1. Chapter Five Physical and Logical Topologies

2. Simple Physical Topologies What does physical topology mean? The physical layout of the network nodes Bus, Ring, & Star What does logical topology mean? Network transmission methods Ethernet, Token Ring, LocalTalk, FDDI, ATM

3. Simple Physical Topologies Physical topology Physical layout of a network Physical layout of a network A Bus topology consists of a single cable—called a bus — connecting all nodes on a network without intervening connectivity devices Figure 5-1: Bus topology network

4. Simple Physical Topologies Figure 5-2: A terminated bus network

5. Simple Physical Topologies Ring topology Each node is connected to the two nearest nodes so the entire network forms a circle Each node is connected to the two nearest nodes so the entire network forms a circle One method for passing data on ring networks is token passing One method for passing data on ring networks is token passing Three byte token used to pass data Three byte token used to pass data Active topology Each workstation transmits data Each workstation transmits data Figure 5-3: A typical ring network

6. Simple Physical Topologies Token passing process: Computer ready to transmit Computer ready to transmit Computer picks up the token packet Computer picks up the token packet Adds control and data information plus the destination node’s address (the token is now a data frame) Adds control and data information plus the destination node’s address (the token is now a data frame) The token is then passed to the next node The token is then passed to the next node Once received by the destination, an acknowledgment is sent to the originating node Once received by the destination, an acknowledgment is sent to the originating node After the originating node receives the acknowledgement, it releases a new free token which is sent down the ring After the originating node receives the acknowledgement, it releases a new free token which is sent down the ring

7. Simple Physical Topologies Star topology Every node on the network is connected through a central device Every node on the network is connected through a central device Figure 5-4: A typical star topology network

8. Hybrid Physical Topologies Hybrid topology Complex combination of the simple physical topologies Complex combination of the simple physical topologies Star-wired ring Star-wired topologies use physical layout of a star in conjunction with token ring-passing data transmission method Star-wired topologies use physical layout of a star in conjunction with token ring-passing data transmission method Fault tolerance of star – reliability of token passing Fault tolerance of star – reliability of token passing Figure 5-5: A star- wired ring topology network

9. Hybrid Physical 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 In a star-wired bus topology, groups of workstations are star-connected to hubs and then networked via a single bus More expensive that star or bus More expensive that star or bus Basis for modern Ethernet networks Basis for modern Ethernet networks Figure 5-6: A star-wired bus network topology

10. Hybrid Physical Topologies Daisy-Chained A Daisy chain is linked series of devices A Daisy chain is linked series of devices Drawback – Large # of hubs may affect transmission integrity Drawback – Large # of hubs may affect transmission integrity Figure 5-7: A daisy- chained star-wired bus topology

11. Hybrid Physical Topologies Hierarchical hybrid topology Uses layers to separate devices by priority or function Uses layers to separate devices by priority or function Figure 5-8: A hierarchical ring topology

12. Enterprise-Wide Topologies Enterprise An entire organization An entire organization Backbone networks (commonly fiber, but may be CAT5 wiring) Serial backbone Serial backbone Distributed backbone Distributed backbone Collapsed backbone Collapsed backbone Parallel backbone Parallel backbone

13. Enterprise-Wide Topologies Serial backbone (identical to daisy-chained networks) Two or more hubs connected to each other by a single cable Two or more hubs connected to each other by a single cable Not suitable for large networks Not suitable for large networks Distributed backbone Hubs connected to a series of central hubs or routers in a hierarchy Hubs connected to a series of central hubs or routers in a hierarchy Figure 5-9: A simple distributed backbone network

14. Enterprise-Wide Topologies Figure 5-10: A distributed backbone connecting multiple LANs

15. Enterprise-Wide Topologies Collapsed backbone Uses a router or switch as the single central connection point for multiple subnetworks (subnetworks may be different types) Uses a router or switch as the single central connection point for multiple subnetworks (subnetworks may be different types) Figure 5-11: A collapsed backbone network

16. Enterprise-Wide Topologies Parallel Backbone Collapsed backbone arrangement that consists of more than one connection from central router or switch to each network segment Collapsed backbone arrangement that consists of more than one connection from central router or switch to each network segment Figure 5-12: A parallel backbone network

17. Enterprise-Wide Topologies Mesh networks Routers are interconnected with other routers, with at least two pathways connecting each router Routers are interconnected with other routers, with at least two pathways connecting each router Internet Internet Figure 5-13: An example of a mesh network

18. Wide Area Network (WAN) Topologies Peer-to-peer topology WAN with single interconnection points for each location WAN with single interconnection points for each location Dedicated circuits Dedicated circuits Continuous physical or logical connections between two access points that are leased from a telecommunication provider Figure 5-14: A peer-to-peer WAN

19. Wide Area Network (WAN) Topologies Ring WAN topology Each site is connected to two other sites so that entire WAN forms a ring pattern Each site is connected to two other sites so that entire WAN forms a ring pattern Figure 5-15: A ring-configured WAN

20. Wide Area Network (WAN) Topologies Star WAN topology Single site acts as the central connection point for several other points Single site acts as the central connection point for several other points Figure 5-16: A star- configured WAN

