Networks

Question 1

Mail server*

Answer 1

Acts as a virtual post office, for all incoming and outgoing mail. They route mail according to their database of local network user’s email address’. They also STORE MAIL UNTIL IT CAN BE RETRIEVED

Question 2

TCP/IP

Answer 2

A set of protocols acting together as four layers connected, passing incoming and outgoing data up and down the layers during network communication. It enables communication with any other computer connected to the internet, regardless of its location

Question 3

Each layer in TCP IP…

Answer 3

Only communicates with adjacent layers.
Envelopes/ unwraps with more packet data.
Has different roles, with various protocols

Question 4

Application layer

Answer 4

Uses protocols relating to the application being used to transfer data over a network (e.g. Internet)
E.g. Browser may use ftp, or http or POP3 as the high level protocol

Question 5

Transport layer

Answer 5

TCP protocol used to establish end to end connection with recipient computer.
Splits data into packets, labels with packet sequence number, total packet number and port number (ensuring correct application handles packets.)
If packets go astray, retransmission requested .
Receipt of packets acknowledged

Question 6

Network layer is aka

Answer 6

IP layer/internet layer

Question 7

Network layer*

Answer 7

Adds source and destination IP addresses (port number + IP address = socket)
Router operates on this layer, forwarding packet onto correct destination according to IP addresses
More ERROR checking
router is hardware that operates at this layer

Question 8

Link layer

Answer 8

LINK LAYER PROTOCOL used e.g. Ethernet
Physical connection between network nodes
Mac addresses are added, identifying NICs of the source and destination computer (where the packets are to be sent to next)- initially of the first router being sent to, unless same network
So once correct network found, correct hardware then can be found
Sent down CABLE
Cable and NIC are hardware that operate at this layer

Question 9

Receiving end of TCP IP

Answer 9

MAC addresses stripped by link layer
IP addresses stripped by network layer
Port numbers removed and packets reassembled at transport layer
Then passed to application and data presented to user

Question 10

Routers in IP TCP

Answer 10

Operate at network layers, and so MAC addresses or source and destination change at each network node
Packets move up and down lower layers at each switch/ router between client and server

Question 11

File transfer protocol definition

Answer 11

An efficient method used to transfer data across a network, often the internet

Question 12

Describe FTP*

Answer 12

Works as a HIGH LEVEL PROTOCOL IN THE APPLIC LAYER USING APPROP SOFTWARE
User is presented with a file management screen with file and folder structure in remote website and local computer
Files transferred via drag and dropping
Often need username and password but can use anonymously

Question 13

Uses of FTP

Answer 13

Uploading images to remote newspaper headquarters by photographers
Companies offering large updates

Question 14

POP3, post office protocol*

Answer 14

Protocol used to retrieve mail from a mail server TEMPORARILY STORING INCOMING MAIL
It is transferred to local computer then deleted from server so can’t synchronise across devices
Developed before WWW when mail stored on hard drive

Question 15

IMAP internet message access protocol

Answer 15

Email protocol designed to keep emails on mail server, ensuring mail is synchronised (synchronicity) across devices
Used in PUSH email (sending email without request)

Question 16

SMTP

Answer 16

Used to transfer mail from one server to another and from a client to a server
Bit after @, domain, shows which mail server to direct mail to. First own mail server then recipient’s

Question 17

Client server network*

Answer 17

1 or more computers: clients are connected to a (or many performing different tasks) powerful central computer called servers
Each client may hold its own files and resources e.g. software and can also access resources held centrally by server
Server also DEALS WITH REQUESTs
EG in schools, businesses, hospitals

Question 18

Why have many servers in a client server network

Answer 18

For many different tasks

Question 19

File server*

Answer 19

Holds and manages DATA for all the clients

Question 20

Print server

Answer 20

Manages print requests

Question 21

Web server

Answer 21

Manages requests to access the web

Question 22

Database server

Answer 22

Manages database applications

Question 23

Requests in client server network

Answer 23

Client sends request to the server which then processes the request and responds with the requested data providing the device has permission to access the data

