Transcript Chapter 5
Chapter 5 Network Architecture Physical Topologies • Bus • Ring • Star Bus Topology • Single cable called the bus • Supports one channel (baseband) • The more nodes on a bus topology, the slower the network will transmit and deliver data • Each node listens to the network to determine if it can transmit • Nodes other that the destination node ignore the transmission • A terminator (resistor) is needed at each end of the bus otherwise signal bounce will occur Properties of Bus Topology • Inexpensive to set up • As you add more nodes, the performance degrades (does not scale well) • Difficult to troubleshoot because it is difficult to identify the location of the problem • Not very fault tolerant – a break in the bus affects the entire network Ring Topology • The network forms a ring • Data is transmitted in one direction around the ring • Each workstation acts as a repeater to regenerate the signal and sends it on to the next node • No terminator needed • Most rings use the token method to determine who can transmit next. • A token is transmitted around the ring. A computer wishing to transmit captures the free token, adds info to it and sends it to another node Ring Topology – Continued • The intermediate nodes recognizes that the token is not fee and simply passes it on around the ring to its destination. • The destination node picks up the frame and returns an acknowledgement to the sender • Upon receipt of the acknowledgement, the originating node releases the token and sends it down the ring. • With this access method, there is no possibility of a collision Properties of Ring Topology • A malfunctioning workstation can disable the network since each node must receive and regenerate the signal • The more workstations added, the slower the ring • Access to ring topology is more fair than with bus topology access (Why?) Star Topology • Each node is connected through a central device such as a hub • Each physical wire connects only two devices Properties of Star Topology • A break in a cable will only affect one computer • A hub failure can bring down the whole LAN • Because of the central connection point, star topologies can be easily interconnected with other networks • Star topology has become the most popular topology for use within LANs Hybrid LAN Topologies • • • • Star-Wired Ring Star-Wired Bus Daisy-Chained Hierarchical Star-Wired Ring • Physical layout of a star is used, but logically it works like a ring • Token passing data transmission method used • One physical connection from central location goes to each workstation • The physical connection, however, has two channels (receive and send) • The center unit is a specialized hub called a MultiStation Access Unit (MAU or MSAU) • Token ring network protocol, specified by IEEE 802.5, uses this topology Star-Wired Bus • Physical layout of a star is used, but logically it works like a bus • This arrangement is being used in CSC Building • Typically this topology is used with Ethernet and Fast Ethernet • One physical connection from central hub to each workstation • The workstation transmits a frame to the hub and then the hub broadcasts this frame to all the workstations • Typical access method is CSMA/CD Daisy-Chained Topology • A daisy chain is a linked series of devices • Hubs can be daisy-chained together to form larger LANs using the star-wired bus topology (See Figure 5-7, p. 158) • MAUs can be daisy-chained together to form larger LANs using the star-wired ring topology (See Figure 4.7, p. 177 of handout) • Daisy-chaining provides for easy expansion of LAN • There is a limit as to how many hubs (MAUs) may be daisy-chained Hierarchical Topology • Attempt to distinguish workgroups by function or priority • One way to divide groups is to divide them into layers • A hierarchical topology uses layers to separate devices based upon their priority or function • You may have any number of layers and you may connect different types of topologies • Figure 5-8 (p. 160) shows a hierarchical ring topology • Figure 5-9 shows a hierarchical star topology Enterprise-Wide Topologies • Strategies for connecting one organization to network • Different from WAN in that only one organization’s resources are connected • Backbone is cabling that connects hubs, switches and routers on a network Types of Backbones • • • • Serial Backbone Distributed or Hierarchial Backbone Collapsed Backbone Parallel Backbone Serial Backbone • Simplest kind of backbone • Consists of two or more hubs connected to each other by a single cable • Identical to daisy-chained networks discussed earlier • Not suited for large networks or long distances Distributed (Hierarchial or tree) Backbone • Consists of a series of hubs connected to a series of central hubs or routers in a hierarchy • See Figure 5-9 for example using hubs • See Figure 5-10 for example using routers • Provides ability to segregate workgroups • Good for enterprise-wide network confined to a single building Collapsed Backbone • Uses a router or switch as the single cerntal connection point for subnetworks • A single router or switch is the highest layer of the backbone • Failure of central router can bring down the entire network • Does centralize all management and troubleshooting chores • See Figure 5-11, p. 163 Parallel Backbone • A variation of the collapsed backbone arrangement • Consists of more than one connection from the central router or switch to each network segment • See Figure 5-12, p. 164 Mesh Networks • Most often used in enterprise-wide networks and WANs • Routers are connected with other routers with at least 2 pathways between each two routers • See Figure 5-13, p. 165 WAN Topologies • • • • • Peer-To-Peer Ring Star Mesh Tiered Peer-To-Peer WAN Topology • Single Interconnection point for each location • Dedicated communication lines are used to connect the sites together • Quite often T1 (1.544 Mbps throughput, 24 channels), T3 (44.736 Mbps throughput, 672 channels), or ISDN (Integrated Services Digital Network) lines are used • See Webopedia for more information • This topology is suitable for only small WANs • All sites must participate in carrying network traffic Ring WAN Topology • Each site is connected to two other sites • A single cable problem does not affect communication as routers can redirect transmissions • Again, T1 and ISDN lines are used to connect sites together Star WAN Topology • A single site acts as the central connection point • A single cable problem only affect communication between the central point and the remote site • Extending a Star WAN is easy • Failure a central point can bring down whole network Mesh WAN Topology • Has each node connected directly to every other node • If one line goes down, routers can redirect transmission around bad link • Very costly to lease a large number of dedicated lines • May implement a partial mesh Tiered WAN Topology • Similar to hierarchical LANs • Interconnection sites are organized into layers Switching • A component of the network’s logical topology that determines how connections are created between nodes in the WAN • Three types of switching – Circuit Switching – Message Switching – Packet Switching Circuit Switching • A connection is established between two network nodes before transmission of data begins • Bandwidth is dedicated to this connection for the duration of the transmission • All data follow the same path • Used in telephone system • Use in ATM, modems, ISDN, T1 and T3 Message Switching • A connection is established between two intermediate nodes and this connection is maintained while all the information is transferred to this intermediate node. • A new connection is established with the next intermediate node and the same thing happens here • Referred to as “store and forward” • The connection between source and destination nodes is not continuously maintained • Some E-mail systems use message switching Packet Switching • Data is broken down into packets before they are sent • The packets associated with a message may travel different paths in getting to the destination • The destination node is responsible for reassembling the packets when they arrive • Examples: Ethernet, FDDI, Internet Ethernet • Uses CSMA/CD • Ethernet Versions – – – – 10Base2 10Base5 10BaseT 100BaseT Fast Ethernet • 100BaseTX • 100BaseT4 Switched Ethernet • The network is divided into smaller segments that can operate simultaneously with the other segments • Transmissions can take place at the same time on the different segments Gigabit Ethernet • IEEE 802.3z – currently finalizing specifications • Can run over UTP, but performs better over fiber • On UTP, distance limitation of 80 ft. currently but IEEE is working to exceed this limitation • On fiber, distance of 3 kilometers can be achieved