1.3.3 Networks

What is the internet?

a global system of interconnected networks

What is the largest WAN?

the internet

What is the world wide web?

a collection of resources accessed via the internet

What is a protocol?

a set of rules to govern data transmission between devices on a network

Describe packet switching

• data split into equal sized blocks = packets

• each packet has a header of information (destination address + place of packet in complete message)

• each packet may travel a different route

• at each node on the network the destination address is read + best route is found

• packets are reordered at destination

What is the backbone?

dedicated connections that connect multiple large networks across the globe

What does an ISP (Internet Service Provider) do?

provides access to individual end users

What does a server do?

receive and serves requests

What is a uniform resource locator (URL)?

full address of an internet resource

What is an IP address?

a numerical address made of 4 numbers (each between 0 & 255) that uniquely identifies a device on a network

What is the process of accessing a website referring to the (Domain Name System) DNS?

1. Type domain name into browser

2. Contacts domain name system (DNS) server

3. DNS translates domain name into IP address (like a phone book)

   • using IP address, browser requests web page from local server

4. DNS server checks cache for IP address

   • if found = server sends back page

   • if not found = hops to different servers until it is found + then returned

What is a DNS server?

dedicated computers with an index of domain names + their corresponding IP addresses

How many roots DNS servers are there?

13

What is an example of a top level domain?

• .com

• .edu

• .org

• .uk

• .fr

• .de

What are the two types of top level domains (TLDs)?

• generic

• country

How is a root DNS sever used when resolving an IP address

• if IP address isn’t found after checking local DNS server cache it contacts root DNS server

• root DNS server directs query to appropriate TLD server (e.g. “.uk”)

• local DNS server queries authoritative DNS server + obtains IP address

• local DNS server caches IP address + returns it to the user

Explain how the DNS plays a role in websites being loaded when it isn’t found in the local server?

• DNS used to resolve IP corresponding to URL

• request sent to DNS resolver

• resolver checks cache if doesn’t hold URL passes to TLD server which checks its cache + returns answer

  • or passes on to the authoritative name server

• Ip address returned back up to requesting client/ error if no resolution can be found

Why do domain names have to be unique?

DNS requests could be confused if otherwise

What is an internet registry?

maintain a database of address assignments ensuring an IP address is used once + domain names are distinct

What does a modem do?

transforms digital info from computer into analogue signals and other way round (transmitted through wires)

What is a router responsible for?

routing data between devices on a network

What are the two main methods for connecting devices?

• wired

• wireless

What are the three main cables used to create a wired connection?

• twisted pair

• coaxial

• fibre optic

What is a twisted pair cable made up of?

a pair of insulated copper wires

What is an advantage of twisted pair cables & what are they generally used for?

• most affordable option(compared to coaxial + fibre optic)

• telephone networks,data networks & cable shielding

What are disadvantages of twisted pair cables?

• affected by noise from external magnetic fields

• provide low bandwidth

Are coaxial cables affected from noise from external magnetic fields?

yes, but to a lesser extent than twisted pair

What bandwidth do coaxial cables provide?

moderate bandwidth

How does the price of coaxial cables compare to the other two options?

• more expensive than twisted pair

• cheaper than fibre optic

What are coaxial cables used for?

• feedlines that connect radio transmitters & receivers to antennas

• computer network connects

• digital audio & cable television

Why do fibre optic cables have the highest noise immunity?

light rays are not affected by electrical noise

What is the bandwidth of fibre optic cables?

high bandwidth

What is a disadvantage of fibre optic cables?

they are the most expensive option

What are fibre optic cables used for?

• support long distance connections between countries

• data centres + organizations to transmit large volumes of data

What is the role of a network interface card (NIC)?

allows a device to connect with a network

(between computers on a LAN or connecting to large scale network using IP)

What is a wireless access point (WAP)?

a device that creates a wireless local area network

What does the WAP do to create a wireless local area network?

connect to wired router,switch/hub via ethernet cable + projects WiFi signal to designated area

What is a disadvantage of WAP?

WiFi range is limited + easily interrupted by materials

(businesses use multiple WAPs for full coverage)

What does a hub allow?

a hub allows multiple devices to connect to one network

What are disadvantages of a hub?

• network can easily become flooded with unnecessary traffic

• slower at transferring data than switches

What does a switch allow?

a switch allows multiple devices to connect to one network

What is the difference between a switch and a hub in terms of its layer and the type of device it is?

