1. CHAPTER 4 Data Interfaces and Transmission
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

2. OVERVIEW Standards Organizations Digital Interfaces (DTE to DCE)
Focus on RS-232-C
Other Interface Standards
Transmission Media
Digital Transmission
Analog Transmission
Modulation Techniques
Types of Modems
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

3. STANDARDS ORGANIZATIONS
A “standard” is an agreed upon method for accomplishing a given task
In data communications standards are used to define interfaces, transmission methods, protocols, etc.
Standards can arise in different ways
Manufacturer’s product becomes default standard.
Federal government develops a requirement that becomes a standard .
Organizations can develop and publish the standard and manufacturers can adhere to it.
Other organizations can adopt similar standards and “rename” them using a different nomenclature.
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

4. STANDARDS ORGANIZATIONS (cont.)
ANSI - American National Standards Institute
IEEE - Institute of Electrical and Electronics Engineers
EIA - Electrical Industry Association
NIST - National Institute of Standards and Technology
Formerly NBS, National Bureau of Standards
ITU - International Telecommunications Union
CCITT - Consultative Committee on International Telephone and Telegraph
ISO - International Standards Organization
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

5. INTERFACE TYPES What is an interface? What is an interface standard?
The point at which one device connects to another
What is an interface standard?
A description which exactly defines the electronic signals required for communication between two devices
In data communication, we look at a standard from two perspectives:
DTE - Data Terminal Equipment
DCE - Data Circuit-terminating Equipment
a.k.a., Data Communications Equipment
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

6. FIGURE 4-3: DTEs AND DCEs Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

7. FIGURE 4-4: THE DB25 CONNECTORS (ISO Standard 2110)
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

8. FIGURE 4-1: RS-232-C VOLTAGE LEVELS
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

9. FIGURE 4-2: RS-232-C TRANSMISSION OF THE ASCII CHARACTER "A” (read right to left)
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

10. FIGURE 4-5: RS-232-C SIGNALS
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

11. MINIMUM RS-232-C SIGNALS Asynchronous Transmission
TD - Transmit Data
RD - Receive Data
SG - Signal Ground
Synchronous Transmission
TC - Transmit Clock
RC - Receive Clock
XTC - External Transmit Clock
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

12. FIGURE 4-6: USING CLOCK SIGNALS TO TIME DATA TRANSMISSION
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

13. RS-232-C CONTROL SIGNALS
Uses voltages to send for control purposes rather than transmission of data
volts: On, Raised, Asserted
volts: Off, Lowered, False
Common Control Signals:
From DTE to DCE From DCE to DTE
DTE - Data Terminal Ready DSR - Data Set Ready
RTS - Request to Send CTS - Clear to Send
RI - Ring Indicator
DCD - Data Carrier Detect
SQ - Signal Quality
DRS - Data Rate Select DRS - Data Rate Select
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

14. FIGURE 4-7: CONNECTING DTEs AND DCEs WITH RS-232-C
Handshaking - the interaction of control signals between devices
Used during establishment of a connection between two DTEs
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

15. TERMINAL EQUIPMENT: HALF VS. FULL DUPLEX Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

16. FIGURE 4-8: AN ASYNCHRONOUS NULL MODEM CABLE
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

17. PROBLEMS WITH RS-232-C
Uses one wire for each signal, with no return, and a common signal ground
Top transmission speed - 20 Kbps
(often used at higher rates but violates original standard).
Distance - 50’ between DTE and DCE
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

18. RS-449, RS-422-A, RS-423-A
RS Basic interface document, referring to the electrical characteristics of RS-422-A and RS-423-A, and the mechanical DB37 and DB9 connectors.
RS-422-A uses two wires for each signal. It can be used at data rates up to 10 Mbps.
RS-423-A uses one wire for each signal, with a common return for each direction. It can be used at data rates up to 100 Kbps.
Secondary Channel moved to separate connector
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

