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Business Data Communications, Fourth Edition

Business Data Communications, Fourth Edition. Chapter 13: Communications Services. Learning Objectives. Differentiate between narrowband and wideband communications services

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Business Data Communications, Fourth Edition

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  1. Business Data Communications, Fourth Edition Chapter 13: Communications Services

  2. Learning Objectives • Differentiate between narrowband and wideband communications services • Describe the switching offices in the public switched telephone network and how the network is connected to a customer’s site • List the types of exchange carriers • Define what is meant by a virtual private network (VPN) Chapter 13: Communications Services 2

  3. Learning Objectives • Explain the concept of telephone number portability • List the differences between narrowband ISDN and broadband ISDN • Differentiate between voice-grade and wideband analog circuits • Describe the types of digital subscriber lines Chapter 13: Communications Services 3

  4. Learning Objectives • Explain how a synchronous optical network (SONET) operates • Define fast packet services including X.25, frame relay, Asynchronous Transfer Mode (ATM), and Switched Multimegabit Digital Service (SMDS) • Define the Advanced Intelligent Network and some of its services • Describe multiprotocol label switching (MPLS) Chapter 13: Communications Services 4

  5. Introduction • Long distance carrier services are very important in today’s digital environment • Enterprise networks use these services • Topics covered: • Switched and dedicated circuits • Integrated Services Digital Network (ISDN) • Fast Packet Services • Other services Chapter 13: Communications Services 5

  6. Categories of Communications Services • Narrowband Services • 64 Kbps or less channels • Wideband Services • 1.5 Mbps to 45 Mbps (North American) • 2 Mbps to 34 Mbps (International) • Broadband Services • 45 Mbps or greater (North American) • 34 Mbps or greater (International) Chapter 13: Communications Services 6

  7. Switched Circuits • Public Switched Telephone Network (PSTN) • Central office – serves local customers • Tandem toll center – connects customers to toll network • Primary toll center – intrastate toll calling • Sectional toll center – interstate calling within a region • Regional toll center – interregional toll calling Chapter 13: Communications Services 7

  8. Chapter 13: Communications Services 8

  9. Switched Circuits • Demarcation Point (DEMARC) • Point of connection between a customer’s telephone equipment and the common carrier network • Network Interface Unit (Residential customer) • Minimum Point of Entry (Business customer) Chapter 13: Communications Services 9

  10. Chapter 13: Communications Services 10

  11. Switched Circuits • Local Exchange Carriers (LECs) • Incumbent LECs (ILECS) • Baby Bells • Originally provided service in a limited area • Now can compete for interLATA services • Competitive Local Exchange Carriers (CLECS) • Not limited in area of coverage • Competitive Access Provider (CAP) connects a user directly to interexchange carrier. Chapter 13: Communications Services 11

  12. Switched Circuits • Virtual Private Network (VPN) • Has components of both a private and public network • Allows a private enterprise network to use a public network, yet maintain privacy • Packets only travel to nodes connected to the VPN, although they use the PSTN Chapter 13: Communications Services 12

  13. Chapter 13: Communications Services 13

  14. Switched Circuits • Telephone Number Portability • Local number portability – if you move within the same city, you can keep the same telephone number • Number is looked up in a database • Interim number portability – a telephone call can be forwarded to another number • Makes it appear that a number follows a user • Also implemented by Personal Communication Services (PCS) Chapter 13: Communications Services 14

  15. Switched Circuits • Integrated Services Digital Network (ISDN) • Digital form of switched circuits • Combines voice, video, data on a single line • Narrowband ISDN • Speeds of 1.5 Mbps or lower • Made up of B channels (data) and D channels (signalling) • Basic Rate Interface (BRI) – 2B + D • Primary Rate Interface (PRI) – 23 B + D Chapter 13: Communications Services 15

  16. Chapter 13: Communications Services 16

  17. Chapter 13: Communications Services 17

  18. Switched Circuits • Integrated Services Digital Network (ISDN) • Broadband ISDN (BISDN) • Speeds above 1.5 Mbps • Common speeds of 25 Mbps up to Gigibit speeds • Newer technology than ISDN • Used with frame relay, ATM and SMDS (fast services described later) Chapter 13: Communications Services 18

  19. Dedicated Circuits • Leased circuit from a common carrier • Data travels over the same line to its destination (as opposed to dial-up line) • Line is available 24 hours a day, 7 days a week Chapter 13: Communications Services 19

  20. Dedicated Circuits • Voice-Grade Circuits • Intended for voice conversations • Operates at 4000 Hz • Category 3 twisted pair cable used • Formerly analog, now primarily digital lines • Wideband Analog Circuits • Multiples of voice-grade circuits • 48,000 Hz can handle 12 voice-grade channels Chapter 13: Communications Services 20

  21. Dedicated Circuits • T-Carrier Circuits • Dedicated digital lines • Switched 56 service used prior to T-1 • Maximum transmission was 56 Kbps • Uses a digital service unit (DSU) instead of a modem • Digital Signal (DS) service • Hierarchy of digital signals • Gives a name to each level of service Chapter 13: Communications Services 21

  22. Chapter 13: Communications Services 22

  23. Dedicated Circuits • T-Carrier Circuits • DS levels are associated with T-Carrier lines • T-1 transmit at 1.5 Mbps • Fractional T1 • For those who don’t need the entire capacity of T1 • Transmit at some fraction of 1.5 Mbps • 128 Kbps, 256 Kbps, 384 Kbps, 512 Kbps, 768 Kbps Chapter 13: Communications Services 23

  24. Dedicated Circuits • Digital Subscriber Line • Fast transmission over dedicated circuit • Used for residential and small business customers • No dial up is needed • Special modem (splitter) is used Chapter 13: Communications Services 24

