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Network Computing > Computer Networks and the Internet > Flashcards

Computer Networks and the Internet Flashcards

1
Q

What are the two ways we can discuss the Internet (when defining what IS the Internet)?

A

The “nuts and bolts”:
-the hardware and software that make up the Internet

As a “networking infrastructure”:
-a service provided to distributed applications

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2
Q

What is the Nuts and Bolts definition of the Internet?

A

The Internet is a computer network that interconnects hundreds of millions of devices. The network is made up of hosts and end systems that transmit data back and forth.

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3
Q

What is a host?

A

A network host is a computer or other device connected to a computer network. A network host may offer information resources, services, and applications to users or other nodes on the network.

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4
Q

What is an end system?

A

An end system is a node or user device.

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5
Q

What is a communication link?

A

A communication link is a channel that connects communicating devices.

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6
Q

What is a packet switch?

A

Takes a packet from an incoming communication link and forwards the packet on one of its outgoing communication links. Examples of these are routers and link layer switches.

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7
Q

What is transmission rate?

A

The rate at which data can be transmitted across a communication link. Transmission rate is measured in bits/second.

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8
Q

What is a packet?

A

A unit of data that is sent over a network.

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9
Q

What is a router?

A

Routers are typically found in the network core and are used to forward packets to their ultimate destinations.

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10
Q

What is a link layer switch?

A

Link layer switches are typically found in access networks and are used to forward packets to their ultimate destinations.

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11
Q

What is a “route” or “path”?

A

The collection of communication links and packet switches that a packet traverses to reach its destination.

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12
Q

How is a packet switched network analogous to a transportation network?

A

At a factory, cargo is divided between trucks. Each truck travels independently through a series of highways to reach their destination and deliver the cargo.

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13
Q

What is an ISP? Give some examples.

A

ISP stands for Internet Service Provider. An ISP is a small network of communication links and packet switches that provides users with access to the Internet. Examples are cable and phone companies.

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14
Q

What is TCP?

A

TCP stands for Transmission Control Protocol. TCP enables two hosts to establish a connection and exchange streams of data. TCP guarantees delivery of data and also guarantees that packets will be delivered in the same order in which they were sent.

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15
Q

What is IP?

A

IP stands for Internet Protocol. IP specifies the format of the packets that are sent and received among routers and end systems.

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16
Q

What is an RFC?

A

RFC stands for Request for Comments and is an Internet standards document.

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17
Q

Why are Internet Applications said to be Distributed Applications?

A

Internet applications are said to be distributed applications because they involve multiple end systems that exchange data with each other.

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18
Q

What is a 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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19
Q

What is a client?

A

an end system that an obtain information from a server.

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20
Q

What is a server?

A

a computer or computer program that manages access to data or a network.

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21
Q

What are the two most prevalent types of broadband residential access? And what is the main difference between them?

A

DSL - digital subscriber line, and cable.

DSL makes use of the existing telephone infrastructure, while cable makes use of the existing cable television infrastructure.

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22
Q

What does WiFi stand for?

A

Wireless LAN access based on IEEE 802.11 technology

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23
Q

What are some examples of physical mediums?

A

Copper wire, coaxial able, fiber-optic cable, + radio and satellite spectrum.

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24
Q

What is the difference between guided and unguided media?

A

With guided media the waves propagate along a physical medium, while unguided media waves propagate through the atmosphere.

25
Q

What is a guided shared medium?

A

Coaxial cable is an example of a guided shared medium. A guided shared medium is a cable with a number of end systems connected directly to it, and receiving whatever is sent by others.

26
Q

What has hindered the deployment of fiber optics in short-haul transport?

A

The high cost of of optical devices such as transmitters, receivers, and switches.

27
Q

What are three groups of terrestrial radio channels?

A

short distance like wireless headphones, local area like wireless LAN, or wide area like cell service.

28
Q

What is the formula for transmission time of a packet of size L?

A

Transmission rate is Rbits/second, and L is the size of the packet being transmitted in bits, so the transmission time will be L/R.

29
Q

What is store-and-forward transmission?

A

Store-and-forward transmission means that the packet switch must receive the entire packet before it can begin to transfer the first bit of the packet on an outbound link.

30
Q

What is an output buffer?

A

An output buffer (or output queue) is used by a packet switch to store packets it is about to transmit.

31
Q

What will happen if a packet arrives at an already full output buffer?

A

Packet loss will occur. Either the packet arriving at the output buffer will be dropped, or a packet already waiting in the queue will be dropped.

32
Q

How does a router know where to send a packet?

