1. count to infinity problem: A problem with distance vector routing that causes it to react slowly of link failures since only a count of hops rather than the full path is exchanged between routers.
2. packet: a small unit of communication. It can be variable or fixed size, but there is a fixed maximum size.
3. virtual circuit vs. packet switched: Virtual circuits involve using a connection establishment message to store traffic connection state in a network. Virtual circuits tend to provide static routing for a single connection and thus ensure in-order delivery of packets.
4. ISDN: Integrated Services Digital Network. A way to provide 2 64kbps circuit switched channels over a single pair of copper wire.
5. flooding: a way to send information from a source to a destination by sending the traffic over all links. It its pure form is generally leads to infinite traffic, but it can be useful as a basis of comparison. Also, by adding ways to control the flood it becomes a practical algorithm.

1. What is the maximum possible transmission rate if the channel is noiseless?

   2 H log₂ N = 2 4,000 log₂ 16 = 32,000

2. What if the signal to noise ratio is 30dB?

   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

Presentation: encryption

Session: cursor movement

Transport: byte ordering

Network: routing, congestion control

Link: sending frames, link errors

Physical: representation of 0's,1's

Link-state:

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

Distance Vector:

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