Question 24

Adv client server network

Answer 24

• better since all files stored in a central location and access rights are managed by the server centrally, as well as authentication
• no need for individual backups of data because done centrally. If breakdown and data is lost- recovery procedures enable restoration
• data and other resources can be shared eg network printers and other peripheral devices
• can access server from any workstation in network and even at home with VPN
• downloading software and patching done centrally, saving time and bandwidth when keeping up to date
• one license rather than individual licenses for clients
• security and antivirus handled centrally

Question 25

Disadvantages client server network

Answer 25

Expensive to install and manage OS and servers Need professional IT staff to maintain servers and run network Server failure = massive disruption to whole network

Question 26

Peer to peer network*

Answer 26

No CENTRAL SERVER. Individual computers are connected to each other and share FILES which are stored on the hard disk. Can be over LANs or WANs. Particularly good if in one site e.g. Small office or home. All computers are 1) of equal importance 2) act as both a client and a host. Hosts can decide access rights for resources

Question 27

Advantages peer to peer

Answer 27

Cheap to set up Not difficult to maintain Enables users to share resources e.g. Printer or router can be more reliable, not dependent on companies server to distribute all requests from all users

Question 28

Uses of peer to peer*

Answer 28

Video on demand and downloading videos. Different computers in different LOCATIONS hold parts of the video so share the load so faster- main principle behind torrent websites: enabling sharing of files, often containing copyright material

Question 29

internet*

Answer 29

a worldwide network of networks set up to allow computers to communicate with each other globally, regardless of their location, by using the same protocol

Question 30

how was internet developed

Answer 30

via ARPANET created in 60s for US defence military project enabling distant departments working together to communicate without physical travel

Question 31

WWW*

Answer 31

world wide web: a collection of webpages (i.e. LINKED HYPERTEXT) that reside on computers connected to the internet. the internet is the service used to communicate information on these pages

Question 32

intranet

Answer 32

a private network using internet protocols

Question 33

who developed WWW

Answer 33

Tim Berners-Lee, developed concept of WWW and browsing for information

Question 34

physical structure of the internet

Answer 34

each continent has backbone cables connected by transcontinental leased lines fed across SEA BEDS and ISPs connect directly to this backbone and distribute and sell internet connection to smaller providers which distribute to individual homes and businesses

Question 35

URL*

Answer 35

uniform resource locator: FULL address of a location of an internet resource inc file type and resource name. BROWSER REQUESTS FROM WEBSITE SERVER

Question 36

http://www.domainname.com/folder/subfolder.html#element

Answer 36

http is the protocol being used, www is the hostID, folder is the pathname, and #element is the resource

Question 37

URN

Answer 37

uniform resource name, unique resource name allowing you to find a resource even if moved to a new site/new page on the same site e.g. isbn (namespace identifier) 02498459 (namespace specific string)

Question 38

URI

Answer 38

uniform resource identifier made up of URN and URL used to identify the target of a hyperlink

Question 39

Internet registrar*

Answer 39

private companies which must be accredited by governing registries, it hold LISTS and RECORDS of all existing website names and details of domains available to purchase currently

Question 40

internet registries*

Answer 40

5 global organisations governed by ICANN (internet corporation for assigned names and numbers) with WORLDWIDE DATABASES holding records of all domain names currently ISSUED to individuals and companies, and their DETAILS e.g. name, type, registered mailing address, registrar that sold and data of registry They allocate IP address' and keep track of corresponding domain name as part of the DNS

Question 41

what does a domain name do* and how its set up

Answer 41

identifies the area/domain a webpage resides in. Theres a HIERARCHY of smaller domains, written as a string with full stops, dictated by RULES of DNS

Question 42

first level domains

Answer 42

generic top level: .com, .edu, .gov | country top level: .uk, .fr

Question 43

second level domains

Answer 43

.sch, .co, .gov

Question 44

third level domains

Answer 44

.bbc, .lidl, .ebay

Question 45

root domain

Answer 45

www.ROOTDOMAIN.com

Question 46

subdomain

Answer 46

WWW.domain.com | www is the subdomain

Question 47

DNS*

Answer 47

CATALOGUES all domain names and IP addresses in a series of GLOBAL DIRECTORIES, which domain name servers access in order to find the correct IP address location for a resource

Question 48

without DNS

Answer 48

have to type in IP address in URL bar instead of domain name

Question 49

process of DNS*

Answer 49

webpage requested by URL entered by user, browser requests for IP address from a local DNS (firstly ISP with preprogrammed database of IP related to domains), if not found, search extended up hierarchy to larger DNS database and when found, user's computer sends data request to that IP address location to find webpage data VIA IP/TCP PROTOCOL

