Major Network Feature Decisions
Your network feature decisions have a major impact on the equipment that you choose to purchase and on the success and profitability of your wireless WAN. The following sections describe those decisions.
Market Versus Equipment Cost
The market that you choose to servecommercial, residential, or some mixture of the twolargely determines the price range for the wireless equipment that you purchase, install, and resell. If you serve primarily residential users, you need to purchase lower-cost equipment. If you provide higher-value service by providing more bandwidth and additional value-added services to businesses, you can select higher-cost equipment with a larger feature set.
802.11b CompatibilityYes or No?
If you choose to use 802.11b equipment for your wireless WAN, you gain some significant advantages and, at the same time, you face several disadvantages. The following sections discuss these advantages and disadvantages.
Advantages of 802.11b Compatibility
The advantages of using 802.11b equipment include the following:
Cost802.11b equipment is available at the lowest cost of any wireless equipment.
Availability802.11b equipment is widely available.
At the time of this writing, 802.11a equipment that is operating in the 5-GHz U-NII bands (with bandwidths up to 54 Mbps) is beginning to become available. This equipment is currently designed for use in indoor LANs and not in outdoor WANs. Further product development might make outdoor versions available in the future.
Disadvantages of 802.11 Compatibility
The disadvantages of using 802.11b equipment outdoors include the following:
SecurityAlthough newer security mechanisms are being developed to supplement the current wired equivalent privacy (WEP) security, there is a somewhat greater chance of security being compromised because many people are familiar with 802.11b technology and more hacking tools are available.
InterferenceAs more 802.11b APs are deployed, spectrum congestion and interference between wireless networks become more of an issue.
SupportMost 802.11b equipment sold today is designed for low-cost in-home use. The level of vendor support for this equipment is likely to be low, especially when the equipment is used in an outdoor WAN environment. Vendors focus on supporting the equipment in its intended (indoor LAN) use and not in the outdoor WAN environment.
Bridged Versus Routed WANs
Every wireless WAN is interconnected with a wired network that includes routing. During the design phase of your wireless WAN, you need to determine how your WAN will interoperate with your wired network. Based on your determinations, you will select wireless equipment that either performs bridging only or that performs both bridging and routing. The following questions can help you decide whether to purchase wireless equipment with built-in routing or whether to use external routers (or perhaps, no routers):
IP-based network servicesWhat advanced IP-based network services are already provided in your existing wired network? What IP-based network services will you need to provide immediately over your wireless network when it is first placed into service? What additional IP-based services (such as voice-over-IP) will you want to offer later to your wireless network users?
Edge routingRelative to your existing core routers, where do you need edge routing? If edge routing is (or will soon be) needed, is it better to select wireless equipment that includes this routing functionality initially, or is it better to select wireless bridges and add external routers later between a customer's wireless bridge and their LAN?
Multiple wireless backbone linksIf you anticipate using multiple wireless backbone links to provide extended wireless area coverage, you are more likely to deploy routing within the wireless backbone. You might decide that selecting wireless equipment with built-in routing is more practical or economical than using external routers.
Backbone Feature Decisions
Your backbone supplies the bandwidth that your APs distribute wirelessly to your end users. The following sections describe some key decisions that you will make as you select backbone equipment.
Your first backbone decision is to determine how much throughput you need. This throughput decision is affected by the following factors:
Market needsHow much throughput do your markets require? A backbone link that serves businesses located in several cities needs to provide more throughput than a link that serves only one or two small residential areas.
Number of usersThe number of wireless end users and the nature of their needs determine the amount of throughput that your backbone needs to provide.
Simplex versus duplex backboneBackbone equipment can be either simplex or duplex. A duplex backbone can provide up to 50 percent more throughput than a simplex backbone. Duplex backbone costs are generally higher because a duplex link contains two complete transmitting systems and two complete receiving systems.
