Network Topology

**kingaff** · 23-Feb-2007, 08:00 AM

What is a Topology?
The physical topology of a network refers to the configuration of cables, computers, and other peripherals. Physical topology should not be confused with logical topology which is the method used to pass information between workstations. Logical topology was discussed in the Protocol chapter .
Main Types of Physical Topologies
The following sections discuss the physical topologies used in networks and other related topics.
„h Linear Bus
„h Star
„h Star-Wired Ring
„h Tree
„h Considerations When Choosing a Topology
„h Summary Chart
Linear Bus
A linear bus topology consists of a main run of cable with a terminator at each end (See fig. 1). All nodes (file server, workstations, and peripherals) are connected to the linear cable. Ethernet and LocalTalk networks use a linear bus topology.

Fig. 1. Linear Bus topology
Advantages of a Linear Bus Topology
„h Easy to connect a computer or peripheral to a linear bus.
„h Requires less cable length than a star topology.
Disadvantages of a Linear Bus Topology
„h Entire network shuts down if there is a break in the main cable.
„h Terminators are required at both ends of the backbone cable.
„h Difficult to identify the problem if the entire network shuts down.
„h Not meant to be used as a stand-alone solution in a large building.
Star
A star topology is designed with each node (file server, workstations, and peripherals) connected directly to a central network hub or concentrator (See fig. 2).
Data on a star network passes through the hub or concentrator before continuing to its destination. The hub or concentrator manages and controls all functions of the network. It also acts as a repeater for the data flow. This configuration is common with twisted pair cable; however, it can also be used with coaxial cable or fiber optic cable.

Fig. 2. Star topology
Advantages of a Star Topology
„h Easy to install and wire.
„h No disruptions to the network then connecting or removing devices.
„h Easy to detect faults and to remove parts.
Disadvantages of a Star Topology
„h Requires more cable length than a linear topology.
„h If the hub or concentrator fails, nodes attached are disabled.
„h More expensive than linear bus topologies because of the cost of the concentrators.
The protocols used with star configurations are usually Ethernet or LocalTalk. Token Ring uses a similar topology, called the star-wired ring.
Star-Wired Ring
A star-wired ring topology may appear (externally) to be the same as a star topology. Internally, the MAU (multistation access unit) of a star-wired ring contains wiring that allows information to pass from one device to another in a circle or ring (See fig. 3). The Token Ring protocol uses a star-wired ring topology.
Tree
A tree topology combines characteristics of linear bus and star topologies. It consists of groups of star-configured workstations connected to a linear bus backbone cable (See fig. 4). Tree topologies allow for the expansion of an existing network, and enable schools to configure a network to meet their needs.

Advantages of a Tree Topology
„h Point-to-point wiring for individual segments.
„h Supported by several hardware and software venders.
Disadvantages of a Tree Topology
„h Overall length of each segment is limited by the type of cabling used.
„h If the backbone line breaks, the entire segment goes down.
„h More difficult to configure and wire than other topologies.

Fig. 4. Tree topology

Summary Chart:
Physical Topology Common Cable Common Protocol
Linear Bus Twisted Pair
Coaxial
Fiber Ethernet
LocalTalk
Star Twisted Pair
Fiber Ethernet
LocalTalk
Star-Wired Ring Twisted Pair Token Ring
Tree Twisted Pair
Coaxial
Fiber Ethernet

What is a Network Operating System?
Unlike operating systems, such as DOS and Windows, that are designed for single users to control one computer, network operating systems (NOS) coordinate the activities of multiple computers across a network. The network operating system acts as a director to keep the network running smoothly.
The two major types of network operating systems are:
„h Peer-to-Peer
„h Client/Server
Peer-to-Peer
Peer-to-peer network operating systems allow users to share resources and files located on their computers and to access shared resources found on other computers. However, they do not have a file server or a centralized management source (See fig. 1). In a peer-to-peer network, all computers are considered equal; they all have the same abilities to use the resources available on the network. Peer-to-peer networks are designed primarily for small to medium local area networks. AppleShare and Windows for Workgroups are examples of programs that can function as peer-to-peer network operating systems.

Advantages of a peer-to-peer network:
„h Less initial expense - No need for a dedicated server.
„h Setup - An operating system (such as Windows XP) already in place may only need to be reconfigured for peer-to-peer operations.
Disadvantages of a peer-to-peer network:
„h Decentralized - No central repository for files and applications.
„h Security - Does not provide the security available on a client/server network.

Fig. 1. Peer-to-peer network

Client/Server
Client/server network operating systems allow the network to centralize functions and applications in one or more dedicated file servers (See fig. 2). The file servers become the heart of the system, providing access to resources and providing security. Individual workstations (clients) have access to the resources available on the file servers. The network operating system provides the mechanism to integrate all the components of the network and allow multiple users to simultaneously share the same resources irrespective of physical location. Novell Netware and Windows 2000 Server are examples of client/server network operating systems.

