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Bandwidth for the Office

The Management of Telecommunications. Houston H. Carr and Charles A. Snyder. Bandwidth for the Office. Chapter 14. Introduction. Convergence, it its basic form, is the brining together of two or more technologies.

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Bandwidth for the Office

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  1. The Management of Telecommunications Houston H. Carr and Charles A. Snyder Bandwidth for the Office Chapter 14

  2. Introduction • Convergence, it its basic form, is the brining together of two or more technologies. • Convergence of technologies is a major cause for the need for greater bandwidth.

  3. Industry Convergence

  4. Compression • Compression has a strong influence on the effect of any bandwidth • A narrow bandwidth channel with good compression can emulate a broadband channel without compression.

  5. Transmission overhead • The overhead associated with data transmission adds 10 percent to the bandwidth for format, framing, control bits, delimiters, and communications protocol.

  6. Representative long distance charges

  7. Bandwidth Requirements for POS

  8. Bandwidth needs • Analog TV channel = 6 MHz • Digital TV channel = 1.2 – 8 Mbps compressed • One analog TV channel, digital, can hold 3 – 10 digital channels • Commercial digital teleconferencing calls for ¼ T1. • Personal videoconferencing can be achieved over ISDN BRI.

  9. Digital Subscriber Line • Digital Subscriber Line (DSL) is a technology that provides digital communications over twisted-pair copper. • Transmission speeds from 64 Kbps and T1 to 6.0 Mbps and beyond over repeaterless local loops of up to 18,000 feet in length.

  10. ISDN • ISDN was the initial DSL technology in use. • ISDN has a bandwidth of 160 Kbps for BRI, delivering two 64 Kbps bearer channels plus a 16 Kbps delta channel to homes and offices. • Original local loop • Provides digital channels over an analog circuit.

  11. Asymmetric Digital Subscriber Line (ADSL) • ADSL allows video-on-demand and other broadband communications over twisted-pair. • ADSL provides 1.2 Mbps to 6.0 Mbps digital bandwidth on an analog twisted-pair (POTS) line. • Primary use is for repeaterless T1 channels, especially for Internet access. • ADSL can not compete with CATV’s simultaneous multi-channel capacity.

  12. Asymmetric Digital Subscriber Line (ADSL)

  13. Digital limits on 24-gauge TW pair

  14. Copper Access Transmission Technologies

  15. Copper Access Transmission Technologies

  16. ISDN • ISDN has modems, but uses transceivers and not carrier based modulation. • There is an analog-to-digital conversion, but the operation converts incoming digital signals into line pulses in such a way that timing can be recovered from the line signal at the receiver. • ISDN and HDSL are transceivers • VDSL and ADSL are modems.

  17. BISDN • BISDN (Broadband ISDN) involves ISDN standards with transmission rates higher than 1.544 Mbps. • BISDN can be defined as an all-purpose, all-digital network that provides a wide range of services including, • High-speed data services • Video phone • Videoconferencing • CATV services • High-resolution graphics transmission • Plus narrowband services such as telephone, data, telemetry and facsimile.

  18. BISDN Services

  19. X.25 • X.25 was designed to provide error-free delivery using high-error-rate links. • Defined for layers 1, 2, and 3 of OSI model • Prepares and sends packets • Has a fixed available bandwidth.

  20. Frame Relay • Frame relay is an ISDN frame-mode service based upon fast packet switching. • A connection-oriented technology that supports variable-length packets at medium- to high-speed data rates. • Offered as a permanent virtual channel (PVC) service.

  21. Frame Relay Frame Format • Flags are used to delimitate the beginning and end of frame. • Header (two to four octets) contains address as well as congestion control bits. • User data field is variable length • Frame check sequence (FCS) is used to detect errors

  22. Frame relay • Operates at layers 1 and 2 of OSI Model. • Can dynamically allocate bandwidth during call setup negotiation at both the physical and logical channel level.

  23. Advantages of Frame Relay • Higher performance that traditional X.25 packet switching • Frame relay is generally a simple hardware upgrade from most X.25 devices • It supports numerous applications • It is supported by a number of firms and standards organizations.

