Digital Communication
Systems
H. S. Jamadagni, CEDT, IISc,
Bangalore
Jamadagni H S
DC/V1/2004
1
Topics in Digital Communications
zDigital communication system
advantages and disadvantages
zDigital communication system
classification
zDigitization of analog signals
zDigital transmission systems
zData communication systems
zIntegrated Services Digital Network
and other advanced digital
communication systems
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Digital Communication advantages
zReliable communication; less sensitivity to changes in
environmental conditions (temperature, etc.)
zEasy multiplexing
zEasy signaling
„ Hook status, address digits, call progress information
zVoice and data integration
zEasy processing like encryption and compression
zEasy system performance monitoring
„ QOS monitoring
zIntegration of transmission and switching
zSignal regeneration, operation at low SNR, superior performance
zIntegration of services leading to ISDN
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Digital Communication System Disadvantages
zIncreased bandwidth
„ 64 KB for a 4 KHz channel, without compression (However,
less with compression)
zNeed for precision timing
„ Bit, character, frame synchronization needed
zAnalogue to Digital and Digital to Analogue conversions
„ Very often non-linear ADC and DAC used, some
performance degradation
zHigher complexity
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Types of Digital Communication Systems
Signal Type
Transmission
Example
Analog
Analog
Classical telephony
Analog
Digital
PCM TDM
Digital
Analog
Modems
Digital
Digital
ISDN, LANs
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Digitization of analogue signals
Amplitude
zSignal sampling
Amplitude
Time
Time
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Nyquist Criterion, Aliasing
Amplitude
Original signal
Time
Amplitude
Aliased signal
Time
Nyquist sampling rate fs > 2. fb
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Spectrum of baseband signals
Amplitude
+B
-B
Frequency
Spectrum of the properly sampled base band
Spectrum of the under sampled base band
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Speech signal digitisation
Input signal
PAM samples
Output signal
LPF
Pulse train
Pulse amplitude modulation
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Pulse Code Modulation (PCM)
PAM
samples
Analog
input
Low pass
filter
Sample
clock
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D/A
A/D
Digitally
encoded
samples
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Low pass
filter
Analog
Output
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Quantisation of speech signal samples
011
Quantisation errors
010
001
000
100
101
110
111
010
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011
010
000
011
001
001
Quantisation of analog samples
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000
101
11
Decoder
output
Quantisation error in PCM
Quantized
output
signal
Input signal
Input amplitude
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Quantisation error as a function of amplitude
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PCM system - Typical parameters
4 KHz Speech signal
8 KHz Sampling
8 bits / sample digitising
per speech channel 8 x 8 bits = 64 kbps
T1 carrier: 24 channels. 8 bits in 125 µs / channel
24 x 8 = 192 bits in 125 µs / frame, 1 bit per frame for sync
193 bits in 125 µs, Line rate 193/125 µsec = 1.544 Mbps
ITU ( EUROPEAN)
32 Channels 8 bits/ 125 µss / channel
32 X 8 bits / 125 µs = 2.048 Mbps
30 channels info; 2 channels management
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Idle channel noise minimisation
Idle channel noise: Caused by uncertainty in coding a sample
near zero value
Mid-riser quantizer
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Mid-tread quantizer
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Signal to quantizing noise of uniform PCM
number of
bits / sample
13
80
60
SNR (dB)
11
40
9
20
-40
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-30
-20
A/Amax
(dB)
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Non-linear AD conversion
Compressed sample values
Uniform
Quantisation
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Input
sample values
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Compression law - µ law
Normalised input
0
0.2
0.4
0.6
0.8
1
0
tuptuo desilamroN
0.2
0.4
0.6
0.8
1
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Compression law - A law
Normalised input
0
0.2
0.4
0.6
0.8
1
tuptuo desilamroN
0
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0.2
0.4
0.6
0.8
1
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Non linear AD conversion laws used in PCM for speech
F z(x) = sgn(x)
ln(1 + z)
ln(1 + z.|x|)
µ law
F A (x) = sgn(x)
1 + ln A
A|x|
A law
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Low bit rate coding: DPCM, Differential PCM
Differentiator
Speech
signal
Band
limiting
filter
+ Σ
A/D
-
Previous
input
estimate
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Sampler
quantizer
encoder
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Encoded
difference
samples
D/A
Accumulator
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DPCM implementation
ADC
LPF
+
-
Σ
S&H
S&H
+
Σ
+
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DAC
LPF
Σ
+
Decoder
+
Encoder DAC
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Delta modulation
Input
+
LPF
Σ
-
+
"1"
LPF
-
Output
Integrator
Decoder
1
Integrator
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0
Pulse generator
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Slope overload distortion in Delta modulation
Slope over load
Granular noise
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Low Data Rate Modulation
zCVSD (Continuous Variable Slope Delta Modulation)
Receive clock
Sample clock
+
S
-
+
-
1
0
FF
P
G
P 1
G 0
C2
All 1s
Step
size
control
P
G
P
G
C1
Encoder
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All 0s
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Decoder
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Conceptual view of ISDN
Telephone
Customer
ISDN
interface
Data
terminal
"Digital
pipe"
"Digital
pipes"
Packet switched
network
Circuit switched
network
Other networks
PBX
Subscriber loop and
ISDN channel
structures
Alarm
Data bases
Other services
Local area
network
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Block diagram of ISDN functions
Integrated
Digital Network
Digital circuit switched backbone
Common
physical
interface
ISDN
central
office
Packet-switched
backbone
Subscriber loop to ISDN channel
structures: Basic = 64 kbps + 64
kbps + 16 kbps
Network-based
processing
services
Primary = multiplexed 64 kbps
channels
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ISDN principles
Ê ISDN
is based on concepts developed for telephony. Therefore,
evolutionary changes
Ê Transition
from the present network to ISDN may require about
one decade.
Ê End-to-end
digital connectivity to be obtained using digital
transmission, TDM switching and or SDM switching.
Ê Present
ITU standards part of new standards
Ê In
early development of ISDN interim measures needed for
interfacing with present networks
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Principles of ISDN (Cont.)
