Transcript Chapter 8. DATA COMMUNICATION

©T.C. Chang
Chapter 8. DATA COMMUNICATION
• Need:
Design file exchange.
Part program downloading.
Person to person communication - e-mail, talk, video
conferencing.
System control: commands, status data, sensor data
Remote login.
• 50% of plant floor computer system cost are allocated to
networking costs.
• How to make control devices talk to each other.
• Solutions:
Point-to-point communication
Networking
7/7/2015
8-1
©T.C. Chang
METHODS OF COMMUNICATION
• Point-to-Point: direct connection of two devices
– Discrete I/O points – one bit at a time.
– Serial port –data byte transmitted in serial pulses.
– Parallel port – data byte transmitted in parallel.
• Network: multiple devices connected to the same
media (cable, radio wave, etc.)
– Ethernet
– FieldBus
– MAP, etc.
7/7/2015
8-2
©T.C. Chang
A COMPUTER
Control Unit
ALU
registers
I/O
address bus
data bus
control bus
Memory
7/7/2015
8-3
©T.C. Chang
AN I/O BUFFER
inter nal to a c omputer
addr es s
bus
decoder
s elect
clock
buff er
Data
Bus
f rom
c ontrol
bus
ex ternal
device
r ead/w rite
Individual bits can be used for
discrete I/O.
7/7/2015
8-4
©T.C. Chang
ASCII CODE
High Bits
7/7/2015
low
000
001
010
011
100
101
110
111
0000
NUL
DLE
SP
0
@
P
\
p
0001
SOH
DC1
!
1
A
Q
a
q
0010
STX
DC2
"
2
B
R
b
r
0011
ETX
DC3
#
3
C
S
c
s
0100
EOT
DC4
$
4
D
T
d
t
0101
ENQ
NAK
%
5
E
U
e
u
0110
ACK
SYN
&
6
F
V
f
v
0111
BEL
ETB
'
7
G
W
g
w
1000
BS
CHN
(
8
H
X
h
x
1001
HT
EM
)
9
I
Y
i
y
1010
LF
SUB
*
:
J
Z
j
z
1011
VT
ESC
+
;
K
[
k
{
1100
FF
FS
,
<
L
\
l
|
1101
CR
GS
-
=
M
]
m
}
1110
SO
RS
.
>
N
^
n
~
1111
SI
US
/
?
O
_
o
DE
8-5
©T.C. Chang
COMMUNICATION MODES
• Simplex can be viewed as a communications "one-way street".
Data only flows in one direction. That is to say, a device can be a
receiver or a transmitter exclusively. A simplex device is not a
transceiver. A good example of simplex communications is an FM
radio station and your car radio. Information flows only in one
direction where the radio station is the transmitter and the
receiver is your car radio. Simplex is not often used in computer
communications because there is no way to verify when or if data
is received.
• Duplex communications overcome the limits of Simplex
communications by allowing the devices to act as transceivers.
Duplex communication data flows in both directions thereby
allowing verification and control of data reception/transmission.
Exactly when data flows bi-directionally further defines Duplex
communications.
7/7/2015
8-6
©T.C. Chang
SIMPLEX AND DUPLEX (CONTINUE)
• Full Duplex devices can transmit and receive data
at the same time.
• Half Duplex devices allow both transmission and
receiving, but not at the same time. Essentially
only one device can transmit at a time while all
other half duplex devices receive.
7/7/2015
8-7
©T.C. Chang
SERIAL COMMUNICATION
UART
TX
UART
TX
RV
RV
Parallel
From the
Data bus
GND
Device 1
DTE
7/7/2015
GND
cable
Null Modem connector
does the swapping
Device 2
DCE
8-8
©T.C. Chang
INTERFACE
DTE: Data Terminal Equipment (terminal), PC, male connector
DCE: Data Circuit-terminating Equipment (modem, computer), female
connector
DTE
DTE
DCE
DCE
RS 232C, RS 422, X.21
RS232C 25 pin connector
DB25 connector
twisted pair balanced
1 < -3V
100 kbps at 1200m
0 > 3V
10 mbps at 12 m
< 20 kbps
< 15 m
unbalanced signal
7/7/2015
RS 422 37 pin or 9 pin
X.21
packet
transmission
mode
or unbalanced (RS 423A)
3 kbps at 1000 m
300 kbps at 10 m
8-9
©T.C. Chang
TRANSMITTING THE LETTER 'S'
0: Space
1: Mark
Volt
letter 'S'
1
start 1
parity bit
1 0 0 1 0 1 0 2 stop bits
0
time
sec/bit
1 start bit
7 data bit
1 parity bit
2 stop bits
Baud rate = 1/ clock
7/7/2015
Even parity
Some modem standards transfer more
than one bit per clock cycle.
e.g. V.32bis transmit 6 bits per baud.
