OCR Computing A Level - Unit 05 - Networks

Internet

A network of Interconnected Networks

World Wide Web

A collection of resources accessed via the Internet

Backbone

A set of dedicated connections that connect several large networks at various points on the globe

URL (Uniform Resource Locator)

Used to specify means of accessing a resource across a network and its location

URL components

Web protocol, domain name, name of resource

DNS (Domain Name System)

Translates between domain names and IP addresses using DNS servers

DNS Server

Dedicated computer with an index of domain names and their corresponding IP addresses

Internet Registries

5 global Internet Registries are responsible for allocating IP addresses to specific domain names, and maintain a database of address assignments that ensure IP addresses and domain names are unique

LAN (Local Area Network)

Two or more computers connected together within a small geographical area

Network Topology

The arrangement of various computing devices which make up a computer network

Bus topology

An arrangement where nodes are connected in a daisy chain by a single central communications channel (backbone cable)

Star topology

An arrangement where a central node or hub provides a common connection point for all other nodes

Peer-to-peer topology

An arrangement where each node is connected to each other

Ring topology

An arrangement where each node is connected in a circle fashion

Hub

Transmits communication with every computer it is connected to

Switch

Transmits communication to only the computer it is intended for

Wi-Fi

A wireless networking technology providing high-speed Internet and network connections

Wireless Access Point (WAP)

A device that creates a WLAN

Network Interface Card (NIC)

A hardware component that enables computers to communicate over a network

Circuit Switching

Assigns a temporary and dedicated link between source and destination with dedicated bandwidth until transmission is complete

Packet switching

Breaks data into packets and sends them staggered via routes with lowest latency
Allows communication channels to be shared

Gateway

A bridge between networks that use different protocols
Header data is removed and reapplied using the correct format of the new network

Protocol

A set of rules for data communication

TCP/IP stack

Application, Transport, Internet, Link

Application Layer (sending)

Provides interface for applications to communicate across networks
Decides which protocol to use

Transport Layer (sending)

Uses TCP to establish end-to-end connection with recipient computer
Splits data into packets and numbers them sequentially
Adds port number to use based on protocol

Internet/Network Layer (sending)

Uses IP to address packets with source and destination IP addresses
A router forwards each packet towards an endpoint, defined by the combination of IP address and port number
Each router uses a routing table to instruct each hop

Link Layer (sending)

Operates across a physical connection
Adds MAC address of physical NIC card that packets should be sent to based on destination hop
MAC addresses change with every hop

Link Layer (receiving)

removes MAC address from each packet

Internet/Network Layer (receiving)

removes IP address from each packet

Transport Layer (receiving)

Confirms packets have been received and requests any missing to be resent
Removes port number from each packet
Reassembles packets in correct order

Application Layer (receiving)

Presents meaningful data for user

MAC address

Uniquely identifies a physical device with an NIC

File Transfer Protocol (FTP)

An applications-layer protocol used to transfer files across a network

Simple Mail Transfer Protocol (SMTP)

Used to send emails and forward them between mail servers to their destination

Post Office Protocol v3 (POP3)

Downloads email stored on a remote server to a local client, then removes from server after download

Interim Mail Access Protocol (IMAP)

Manages emails on a server so multiple clients access the same email account simultaneously

Time to Live (TTL)

the maximum amount of time a packet is allowed to circulate through a network before it is destroyed/ hop limit

Latency

The time data takes to travel across a network from source to destination

Packet trailer

Contains error checking components, i.e. checksums or Cyclic Redundancy checks; end of packet flag

Packet Header

Contains source and destination IP address, packet number, protocol/port number

Routing

Routers forward data packets from one network to another, and each looks up destination IP address in routing table to find best route

Application Programming Interface (API)

A set of tools that can be used for building software applications