Question 50

FQDN

Answer 50

fully qualified domain name containing host server name e.g. mail.google or www.google, depending on server resource is hosted on

Question 51

IP address*

Answer 51

internet protocol address, a unique address assigned to a NETWORK DEVICE indicating where a packet of data is to be sent/has been sent from. routers use this to direct packets

Question 52

IP addresses of domain names*

Answer 52

the address is of the server the site is residing on

Question 53

IP addresses are made of

Answer 53

four numbers IPv4 with number between 0-255 and now IPv6 has 6 numbers because so many IP address being used

Question 54

272.15.63.144

Answer 54

272 is the geographical location 272.15.63 is the network ID identifying a network 144 is the hostID identifying hosts (individual devices) on a network

Question 55

computer network

Answer 55

a number of computers linked together to allow the sharing of resources e.g. software, hardware, data

Question 56

server

Answer 56

a powerful central computer able to provide one or more services to a network and its users e.g. file storage

Question 57

WAN

Answer 57

wide area network, a network of interconnecting networks inc LANs that spread over a large geographical locations (e.g. continents) can be connected using internet, satellite links and leased lines (rely on third party carriers eg british telecom) e.g. internet, bank cash dispensers. LANs use routes to connect to these other networks

Question 58

LAN*

Answer 58

local area network, a number of a COMPUTING DEVICES single site/building consisting of computers, printers and a central server for example. Users SHARE hardware and data and can COMMUNICATE to each other. data travels quickly over these short distances

Question 59

physical bus topology

Answer 59

all computers connected to a single cable and the end of cable is connected to a terminator

Question 60

adv of physical bus

Answer 60

inexpensive to install as less cable and no additional hardware effective for small networks

Question 61

disadv of physical bus

Answer 61

low security, all other computers can see data transmissions traffic means degraded performance if main cable fails then network data can't be transmitted to any of the nodes troubleshooting individual devices issues is hard collisions

Question 62

physical star topology

Answer 62

has a central node, a switch or computer which acts as a router to transmit messages. switch has a record of MAC addresses of each device on a network and can identify particular computers on networks to send data to

Question 63

adv of physical star*

Answer 63

- one cable FAILS, only one station affected - consistent performance even if heavily used - COLLISIONS aren't a problem: each station has own cable to server - higher transmission speeds: better performance - more SECURE: messages sent directly to central node and harder to intercept - easier to add new stations without disrupting networks

Question 64

disadv of physical star

Answer 64

- costly installation e.g. cost of cable - if central switch goes down, network data can't be transmitted to any more nodes - number of nodes restricted by capacity of central device

Question 65

physical topology

Answer 65

the physical design layout of a network, important for when deciding wiring layout

Question 66

logical topology

Answer 66

shape path of data travels in and describes how components communicate

Question 67

topologies are...

Answer 67

independent of each other so a physical star topology can act logically like a bus topology using appropriate PROTOCOLS and physical SWITCHING

Question 68

ethernet topology

Answer 68

logical bus topology regardless of physical layout

Question 69

wifi*

Answer 69

local area wireless technology allowing devices to connect a device to a network resource or internet via a wireless network access point (usually 20m indoors but more outdoors)

Question 70

1999 WiFi alliance

Answer 70

group of 100s of worldwide companies formed to establish international standards for interoperability and backward compatibility enforces use of standards for device connectivity and network connections

Question 71

mesh network topology

Answer 71

each nodes is connected to all other nodes by transmitting data over intermediate nodes only one node requires internet access, others share connection

Question 72

use of mesh network topology

Answer 72

more common with widespread use of wireless technology. can spread over whole cities

Question 73

adv of mesh network topologies*

Answer 73

- no cabling COSTS - self healing- if one connection breaks it can be circumvented by another route so more nodes = faster and more RELIABLE - new nodes automatically incorporated into network - FASTER communication as data packets don't pass through central switch

Question 74

disadv of mesh network topologies

Answer 74

- harder to manage: continuous supervision | - many devices needed = expensive

Question 75

circuit switching

Answer 75

creates a direct link between two devices for the duration of the communication e.g. public telephone system. so you have all the bandwidth between two points and no other messages can use the connection