Ê Supports
a wide range of voice and non-voice applications
Ê Switched
and non-switched connections Circuit switching and packet
switching
Ê Based
on 64 Kbps channels
Ê Intelligence
for providing service features, maintenance and
management integrated
Ê Layered
protocol used
Ê Flexibility
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for implementation at specific national situations
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ISDN evolution
z
Digital exchanges commissioned in late 60's and 70's
Integrated digital transmission and switching established
(IDN)
z
Integrating services in IDN is the latest step leading to
ISDN INTEGRATED SERVICES DIGITAL NETWORK
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ISDN services: Definition of attributes
All services on the ISDN network are characterised by
"attributes" defined in ITU 1.130 standards
z
z
Attributes have a definition and allowable values
z
Any service has a set of valid attributes
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ISDN services: Attributes
Attribute Name
Values
Info. transfer mode
Info. transfer rate
Info. transfer capability
Circuit, packet
Bit rate
Speech,
3.1 KHz audio
7 KHz audio
15 KHz audio
Video
Other values
Bit error rate
Connection performance
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ISDN service classification
Services defined by attributes
ÊBearer
services
ÊTeleservices
ÊSecondary services
Bearer services provide capability to transfer information
between ISDN access points and involve only low level layers
(1,2 and 3)
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ISDN teleservices
ÊLow
layer attributes
ÊHigh
layer attributes
ÊType of user information
ÊLayer 4 protocols
ÊLayer 5 protocols
ÊLayer 6 protocols
ÊLayer 7 protocols
ÊGeneral
attributes
ÊQuality of service
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Customer access to services supported by ISDN
3
5
TEI
TE2
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4
R
2
S
1
T
NT2
NT1
TA
S
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Functional grouping
z
z
z
z
TE: Terminal equipment
TE1: S interface terminal
TE2: R interface terminal
TA: Terminal adapter
adapts TE2 to S interface
NT: Network termination
NT2: Optional, PBX applications
NT1: S/T interface to U interface
Interface structure
2B + D 192 Kbps line rate
23B + 4536 Kbps line rate
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Network functional principles
Services to be internationally compatible
zUNI standardised so that TE is portable
zStandardise network capability
z
High Layer
Low Layer
Operation & manage
Layer 1:
Physical layer connection activation deactivation, bit transmission
channel structure mutiplex.
Layer 2:
Data link connection establishment, Data link congestion handling
How control, error, sequence control, frame sync.
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Access channel and rate
Channel name
Bit rate
D
16 Kbps
64 Kbps
B
H0
H1
H11
H12
64 Kbps
384 Kbps
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1536 Kbps
1920 Kbps
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Bearer services
64 Kbps unrestricted, 8 KHz structured
z 64 Kbps 8 KHz structured, speech
z 64 Kbps 8 KHz structured, 3.1 KHz audio
z 384 Kbps unrestricted
z 1536 Kbps unrestricted
z 1920 Kbps unrestricted
z Packet - mode services
z
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ISDN subscriber premises connections
<1 km
TE
T
R
T
R
(a) Point-to-point
NT
< 100-200m
TE
T
R
T
R
TE
NT
TE
(b) Short passive bus
TR = Terminating Resistor
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Extended passive bus
< 500m
< 25-50m
T
R
T
R
TE
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NT
TE
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NT1 star
TE
T
R
<1 km
T
R
NTI
T
R
TE
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T
R
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User - Network Interface: Layer 1 specifications
B channel:
64 Kbps, two channels
Bit timing and rate:
192 Kbps
Octet timing
Frame alignment
D channel:
16 Kbps
Power feeding :
40 V DC 1--mW max.
Activating and deactivating
Frame structure and organisation
Line code:
Pseudo - ternary
D channel access control : Similar to HDLC
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Layer 1 functions
ÊEncoding
of digital data for transmission across the interface.
ÊFull-duplex transmission of B channel data
ÊFull-duplex transmission of D channel data.
ÊMultiplexing of channels to form basic or primary access transmission
structure.
ÊActivation and deactivation of physical circuit.
ÊPower feeding from network termination to the terminal.
ÊTerminal identification.
ÊFaulty terminal isolation.
ÊD channel contention access
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ISDN Layer 2
Traffic over D channel (control Info and data over D) Q 921
Q921 services
ÊConvey
user Info between layers entities using D channel
ÊSupport multiple terminals at user-NW installation
ÊMultiple layer 3 entity support two types of transfer
ÊUnacknowledged transfer (un no: frames)
ÊAcknowledged transfer (like X 25) HDLC
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Function of other layers
layer 3 :
layer 4 :
Layer 5 :
layer 6 :
Layer 7 :
Jamadagni H S
routing
network connection establishment
release
multiplexing
congestion control
addressing
error detection / recovery
flow control
layer 4 connection, release, muxing
session connection, etc.
management
session - transport management
encryption / decryption
compression / expansion
application related functions
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Modelling of basic and supplementary services
Terminal Call
Processing
Basic Service
Protocol
(Q.931)
Supplementary
Services
Protocol
(Facility)
Q.931 Messages
Exchange Call
Processing
Basic Service
Protocol
(Q.931)
Supplementary
Services
Protocol
(Facility)
Q.931 Messages
LAPD
LAPD
1.430/1.431
1.430/1.431
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Basic Call Control
interact with layer 2 (LAPD) to transmit / receive messages
z generate & interpret layer 3 messages
z admin of times and logical entities (call reference) used in control
z admin of resources (like B ch1)
z check to provide proper service consistent with user requirements
z routing / relaying
z network connection control
z error detection (sequences)
z error recovery
z sequencing layer 3 information
z
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Protocol reference model I 320
1. Protocol reference model I320
Circuit - switched connection under common channel signalling
zPacket - switched comm over B/D/H
zSignalling between users and network based facilities (data base fores.)
zEnd - to - end signalling for users
zCombinations for multimedia comm.
z
2. Types of Info flow
1. User Info: digitised voice, data between users. Transmitted transparently through ISDN
or processed (encrypted for e.g.)
