Introduction to Local Area Networks 11/23/2018 Chapter 1: Introduction to Local Area Networks 11/23/2018

What is a LAN? A type of network where nodes are connected at high speed in a confined geographical area. Network: A connection between two or more computers to exchange data or provide shared access to resources Node: Any device that can send or receive data via a network 11/23/2018

Why use a LAN? LANs provide the ability to share resources to other nodes on the network. Resources include: Shared files Shared printers Shared applications such as database and e-mail servers Shared Internet connection 11/23/2018

The First LAN Was built at the Xerox Palo Alto Research Center (PARC) in 1973. Xerox PARC was also responsible for the invention of: The first personal computer (the Alto) The first laser printer The first Graphic User Interface Although Xerox PARC pioneered many of these technologies, other companies, such as Apple, Microsoft, 3Com and Cisco would make them famous. 11/23/2018

Other Types of Networks Campus area network (CAN): Spans a group of buildings, generally within walking distance of each other that belong to the same organization. Metropolitan area network (MAN): Medium speed network that connects sites over distances up to 50 miles. Generally used by organizations that have several locations over the same city. Most MANs can also be described as WANs 11/23/2018

Other Types of Networks WANs are made up of LANs connected by lower speed long distance links. WANs usually cover a significant geographical area. Wide area network (WAN): WANs use slightly different transmission methods & media and often use a greater variety of technologies than LANs. 11/23/2018

LAN vs. WAN Geography – small / large Ownership – self owned / leased Management – self admin / contract leased Speed – faster / slower Cost – hundreds / thousands or millions 11/23/2018

Authentication The process by which a user is identified on the network. Most frequently accomplished by means of a logon account and a password. Each user must have a valid logon account on the computer or network to be authenticated. Sometimes authentication is centralized and sometimes each resource requires individual authentication. 11/23/2018

Client/Server Network Server provides specific services for a specific purpose. Users connected to the LAN through client computers can access resources on any server on the network. Centralized database illustrate the concept: Client requests Information. Server responds to request. Servers tend to have faster processors, more RAM, and more hard disk space. They perform the processing for many clients. A slow server slows all clients that use it. 11/23/2018

Peer-to-Peer (P2P) Network Decentralized. There are no dedicated servers and no single set of resources that all clients access. Each host on a P2P network can act as a client, a server or both. Each host performs authentication for other hosts that request its resources. Advantage: Loss of a single computer doesn’t mean that all data is lost. Disadvantages: Can be difficult to find a resource, and a user must remember many different passwords. Individual P2P servers grant/deny access. P2P clients request authentication. 11/23/2018

Centralized Networks Rather than having to authenticate against each computer, a user authenticates once and then can access all resources on a LAN. Assuming that their account has permissions of course! 11/23/2018

Centralized Networks Advantages of Centralized Networks: Files can be stored and backed up centrally. Servers can be located centrally for easy access. Centralized administration Fewer support personnel required. Disadvantages of Centralized Networks: Fewer points of failure If a central resource like a file share goes offline, many more users are inconvenienced. Security If you get a users password, you can access all resources on the network, not just on one computer. 11/23/2018

Centralized Network Administration Centralized networks allow an administrator to: Deploy an application to a thousand desktop computers at the same time rather than visit each computer with the installation CD-ROM. Standardize of modify the look and feel of all client computers or make configuration changes centrally. Have security updates automatically deployed to all computers as they become available rather than having to visit each computer, check which updates are installed, and then finally install relevant updates. 11/23/2018

The OSI Reference Model The OSI Reference Model is a complete conceptual model for describing functions performed by network hardware and software. Each layer of the OSI model describes a particular aspect of the network communication process. Services provided at each layer interact directly with those provided by the layers immediately above and/or below. 11/23/2018

Layer 7 Application Layer Layer 6 Presentation Layer Layer 5 Layer 4 Initiates communication to use the network, such as starting a file transfer or displaying a Web page. Application Layer Layer 6 Translates data into formats such as text, graphics, audio and video. Also includes data compression and encryption. Presentation Layer Layer 5 Establishes a logical communication channel for data transfer between hosts. Layer 4 Breaks data message into transmittable segments and ensures accurate and reliable transmission of data packets in the proper sequence between hosts. Session Layer Layer 3 Identifies the location of source and destination hosts and routes the best pathway between. Transport Layer Layer 2 Ensures that data transmitted on the transmission media has a destination on the local network. Network Layer Layer 1 Transmits data across the physical media as a stream of binary numbers in the form of electrical signals, light pulses of radio waves. Data Link Layer Physical Layer 11/23/2018

Summary A LAN is a type of network where two or more hosts are connected at high speed. LANs are used to share a small number of resources with a large number of hosts. P2P networks allow hosts to act as both client and server. Client/server networks have resources centralized on servers which clients access. The benefits of LANs is that they allow centralized administration, centralized applications and centralized file storage and backup. The OSI Reference Model has seven layers, which can conceptually be used to represent how software and hardware interact with one another on a network. 11/23/2018

Discussion Questions What is the difference between a LAN and a WAN? What are the differences between a client and a server? What are the advantages of a client/server network model over a peer-to-peer network model? What are the benefits of centralized administration of computers on a LAN? 11/23/2018