8 - 10
©T.C. Chang
RS 232
PIN
NAME
1
FG
2
TD
3
RD
4
RTS
5
CTS
6
DSR
7
SG
8
CD
9
-
10
FUNCTION
EIA
CCITT
Frame Ground
AA
101
Transmitted Data
BA
103
Receive Data
BB
104
Request to Send
CA
105
<
Clear to Send
CB
106
<
Data Set Ready
CC
107
Signal Ground
AB
102
Carrier Detect
CF
109
Reserved
-
-
-
Reserved
-
-
11
-
Unassigned
-
-
12
(S)CD
<
Sec. Carrier Detect
SCF
122
13
(S)CTS
<
Sec. Clear to Send
SCB
121
14
(S)TD
Sec. Transmitted Data
SBA
118
15
TC
<
Transmitter Clock
DB
114
16
(S)RD
<
Sec. Received Data
SBB
119
17
RC
<
Receiver Clock
DD
115
18
-
Unassigned
-
-
19
(S)RTS
>
Sec. Request to send
SCA
120
20
DTR
>
Data Terminal Ready
CD
108.2
21
SO
<
Signal Quality Detector
CG
110
22
RI
<
Ring Indicator
CE
125
Data Rate Selector
CH
111
Data Rate Selector
CI
112
23
7/7/2015
<TO DTE
TO DCE>
>
<
>
<
>
>
24
(E)TC
>
Ext. Transmitter Clock
DA
25
-
Unassigned
-
-
113
8 - 11
©T.C. Chang
RS 422
RS422 is a "drop-in" replacement for most RS232 applications. It is full-duplex
and capable of long distance communications. Use balanced signal over
twisted pair of wire, allows much faster speed and longer distance.
7/7/2015
8 - 12
©T.C. Chang
COMPARISIONS
7/7/2015
RS 232
RS 422
RS 485
Cabling
single ended
single ended
multi-drop
multi-drop
Number of Devices
1 transmit
1 receive
5 transmitters
10 receivers
32 transmitters
32 receivers
Communication
mode
full duplex
full duplex
half duplex
half duplex
Max. Distance
50 feet at 19.2 kbps
4000 feet at 100 kbps
4000 feet at 100 Kbps
Max. Data Rate
19.2 kbps for 50 feet
10 Mbps for 50 feet
10 Mbps for 50 feet
Signaling
Unbalanced
Balanced
Balanced
Mark (data 1)
-5 V min.
-15 V max.
2 V min. (B>A)
6 V max. (B>A)
1.5 V min. (B>A)
5 V max. (B>A)
Space (data 0)
5 V min.
15 V max.
2 V min. (A>B)
6 V max. (A>B)
1.5 V min. (A>B)
5 V max. (A>B)
Input Level Min.
+/- 3 V
0.2 V difference
0.2 V difference
Output Current
500 mA
150 mA
250 mA
8 - 13
©T.C. Chang
Modem
• Flow control
– Software through XON and XOFF
– Hardware through pin outs, I.e. request to send (RTS), clear to
send (CTS), data terminal ready (DTR), and data set ready
(DSR)
• Modulating the Signal
– 1 baud = one audio signal transitions per second
– Frequency-shift keying (FSK): 1750 Hz for 1, 1080 Hz for 0. 1
baud = 1 bps
– Phase-shift keying (PSK): 0 and 1 are represented by the
alteration of the carrier’s phase. Bit is coded at fixed phase
shift, e.g. 0, 90, 180, and 270 degrees. More bits per baud.
– Quadrature-amplitude modulation (QAM): combine both phase
and frequency. At 1700 Hz or 1800 Hz of 2400 baud, each
phase-shift keyed. Six bps data per baud. Only 4 data bits
usable.
