Analog to Digital (digital telephony) Given an analog function (voice?) we wish to represent it as a...
-
Upload
philippa-daniels -
Category
Documents
-
view
217 -
download
3
Transcript of Analog to Digital (digital telephony) Given an analog function (voice?) we wish to represent it as a...
![Page 1: Analog to Digital (digital telephony) Given an analog function (voice?) we wish to represent it as a sequence of digital values Pulse Amplitude Modulation.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649d1f5503460f949f315d/html5/thumbnails/1.jpg)
Analog to Digital(digital telephony)
• Given an analog function (voice?) we wish to represent it as a sequence of digital values
Pulse Amplitude Modulation (PAM)
![Page 2: Analog to Digital (digital telephony) Given an analog function (voice?) we wish to represent it as a sequence of digital values Pulse Amplitude Modulation.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649d1f5503460f949f315d/html5/thumbnails/2.jpg)
Pulse Code Modulation (PCM)• Pulse Code Modulation is a variation of PAM
Measurements are changed to a set of integral values
• How often should the analog signal be sampled?
• A result of Nyquist’s Theorem says
For a signal with frequency xMaximum sampling rate = 2 * x
• For a voice channelMax frequency of voice channel = 4000 HzMaximum sampling rate needed = 2 * 4000
= 8000 samples per second
![Page 3: Analog to Digital (digital telephony) Given an analog function (voice?) we wish to represent it as a sequence of digital values Pulse Amplitude Modulation.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649d1f5503460f949f315d/html5/thumbnails/3.jpg)
Pulse Code Modulation
• Establish a set of integral valuesPlus/minus 7 bitsTotal of 8 bits per sampleTotal of 256 distinct values
• This is how voice is encoded as a digital signal• Sample 2 * 4000 = 8000 samples per second• One sample every 125 microseconds
![Page 4: Analog to Digital (digital telephony) Given an analog function (voice?) we wish to represent it as a sequence of digital values Pulse Amplitude Modulation.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649d1f5503460f949f315d/html5/thumbnails/4.jpg)
Pulse Code Modulation
These samples are pooled into groups of 24
CodecVOICE 64 Kbps
Codec
1
2
24
Frame
8 bits 8 bits 8 bits 8 bits 8 bits F
8 * 24 = 192 bits1 frame bit
8000 samples/sec
![Page 5: Analog to Digital (digital telephony) Given an analog function (voice?) we wish to represent it as a sequence of digital values Pulse Amplitude Modulation.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649d1f5503460f949f315d/html5/thumbnails/5.jpg)
Pulse Code Modulation (PCM)• 24 channels• Each frame is 193 bits• Sampled 8000 times per second
193 bits * 8000 samples = 1,544,000 bits per second
• This is called a T1 facility• The circuit is also called a Digital Service-1 (DS-1)• This is the fundamental digital circuit from the telephone
company• A single channel within the DS-1 is often called a DS-0• There is a European standard that groups 30 channels
instead of 24 – Called an E1 circuit
![Page 6: Analog to Digital (digital telephony) Given an analog function (voice?) we wish to represent it as a sequence of digital values Pulse Amplitude Modulation.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649d1f5503460f949f315d/html5/thumbnails/6.jpg)
Digital Service• Uses Alternate Mark Inversion or AMI
encoding
• Requires all one bits to be alternating positive and negative voltages
• Zero bits have 0 voltage
0 1 1 1 0 0 0 1
![Page 7: Analog to Digital (digital telephony) Given an analog function (voice?) we wish to represent it as a sequence of digital values Pulse Amplitude Modulation.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649d1f5503460f949f315d/html5/thumbnails/7.jpg)
Multiplexing
• To more fully utilize channel capacity more than one transmission can ‘share’ a single channel
• The is called multiplexing• Multiplexing can take many forms
Frequency Division
The total bandwidth is divided a number into a number of frequency ranges
Each transmission utilizes one of these ranges
![Page 8: Analog to Digital (digital telephony) Given an analog function (voice?) we wish to represent it as a sequence of digital values Pulse Amplitude Modulation.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649d1f5503460f949f315d/html5/thumbnails/8.jpg)