19. FIGURE 4-9: DB37 AND DB9 CONNECTORS (ISO Standard 4902)
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

20. FIGURE 4-10: RS-232-C AND RS-449 SIGNAL EQUIVALENTS
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

21. FIGURE 4-11: RS-422-A AND RS-423-A SPEED AND DISTANCE LIMITATIONS
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

22. OTHER ALTERNATIVES Serial Alternatives Non-Serial Alternatives
USB - Universal Serial Bus (12 Mpbs)
IEEE High Performance Serial Bus (400 Mbps)
a.k.a., Firewire
Non-Serial Alternatives
Internal Modems (PCI/ISA)
On-Board Modems
Parallel Transmission
LAN Interface
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

23. FIGURE 4-21: USING MODEMS WITH ANALOG CIRCUITS
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

24. FIGURE 4-12: USING DSUs AND CSUs WITH DIGITAL CIRCUITS
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

25. ANALOG VS. DIGITAL DCE Analog DCE - translates D/A and A/D at each end
Converts digital signals received from DTE to analog carrier signals
Converts analog carrier signals into digital signals sent to DTE
Digital DCE
Analog to Digital conversion
Uses a Digital Service Unit (DSU) to shape the waveform for the digital transmission media
Digital to Digital conversion
Converts digital signals from DTE to digital carrier signal
Converts digital carrier signals into digital signals to DTE
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

26. ANALOG VS. DIGITAL DCE (cont.)
Analog DCE (modems)
Used for both dial up and leased line services
Digital DCE (DSUs)
Used primarily with leased line services
Similar devices used with switched services (ISDN, DSL)
Requires a Channel Service Unit (CSU) for testing and conditioning purposes
A DSU & CSU may be included in same unit
Both modems and DSU/CSUs are considered CPE
Interface to carrier network differs but DTE to DCE interface usually EIA RS-232-C or RS-449
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

27. BANDWIDTH:
Definition: Measure of information carrying capacity of signals
Digital Bandwidth
Measured in bits per second
some LANs require millions of bits per second (Mbps)
Analog Bandwidth
Measured by the frequency range required to transmit signals
voice transmission uses range from 300 to 3,300 cycles per second (Hz) or a total of 3000 Hz
In data communication, people generally don’t use this measurement very often
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

28. INFORMATION CONTENT MESSAGE TYPE BITS
A typical airline reservation 200
A typical telegram 400
A typical electronic funds transfer 500
A videophone frame 100,000
A newspaper-quality photograph 100,000
A document page in facsimile form 200,000
A brief telephone voice message 1,000,000
A color television frame 1,000,000
A high-quality color photograph 2,000,000
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

29. DETERMINING BANDWIDTH REQUIREMENTS
Amount of data transmitted
Overhead Associated with transmission method
Start/Stop bits, Parity, Sync Characters, etc.
Anticipated Error Rate
Time allowed to complete transmission
How long you’re willing to wait
What you want is a figure in “bits per second”
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

30. CARRIER SERVICES BY BANDWIDTH
Voice Grade Channel (DS-0)
Up to 56 Kbps analog
64 Kbps digital
Dial up or leased line
T-1 Carrier (DS-1)
1.544 Mbps
24 VG Channels using Time Division Multiplexing (TDM)
Voice digitized using Pulse Code Modulation (PCM)
Uses two twisted pair, one for transmit and one for receive
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

31. CARRIER SERVICES BY BANDWIDTH (cont.)
Fractional T-1
Uses only a portion of the 24 channels
Requires T-1 access to CO or POP
T-1C (DS-1C)
48 VG channels, Mbps (2 T-1s)
T-2 (DS-2)
96 VG channels, Mbps (4 T-1s)
T-3 (DS-3)
672 VG channels, Mbps (28 T-1s)
SONET (Fiber Optics)
From Mbps (OC-1) and up
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

