Week 6 - Multiplexing + Data-link layer

Question 1

What is point of multiplexing?

Answer 1

Fully utilize the bandwidth of a single link for multiple signals.

Question 2

What are the 3 multiplexing techniques?

Answer 2

1. FDM - Freq division (Analog)
2. WDM - Wavelength division (Analog)
3. TDM - Time division (Digital or analog converted to digital)

Question 3

How does Frequency division multiplexing work?

Answer 3

Multiple sender frequencies are combined into a single composite signal that can be filtered at the receiver

Question 4

How does Wavelength division multiplexing work?

Answer 4

Like FDM but combines optical signals.

Question 5

How does Time-Division multiplexing work?

Answer 5

Divides dataflow from multiple digital signals into frames. The bandwidth is time-shared between the signals.

Question 6

What are the 3 methods for handling disparity in input data rates?

Answer 6

1. Multiplexing
2. Multiple- slot allocation (DEMUX)
3. Pulse stuffing

Question 7

Why do we need to encapsulate and decapsulate the frame at each node in the data-link layer? (2 reasons)

Answer 7

1. Each link may be using a different protocol.
2. MAC addresses need to be updated.

Question 8

What are 4 services provided by the data-link layer for the network layer?

Answer 8

1. framing
2. flow control
3. error control
4. controlling how medium used

Question 9

What are the 2 sublayers of data-link?

Answer 9

1. Data Link Control (DLC) - Deals with both point-to-point AND broadcast links
2. Media Access Control (MAC) - deals with broadcast links

Question 10

Why do we need link-layer addressing?

Answer 10

IP addresses define the source and dest, but do not help in determining the route the packet takes at the data-link layer.

Question 11

What is ARP?

Answer 11

Address Resolution Protocol: auxiliary protocol of network layer.

Will use the IP addresses to send ARP requests and receive ARP replies at the network layer which allows datagrams to be framed with the corresponding MAC addresses (using a forwarding table).