Cable Television• A single coax cable system can have a total capacity of
350 Mhz and to over 650 Mhz• Each TV channel occupies 6 Mhz
Channel Band Number Mhz
2 54-60 3 60-66 4 66-72…… ………. 20 156-162……. ………. 40 318-324……. ……….. 61 444-450
![Page 9: Analog to Digital (digital telephony) Given an analog function (voice?) we wish to represent it as a sequence of digital values Pulse Amplitude Modulation.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649d1f5503460f949f315d/html5/thumbnails/9.jpg)
Wave Division Multiplexing
• Using multiple ‘colors’ over fiber optical cable is a form of frequency division
• Multiple transmission can exist concurrently over the same fiber cable
• Each uses a different wave length, typically called a ‘lamda’
![Page 10: Analog to Digital (digital telephony) Given an analog function (voice?) we wish to represent it as a sequence of digital values Pulse Amplitude Modulation.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649d1f5503460f949f315d/html5/thumbnails/10.jpg)
Time Division Multiplexing
• Total bandwidth is divided into a series of ‘n’ time slots
• Each transmission gets one of the time slots in a round robin fashion
T1
T2
T3
T4
T1
T2
T3
T4
T1T2T3T4T1T2T3T4
Communications Channel
![Page 11: Analog to Digital (digital telephony) Given an analog function (voice?) we wish to represent it as a sequence of digital values Pulse Amplitude Modulation.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649d1f5503460f949f315d/html5/thumbnails/11.jpg)
Statistical Multiplexing
• Like time division except when a station does not have data to send, slot is passed on to next transmission
• Could have variable length data for each transmission
• Any one link can actually get use of full link of other are idle
• Better link utilization• More overhead
![Page 12: Analog to Digital (digital telephony) Given an analog function (voice?) we wish to represent it as a sequence of digital values Pulse Amplitude Modulation.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649d1f5503460f949f315d/html5/thumbnails/12.jpg)
Statistical Multiplexing
T1
T2
T3
T4 T4
T3
T2
T1
T1dd T3dd T1d T4ddd T3dd T1d
Communications Channel
![Page 13: Analog to Digital (digital telephony) Given an analog function (voice?) we wish to represent it as a sequence of digital values Pulse Amplitude Modulation.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649d1f5503460f949f315d/html5/thumbnails/13.jpg)
Inverse Multiplexing
• A number of slower speed lines are grouped together to form a higher speed circuit
MUX
MUX
MUX
MUX
Multiplexing
Inverse multiplexing
![Page 14: Analog to Digital (digital telephony) Given an analog function (voice?) we wish to represent it as a sequence of digital values Pulse Amplitude Modulation.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649d1f5503460f949f315d/html5/thumbnails/14.jpg)
Recall PCM
• Establish a set of integral valuesPlus/minus 7 bitsTotal of 8 bits per sampleTotal of 256 distinct values
• This is how voice is encoded as a digital signal• Sample 2 * 4000 = 8000 samples per second• One sample every 125 microseconds
![Page 15: Analog to Digital (digital telephony) Given an analog function (voice?) we wish to represent it as a sequence of digital values Pulse Amplitude Modulation.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649d1f5503460f949f315d/html5/thumbnails/15.jpg)
Pulse Code Modulation
These samples are pooled into groups of 24
CodecVOICE 64 Kbps
Codec
1
2
24
Frame
8 bits 8 bits 8 bits 8 bits 8 bits F
8 * 24 = 192 bits1 frame bit
8000 samples/sec
![Page 16: Analog to Digital (digital telephony) Given an analog function (voice?) we wish to represent it as a sequence of digital values Pulse Amplitude Modulation.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649d1f5503460f949f315d/html5/thumbnails/16.jpg)
Multiplexing Voice Conversations
![Page 17: Analog to Digital (digital telephony) Given an analog function (voice?) we wish to represent it as a sequence of digital values Pulse Amplitude Modulation.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649d1f5503460f949f315d/html5/thumbnails/17.jpg)
Digital Hierarchy
Phone Company pools T1s into larger circuits