32. TRANSMISSION MEDIA Twisted Pair Coaxial Cable Fiber Optic Cable
Satellite
Microwave
Others
Wireless (radio signals)
Private using CPE, Public using Cellular Carrier services
Infrared
Between buildings, between devices (PC to Printer)
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

33. TWISTED PAIR Copper wire coasted with insulating material
Twisting helps reduce noise do to radio and electromagnetic interference
Often used in buildings for LAN and PBX station connections
Also used in telco outside plant (local loops)
Over telco facilities generally limited to Hz range
Maximum possible in telco environment Hz
Higher data rates (100 Mbps) possible on short connections with shielding or without going through telco equipment
Example: CAT5 cabling for LANs
Big advantage - Cheap to purchase and install
Uses modular jacks
Can carry both voice and data
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

34. FIGURE 4-16: TELEPHONE CHANNEL BANDWIDTH
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

35. FIGURE 4-17: COAXIAL CABLE
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

36. FIGURE 4-18: SATELLITE TRANSMISSION
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

37. FIGURE 4-19: TERRESTRIAL MICROWAVE TRANSMISSION
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

38. FIBER OPTIC Very high bandwidth (can exceed 1 trillion bps)
Light shined through a glass fiber
Turn light on/off
Use different frequencies (colors) to carry multiple signals and increase bandwidth - wave division multiplexing
Expensive to install
special terminating equipment and training required
Used primarily for high volume applications
Internet backbone, intertoll trunks
can also be used for connection of switches/hubs in single building or campus environment
Not affected by electromagnetic or radio interference
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

39. FIGURE 4-20: A COMPARISON OF TRANSMISSION MEDIA
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

40. TRANSMISSION MEDIA (cont.)
Choice of media (if possible) varies on application
LAN (intra-building/campus)
WAN (long distances between locations)
Often a leased circuit or dialup connection is a combination of media
“Last mile” generally most important (limiting)
Baseband vs. Broadband
Baseband: Single signal over single media
Broadband: Multiple signals over same media
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

41. DIGITAL TRANSMISSION
Requires DSUs/CSUs at each end of leased line connection
Similar equipment required for switched digital services
AT&T Dataphone Digital Service
First truly digital leased line service
Four wire (two pair) required
2400, 4800, 9600, 56K, 64K bps
T-1 Carrier Service
Single Mbps
24 VG channels
Fractional (requires full T-1 local loop)
Others available (ISDN, DSL, T-2, T-3, SONET)
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

42. FIGURE 4-13: DIGITAL REPEATERS AND SQUARE WAVE REGENERATION
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

43. FIGURE 4-14: DIGITAL AND ANALOG SIGNALS
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

44. FIGURE 4-15: SINE WAVE Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

45. MODEMS Modulation - conversion of digital signals to analog
Demodulation - conversion of analog signals to digital
Modems required for any broadband transmission medium
Leased line modems
Dial up modems
Dumb - user dials destination number on telephone
Smart - modem capable of dialing and establishing connection
Different modems use different modulation techniques
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

46. FIGURE 4-22: AMPLITUDE MODULATION (Amplitude Shift Keying - ASK)
Susceptible to variations in transmission quality
Full duplex: add second signal on another frequency
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

47. FIGURE 4-23: FREQUENCY MODULATION (Frequency Shift Keying - FSK)
Less susceptible to variations in transmission quality
Full duplex: add two more frequencies
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

48. 300 BPS, BELL 103/113 USING FSK ORIGINATING END ANSWERING END
Transmit 1070 Hz SPACE 2025 Hz SPACE
1270 Hz MARK 2225 Hz MARK
Receive 2025 Hz SPACE 1070 Hz SPACE
2225 Hz MARK 1270 Hz MARK
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

49. FIGURE 4-24: PHASE MODULATION (Phase Shift Keying - PSK)
Less susceptible to variations in transmission quality
Uses fewer frequencies than FSK
Full duplex: add second frequency
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

