Overview
Probably the hottest topic in computing in the new millenium has been wireless networking. The obvious advantage is the mobility that it provides and the possibility of ubiquitous networking - networking everywhere. There are a number of legal and social issues that are important, but from a technical standpoint, its just plain phat (groovy, neat, cool, far out, ...). So we should be interested in this newest type of technology. There isn't time to cover everything, but we will look at the most common form of wireless, IEEE 802.11b, or WLAN as it is commonly called.
Objectives
- Understand the physical properties of IEEE 802.11b.
- Understand the access algorithm of IEEE 802.11b.
- Understand the IEEE 802.11b distribution algorithm.
Preparation
Study sections 2.8 in the book and the notes.
Knowledge, Comprehension & Problem Solving
Terms
- Access point
- Association request/response
- Beacon frame
- Chipping sequence
- Clear-to-send
- Direct Sequence Spread Spectrum (DSSS)
- Exposed node
- Frequency hopping spread spectrum (FHSS)
- Hidden node
- Probe request/response
- Request-to-send
- Scanning
Questions
- Given the bit-pattern 1010 and the 4-bit chipping sequence 101011000011, what is the output pattern?
- Why is the Duration Field present in the 802.11 frame?
- What are the places in the access algorithm where a collision could occur?
- Draw a diagram of the hidden node problem and of the exposed node problem.
- Suppose you have a distribution system with 3 AP's (AP1, AP2, AP3). Station A is associated with AP1 and station B is associated with AP3. AP1 and AP3 can only communicate through AP2. Show the Address and ToDs and FromDS fields as a frame from A to B moves through the network.
Analysis, Synthesis & Evaluation
- Compare the 802.11b, 802.3 and 802.5 access algorithms? Explain the differences that you find in 802.11b?
- If an IEEE 802.11b network uses FHSS and hops 10 times per second, can a station send a maximum length message without hopping to another frequency (assume 1 Mbps for the data rate)?
- What do you suppose the "Sleeper is sending" bit does in the Frame Control field is for? Why didn't the 802.3 and 802.5 networks have something like this?
- Several fields in the 802.11b frame format refer to fragmentation. What do you think this is, and how are the fields used?
- Image that you are driving down the road in your Mercedes with your cool wireless laptop (note that in this particular dream we have excellent wireless coverage). Explain how you stay connected seamlessly using the management frames discussed.
- Is 802.11 using FDM or TDM?