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Kommunikasjon - Tjenester og nett > Chapter 1: Introduction > Flashcards

Chapter 1: Introduction Flashcards

1
Q

Hosts

A

End systems

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2
Q

Packet switches

A

Forward packets

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3
Q

Route

A

The sequence of communication links and packet switches traversed by a packet from the sending end system to the receiving end system

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4
Q

Communication links

A

Fiber, copper, radio & satellite

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5
Q

Transmission rate

A

Bandwidth (bits / second)

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6
Q

Networks

A

Collection of devices, routers, links that are managed by an organization

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7
Q

Internet

A

“Network of network”. Consists of interconnected ISPs

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8
Q

What do protocols do?

A

Control sending and receiving of information within the Internet

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9
Q

A “service” description of the Internet could be:

A
  • Infrastructure that provides services to applications
  • Provides programming interface to distributed applications
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10
Q

Distributed applications

A

Involve multiple end systems that exchange data with each other

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11
Q

What do “hooks” allow application to do?

A

Connect to / use the Internet “transport service”

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12
Q

What do protocols define?

A

The format, order of messages sent & received among network entities, and actions taken on message transmission & receipt

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13
Q

What is the network edge?

A

Consists of hosts; clients and servers

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14
Q

Which part of the Internet structure do access networks & physical media make up?

A

Wireless & wired communication links

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15
Q

Which part of the Internet structure does the network core make up?

A

Interconnected routers & network of networks

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16
Q

How can end systems be connected to the first router in an access network (also known as the edge router)?

A

Residential access networks & mobile access networks

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17
Q

How does the Digital Subscriber Line access network work?

A

DSL modems at customer convert digital data to high-frequency signals. They travel over existing telephone lines to local telephone exchange. DSLAM aggregates signals from several customers & converts them into a format for high-speed data transmission. The data is sent over high capacity fiber optic to the internet backbone.

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18
Q

What sort of access does the DSL have?

A

Asymmetric

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19
Q

Is DSL a shared or dedicated access network?

A

Dedicated access network

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20
Q

How do cable-based access networks work?

A

Uses Hybrid Fiber Coax to transmit signals, using FDM, from a hub to cable modems at client, that turn the analog signal into a digital format.

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21
Q

What sort of access do cable-based access networks (HFC) have?

A

Asymmetric

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22
Q

Are cable-based access networks shared or dedicated access networks?

A

Shared

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23
Q

How do entreprise access networks work?

A

Mix of wired and wireless link technologies, connecting a mix of switches and routers

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24
Q

Are entreprise networks wired or wireless?

