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Class 10

Class 10. Chapter 10 - Network Access and Transmission Methods. Network Access Objectives. In this chapter, you will learn to: Recognize simple and complex physical topologies used in data networks Describe Ethernet and the CSMA/CD network access method

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Class 10

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  1. Class 10 Chapter 10 - Network Access and Transmission Methods

  2. Network Access Objectives In this chapter, you will learn to: • Recognize simple and complex physical topologies used in data networks • Describe Ethernet and the CSMA/CD network access method • Understand the different types of Ethernet access methods • Describe the techniques used in the Token Ring, ATM, and FDDI network access methods • Identify the main characteristics of network transmission methods, such as X.25, Frame Relay, T-Carriers, ISDN, DSL, cable, and SONET

  3. Bus A bus topology consists of a single cable connecting all nodes without intervening devices. With just 1 channel, every node shares the bus’s total capacity. When one node wishes to transmit, it broadcasts an alert informing all other stations to be silent. At the ends of the bus are terminators – resistors that absorb signals so that they don’t bounce back through the bus. Simple to build, but very limited in terms of expansion (rarely above 12 nodes), and not fault tolerant – 1 break in the circuit will take down the entire bus. With termination

  4. Ring A ring topology is a closed loop system, with packets flowing in one direction around the loop Data transmission is handled by token passing – a 3-byte packet is passed from node to node. If a node needs to transmit, it adds control, destination info, and data to the token and sends it along the ring. Since each node acts as a repeater, both breaks in the cable and failures in workstations will affect traffic flow. Pure rings are cumbersome to wire, thus limiting the number of nodes.

  5. Star In a star topology, every node is connected through a central device. It uses the bus system’s broadcast method of gaining permission to send data. A failure of any single cable only affects 1 node of the system – thus making the topology fairly fault-tolerant. However, a failure of the hub could take out the entire network. This topology require the most cabling, but connection points can be easily moved, and the system is highly scalable.

  6. Hybrid Physical Topologies The Star-Wired Bus: The most popular topology combines busses with star centralization. The central hubs are wired together in a bus, but the nodes come off the hubs in star fashion. This design can cover longer distances, and administrators can easily isolate or interconnect different parts of the network. This is the basis for the modern Ethernet network.

  7. Hybrid Physical Topologies, cont. The Star-Wired Ring uses a physical star topology with a network ring topology. A token is passed through each machine, but in between nodes passes through a hub. This provides some fault-tolerance in the event that one of the nodes fails. This is the basis of the modern Token Ring network.

  8. Mesh Topologies A mesh topology interconnects all nodes with one another, so that there are at least 2 pathways to each node. This is the most fault tolerant of all topologies. While it can be used on a LAN, it is most often used in MANs and WANs.

  9. Mesh Topologies, cont Due to the cost of a full mesh, it is often easier and cheaper to eliminate some of the links and create a partial mesh.

  10. Network Access Methods • A standard that determines how nodes communicate and avoid interfering with one another is called a network access method. • Network access methods belong to both the physical and data link layers of the OSI model, while the addressing and delivery methods belong to the network and transport layers. • For instance, an Ethernet access method can use either TCP/IP or IPX/SPX as addressing/routing protocols.

  11. The Ethernet Network Access Method • Ethernet: A network access method originally developed by Xerox in the 1970s and later improved by Xerox, Digital Equipment Corporation (DEC), and Intel. • Is IEEE standard 802.3 • Can run on a variety of network media, including both wireline and wireless channels • Uses packet switching • Frame – a data packet used in Ethernet that is between 64 and 1518 bytes. • Multiple Access - refers to the fact that multiple Ethernet nodes can be connected to a network and can monitor and issue traffic. • Is a baseband method- a transmission form in which digital signals are sent through direct current (DC) pulses applied to the wire, to the exclusion of all other transmissions.

  12. The Ethernet Network Access Method, cont. • Carrier Sense Multiple Access/Collision Detection (CSMA/CD) – The basis for Ethernet: The rules for communication used by shared Ethernet networks.