  25. Dedicated Circuits • Digital Subscriber Line • Types • Asymmetric DSL (ADSL) • Upstream and downstream speeds are different • ADSL Lite • Slower version of ADSL • High Bit-Rate DSL (HDSL) • Oldest DSL • Transmission speed 1.5 Mbps • HDSL2 transmits up to 3Mbps Chapter 13: Communications Services 25

  26. Dedicated Circuits • Digital Subscriber Line • Types • ISDN DSL (IDSL) • Transmits digital data on twisted pair lines • Bypasses central office switches • Transmits 128 Kbps in each direction • Rate Adaptive DSL (RADSL) • Modems adjust transmission rate based on network conditions • 40 Kbps to 7 Mbps (downstream), 768 Kbps (upstream) Chapter 13: Communications Services 26

  27. Dedicated Circuits • Digital Subscriber Line • Types • Very High-Rate DSL (VDSL) • Must be 1,000 feet or less from central office • Used by the telephone company to connect parts of the telephone network • 12.96 Mbps to 55 Mbps (downstream), 3 Mbps (upstream) • Voice Over DSL (VoDSL) • Voice and data on the same copper line • Special version of Voice over IP (VoIP) Chapter 13: Communications Services 27

  28. Dedicated Circuits • Synchronous Optical Network (SONET) • Used in fiber-optic networks • Standard set by the Exchange Carriers Standards Association (ECSA) • Subset of Synchronous Digital Hierarchy (SDH) • Optical Carrier levels defined at the physical layer of the OSI model • Speeds from 51.8 Mbps to 2.48 Gbps Chapter 13: Communications Services 28

  29. Chapter 13: Communications Services 29

  30. Fast Packet Services • Faster, more reliable transmission services • X.25 • First fast packet service • Uses store-and-forward on packet switching networks • Servers and clients do not have to transmit at the same speed • Ensures data integrity Chapter 13: Communications Services 30

  31. Fast Packet Services • Frame Relay • Faster than X.25 at a lower cost • No data integrity • Packets switched to destination without store-and-forward • Little or no error checking done • Digital networks have few errors, so frame relay works well • Upper layer software must catch any errors Chapter 13: Communications Services 31

  32. Chapter 13: Communications Services 32

  33. Fast Packet Services • Frame Relay • No flow control, so some frames may be discarded if not accepted by receiving device • Users specify lines speed and Committed Information Rate (CIR) • CIR is maximum rate for delivery of packets • If more transmitted than the CIR, some will be discarded • Notifications can be sent if packet transmission is slowing due to network conditions Chapter 13: Communications Services 33

  34. Fast Packet Services • Asynchronous Transfer Mode (ATM) • Very fast form of packet switching • Packets are called “cells” • 53 bytes long • Transmitted on a virtual circuit • Transmits video, audio, data • Used to implement BISDN • 1.5 Mbps to 622.1 Mbps Chapter 13: Communications Services 34

  35. Fast Packet Services • Asynchronous Transfer Mode (ATM) • No error detection done, which makes transmission much faster • Validity of data checked at upper layers • Connection-oriented network • Permanent virtual circuit (PVC) • Switched virtual circuit (SVC) • Quality of Service (QoS) Chapter 13: Communications Services 35

  36. Chapter 13: Communications Services 36

  37. Fast Packet Services • Switched Multimegabit Data Service (SMDS) • Used on packet switching networks • Used for intermittent data transmission • One use is to connect LANs via a switched WAN circuit for large data transfers • Speeds between 1 Mbps and 34 Mbps • Connectionless service Chapter 13: Communications Services 37

  38. Chapter 13: Communications Services 38

  39. Chapter 13: Communications Services 39

  40. Fast Packet Services • Advanced Intelligent Networks • Signaling System 7 (SS7) • Used in 1970s to implement packet switching on the telephone network • It is a protocol • Allowed services such as caller ID • Services controlled by signaling transfer points (STPs) Chapter 13: Communications Services 40

  41. Chapter 13: Communications Services 41

  42. Fast Packet Services • Advanced Intelligent Networks • Intelligent Network 1 (IN/1) • Developed to provide logic for new services • Service control points (SCPs) • Database to store special telephone services • 800 service, calling card were introduced Chapter 13: Communications Services 42

  43. Fast Packet Services • Advanced Intelligent Network (AIN) • Advanced Intelligent Network (AIN) • Improvement on IN/1 • Many new services • 866, 877, 888 as well as 800 • Disaster recovery service • Area number calling service • Do not disturb service • Alternate destination on busy Chapter 13: Communications Services 43

  44. Fast Packet Services • Multiprotocol Label Switching (MPLS) • Allows connection of many different types of networks • Combines layer 2 switching with layer 3 routing • Defines a set of protocols to allow fast packet services to operate over IP networks • Label switching routers (LSRs) used to route packets • Label edge routers (LERs) labels packets and route them on the MPLS network Chapter 13: Communications Services 44

  45. Chapter 13: Communications Services 45

  46. Summary • Standards such as narrowband, wideband, and broadband have been developed for communications services • Many types of switching centers in the telephone system • Point of connection is used for business and residential customers • Local exchange carriers provide service Chapter 13: Communications Services 46

  47. Summary • Virtual Private Networks use components of private and public networks • ISDN was the first totally digital network • Several types of dedicated circuits exist, from voice-grade circuits to DSL • SONET is used on fiber-optic networks Chapter 13: Communications Services 47

  48. Summary • X.25, frame relay, ATM, and SMDS are packet-switching services • Telephone system has evolved into a very sophisticated intelligent system • MPLS allows the interconnection of many of the fast switching systems in today’s networks Chapter 13: Communications Services 48

  49. Chapter 13 Complete

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