– Trellis-coded quadrature-amplitude modulation (TCQAM or
TCM): Use all 6 data bits. 14,400 bps modems use this.
7/7/2015
8 - 14
©T.C. Chang
MODEM STANDARDS (reference only)
CCITT V.XX standards (Consultative Committee for International Telephone
and Telegraph)
V.22, V.22 bis. : synchronous/asynchronous data transmission, full-duplex
operation over 2 wire at 1,200 bps (2,400 and 1,200 bps for V.22 bis) data
rate.
V.32 : synchronous/asynchronous data transmission, full-duplex operation
over 2 wire at 9,600 bps data rate.
V.32 bis: synchronous/asynchronous data transmission, full-duplex
operation over 2 wire at 14,400, 12,000, 9,600, 7,200, 4,800 bps data rate.
V.34 bis: synchronous/asynchronous data transmission, full-duplex
operation over 2 wire at 28.8k, ...
Modem-connection negotiations (training and retraining), may reduce the
data rate due to line noise. Fastrain: may go up the speed as well.
V.35
Duplex: full (two lines, two way), half (one line, one way)
Bell standard: Bell 103, 300 bps; Bell 201B: 2,400 bps, full duplex on 4 wire,
or 1,200 bps, half duplex on 2 wire. Bell 201C: 2,400 bps, half duplex on
2 wire; Bell 208 A & B: 4,800 bps
Data compression: compress the data before transmission.
7/7/2015
8 - 15
©T.C. Chang
PARALLEL INTERFACE ADAPTER
address
decoder
Data
Bus
from
com put er
7/7/2015
enable
Data
Bus
Buffer
Chip
Select
and Read
Writ e
Control
Control
Regist er
Data Direction
Regist er
Peripheral
Int erface
Data
Output
Regist er
8 - 16
©T.C. Chang
PC Parallel Port
Pin
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
7/7/2015
Descritpion
Strobe +Data Bit 0
+Data Bit 1
+Data Bit 2
+Data Bit 3
+Data Bit 4
+Data Bit 5
+Data Bit 6
+Data Bit 7
-Acknowledge
+Busy
+Paper End
+Select
-Auto Feed
-Error
-Initialize Printer
-Select Input
-Data Bit 0 returnn (GND)
-Data Bit 1 returnn (GND)
-Data Bit 2 returnn (GND)
-Data Bit 3 returnn (GND)
-Data Bit 4 returnn (GND)
-Data Bit 5 returnn (GND)
-Data Bit 6 returnn (GND)
-Data Bit 7 returnn (GND)
I/O
Out
Out
Out
Out
Out
Out
Out
Out
Out
Out
In
In
In
In
Out
In
Out
In
In
In
In
In
In
In
In
8 - 17
©T.C. Chang
IEEE 488
•
Standard digital interface for programmable instrumentation
•
HP interface (originally, is available on most instruments)
•
GPIB (General Purpose Interface Bus)
•
1 mbps
•
The IEEE-488 interface system consists of 16 signal lines and 8 ground
lines. The 16 signal lines are divided into 3 groups (8 data lines, 3
handshake lines, and 5 interface management lines).
•
Devices on the bus are: Listeners, Talkers, and Controllers
•
up to 15 devices to be interconnected on one bus. Each device is assigned
a unique primary address, ranging from 0-30, by setting the address
switches on the device. A secondary address may also be
specified,ranging from 0-30.
•
Total cable length is limited to 20 meters with a maximum of 20 devices.
•
TTL level signal.
7/7/2015
8 - 18
©T.C. Chang
OTHER INTERFACES
Mostly for instrumentation. GPIB (IEEE 488) is still the
major players.
7/7/2015
Theoretical
Actual
First-Byte Latency
USB
1.5 Mbytes/s
1.25 Mbytes/s
20 ms
1394
50 Mbytes/s
9.6 Mbytes/s
6 ms
GPIB
1 Mbytes/s
1 Mbytes/s
110 µs
HS488
8 Mbytes/s
7.7 Mbytes/s
110 µs
8 - 19
©T.C. Chang
DATA EXCHANGE METHODS
• Polling
• Interrupt
• Direct Memory Access (hard disk to computer)
7/7/2015
8 - 20
©T.C. Chang
POLLING
st at u s
o f in p u t
po rt
lo o p
no
s t at u s
of out put
po rt
no
7/7/2015
yes
lo ad in p u t b y t e t o
t h e ac c u m u lat o r
yes
se n d a b y t e t o
t he o ut p ut p ort
8 - 21
©T.C. Chang
INTERRUPT
high priority interrupt
low priority interrupt
Main CPU Loop
7/7/2015
8 - 22
©T.C. Chang
NETWORKS
No longer a point-to-point connection.
