Wireless Broadband and Other Fixed-Wireless Systems page 4

★ wanayoo — archive 1999 http://www.networkcomputing.com/netdesign/bb4.html

Nouvelle recherche | Portail wanayoo

NWC Internet Site Map

Wireless Broadband and Other Fixed-Wireless Systems

Using Fixed-Wireless Systems
Now that you are an expert in how fixed-wireless communications work, here are some practical pointers on how to determine whether one of these systems is for you, which one to use, and the questions to ask your prospective vendors. In this section we cover:
Choosing Between Wireless and Wireline | Understanding Geography and Climate
Choosing Between Private and Carrier | How To Deploy a Private Connection
How To Use a Wireless Broadband Carrier | When To Use Satellites

Choosing Between Wireless and Wireline
In many instances both wireless and wireline alternatives will be available. Here are some guidelines for choosing which to use.

· Remember line of sight. You must be able to see the point with which you wish to connect, whether it is your own site or a wireless carrier. Depending on the technology used, effective range is from about three (5 km) to about 20 miles (30 km). Multiple hops also are an option but add complexity.

· Consider wireless if there are no good wireline options available. Perhaps you are in a suburban area and need high-bandwidth connectivity, but no fiber runs to your building. Even if wireline options exist, the length of time to obtain wireline service may be prohibitive.

· Consider wireless if you need to bridge LANs in two buildings in close proximity. An unlicensed spread-spectrum or licensed microwave connection could be cost-effective, particularly if you have to pay $500 or more for a monthly T1 connection. Wireless equipment providers claim a typical payback of two years.

· Consider wireless if crossing wireline service boundaries. Wireline service might be exceptionally expensive if crossing different LEC areas and a wireless connection could be cost-effective.

· Consider wireless for temporary or backup connectivity. If you need a temporary connection between two nearby sites, or if you need a backup connection, wireless might be your best option.

· Compare offerings between wireless and wireline carriers. If a wireless carrier is offering service to your building, investigate its pricing because it may be undercutting wireline providers to develop its business. Wireless carriers may also have greater flexibility in their offerings, such as the ability to easily increase bandwidth on demand.

Understanding Geography and Climate
With most data communications you don't care if there is a hill between you and another location, or whether it is sunny or raining. But with wireless communications, you must consider both geography and climate. This applies both to private and carrier systems. First the geography.

We have already emphasized line of sight. But what does this mean exactly? It means the two antennas must be clearly visible to each other. So beware of items like foliage or future construction. If your sites are separated by miles, how can you even tell if you have line of sight? There are companies that specialize in wireless integration that will be able to assist you with a site survey. Software packages that characterize the terrain of particular areas also may be helpful. Low technology approaches, such as flashing a mirror, also work. The advantage of a carrier service is that the carrier does all this work as part of the deployment.

Weather should not be a factor for the unlicensed 2.4 GHz and 5.8 GHz bands. But it is a factor in the millimeter wave bands of 28 GHz and higher. A three-mile (5 km) link operating at 38 GHz in heavy rainfall of one inch per hour will suffer a degradation of 1,000 times the received signal strength. Carriers design margin into their links to account for weather, but you should review their design parameters and ask what link reliability to expect over a course of a year.

Choosing Between Private and Carrier
This is relatively simple. If you need to interconnect your own sites and have line of sight, consider a private wireless connection. If you want Internet or telephony services, consider a carrier solution. But there are other topologies as well. For instance, the wireless carrier might offer a cost-effective wireless Internet connection to your site "A." If your site "B" has an Internet connection, you could then consider a VPN (virtual private network) connection between the two sites. Another option is where the wireless carrier provides coverage to both your sites. You could obtain a private virtual circuit between your two sites that never leaves the carrier's backbone network. Think of this as a public frame relay or ATM network that happens to use wireless links in its infrastructure. The bottom line is you will need to research all the options available, including whether wireless carrier service is even available. Service options are limited today but will be expanding rapidly over the next two years.

How To Deploy a Private Connection
If you have determine that a private fixed-wireless system addresses your communications requirements, there are a number of decisions you will need to make. One important decisions is whether to use licensed or unlicensed bands. The following table summarizes the principal characteristics of each.

Unlicensed Spread Spectrum Licensed Microwave

Ease of deployment Simpler.
No licensing required.
Simpler antennas for shorter distances.
End-user installable in many instances.
More difficult.
License required.Frequency coordination sometimes required.
Generally need services of integrator.

Performance 1 to 11 Mbps.
Error rates match wireline. 1 to 10 Mbps typical, but higher rates to OC-3 (155 Mbps) available.
Greater flexibility for increasing throughputs.
Error rates match wireline.

Interference Potential for interference because bands are unlicensed, allowing multiple simultaneous users. Potential for interference very low.

Costs Equipment costs are comparable to microwave, but installation costs can be lower. Slightly higher due to higher installation costs.

