Computer Networks Ch1

What 3 layers must a router implement?

Physical, Link, Network

Protocol Stack Order

Application → Transport → Network → Link → Physical

Application Layer

handles messages from a variety of network applications

Transport Layer

handles the delivery of segments from the application layer, which may be reliable or unreliable

Network Layer

moves datagrams from the source host to the destination host

Link Layer

passes frames from one node to another across some medium

Physical Layer

transmits bits directly over the wire

Data-unit order

Messages --> Segments --> Datagrams --> Frames --> Bits

What is Packet Switching?

Network resources are shared and used on demand; packets may queue; congestion, loss, and variable delay are possible. Used by the Internet.

What is Circuit switching

Resources are reserved for an end-to-end connection before communication; traditionally used by telephone networks

What causes packet queuing?

Multiple packets/users competing for the same link/resources

What can congestion cause?

Queuing delay and packet loss

What is throughput?

Rate at which data is successfully transferred, usually measured in bps

What determines end-to-end throughput?

The bottleneck, the smallest available transmission rate along the path

What is a bottleneck link?

Link with the smallest available transmission rate along the path

What is 1 Mbps

10^6 = 1,000,000 bits per second

What is store-and-forward?

A router must receive the entire packet before transmitting it onto the next link

Probability all independent components work

P(success) = p^n

Probability at least one component fails

P(failure) = 1 - p^n

Suppose a communication involves 60 components that work correctly (independently) 98% of the time. What's the likelihood that the communication fails at a given point in time? (Show the result as ab.x%, rounded to the closest .x, e.g., 39.5%)

P(success) = (reliability)^(number of components) so then P(failure) = 1 - (reliability) ^ (number of components)

Success requires that they all function so failure probability = 1 - 0.98^(60) * 100% = 70.2%