Many devices connected together and information can be
passed by one device to any of the devices on the
network.
Local area network - Ethernet, FDDI (Distributed Data
Interface), ATM (Asynchronous Transfer Mode)
Wide area network
High speed local network
7/7/2015
8 - 23
©T.C. Chang
GLOSSARY OF SELECTED TERMS
Bandwidth: frequency range used by the communication system.
Baseband: use voltage difference (digital)
Broadband: use coaxial cable and analog (RF) signals. Higher band width,
multiple channels on the same cable. Digital signals are modulated on
a carrier frequency.
CTV: 5 mbps per channel
Carrier from 5-300 M Hz
Carrier: A continuous frequency capable of being modulated or impressed
with a second (information) signal.
DDS (Dataphone Digital Service): AT&T service in which data is transmitted
in digital rather than analog form. Need no modem.
FDDI (Fiber Distributed Data Interface): ANSI standard for fiberoptic links
with data rates up to 100 mbps. LED or laser light source; 2 km for
unrepeated data transmission at 40 mbps.
ISDN (Integrated Services Digital Network): mixed digital-transmission
services, basic rate at 144 kbps, and primary rates at 1.544 and 2.048
mbps.
7/7/2015
8 - 24
©T.C. Chang
GLOSSARY OF SELECTED TERMS
Medium Access Control: controls which device on the network get the
to send data to the medium.
CSMA/CD
Token Ring
Token Bus
Packet: small chunk of data.
Protocol: a set of rules that governs the operation of functional units to
achieve communication.
TCP/IP: Transport protocols concurrently with existing Ethernet.
NFS: network file system - file system sharing, remote disk mounting.
7/7/2015
8 - 25
©T.C. Chang
IDEAL LAN CHARACTERISTICS
• high speed: greater than 10 mega bits per second
• low cost: easily affordable on a microcomputer and/or
machine controller
• high reliability/integrity: low error rates, fault tolerant, reliable
• expandability: easily expandable to install new nodes
• installation flexibility: easy to be installed in an existing environment
• interface standard: standard interface across a range of computers
and controllers.
7/7/2015
8 - 26
©T.C. Chang
COMMUNICATION NETWORK
• Protocol – defines both physical and software
rules.
• Most widely accepted model is a 7 layered
protocol model.
7/7/2015
8 - 27
©T.C. Chang
ISO/OSI MODEL
Dev i ce B
Dev i ce A
User Pro gra m
User Pro gra m
Lay er 7
Ap pl icat io n
Ap pl icat io n
Lay er 6
P resen tat io n
P resen tat io n
Lay er 5
Ses si on
Ses si on
Lay er 4
Trans p ort
Trans p ort
Lay er 3
Net wo rk
Net wo rk
Lay er 2
Dat a Lin k
Dat a Lin k
Lay er 1
P hys ical
P hys ical
med iu m
7/7/2015
8 - 28
©T.C. Chang
LAYERED PROTOCOL
2. DATA LINK LAYER
• flow control
• error control
Activate, maintain and deactivate the link. Error free transmission on
the same network. Detecting noise. (media access, logical link)
3. NETWORK LAYER
provides the transparent transfer of data between transport entities.
Responsible for establishing, maintaining, and terminating
connections (between networks). Use globally unique node address.
4. TRANSPORT LAYER
Ensures that data units are delivered error-free, in sequence, without
no losses or duplications.
Connection management
7/7/2015
8 - 29
©T.C. Chang
LAYERED PROTOCOL
5. SESSION LAYER
Controlling the dialogue between applications.
Dialogue type: two-way simultaneous (TWS), two-way alternate (TWA),
one-way, etc.
Recovery after network breakage.
6. PRESENTATION LAYER
Syntax of the data exchanged between application entities.
e.g. teletext, videotex, encryption, virtual terminal.
