1.3.3/1.3.4: networks/ web technologies

Describe a network + 2 types of network

• Two or more computers joined together and able to transmit data between them

• either LAN (local area network- small geographical area) or WAN (wide area network- large geographical area requiring extra telecommunication hardware)

What is a protocol

Rules for how computers in a network communicate with each other

What is the internet

Network of networks spanning across the globe, connected via large international backbone cables

describe all the layers of the TCP/IP stack model

• application- HTTP(S), POP3/IMAP, FTP

• transport- establishes end-to-end connection between sender and recipient, where senders split data into packet and label with order, port & total number of packets, and the recipient orders packets and requests transmission of any lost packets (TCP)

• network- add sender & recipient IP address (32 hex logical address, combined with port no.= socket address), where routers use IP to route & use socket to specify recipient device & application used

• link- provides connection between network devices (adds MAC- computer or router address- and NIC- network interface card allowing computer to connect to a network)

What changes between hops of packets

MAC address of routers, Time to Live

Describe DNS

domain name system- process used to name and organise internet resources

-TLD= top level domain, first and largest domain called

-2LD= second level domain, second largest and separated from TLD by a full stop

This is easier to remember than IP addresses= domain name server translates domain names into IP addresses

What are data packets

Segments of data containing

• header : sender/recipient IP address, protocol used, order of packets, time to live-TTL (= expires after set time)

• payload : raw data being transmitted

• Trailer : checksum, cyclic redundancy check (check for errors in transmission)

Describe packet switching

Process of sending packets across the most efficient route during transmission in order to communicate data

-done using routers with the internet, with each transfer being a ‘hop’

advantages/ disadvantages of packet switching

• contains multiple methods to make sure data comes intact (in trailer)

• multiple routes possible (if one path unavailable, another path possible)

• they allow for global communication (as packets can be transferred over large networks)

• long time spent constructing/ deconstructing packets

• have to wait for all packets to arrive before data is received by recipient

describe circuit switching

The use of a direct link between two devices during communication, where data is transferred/ received at the same rate

advantages/disadvantages of circuit switching

• quicker reconstruction as data arrives in the same order as it was transferred

• allows for no delay (e.g. during calls)

• wasted bandwidth when no data is being sent

• data must be transferred/ received at the same rate

• use of switches= if interference, data can be lost/ corrupted

• sections of network can only be used once transmission is complete

describe different network security methods

firewall

proxies

encryption

describe firewalls

two network interface cards (NICs) that checks packets against the firewall software rules (packet filters) between the user and the Internet = prevents unauthorised network access by opening/blocking ports

describe how packet filtering works

It examines packet’s source IP, destination IP and protocols and limits network access depending on the administrator rules

• packets can be dropped/rejected when denied by the firewall and the sender is notified

describe proxies

A server acting as an intermediary that collects and sends data on behalf of the user

advantages of proxies

• anonymous user (different IP address to user)= privacy of user is protected

• server can store frequently-used website data in cache= faster to load & less latency+bandwidth

• block possible sensitive/ restricted data from the user

• less web traffic

• data can be encrypted when transmitted

Name 5 pieces of network hardware

• network interface card (NIC)

• switch

• wireless access point (WAP)

• router

• gateway

purpose of network interface card

Card containing the media access control address( MAC address- unique 48-bit value, made during manufacturing, converted to 12 hex code) required for a device to connect to a network.

purpose of a switch

Directs the flow of data/packets within a network using a device’s MAC address in the packet’s header

-usually in star topologies

purpose of wireless access point

Device allowing devices to wirelessly connect to a network, usually used with routers to connect devices to the internet

-usually in mesh networks

purpose of gateways

To transmit packets between networks with different protocols by translating the different protocols to allow for communication

-done by removing the header of a packet and adding the data to packets using the new protocol

describe client-server models

clients (terminals containing devices) are connected to a server (large central computer system containing the clients’ data)

