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cs A2 > ch14 > Flashcards

ch14 Flashcards

1
Q

Protocol

A

a set of rules governing communication across a network: the rules are agreed by both sender and recipient.

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2
Q

what are the four layer structure for TCP/IP protocols

A

4- application layer
3- transport layer
2- internet (network) layer
1- link network
sending 4-1 // receiving 1-4

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3
Q

application layer

A

contains all the programs that exchange data, such as web browsers or server software; it sends files to the transport layer.The application layer enables applications to access network services and defines the protocols for data exchange between them

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4
Q

Give two benefits of packet switching

A

*Accuracy – Ensures accurate delivery of the message
* Completeness – Missing packets can be easily detected and a re-send request sent so the message arrives complete
*Better security as packets hashed and sent by different routes

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5
Q

give two drawbacks of packet switching

A

*Network problems may introduce errors
in packets
* Requires complex protocols for delivery
* Unsuitable for real time transmission applications

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6
Q

Explain how packet switching is used to transfer messages across the internet.

A

A large message is divided up into a group of smaller chunks of the same size called packets
* The packet has a header and a payload
* The header contains a source IP address, destination IP address (and
sequence number)
* Each packet is dispatched independently
* … and may travel along different routes / paths
* If packets are missing / corrupted a re-transmission request is sent

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7
Q

Outline the function of a router in packet switching.

A

The router examines the packet’s header
* It reads the IP address of the destination (from the packet header)
* A router has access to a routing table
* …containing information about, e.g., available hops / netmask / gateway
used
* … and the status of the routes along the route
* … the router decides on the next hop / best route
* … and sends the packet on its next hop.

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8
Q

application layer protocols

A

HTTP(S) (1) for sending and receiving web pages / hypertext documents (1)
 FTP (1) for sending and receiving files over a network / between devices (1)
 SMTP (1) for sending/uploading emails /push protocol (1)
 POP(3) (1) for receiving/downloading emails /pull protocol (1)
 IMAP (1) for receiving/downloading emails /pull protocol (1)

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9
Q

TCP/IP layers function

A

Transport (1) handles packets (1)
 Internet (1) handles transmission of data using
IP addresses // provides (optimal) route (1)
 Network Access (Interface) // (Data) Link // Physical (1) Handles how data is physically sent (1)

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10
Q

Explain why a protocol is used in communication between computers

A

Protocols set a standard for communication
* Protocols enable communication/compatibility between devices from different manufacturers/platforms
* If two devices were sending messages to each other but using different protocols, they would not be able to
communicate properly

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11
Q

Describe the purpose of the IMAP protocol

A

used by email clients to retrieve email messages // a pull protocol
* from a mail server (over a TCP/IP connection)
* keeps the server and client in sync

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12
Q

State, with a reason, where it would be appropriate to use circuit switching.

A

Circuit switching is used where a dedicated path needs to be sustained
throughout the call / communication // where the whole bandwidth is
required // where a real time communication is used.
 A typical application is standard voice communications / video streaming /
private data networks

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13
Q

Give two benefits and two drawbacks of circuit switching

A

B:
MP1 Whole of bandwidth is available
MP2 Dedicated communication channel increases the quality of transmission
MP3 Data is transmitted with a fixed data rate
MP4 No waiting time at switches
D:
MP1 A dedicated connection makes it impossible to transmit other data even
if the channel is free
MP2 Not very flexible
MP3 No alternative route in case of failure

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14
Q

State two examples of where it would be appropriate to use packet switching.

A

Packet switching is most commonly used on data networks such as the internet to send large data files that don’t need to be live streamed
MP2 Packet switching is used when it is necessary to be able to overcome
failed/faulty lines by rerouting

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15
Q

Give four differences between circuit switching and packet switching

A

Circuit switching uses a dedicated channel to make communication,
whereas packet switching forms data into packets to transmit over a
digital network.
MP2 The dedicated path for circuit switching must be established before
the transfer of data can commence, which is not the case with packet
switching (as it doesn’t require a dedicated path).
MP3 Data in packet switching is split into packets, in circuit switching the
message remains intact.
MP4 All of the transmission in circuit switching follows the same path
whereas different packets in packet switching can take different
routes

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16
Q

BitTorrent is a protocol used at the Application layer for the exchange of data.
State the network model used with this protocol.

A

peer-to-peer

17
Q

State the use of BitTorrent

A

File sharing

18
Q

Explain how applications use BitTorrent to exchange data.

