No Strings (Wires) Attached: Wireless LANs, Part I

Evil Wire Monster! Run!

The evolution of networking has been rapid over the past several decades as computing moved from a single centralized mainframe to a more distributed model with server farms.  Alongside computing has been vast arrays of cable plants, originally consisting of thick coaxial cable, migrating to thin coaxial cable, to the twisted pair cables we all know and love.  However, just as a puppet without strings would be considered a marvel, a network without wires is equally impressive and desirable; this brings us to the subject of wireless LAN’s, or WLANs, as they are affectionately called.

The umbrella IEEE standard for wireless is designated as 802.11, representing a wide family of other standards, protocols, and so forth.  The establishment of the Wi-Fi Alliance (http://www.wi-fi.org/) in 1999 to promote interoperability has not only created widespread awareness of the technology, but has become synonymous with te technology itself (users frequently refer to WLAN’s as “wi-fi networks.”)

It probably sounds overly simplistic to say that the differences between wired and wireless networks are vastly different, but there is more truth to that than simply saying one medium uses wires and the other does not.  There are some similarities, however, that should not be overlooked:

  1. Layer 2 Technology: While they implement it differently, both operate at Layer 2 of the OSI stack.
  2. Communication Between Devices: Both allow for inter-device communication and data transmission.
  3. Frame Formats: While not identical, both use frame formats constructed with a similar anatomy, including headers/trailers, source/destination MAC addresses, etc.

One of the most striking differences between the 802.11 family of wireless standards and their 802.3 relatives has to do with the mechanics of data transmission; Ethernet uses Carrier Sense Multiple Access with Collision Detect (CSMA/CD), and responds to frames which collide in transit, while a WLAN uses CSMA/CA, in which is the stands for avoidance.  If you think of an intersection with cars crashing into one another as analogous of Ethernet, cars constantly swerving to get out of the way would be closer to wireless operation.  Here is the basic process a wireless devices uses to transmit data:

  1. Listen to make sure there is no traffic on the medium (in this case, the channel/air)
  2. Set a random timer and do nothing until it expires
  3. Listen again to make sure that there is no traffic
  4. Send the frame
  5. Wait for an acknowledgement
  6. If there is no acknowledgement, assume the frame was lost and start over at #1

Keep in mind that this is the process for transmitting a single frame, and you don’t have to be a rocket scientist to see the amount of overhead this takes.  The reason?  While you can control things that happen on a wire, you have no control over the air, namely transmitted signals.  Lots more to come!

– Joe

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: