OCR Computing for GCSE © Hodder Education 2011 Chapter 6: Networks OCR Computing for GCSE © Hodder Education 2011

OCR Computing for GCSE © Hodder Education 2011 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 Computing for GCSE © Hodder Education 2011

OCR Computing for GCSE © Hodder Education 2011 Advantages of a LAN 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 Computing for GCSE © Hodder Education 2011

OCR Computing for GCSE © Hodder Education 2011 LAN hardware NIC – network interface card 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 Computing for GCSE © Hodder Education 2011

OCR Computing for GCSE © Hodder Education 2011 LAN hardware Wireless access point Wireless technology has many advantages over wired networks. No building work needed Quick to add new workstations Flexible deployment of nodes Visitors can access network / internet But there are drawbacks Slower performance Security issues OCR Computing for GCSE © Hodder Education 2011

Peer-to-peer networks All computers have the same status. May be very slow because of data collisions shared processor power Only suitable for small low traffic networks. OCR Computing for GCSE © Hodder Education 2011

Client–server networks One or more 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. Servers control network traffic. Log usage of resources. Provide security. Clients have to log in – this identifies users and assigns rights. Big networks may have hundreds of servers. OCR Computing for GCSE © Hodder Education 2011

OCR Computing for GCSE © Hodder Education 2011 Network topologies The topology is the physical layout of the network. It affects cost performance ease of installation. OCR Computing for GCSE © Hodder Education 2011

OCR Computing for GCSE © Hodder Education 2011 Star topology Shared link to server(s) Most common Few data collisions Fast Can set up independent segments OCR Computing for GCSE © Hodder Education 2011

OCR Computing for GCSE © Hodder Education 2011 Ring topology Ring topology One common linking cable Passes all nodes One direction traffic Fast performance But any problems and the whole network goes down OCR Computing for GCSE © Hodder Education 2011

OCR Computing for GCSE © Hodder Education 2011 Bus topology 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 affect whole network Limited distance covered OCR Computing for GCSE © Hodder Education 2011

OCR Computing for GCSE © Hodder Education 2011 LANs and WANs LAN 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 Computing for GCSE © Hodder Education 2011

OCR Computing for GCSE © Hodder Education 2011 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. 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 Computing for GCSE © Hodder Education 2011

OCR Computing for GCSE © Hodder Education 2011 IP addressing Each node on a network running IP has an IP address. It uniquely identifies the node. 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 Computing for GCSE © Hodder Education 2011

OCR Computing for GCSE © Hodder Education 2011 MAC addressing MAC – Media Access Control This is a unique number on network interfaces. Used to communicate with physical layer of network. Can use it to restrict access to a network. OCR Computing for GCSE © Hodder Education 2011

OCR Computing for GCSE © Hodder Education 2011 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 Computing for GCSE © Hodder Education 2011

OCR Computing for GCSE © Hodder Education 2011 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 Computing for GCSE © Hodder Education 2011

OCR Computing for GCSE © Hodder Education 2011 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 Computing for GCSE © Hodder Education 2011

OCR Computing for GCSE © Hodder Education 2011 Disasters Disasters do happen. 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 Computing for GCSE © Hodder Education 2011