1. Chapter 5 Network Architecture

2. Physical Topologies Bus Ring Star

3. 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

4. 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

5. 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

6. 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

7. 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?)

8. Star Topology Each node is connected through a central device such as a hub Each physical wire connects only two devices

9. 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

10. Hybrid LAN Topologies Star-Wired Ring Star-Wired Bus Daisy-Chained Hierarchical

11. 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 Multi- Station Access Unit (MAU or MSAU) Token ring network protocol, specified by IEEE 802.5, uses this topology

12. 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

13. 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

14. 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

15. 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

16. Types of Backbones Serial Backbone Distributed or Hierarchial Backbone Collapsed Backbone Parallel Backbone

17. 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

18. 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

19. 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

20. 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

21. 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

22. WAN Topologies Peer-To-Peer Ring Star Mesh Tiered

23. 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 A single failure can cause communication between sites to fail

24. 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

25. 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

26. 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

27. Tiered WAN Topology Similar to hierarchical LANs Interconnection sites are organized into layers

28. 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

29. 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

30. 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

31. 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 re- assembling the packets when they arrive Examples: Ethernet, FDDI, Internet

32. Ethernet Uses CSMA/CD Ethernet Versions –10Base2 –10Base5 –10BaseT –100BaseT Fast Ethernet 100BaseTX 100BaseT4

33. 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

34. 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