2. Control Info : acted upon this Info switching a connection / clearing change service
characteristics
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Frame format in ISDN layer 2
FLAG
8 bits
ADDRESS
16
CONTROL
INFORMATION
8 or 16
Variable
FCS
FLAG
16
8
(a) Frame format
0
C/R
SAPI
1
TEI
C/R is Command/response
SAPI is Service access point identifier
TEI is Terminal endpoint identifier
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LAPD format
0
N(S)
P/F
1 0 SS0
0 0 0
P/F
1 1 M M P/F M M M
N(S)
N(R)
S
M
P/F
N(R)
N(R)
Information
transfer
Supervisory
Unnumbered
= Transmitter send sequence number
= Transmitter receive sequence number
= Supervisory function bit
= Modifier function bit
= Poll/final bit
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LAPD commands and responses
Name
Control Field
C/R
Description
Information format
I (Information)
0-N(S)--P-N(R)-- C
Exchange user data
Supervisory Format
RR (Receive Ready) 10000000*-N(R)-RNR (Receive Not
Ready)
REJ (Reject)
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C/R
Positive ack; ready to receive
I-frame
10100000*-N(R)-C/R
Positive ack; not ready top
receive
10010000*-N(R)-C/R
Negative ack; go back N
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Unnumbered format
SABME (Set Asyn
1111P110
chronous Balanced
Mode)
DM (Disconnected
1111F000
Mode)
UI (unnumbered
1100P000
Information)
DISC (Disconnect)
1100P010
UA (Unnumbered
1100F110
Acknowledgement)
FRMR (Frame Reject) 1110F001
XID (Exchange IDidentification)
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1111*101
C
Request logical connection
R
Unable to establish or main
maintain logical connection
C
Used for unacknowledged
information transfer service
C
Terminate logical connection
R
Acknowledge SABME or DISC
R
C/R
Reports receipt of unacceptable frame
Exchange identification information
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Q931 message types
Circuit - mode connection control functions needed for circuit-switched B
channel calls
Packed - mode connection control functions needed for circuit-switched
connections to ISDN packet-switched node.
User - user signalling messages with global call reference
functions are 4 types
Êcall
establishment set up a call on B chl.
Êcall information user-NW Info transfer after set-up
Êcall clearing
Êmiscellaneous
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Messages
Signalling exchanged between user - network, network - network.
Protocol discriminator (0001000) for Q931 call reference
message type
length (1 for BRI, 2 for PRI)
call reference
call reference value
(assigned by TE for 0/9 NT for calls)
(local significance)
flag: 0: originator , 1: remote end
call reference length = 0
CRF = φ
global CRF
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supp.services Q932
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SAPI and TEI assignments
SAPI Value
(a) SAPI Assignments
Related Protocol or Management Entity
0
16
32-61
63
All others
Call-control procedures
packet communication conforming to X.25 level 3
Frame relay communication
Layer 2 management procedures
Reserved for future standardisation
TEI Value
0-63
64-126
127
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(b) TEI Assignments
User Type
Nonautomatic TEI assignment user
equipment
Automatic TEI assignment user equipment
Used during automatic TEI assignment
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Q931 messages for circuit mode connections
Call Establishment Messages
Message
Significance
Direction
ALERTING
global
CALL PROCEEDING
local
both
both
CONNECT
CONNECT
ACKNOWLEDGE
PROGRESS
set-up
set-up
ACKNOWLEDGE
both
both
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global
local
global
both
global
both
local
both
Function
Indicates that user alerting has begun
Indicates that call establishment has
been initiated
Indicates call acceptance by called TE
Indicates that user has been
awarded the call
Reports progress of a call
Initiates call establishment
Indicates that call establishment
has been initiated but requests
more information
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Call information phase messages
Message
RESUME
Significance
local
RESUME
local
ACKNOWLEDGE
RESUME REJECTlocal
SUSPEND
local
SUSPEND
local
ACKNOWLEDGE
SUSPEND REJECT local
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Direction
Function
u n
Requests resumption of previously
suspended call
n u
Indicates requested call has
been re-established
n u
Indicates failure to resume suspended
call
u n
Requests suspension of a call
n u
Indicates call has been suspended
n u
Indicates failure of requested call
suspension
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Call clearing messages
Message
Significance
Direction
DISCONNECT
global
both
RELEASE
local
RELEASE
COMPLETE
INFORMATION
NOTIFY
STATUS
local
STATUS
INQUIRY
local
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local
access
local
both
both
both
both
both
both
Function
Sent by user to request connection
clearing; sent by network to indicate
connection clearing
Indicates intent to release channel and
call reference
Indicates release of channel and call
reference
Provides additional information
Indicates information pertaining to a call
Sent in response to a STATUS
INQUIRY or at any time to report an error
Solicits STATUS message
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Digital Signal Encoding Format in ISDN
0
1
0
0
1
1
0
0
0
1
1
NRZ-L
Bipolar-AMI
Pseudoternary
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Physical connector in ISDN
Contact Assignments for Plugs and Jacks of ISDN
Contact
Number
a
b
c
d
e
f
g
h
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TE
Power Source 3
Power Source 3
Transmit
Received
Received
Transmit
Power Sink 2
Power Sink 2
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NT
Power Sink 3
Power Sink 3
Receive
Transmit
Transmit
Received
Power Source 2
Power Source 2
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The U interface
Fixed by local administration
z
z
z
4 wire interface
no echo cancellation procedures, simple line termination
2 wire interface
Ping-Pong operation, no echo cancellation, only one
cable pair, simple termination, limited lengths, extra
processing for comm. direction handling
2 wire interface
full duplex operation, echo cancellation, only one cable
pair, no limitation on length , extensive processing for echo
cancellation
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U interface circuit
Line
Encoding
TX Data
Echo
Cancellor
RX Data
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Decision
Feedback
Equalisation
Σ
Hybrid
DSL
+
AD
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ANSI U interface frame and superframe structure
18
1
2
3
4
5
6
7
8
18
ISW
SW
SW
SW
SW
SW
SW
SW
2B + D
2B + D
2B + D
2B + D
2B + D
2B + D
2B + D
2B + D
18
18
2B + D
2B + D
2B + D
2B + D
2B + D
2B + D
2B + D
2B + D
2B + D
2B + D
2B + D
2B + D
2B + D
2B + D
2B + D
2B + D
6 total 240 bits
M1 to M6
M1 to M6
M1 to M6
M1 to M6
M1 to M6
M1 to M6
M1 to M6
M1 to M6
SW = Sync Word = +3+3-3-3-3+3-3+3+3
ISW= Inverted SW=-3-3+3+3+3-3+3-3-3
2B+D = |B1 |B2 |D | (|8|8|2) M1 to M6 over head bits
Data are encoded as 00 = -3, 01= -1, 11=+1, 10 = +3
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TEI and SAPI assignment
Network
User
Customer premises
PD
B
S
I
B
1
* *16
Data link
layer
TEI = 5
TE(1)
Layer 3
TE(2)
S
I
1
B1 2
* *0
* * *0
Data link
layer
TEI = 5
TEI = 127
ET/NT2
Connection endpoint suffix
PD
S
I
1
321 B
****
Data
link
layer
16
0
*
B
*
SAP
identifier
TEI = 3, 8, 127
TEI = 127
SI: Signalling information
PD: Packet data
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SAPI = 0
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SAPI = 16
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Asymetric Digital Subscriber Line
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1
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ADSL basics (contd 1)
ADSL will play a crucial role over the next ten or more years for
delivering information in video and multimedia formats.