Overselling ratioInternet usage is bursty. Most Internet users use bandwidth intermittently; therefore, ISPs can oversell bandwidth knowing that not all users will be on all the time. The number of times that you resell the same bandwidth (your overselling ratio) affects the amount of backbone bandwidth that you need. Your ISP experience combined with your observation of the usage patterns on your network help you determine your best overselling ratio and your backbone bandwidth needs.
Wired Versus Wireless Backbone
If economical wired backbone connectivity is available at your wireless AP location, it makes sense for you to use that wired connectivity. If wired backbone connectivity is not available or if the cost is too high, a wireless distribution system is the logical choice.
License-Free Versus Licensed Backbone
After you choose to use a wireless backbone, it is important for you to evaluate and compare the cost and the bandwidth of licensed wireless backbone equipment with the cost and the bandwidth of license-free wireless backbone equipment.
The advantages of using a license-free wireless backbone are
CostThe cost is generally lower.
AvailabilityEquipment is generally available more rapidly.
LicensingThere is no licensing cost, licensing paperwork, or licensing delay.
The disadvantage of using a license-free wireless backbone is that interference from other license-free networks is a possibility, and it is your responsibility to ensure that license-free equipment does not interfere with licensed equipment.
Given these advantages and disadvantages, it makes sense to use a license-free wireless backbone if you are reasonably certain that interference levels (both from other networks and from your own network) will remain reasonably low.
Dedicated Versus Shared Backbone Bandwidth
Wireless backbone links can be either of the following:
Dedicated to providing only backbone bandwidth.
Shared between backbone bandwidth and last-mile bandwidth. Examples of shared bandwidth include mesh networks and 802.11b repeaters that both connect end users and provide backbone connectivity for other APs.
Heavy bandwidth demands at one AP can cause slow performance at other APs. If possible, try to avoid sharing wireless link bandwidth between backbone use and last-mile access use. If you choose to share backbone bandwidth, you might find it necessary to use additional routers throughout the backbone to allocate and manage the bandwidth demands.
AP Feature Decisions
The list that follows describes some of the key decisions that you need to make as you select your AP equipment:
Frequency bandYour choice of frequency band is probably the most important equipment decision that you will make. The difference in wireless propagation characteristics and interference levels between the license-free bands means that a poor decision here might result in an unusable network. Before making this decision, you should review the propagation characteristics of each band (discussed earlier in this chapter). You should also perform a wireless site survey (see Chapter 4, "Performing Site Surveys") to determine potential interference levels on a frequency band before you select equipment for that band. The information in Chapter 8 can help you if you find high levels of interference.
NLOS environmentIf you are considering buying equipment that operates in an NLOS environment, you need to either rule out or verify the range claims that the equipment manufacturer has made. You can do this by visiting an ISP that has the equipment deployed in an NLOS environment that is similar (such as the same density of trees and the same type of obstructions) to yours.
Modulation typeYour choice of modulation type (DSSS, FHSS, or proprietary) is an important factor in the ultimate success of your network. Choose a modulation type that is compatible with the level and the type of interference in your coverage area.
802.11b or proprietaryEvery organization needs to match its budget to its mission. If your budget is modest, the lowest-cost indoor 802.11b equipment might be your only choice. A somewhat larger budget allows you to choose higher-cost 802.11b equipment with expanded feature and management capabilities. An even larger budget allows you to choose from the full range of wireless equipment.
Hot spot use802.11b APs deployed for hot spot use should be 802.1x-capable to implement improved security and to interface to external authentication and accounting servers.
End user pollingSome APs implement end user polling as an option to the 802.11b CSMA/CA and RTS/CTS collision-avoidance mechanisms. If you plan to serve more than about 25 busy end users from one AP, polling increases your network reliability and performance.
Bandwidth managementA few APs contain a bandwidth management capability that allows you to set bandwidth for each end user link. If the AP that you choose does not include this feature, consider adding this capability with an external bandwidth manager.
SupportVendor support is important when your wireless customers are looking to you to provide reliable Internet service. Talk with other wireless network operators to assess the availability of driver and firmware upgrades, as well as the response time and quality of support from their equipment vendors.
