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DC 10 - 1
DATACOMM
John Abbott College JPC
Digital TelecommM. E. Kabay, PhD, CISSP
Director of Education, ICSA
President, JINBU Corp
Copyright © 1998 JINBU Corp.
All rights reserved
DC 10 - 2
Digital Telecomm
Digital CPE ISDN ATM Infobahn
DC 10 - 3
Digital CPE
Digital PBX Digitized Voice T-1
DC 10 - 4
Digital CPE
Digital PBX a hot seller today Turns analog signal (voice) into digital pulses Allows voice and data to be controlled from a
single central switch Digital phone converts voice to bits Codec is Coder-Decoder (opposite of Modem)
DC 10 - 5
Digital CPE
Digitized Voice Pulse code modulation (PCM)
– 8 Khz sampling– 8 bits/sample– 64Kbps data stream
Human hearing cannot distinguish digital and analog signals
Allows full range of digital transmission controls– error checking– signal regeneration
DC 10 - 6
Digital CPE
T-1 1.544 Mbps channel 24 channels using TDM Applications
– PCM on T-1 allows 24 voice links– need only 2 twisted pairs + special
equipment– resistant to EMI (high signal-to-noise ratio)– can be highly cost-effective
DC 10 - 7
Digital CPE
T-1 signalling– voice runs 64 Kbps– data needs 1 parity bit/byte: 56 Kbps
Multiplexers for T-1 lines– can share single channel among several
lower-speed devices– rent fractional T-1 from carrier
DC 10 - 8
ISDN
Integrated Services Digital Network Channels Rates Services Trends
DC 10 - 9
ISDN
Standards still in evolution CCITT working on intl agreements Expect eventual hardware interoperability
DC 10 - 10
ISDN
ISDN Channels Different bandwidths = channels Bearer channel (B-channel) 64 Kbps D-channel
– signalling data @ 16 Kbps or 64 Kbps– usually used for out-of-band signalling– often relatively low usage– used for low-priority data; e.g., e-mail
A-channel : analog communications C-channel: very low-speed data
DC 10 - 11
ISDN
Basic-Rate I/F (BRI)– 2 B-channels + 1 D-channel (2B+D)
Primary-Rate I/F (PRI)– US/Canada: 23 B-channels + 1 D-channel– 1.544 Mbps
European PRI: 30 B + D– 2.048 Mbps
Other channel arrangements– A+C: hybrid I/F– voice + data for non-ISDN phones/terminals
DC 10 - 12
ISDN
Equipment Functions TE1: Terminal Equipment Type 1
– compatible with ISDN network– e.g., ISDN-compatible phone, workstation
TE2: Terminal Equipment Type 2– not compatible with ISDN network– requires terminal adaptor (TA) to link into
ISDN
DC 10 - 13
ISDN
Network Termination Equipment NT1: Network Termination 1
– OSI Layer 1– physical and electrical connection to
network– can be changed if digital transmission
medium changes (e.g., change to optical) NT2: Network Termination 2
– OSI Layers 2 and 3– e.g., PBX, LANs
DC 10 - 14
ISDN
ISDN Services D-channel can carry info about callers Individualized call-forwarding for specific
callers Long-distance camp-on-busy function Automatic routing of 800-calls to local outlet
DC 10 - 15
ISDN
Video Motion Pictures Experts Group (MPEG) Developing standards for video signal
compression– uncompressed requires 21 Mbps for
broadcast-quality real-time digital video– MPEG II requires only 7 Mbps
Video conferencing: most of image is static– send only changes– use multirate ISDN such as 384 Kbps
channels (6 B-channels)
DC 10 - 16
ISDN
ISDN Today Not likely to see instant conversion of all
existing telecomm to ISDN Primary Rate I/F (PRI) is about same cost as
T-1: but much more flexible Residential customers a huge market
– can have voice and data on same line– but only minority of residential customers
use existing analog services--so will ISDN be commercially viable?
DC 10 - 17
ISDN
Broadband ISDN (BISDN) In initial planning phase Extremely high bandwidth (150 Mbps) Real-time broadcast video services Entertainment applications Telecommuting applications
DC 10 - 18
ATM
Asynchronous Transfer Mode Protocol for implementing BISDN Independent of bandwidth Data chunked into cells Being promoted by ATM Forum
– founded 1991– consortium of many players in datacomm
DC 10 - 19
ATM
ATM Cells 53-bytes (bytes called octets in ATM) header: 5 octets payload: 48 octets
DC 10 - 20
ATM
Physical Transmission SONET: Synchronous Optical Network SONET line speeds defined in OC-N form
– N is 51.84 Mbps– OC-1 = 51.84 Mbps– OC-3 = 155.52 Mbps
Other transmission media quite feasible
DC 10 - 21
ATM
Routing Cells Set up equivalent of virtual circuits Transmission path remains fixed for a
session Headers include routing information
– Virtual Channel Identifiers (VCIs)– Virtual Path Identifiers (VPIs)
Main differences from Frame Relay:– fixed cell sizes– different data formats
DC 10 - 22
Infobahn
Information Superhighway NOT the current Internet Usually refers to high-speed backbones BISDN is chief candidate Most of media reporting focuses on
applications, not transmission channel
DC 10 - 23
Homework Read Chapter 10 of your textbook in detail,
adding to your workbook notes as appropriate. Review and be prepared to define or expand all
the terms listed at the end of Chapter 10 of your textbook (no hand-in required)
Answer all the exercises on page 232 of the textbook using a computer word-processing program or absolutely legible handwriting (hand in with final quiz)