24 DS-0
64 kbps
4 DS-1
1.544 mbps
DS-2
6.312 Mbps DS – 3
44.736 Mbps DS-4
7 DS-2
6 DS-3
274.176
![Page 18: Analog to Digital (digital telephony) Given an analog function (voice?) we wish to represent it as a sequence of digital values Pulse Amplitude Modulation.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649d1f5503460f949f315d/html5/thumbnails/18.jpg)
Synchronous Optical NetworkSONET
• Standard for digital transmission over fiber optics• Also called Synchronous Digital Hierarchy (SDH)
by the ITU• Provides for interoperability between carriers• Standardizes US and European hierarchy• Extends Digital Hierarchy beyond existing DS-3
and DS-4• Makes provision for Operations, Administration,
and Maintenance
![Page 19: Analog to Digital (digital telephony) Given an analog function (voice?) we wish to represent it as a sequence of digital values Pulse Amplitude Modulation.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649d1f5503460f949f315d/html5/thumbnails/19.jpg)
SONET
• Synchronous• Basic frame
810 bytes
8,000 frames per second
6480 bits per frame or 51.84 Mbps
• This forms a basic SONET channel
6480 6480 6480 6480
Synchronous Transport Signal -1
STS-1
![Page 20: Analog to Digital (digital telephony) Given an analog function (voice?) we wish to represent it as a sequence of digital values Pulse Amplitude Modulation.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649d1f5503460f949f315d/html5/thumbnails/20.jpg)
SONET Signal Hierarchy
![Page 21: Analog to Digital (digital telephony) Given an analog function (voice?) we wish to represent it as a sequence of digital values Pulse Amplitude Modulation.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649d1f5503460f949f315d/html5/thumbnails/21.jpg)
Integrated Services Digital NetworkISDN
• Designed to provide digital services to end users (total telephone redesign)
• Approved in 1984 (ISO, ITU)• All digital services all the way to the home• Uses same twisted pair cabling• Initially slow implementation• Usually priced as a measured service, even for
local calling• Very limited user acceptance
![Page 22: Analog to Digital (digital telephony) Given an analog function (voice?) we wish to represent it as a sequence of digital values Pulse Amplitude Modulation.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649d1f5503460f949f315d/html5/thumbnails/22.jpg)
ISDN Services
• Basic Rate Interface (BRI)
2 B (basic rate) channelseach 64 Kbpsused for voice, concurrent data
1 D channel16 Kbps, used for signaling
• Primary Rate Interface (PRI)
23 B channels1 D channel (at 64 Kbps)
![Page 23: Analog to Digital (digital telephony) Given an analog function (voice?) we wish to represent it as a sequence of digital values Pulse Amplitude Modulation.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649d1f5503460f949f315d/html5/thumbnails/23.jpg)
Digital Subscriber Line (DSL)
• Effort by telephone company to bring lower cost, high speed service to home
• Provides concurrent voice/data
• Uses regular phone twisted pair
• Intended to compete with cable service
• Multitude of variations
• Speeds from several hundred Kbps to several Mbps
![Page 24: Analog to Digital (digital telephony) Given an analog function (voice?) we wish to represent it as a sequence of digital values Pulse Amplitude Modulation.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649d1f5503460f949f315d/html5/thumbnails/24.jpg)
DSL Variants
• Asymmetric DSL Frequency division multiplexing 0 – 25 Khz Voice 25 – 200 Khz Upstream data 250 – 1000 Khz Downstream data
• Rates up to 1 Mbps upstream
8 Mbps Downstream
are theoretically possible
![Page 25: Analog to Digital (digital telephony) Given an analog function (voice?) we wish to represent it as a sequence of digital values Pulse Amplitude Modulation.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649d1f5503460f949f315d/html5/thumbnails/25.jpg)
Asymmetric DSL
![Page 26: Analog to Digital (digital telephony) Given an analog function (voice?) we wish to represent it as a sequence of digital values Pulse Amplitude Modulation.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649d1f5503460f949f315d/html5/thumbnails/26.jpg)
Digital Subscriber Lines
Operation of ADSL using discrete multitone modulation (DMT).