7. APPLICATION LAYER
Common application services (CASE)
Specific application services (SASE)
Management
file transfer
job transfer
7/7/2015
8 - 30
©T.C. Chang
A PACKET
Preamble
SYN code
Physical layer message
Data link layer message
Network layer message
Transport layer message
Session layer message
Presentation layer message
Application layer message
Data
Checksum
Postamble
7/7/2015
SYN code
8 - 31
©T.C. Chang
CABLES
insulators
Twist pair cable
ground wire
Unshielded:
Shielded: signal loss, thick
core wire
Coaxial cable
Thick: CATV, RG-59, 75 ohms
Thin: Ethernet, RG-58, 52 ohms
core
(62.5 micron)
cladding
Fiber-optic Cable
noise immune
7/7/2015
8 - 32
©T.C. Chang
LAN TOPOLOGIES
Ring
Star
Bus
7/7/2015
8 - 33
©T.C. Chang
ETHERNET
Terminator
Tap
Transceiver
RF
T/S
50 ohmcoaxial cable
T/S
digital
Computer
C1
T/S
T/S
C3
C4
Repeater
C2
bridge
T/S
7/7/2015
8 - 34
©T.C. Chang
COLLISION DETECTION
CSMA/CD (Carrier sensing) protocol
t0
A
A begin transmi ss ion
a is t he t ime f or s ignal to t rav el to B,
B
trans mis s ion time > 2a
t 0 +a- e
A
B begin transmi ss ion bef ore s ignal
reach B
B
A
B detect s coll is on
B
t 0 +a
t 0 +2 a- e
A
7/7/2015
A detect s coll is on j us t bef ore the end
of transm iss ion.
B
8 - 35
©T.C. Chang
ETHERNET CONNECTIONS
Standard Ethernet (10BASE5)
• segment length  500 m
• cable  4 km
• transceiver cable  50 m
• between transceivers  2.5 m
•  100 transceivers per segment
• 50 ohm terminators
ThinNet Ethernet (10BASE2)
Twisted-pair Ethernet (10BASE-T)
• segment length  100 m
• unshielded twisted-pair cable
• devices connected to a hub
in a star configuration
• Hub connected to the
standard Ethernet
• Use twisted-pair transceiver.
computers
• segment length  185 m
• cable length  4 km
• T-connectors, 0.5 m between each
T-connector
Hub
•  30 connections
7/7/2015
• 50 ohm terminators
• T-connectors plugged directly to the
Ethernet card.
computers
8 - 36
©T.C. Chang
A TOKEN RING
computer
repeater
A
B
direction of token
and data packet
D
C
Only one token is passed
around the network.
The device who has the token
may transmit.
7/7/2015
8 - 37
©T.C. Chang
A TOKEN BUS
Logical ring
C
A
C
A
B
D
B
D
C
D
E
predecessor
D
E
B
Add a new node
A
B
E
successor
Token passing network. Whoever has the token may transmit one or
more packets. When it is done, or the time has expired, it passes the
token to the next station.
7/7/2015
8 - 38
©T.C. Chang
RS 485 BASED NETWORK
S485 is sometimes termed as RS485 Multidrop LAN since it can connect several
devices in a LAN network environment. These devices are all connected to a single
pair wire. Transmit and receive share the same two wires.
Officially the RS485 specification allows only 32 nodes (devices) on the LAN.
However, I.C. manufacturers have developed RS485 drivers capable of allowing
128 to 255 nodes on an RS485 LAN.
7/7/2015
8 - 39
©T.C. Chang
FIELD BUS
• Foundation Field Bus - A Fieldbus is a digital, two-way,
multi-drop communication link among intelligent
measurement and control devices. It serves as a Local Area
Network (LAN) for advanced process control, remote
input/output and high speed factory automation
applications.
• The Fieldbus Access Sublayer (FAS) maps the Fieldbus
Message Specification (FMS) onto the Data Link Layer
(DLL).
• High Speed Ethernet (HSE) is the Fieldbus Foundation's
backbone network running at 100 Mbit/second.
• Bus speed is 31.25 kbit/s.
• Can communicate with other devices through HSE using
Ethernet protocols such as TCP/IP, SNTP, etc.
7/7/2015
8 - 40
©T.C. Chang
FIELDBUS MODEL
Layer 7. Application
Fieldbus message specification
Fieldbus access sublayer
7/7/2015
Layer 2. Data link
Data link layer
Layer 1. Physical
Physical layer
8 - 41
©T.C. Chang
MEDIA ACCESS CONTROL
• Token passing network
• Token controlled by a Link Active Scheduler
(master of the network).
