Communications technology Flashcards
Fundamental network models
TCP/IP and OSI.
Open system interconnection (OSI)
“Please do not throw sausage pizza away”
-Application
-Presentation
-Session
-Transport
-Network
-Data link
-Physical
Application (OSI model)
Top layer of the model, that directly interacts with data from the user. Software application (web applications and client emails) rely on this layer to communicate, User application (word processing packages) are not included in this function.
Application layer is responsible for managing protocols, such as HTTP and Simple mail transfer protocol (SMTP) that allow meaningful data to be presented to user
Presentation (OSI model)
Prepare data for use in application layer, such as translation, encryption and compression of data, Makes sure data is transmitted in a format that is understood by the receiving device.
Data will be encrypted if communication over a secure connection and also will decrypt data thats received. To increase speed of transmission data will be compressed.
Session (OSI model)
Responsible for opening and closing communication links between devices. Ensures session is open for long enough to allow all data to be transmitted, and close immediately. Once transmission is complete.
Transport (OSI model)
Responsible for breaking down the data from session layer into segments, then segments are given to network layer. Also responsible for reassembling the segments at the receiving device, flow control and error checking. Ensures all data has been received, otherwise requests a retransmission
Network (OSI model)
Breaks down segments from transport layer into smaller units (packets). Responsible for reassembling packets after transmission, and routing. Router is a key component in network layer.
Data link (OSI model)
Similar role to network layer, rather than transmitting data from layer to layer, it transmits from node to node within a network. Coverts packets into frames. Switch is key component in this layer.
Physical (OSI model)
Involves physical equipment used to transmit the data, such as cables. Data is broken down into bits and transmitted as binary. Is responsible for reassembling the bits into frames, after transmission.
Packet:
A unit of data in data transmission
Router:
A network component that uses a computer IP address to send data packets to a destination outside the current network
Switch:
A network component that uses a computers MAC address to send the data packets to a destination within a network
TCP/IP Protocol layers:
TCP/IP model is more condensed than the OSI model, which only has 4 layers, compared to OSI, which has 7 layers.
-Application
-Transport
-Network
-Link
Application Layer (TCP/IP):
Condenses application, presentation and session layer from OSI model. Uses several protocols to provide standardised exchange of data (HTTP, SMTP, Post office protocol (POP), file transfer protocol (FTP).
Transport Layer (TCP/IP):
Comparable to transport layer in OSI model, Responsible for maintaining end-to-end communications between devices. TCP and UDP are the main protocols used in this level.
Network Layer (TCP/IP):
Comparable to network layer in OSI model. Breaks down data into packets and transmits it network to network. IP and internet control message protocol(ICMP) are the main protocols used in this level.
Link Layer (TCP/IP):
AKA physical layer< It condenses the role of data link and physical layer from OSI model. address resolution protocol (ARP) is the protocol used.
IP (internet protocol) Address:
A unique address given to a device, normally by a router
MAC (Media Access Control) Address:
A unique address given to a device by the manufacturer
Structure of data packets:
A Data packet is sent across a network, which contains several elements.
The normal elements include: Header, Payload and Trailer.
Header (Data packets) Includes:
-IP address of sender, source IP
-IP address of receiving device, Destination IP
-Sequence number of packet, so receiving device can reorder the packets to obtain original data.
-MAC address of the sender and receiver
-Any protocol that is used
Payload (Data packets) includes:
-The actual data from the file that is being transmitted
Trailer (Data packets) includes:
-A flag that tells a device it has reached the end of the packet
-Any error checking methods that are used
The data sent to header and trailer are designed to make sure payload data arrived at its intended destination without any errors.
Transmitting data packets
-Circuit Switching: Direct path is created between the sending and receiving device, there are dedicated pathways to transmit data packets. A pathway can only be used if data transmission is completed.
-Packet switching: Data packets sent across the network can take any available path. Normally used when packets are sent over the internet, via routers.
Two methods of packet switching are Connection-oriented and connectionless. In Connection-oriented packet switching a session is created before any data is transferred. Connectionless, does not require prior set up between devices to transmit the data.
-Message switching: An intermediate method between circuit switching and packet switching. Once data packets are sent from computers to the first witch device, The device holds the data packets untill all units have arrived. data packets are sent from switch to switch, until they reach the final computer. (Strore and forward method).
Connection-Oriented Packet switching:
-Frame relay: Data is separated into units called, frames. Error correction is carried out by devices at end points of transmission, which speeds up transmission.
If error is detected in a frame, The frame is dropped and the endpoints will detect the dropped frames and retransmit them. Thus more suitable as error rate is low.
The two main methods of connections in frame relay is Permanent virtual circuits (PVC), connections intended to exist for long periods of time, And Switched virtual circuits (SVC), temporary connections designed to exists for a single session.
-TCP: Connection is created and maintained until application software at each endpoint has finished exchanging data. It determines how data is broken down into packets, which it sends and receives from network layer in TCP/IP model. It is responsible for providing error free data transmission and managing flow of data
Connectionless Packet switching:
-Ethernet: Wired connection to form a network, Makes sure data is formated and transmitted in a way that other devices on the network will understand. Used in homes or schools.
-IP: Protocol used when data is sent across the internet, responsible for delivering packets of data to the receiving device.
-UDP: Alternative protocol to TCP, sends data in datagrams, does not control the flow of data or carry out error checking, Thus is more faster than TCP
Differences of TCP and UDP: UDP sends data in units called datagrams, and TCP sends data in packets. TCP carries out error checking and manages the flow of data, thus is more secure. However UDP is more faster.
