. This is because data networking is far more tolerant of packetloss, delivery delays and jitter than voice, which requires stable, ubiquitouscoverage and minimum delays when connections are handed off from AP to AP as auser roams.

For data access, installing an AP in public areas, such asmeeting rooms, cafeteria and lobby, might be sufficient for some organizations.However, consistent voice and location service support will require coveragenearly everywhere. That means more APs and more cabling runs to more places.The same density consideration applies to data connections in areas where largegroups of people congregate to use the network simultaneously. It's important that all of these factors beconsidered up front to avert wireless coverage problems
later on.

Choosing a Wi-Fi Technology

Selecting the Wi-Fi technology that best suits theorganization's needs is an important early phase decision to be made by thenetwork designer. Whether the choice is 802.11n, 802.11g, 802.11a or somecombination, this decision will affect cabling and other downstream choicesbecause these WLAN types run at differing throughput speeds and coverage rangesand 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 bethe ideal choice for high-bandwidth, high-consumption applications. However,the equipment costs for 802.11n can be higher than for earlier Wi-Fitechnologies. A good strategy is to discuss this critical decision with anexperienced and knowledgeable network system provider to ensure the correctdecision is made based upon current and potential future use.

Additional Factors to Consider

Once the range of coverage and the 802.11 technology isdetermined, several other factors enter into the wired and wireless LAN designphase.

For example:

  • APs, Placement and Channel Planning. The WLAN site-planningtool can be used to automatically lay out the wireless network. Given theproper input, the program will calculate the number and location of APsrequired, and on what channels they should operate to avoid interference. Theprogram will automatically build the layout and specify at what power levelseach AP should transmit for the best overall operation, keeping in mind FCC andother regulatory power limitations.

  • Outfitting the Telecommunications Room. Taking into accountthe number of APs to be installed on each floor, the network system consultantcan 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 theplan is to deploy 802.11n now or in the future and procure gigabit-speed switchports accordingly, it is advisable to install Category 6 copper cabling fromthe telecommunications room out across the floors and throughout walls andceilings. Category 6 twisted-pair cabling provides better noise immunity andmore signal-to-noise headroom for supporting gigabit-per-second speeds acrossEthernet's 100m standard distance.

Ali Safari is directorof business development and product management for Trapeze Networks, a Beldenbrand; Paul Kish is director of systems and standards for Belden.

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