Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Computer Systems & Networks > Unit 6: Introduction > Flashcards

Unit 6: Introduction Flashcards

1
Q

Define bandwidth and unit it is measured in

A

Transmission rate of data - bits per second

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What does a packet switch do?

A

Forwards packets (chunks) of data

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is the ‘nuts and bolts’ view of a network?

A

The internet is a network of networks i.e. consisting of interconnected ISPs. It consists of protocols that control sending and receiving of messages

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is the ‘service’ view of a network?

A

The internet is an infrastructure that provides services to applications and a programming interface to applications

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Define a protocol

A

Protocols define the format and order of messages sent/received among network entities, and the actions taken on message transmission/receipt

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What constitutes network edge?

A

The hosts - clients and servers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What constitutes access networks?

A

The wired and wireless communication links

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the network core?

A

A mesh of interconnected routers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

a) What does DSL stand for?

b) Describe a DSL access net (what is transmitted/where?)

A

a) DSL = Digital Subscriber Line
b) In DSL, voice and data are transmitted at different frequencies over a dedicated existing telephone line to a central office. The data goes to the internet, voice goes to the telephone net

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is frequency division multiplexing?

A

Where different channels are transmitted in different frequency bands

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Describe a cable network access net

A

In a cable network a fibre cable attaches homes to an ISP router. Home share access networks to cable headend

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

State a difference between DSL and cable networks

A

Access networks are shared in cable networks, whereas DSL have dedicated access to the central office

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What type of cable is used in cable networks?

A

Hybrid fiber coaxial (HFC) cables which are asymmetric (one direction)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Describe the modern home network access net and the different connection points

A

A wireless access point connects wireless devices to the router, in which wired devices are connected directly via wired ethernet. The router is connected to a cable or DSL modem.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Briefly describe wide-area wireless access

A

Cellular operators (e.g. Telco) provide 3G, 4G etc. by using technologies such as LTE

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Define a bit in the context of physical media

A

What propagates between the transmitter and receiver pairs

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Define a physical link in the context of physical media

A

What lies between a transmitter and receiver

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Define guided media in the context of physical media

A

Signals that propagate in solid media e.g. copper

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Define a unguided media in the context of physical media

A

Signals that propagate freely e.g. radio

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Define a twisted pair in the context of physical media

A

Two insulated copper wires used in ethernet with high access speed

21
Q

a) Define a coaxial cable in the context of physical media.

b) Where is it used?

A

a) Two concentric copper conductors which are

b) Broadband

22
Q

a) Define a fiber optic cable in the context of physical media
b) Give and explain a benefit of fiber optic cables

A

A high speed glass fiber that carries light pulses (each represent a bit). It has a low error rate as it is immune to electromagnetic noise and repeaters are spaced far apart

23
Q

a) Describe radio signals in the context of physical media

b) Give and explain a drawback of radio signals

A

Signals are carried in the electromagnetic spectrum. It is bidirectional. Radio is susceptible to the environment because of reflection, obstruction and interference

24
Q

Give 4 types of radio link

A

Terrestrial microwave, LAN (wifi), wide-area (cellular), satellite

25
Q

Define packet switching

A

Hosts break application-layer messages into packets, forward them from one router to the next across links

26
Q

Briefly describe the store and forward approach

A

The entire packet must arrive at the router before it can be transmitted on the next link

27
Q

Give the equation for calculating how long it takes to transmit a packet using store-and-forward:

a) one way
b) 2 ways

A

L = packet size (bits), R = bandwidth (bps)

a) L/R
b) 2*L/R

28
Q

What causes queuing and loss in packet switching?

A

When arrival rate > transmission rate, packets will queue. If memory buffer fills up, packets can be dropped

29
Q

What happens in circuit switching? Give an example where circuit switching is used

A

Dedicated rources are allocated to a ‘call’ between source and destination. There is no sharing of resources and the circuit is idle if not used a call. It is used in telephone networks

30
Q

What is FDM?

A

Frequency Division Multiplexing - each user occupies a certain band of frequencies

31
Q

What is TDM?

A

Time Division Multiplexing - time is divided into frames of a fixed duration which is divided into a fixed number of timeslots. Each connection occupies one timeslot

32
Q

Given a 1Mb/s link and each user needing 100kb/s, how many users can be supported in circuit switching?

A

10 users by pre-allocating

33
Q

Give 2 reasons why packet switching is good for ‘bursty data’

A
  1. It allows resource sharing

2. It is simpler, has no call setup

34
Q

State a problem with packet switching

A

Excessive congestion is possible due to packet delay and loss meaning protocols are needed for rdt and congestion control

35
Q

Which is the provider and which is the customer in the following:

  1. Global ISP & Regional ISP
  2. Regional ISP & Access ISP
A
  1. Global ISP = provider Regional ISP = customer

2. Regional ISP = provider Access ISP = customer

36
Q

What is tier-1 in an internet structure?

A

Commerical ISPs e.g. AT&T

37
Q

What is a content provider network?

A

A private network that connects its data centers to the internet by often bypassing tier-1 and regional ISPs, e.g. Google

38
Q

What is a message in the ___ layer called?

  1. Link
  2. Network
  3. Transport
  4. Application
A
  1. Frame
  2. Datagram
  3. Segment
  4. Message
39
Q

Why use layering as an architecture?

A

When dealing with complex systems, an explicit structure allows identification and relationship between the system’s pieces. Modularisation eases maintenance and updating of the system

40
Q

Give formula to calculate nodal processing delay

A

nodal processing delay = queueing delay + transmission delay (L/R) + propagation delay (length of link/propagation speed) + processing delay

41
Q

Give the formula to calculate traffic intensity

A

L = packet length (bits), R = link bandwidth (bps), a = average packet arrival rate
= La/R

42
Q

If La/R ~ 0, what does this mean?

Answer the same for if La/R is 1 or > 1?

A

0 = average queueing delay is small
1 = average queueing delay is large
> 1 = more work arriving than can be serviced

43
Q

What is throughput?

A

The rate (bps) at which bits are transferred between sender/receiver (either as an average or instantaneous measurement)

44
Q

When comparing capacity, what does R(s) and R(c) represent?

A 
R(s) = capacity of server link (bps)
R(c) = capacity of client link (bps)
45
Q

Give the throughput and bottleneck link for the following:

a) R(s) < R(c)

A

a) throughput = R(s) (max capacity), bottleneck = R(s)

b) throughput = R(c), bottleneck = R(c)

46
Q

When Rs and Rc for a total of 10 connections are connected to network core (R), how do you calculate the throughput?

A

Throughput = min(Rs, Rc, R/10)

47
Q

Give two advantages of message segmentation

A
  1. If a single bit error occurs, a whole large message doesn’t have to be retransmitted
  2. Huge packets would have to be sent into the network and smaller packets have to unfairly queue
48
Q

Give two disadvantages of message segmentation

A
  1. Packets must be put in sequence so more techniques are needed to guarantee this order at destination
  2. More packets = more headers which do not change size according to packet size, therefore overall header size across all packets is larger

Computer Systems & Networks (4 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions