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Computer Network > Chapter 1: Computer Networks and the Internet > Flashcards

Chapter 1: Computer Networks and the Internet Flashcards

1
Q

A Nuts-and-Bolts description of the internet

A

The Internet is a computer network that interconnects billions of computing devices throughout the world.

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2
Q

Internet Service Provider (ISP)

A

Provide internet access

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3
Q

Types of Host/End System

A
  • Two types
    • Client
    • Server/Data centers
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4
Q

Server/Data centers

A

More powerful machines that store and distribute web pages

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5
Q

Communication link

A

Different links transmit at different transmission rate (bits per second, bps)

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6
Q

Packet

A
  • Host divide data into segments, add header to each segment to generate a packet
  • Destination reassemble packets into data
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7
Q

Packet switch

A

Receive and forward packets towards their destinations

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8
Q

Types of switch

A
  • Router

- Link-layer switch

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9
Q

Router

A

Used in core networks

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10
Q

Link-layer switch

A

Used in access network

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11
Q

Route / path

A

End-to-end connections from hosts to destinations

- Comprised of links and switches

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12
Q

A service description of Internet

A

An infrastructure that provides services to applications

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13
Q

Protocol

A

A protocol defines the format and the order of messages exchanged between two or more communicating entities, as well as the actions taken on the transmission and/or receipt of a message or other event.

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14
Q

Access Network

A

Connect hosts to edge router

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15
Q

Edge route

A

the first router in the global or regional ISPs

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16
Q

Two Types of the network core

A
  • Packet switching

- Circuit switching

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17
Q

Requirement on end-to-end resource reservation(Packet switching)

A

No.
A source host wants to communicate with a destination host.
- It use resource from source host to destination host in an on demand manner.
- ex. Internet.

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18
Q

Requirement on end-to-end resource reservation(Circuit switching)

A

Yes.
A source host wants to communicate with a destination host
- It must reserve resources along a path (called circuit or dedicated end-to-end connection) from source host to destination host
- The resource must be reserved for the entire duration of the communication session.
- ex. Telephone networks

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19
Q

Main concept of packet switching

A

Store-and-forward transmission
- Packet switch mush receive (store) all bits of a packet, then only it can transmit (forward) the first bit of the packet.

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20
Q

Network performance of packet switching

A
  • Queuing delay

- Packet loss

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21
Q

Routing protocol

A

Each router determine the shortest path to each destination and use the shortest path to configure its forwarding table.

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22
Q

Forwarding table

A
  • Each host has IP address.

- Each router use forwarding table to map a destination IP address to one of its outgoing link.

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23
Q

Two types of circuit switching

A
  • Frequency-Division Multiplexing (FDM)

- Time-Division Multiplexing (TDM)

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24
Q

Frequency-Division Multiplexing (FDM)

A

A link dedicate a frequency band to each connection

  • The width of the frequency band indicate bandwidth
  • ex. 4 kHz
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25
Q

Time-Division Multiplexing (TDM)

A

A link dedicate one time slot in every frame to each connection

  • Time is divided into fixed duration frames.
  • Each frame is divided into a fixed number of time slots.
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26
Q

Performance efficiency of packet switching

A

Higher

  • No reservation
  • More sharing of link capacity
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27
Q

Performance efficiency of circuit switching

A

Lower

  • Required reservation
    • Reserved resources may not be fully utilized
    • Reserved resources may not be sufficient
      • Underutilized reserved resources cannot be used for other packets
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28
Q

Do the packets in packet switching need to wait at queue?

A

Yes

  • There is variable and unpredictable delay
  • Not suitable for real-time service
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29
Q

Do packets in circuit switching need to wait at queue?

