Chapter Six

1. 1 Chapter Six Network Architecture

2. 2 Chapter Objectives Describe the basic and hybrid LAN technologies Describe a variety of enterprise-wide and WAN topologies Explain the benefits and uses of different topologies Discuss several versions of the Ethernet transport system Explain the structure and functioning of the Token Ring network transport system

3. 3 Simple LAN Topologies Physical topology vs. Logical topology Physical layout of a network Classified as being one of three: Bus Ring Star

4. 4 Simple LAN Topologies Bus topology consists of a single cable�called a bus� connecting all nodes on a network without intervening connectivity devices Bus � single cable and can only support on channel, so every node shares the bus�s total capacity. Peer-to-peer (equal responsibility)

5. 5 Simple LAN Topologies Bus Topology (continued) Because of the single channel, the more nodes, the slower the network Each node passively listens for data directed to it When one node wants to transmit, it broadcasts an alert to the entire network, informing all nodes that a transmission is being sent Destination node picks it up All other ignore it

6. 6 Simple LAN Topologies Terminators stop signals after they have reached their destination Signal bounce Phenomenon in which signals travel endlessly between the two ends of a bus network

7. 7 Simple LAN Topologies Bus Topology (continued) They do not scale well More nodes => worse performance Difficult to troubleshoot Not very fault tolerant Early �flat� ethernet

8. 8 Simple LAN Topologies Ring topology Each node is connected to the two nearest nodes so the entire network forms a circle Data are transmitted in one direction around the ring

9. 9 Simple LAN Topologies Ring topology (continued) Each workstation accepts and responds to packets addressed to it, then forwards the other packets to the next workstation in the ring No �ends� => no need for terminators One method for passing data is token passing- a 3-byte packet is transmitted from one to another around the ring If a node has data to transmit, it picks up the token packet, and adds control and data info plus the destination node�s address to transform into a data frame and passes to the next node �

10. 10 Simple LAN Topologies Ring topology (continued) � The transformed token (a frame) circulates around the network until it reaches its intended destination The destination node picks it up and returns an ack to the originating node After originating node gets this ack, it releases a new free token and sends it down the ring This ensures that only one workstation transmits data at any given time

11. 11 Simple LAN Topologies Ring topology (continued) Each workstation is then considered to be a repeater A single malfunctioning workstation can disable the network The more workstations, the slower the response time Not very flexible or scalable Early token ring

12. 12 Simple LAN Topologies Star topology Every node on the network is connected through a central device

13. 13 Simple LAN Topologies Star topology (continued) Any single physical wire connects only two devices, so cabling problem affects 2 nodes at most Requires slightly more cabling and configuration than ring or bus Single cable can�t bring network down, but central device can bring down a segment (or entire network) Easily moved, isolated, or interconnected Easily scalable Most popular in use today More modern ethernet is an example

14. 14 Hybrid LAN Topologies Hybrid topology Complex combination of the simple physical topologies 4 models Star-wired ring Star-wired bus Daisy chained Hierarchical

15. 15 Hybrid LAN Topologies Star-wired ring Star-wired topologies use physical layout of a star in conjunction with token ring-passing data transmission method Data sent around the star in a circular pattern Benefits from the fault tolerance of the star topology and the reliability of token passing Modern token ring networks (IEEE 802.5) use this

16. 16 Hybrid LAN Topologies Star-wired bus In a star-wired bus topology, groups of workstations are star-connected to hubs and then networked via a single bus

17. 17 Hybrid LAN Topologies Star-wired bus (continued) Covers longer distances Easily interconnects different network segments More expensive than using star or bus alone Common format for ethernet and fast ethernet Forms segments

18. 18 Hybrid LAN Topologies Daisy-Chained Daisy chain is linked series of devices Logical solution for growth Little additional cost is needed to expand Watch how many you chain together!

19. 19 Hybrid LAN Topologies Hierarchical Uses layers to separate devices by their priority or function Each segment is associated with a different task within the organization

20. 20 Hybrid LAN Topologies Hierarchical (continued) Similar to an organizational chart, by may also be based on security, cost, scalability, bandwidth needs or reliability One way is to divide into layers Simple logical division between devices on a network Each layer can be represented by its own topology I.e. ring, then bus, then ring again, etc.

21. 21 Enterprise-Wide Topologies Enterprise An entire organization � all local, remote, mixture of departments Must take into account all computing needs Backbone networks � connects core network components � usually capable of more throughput Serial backbone Distributed backbone Collapsed backbone Parallel backbone Mesh backbone

22. 22 Enterprise-wide Topologies Serial backbone - simplest Two or more hubs connected to each other by a single cable Identical to daisy-chained Not suitable for large networks or long distances

23. 23 Enterprise-wide Topologies Distributed backbone A number of hubs connected to a series of central hubs or routers in a hierarchy Allows for simple expansion and limited capital outlay for growth Just add more layers to existing layers

24. 24 Enterprise-wide Topologies

25. 25 Enterprise-wide Topologies Collapsed backbone Uses a router or switch as the single central connection point for multiple subnetworks Central point of failure

26. 26 Enterprise-wide Topologies Collapsed backbone (cont) Allows you to easily interconnect different types of subnetworks Interfaces on devices Central management and troubleshooting

27. 27 Enterprise-wide Topologies Parallel Backbone Most robust A variation on collapsed backbone arrangement that consists of more than one connection from the central router or switch to each network segment

28. 28 Enterprise-wide Topologies Parallel Backbone (continued) Redundant link More $ Usually increased performance Can put most critical devices on parallel portion

29. 29 Enterprise-wide Topologies Mesh networks Routers are interconnected with other routers with at least two pathways connecting each router More complex and $ Most often used for large networks

30. 30 WAN Topologies Wide area network (WAN) topologies WAN is a network connection made up of geographically distant locations Uses both LAN and enterprise-wide topologies as building blocks, but has the added complexity of the distances involved Vendor relationships important Telco�s Also differ from LAN by the multitude of devices used

31. 31 WAN Topologies Wide area network (WAN) topologies 5 models: Peer-to-peer Ring Star Mesh Tiered

32. 32 WAN Topologies Peer-to-peer topology (Like daisy chain / serial backbone) Single interconnection for each location Good for organizations with only a few sites and the capability to use Dedicated circuits Continuous physical or logical connections between two access points that are leased from a communication provider

33. 33 WAN Topologies Ring WAN topology Each site is connected to the two nearest nodes so that entire network forms a circle (ring pattern)

34. 34 WAN Topologies Ring WAN topology (continued) Similar to local LAN ring, except that the WAN connects locations and not nodes If designed properly, a single cable problem will not affect the entire network and routers at each site can redirect traffic Expansion is difficult - $ Good for ~4-5 locations

35. 35 WAN Topologies Star WAN topology (mimics LAN star) Single site acts as the central connection point for several other points

36. 36 WAN Topologies Star WAN topology (continued) More reliable than peer-to-peer and ring Reliability increases with the number of potential routes that data can follow Provides shorter data paths between any two sites D.R. can be done with alternate communication links ISDN Expansion is easy and costs less Disadvantage � central point of failure

37. 37 WAN Topologies Mesh WAN topology Many directly interconnected locations forming a complex mesh (full and partial) Multiple paths � most fault tolerant $ - very expensive

38. 38 WAN Topologies Tiered WAN topology Sites are connected in star or ring formations and interconnected at different levels with the interconnection points organized into layers Use of more powerful routers at top and less as you move down Based on traffic patterns and functionality, so the growth is pre-determined