SYSTEM ADMINISTRATION Chapter 1 Logical and Physical Network Topologies

Understanding Networks Networking is the process of connecting two or more devices together in order to share resources. Resources can be hardware or software. –Hardware: printers, CD-ROMS, modems –Software: files, folders, applications Reduced costs Increased productivity Increased usefulness and efficiency of computers

Understanding Network Structure Defined by: –Size of area that it covers –Type of security being used Two basic types of networks –Local Area Network (LAN) –Wide Area Network (WAN)

Local Area Network (LAN) Limited to one or more buildings in close proximity Does not use a public carrier Categorized as: –Peer-to-peer –Client-server

Peer-to-Peer Network Limited in size, no more than 10 nodes All computers are equal members No centralized security Uses share-level security –Assigns passwords to shares Easy and inexpensive to implement

Client-Server Network One or more servers centrally control security Servers run a network operating system (NOS) Administrators assign user names and passwords Uses user level security –Access to shared resources is granted to a user or group May be any size

Wide Area Network (WAN) Unlimited in size and scope WANs are used to connect LANs WANs use telecommunications lines and one or more routers Data transfer speeds on WAN are slower than LAN Largest WAN today is the Internet

Topologies Logical topology –Determines media access methods Collision Sense Multiple Access with Collision Detection Token Passing Physical topology –Location and arrangement of nodes –How they are interconnected –Includes network hardware –Most common: star, bus, ring, and wireless

Star Topology Most common topology in use today Each node is connected directly to a MAU Commonly uses twisted pair cable Advantages of a star topology: –Easy to install. –The failure of a single node or cable segment affects only that node. –Network faults are easier to troubleshoot and repair. –Components are common and supported by many manufacturers. Disadvantages of a star topology: –The MAU constitutes a potential single point of failure. –The star requires more wiring than other topologies.

Bus Topology Linear topology using several pieces of cable in linear arrangement Uses coaxial cable and BNC connectors Must be terminated on each end Advantages of the bus topology: –Uses less cable and hardware than other topologies. –Less expensive. –Easier to manage and keep track of wiring. –Simpler to install. Disadvantages of the bus topology: –A single break can bring down a segment or the entire network. –Adding additional nodes may affect network performance. –Can be tough to troubleshoot connection problems. –Coaxial cable and network adapter cards are more difficult to find.

Mesh Topology Every node has a connection to every other node Provides a high level of fault tolerance The Internet uses a hybrid mesh Advantages of the mesh topology: –Provides a high level of fault tolerance. –Network problems are generally easy to isolate. Disadvantages of the mesh topology: –Complexity makes installation and management difficult. –Redundancy makes it expensive. –Reconfiguration of the network or the addition of another node affects all of the other nodes.

Ring Topology A “circle” of cable connects each device to another Data travels around the circle in one direction Uses token passing Advantages of the ring topology: –Requires less wire than a star network. –Each workstation can act as a repeater to regenerate the signal. Disadvantages of the ring topology: –Lack of fault tolerance. –Most rings are actually wired as a star.

Wireless Use either radio frequency (RF) or infrared (IR) Ad hoc mode –When devices connect directly to each other Infrastructure or multipoint –Nodes connect to an access point that is wired to a network

Troubleshooting Problems with Shared Resources Begin by browsing to the resource with Network Neighborhood or My Network Places. –If you can see the resource but it does not allow you access, check the permissions on the share. On the other hand, if you cannot see the shared resource on the network, try these steps: –Ensure that the computer that hosts the resource is turned on. For example, if another user is sharing a folder of Microsoft Excel spreadsheets and the folder is physically located on the hard drive of the user’s computer, you will not be able to see or access the shared folder. (continued)

Troubleshooting Problems with Shared Resources (continued) –If the computer is on, check the resource to ensure it is still shared. –See if you can see other computers on the network. –Since a connectivity issue may be causing the problem, you must determine if the problem is at your computer, the computer with the share, or the entire network. If you can see other computers on the network and access their resources, check the connectivity at the computer hosting the share. –If you cannot see any other computer on the network, check your connectivity.