New broadband cabling will take decades to reach all prospective
subscribers.
Success of these new services will depend upon reaching as many
subscribers as possible during the first few years.
By bringing movies, television, video catalogs, remote CD-ROMs,
corporate LANs, and the Internet into homes and small businesses,
ADSL will make these markets viable, and profitable, for telephone
companies and application suppliers alike.
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ADSL basics (contd 2)
Three information channels
a high speed downstream channel
Speed ranges from 1.5 to 6.1 Mbps
a medium speed duplex channel
Speed range from 16 to 640 kbps
a POTS (Plain Old Telephone Service) or an ISDN channel.
The POTS/ISDN channel is split off from the digital modem by filters, thus
guaranteeing uninterrupted POTS/ISDN, even if ADSL fails.
Each channel can be submultiplexed to form multiple, lower rate channels,
depending on the system.
Consistent with North American and European digital hierarchies
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ADSL reach
Data Rate
Distance
Wire Size
Distance
1.5 or 2 Mbps
1.5 or 2 Mbps
6.1Mbps
6.1 Mbps
18,000 ft
15,000 ft
12,000 ft
9,000 ft
0.5 mm
0.4 mm
0.5 mm
0.4 mm
5.5 km
4.6 km
3.7 km
2.7 km
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Communication Systems
POINT-TO-POINT
ÊONE
SOURCE
ÊONE SINK
FOR INFORMATION
ÊFEED BACK
FROM SINKS, IN
FACT TWO WAY COMM.
ÊPRIVACY NEEDED
EAVES DROPPING TO
BE AVOIDED
ÊPRIVATE DATA, INFO
EXCHANGE
ÊREQUIRES ESTABLISHMENT
OF PATH BETWEEN
PARTIES
ÊTHIS PATH ESTABLISHMENT
IS CALLED "SWITCHING"
ÊREQUIRES "SIGNALLING"
Jamadagni H S
BROADCAST
ONE SOURCE
MANY SINKS
FOR INFORMATION
SINKS
PRIVACY PROHIBITED
NO SUCH REQUIREMENT
PUBLIC INFO TRANSFER
NO
NO SWITCHING
NO
DC/V1/2004
1
History of Switching
Manual - through operator
zStep-by-Step
Strowger
zFirst "big" strowger exchange
z# 1
Cross bar
z# 5
Cross bar
z# 3
Cross bar
zESS
I
zESS
II
zESS
III
zESS
ZB
zESS
IA
z
1880 onwards
~1897
1919
1938
1948
1974
1965
1970
1976
1976
1980 onwards
PAX : Private automatic exchange useful for local connections
only
PABX: Private automatic branch Exchange useful for local and
trunk connections
Jamadagni H S
DC/V1/2004
2
Types of Switching Systems
SWITCHING
SYSTEMS
CIRCUIT
SWITCHES
NON-CIRCUIT
SWITCHES
Mainly for interactive
communication
Voice, Video, etc.
For example: X25
service
Jamadagni H S
DC/V1/2004
Mainly for noninteractive
communication
Data terminals
Computer
communication
3
Switching system topology
EPABX
Local Exchange
1000's of lines
Primary
Trunks
10 to 15% of sub lines
Secondary
Jamadagni H S
DC/V1/2004
4
Signals in Switching Systems
Switching system objective: To interconnect two
circuits for information exchange
Information: Voice, Data, FAX, Still Video, moving video, etc.
Type of signal
Bandwidth
Data rate
Voice
Data
4 KHz
64 Kbps
300 bps to several mbps
Still video
Moving video
Mbps
FAX
150 Mbps
1 to 4 MHz
4 to 10 MHz
1 to 30
30 to
9.6 Kbps
Jamadagni H S
DC/V1/2004
5
Tasks of a Switch
1. SWITCHING: ESTABLISHING CONNECTIONS BETWEEN
SUBSCRIBERS
2. SIGNALLING
CHANNEL ASSOCIATED - COMMUNICATION
CHANNEL (ZW) USED FOR SIGNALLING
FEED TONES
REMOVE TONES
DTMF, PULSE DIALLING
FLASH DETECTION
TONE OVER CONVERSATION..LINE SIGNALLING - SIGNALS TRANSMITTED
BETWEEN EQUIPMENT THAT TERMINATE &
CONTINUOUSLY MONITOR TRAFFIC
CIRCUIT
OFF-HK, ON-HK ETC. ARE EXAMPLES
SELECTION SIGNALLING - ROUTING INFO
DIGITS, C-O-S INFO ETC.
