Topologies, Backbones, Switching, and Ethernet ITNW 1325, Chapter V, Part I

1. Topologies, Backbones, • Switching, and Ethernet • ITNW 1325, Chapter V, Part I

2. Physical Topologies

3. Physical Topologies • Overview: • Reflect geometry of physical connections only – without devices, connectivity methods, or addressing • Don’t reflect device types, connectivity methods, or addressing schemes in use • Three fundamental types are bus, ring, and star – can be mixed to create hybrid topologies • Important to understand in order to troubleshoot related problems or change communications infrastructure • Differ from logical topologies – reflect how digital data propagates between nodes

4. Physical Topologies • Overview (continued): • Physical and logical topologies used within the same network may be very different • The term topology commonly refers to a physical topology when used alone – with logical used explicitly • Too restrictive – rarely seen in their pure form in medium-sized and large networks

5. Physical Topologies Bus: • Implies nodes connected by a single cable without employing connectivity devices • Provides only one communications channel – baseband transmission is supported only • Enables only one node to transmit at a time – nodes compete for the right to transmit • Requires each node to passively listen for and accept data directed to it – passive topology • Nodes other than sending and receiving ones sense the transmission but ignore the information sent

6. Physical Topologies Bus (continued): • A broadcast transmission would be processed by all connected nodes – parts of a single broadcast domain • Requires resistors – terminators – at the cable ends to prevent endless travel of the signal (signal bounce) • Without terminators, old signals would keep bouncing off the wire ends – prevent propagation of new signals • Must be grounded at one end – helps to remove static electricity that could adversely affect the signal • Example – nodes connected with a coaxial cable and sharing the available bandwidth (50-Ohm terminators)

7. Physical Topologies Bus (continued): • Not scalable – performance degrades as more nodes are added and compete for the right to transmit • Hard to troubleshoot – errors are easily detected but their exact source or location are difficult to locate • Not fault tolerant – any single break or defect affects the entire network disrupting transmissions • Lack security – every connected node can read any data transmission destined to it or to someone else • The least expensive topology to set up – rarely used today due to multiple carried drawbacks

8. Physical Topologies Bus (continued):

9. Physical Topologies Bus (continued): BNC T-Connector BNC Terminator

10. Physical Topologies Ring: • Implies that each node is connected to the two nearest ones – with the entire topology forming a circle • Each node accepts and responds to frames addressed to it – while forwarding other packets to the next node • Implies that each node to participates in delivery acting as a repeater – active topology • Employs twisted pair of fiber optic cable as medium

11. Physical Topologies Ring (continued): • Not scalable – performance degrades as more nodes are added and introduce additional transmission delays • Not fault tolerant – a single malfunctioning node would break the ring and disable the entire network • Used by obsolete Token Ring networks

12. Physical Topologies Ring (continued):

13. Physical Topologies Star: • Implies nodes connected through a central connectivity device – forwards frames to the recipient’s segment • Requires more cabling – twisted pair of fiber optic – and more configuration than bus or star topologies • Requires proper configuration and constant availability of the central device • Enables connecting two devices only to each physical segment – a cabling problem affects two nodes at most • Enables many nodes to transmit at a time – depending on the ability of the central device to handle the load

14. Physical Topologies Star (continued): • The most scalable topology – can be easily easily moved, isolated, or interconnected with other networks • The most fault tolerant – a malfunctioning node would not affect any other node or a communication device • The easiest to troubleshoot – having one node per segment makes an error easier to locate • Carries single point of failure – a problem with the central connectivity device affects all connected nodes • More expensive to set up and maintain – requires more cabling and administration than other topologies

15. Physical Topologies Star (continued): • Limits the number of nodes per segment – may result in reduced or eliminated competition for the medium • Most widely used topology on modern networks

16. Physical Topologies Star (continued):

17. Logical Topologies

18. Logical Topologies • Overview: • Reflect how information propagates between nodes – may differ from a physical topology used • Important to understand when building networks, troubleshooting them, or optimizing their performance • Represented by two fundamental types – bus and ring