21. Wide Area Network (WAN) Topologies Mesh WAN topology Many directly interconnected locations forming a complex mesh Many directly interconnected locations forming a complex mesh Figure 5-17: Full-mesh and partial-mesh WANs

22. Wide Area Network (WAN) Topologies Tiered WAN topology Sites connected in star or ring formations are interconnected at different levels, with interconnection points organized into layers Sites connected in star or ring formations are interconnected at different levels, with interconnection points organized into layers Figure 5-18: A tiered WAN topology

23. Logical Topologies Refers to the way in which data are transmitted between nodes Describes the way: Data are packaged in frames Data are packaged in frames Electrical pulses are sent over network’s physical media Electrical pulses are sent over network’s physical media Logical topology may also be called network transport system Examples include: Ethernet, Token Ring, LocalTalk, FDDI, and ATM

24. Switching Component of network’s logical topology that determines how connections are created between nodes Circuit switching Circuit switching Connection is established between two network nodes before they begin transmitting data Monopolized bandwidth between two nodes (not efficient) PC - ISP Message switching Message switching Establishes connection between two devices, transfers information to second device, and then breaks connection E-mail systems Packet switching Packet switching Breaks data into packets before they are transmitted Ethernet and FDDI (including the Internet)

25. Ethernet Carrier Sense Multiple Access with Collision Detection (CSMA/CD) The access method used in Ethernet The access method used in Ethernet Collision Collision In Ethernet networks, the interference of one network node’s data transmission with another network node’s data transmission Collision rate > 5% is unusual Jamming Jamming Part of CSMA/CD in which, upon detection of collision, station issues special 32-bit sequence to indicate to all nodes on Ethernet segment that its previously transmitted frame has suffered a collision and should be considered faulty

26. Ethernet Figure 5-19: CSMA/CD process

27. Ethernet On an Ethernet network, an individual network segment is known as a collision domain Portion of network in which collisions will occur if two nodes transmit data at same time Portion of network in which collisions will occur if two nodes transmit data at same time Data propagation delay Length of time data take to travel from one point on the segment to another point Length of time data take to travel from one point on the segment to another point If to long, cannot identify collisions accurately If to long, cannot identify collisions accurately

28. Ethernet Demand priority Method for data transmission used by 100BaseVG Ethernet networks Method for data transmission used by 100BaseVG Ethernet networks Demand priority requires an intelligent hub Demand priority requires an intelligent hub Figure 5-20: CSMA/CD versus demand priority

29. Ethernet Traditional Ethernet LANs, called shared Ethernet, supply fixed amount of bandwidth that must be shared by all devices on a segment Switch Device that can separate network segments into smaller segments, with each segment being independent of the others and supporting its own traffic Device that can separate network segments into smaller segments, with each segment being independent of the others and supporting its own traffic Switched Ethernet Newer Ethernet model that enables multiple nodes to simultaneously transmit and receive data over logical network segments Newer Ethernet model that enables multiple nodes to simultaneously transmit and receive data over logical network segments

30. Ethernet Figure 5-21: A switched Ethernet network * Increase the effective bandwidth of a network segment

31. Ethernet Gigabit Ethernet 1 Gigabit Ethernet 1 Gigabit Ethernet Ethernet standard for networks that achieve 1- Gbps maximum throughput 10 Gigabit Ethernet 10 Gigabit Ethernet Standard currently being defined by IEEE 802.3ae committee Will allow 10-Gbps throughput Will include full-duplexing and multimode fiber requirements

32. Ethernet Ethernet frame types: IEEE 802.3 (“Ethernet 802.2” or “LLC”) IEEE 802.3 (“Ethernet 802.2” or “LLC”) Novell proprietary 802.3 frame (or “Ethernet 802.3”) Novell proprietary 802.3 frame (or “Ethernet 802.3”) Ethernet II frame Ethernet II frame IEEE 802.3 SNAP frame IEEE 802.3 SNAP framePadding Bytes added to data portion of an Ethernet frame to make sure this field is at least 46 bytes in size Bytes added to data portion of an Ethernet frame to make sure this field is at least 46 bytes in size

33. IEEE 802.3 (“Ethernet 802.2” or “LLC”) Default frame type for versions 4.x and higher of Novell NetWare network operating system Sometimes called LLC (Logical Link Control) frame Sometimes called LLC (Logical Link Control) frame In Novell’s lingo, this frame is called Ethernet 802.2 frame In Novell’s lingo, this frame is called Ethernet 802.2 frame Figure 5-22: An IEEE 802.3 frame

34. IEEE 802.3 (“Ethernet 802.2” or “LLC”) Service Access Point (SAP) Identifies node or internal process that uses LLC protocol Identifies node or internal process that uses LLC protocol Frame Check Sequence (FCS) This field ensures that data are received just as they were sent This field ensures that data are received just as they were sent Cyclical Redundancy Check (CRC) Algorithm used by FCS field in Ethernet frames Algorithm used by FCS field in Ethernet frames