COMMON CHANNEL SIGNALLING
SEPARATE CHANNEL FOR SIGNALS
3. MANAGEMENT
METERING , DIAGNOSTICS, CLASS OF SERVICE
Jamadagni H S
DC/V1/2004
6
Call processing in a Switch
CALLING
SWITCH
OFF-HOOK
(ORIGINATE)
IDENTITY
SUBSCRIBER
DIAL TONE
ALLOCATE
COMMON
RESOURCES
DIAL DIGITS
DIGIT COLLECT
ANALYSE
RING BACK
TONE
CONVERSE
ON-HOOK
(FORWARD
CLEAR)
Jamadagni H S
PATH SET UP
DISCONNECT
TONES
DISCONNECT
RETURN
RESOURCES
DC/V1/2004
CALLED
RINGING
CURRENT
OFF-HOOK
CONVERSE
DISCONNECT
CALL
7
Switching System Architectures
SPACE DIVISION
zestablish connection
through' galvanic connections
zonce established, contact
remains till disconnection
zdedicated paths
zexpansion requires
additional "paths"
zThe actual switch is
called a "CROSS POINT"
TIME DIVISION
zestablish connections through data
exchange in a memory
zcontact between two parties at
specific "time-slot"
zdedicated time-slot
zExpansion requires additional
"time-slots"
zThe actual switch is called a
"SPEECH MEMORY"
SLOT ALLOTTED TO #6
SLOT ALLOTTED #1
Jamadagni H S
DC/V1/2004
8
Switching System Operations
Ê Path
establishment - using extensive signalling
Ê Information interchange - using error free communication
Ê Facilities - offering extensive facilities to subscribers
Ê Tariff computation - using extensive signalling
Ê Tearing down the path after information exchange is complete using signalling
Ê Billing - using computation facilities
Ê Maintenance - using computation facilities and a few added
equipment
Ê Performance measurement - using computation facilities and a
few added equipment
Jamadagni H S
DC/V1/2004
9
Electronic Stored Program Control Switches
z
z
z
COMMON CONTROL
CONTROL through' COMPUTER HW + SW
BOTH TIME DIVISION & SPACE DIVISION POSSIBLE
SPACE DIVISION SWITCHING
Ê
Ê
Ê
Jamadagni H S
USING REED CONTACTS FOR CROSS POINTS
USING SOLID STATE (JFETS/MOS FETs) FOR CROSS POINTS
USING THYRISTORS/TRIACS FOR CROSS POINTS
DC/V1/2004
10
Analogue Switch Features
ÊLow
cost for small switches (say up to 64 subscribers)
ÊLow distortion due to direct speech switching
ÊIntroducing tones very easy
ÊCost vs service trade-off possible
ÊFairly good bandwidth
ÊBlocking switch, particularly for large number of subscribers
ÊCost increases with number of switches
ÊExpansion is difficult
ÊHandling data difficult
ÊLower reliability due to switches
Jamadagni H S
DC/V1/2004
11
N input lines
A generic N by N switch
N output lines
Jamadagni H S
DC/V1/2004
12
Space division switch
First stage
Second stage
Third stage
Three-stage space-division switch
Jamadagni H S
DC/V1/2004
13
Number of cross points for a non-blocking switch
Lines
128
512
2,048
8,192
32,768
131,072
Jamadagni H S
Single-Stage
7,680
63,488
516, 096
4.2 x 10e6
3.3 x 10e7
2.6 x 10e8
Three stage
16,384
262,144
4.2 x 10e6
6.7 x 10e7
1 x 10e9
1.7 x 10e10
DC/V1/2004
14
SPC Digital Switch Block schematic
SUB
SUB
LINE
TERMINATE
SWITCH
MATRIX
ANALOG
TRUNK
TERMINATE
ANALOG
TRUNKS
SUB
LINE
CONTROL
SWITCH CONTROL SYSTEM
TERMINALS
CONSOLES
Jamadagni H S
DC/V1/2004
15
Time slot interchange
I/P
Stream
Channel
No.
O/P
Stream
Channel
No.
X
1
Y
2
Y
1
3
4
5
X
2
3
1
2
3
Y
4
5
1
4
5
4
5Time
Time
X
2
3
* One Frame delay
Jamadagni H S
DC/V1/2004
16
Implementation of a digital TSI switch
CONTROL
1
INFORMATION MEMORY
1
8
19
8
19
8
19
24
24
Jamadagni H S
DC/V1/2004
CONTROL MEMORY
PCM INPUT BUS
PCM output bus)
17
n I O Pairs
n outlets
n inlets
TDM Bus switch
A Simple Time-Division
Switch
Jamadagni H S
A Simple Folded Time-Division
Switch
DC/V1/2004
18
Time-space-time Switch
TML
1 5
38
2
5
TML
output
1
20
TML
output
2
14
38
TML 20
2
14
2
.
.
.
.
TML
n
Jamadagni H S
.
.
.
.
k
DC/V1/2004
.
.
.
.
TML
output
n
19
Space-time-space switch
SPACE
TML 16
1
3
TML 3
2
16
.
.
.
.
TML
n
Jamadagni H S
SPACE
TIME
1
16
3
TML
OUTPUT
1
2
3
16
TML
OUTPUT
2
.
.
.
.
K
DC/V1/2004
.
.
.
.