• Other devices on the network are basic devices.
• The device which holds the token can transmit to
any other devices on the network.
7/7/2015
8 - 42
©T.C. Chang
APPLICATIONS OF FIELDBUS
Sensors and actuators.
7/7/2015
8 - 43
©T.C. Chang
NETWORK HIERARCHY
Plant wide
Office automation and
department computers
network
Automation and display
systems
Control system and
LANs
Fieldbus network
7/7/2015
Factory/plant instrumentation
and control devices
8 - 44
©T.C. Chang
Allen-Bradley Networks
7/7/2015
8 - 45
©T.C. Chang
DEVICE NET
• From Rockwell Automation, Allen-Bradley
devision.
• Based on the Fieldbus.
• Low level, 64-node multidrop network using
single cable to interface devices up to 500 m to
PLC.
• Use either two twisted pair wires (24V) in a round
cable, or two pair wires flat cable.
• Data rates, 500 kbps (100 m), 250 kbps (250 m),
125 kbps (500 m).
• Many sensors are device net ready.
7/7/2015
8 - 46
©T.C. Chang
CONTROL NET
• By Rockwell Automation, Allen-Bradley
• For time critical applications.
• High-speed link between controller and I/O
devices.
• 5 mbps
• 30 km or more using repeaters (in star, tree, or
bus configuration), 1000 m w/o repeater.
• Physical layer can be fiber optic or 75 o cable.
7/7/2015
8 - 47
©T.C. Chang
ETHERNET II
•
•
•
•
•
•
•
Preamble 8 bytes
Destination
6 bytes
Source
6 bytes
Ethernet type
2 bytes (IPX/SPX, TCP/IP, etc)
Data
46 – 1500 bytes
Pad Character up to 46 bytes
Frame check sequence
4 bytes
• Frame length: 64-1518 bytes (not including
preamble)
7/7/2015
8 - 48
©T.C. Chang
NOVELL’S LAN
Physical layer – 3C5X9.com
LAN driver
Data link Layer – LSL.com
Network Layer – IPX0D1.com
ODI
NDIS
Transport – TCP/IP.exe
Socket API - winsock.dll
Application layer - windows
ftp, http, telnet
7/7/2015
8 - 49
©T.C. Chang
MAP 2.1 STANDARD
Layer
MAP implementation
Layer 7
ISO FTAM {DP} 8571
Application
File Transfer Protocol
Manufacturing Messaging Format Standard (MMFS)
MAP Directory Services
MAP Network Management
Layer 6
Presentation
NULL/MAP transfer
Layer 5
ISO Session{IS} 8327
Session
Basic Combined Subset & Session Kernel, Full Duplex
Layer 4
Transport
ISO Transport{IS} 8073
Class 4
Layer 3
ISO Internet{DIS} 8473
Network
Connectionless, SubNetwork Dependent Convergence Protocol
Layer 2
ISO Logical Link Control {DIS} 8802/2 (IEEE 802.2)
Data Link
Type 1, Class 1
ISO/IEEE 802.4 Token Passing Bus Medium Access Control
7/7/2015
Layer 1
ISO Token Passing Bus{DIS} 8802/4 (IEEE 802.4)
Physical
10 Mbps Broadband
8 - 50
©T.C. Chang
An Integrated Corporate
Communication Network
Gateway
Corporate
Ethernet
Gateway
Office
Finance/accounting
Corporate
TOP network
IBM
SNA network
Bridge
Division
TOP network
Corporate
Offices
CAD/CAM
CRT
Factory
Gateway
CRT
Terminal
server
Gateway
Office
TOP network
Router
Robots
MAP
Sub Network
Machines
PLCs
Gateway
PLCs
Robots
7/7/2015
Data base
MAP
Backbone
Vendor
Network
8 - 51
©T.C. Chang
ISDN: Integrated Service Digital Network
packet-switched capabilities
terminal
equip.
