Telecom Network
- 1. 6 C H A P T E R Telecommunications and Networks for all
- 2. Communications The transmission of a signal by way of a medium from a sender to a receiver.
- 3. Telecommunications The electronic transmission of signals for communications, including such means as: Telephone Radio Television Computer Network
- 4. Benefits of Telecommunications • Better Communication E-mail, voice mail, faxes, teleconferencing • Greater Efficiency Workflow, concurrent access • Better Access to Data File transfer, distributed databases
- 5. Modes of Data Transfer • Parallel More than one bit at the same time Printers, Processors, Motherboards • Serial One bit at a time Slower, but longer distances
- 8. Modes of Data Transfer • Simplex One-way transmission • Half-Duplex One-way at a time • Full-Duplex Two-way transmission
- 9. The Concept of Networking • Computers connected to each other so they can share data • Before Networking: SneakerNet Copy information to a floppy disk and pass it to anyone who needs it Risks?
- 10. Why Network • File Management Sharing, transferring • Application Sharing • Device Sharing Printers, Storage Devices, Modems • Workgroup Activities Scheduling, e-mail, conferencing
- 11. A Computer Network • Hardware Modems, servers, routers, NICs • Software Network operating systems Communications software • Communication Channels Cabling, microwave, etc.
- 12. Networking • Local Area Network (LAN) A group of computers (physically) connected together within a certain area • Wide Area Network (WAN) A network that extends over a larger area, such as a city block or a country
- 13. Categories of Networks • Peer-to-Peer (workgroups) Typically <10 people No central communication control device Each computer acts as client and server Inexpensive Limited security Uses each PC’s resources Windows, Windows NT/2000
- 14. Categories of Networks • Server-based Dedicated servers File, application, mail, fax, communication Centralized, shared resources Security Backup Thousands of users
- 15. Terminal-to-Host “Dumb” terminal Applications and databases reside on the host computer (server). User interacts with the application using a terminal with no processing power. 29
- 16. File/Application Server Databases (and applications) reside on the host computer (server). File server transfers data (and programs) to PCs on the network, where these “fat” PCs perform most of the processing. 30 File/Application downloaded to user
- 17. Client/Server Applications and databases reside on specialized servers. Servers do most or all of the processing and transmit the results to the “thin” clients. 31
- 18. Client/Server • The client makes a request and the server fulfills it… The client application (front-end) requests data The request is sent over the network The server (back-end) processes the request Only the requested information is returned to the client The data is presented to the user • Improved Performance Minimizes network traffic – only the information needed is transmitted
- 19. Network Terminology • Workstation Each computer attached to the network • Node Each device attached to the network (each has a unique hexadecimal MAC - Media Access Control – address e.g. 08:00:69:02:01:FC ) • Server A central repository for information • Topology The overall configuration of the network
- 20. Network Topology • Connecting every node to every other node would require N x (N-1)/2 cables • Network Topology A logical model that describes how networks are structured or configured. Bus Star Ring 24 …or combinations
- 21. Network Topologies Ring A typology that contains computers and computer devices placed in a ring. Bus Computers and computer devices are on a single line. Each device can communicate directly to all devices on the bus. Star All computers are connected via a central hub. Ring Hierarchical Star Bus Hierarchical A typology arranged in a tree-like structure.
- 22. The Role of Network Communications Software • Sending data from one node to another Recognize the data Divide the data into manageable chunks Add information to each chunk of data to identify the receiver Add timing and error checking information Put the data on the network and send it on its way
- 23. The OSI Model (Open Systems Interconnection) • Describes how network hardware and software work together in a layered fashion Each layer provides some service or action that prepares the data for delivery over the network Requests are passed from one layer to the next Each layer adds information to the data packet
- 24. The OSI Layers 7) Application – Provides application with access to the network 6) Presentation – Determines format used to exchange data among networked computers 5) Session – Allows two applications to establish a connection (name recognition, security) 4) Transport – Ensures data is error free. Repackages long messages. 3) Network – Addresses messages to proper location. Translates logical addresses into physical addresses and determines path. 2) Data Link – Packages and un-packages data packets 1) Physical – Transmits bits over physical devices
- 25. Slide 5 of 26 Mail Delivery Analogy
- 26. Data Packets • Packets are the basic units of network communications Each packet has three sections: Header: An alert signal Source & destination addresses Clock information Data Trailer – Error checking information
- 27. Protocols • From the Greek protocollon, which was a leaf of paper glued to a manuscript volume, describing its contents • The special set of rules that nodes in a telecommunication connection use when they communicate. • Protocols exist at several OSI levels in a telecommunication connection. • Both nodes must recognize and observe a protocol.