Upstream: Usually 512 Kbps or less
Downstream: Up to 8 Mbps
![Page 27: Analog to Digital (digital telephony) Given an analog function (voice?) we wish to represent it as a sequence of digital values Pulse Amplitude Modulation.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649d1f5503460f949f315d/html5/thumbnails/27.jpg)
Digital Subscriber Lines
Bandwidth versus distanced over category 3 UTP for DSL.
![Page 28: Analog to Digital (digital telephony) Given an analog function (voice?) we wish to represent it as a sequence of digital values Pulse Amplitude Modulation.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649d1f5503460f949f315d/html5/thumbnails/28.jpg)
Other DSL Variants
• Symmetric DSL (SDSL) Upstream and downstream speeds the same Single copper pair
• High Data Rate DSL (HDSL) Symmetric services Requires two copper pairs Cost effective way to deliver T1 equivalent service
• Very High Data Rate (VDSL) Asymmetric Up to 50 Mbps downstream possible
![Page 29: Analog to Digital (digital telephony) Given an analog function (voice?) we wish to represent it as a sequence of digital values Pulse Amplitude Modulation.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649d1f5503460f949f315d/html5/thumbnails/29.jpg)
DSL Modem
Digital Subscriber Line Access Multiplexor
![Page 30: Analog to Digital (digital telephony) Given an analog function (voice?) we wish to represent it as a sequence of digital values Pulse Amplitude Modulation.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649d1f5503460f949f315d/html5/thumbnails/30.jpg)
Cable Modems
• Why cable? Infrastructure exists Coax cable better characteristics than twisted pairs
• TV channels are 6 Mhz Allows for high speed data What is maximum possible data rate?
• Shared channel – many users on a segment• Now a standard
Data Over Cable System Interface Standard
DOCSIS
![Page 31: Analog to Digital (digital telephony) Given an analog function (voice?) we wish to represent it as a sequence of digital values Pulse Amplitude Modulation.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649d1f5503460f949f315d/html5/thumbnails/31.jpg)
Cable Spectrum Allocation
Frequency allocation in a typical cable TV system used for data
![Page 32: Analog to Digital (digital telephony) Given an analog function (voice?) we wish to represent it as a sequence of digital values Pulse Amplitude Modulation.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649d1f5503460f949f315d/html5/thumbnails/32.jpg)
Cable modems
• Upstream: 5-42 Mhz Uses an encoding scheme of 2 bits per baud 1 baud per Hz 12 Mbps per channel possible per 6 Mhz
channel
• Downstream: 550-750 Mhz Uses 64-QAM 6 bits/baud, 1 bit is used for error correction Theoretical 30 Mbps per 6 Mhz channel
![Page 33: Analog to Digital (digital telephony) Given an analog function (voice?) we wish to represent it as a sequence of digital values Pulse Amplitude Modulation.](https://reader036.fdocuments.us/reader036/viewer/2022062421/56649d1f5503460f949f315d/html5/thumbnails/33.jpg)
Wireless Broadband Alternatives
• Current efforts are to provide 802.11 wireless in large areas through meshed access points
• Wireless broadband to the home standard being developed
• IEEE 802.16 - WiMAX Potential of upto155 Mbps Over wide areas (miles) Considered a replacement for last mile
http://grouper.ieee.org/groups/802/16/index.html