  24. Disadvantages of Frame Relay • If an error occurs, the time to correct the error is longer than in an X.25 network operating at the same speed. • Frame relay suffers longer delays at the switching point than cell-based systems. • More difficult to manage as network grows.

  25. Switched Multimegabit Data Services • Switched Multimegabit Data Services (SMDS) is a high-speed connectionless (datagram), cell-oriented, public, packet-switched data service developed to meet the demands for broadband services. • Uses 53-byte cell (like ATM)

  26. Advantages of SMDS • Provides any-to-any connectivity with no theoretical distance limitations. • Based on a single set of standards • Offers enhanced network services, such as call screening, call verification, and call blocking.

  27. Disadvantages of SMDS • Can not easily handle delay-sensitive traffic, such as voice and video traffic. • Implementation costs related to new SMDS switches and modifications to SDMS access equipment.

  28. Synchronous Optical Network • Synchronous Optical Network (SONET) provides high-speed, highly reliable, serial digital transmission over optical fiber cable. • Provides carrier mechanisms to flexibly supply multiplex, and manage transmission rates beyond T1 and T3 speeds.

  29. Synchronous Optical Network • Transmission rates are multiples of a basic signal rate of 51.84 Mbps. • Referred to as synchronous transport signal 1 (STS-1) when an electrical signal is used or • Optical carrier 1 (OC-1) when an optical signal is used. • Higher rates are formed by combining multiple OC-1/STS-1 signals to form OC-n/STS-n.

  30. SONET/SDH Rates

  31. Advantages of SONET • SONET defines a multiplexing standard for combining lower-speed digital channels into high-speed digital transmission signals. • SONET defines standard optical interfaces for interconnecting fiber terminals from different vendors. • SONET defines a set of network management protocols to allow network to be monitored, reconfigured, and maintained form a central location.

  32. Advantages of SONET • SONET Has a flexible payload structure that can accommodate most types of digital signals. • SONET is a more stable standard than more recent entrants.

  33. Disadvantages of SONET • SONET is specifically intended for local exchange (LEC) and interexchange (IXC) carriers.

  34. Asynchronous Transfer Mode (ATM) • ATM is a variation of packet-switching technology that transmits fixed-length units of data called cells, at very high speeds. • Speeds specified for ATM range from 155.52 Mbps to 2.488 Gbps.

  35. Advantages of ATM • ATM will operate on different physical media. • Low and predictable delay • ATM’s able to support different types of traffic (voice, video, and data), either separately or in multimedia applications. • Many companies produce ATM switches.

  36. Disadvantages of ATM • ATM is expensive. • ATM is a new transfer technique, so its standards are still evolving and product stability is not ensured. • ATM creates a new set of problems for network designers and planners.

  37. 53-Byte ATM Cell (Bullet)

  38. Pros and Cons of T1 ATM • Pros • T1 lines are relatively inexpensive • Can carry LAN, voice, and video traffic from remote sites • Cons • ATM is tariffed much higher than frame relay • Voice-over-frame-relay standards should make transport of multiple data types over frame-relay more competitive against ATM.

  39. Broadband Integrated Services Digital Network • BISDN is based on transmission speeds and capabilities at the 155.52 Mbps, 622.08 Mbps, and 2.488 Gbps levels. • Differences from ISDN • ISDN uses existing telephone network infrastructure copper wires. BISN uses optical fiber. • ISDN is circuit based and only uses the D-channel for packet switching. BISDN only uses packet switching • ISDN channel bit rates are prespecified, whereas BISDN uses virtual channels without any prespecified bit rate. • BISDN is often implemented with SONET transport and ATM switching.

  40. Advantages of BISDN • BISDN can be used to interconnect LANs over wide areas at speeds equal to or greater than today’s LAN speeds. • BISDN makes large file transfers quick and easy. • BISDN can reduce cost for operating a network due to its ability to integrate a broad mix of services so the network operator can handle special services in a more standardized manner.

  41. Disadvantages of BISDN • The present cost of BISDN is greater than that of ISDN.

  42. Comparison of Broadband Technologies

  43. Compatibility of Broadband Technologies

  44. Wireless Technologies • Cellular • Microwave • Satellite and VSAT • LMDS/MMDS • Wireless T1

  45. The Management of Telecommunications: Houston H. Carr and Charles A. Snyder End of Chapter 14

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