- 28. Protocols • Rules & procedures for communicating Sending Computer Breaks the data into packets Adds addressing information Prepares the data for transmission Receiving Computer Takes packets off the cable Strips the packets of addressing information Reassembles the data form the packets
- 29. Protocols • For two computers to communicate, they must be using the same set of protocols (rules) • Examples of protocols SMTP – Mail transfer protocol FTP – File transfer protocol TCP/IP – Internet protocol IPX/SPX – Novell protocol Ethernet – Physical layer protocol
- 30. Traffic Control • If two computers put data onto the cable at the same time, the packets will collide and be destroyed • There must be a way to… Access the cable without running into other data Be accessed by the receiving computer with assurance that it is intact
- 31. Access Methods • Carrier-Sense Multiple Access Each node checks the cable for traffic before sending No node can transmit data until the cable is free (no contention) If two computers transmit at the same time, they detect the collision and wait a random time to re-transmit • Token Passing
- 32. Communication Media/Channels • Cabling • Microwave/Satellite • Cellular • Infrared • Telephone Lines
- 33. Cabling Considerations • Cost • Ease of Installation & Maintenance • Reliability • Speed • Distance
- 34. Distance Considerations • Attenuation Loss of signal quality & strength Repeaters can extend the distance • Packet Collisions • Susceptibility to RF Noise
- 35. Types of Cabling • Twisted Pair Wire Cable Insulated pairs of wires historically used in telephone service Category 1 – Telephones Category 3 – Up to 10Mbps Category 5 – Up to 100Mbps
- 36. Twisted Pair Details • RF Noise Twisting cancels out electrical noise Shielded is less susceptible • Crosstalk • 10Base-T • Maximum segment ~100 meters • RJ-45 connectors
- 37. Types of Cabling • Coaxial Cable (BNC) Consists of an inner conductor wire surrounded by insulation, called the dielectric. The dielectric is surrounded by a conductive shield, which is surrounded by a non- conductive jacket. Coaxial cable has better data transmission rate than twisted pair
- 38. Coax Details • More resistant to interference and attenuation than TP • Supports longer distance and faster rates • BNC or RG6 connectors
- 39. Types of Cabling • Fiber-optic Cable Many extremely thin fibers of glass or plastic coated with a cladding and bound together in a sheathing which transmits signals with light beams. Fast transfer rates Immune to electrical interference (long distances) Hard to tap into Takes less space
- 40. Wireless Networks • Microwave Terrestrial Satellite • Cellular • Infrared Line-of-sight
- 41. Channels and Media Figure 6.7 Characteristics of channel media
- 42. Data Communications Over Telephone Lines • Computers generate a digital signal • Phone circuits were designed to accommodate an analog signal
- 43. Analog Signals • Signals of varying frequency (pitch) and amplitude (loudness) Continuous (infinite number of values) “Analogous” to the original data e.g. phone lines carry electronic signals analogous to the original voices Must be amplified (repeated) Signal picks up (and amplifies) noise Cannot differentiate between signal and noise
- 44. Digital Signals • Signals with only two possible values Discrete (fixed number of values) Repeaters can clean up noise Expects only “0” or “1” • Telephones Use analog over “local loop” to local phone office Converted to digital for longer distances Analog wave is converted to discrete digital signals
- 45. What a Modem Does Modem Modulates a digital signal into an analog signal for transmission via analog medium, then demodulates the signal into digital for receiving.
- 46. Modulation • Converts digital signals into analog signals Frequency Modulation – Vary the frequency (pitch) to express a “1” or “0” Amplitude Modulation – Vary the amplitude (volume) to express a “1” or “0” • Demodulation converts them back
- 49. Synchronization • How do analog noises get divided up into bits? Asynchronous Communications Sends stop bit (1) after 7-8 bits per character Sends start bit (0) to indicate next character Synchronous Communications Splits the channel into two channels Uses the second channel to send a clock
- 50. Error Detection • Redundancy Send everything twice • Parity 8th bit makes parity even or odd • Longitudinal Redundancy Check (LRC) Checks parity vertically & horizontally per block • Checksum Checks the last 7 digits of the sum of a block
- 51. Error Correction • Automatic Repeat Request (ARQ) Sender sends a block Receiver ACKnowledges or… Receiver sends a Negative Acknowledgement (NAK) • Full Duplex Sender keeps sending numbered blocks while awaiting acknowledgements
- 52. Finding a Path • Circuit Switching A dedicated channel (circuit) is established for the duration of the transmission (e.g. a phone call) • Packet Switching A message is divided into packets and each may take a different path (e.g. TCP/IP) • Dedicated Lines
- 53. Multiplexing • Sharing Channels Phone conversation has 4Khz bandwidth Copper wire pair has 3Mhz bandwidth • Allows multiple TV signals on coax • Frequency Division Multiplexing • Time-Division Multiplexing
- 54. Multiplexer (mux) Figure 6.11 Multiplexer Allows several telecommunications signals to be transmitted over a single communications medium at the same time.
- 55. Carriers and Services • Plain Old Telephone Service (POTS) 56Kbps • Integrated Services Digital Network (ISDN) 128Kbps • Digital Subscriber Line (DSL) 1,544Kbps • Cable Modem Receive 256K-36Mbps; send at 64K-2Mbps • T-1 1,544Kbps (or multiples/fractions thereof)
- 56. Network Management • Network Monitors Keep track of network traffic, number of packets, packet size, collisions, re- transmissions, etc. Enables planning • Network Analyzers Randomly dissects packets, analyzes problems, and determines the source
- 57. Networks and Distributed Processing • Centralized Processing Data processing that occurs in a single location or facility. • Decentralized Processing Data processing that occurs when devices are placed at various remote locations. • Distributed Processing Data processing that occurs when computers are placed at remote locations but are connected to each other via telecommunications devices. 23
- 58. Bridges, Routers, Gateways and Switches Repeaters Repeat transmission signals, allowing a cabled network to extend farther than it ordinarily would Bridges Connects two or more networks, with the same or different protocols. Can also solve traffic problems by splitting a network into two segments. Routers Feature more sophisticated addressing software than bridges. Can determine preferred paths, translating only those packets that need to be routed. Gateways Devices that monitors/controls entry to another network Switches/Hubs Points of convergence where data arrives from one or more directions and is forwarded out in one or more other directions