CPE Feature Decisions
Price is often the top consideration in the selection of CPE. The competition between broadband DSL and cable Internet access providers has driven the cost of broadband service down. It can be difficult for broadband wireless companies to compete at these low price points. For this reason, wireless providers constantly seek to lower the cost of CPE. Business users usually understand that they need to pay for value received; in contrast, residential users often seek to pay little (or nothing) for their CPE. Try not to cut too many corners in seeking and deploying low-cost CPE. Although cost is important, it is more important to deploy reliable, supportable, and manageable networks. The following discussion can help you make these cost-benefit decisions:
Wireless card versus external radio-based CPETraditionally, license-free broadband wireless equipment is mounted indoors with a coaxial cable running to the outdoor antenna. In the drive to minimize CPE costs, wireless IPSs often choose to install wireless network interface cards (NICs) in their customers' computers, rather than purchase full-size (and higher priced) wireless bridges or routers. If you choose to deploy NICs in customer computers as CPE, recognize that some customers might expect you to provide no-cost PC support indefinitely, and this can be a costly situation for you. Also, be aware that the software tools needed to adequately monitor the quality of the customers' connection might not be available. This, too, can increase your customer support costs and raise your costs above the level where you can make a reasonable profit.
Separate versus integrated radio and antennaAn alternative to the traditional wireless model is the integrated radio and antenna model. To reduce CPE costs and installation costs, wireless ISPs are now using (wherever possible) integrated radio and antenna equipment. These integrated units combine the radio and the antenna into one plastic or fiberglass enclosure that is mounted outdoors in a location with an LOS path to the AP. The integrated unit connects to the end user PC or network through either an Ethernet cable or, in a few cases, through a universal serial bus (USB) connection. The wireless performance is better because there is no coaxial cable loss between the antenna and the radio.
Split radio architectureThere is one additional equipment configuration for you to evaluate: the split architecture. Split architecture actually divides the wireless unit into two physical pieces: an indoor section and an outdoor section. The indoor section contains the lower-power, lower-frequency circuits. The outdoor section contains the higher-power, higher-frequency circuits and mounts just below the antenna. Split architecture provides the benefits of the integrated radio and antenna architecture but also allows a greater choice of antennas because the antenna and radio are not built into one unit. Split architecture is often the most expensive configuration; however, it might be the best in terms of both performance and flexibility.
Wireless Network Card Decisions
If you decide to deploy wireless 802.11b cards as the customer CPE or if wireless cards plug into the AP that you are using, you must evaluate the following wireless card characteristics:
TransmitterOutlined earlier in this chapter; wireless cards share these same characteristics. The key characteristic is transmitter power output. The ideal transmitter would have a power output of 100 to 200 mW with a software-configurable power level.
Receiver characteristicsAlso outlined earlier, the better the receiver sensitivity (when combined with good selectivity), the better your wireless system performance will be.
External antenna connectorAn antenna is the key element in any wireless system. A wireless card needs to have a connector that allows an external antenna to be attached.
Form factorThe most frequently used wireless card form factor is PCMCIA; however, other form factors are sometimes used. These other form factors include industry-standard architecture (ISA), peripheral component interconnect (PCI), and Compact Flash (CF).
Mesh Network Feature Decisions
You can evaluate mesh network equipment using the same considerations that you do for all other wireless equipment. Keep the following differences in mind, however:
Network deployment processDeploying a mesh network is different from deploying a point-to-multipoint network. Every mesh network node serves as a repeater and relay point for other network nodes. Nodes that are located farther away from the Internet connection must be relayed through closer network nodes. Before distant nodes can be deployed, nodes must be deployed closer to the Internet node. To provide coverage to an entire geographical area, the area must be seeded. Some nodes must be installed initially even if no end user is available to pay for the cost of the node.