Question 76

adv circuit switching

Answer 76

- you have all the bandwidth between two points and no other messages can use the connection - exclusive connection means packets arrive in the same order that they are sent, simplifying the reconstruction process

Question 77

disadv circuit switching

Answer 77

- bandwidth is being wasted when no data is being sent - data has to be transmitted at the same RATE by both devices so only devices operating at same transfer rate can be connected - switches connecting and disconnecting circuits cause electrical interference so data is lost and corrupt if path is used to transmit data: so leased line can be used instead if problem

Question 78

packet switching*

Answer 78

method of communicating packets of data across a network whilst other network communications are happening simultaneously e.g. website data and emails are sent and RECEIVED as a series of PACKETS. relies on packets to travel via entirely different ROUTES (fastest and least congested)

Question 79

what are data packets*

Answer 79

manageable chunks/packets of data BROKEN DOWN from data to be sent across a network. the size can be FIXED or VARIABLE: usually between 500-1500 bytes

Question 80

payload of data packet

Answer 80

body of data being sent

Question 81

trailer of data packet

Answer 81

cyclic redundancy check/checksum: a hash total is created and attached, calculated from packet data to detect transmission errors. calculated by number of 1s in transmission. CRC is RECALCULATED and MATCHED at end of transmission to verify data is unchanged- if totals differ packets refused with suspected data corruption and a NEW COPY requested from sender

Question 82

header*

Answer 82

IP address of sender and recipient, PROTOCOL used for this packet type, packet sequence number, time to live/hop limit when packet expires and discarded

Question 83

packets at other end

Answer 83

reassembled in correct order and packets requested for again if didn't make it. data extracted

Question 84

advantages of packet switching

Answer 84

- network failures don't stop messages - easy to add more nodes - secure, unpredictable route and packet split - takes advantage of unused connections - cheap as efficient use of bandwidth (only charged per unit of data rather than connection time)

Question 85

disadvantages

Answer 85

- can be corrupted in transmission | - must be reassembled at end of transmission

Question 86

end to end principle

Answer 86

endpoints control communication and security, midpoints just pass on packets

Question 87

open architecture principle

Answer 87

anyone can design a network just through creating a linking computer called a gateway

Question 88

MAC address*

Answer 88

media access control address. each device capable of connecting to a network has a wired or wireless NIC with a unique MAC address ASSIGNED to and hardcoded by a manufacturer uniquely identifying a device (48bits long, 12 hex digits)

Question 89

protocol*

Answer 89

a set of rules defining common methods of DATA communication- standard rules allow devices to COMMUNICATE with each other

Question 90

HTTP

Answer 90

standard protocol for browsers to render webpages

Question 91

telnet*

Answer 91

- allows communication between one computer and another | - allowing a user on one computer to log into another computer on the SAME NETWORK

Question 92

sending mail from one place A to another B

Answer 92

``` A uses SMTP to send message; this goes via her LOCAL EMAIL SERVER which checks the DOMAIN to which the email is addressed e.g.@domain.com; and forwards the message (often via other mail servers); to B webmail server. B logs in via his local ISP; and downloads his message using POP3/IMAP. ```

Question 93

switches and router are used for?

Answer 93

handling traffic and ensuring requests and files get to the correct location

Question 94

wifi workstations

Answer 94

when you connect to a network using a wireless access point

Question 95

router

Answer 95

connects at least two networks: 2 LANs/WANs or LAN with ISP's network. Reads the recipient's IP address in each packet and forwards it on to recipient using fastest, least congested route to next router. This continues until destination is reached. routers use routing tables to store and update locations of other network devices and most efficient routes to them. Uses routing algorithm. When router is connected to internet, IP address of port connecting it must be registered with internet registry bc it must be unique across the internet

Question 96

routing algorithm

Answer 96

Finds optimum route between network devices. This routing algorithm can become a bottleneck in network traffic since decision making process is complicated. Shortest path algorithm: Dijkstra's algorithm.

Question 97

hop

Answer 97

traversing between one router and another across a network

Question 98

gateway

Answer 98

routes packets between networks if the protocols differ. strips header data, leaving raw data only. new data is added in the format of the new network before packet sent again.