A

Both

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25
Are home networks wired or wireless?
Wired
26
How do wireless access networks work?
The network connects end systems to a router via. a base station/ Access Point (AP) that uses radio waves to transmit data
27
What's the range of Wireless Local Area Networks?
Around a building
28
What's the range of wide-are cellular access networks?
10 km ++
29
What propagates between transmitter & receiver pairs?
Bits
30
Where is a physical link located?
Between transmitter and receiver
31
Guided media
Signals propagate in solid media
32
Unguided media
Signals propagate freely
33
Twisted Pair (TP)
Two insulated copper wires. Data rates depend on wire thickness and distance. Bidirectional.
34
Coaxial cable
2 concentric copper conductors. Bidirectional & broadband.
35
Fiber optic cable
Glass fiber carrying light pulses, each pulse a bit. Bidirectional. Low error rate & high speed operation.
36
Wireless radio
Signal carried with EM-waves. Broadcast & half-duplex.
37
What type of link are these: terrestrial microwave, wireless LAN, wide-area cellular access network & satellite?
Radio link
38
Packets
Segmented data with added header bytes to each segment
39
How does a host send an application message?
Breaks the message into packets, transmits the packets into access networks at transmission rate
40
Packet transmission delay
L / R
41
End-end delay for N links
N*L/R
42
How does the "store-and-forward" packet-switching technique work?
Entire packet must arrive at the router before it can be transmitted on next link
43
What does packet-switching allocate link use based on?
Deman
44
Packet-switching
Hosts break application layer messages into packets. Then forward packets from one router to the next, across links of path from source to destination.
45
Output buffer
Stores packets that the router is about to send into a link
46
What happens if the arrival rate > transmission rate of a link for a period of time when using packet-switching?
Packet queueing & loss
47
Forwarding
Moving arriving packet from router's input link to appropriate router's output link
48
Is forwarding a local or global action?
Local
49
Forwarding tables
Maps destination addresses to a router's outbound link
50
Is routing a global or local action?
Global
51
Routing protocol
Automatically sets the forwarding tables
52
How does the network core use routing protocols for routing?
Determines the best source-destination paths that packets should take
53
Circuit switching
The resources needed along a path are reserved for the duration of the communication session. They're dedicated.
54
What are the two forms of multiplexing in circuit-switched networks?
Frequency Division Multiplexing (FDM) and Time Division Multiplexing (TDM)
55
Frequency Division Multiplexing
Each connection dedicated a frequency band to, where it can transmit at the max rate of the band
56
Time Division Multiplexing
Each connection is allocated periodic slots, and can transmit at the maximum rate of the frequency band during its set time slots
57
What is the main benefit of packet switching in comparison to circuit switching?
More users can use the network
58
What's a possible con of packet switching without protocols for reliable data transfer & congestion control?
Excessive congestion
59
Describe the internet structure from a "network of networks" POV
1. Hosts connected to internet with ISPs 2. Customer ISPs connected to provider ISP through PoPs. 3. Provider/Regional ISPs connected to Tier 1 ISPs / content provider networks through IXPs
60
ISP
Internet Service Provider
61
PoP
A group of one or more routers in the provider's network where customer ISPs can connect into the provider ISP
62
Internet Exchange Point (IXP)
A meeting point where multiple ISPs can peer together.
63
"Tier-1" commercial ISPs
National & international coverage networks
64
Content provider networks
Private networks that connect data centers to the Internet.
65
When does packet delay occur?
When packets queue in router buffers
66
When does packet loss occur?
When the arrival rate to the link exceeds the output link capacity
67
Give the definition: A program that provides delay measurement from source to router along end-end Internet path towards destination
Traceroute program
68
Equation for packet delay
d_proc + d_queue + d_trans + d_prop
69
What does it say about the queuing delay if the traffic intensity is approaching 1?
The average queueing delay is large
70
What does it say about the queuing delay if the traffic intensity is bigger than one?
The average packet delay is infinite - arriving packets have to be dropped
71
Traffic intensity
L (packet length) * a (average packet arrival rate) / R (link bandwidth)
72
d_queue
Queueing delay
73
d_end-end =
N(d_proc + d_trans + d_prop)
74
d_proc
Nodal processing delay
75
What does it say about the queuing delay if the traffic intensity is 0?
The queueing delay is small
76
d_trans
Transmission delay
77
d_prop
Propagation delay
78
d_trans =
L (packet length) / R (link transmission rate)
79
d_prop =
d (length of physical link) / s (propagation speed)
80
Throughput
Rate at which bits are being sent from sender to receiver
81
Instantaneous throughput
Rate at which receiver is receiving the bits at any instant point in time
82
Average throughput
Rate over longer period of time
83
Bottleneck link
Link on end-end path that constrains throughput
84
Virus
Self-replicating infection by receiving/executing object
85
Worm
Self-replicating infection by passively receiving object that gets itself executed
86
Denial of Service
Attackers make resources unavailable to legitimate traffic by overwhelming resource with bogus traffic
87
Packet sniffing
Promiscuous network interface that reads / records all packets passing by
88
IP spoofing
Sending packets with false source addresses
89
How do the protocol layers work?
Each layer implements a service via its own internal layer actions & by relying on services provided by a layer below
90
Why do we use protocol layering?
- Dealing with complex systems - Modularization eases maintenance & updating of system
91
Describe the internet protocol stack
Application Transport Network Link Physical
92
Application layer
Supports network applications. Implemented in software in end-systems.
93
Transport layer
Transports application-layer messages between application endpoints
94
Network layer
Routing of datagrams (network-layer packets) from source to destination.
95
Link layer
Data transfer of network-layer packets between neighboring network elements
96
Frames
Link layer packets
97
Physical layer
Moves individual bits within a frame (link layer packet)
98
Describe the encapsulation structure
Frame (Datagram (Segment (Message)))

Kommunikasjon - Tjenester og nett (9 decks)

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