# A bus topology uses a single backbone cable that is terminated at both ends. All the hosts connect directly to this backbone. # A ring topology connects one host to the next and the last host to the first. This creates a physical ring of cable. # A star topology connects all cables to a central point. # An extended star topology links individual stars together by connecting the hubs or switches. # A hierarchical topology is similar to an extended star. However, instead of linking the hubs or switches together, the system is linked to a computer that controls the traffic on the topology. # A mesh topology is implemented to provide as much protection as possible from interruption of service. For example, a nuclear power plant might use a mesh topology in the networked control systems. As seen in the graphic, each host has its own connections to all other hosts. Although the Internet has multiple paths to any one location, it does not adopt the full mesh topology. Protocols control all aspects of data communication, which include the following: * How the physical network is built * How computers connect to the network * How the data is formatted for transmission * How that data is sent * How to deal with errors Local area network ================== LANs consist of the following components: * Computers * Network interface cards * Peripheral devices * Networking media * Network devices LANs allow businesses to locally share computer files and printers efficiently and make internal communications possible. A good example of this technology is e-mail. LANs manage data, local communications, and computing equipment. Some common LAN technologies include the following: * Ethernet * Token Ring * FDDI Wide area network ================= WANs interconnect LANs, which then provide access to computers or file servers in other locations. Because WANs connect user networks over a large geographical area, they make it possible for businesses to communicate across great distances. WANs allow computers, printers, and other devices on a LAN to be shared with distant locations. WANs provide instant communications across large geographic areas. Collaboration software provides access to real-time information and resources and allows meetings to be held remotely. WANs have created a new class of workers called telecommuters. These people never have to leave their homes to go to work. WANs are designed to do the following: * Operate over a large and geographically separated area * Allow users to have real-time communication capabilities with other users * Provide full-time remote resources connected to local services * Provide e-mail, Internet, file transfer, and e-commerce services Some common WAN technologies include the following: * Modems * Integrated Services Digital Network (ISDN) * Digital subscriber line (DSL) * Frame Relay * T1, E1, T3, and E3 * Synchronous Optical Network (SONET) Metropolitan area network ========================= Wireless bridge technologies that send signals across public areas can also be used to create a MAN. A MAN usually consists of two or more LANs in a common geographic area. For example, a bank with multiple branches may utilize a MAN. Typically, a service provider is used to connect two or more LAN sites using private communication lines or optical services. A MAN can also be created using wireless bridge technology by beaming signals across public areas. Storage area network ==================== A storage-area network (SAN) is a dedicated, high-performance network used to move data between servers and storage resources. Because it is a separate, dedicated network, it avoids any traffic conflict between clients and servers. SAN technology allows high-speed server-to-storage, storage-to-storage, or server-to-server connectivity. This method uses a separate network infrastructure that relieves any problems associated with existing network connectivity. SANs offer the following features: * Performance – SANs allow concurrent access of disk or tape arrays by two or more servers at high speeds. This provides enhanced system performance. * Availability – SANs have built-in disaster tolerance. Data can be duplicated on a SAN up to 10 km (6.2 miles) away. * Scalability – A SAN can use a variety of technologies. This allows easy relocation of backup data, operations, file migration, and data replication between systems. Virtual private network ======================= A vitual private network (VPN) is a private network that is constructed within a public network infrastructure such as the global Internet. Using VPN, a telecommuter can remotely access the network of the company headquarters. Through the Internet, a secure tunnel can be built between the PC of the telecommuter and a VPN router at the company headquarters. -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= The following are the three main types of VPNs: * Access VPNs provide remote access for mobile and small office, home office (SOHO) users to an Intranet or Extranet over a shared infrastructure. Access VPNs use analog, dialup, ISDN, DSL, mobile IP, and cable technologies to securely connect mobile users, telecommuters, and branch offices. * Intranet VPNs use dedicated connections to link regional and remote offices to an internal network over a shared infrastructure. Intranet VPNs differ from Extranet VPNs in that they allow access only to the employees of the enterprise. * Extranet VPNs use dedicated connections to link business partners to an internal network over a shared infrastructure. Extranet VPNs differ from Intranet VPNs in that they allow access to users outside the enterprise. -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= INTRANETS AND EXTRANETS ======================= One common configuration of a LAN is an intranet. Intranet Web servers differ from public Web servers in that the public must have the proper permissions and passwords to access the intranet of an organization. Intranets are designed to permit users who have access privileges to the internal LAN of the organization. Within an intranet, Web servers are installed in the network. Browser technology is used as the common front end to access information on servers such as financial, graphical, or text-based data. Extranets refer to applications and services that are Intranet based, and use extended, secure access to external users or enterprises. This access is usually accomplished through passwords, user IDs, and other application-level security. An extranet is the extension of two or more intranet strategies with a secure interaction between participant enterprises and their respective intranets. =--=-=-=-=-=-=-=-= BANDWITH -Bandwidth is defined as the amount of information that can flow through a network connection in a given period of time. It is important to understand the concept of bandwidth for the following reasons. -=-=-=-= THROUGHTPUT - Throughput refers to actual measured bandwidth, at a specific time of day, using specific Internet routes, and while a specific set of data is transmitted on the network. Unfortunately, for many reasons, throughput is often far less than the maximum possible digital bandwidth of the medium that is being used. The following are some of the factors that determine throughput: * Internetworking devices * Type of data being transferred * Network topology * Number of users on the network * User computer * Server computer * Power conditions ======================--------------------===================== OSI LAYERS ENC. UNITS TCP/IP APPLICATION DATA APPLICATION PRESENTATION DATA APPLICATION SESSION DATA APPLICATION TRANSPORT SEGMENTS TRANSPORT NETWORK PACKETS INTERNET DATA LINK FRAMES NETWORK ACCESS PHYSICAL BITS NETWORK ACCESS