  13. The Ethernet Network Access Method, cont. Identification of the various forms of Ethernet: The format of the type is broken into 3 parts – • The bandwidth in Mbps • The type of transmission (always “Base” as a reference to baseband ethernet) • The media involved, and the run-length specified for the media. • Here are some popular combinations: • 10Base2 and 10Base5 – 10Mbps over coax • 10BaseT- 10Mbps over twisted 2-pair CAT3 lengths of up to 100meters • 10BaseF - 10Mbps over 2 strands of multimode fiber up to 1000 meters using ST connectors • 100BaseTand 100BaseTX - 100Mbps over twisted 4-pair CAT5 lengths of up to 100meters • 100BaseT4and 100BaseVG - 100Mbps over twisted 4-pair CAT3 lengths of up to 100meters at half-duplex only. • 100BaseF - 100Mbps over 2 strands of multimode fiber up to 400 meters • 1000BaseT - . 1Gbps over 4-pair CAT5e up to 100 meters

  14. The Ethernet Network Access Methods, cont.

  15. The Ethernet Network Access Methods, cont.

  16. The Ethernet Network Access Methods, cont. Switched Ethernet - enables multiple nodes to simultaneously transmit and receive data over different network segments. Switches break up broadcast domains or segments into localized areas.

  17. Token Ring • Popularized by IBM for the interconnection of mainframes and terminals • Was made into IEEE standard 802.5 • Transmits at either 4, or 16 Mbps over TP or coax. • Uses the token-passing routine and a star-ring hybrid physical topology. • There is no limit on the length of the ring. • You can put a practically unlimited number of nodes on a ring, but each node reduces the effective throughput of the ring at each station. • However, a token ring switch can divide a large ring into several virtual sub-rings. • High Speed Token Ring (HSTR) - can use either twisted pair or fiber cable as its transmission medium for speeds up to 100Mbps.

  18. FDDI and CDDI • Fiber Distributed Data Interface and Copper Distributed Data Interface -- Network access methods whose standards were originally specified by ANSI in the mid-1980s and later refined by ISO. It works similarly to Token Ring, but with 2 fault-tolerant rings running in opposite directions. • Typically used on backbones and CAN/MAN interconnects. • Uses a double ring of fiber (FDDI) or copper (CDDI) to transmit data speeds of up to 100 Mbps. • FDDI can have a run length of up to 62 miles. CDDI can cover several miles.

  19. ATM • Asynchronous Transfer Mode (ATM) - a standard that describes both a network access method and a multiplexing technique. Is typically used for convergent systems. Developed by Bell Labs in 1993, but has spent the years since in cross-development because there has been little agreement on standards. • ATM is the among the most expensive and complex of all the access protocols. Simpler technologies (like GigE) have caught up with many of the potential benefits. • Terminology in ATM: • Cells – all data is sent out in packets that are 48 bytes of data plus a five-byte header. The fixed packet size allows data transfer rates of up to 9.95Gbps. • Virtual circuits - logical connections between network nodes, as a method of conserving bandwidth. A physical channel is used only when there is data to transmit (no “keep-alives” or circuit maintenance) • Quality of Service (QoS) - a standard that specifies that data will be delivered within a certain time period after its transmission. 4 levels of QoS are available, depending on the priority or type of data being sent. • Compatibility - ATM cells can support multiple types of higher-layer protocols, including TCP/IP and IPX/SPX through the use of LAN Emulation.

  20. Network Transmission Methods As opposed to network access methods (that deal largely with nodes connecting to channels), Network Transmission Methods deal with how to maximize throughput over long-distance leased lines. • X.25 - a set of protocols designed for long-distance data transmission and standardized by the ITU in the mid-1970s. • X.25 transmits analog signals via packet-switched technology up to 2.048 Mbps. • X.25 ensures data reliability by verifying the transmission at every hop along the path between transmitter and receiver. • Is used widely in Europe, but not so much in the US.

  21. Network Transmission Methods, cont. • Frame Relay - an updated, digital version of X.25 (ITU standardized in 1984) that also relies on packet switching. • It does not guarantee the delivery of data, and relies on a shared “cloud” of backbones to make connections. • Offers bandwidths of up to 45 Mbps, but the NSP guarantees a Committed Information Rate(CIR) – a minimum amount of bandwidth between source and destination. • By using a cloud, the user only has to pay for the CIR – which is cheaper than paying for a point-to-point dedicated connection.