TML
OUTPUT
n
20
Overview
•
•
•
•
•
•
Copper Access
Bandwidth Requirements
Distance vs. Rate
ADSL
Modulation Techniques
Competing Technologies
Jamadagni H S
DC/V1/2004
1
Copper Access Technologies // Voice
• Voice Grade Modems
z
V.22 // V.32 // V.34
z
z
z
z
1,200 to 28,800 bps (33,600 bps)
Full Duplex
Data communications
56kbps modems are not full duplex
(asymmetric much like ADSL)
Core
Network
Jamadagni H S
DC/V1/2004
2
Copper Access Technologies // Voice (V-series)
Leased Lines
PSTN
<300
600
1200
V.19
V.20
2400
V.22bis
V.26ter
V.26
4800
9600
V.27ter V.32
14.4K
V.32bis
V.22bis
V.23
V.21
Jamadagni H S
28.8K
V.34
V.26 V.27
V.29
V.27bis
DC/V1/2004
V.33
3
Copper Access Technologies // DSL (ISDN)
• Digital Subscriber Line
z
DSL (ISDN BRI)
z
z
z
160 kbps (two 64 kbps (B) +
one 16 kbps (D) + 16 kbps operation
and maintenance channel [OMC])
Full Duplex
ISDN, voice and data communications
DSL
Jamadagni H S
DSL
Core
Network
DC/V1/2004
DSL
DSL
4
Copper Access Technologies // HDSL and SDSL
• High Data Rate and Single Line
(Symmetric)
z
HDSL and SDSL
z
z
z
z
1.544 Mbps // 2.048 Mbps
Full Duplex
T1/E1, telco feeders, WAN
SDSL (single twisted pair)
Jamadagni H S
DC/V1/2004
5
Copper Access Technologies // ADSL and RADSL
• Asymmetric Digital Subscriber
Line (Rate Adaptive)
z
ADSL // RADSL
z
z
z
z
1.5 Mbps to 9 Mbps (downstream)
16 kbps to 1.5 Mbps (upstream)
Internet access, video on demand,
remote LAN access, multimedia
RADSL = adapt speeds based on
conditions and distances
Jamadagni H S
DC/V1/2004
6
Bandwidth Requirements
Application
Type
File
Size
Modem ISDN
DSL
DSL
DSL
128kbps 384kbps 768kbps 1.544M
bps
8.3 s
1.9 s
0.63 s
0.31 s
0.16 s
DSL
6.144
Mbps
0.04 s
E-mail
30k
Digitized
Photo
125k 34.7 s
7.8 s
2.6 s
1.3 s
0.6 s
0.2 s
250k 69.4 s
15.6 s
5.2 s
2.6 s
1.3 s
0.3 s
Yes
Yes
Yes
Yes
1.7 m
52.1 s
25.9 s
6.5 s
6.9 m
3.5 m
1.7 m
26.0 s
Documents
384k No
No
Video
Conferencing
5M
23.1 m 5.2 m
X-Ray
Bulk File
Transfer
Jamadagni H S
20M
1.5 h
20.0 m
DC/V1/2004
7
Distance vs. Rate (downstream)
• ADSL (24g wire)
z
z
z
z
1.544 Mbps @
18,000 ft
2.048 Mbps @
16,000 ft
6.312 Mbps @
12,000 ft
8.448 Mbps @
9,000 ft
Jamadagni H S
• VDSL (24g wire)
z
z
z
12.96 Mbps @
4,500 ft
25.82 Mbps @
3,000 ft
51.84 Mbps @
1,000 ft
Distance is from Central
Office or RT (repeater
terminal) unit
DC/V1/2004
8
ADSL
• Asymmetric data streams
z
Most applications fit this model
z
z
z
z
video on demand
home shopping
Internet access
remote LAN access
Jamadagni H S
DC/V1/2004
9
Jamadagni H S
DC/V1/2004
10
ADSL basics (contd 1)
ADSL will play a crucial role over the next ten or more years for
delivering information in video and multimedia formats.
New broadband cabling will take decades to reach all prospective
subscribers.
Success of these new services will depend upon reaching as many
subscribers as possible during the first few years.
By bringing movies, television, video catalogs, remote CD-ROMs,
corporate LANs, and the Internet into homes and small businesses,
ADSL will make these markets viable, and profitable, for telephone
companies and application suppliers alike.
Jamadagni H S
DC/V1/2004
11
ADSL basics (contd 2)
Three information channels
a high speed downstream channel
Speed ranges from 1.5 to 6.1 Mbps
a medium speed duplex channel
Speed range from 16 to 640 kbps
a POTS (Plain Old Telephone Service) or an ISDN channel.
The POTS/ISDN channel is split off from the digital modem by filters, thus
guaranteeing uninterrupted POTS/ISDN, even if ADSL fails.
Each channel can be submultiplexed to form multiple, lower rate channels,
depending on the system.
Consistent with North American and European digital hierarchies
Jamadagni H S
DC/V1/2004
12
ADSL in operation
up
POTS splitter
DSLAM
Broadband
Network
down
1.5 to 6 Mbps
Narrowband
Network
(PSTN)
Jamadagni H S
16kbps
to 1.5 Mbps
Existing
copper line
POTS splitter
DC/V1/2004
13
Jamadagni H S
DC/V1/2004
14
ADSL reach
Data Rate
Distance
Wire Size
Distance
1.5 or 2 Mbps
1.5 or 2 Mbps
6.1Mbps
6.1 Mbps
18,000 ft
15,000 ft
12,000 ft
9,000 ft
0.5 mm
0.4 mm
0.5 mm
0.4 mm
5.5 km
4.6 km
3.7 km
2.7 km
Jamadagni H S
DC/V1/2004
15
Jamadagni H S
DC/V1/2004
16
Jamadagni H S
DC/V1/2004
17
ADSL (spectrum)
Frequency Spectrum
T1/T3 circuits, Bridge Taps, load coils are disturbers when
in the same or adjacent binder as ADSL twisted pair.
