Click Here!
home account info subscribe login search My ITKnowledge FAQ/help site map contact us


 
Brief Full
 Advanced
      Search
 Search Tips
To access the contents, click the chapter and section titles.

Wireless Networking Handbook
(Publisher: Macmillan Computer Publishing)
Author(s): Jim Geier
ISBN: 156205631x
Publication Date: 09/01/96

Bookmark It

Search this book:
 
Previous Table of Contents Next


SNMPv1 is a simple request-response protocol offering the following operations:

  Get. Retrieves a block of information from a table or list within the agent.
  Get-next. Retrieves the next block of information from a table or list within an agent.
  Set. Sets information within an agent.
  Trap. Asynchronously informs the network management station of some event. Unlike the get, get-next, and set operations, the trap operation does not elicit a response from the receiver.

SNMPv1 is very mature and is highly available, but it has high overhead because each object from the agent requires a separate transfer of data across the network. In addition, SNMPv1 does not incorporate any security features. Therefore, someone can easily spoof a network management station. SNMPv2 is just emerging as a replacement to SNMPv1 and offers several advantages. For instance, SNMPv2 has a GetBulkRequest command that provides a transfer of bulk data, reducing the amount of overhead. Also, SNMPv2 supports authentication and encryption to combat spoofing.

Identifying Products

After you have defined the technologies necessary to support network requirements, you need to identify appropriate products. In some cases, such as the NOS and applications, you might have already selected the product as part of the network element definition phase. Regardless, select all products and materials necessary for implementing the network and create a bill of materials.

In general, select products based on the following criteria:

  Ability to provide a necessary degree of functionality
  Product availability
  Level of vendor support after the purchase
  Price

The following criteria are also important when selecting wireless products:

  For wireless LANs, compliance with the IEEE 802.11 standard
  Availability of tools that assist with installation (site survey tools, field strength meters, and so forth)
  Availability of encryption for higher security
  Ability to fit the form factors of your computers (ISA, PCMCIA, and so forth)
  Ability to interoperate with the selected network operating system


NOTE:  

Appendix B, “Wireless Networking Products and Services,” contains many of the wireless network products. You can use this as a guide for selecting wireless LAN, MAN, or WAN products.


Identifying the Location of Access Points

Most environments, such as hospitals, factories, and warehouses, cover an area exceeding the range of wireless LAN devices. As described in Chapter 2, wireless LAN vendors sell wireless local bridges (often called access points) to provide an interface between wireless users and wireline technologies such as IEEE 802.3 ethernet or IEEE 802.5 token ring. In addition, most of these access points also support wireless users who roam from one cell to another. A major design concern is identifying the location of these access points to provide an interface to network resources located on wired networks and to provide adequate coverage for roaming users throughout the facility.

It would be easy to deploy a wireless network in a completely open area, free from obstacles like walls, desks, and window blinds. This would allow radio waves from the wireless devices to maintain an omnidirectional radiation pattern, making it simpler to predict the maximum operating range between all devices and the locations of the access points. The presence of objects and the construction of the facility, however, causes attenuation to radio wave signals that distorts the radio propagation pattern, making it difficult, if not impossible, to predict. Table 8.1 gives you an idea of the degree of attenuation of various types of RF barriers.

Table 8.1 RF Attenuation for various types of barriers.

RF Barrier Relative Degree
of Attenuation
Examples

Air Minimal
Wood Low Office partitions
Plaster Low Inner walls
Synthetic Material Low Office partitions
Asbestos Low Ceilings
Glass Low Windows
Water Medium Damp wood, aquariums
Bricks Medium Inner and outer walls
Marble Medium Inner walls
Paper High Paper rolls
Concrete High Floors and outer walls
Bullet Proof Glass High Security booths
Metal Very High Desks, office partitions, re-enforced concrete, elevator shafts

When establishing requirements for the network, review the environment (see Chapter 6, “Defining Requirements for Wireless Networks”) to give you enough information to select the appropriate type of wireless medium. To identify the location of access points, though, you need to evaluate the environment to a much higher level of detail, especially the effects of the environment on propagation of radio waves.

The best method for identifying the location of access points is to perform an RF site survey. Start by obtaining the following items:

  Blueprints of the facility
  At least one master station and NIC (PCMCIA form factor) from the selected vendor
  Portable computer (the smaller the better) having a PCMCIA slot suitable for the wireless NIC


Previous Table of Contents Next


Products |  Contact Us |  About Us |  Privacy  |  Ad Info  |  Home

Use of this site is subject to certain Terms & Conditions, Copyright © 1996-2000 EarthWeb Inc.
All rights reserved. Reproduction whole or in part in any form or medium without express written permission of EarthWeb is prohibited. Read EarthWeb's privacy statement.