19. Logical Topologies Bus (“Local Broadcast”): • Data travels from one network device to all other ones on the segment – each connected node can access data • Commonly supported by networks that use a bus, a star, or a star-wired bus physical topology Ring: • Data follows a circular path between sender and receiver – even in case physical connections form a star • Supported by networks that use a ring or a star-wired ring physical topology

20. Logical Topologies Bus (continued):

21. Logical Topologies Ring (continued):

22. Hybrid Physical Topologies

23. Hybrid Physical Topologies • Overview: • Complex combinations of fundamental physical topologies – more suitable for modern networks • Minimize weaknesses and increase scalability of networks – better fit large and growing networks • Two primary kinds – star-wired ring and star-wired bus

24. Hybrid Physical Topologies Star-Wired Bus: • Implies groups of nodes that are star-connected to connectivity devices that are connected via a bus • Enables covering longer distances and interconnecting or isolating different network segments • Inherits fault-tolerance, scalability, and manageability from a star topology • Requires more cabling and more connectivity devices than a star or a bus – more expensive than basic ones • A basis for modern midsize and large Ethernet networks

25. Hybrid Physical Topologies Star-Wired Bus (continued):

26. Hybrid Physical Topologies Star-Wired Ring: • Implies groups of nodes that are star-connected to connectivity devices – and the ring logical topology • Data flows in a circular pattern over the star-like wiring • Inherits fault-tolerance, scalability, and manageability from a star topology • A basis for obsolete Token Ring networks

27. Hybrid Physical Topologies Star-Wired Ring (continued):

28. Backbone Networks

29. Backbone Networks • Overview: • Cabling that interconnects various parts of enterprise – local and remote offices, departments, and computers • Commonly carry substantially more traffic than cables connecting to workstations – possess increased capacity • Designed for continuous high throughput to avoid congestion – complex and require careful planning • Four fundamental types – serial, distributed, collapsed, and parallel

30. Backbone Networks Serial: • Implies two or more internetworking devices connected to each other in a daisy-chain fashion (linked series) • Used for extending networks and adding device ports to connect more user workstations • Requires to observe the maximum number of connected devices and segments – depends on the network type • Not scalable – delays in information delivery increase as more devices are added to the backbone • Not fault tolerant – any single break or defect affects the entire backbone disrupting transmissions

31. Backbone Networks Serial (continued): • The simplest logically, the least expensive, and the easiest to implement backbone type

32. Backbone Networks Distributed: • Consists of a number of connectivity devices connected to multiple central devices in a hierarchy • More devices can be added to existing layers – allows for simple expansion at lower costs of adding networks • Can employ advanced devices for connecting LAN segments – raise effectiveness of data transmissions • Maps onto the structure of a building – with some devices serving floors and/or departments and other ones connecting these segments together • Enables segregation and easy management of networks

33. Backbone Networks Distributed (continued): • May include a daisy-chain linked bus – inherits its limitations requiring to place it thoughtfully • Device at the upper layers represent potential single points of failure – can damage the entire network • Brings relatively simple, quick, and inexpensive implementation – popular on today’s LANs and MANs

34. Backbone Networks Distributed (continued):

35. Backbone Networks Collapsed: • Implies having the single central connection point for multiple networks – connects multiple LANs together • Makes the central device the highest level of the backbone – must be able to handle heavy traffic loads • Scalable – makes addition of new segments easy, with potential necessity to upgrade the central device only • The central network device represents single point of failure for the entire network – must be available • Fault tolerant – a failed segment does not affect others

36. Backbone Networks Collapsed (continued): • Centralizes maintenance and troubleshooting and enables interconnecting networks of different types

37. Backbone Networks Collapsed (continued):

38. Backbone Networks Parallel: • Resembles other backbone types – implies duplicate connections between connectivity devices • Doubles the amount of cable needed and physical ports used on network devices – can be quite expensive • Provides network load balancing, redundancy, and increased performance • Most robust backbone type – commonly implemented within critical segments of the network