A

No

- Reserved resource provides guaranteed constant rate

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30
Q

Complexity of packet switching

A

Lower

31
Q

Complexity of circuit switching

A

Higher

- Reservation requires end-to-end signaling protocol

32
Q

Cost efficiency of packet switching

A

Higher

  • No reservation
    • Less cost involve
33
Q

Cost efficiency of circuit switching

A

Lower

34
Q

Popularity of packet switching

A

More popular

35
Q

Popularity of circuit switching

A

Less popular

36
Q

Formula of Node delay

A

Node delay = Processing delay + Queuing delay + Transmission delay + Propagation delay

d(node) = d(proc) + d(queue) + d(trans) + d(prop)

37
Q

Processing delay

A
  • Read packet header
  • Determine the outgoing link
  • Check bit errors
  • Value: μs
38
Q

Queuing delay

A
  • Wait to be transmitted

- Value: ms

39
Q

Transmission delay

A
  • Push all bits of a packet into the link
  • d(trans) = L/R
  • Value: ms
40
Q

Propagation delay

A
  • Travel from one router to another across a link
  • Speed depends on
    • Propagation speed of physical media, s
    • Distance between the routers, d
  • d(prop) = d/s
    s : 3 x 10^8 meters/sec
41
Q

Traffic Intensity

A
  • Ratio of bits arrival rate (bits/second) to transmission rate
  • Traffic intensity = La/R
  • L = packet length (bits)
  • a = Packet arrival rate (packets/second)
  • R = Transmission rate (bits/second)
42
Q

When La/R(Traffic Intensity) ~ 0

A

queue size decress, and so queuing delay approaches zero

43
Q

When La/R(Traffic Intensity) -> 1

A

queue size increases without bound, and so queuing delay approaches infinity

44
Q

How queuing delay increase?

A

Queuing delay increases exponentially

- small increment in traffic intensity provide large increment in queuing delay

45
Q

Packet loss

A

Packet arrive at a full queue will cause packet drop

- Lost packet may be retransmitted

46
Q

Throughput

A
  • Rate (bits/seconds) at which bits are transferred between source host and destination host
47
Q

Types of throughput

A
  • Instantaneous throughput

- Average throughput

48
Q

Instantaneous throughput

A

Rate at a given point in time

49
Q

Average throughput

A

Rate over a longer period of time

50
Q

Bottleneck link

A
  • Link on end-to-end path that constraints end-to-end throughput
51
Q

Bottleneck bandwidth

A
  • min { R(c), R(s) }

- Bottleneck bandwidth is transmission rate of client or servers for which is lower.

52
Q

What is the end-to-end delay in bottleneck link?

A

F / min{ R(c), R(s) },

where F is file size.

53
Q

Types of Protocol stack

A
  • Internet Protocol Stack

- ISO Open System Interconnection (OSI) Reference Model

54
Q

Each layer of protocol layers

A
  • Perform certain actions

- Use services of the layer directly below it

55
Q

Layering of Protocol layers

A
  • Divide a complex system into layers
56
Q

Advantage of protocol layers

A

Can maintain and update each layer without affecting the entire system

57
Q

Disadvantage of protocol layers

A

Similar function in more then one layer

-eg. error recovery in link layer and network layer

58
Q

Packet of Application layer

A

Message

59
Q

Packet of Transport layer

A

Segment

60
Q

Packet of Network layer

A

Datagram

61
Q

Packet is Link layer (Ethernet, WiFi)

A

Frame

62
Q

Packet is Physical layer

A

Bit

63
Q

Function of Application layer

A
  • Support network applications
  • Provide Domain Name System (DNS)
    • Translate address (e.g., www.ietf.org to 32-bit address)
  • e.g.: HTTP, email
64
Q

Function of Transport layer

A
  • Break a long message into shorter segment
  • Reduce source host transmission rate during congestion
  • e.g.: HTTP, email
65
Q

Function of Network layer

A
  • Determine routers between source host and destination host

- e.g.: IP Protocol

66
Q

Function of Link layer

A
  • Transmit frame from a transmitting host to receiving host over one link
  • e.g.: Ethernet, WiFi
67
Q

Function of Physical layer

A
  • Transmit bits on physical media (e.g., wireless, fiber optic)
68
Q

Packet switch

A
  • Link-layer switch

- Router

69
Q

Link-layer switch

A
  • Used in access networks

- Consist layer 1 and 2

70
Q

Router

A
  • Used in core networks

- Consist layer 1, 2 and 3

71
Q

Encapsulation

A

At each layer, a packet consist

  • Header
  • Payload (a packet from the upper layer)
72
Q

Segment consists

A

Segment = Message + Header of Transport Layer

73
Q

Datagram consists

A

Datagram = Segment + Header of Network Layer

74
Q

Frame consists

A

Frame = Datagram + Header of Link Layer

Computer Network (3 decks)

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