Fig. 2. Client/server network

Advantages of a client/server network:
„h Centralized - Resources and data security are controlled through the server.
„h Scalability - Any or all elements can be replaced individually as needs increase.
„h Flexibility - New technology can be easily integrated into system.
„h Interoperability - All components (client/network/server) work together.
„h Accessibility - Server can be accessed remotely and across multiple platforms.
Disadvantages of a client/server network:
„h Expense - Requires initial investment in dedicated server.
„h Maintenance - Large networks will require a staff to ensure efficient operation.
„h Dependence - When server goes down, operations will cease across the network.
Examples of network operating systems
The following list includes some of the more popular peer-to-peer and client/server network operating systems.
„h AppleShare
„h Microsoft Windows Server
„h Novell Netware

23-Feb-2007, 08:00 AM	#1 (permalink)
kingaff Fixed Error! Posts: 330 Join Date: Feb 2007 Rep Power: 2 IM:	Network Topology What is a Topology? The physical topology of a network refers to the configuration of cables, computers, and other peripherals. Physical topology should not be confused with logical topology which is the method used to pass information between workstations. Logical topology was discussed in the Protocol chapter . Main Types of Physical Topologies The following sections discuss the physical topologies used in networks and other related topics. „h Linear Bus „h Star „h Star-Wired Ring „h Tree „h Considerations When Choosing a Topology „h Summary Chart Linear Bus A linear bus topology consists of a main run of cable with a terminator at each end (See fig. 1). All nodes (file server, workstations, and peripherals) are connected to the linear cable. Ethernet and LocalTalk networks use a linear bus topology. Fig. 1. Linear Bus topology Advantages of a Linear Bus Topology „h Easy to connect a computer or peripheral to a linear bus. „h Requires less cable length than a star topology. Disadvantages of a Linear Bus Topology „h Entire network shuts down if there is a break in the main cable. „h Terminators are required at both ends of the backbone cable. „h Difficult to identify the problem if the entire network shuts down. „h Not meant to be used as a stand-alone solution in a large building. Star A star topology is designed with each node (file server, workstations, and peripherals) connected directly to a central network hub or concentrator (See fig. 2). Data on a star network passes through the hub or concentrator before continuing to its destination. The hub or concentrator manages and controls all functions of the network. It also acts as a repeater for the data flow. This configuration is common with twisted pair cable; however, it can also be used with coaxial cable or fiber optic cable. Fig. 2. Star topology Advantages of a Star Topology „h Easy to install and wire. „h No disruptions to the network then connecting or removing devices. „h Easy to detect faults and to remove parts. Disadvantages of a Star Topology „h Requires more cable length than a linear topology. „h If the hub or concentrator fails, nodes attached are disabled. „h More expensive than linear bus topologies because of the cost of the concentrators. The protocols used with star configurations are usually Ethernet or LocalTalk. Token Ring uses a similar topology, called the star-wired ring. Star-Wired Ring A star-wired ring topology may appear (externally) to be the same as a star topology. Internally, the MAU (multistation access unit) of a star-wired ring contains wiring that allows information to pass from one device to another in a circle or ring (See fig. 3). The Token Ring protocol uses a star-wired ring topology. Tree A tree topology combines characteristics of linear bus and star topologies. It consists of groups of star-configured workstations connected to a linear bus backbone cable (See fig. 4). Tree topologies allow for the expansion of an existing network, and enable schools to configure a network to meet their needs. Advantages of a Tree Topology „h Point-to-point wiring for individual segments. „h Supported by several hardware and software venders. Disadvantages of a Tree Topology „h Overall length of each segment is limited by the type of cabling used. „h If the backbone line breaks, the entire segment goes down. „h More difficult to configure and wire than other topologies. Fig. 4. Tree topology Summary Chart: Physical Topology Common Cable Common Protocol Linear Bus Twisted Pair Coaxial Fiber Ethernet LocalTalk Star Twisted Pair Fiber Ethernet LocalTalk Star-Wired Ring Twisted Pair Token Ring Tree Twisted Pair Coaxial Fiber Ethernet What is a Network Operating System? Unlike operating systems, such as DOS and Windows, that are designed for single users to control one computer, network operating systems (NOS) coordinate the activities of multiple computers across a network. The network operating system acts as a director to keep the network running smoothly. The two major types of network operating systems are: „h Peer-to-Peer „h Client/Server Peer-to-Peer Peer-to-peer network operating systems allow users to share resources and files located on their computers and to access shared resources found on other computers. However, they do not have a file server or a centralized management source (See fig. 1). In a peer-to-peer network, all computers are considered equal; they all have the same abilities to use the resources available on the network. Peer-to-peer networks are designed primarily for small to medium local area networks. AppleShare and Windows for Workgroups are examples of programs that can function as peer-to-peer network operating systems. Advantages of a peer-to-peer network: „h Less initial expense - No need for a dedicated server. „h Setup - An operating system (such as Windows XP) already in place may only need to be reconfigured for peer-to-peer operations. Disadvantages of a peer-to-peer network: „h Decentralized - No central repository for files and applications. „h Security - Does not provide the security available on a client/server network. Fig. 1. Peer-to-peer network Client/Server Client/server network operating systems allow the network to centralize functions and applications in one or more dedicated file servers (See fig. 2). The file servers become the heart of the system, providing access to resources and providing security. Individual workstations (clients) have access to the resources available on the file servers. The network operating system provides the mechanism to integrate all the components of the network and allow multiple users to simultaneously share the same resources irrespective of physical location. Novell Netware and Windows 2000 Server are examples of client/server network operating systems. Fig. 2. Client/server network Advantages of a client/server network: „h Centralized - Resources and data security are controlled through the server. „h Scalability - Any or all elements can be replaced individually as needs increase. „h Flexibility - New technology can be easily integrated into system. „h Interoperability - All components (client/network/server) work together. „h Accessibility - Server can be accessed remotely and across multiple platforms. Disadvantages of a client/server network: „h Expense - Requires initial investment in dedicated server. „h Maintenance - Large networks will require a staff to ensure efficient operation. „h Dependence - When server goes down, operations will cease across the network. Examples of network operating systems The following list includes some of the more popular peer-to-peer and client/server network operating systems. „h AppleShare „h Microsoft Windows Server „h Novell Netware

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