-server is powerful with more processing power than the terminals

advantages of client-server models

• data can be backed up centrally

• clients can access other clients’ data

• more security with data stored in one location

disadvantages of client-server models

• expensive to set up

• required trained professionals to maintain the server

• if server fails, the network performance falls

describe peer-to-peer models

devices act as their own client and server and connect directly to other devices and are able to share and request information from eachother

advantages of peer-to-peer networks

• cheaper

• no specialist staff needed to maintain server

• no reliance on central server

• easy to maintain

• users can share resources

disadvantages or peer-to-peer networks

• poorer security

• harder to source files’ origins

• harder to locate files

• have to perform backups separately

difference between physical and logical topology

physical= layout of network

logical= how data is transmitted across the network

purpose of URL

Uniform resource locator- used to specify the means of how a resource is located and accessed across a network

-contains protocol and domain name

process of resolving an IP address

• URL sent to local DNS (DNS resolver) , where frequently-accessed URLS are stored in cche

• If unknown, the URL is sent to the root servers (catalogue domain names/ TLD servers)

• process is recursively handled to form an IP address, or the authoritative name server returns IP

describe buffer overflow

• Writing data into a too small memory space so that it may write into instruction memory

• Malware can deliberately cause and manipulate overflow data which may then be read as a malicious ‘instruction’

How to improve code quality to improve network security

Guarding against buffer overflow attack

Guarding against SQL injection attack

Use of strong passwords for login credentials

Two-factor authentication

Use of access rights (file system permissions)

What is the world wide web

System of hyperlinked documents accessed using the HTTP protocol over the internet

Purpose of internet registrars

Provide a marketplace for available domain names, manages available domain names, dispute resolution services (cybersquatting), registers individual or company details such as name, address, date of registration or type of organisation.

Purpose of Internet Service Providers (ISP)

Allow users to access the internet (backbone)

What are search engines

Systems that locate resources on the Internet

describe search engine indexing

Search engine indexing provides fast and accurate information retrieval by storing web pages’ URL, content and relevance to search in an index

-When users search the web using the search engine, they are actually searching the index, not the web.

Process of creating a search engine indexing

Uses a software called web crawler'/spider to go to known pages and following hyperlinks to record in an index

-The index is then searched when a user does a web search

Information stored by web crawler

• The URL of the resource

• The content of the resource (ie. Text on a web page)

• The last time the resource was updated

• The quality of the resource (ie. How credible it is)

purpose of meta tags/ descriptions

Lists of keywords specified by website owner inside html tags to allow the webpage more likely to be seen (only viewable by web crawler)

descriptions are phrases shown alongside the webpage title when searched for

Describe how PageRank works

Developed by founders of Google to rank webpages based on credibility and usefulness when searched for

Based on:

• Domain name – relevance to the search item

• Frequency of search term in web page

• Age of web page

• Frequency of page updates

• Magnitude of content updates

• Keywords in <H1> tags

• number of inbound links

Purpose of dampening factor in page rank algorithm

likelihood that a user stops following hyperlinks after 5/6 clicks, or probability that a website is accessed directly

describe server-side processing

client sends data to a server for it to be processed = no information is processed on the client computer

-e.g. SQL, PHP

advantages of server-side processing

• Does not require plugins

• Can perform large calculations much faster than clients

• Not browser dependent

• More secure

describe client-side processing

when a client processes the data on a local device. This means that all of the information is processed on the client computer

-e.g. Javascript

advantages of client side processing

• Webpage can immediately respond to user actions

• Executes quickly

• Gives developers more control over the behaviour and look of the website

Why does validation happen twice

• performed client-side to prevent unnecessary load on server, and allows for interactivity by having an immediate response

• performed server-side as data can be circumvented

Why is JavaScript interpreted instead of compiled

• The programmer does not know what type of computer will be running the browser, which will require source code dependent of the type of processor

Advantage of CSS within HTML file

Inline styles can override global styles

Keeps html/css in the same document

Describe Javascript

Programming language that runs in the browser and is embedded in HTML, allowing for interactivity with a webpage

-defined using <script> tags