Number of vendors Greater. Many wireless LAN companies offer bridge products. Fewer.

Security Spread-spectrum signal harder to eavesdrop, but proper security still requires encryption of the data. Easier to eavesdrop.

You can think of microwave systems as offering higher performance with a lower potential for interference, but costing more and being slightly more difficult to install.

In choosing a private link, you should have determined that you have line of sight. But you will also need to check vendors specifications for trade-offs between distance and throughput. For example, a spread-spectrum product might offer 4 Mbps at distances to 10 miles (16 km) but only 2 Mbps at 25 miles (40 km).

You must also decide where to mount your antennas and what type of antennas to use. There are many types of antennas available. At shorter distances of a mile (1.6 km) or less when using spread spectrum you may be able to use a patch antenna that mounts on the inside of a window. At even smaller distances of a hundred meters, you could use an omnidirectional antenna. For longer distances to 20 miles (30 km), you will need an antenna that needs to be carefully aimed, usually on a roof or suitable tower. Some products, for example, have an LED that lights when the antenna is aligned correctly. Check with your vendor for their antenna options and installation procedures. In all cases, the antennas you will be working with will be compact, generally about a half meter in diameter or smaller.

Don't just choose a wireless solution based just on distance and throughput. Make sure it provides the data interfaces you need, supports the protocols you need and supplies suitable network management functions.

Various value-added resellers and systems integrators specialize in wireless communications. Some of these offer both licensed and unlicensed products. They can help you choose which technology to use, obtain licenses, determine how to factor in local climate conditions, conduct site surveys and install your equipment.

Proxim Directional spread-spectrum antenna.

How To Use a Wireless Broadband Carrier
Using a wireless broadband carrier is easy. You may not even know that the carrier is using a wireless infrastructure. In many instances, the carrier will provide comparable services to a CLEC or an ISP. Or their services might be resold by existing LECs, CLECs or ISPs.

Nevertheless, there are a number of questions worth asking if you are considering wireless-broadband services.

1. What carriers are available? Since wireless broadband carriers are only now deploying service, you may not even be aware that a wireless carrier is offering service to your building or area.

2. Where does the carrier have licenses and what is their deployment plan? Carriers only hold licenses on a regional basis. And most are deploying their networks building by building. Find out also what kind of license they have. Are they operating on the basis of a license waiver and if so, what are the terms of that waiver?

3. Is the deployment on a network basis or customer basis? Some carriers have a rigid deployment plan. Others will respond to individual customer demand.

4. What value-added services do they offer? Some carriers will be telephony-centric. Others are Internet-centric with Web hosting, mailbox services, network management and so forth.

5. What interfaces, protocols, data rates, error rates do they support? Because broadband services have an inherent upper end in throughput because of the width of radio channels, find out what options exist for increasing your throughput.

6. What reliability do they guarantee? Because wireless broadband signals at 28 GHz and 38 GHz are affected by weather, ask to see an analysis of reliability that takes regional weather patterns into account.

7. What networks to they interconnect with? If they connect to the Internet, who is their backbone provider? Do they interconnect with existing frame networks?

In summary, the wireless carrier will provide services that look very much like wireline services, and the wireless portion of their infrastructure should be mostly invisible to you. But nevertheless, obtaining answers to the questions above could head off potential difficulties.

When To Use Satellites
A variety of satellite systems are available today for broadband communications to 155 Mbps. Today these all involve geosynchronous satellites, but soon LEO systems also will be available. Satellites today are not usually competitive when good landline communications options exist. Rather they make the most sense in the following types of situations:

· There are no good terrestrial options. This is especially true in developing nations or out at sea.

· You are deploying a mesh network of more than fix or six nodes that spans a large geographic area, e.g. multiple countries.

· You are broadcasting data to a large number of locations.

Figure: Geosynchronous versus low earth orbit satellites.

Print This Page

E-mail this URL

VPN Devices
Article
Guide
Full Chart
Customize Chart
Product Directory
Search

Find more Buyer's Guides.

Get IT Training.

Get a Job.

Shop Our Advertisers.

Contact Our Advertisers.

Storage Shoot-Out
Looking for the perfect Storage solution? Come to our full-day event this September and see vendors respond to a live RFP. You can register to attend, participate, or sponsor our event here.

Attend other events.

Administering IIS 5.0,
Part One
If you're looking to better manage Web content via Internet Information Server, you'll like our latest chapter, Administering Virtual Directories and Servers. We also have more Beginning Perl questions and answers -- all in the latest Network Design Manual.

Read more Design Manual chapters.


		Subscribe to Network Computing magazine and our Free, weekly E-Mail newsletter.


		E-Commerce Survey! Are you conducting E-business? If so, we want to hear from you. Please take a few minutes and fill out our online questionnaire on payment services. You could win a $200.00 American Express gift certificate!