Message switching:
An intermediate method between circuit switching and packet switching. Once data packets are sent from computers to the first witch device, The device holds the data packets untill all units have arrived. data packets are sent from switch to switch, until they reach the final computer. (Strore and forward method).
Network
Two or more computers or devices connected together so they can communicate and share data and resources
Local area network (LAN)
A relatively small network that is located withing a single building or site
Wide area network (WAN)
A relatively large network that is normally two or more LAN’s that are linked.
Cient-server
Contains two types of computers, client and server. Servers in client-server network is the central point of control, and provide dedicated function for the network. All other computer are called network.
-Client: A computer in a network that is not a central point of control
-Server: A computer in a network that is a point of control
Advantages of Client-server network:
-Files can be located in a single place and backed up on regular basis, thus each user not responsible to do this.
-Security for network can be controlled from a central point, thus each user not responsible for this
-Levels of access can be applied to resources and data on the servers. Beneficial when data and resources have to be confidential.
-Updates for any software or network peripherals can be carried out from central location. Thus business not reliant on each user installing updates.
Disadvantages of Client-server network:
-Expensive to set up as you require expensive equipment such as servers
-Expensive to maintain, specialist knowledge is required to set up and maintain servers.
-Failure of server means functionality isnt available for all users. Ex: no user can access their files if a file server fails.
Peer-to-peer
Network that contains Peers (A computer of equal inprotance in a peer-to-peer) in order to share data.
Advantages of Peer-to-peer
-Relatively cheap to setup, does not require expensive servers
-Requires little technical knowledge to set up
-Users are able to share data and resources
-Often has less traffic than the alternative client-server structure.
Disadvantages of Peer-to-peer
-If peer computer is accessed by another peer computer, it affects the performance of the computer and causes it to run slower
-The data stored on each peer computer is not centrally backed up by the network. Thus if peer loses the data, its lost for everyone, unless a copy is saved locally on their computer
-The public files shared by a peer computer may be disorganised and difficult to navigate, as no central organisation system in place.
-Each user in the network is responsible for the security of their peer computer. If users arnt vigilant and their computer gets a virus, it could be passed to other peer computers in the network.
Virtual Private Network (VPN)
Advantages of VPN:
-Data is encrypted before it is sent across the network
-Identity of sender is kept private from the destination and any hacker who intercepts a data package.
-Maintenance is not the responsibility of user, so user does not have to worry about it
Disadvantages of VPN:
-Use of VPN is illegal or controversial in some countries, as they can be used to create anonymity in certain criminal activity
-Security of the data is reliant upon a third party and their ability to create effective software and maintenance of VPN server
-Cost is involved in purchasing a VPN, such as monthly subscription fee
Mobile networks
Wireless WAN that uses radio to transmit and recieve communications from portable devices, such as smartphones. Mobile networks are broken down into cells
Cell vary in size:
-Picocell: Covers an area of less than 200 meters
-Microcell: Covers area up to 2 km
-Macrocell: Covers larger reigons
Different generations of mobile network
1G: Uses analogue signals, limited to voice and text message communication
2G: Digital transmission, improved signal quality
3G: Increased data transmission, speeds up to 2Mbps, allowing internet access, video transmission and online gaming
4G: Allow data transmission speeds up to 1 Gbps, allowing greater use of video streaming facilities
5G: Fastest and more reliable connections, average download speed 1Gbps, upto 1.5 Gbps, possibly even faster.
Advantages of mobile networks
-Enables communication with others and access to internet while on the move, often through smart phones
-Breaking network down into cells allows for lower power radio transmitters being used, saving on energy and costs
-Limited radio frequencies used for mobile communication, frequencies can be split among neighboring cells, and reused in more distant cells. Increasing number of communications that take place at the same time.
-Larger geographical areas can be covered than by using a single transmitter, by using several low power transmitters, cover wider area
-Use of multiple transmitters means network is more robust, failure of one base station only affects one cell, leaving other areas of the network unaffected.
Disadvantages of mobile networks
-Quality of reception can vary and be poor towards the edge of a cell, leading to interrupted of delayed transmissions
-The use of frequency must be carefully planned to avoid interference between cells
-Technology for 5G is limited at present and could take a while and be costly to make the full technology useable.
Network protocols
These protocols mainly designed to increase privacy and security of data
Tunneling
Communication protocol, allows for secure transmission of data from one network to another. Allows private data packets to be sent through public network (encapsulation), This is when private data packets are made to look like public data packets, in order to send across public network. Tunneling is used in VPN
SSL
Ensures connections made between web clients (User devices, web/mail servers) are secure. Uses both public and private key to encrypt data transmitted over secure connection
TLS
Updated version of SSL, uses updated and more secure encyrption algorithms
Internet protocol security (IPsec)
Network protocol that is designed to encrypt and authenticate data packets that are sent across the internet. IPSec is part of tunnelling process of VPN.
BitTorrent
Communications protocol, often used in peer-to-peer file sharing. Allows the transfer of large files such as videos. It does this through distributing the load of downloading the file across several sources on the network. Several sources (known as hosts) are collated to create a swarm. Each host will be given pieces of the file. The BitTorrent protocol allows the user to join the swarm and download the file from the available hosts. The protocol will download the file in pieces, simultaneously, from various hosts in the swarm.