Upstream
Data spectrum
Downstream
Data spectrum
POTS
4Khz
Jamadagni H S
20Khz
1.1 Mhz
DC/V1/2004
18
Modulation Techniques (ADSL)
• Discrete Multitone modulation
(DMT)
z
z
multicarrier sub-channels (256
downstream, 32 upstream) [4 Khz]
inferior quality, traffic reassigned to
different channel
z
z
6 Mbps downstream
640 kbps upstream
Jamadagni H S
DC/V1/2004
19
Modulation Techniques (ADSL)
• Carrierless Amplitude/Phase
modulation (CAP)
z
z
z
proprietary, mature technology
single carrier system similar to V.34
automatic bit rate adjustments for
line impairments
z
z
1.5 Mbps downstream
64 kbps upstream
Jamadagni H S
DC/V1/2004
20
Competing Technologies
• Cable Modems
z
z
z
z
z
18,000 ft limit (head-end)
Most cable operators need to upgrade
their networks to support bi-directional
service
128 kbps up to 30 Mbps (shared
bandwidth, up to 200 users on a loop)
Security
Reliability in question
Jamadagni H S
DC/V1/2004
21
Competing Technologies
• Digital Satellite transmission
z
z
z
Still need upstream data provider (usually
handled through modem or ISDN)
up to 30 Mbps downstream
Also used for push-technology
Jamadagni H S
DC/V1/2004
22
Q. 931 Message format
Protocol discriminator
0 0 0 0
F
Length
Call reference value
0
1
Info. element
identifier
Info. element
identifier
1
Contents of
info. element
Contents of
info. element
Message type
0
Other infromation
elements if
required
Jamadagni H S
Infromation element identifier
Contents of information element
DC/V1/2004
1
Bearer capability infromation element identifier
1
2
3
4a
4b
5
5a
5b
5c
5d
5e
6
7
0 0 0 0 0 1 0 0
1 X X X X X X X
X X X X X X X X
Bearer capability info.element identifier
Length of bearer capability contents
Codinbg std., info. transfer capability
Transfer mode, transfer rate
X X X X X X X X
0/1 X X X X X X
Rate multiplier
Layer 1 identity, user info. layer 1
1 X X X X X X X
1 X X X X X X X
Layer 2 identity, user info. layer 2
Layer 3 identity, user info. layer3
Jamadagni H S
DC/V1/2004
2
Procedure for a circuit-switched call
off hk Set up
Set up
eding
e
c
o
r
p
l
l
a
C
k
c
a
b
g
n
i
R
RB stop
S1
Jamadagni H S
Ringing
Alerting
Connect
connect
Data Flow
ST1
ET1
DC/V1/2004
ET2
ST2
S2
3
Modelling of basic and supplementary
services
Terminal Call
Processing
Basic Service
Protocol
(Q.931)
Supplementary
Services
Protocol
(Facility)
Q.931 Messages
LAPD
1.430/1.431
Jamadagni H S
Exchange Call
Processing
Basic Service
Protocol
(Q.931)
Supplementary
Services
Protocol
(Facility)
Q.931 Messages
LAPD
1.430/1.431
DC/V1/2004
1
Layer 3
Functions
Routing
Network connection establishment
Connection release
Multiplexing
Congestion control
Addressing
Jamadagni H S
DC/V1/2004
2
Layer 2
Functions
Traffic over D channel (control Info and data over D) Q 921
Q921 services
ÊConvey
user Info between layers entities using D channel
ÊSupport multiple terminals at user-NW installation
ÊMultiple layer 3 entity: support two types of transfer
ÊUnacknowledged transfer (unnumbered frames)
ÊAcknowledged transfer (like X 25) HDLC
Jamadagni H S
DC/V1/2004
3
Function of other layers
layer 4 :
Layer 5 :
layer 6 :
Layer 7 :
Jamadagni H S
error detection / recovery
flow control
layer 4 connection, release, muxing
session connection
management
session - transport management
encryption / decryption
compression / expansion
application related functions
DC/V1/2004
4
Protocol reference model I
320
1. Protocol reference model I320
Circuit - switched connection under common channel signalling
zPacket - switched comm over B/D/H
zSignalling between users and network based facilities (data base fores.)
zEnd - to - end signalling for users
zCombinations for multimedia comm.
z
2. Types of Info flow
1. User Info: digitised voice, data between users. Transmitted transparently through ISDN
or processed (encrypted for e.g.)
2. Control Info : acted upon this Info switching a connection / clearing change service
characteristics
Jamadagni H S
DC/V1/2004
5
Basic Call Control
interact with layer 2 (LAPD) to transmit / receive messages
z generate and interpret layer 3 messages
z admin of times and logical entities (call reference) used in control
z admin of resources (like B ch1)
z check to provide proper service consistent with user requirements
z routing / relaying
z network connection control
z error detection (sequences)
z error recovery
z sequencing layer 3 information
z
Jamadagni H S
DC/V1/2004
6
Layer 1 Functions
ÊEncoding
of digital data for transmission across the interface
ÊFull-duplex transmission of B channel data
ÊFull-duplex transmission of D channel data.
ÊMultiplexing of channels to form basic or primary access transmission
structure.
ÊActivation and deactivation of physical circuit.
ÊPower feeding from network termination to the terminal.
ÊTerminal identification.
ÊFaulty terminal isolation.
ÊD channel contention access
Jamadagni H S
DC/V1/2004
7
Q931 message types
Circuit - mode connection control functions needed for circuit-switched B channel
calls
Packed - mode connection control functions needed for circuit-switched
connections to ISDN packet-switched node.
User - user signalling messages with global call reference
functions are 4 types
Êcall
establishment set up a call on B chl.
Êcall information user-NW Info transfer after set-up
Êcall clearing
Êmiscellaneous
Jamadagni H S
DC/V1/2004
8
Messages
Signaling exchanged between user - network, network - network.
