Ch1

Question 1

Circuit switching vs. packet switching

Know what it is and what the differences are

Answer 1

Circuit switched networks set up a connection between two devices (with a fixed bandwidth)

• “Private” connection between devices, not shared
• inefficient in terms of connections

Packets switching:

• Computers transmit individual packets
• Shares the same network as other connections. Possibility for packet loss

Question 2

Statistical multiplexing

Know what it is and understand why that leads to potential performance problems

Answer 2

Packets come together in single device from which they are sent onwards.
This can create bottlenecks since the device may only able to handle a certain amount of data

Question 3

Bandwidth vs. throughput

Know what it is and what the differences are

Answer 3

Bandwidth:
- Data transmission rate

Throughput:(goodput)

• Number of bits per time unit that you actually get
• Actually achieved bandwidth

Question 4

Latency, delay, round-trip times

Know what it is

Answer 4

Latency:
- How long does it take to send 1 bit from A to B

Delay:
- Time before a packet has been fully received

Transmit time:
- How long does it take for the sender to send the packet

RTT:
- Time it takes for a bit to be sent from A to B, and back

Question 5

Bandwidth- vs. delay-bound

Know what it is and the difference is

Answer 5

The bound says what the bottleneck is. So if the transmission is bound by either bandwidth or delay.

Small packets are usually delay-bound
Where large packets are usually bandwidth-bound

Question 6

Mice and elephants

Know what is meant by that

Answer 6

Object on the internet are usually either:

• very big, or (RTT usually important)
• very small (throughput usually important, also max. congestion window)

Question 7

Hourglass model

Know what it is

Answer 7

There are various types of applications, which run using various protocols. But all these protocols run over an IP connection. Making IP the middle of the hourglass, as the IP packets in turn use different networks.

Question 8

ISO reference model and encapsulation

Know what it is and understand the functionalities at different layers (see also slides course 2)

Answer 8

Used as layers of abstraction.
Each layer handles a different part of the connection/interaction
Different protocols for each part of the abstraction

Physical layer: hardware, cables
Data link layer: Medium Access Control, sharing of the medium. Synchronization, error checking.
Network layer: Switching / routing between nodes
Transport layer: TCP/UDP
Session layer: Establishes connections between applications
Presentation layer: Converts data into form handleable for the application
Application layer: end-user processes. Email, HTTP, etc.