HUB:

• passive device - broadcasts transmissions to all other connected devices (not specific)

• works on physical layer

SWITCH:

• active device - can inspect transmissions + rote them to correct device (keeps traffic to minimum)

• works on data link layer

What are the two main types of networks?

• Local Area Network (LAN)

• Wide Area Network (WAN)

What is a LAN?

(two or more computers connected together)a network within small geographical area

What is a standalone?

a computer not connected to any other computing device

What is a WAN?

(two or more computers connected together) a network that covers a large geographical area

What is a network topology?

the arrangement of computing devices which make up a network

What are the two main network topologies?

• bus

• star

What is a bus topology?

nodes are connected in daisy chain by a single central communications channel

What is a star topology?

central node/hub provides common connection point for all other nodes

Advantages of bus network

• inexpensive to et up

• devices added easily

• good for small networks

Disadvantages of bus network

• main cable point of failure

• limited cable length

• performance degrades with heavy use

• poor security

What is the usual central node of a star topology?

a switch

Advantages of star topology

• easy to isolate problem

• good performance

• more secure if switch used (data only sent to recipient)

Disadvantages of star topology

• expensive to set up because of length of cable

• central device point of failure

What is circuit switching?

creates communication connection between two endpoints for the duration of a phone call/transfer of data

What is the purpose of common protocols TCP,IP and UDP?

Communication over LAN/WAN

What is the purpose of common protocols HTTP and HTTPS?

web page requests

What is the purpose of common protocol FTP?

file transfer

What is the purpose of common protocols POP,IMAP and SMTP?

email

What does a bridge device do?

provides a link between LANs

What does a gateway device do?

provides a link between two dissimilar networks

What is the concept of layering?

to divide complex task of network into small,simpler tasks

(each layer provides a service to the one above it)

What are advantages of layering?

• reduces complex problem into smaller sub problems

• devices can be manufactured to operate at a particular layer

What is the TCP/IP protocol stack?

a set of rules used to format message so it can be sent over a network

What are the 4 layers of the TCP/IP protocol stack?

• application

• transport

• internet/network

• link

What operates at the application layer?

network applications operate (e.g. web browsers/email programs)

(specifies rules of what should be sent)

What are the protocols associated with the application layer?

• FTP

• SMTP

• IMAP

• HTTP

• HTTPS

What is the responsibility of the transport layer?

• sets up communication between two hosts

  • agree settings (e.g. language and packet size)

• TCP used to:

  • split data into packets & number them sequentially

  • add port number (to header) to be used (based on HTTP protocol)

  • confirms if packets received + requests missing packets

What are the protocols associated with the transport layer?

• TCP

• UDP

What is the responsibility of the internet/network layer

• addresses & packages data for transmission

• routes packets across network

IP:

• router forwards packet towards an endpoint (called socket) defined by IP address + port number

What is the responsibility of the kink layer?

• represents actual physical connectoon between devices

  • adds MAC address of physical NIC packets should be sent to (based on destination of IP address)

  • MAC address changes with each hop (between router on WAN)

• network hardware + connection port standards

• OS device drivers here

• facilitates transmission of binary via any media

What happens, in terms of layers, when data is received at its destination

• link layer removes MAC address from each packet & passes to internet layer

• internet layer removes IP address from each packet & passes to transport layer

• transport layer removes port number from each packet, reassembles packets in correct order + passes them to application layer

• application layer presents image data for use in a browser

What is a Media Access Control (MAC) Address?

uniquely identifies a physical device with a NIC

What is the client server model

• client accesses data,services and files from server

• client initiates communication to server

• server wits for requests from clients

Describe client server architecture

• client computer connect to server

• server provides access to resource/service

What is the role of a server in a client server model?

• controls access + security for shared file stored

• manages access to the internet

• manages printing jobs

• provides email services

• runs regular backups of data

What are advantages of client server model?

• easy to manage file security

• easy to back up shared data

• easy to install software updates

What are disadvantages of client server model?

• expensive to set up + maintain

• reuire IT specialist to maintain

• sever = single point of failure

Where are client server networks best suited>

• organisations with a large number of computer

• situation where many computers need to access same info

What are features of peer to peer network?

• no central server + all peers are equal

• all computers can see files on all other computers

• each peer responsible for own security + backup

Advantages of peer to peer model?

• cheaper

• easy to maintain

• no dependency on single computer

Disdvantages of peer to peer model?

• network less secure

• users need to manage own backups

What are peer to peer networks best suited to?

• smaller organisations with fewer computers

• fewer users need access to the same data

What is client processing?

• data is processed before it is sent to a server y the client