  22. Network Transmission Methods, cont. • Integrated Services Digital Network (ISDN) An international standard, established by the ITU for transmitting data over digital lines. • Typically relies on the PSTN network • Connections may be dial-up or dedicated • Run lengths are typically 18000 feet • To use analog equipment on an ISDN line, you need a Terminal Adapter – a kind of inverse modem. • All ISDN connections are based on two types of 64 Kbps channels: • B Channels: employ circuit-switching techniques to carry voice, video and other types of data over the ISDN connection. • D Channels: employ packet switching techniques to carry information about the call, such as session initiation and termination signals, caller identity, call forwarding, and conference calling signals.

  23. Network Transmission Methods, cont. ISDN circuit

  24. Network Transmission Methods, cont. ISDN circuit

  25. Network Transmission Methods, cont. A T-Carrier is the general name for a group of transmission methods that includes T1s, fractional T1s, and T3s. • T- technology can use unshielded or shielded twisted-pair copper wiring. • T-carriers are examples of dedicated leased lines. • They are also private/dedicated circuits.

  26. Network Transmission Methods, cont.

  27. Network Transmission Methods, cont. • CSU/DSU (Channel Service Unit/Data Service Unit) - the connection point for a T-carrier line at the customer’s site. • CSU: provides termination monitoring. • DSU: converts the digital signals used by bridges, routers and multiplexers into the digital signal sent via the cabling.

  28. Network Transmission Methods, cont. A multiplexer (MUX) is a device used to combine multiple incoming channels for transmission over one circuit. An inverse multiplexer (IMUX) is a device that combines multiple T-class circuits into 1 virtual channel.

  29. Network Transmission Methods, cont. A Digital Access and Cross-connect System (DACS) is a takeoff from the IMUX in that it can split a T-carrier down to the DS-0 level, and recombine several of those DS-0’s into smaller virtual T’s.

  30. Network Transmission Methods, cont. • Digital Subscriber Line (DSL) uses advanced data modulation techniques to achieve extraordinary throughput over regular phone lines or ISDN lines. • DSL is best suited for communications along the local loop (around 3 miles, depending on type). • Downstream - data traveling from the telecommunications carrier’s end office. • Upstream - data traveling from the customer to the carrier’s end office. • Types of DSL • ADSL-Asymmetrical: downstream throughput is usually much higher than upstream throughput. • SDSL-Symmetrical - provides equal capacity for data traveling both upstream and downstream. • VDSL-Very-High Bit Rate – very high speed over short distances • IDSL-ISDN Based

  31. Network Transmission Methods, cont. Browse to http://www.frii.com/services/nendsl.html to see the variety speeds and types of DSL avaialble from a typical provider

  32. Network Transmission Methods, cont.

  33. Network Transmission Methods, cont. Cable Modems take advantage of existing CATV media and facilities by sending data over an unused portion of the CATV spectrum

  34. Network Transmission Methods, cont. Synchronous Optical Network (SONET) implements a fault-tolerant ring structure over aggregates of T-class lines of fiber to interconnect WANs over long distances.

  35. Network Transmission Methods, cont. Grades of SONET rings are measured by Optical Carrier (OC) levels.

  36. Summary • Three simple physical topologies exist: bus, star, and ring. • Ethernet is a network access method that uses Carrier Sense Multiple Access with Collision Detection (CSMA/CD) to determine how multiple nodes share a single channel. • Token Ring is a network access method originally designed by IBM and now specified by IEEE in its 802.5 project. • Digital subscriber line (DSL) is a transmission method that uses advanced data modulation techniques to achieve extraordinary throughput over regular phone lines. It comes in several different varieties.

  37. Assignments • Review Questions: (chap10) 1-25,

  38. End of Class Quiz • Which physical topology requires terminators? • What physical and logical topologies form the bases of modern token ring networks? • What physical topology is most expensive to implement? • What occurs when 2 nodes on an ethernet network transmit simultaneously? • What occurs when 2 nodes on an token ring network transmit simultaneously? • Go to http://www.cctc.demon.co.uk/net3.htm for a clearer description of repeaters, switches, and bridges.

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