Protocol discriminator (0001000) for Q931 call reference
Message type: length (1 for BRI, 2 for PRI)
Call reference: call reference value (assigned by TE local significance)
Flag: 0: originator, 1: remote end
Call reference length = 0, Supplementary services Q932
CRF = 0, global CRF
Jamadagni H S
DC/V1/2004
9
Q931 messages for circuit mode connections
Call Establishment Messages
Message
Significance
Direction
ALERTING
CALL PROCEEDING
global
local
both
both
CONNECT
CONNECT
ACKNOWLEDGE
PROGRESS
SETUP
SETUP
ACKNOWLEDGE
global
local
both
both
global
global
local
both
both
both
Jamadagni H S
DC/V1/2004
Function
Indicates that user alerting has begun
Indicates that call establishment has
been initiated
Indicates call acceptance by called TE
Indicates that user has been
awarded the call
Reports progress of a call
Initiates call establishment
Indicates that call establishment
has been initiated but requests
more information
10
Call information phase messages
Message
Significance
Direction
RESUME
local
u n
RESUME
ACKNOWLEDGE
RESUME REJECT
local
n u
local
n u
local
local
u n
n u
local
n u
SUSPEND
SUSPEND
ACKNOWLEDGE
SUSPEND REJECT
Jamadagni H S
DC/V1/2004
Function
Requests resumption of previously
suspended call
Indicates requested call has
been reestablished
Indicates failure to resume suspended
call
Requests suspension of a call
Indicates call has been suspended
Indicates failure of requested call
suspension
11
Call clearing
messages
Message
Significance
Direction
DISCONNECT
global
both
RELEASE
local
both
RELEASE
local
COMPLETE
INFORMATION
local
NOTIFY
STATUS
local
STATUS
INQUIRY
Jamadagni H S
local
both
both
both
both
both
Function
Sent by user to request connection
clearing; sent by network to indicate
connection clearing
Indicates intent to release channel and
call reference
Indicates release of channel and call
reference
Provides additional information
Indicates information pertaining to a call
Sent in response to a STATUS
INQUIRY or at any time to report an error
Solicits STATUS message
DC/V1/2004
12
Frame format in ISDN layer 2
FLAG
ADDRESS
8 bits
16
CONTROL
8 or 16
INFORMATION
Variable
16
FCS
FLAG
8
(a) Frame format
0 C/R
SAPI
1
TEI
C/R is Command/response
SAPI is Service access point identifier
TEI is Terminal endpoint identifier
Jamadagni H S
DC/V1/2004
13
LAPD format
0
N(S)
P/F
1 0 SS0
0 0 0
P/F
1 1 M M P/F
N(S)
N(R)
S
M
P/F
M M M
N(R)
N(R)
Information
transfer
Supervisory
Unnumbered
= Transmitter send sequence number
= Transmitter receive sequence number
= Supervisory function bit
= Modifier function bit
= Poll/final bit
Jamadagni H S
DC/V1/2004
14
LAPD commands and responses
Name
Control Field
C/R
Description
Information format
I (Information)
0-N(S)--P-N(R)-- C
Exchange user data
Supervisory Format
RR (Receive Ready)
RNR (Receive Not
Ready)
REJ (Reject)
Jamadagni H S
10000000*-N(R)-- C/R
Positive ack; ready to receive
I-frame
10100000*-N(R)-- C/R
Positive ack; not ready top
receive
10010000*-N(R)-- C/R
Negative ack; go back N
DC/V1/2004
15
Unnumbered format
SABME (Set Asyn
1111P110
chronous Balanced
Mode)
DM (Disconnected
1111F000
Mode)
UI (unnumbered
1100P000
Information)
DISC (Disconnect)
1100P010
UA (Unnumbered
1100F110
Acknowledgement)
FRMR (Frame Reject) 1110F001
XID (Exchange IDidentification)
Jamadagni H S
1111*101
C
Request logical connection
R
Unable to establish or main
maintain logical connection
Used for unacknowledged
information transfer service
Terminate logical connection
Acknowledge SABME or DISC
C
C
R
R
C/R
Reports receipt of unacceptable frame
Exchange identification information
DC/V1/2004
16
SAPI and TEI assignments
SAPI Value
(a) SAPI Assignments
Related Protocol or Management Entity
0
16
32-61
63
All others
Call-control procedures
packet communication conforming to X.25 level 3
Frame relay communication
Layer 2 management procedures
Reserved for future standardisation
TEI Value
0-63
64-126
127
Jamadagni H S
(b) TEI Assignments
User Type
Nonautomatic TEI assignment user
equipment
Automatic TEI assignment user equipment
Used during automatic TEI assignment
DC/V1/2004
17
TEI and SAPI assignment
Network
User
ET/NT2
Connection endpoint suffix
Customer premises
PD
SI
B
B
1
* *
16
Data link
layer
TEI = 5
SI
1
B1 2
* *0
* * *0
Data link
layer
TEI = 5
TEI = 127
TE(1)
Layer 3
TE(2)
SI
PD
1
321 B
****
Data
link
layer
0
16
*
B
*
SAP identifier
TEI = 3, 8, 127
TEI = 127
SI: Signalling information
PD: Packet data
Jamadagni H S
SAPI = 0
DC/V1/2004
SAPI = 16
18
Digital Signal Encoding Format in ISDN
0
1
0
0
1
1
0
0
0
1
1
NRZ-L
Bipolar-AMI
Pseudoternary
Jamadagni H S
DC/V1/2004
19
Physical connector in ISDN
Contact Assignments for Plugs and Jacks of ISDN
Contact
Number
a
b
c
d
e
f
g
h
Jamadagni H S
TE
Power Source 3
Power Source 3
Transmit
Received
Received
Transmit
Power Sink 2
Power Sink 2
DC/V1/2004
NT
Power Sink 3
Power Sink 3
Receive
Transmit
Transmit
Received
Power Source 2
Power Source 2
20
The U interface
Fixed by local administration
z
z
z
4 wire interface
no echo cancellation procedures, simple line termination
2 wire interface
Ping-Pong operation, no echo cancellation, only one cable pair,
simple termination, limited lengths, extra processing for comm.
direction handling
2 wire interface
full duplex operation, echo cancellation, only one cable pair, no
limitation on length , extensive processing for echo cancellation
Jamadagni H S
DC/V1/2004
21
U interface circuit
Line
Encoding
TX Data
Echo
Cancellor
RX Data
Jamadagni H S
Decision
Feedback
Equalisation
Σ
Hybrid
+
DC/V1/2004
DSL
AD
22
ANSI U interface frame and superframe structure
18
1
2
3
4
5
6
7
8
18
ISW
SW
SW
SW
SW
SW
SW
SW
2B + D
2B + D
2B + D
2B + D
2B + D
2B + D
2B + D
2B + D
18
18
6 total 240 bits
2B + D
2B + D
2B + D
2B + D
2B + D
2B + D
2B + D
2B + D
2B + D
2B + D
2B + D
2B + D
2B + D
2B + D
2B + D
2B + D
M1 to M6
M1 to M6
M1 to M6
M1 to M6
M1 to M6
M1 to M6
M1 to M6
M1 to M6
SW = Sync Word = +3+3-3-3-3+3-3+3+3
ISW= Inverted SW=-3-3+3+3+3-3+3-3-3
2B+D = |B1 |B2 |D | (|8|8|2) M1 to M6 over head bits
Data are encoded as 00 = -3, 01= -1, 11=+1, 10 = +3
Jamadagni H S
DC/V1/2004
23