A

The packet’s destination address (IP address) is included in the packet header. The router will use its forwarding table to find an outbound link that will help to send the packet towards its destination.

33
Q

How is an end to end routing system analogous to a car driver who does not use maps, but instead asks directions at intervals.

A

Imagine for example that a car driver stops and asks for directions to an address: street, city, province. The first person they ask directions for will direct them to the province. When they arrive in the province they will stop and ask directions again, and they will be given directions to the city. They will arrive at the city and ask for directions to the street address and then ultimately reach their destination.

34
Q

What is a circuit-switched network? How is this different from a packet-switched network?

A

In a circuit switched network the resources required along a path are reserved for the duration of the communication session between end systems. Conversely, in a packet switched network the resources required are used as needed which may create some waiting time.

35
Q

What types of delay make up “total nodal delay”?

A

nodal processing delay, queuing delay, transmission delay and propagation delay

36
Q

What is the processing delay?

A

processing delay is the time it takes to examine the packet header and determine where to send the packet

37
Q

What is a queuing delay?

A

The delay a packet experience while waiting in the output queue.

38
Q

What is propagation delay?

A

The amount of time it takes for a packet to travel from one router to another once it has been pushed onto the link. (distance/second)

39
Q

What is the difference between propagation delay and transmission delay?

A

The transmission delay is the amount of time it takes to push the packet onto the link, it has to do with the length of the packet rather than the distance between the routers.

Propagation delay depends on the distance it takes for the packet to travel between router A and B.

40
Q

What is the ratio La/R and what does it mean?

A

La/R is called traffic intensity. It is made up of the average rate of bits/sec(La) arriving at the queue, and the transmission rate (R).

41
Q

How should we design our system in terms of traffic intensity?

A

Design your system so that the traffic intensity is never greater than 1.

42
Q

What is instantaneous throughput?

A

The rate in bits/sec at which Host B is receiving the file

43
Q

What is the average throughput?

A

F/T where F is the size of the entire file in bits and T is the amount of time it takes for Host B to receive all of F

44
Q

How do we find the throughput for a file transfer from a server to client?

A

min{R1, R2….. RN} where R is the transmission rate of each link between server and client

45
Q

What is the service-model of a layer?

A

Each layer provides its service by performing certain actions within that layer, and by using the services of the layer directly below it.

46
Q

What is a potential drawback of layering?

A

One layer may duplicate lower-layer functionality. For example, many protocol stacks provide error recovery on both a per-link basis and an end to end basis.

A second drawback is that the functionality at one layer may need info that is present only in another layer; this violates the goal of separation of layers

47
Q

What is the application layer?

A

The application layer is where network applications and their application layer protocols reside. An example is HTTP.

48
Q

What is the Transport Layer?

A

The transport layer transports application layer messages between application endpoints. There are two transport layer protocols TCP and UDP.

49
Q

What is the difference between TCP and UDP?

A

TCP provides connection oriented service to its applications, this includes guaranteed delivery of application layer messages to the destination and flow control. TCP also provides a congestion-control mechanism.

UDP provides conectionless service to its application. No reliability, no flow control and no congestion control.

50
Q

What are packets called on different layers?

A

On the application layer a packet is called a message.

On the transport layer a packet is called a segment.

On the network layer a packet is called a datagram.

Link layer packets are called frames.

51
Q

What is the network layer?

A

The network layer is responsible for moving network layer packets from one host to another. Datagram is made up of a segment plus a destination address. The network layer protocol that is most famous is the IP protocol

52
Q

What is the link layer?

A

The link layer passes the datagram from node to node. Examples of link layer protocols include Ethernet and WiFi

53
Q

What is the physical layer?

A

The physical layer is responsible for moving the individual bits within the frame from one node to the next. Physical layer protocols include twisted pair copper wire, coaxial cable, fiber etc.

54
Q

What is a denial of service (DoS) attack?

A

A DoS atatck renders a network, host, or other piece of infrastructure unusable by legitimate users.

55
Q

What is a packet sniffer?

A

A passive receiver that records a copy of every packet that flies by.

56
Q

What is IP spoofing?

A

IP spoofing is the ability to inject packets into the Internet with a false source address.

57
Q

How can we calculate total nodal delay?

A

Transmission delay + Propagation delay + Queuing delay + Processing delay….

More generally (L/R)+(m/s)

58
Q

How can we calculate queuing delay?

A

(nL+(L-x))/R

59
Q

How can we calculate average queuing delay?

A

I = La/R (where a is the number of packets/sec)

I/1-I))x(L/R

Network Computing (4 decks)

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