35. Novell Proprietary 802.3 (or “Ethernet 802.3”) Original NetWare frame type (NetWare 3.12-) Also called: 802.3 Raw 802.3 Raw Ethernet 802.3 frame Ethernet 802.3 frame Rarely used anymore Rarely used anymore Figure 5-23: A Novell proprietary 802.3 frame

36. Ethernet II Original Ethernet frame type developed by DEC, Intel and Xerox, before IEEE began to standardize Ethernet Figure 5-24: An Ethernet II frame

37. IEEE 802.3 SNAP Adaptation of IEEE 802.3 and Ethernet II SNAP stands for Sub-Network Access Protocol Organization ID (OUI) – identifies network type Rarely used on current networks Figure 5-25: An IEEE 802.3 SNAP frame

38. Understanding Frame Types Learning about networks is analogous to learning a foreign language, with the frame type being the language’s syntax Just as you may know the Japanese word for go but how to use it in a sentence, you may know all about the IPX/SPX protocol but not how devices handle it Just as you may know the Japanese word for go but how to use it in a sentence, you may know all about the IPX/SPX protocol but not how devices handle itAutosense Feature of modern NICs that enables a NIC to automatically sense what types of frames are running on a network and set itself to that specification Feature of modern NICs that enables a NIC to automatically sense what types of frames are running on a network and set itself to that specification

39. Design Considerations for Ethernet Networks Cabling – coax or twisted-pair Connectivity devices – less expensive than comparable Token Ring or LocalTalk Number of stations – 10BaseT/100BaseTX limited to 1024 Speed – 10/100 Mbps, 1 and 10 Gbps (soon) Scalability – easily expandable Topology – 10BaseT/100BaseTX use star-wired bus hybrid topology (highly fault tolerant)

40. LocalTalk Logical topology designed by Apple Computer, Inc. Uses a transmission method called Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) Similar to CSMA/CD, except node signals intent before it actually does Similar to CSMA/CD, except node signals intent before it actually does A teleconnector is a transceiver used on a LocalTalk network Macintosh version of TCP/IP is called MacTCP

41. Token Ring Token Ring networks use the token passing routine and a star-ring hybrid physical topology The 100-Mbps Token Ring standard is known as High-Speed Token Ring (HSTR) On a Token Ring network, one workstation, called the active monitor, acts as the controller for token passing

42. Token Ring Multistation Access Unit (MAU) Regenerates signals Regenerates signals Figure 5-26: Interconnected Token Ring MAUs

43. Token Ring Control Access Unit (CAU) Connectivity device used on a Token Ring network, similar to MAU but more flexible and allows easier management of nodes Connectivity device used on a Token Ring network, similar to MAU but more flexible and allows easier management of nodes Lobe Attachment Module (LAM) Device that attaches to a CAU to expand the capacity of that device Device that attaches to a CAU to expand the capacity of that device

44. Token Ring Token Ring networks with STP cabling may use a type 1 IBM connector A DB-9 connector is another type of connector found on STP Token Ring networks Figure 5-27: Type 1 IBM and DB-9 Token Ring connectors

45. Token Ring Media filter Device that enables two types of cables or connectors to be linked Device that enables two types of cables or connectors to be linked Token Ring media filter Enables DB-9 cable and type 1 IBM cable to be connected Enables DB-9 cable and type 1 IBM cable to be connected Figure 5-28: A Token Ring media filter

46. Token Ring Token Ring switching Like Ethernet networks, Token Ring networks can take advantage of switching to better utilize limited bandwidth Like Ethernet networks, Token Ring networks can take advantage of switching to better utilize limited bandwidth Token Ring frames IEEE 802.5 Token Ring frame IEEE 802.5 Token Ring frame IBM Token Ring frame IBM Token Ring frame Figure 5-29: An IBM Token Ring frame

47. Design Considerations for Token Ring Networks Cabling – shielded/unshielded twisted pair Connectivity devices – more expensive than Ethernet Number of stations – 255 STP – 72 UTP Speed – 4/16/100 Mbps Scalability – Easily daisy-chain MAUs Topology – Star-wired ring topology (highly fault-tolerant)

48. Fiber Distributed Data Interface (FDDI) Logical topology whose standard was originally specified by ANSI in mid-1980s and later refined by ISO Double ring of multimode or single mode fiber to transmit data Figure 5-30: A FDDI network

49. Asynchronous Transfer Mode (ATM) Describes both a network access method & a multiplexing technique Logical topology that relies on a fixed packet size to achieve data transfer rates up to 9,953 Mbps Typically used on WANs The fixed packet in ATM is called a cell A unique aspect of ATM technology is that it relies on virtual circuits Connections between network nodes logically appear to be direct, dedicated links between the two nodes Connections between network nodes logically appear to be direct, dedicated links between the two nodes

50. Asynchronous Transfer Mode (ATM) ATM uses circuit switching, which allows ATM to guarantee a specific quality of service (QoS) QoS – standard that specifies that data will be delivered within a certain period of time after the transmission ATM technology can be integrated with Ethernet or Token Ring networks through the use of LAN Emulation (LANE) ATM is very expensive Gigabit Ethernet is a better choice