Computer Networks

Standalone or Networked Standalone refers to a computer or device that is not connected to a network. A computer network includes computers and devices that are connected in order to share resources or information.

Chapter 6: Networks LAN A LAN is a Local Area Network. It is a connected set of computers and other devices. Each device is called a node. A LAN is installed on one site. It does not cover a wide geographical area. All the infrastructure is owned by the organisation or individual who owns the LAN. OCR GCSE Computing © Hodder Education 2013 Slide 3

Chapter 6: Networks Advantages It allows communications between workers. It allows data to be shared. It allows peripherals to be shared. It allows computers to be upgraded more easily. It allows distributed processing. OCR GCSE Computing © Hodder Education 2013 Slide 4

Chapter 6: Networks Disadvantages Expertise required to set up a large network Security issues from unauthorised access to data Measures to secure a network include: Passwords – strong passwords use a range of character types; Changing passwords frequently; Do not allow users to install software; With wireless access, use encryption. OCR GCSE Computing © Hodder Education 2013 Slide 5

Chapter 6: Networks Hardware NIC – network interface card Hub Each node needs a NIC to connect to the LAN. Produces the electrical signals that carry data. Hub A device that connects nodes together. Makes them act as a single segment. Not smart – all data packets are transmitted. Cheap devices – USB hubs useful in home computer installations. OCR GCSE Computing © Hodder Education 2013 Slide 6

Chapter 6: Networks Hardware Switch a smart device that can create and connect to different segments of the network This reduces network traffic because data is confined to the segment where it is needed rather than being broadcast to the whole network. Routers Routers work with data packets to send data between networks. OCR GCSE Computing © Hodder Education 2013 Slide 7

Chapter 6: Networks Hardware Wireless access point Wireless technology has many advantages over wired networks: No building work needed Quick to add new workstations Flexible deployment of node Visitors can access network / internet But there are drawbacks: Slower performance Security issues OCR GCSE Computing © Hodder Education 2013 Slide 8

Chapter 6: Networks Network types: peer to peer All computers have the same status. May be very slow because of data collisions shared processor power Only suitable for small, low traffic networks. 11P to start next week OCR GCSE Computing © Hodder Education 2013 Slide 9

Chapter 6: Networks Network types: client server At least one computer is designated as a server. A high specification machine. It offers services to client machines, such as centrally held software, data, file storage and peripheral access. A server controls network traffic. Logs usage of resources. Provides security. Clients have to log in – this identifies users and assigns rights. Big networks may have hundreds of servers. OCR GCSE Computing © Hodder Education 2013 Slide 10

Chapter 6: Networks Network topology The topology is the physical layout of the network. It affects: cost, performance, ease of installation. OCR GCSE Computing © Hodder Education 2013 Slide 11

Chapter 6: Networks Star topology Shared link to server(s) Most common Few data collisions Fast Can set up independent segments OCR GCSE Computing © Hodder Education 2013 Slide 12

Chapter 6: Networks Ring topology One common linking cable Passes all nodes One direction traffic Fast performance But any problems and the whole network goes down. OCR GCSE Computing © Hodder Education 2013 Slide 13

Chapter 6: Networks Bus topology One common linking cable Nodes connected off the cable Cheap But: Slows down when heavy traffic Lots of data collisions Breakage to cable affects the whole network Limited distance possible OCR GCSE Computing © Hodder Education 2013 Slide 14

Chapter 6: Networks LANs and WANs LAN WAN VPN Local Area Network Located on one site Owner of network owns the infrastructure WAN Wide Area Network Covers a large geographical area – may be worldwide Infrastructure may be provided by telecoms companies VPN Virtual Private Network Uses internet for infrastructure Need for enhanced security OCR GCSE Computing © Hodder Education 2013 Slide 15

Chapter 6.1 Networks Protocols Protocols are the rules for communication between devices. Standard protocols encourage network development. Network protocols are constructed in layers. This allows independent development of small parts of a protocol. Internet Protocol is a group of protocols that underlies the internet. TCP/IP now the most important set of protocols. Includes many special protocols. OCR GCSE Computing © Hodder Education 2013 Slide 16

Chapter 6: Networks Common protocols Protocol Meaning Application DNS Domain Name System Translates domain names such as ocr.org.uk into IP addresses. TLS/SSL Transport Layer Security / Secure Sockets Layer Cryptographic protocols designed for secure communications. FTP File Transfer Protocol For copying files from one host to another. Gopher An early means of searching for files on the Internet. HTTP Hypertext Transfer Protocol For distributing hypermedia files – essentially web pages. IMAP Internet Message Access Protocol One method for accessing emails. POP3 Post Office Protocol (version 3) Another method for accessing emails, used by most webmail services. Telnet Allows bidirectional text communications on a network. OCR GCSE Computing © Hodder Education 2013 Slide 17

Chapter 6: Networks IP addressing Each node on a network has an IP address. It uniquely identifies the node. In IPv4 this consists of four octets (8-bit bytes). Written as four numbers separated by dots, e.g. 212.1.45.67. DNS servers convert domain names such as OCR.org.uk into IP addresses. OCR GCSE Computing © Hodder Education 2013 Slide 18

Chapter 6: Networks MAC addressing MAC – Media Access Control. This is a unique number on network interfaces. Used to communicate with the physical layer of a network. Can be used to restrict access to a network. OCR GCSE Computing © Hodder Education 2013 Slide 19

Packet sequence number Chapter 6: Networks Packets Data is split into packets on an IP network. Packets get sent by different routes according to availability. Packets reassembled at receiving end. Typical packet structure: source address destination address Packet sequence number data checksum OCR GCSE Computing © Hodder Education 2013 Slide 20

Chapter 6: Networks The packet address is like the address on a letter The data is sent from one router to another until it arrives at its destination. A B OCR GCSE Computing © Hodder Education 2013 Slide 21

Chapter 6: Networks Security Transmitted data is vulnerable. Users on a network do not need to see all the data. Access levels Users granted privileges. Associated with login names. Passwords Must be changed regularly. Passwords should be strong. Encryption Especially important on wireless networks. WEP or WPA should be used. OCR GCSE Computing © Hodder Education 2013 Slide 22

Chapter 6: Networks Policies Network owners should have policies to protect their assets. Users have responsibilities. Acceptable use policies are common. Policy ensures that users understand what is expected of them. Sanctions used if users misuse resources. OCR GCSE Computing © Hodder Education 2013 Slide 23

Chapter 6: Networks Disasters Need to plan for worst case scenario. Example strategies: mirrors of systems; use of disk protection technology such as RAID; surge protectors — to minimise the effect of power surges on delicate electronic equipment; uninterruptible power supply (UPS); back-up generator in case of a power failure; fire preventions — alarms, fire extinguishers; anti-virus software and other security measures; failover systems. OCR GCSE Computing © Hodder Education 2013 Slide 24