Bandwidth and throughput limitationsMesh networks share backbone bandwidth with last mile bandwidth, which can reduce the amount of bandwidth to each end user. Be sure to factor this throughput limitation into your evaluation process and into your business plans.
Maximum hop limitationsThe multihop nature of mesh networks increases network latency and reduces network throughput. You will be limited to a maximum number of hops, so be sure to factor this limitation into your business plan.
Wireless Equipment Environmental Decisions
Remember environmental considerations when evaluating wireless equipment:
Operating temperature rangeAll wireless equipment is designed to operate correctly between certain specified temperatures. Indoor equipment is designed to operate within a narrower temperature range than outdoor equipment. If you choose to use indoor equipment outdoors, be sure to provide cooling for it in the summer. In severe winter climates, it might also be necessary to add a heat source to keep the equipment warm.
Radio frequency (RF) immunityMany models of broadband wireless equipment are not designed to be used in a high-level RF environment. For example, locating a wireless LAN AP designed for home use in the equipment vault of a mountaintop transmitter site can lead to operating failures. The high-power transmitter energy can either come down the antenna cable and overload the AP receiver, or the energy can pass through the plastic case of the AP and disrupt the AP operation. If you plan to deploy equipment like this, plan to use an external bandpass filter in the antenna system. Also plan to mount the AP in a shielded and grounded metal equipment case. As an alternative, you can select equipment designed for high-RF environments. This equipment is usually designed for mounting in a standard 19-inch metal equipment rack.
Wireless Amplifier Feature Decisions
Wireless network operators often add external bidirectional amplifiers to their wireless systems. External means that the amplifier is external to the wireless equipment. Bidirectional amplifiers actually contain two amplifiers: one to amplify the transmitter signal and one to amplify the incoming received signals.
In the United States, FCC regulations require that external power amplifiers be marketed and sold only as part of a complete legally certified radio-cable-amplifier-antenna combination. The purpose of this regulation is to minimize the use of illegal overpowered equipment. Excess transmitter power raises the noise level, increases interference, and makes it harder for other, legal networks to operate correctly. Unfortunately, some wireless WAN operators ignore this regulation and intentionally use external power amplifiers in violation of FCC regulations. This behavior can result in heavy fines and equipment confiscation and also decreases the usability of the license-free bands for everyone.
Illegal amplifier use is not the answer to making your WAN operate over longer distances. Often, a power amplifier actually decreases the receiving range of your WAN. In addition, using illegally high transmitter power causes substantial interference to other network operators who are operating legally. Finally, if illegal amplifier use increases, the FCC might be forced to step in with new, more restrictive regulations that could reduce license-free operating privileges for everyone. Resist the urge to amplify. Proper wireless network design and proper antenna system design provides you with the best network performance.
The following sections explain how external amplifiers work and how to use these amplifiers properly.
On transmit, an external amplifier increases the transmitter power that reaches the antenna. This is useful when the power output of the transmitter is low and the cable length between the wireless equipment and the antenna system is long. Without an amplifier placed at the antenna, the high cable loss results in little signal reaching the antenna.
Here is an example of the correct way to use an amplifier. Start with a transmitter that has an output of 50 mW (+17 dBm). If the antenna cable has a loss of 14 dBm, the power reaching the antenna system is (+17 dBm 14 dBm) = 3 dBm (2 mW). This is a low level of transmit power. If an amplifier with +14 dB of gain is added at the antenna, the +3 dBm that reaches the amplifier is amplified by +14 dB, resulting in a total of (3 dBm + 14 dB) +17 dBm (50 mW) reaching the antenna. The amplifier has added back the power that was lost in the antenna cable.
On receive, an external amplifier mounted at the antenna performs two functions:
It helps to overcome the signal loss that occurs in the antenna cable.
It sets the SNR of the receiving system.
These two functions can lead to a small improvement in receiver performance if the amplifier has a good, low-noise design. In addition, a properly designed antenna should be used with the amplifier. If the antenna system design is poor, the amplifier can actually reduce the receiving range of the system.