50. FIGURE 4-25: DIBIT PHASE SHIFT KEYING USING THE BELL 212A SPECIFICATION
1200 bps , 600 baud (changes per second)
Must recognize four different phase changes
Each transition / change, represents 2 bits
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

51. BELL 212A SPECIFICATIONS Channel Assignment (1200 bps):
ORIGINATING END ANSWERING END
Transmit Fc=1200 Hz Fc=2400 Hz
Receive Fc=2400 Hz Fc=1200 Hz
Phase Shift:
DIBIT 212A Shift
degrees
01 0 degrees
degrees
degrees
Can fall back to 300 bps using different tones
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

52. OTHER MODULATION METHODS
Quadrature Amplitude Modulation
Uses changes in both amplitude and phase shifting
Total of 16 possible states
Each state represents different four bit sequence
Quadbit
600 baud * 4 bits = 2400 bps
2400 baud * 4 bits = 9600 bps
High Speed Dial Up Modems (56 Kbps)
Requires 1/2 of connection (ISP end) to be digital
If not, drops to 28.8 or 33.6
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

53. FIGURE 4-26: COMMON MODEM STANDARDS
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

54. MAXIMUM LINE TRANSMISSION RATES
4000 Hz - highest bandwidth on telco dialup circuit
Pulse Code Modulation (chapter 10)
Line sampled 8000 times per second (twice the maximum bandwidth)
Each sample converted to 8-bits bytes
8 bits * 8000 samples / second = 64,000 bps
1 bit per byte may be “robbed” for signaling over T- carrier systems
Can’t be guaranteed a “clear” channel
Therefore, for data each sample limited to 7 usable bits
7 bits * 8000 samples / second = 56,000 bps
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

55. MAXIMUM MODEM TRANSMISSION RATES
In perfect world, modems would same in the exact same way and exact same time as telco equipment
Unfortunately, this is not a perfect world
To increase throughput (bps)
Use highest, most reliable frequency possible
Use multi-bit encoding (dibit, quadbit,etc)
Use data compression
Use error detection
Make circuit as digital as possible
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

56. DATA COMPRESSION IN MODEMS
MNP-5 (Microcom Network Protocol)
up to 2:1 in theory but actually less
adds overhead even if data not compressible
not good on pre-compressed files (e.g., zipped)
v.42bis (CCITT/ITU)
up to 4:1 in theory but actually less
senses compressibility of data and shuts off if data not warranted
works well with pre-compressed files (e.g., zipped)
studies show 2.3:1 is more accurate estimate
v.44 (CCITT/ITU)
newest standard developed for internet applications
twice as efficient as v.42 with web pages
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

57. ERROR CHECKING/CORRECTION MODEMS
Data reorganized into small packets called frames
Parity bits removed from each byte
Checksum added to each frame to detect errors
Frames sent in method similar to block, synchronous communication
Two popular standards:
MNP (Microcom Network Protocol)
Levels 1, 2, 3 & 4
Some data compression included in levels 3 & 4
V.42 (CCITT/ITU)
Link Access Procedure for Modems, or LAPM
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

58. STATE OF THE ART v.92 (introduced in 2000)
Preceded by v.90, K56 and X2 modems
56 kbps modem
Uses technology similar to v.34 & v.90
Downstream speed appr kbps
Adds new features
Modem on hold (longer call waiting times)
Quick Connect (faster handshaking)
PCM Upstream (48,000 bps)
Incorporates v.44 data compression
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved

59. FACSIMILE AND FAX MODEMS
Facsimile, or fax, is the electrical transmission of documents over telephone lines.
Analog:
Group lines per inch 3 min/page
Group lines per inch 6 min/page
Digital:
Group lines per inch <1 min/page 4800bps +
Group lines per inch <1 min/page up to 64 kbps
Facsimiles use data compression to speed document throughput
Based on:
Companion to Data Communications: From Basics to Broadband, Third Edition by William J. Beyda © 2000 Prentice Hall, Inc. All Rights Reserved