A

BitTorrent client software made available
A computer joins a swarm by using this to load a Torrent descriptor file
A server called a tracker that keeps records of all the computers in the
swarm …
… and shares their IP addresses allowing them to connect to each other
One computer in the swarm must have a complete copy of the torrent to be
shared
Torrent is split into small pieces
Pieces of the torrent are both downloaded and uploaded
Once a computer has a piece it can become a seed and upload
Leeches download much more than they upload

19
Q

Host-to-host

A

a protocol used by TCP when
communicating between two devices

20
Q

Explain what is meant by CSMA/CD. (3)

A

Carrier Sense Multiple Access (with) Collision Detection
* Before transmitting a device checks if the channel is busy
* If it is busy the device waits // if channel free data is sent
* When transmission begins the device listens for other devices also
beginning transmission
* If there is a collision, transmission is aborted / transmitting a jam signal
* Both devices wait a (different) random time, then try again

21
Q

function of CSMA/CD (2)

A

1- monitor traffic on the network
to detect a collision on the network
* to halt transmissions when a collision occurs
* calculates random wait time
* allow retransmission after a random amount of time

22
Q

State three functions of the TCP part of this protocol (3)

A

allows applications to exchange data
* establishes and maintains a connection «
* « until exchange of data is complete
* determines how to break application data into packets
* adds sequence / packet number to (TCP) header
* sends packets to and accepts packets from the network / Internet layer
* manages flow control // manages congestion avoidance
* acknowledges all packets that arrive
* detects when a packet has not arrived at destination

23
Q

State two functions of the IP part of this protocol.

A
  • routes the packets around the network
  • adds to the IP header a source/destination address for each packet
  • encapsulates data into datagram
24
Q

The TCP/IP protocol is used to send an email message from one node on a LAN to a node on a different LAN. State the steps that take place when the email message is sent and received.

A
  • Message is split into packets
  • Each packet is a fixed size
  • Each packet is given a header«.
  • «including destination IP address, sequence number etc.
  • Packets are forwarded from one LAN to the other LAN
  • Packets may take different routes
  • Missing packets are requested to be resent
25
Q

why we use layer structure for TCP/IP protocols

A

Using layers breaks the process down into manageable self-contained modules (this process is known as decomposition), making it easier to develop and easier to make software and hardware compatible

26
Q

anonymous ftp

A

this allows a user to access files without the need to
identify who they are to the ftp server;

27
Q

ftp commands

A

a user is able to carry out actions that can change files
stored on the ftp server

28
Q

ftp server

A

this is where the files, which can be downloaded as required by
a user, are stored

29
Q

MIME

A

multi-purpose internet mail extension. A protocol that allows email attachments containing
media files as well as text to be sent (binary file)

30
Q

difference between POP3/4 and IMAP

A

is synchronisation:
POP3/4 does not keep the server and client in synchronisation; when emails are downloaded by the client, they are then deleted from the server which means it is not further updated

IMAP keeps the server and client in synchronisation; only a copy of the email is downloaded with the original remaining on the server until the client manually deletes it

31
Q

Transport layer

A

regulates the network connections; this is where data is broken up into packets which are then sent to the internet/network layer (IP protocol). The transport layer ensures that packets arrive in sequence, without errors, by swapping acknowledgements and retransmitting packets if they become lost or corrupted.

32
Q

The main protocols associated with the transport layer

A

transmission control protocol (TCP)

33
Q

transmission control protocol

A

TCP (Transmission Control Protocol) is a crucial protocol responsible for ensuring the reliable delivery of data across networks. It achieves this through several key mechanisms:

Packetization: TCP divides data into smaller packets for efficient transmission across networks.

Positive Acknowledgement with Retransmission (PAR): TCP employs a method where it expects acknowledgment from the receiver after sending data packets. If acknowledgment isn’t received within a specified timeframe, TCP automatically retransmits the packet to ensure delivery.

Connection-oriented: TCP establishes a connection between two host computers before data transfer begins. This process involves a handshake to set up parameters for the communication session.

Due to its focus on establishing connections and ensuring reliable delivery, TCP is often referred to as a host-to-host transmission protocol.

34
Q

a summary of the IP functions

A

» Ensure correct routing of packets of data over the internet/network.
» Responsible for protocols when communicating between networks.
» Take a packet from the transport layer and add its own header which will
include the IP addresses of both sender and recipient.
» The IP packet (datagram) is sent to the data-link layer where it is assembles
the datagrams into frames for transmission.

35
Q

When sending data across a network, there are three stages:

A

1 First, a circuit/channel between sender and receiver must be established.
2 Data transfer then takes place (which can be analogue or digital);
transmission is usually bi-directional.
3 After the data transfer is complete, the connection is terminated.

36
Q

packet switching

A

» each packet follows its own path
» routing selection depends on the number of datagram packets waiting to be
processed at each node (router)
» the shortest path available is selected
» packets can reach the destination in a different order to that in which they
are sent

37
Q

Hop number/hopping

A

number in the packet header used to stop packets which
never reach their destination from ‘clogging up’ routes

38
Q

why use four-layer structure e for TCP/IP protocols

A

layers breaks the process down into manageable self-contained modules (this process is known as decomposition), making it easier to develop and easier to make software and hardware compatible

cs A2 (9 decks)

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