Up/down converters translate wireless signals from one frequency band to another. If the 2.4-GHz band is crowded in your area and the 5.8-GHz band is less crowded, you might want to use a 2.4-to-5.8 converter. Here is how this works. Each AP and end user station is equipped with a converter. Then, the following occurs:
During transmit, each 2.4-GHz transmit signal is upconverted (translated up in frequency) to the 5.8-GHz band.
During receive, the 5.8-GHz signal from the other station is downconverted to the 2.4-GHz band.
Using lower-cost 2.4-GHz equipment, communication actually takes place on the less crowded 5.8-GHz band. The advantage of this approach is that it usually costs less than buying more expensive equipment for 5.8 GHz. The disadvantage of this approach is that only a few manufacturers supply frequency converters, so your choice is limited. Converters need to be mounted at the antenna.
Several compatibility issues can reduce the reliability of your network and consume troubleshooting time. If you are deploying an 802.11b network, never assume that different brands of wireless cards and wireless APs will work reliably together. Even hardware that is wireless fidelity (WiFi)-certified sometimes has firmware, software, operating system, and feature differences that can result in certain equipment combinations that do not work together. In most cases, equipment manufacturers do not cause these issues intentionally. There have, however, been a few instances in which large equipment vendors have intentionally created incompatibilities to boost the sales of their equipment and hinder the sale of lower-cost competitive equipment.
Watch for the folowing incompatibility issues:
Operating system softwareNew features might not work with older software versions, or older features might not work in newer software versions. This situation can require that you upgrade all your wireless equipment software simultaneously.
NIC firmwareUpgrades might have features that do not work even though they did work in earlier versions. NIC firmware might work when matched with older versions of AP software but not with upgraded AP software versions.
MAC incompatibilitiesDifferent brands of equipment that should work together do not work together or some of the features do not work.
NIC driversDrivers might not be available for your OS or, if available, they might not be upgraded to work with newer versions of your OS.
USBThere might be incompatibilities between wireless USB devices and certain PC operating systems.
Network managementNetwork management software and diagnostics software can be unavailable or can be limited in their capability to manage mixed-equipment networks.
TimingEquipment that has timing designed for indoor (several hundred foot) distances might not work outdoors at longer (several mile) distances.
Here are some of the things that you can do to minimize the loss of time and money caused by these incompatibilities:
StandardizeAs much as possible, standardize on one brand of equipment for your APs and your CPE. Minimize the mixing and matching of different wireless equipment brands that talk to the same AP. Using a different brand of equipment is fine for wireless backhaul links; however, the fewer types of AP/CPE equipment that you use, the more efficiently you will be able to support that equipment and the more reliable your service will be.
Test timeBe sure to plan for enough test time between the time that you build an AP and the time that you begin service from that AP. The more dissimilar your equipment, the more test time you need.
Wireless Support Issues
The quality of support from wireless vendors varies widely and ranges from excellent to none. In addition, technology changes rapidly; new software, new hardware, new firmware, and new drivers constantly become available. To maximize your chances of receiving effective support, do the following:
ResearchDuring your equipment research process, be sure to visit other organizations that have deployed the equipment you are considering. Ask the organizations to comment about the quality of vendor support they are receiving, including warranty support.
Realistic approachThere still is no free lunch. Be realistic with your support expectations. You deserve to be notified by your vendor when equipment problems are discovered. You should rightfully expect that your vendor would not discontinue support for equipment that you have purchased; however, after your warranty period has expired, it is not unreasonable for a vendor to charge for software upgrades or new and improved hardware. Expect to pay a reasonable amount to receive a high level of continuing vendor support. You need your equipment vendor to make a profit so that it will continue to be there when you need it.
Support groupsA number of online support groups are available for specific brands of wireless equipment. Find a discussion group for your equipment and join it, if possible, even before you purchase your equipment. You, your end users, and the entire industry will benefit from this helpful and friendly sharing of information.