2 H log2 N = 2 4,000 log2 16 = 32,000
X dB = 10 log10(S/N) 10 = 30 log10(S/N) S/N = 1,000
H log2(1 + S/N) = 4,000 log2(1 + 1,000) 4,000 log2(1024) = 40,000
Space Division: many cells permit re-use of the same channels in any two non-adjacent cells.
Frequency Division: the cellular band is divided into 800 separate channels.
Time Division: frequencies are only allocated when they are in use. Since most cell phones in a single cell are not in use at any one time, this is a type of time division multiplexing.
Application: mail header format
Session: cursor movement
Transport: byte ordering
Network: routing, congestion control
Link: sending frames, link errors
Physical: representation of 0's,1's
For each link, each router sends <neighbor id, link state> (2 bytes should be fine)
For each route update, each router sends a sequence number (4 bytes is safe)
Therefore each routing message contains: 4 links x 2 bytes/link + 4 bytes = 12 bytes.
Each routing message travels over every link (flooding with sequence numbers)
200 routers x 4 links/router / (2 end-points per link) = 400 links.
Routing messages are send 1/100msec = 10 messages/second
So 200 routers x 10 msgs/sec-router
x 400 links x 12 bytes/msg = 9.6M bytes/sec
Each routing table entry contains <dest, hop count (metric), next hop> 3 bytes
Each host maintains a 200 entry routing table
At each update, each router sends all of its neighbors its entire table
So 200 routers x 10 updates/sec-router x 4 link/router x 3 x 200 bytes/link = 4.8 MB/sec
A collision is two or more stations
sending a once. Let P(x) denote the probability of x stations
sending at once.
P(>=2) = 1 - P(0) - P(1)
P(0) = (1-P)n
P(1) = n p (1-P)n-1
(>=2) = 1 - (1-P)n
- n p (1-P)n-1