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Avoiding collisions

Service providers can use wireless links and protocol solutions to help avoid data collisions and bottlenecks on the information highway

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Data needs elbow room (bandwidth) and open lanes (communication links) to move rapidly from source to destination. Keeping data moving in an orderly fashion, preventing data “collisions,” reducing delays for new data to enter the freeway (communication links) and keeping tabs on requests for entry and exit are the functions of the network controller, a.k.a. the server.

The typical computer network uses a central server. Requests for data all go to the central server in a random sequence. Data is returned to the computers on the network in pretty much a first-come/first-served order. Additional requests for data are also handled randomly. The potential for data collisions during distribution is ominously present.

Select the Best Route

Currently, there are two major types of transmission channels: 

  • wired--copper wire or fiber optic cable
  • wireless--radio link. 

Each has its pros and cons. Consider first the older, established standard of transmission–wired.

When data first began to be distributed rapidly, in-place telephone wiring was used. Even today it is still the most common transmission path because it’s available. But copper wiring limits the speed with which data can be exchanged, and when video data is transmitted, copper wiring imposes severe delays on transmission speeds due to its limited bandwidth.

On the other hand, optical paths offer greater speed capabilities. That’s why fiber optic cable is being installed widely. Not only can data be sent hither and yon faster, but data such as video that requires wider bandwidth can be sent without the long delays copper wire would require. However, fiber optic cable is expensive, and it takes time and labor to install.

Using wireless, sender and receiver need only be within a line-of-sight of each other. Put up an antenna or dish at both ends of the link, and instantly, data can be exchanged. Fiber optic cabling is still the speed leader, but wireless is catching up rapidly.

Which Way Should the Data Go?

Economics is the key. First, fiber optics is almost synonymous with high-speed data transmission. But with its high cost of installation, it becomes unaffordable in sparsely populated outlying areas such as those needing Internet service. Schools distributing data among multi-building classrooms can decimate their plant budgets when considering fiber optic wiring of the entire campus. Business organizations strung out among multiple buildings face equal financial burdens. Thus, the economies of wireless offer good value for the cost expended in addition to the higher transmission rates provided.

In any single server/multi-customer activity, the server has to decide whom and when to serve first. This is particularly complicated in Internet systems with some customers subscribing for wider bandwidth than others. How can an Internet service provider offer equal access to all and still provide additional server time to wider bandwidth customers paying higher monthly fees?

A brief review of existing computer network service techniques illustrates the difficulties.

Wireless Options

Carrier sensing multiple access/collision avoidance (CSMA/CA) is similar to a party-line telephone linkage. Using the Ethernet protocol to avoid data collisions, several computers are linked together. Then, through a common cable, they are linked to the server. In larger systems, an intelligent hub or switch (or several hubs and switches) may segment the network for faster data rates. Every network computer receives all data sent even though intended for a single computer. Similarly, all network members transmit simultaneously to the server. Data collisions may occur.

Central server has no intelligence and passes all data back out to everyone on the net though only intended for one.

Token ring
A ‘smart’ version of Ethernet in that the central server communicates only with the computer intended to receive the data. Each computer has its own link to the server. And of course, all those links cost more.

Wireless Internet polling protocol (WIPP) uses token ring architecture. The server examines each data packet to determine where to send it. Requests for data are taken in the order received, and the server is constantly polling its network members looking for data requests. With the token ring architecture, only the intended receiver accepts data sent out from the server.

CSMA/CA uses an Ethernet protocol to avoid data collisions. However, with several computers linked by common cable to the server, two or more computers sending data simultaneously can have their data collide. 

This system is passive and doesn’t have a network controller to tell each computer when to take its turn entering/receiving data from the server. The central network server could use an intelligent controller to provide more efficient and faster service. But data collisions are still possible, and data integrity may be diminished.

WIPP offers a better approach because its server is constantly polling its computers--not waiting for random data service requests. Each data packet is examined for destination and is directed accordingly. 

Network computers using wider bandwidth links are polled more often than those with narrower bandwidth links, thereby providing the faster data rates such computers require. Computers not active are polled less often. Using the token ring concept, everyone on the network is sent outbound data, but only the intended computer actually accepts it.

Better Service

In any network there will be a constant tradeoff between more servers, more linkages, wider bandwidth links, faster service and escalating cost. However, the use of wireless links accompanied by the WIPP architecture can offer a cost-effective solution.

This kind of networking could help stretch a thin budget into a fast-reacting, lower-cost system catering to both narrow and wide bandwidth users. In costly to wire older building clusters or with widely spaced clients in suburban network service, the cost-savings would be substantial.
Jerrold Asher is retired consultant and freelance writer in Thousand Oaks, Calif. His e-mail address is


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Principles of Digital Transmission:
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© 2014 Penton Media Inc.

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