ISDN
switch
circuit-switched
ISDN
switch
terminal
equip.
nonswitched
common-channel signaling
•
•
•
•
•
B channel: 64 kbps - basic user channel
D channel: 16 or 64 kbps - control, setup, calls on B.ch. common chan
H0: 384 kbps
H11: 1.536 Mbps
H12: 1.92 Mbps
Basic access: two B-channels and one D channel - total 144 kbps
Primary access: T-1 transmission at 11.544 Mbps, 23 B-channels, 1 D
channel
7/7/2015
8 - 52
©T.C. Chang
Frame Relay and ATM
• On top of the physical layer
• Frame Relay:
– Use on ISDN line, assume less transmission error. Less
overhead than X.25 packet-switching.
– Block data transfer, up to 2 Mbps
• ATM: Asynchronous Transfer Mode
– For broadband ISDN
– packet switching
» X.25 - control, data on the same channel, variable length
» ATM - separate, fixed length (cells), 10s and 100s Mbps
7/7/2015
8 - 53
©T.C. Chang
COMMUNICATION REQUIREMENTS
High quality compressed video
(6 Mbps - 24 Mbps)
Medium quality compressed video
(1.5 Mbps - 6 Mbps)
1.2 Gbps
Low quality compressed video
(50 Kbps - 1.5 Mbps)
High fidelity audio
(64 Kbps - 1.5 Mbps)
Speech grade audio
(32-64 Kbps)
1.54 Mbps
10 Kbps
Ordinary Phone
7/7/2015
100 Mbps
10 - 16 Mbps
56 Kbps
Basic rate
ISDN
Primary rate
ISDN
Ethernet and
Token Ring
Fast Ethernet,
FDDI
Asynchronous
Transfer Mode
(ATM)
8 - 54
©T.C. Chang
COMMUNICATION ON UNIX
NETWORK INTERFACE LAYER
PROTOCOL LAYER
SOCKET LAYER
when a communication is desired, create a socket
get
Protocol
protocol
Application
e.g. ftp
telnet
IN buffer
Out buffer
out packet
Network
interface
Hardware
In packet
determines the route of travel
7/7/2015
8 - 55
©T.C. Chang
EXAMPLE
#include <sys/types.h>
#include <sys/socket.h>
sockaddr server;
internet domain
for TCP protocol
s = socket(AF_INET, SOCK_STREAM,0); /* create a socket*/
connect(s,&server, sizeof(server)); /* establish connection */
write(s,buf,sizeof(buf));
/* send data */
close(s); /* close socket*/
7/7/2015
8 - 56
©T.C. Chang
TCP/IP PROTOCOL
User Program
Layer 7
Application
Layer 6
Presentation
Layer 5
Session
Layer 4
Transport
T CP
Layer 3
Network
IP
Layer 2
Data Link
UD P
FT P
SM T P
T ELNET
ET HERNET
Layer 1
Physical
UDP: User datagram protocol
FTP: File transfer protocol
SMTP: Simple mail transfer protocol
TELNET: Virtual terminal protocol
7/7/2015
TCP: Transmission control protocol
IP: Internetwork protocol
8 - 57
©T.C. Chang
DATA COMMUNICATION
ALTERNATIVES
• Phone and fax
• BBS (bulletin board system) run your own.
• Commercial information vendors: CompuServe,
Prodigy, America Online, GEnie
• Internet connection
7/7/2015
8 - 58
©T.C. Chang
WHAT IS INTERNET?
Internet is a loosely connected wide area network. It is a group of
worldwide information resources open to everyone on the network.
Some characteristics of the internet:
• Origin: Arpanet sponsored by US DOD in the 1970s.
• Who may participate? Anyone who pays a nominal fee to connect to a
nearby network and agrees to follow a set of rules.
• Who runs the network? Nobody is in charge.
• Who pays for it and to whom? The organization who is connected to the
network must pay it own segment of the network. There is no central
organization to collect the payment.
• What kind of hardware is needed to run the network? Any kind of
computer hardware.
• How to connect to a network? Find a closest node and negotiate the
connection.
• What is the limitation of using it? No direct commercial use.
• What is most widely used operating system on the net? Unix.
• How big is the network? Too big and growing to be even bigger every
minute.
7/7/2015
8 - 59
©T.C. Chang
INTERNET ROUTERS
INTERNET
network
layer
data
link
physical
layer
Network A
7/7/2015
network
layer
data
link
physical
layer
Network B
network
layer
data
link
physical
layer
Network C
8 - 60