Physical layer interface & standards

Data Communication & Networking

Physical Layer-Interface, Standards, Connectors

Prepared By: Srashti Vyas

Connecting Devices



Electronic Industries Association (EIA) Standard /RS-232

• RS-232 is a standard for serial communication transmission of data.

• It formally defines the signals connecting between a DTE (data terminal equipment) such as a computer terminal, and a DCE (data circuit-terminating equipment or data communication equipment), such as a modem


EIA 232-D Interface Specification

1. Mechanical specifications:-gives details of the mechanical dimensions and the type of connectors to be used on the device & the medium. Pin assignment of the connector are also specified.

2. Electrical specifications:-defines the permissible limits of the electrical signal appearing at the interface in terms of voltage, current, impedance, rise time etc. The required electrical characteristics of the medium are also specified.

3. Functional specifications:- indicates the functions of various control signals

4. Procedural specifications:- indicates the sequence in which the control signals are exchanged between the physical layer for carrying out their functions.


EIA 232 interface is applicable to the following modes of transmission:

1. Serial transmission of data2. Synchronous and asynchronous transmission3. Point-to-point and point-to-multipoint working4. Half duplex and full duplex transmission


EIA 232/RS 232

EIA 449/ RS-449

• RS-449 mechanical specifications defines a combination of two connectors that uses a

DB-37 connector and a DB-9 for combined 46pins.

• Its functional specifications gives the data-37 pins properties similar to those of DB-

25.

• The major functional difference between the 25 & 37 pin connectors is that all

functions relating to the secondary channel have been removed from DB-37.

• To maintain compatibility with EIA-232,EIA-449 defines two category of pins to be

used in exchanging data, control & timing information.

1. Category I Pins :-includes those pins whose functions are compatible with

RS232,though most have been removed.

2. Category II Pins :- those that have been redefined and no equivalence with EIA-

232.Prepared By: Srashti Vyas

EIA-449 DB’s



Pin Signal Name Description Pin Signal Name Description

1 Shield 19 SG Signal Ground

2 SI Signal Rate Indicator 20 RC Receive Common3 n/a unused 21 n/a unused4 SD- Send Data (A) 22 SD+ Send Data (B)

5 ST- Send Timing (A) 23 ST+ Send Timing (B)

6 RD- Receive Data (A) 24 RD+ Receive Data (B)

7 RS- Request To Send (A) 25 RS+ Request To Send (B)

8 RT- Receive Timing (A) 26 RT+ Receive Timing (B)

9 CS- Clear To Send (A) 27 CS+ Clear To Send (B)

10 LL Local Loopback 28 IS Terminal In Service

11 DM- Data Mode (A) 29 DM+ Data Mode (B)

12 TR- Terminal Ready (A) 30 TR+ Terminal Ready (B)

13 RR- Receiver Ready (A) 31 RR+ Receiver Ready (B)

14 RL Remote Loopback 32 SS Select Standby

15 IC Incoming Call 33 SQ Signal Quality

16 SF/SR+ Signal Freq./Sig. Rate Select. 34 NS New Signal

17 TT- Terminal Timing (A) 35 TT+ Terminal Timing (B)18 TM- Test Mode (A) 36 SB Standby Indicator

37 SC Send Common

DB-37 Pin Description


DB-37


DB-9 Pin DescriptionPin Signal Name Description

1 Shield

2 SRR Secondary Receive Ready

3 SSD Secondary Send Data

4 SRD Secondary Receive Data

5 SG Signal Ground

6 RC Receive Common

7 SRS Secondary Request to Send

8 SCS Secondary Clear to Send

9 SC Send Common


DB-9


Standard telephone cable connectors, RJ-11 has 4 wires (and RJ-12 has 6 wires). RJ-11 is the acronym for Registered Jack-11, a four- or six-wire connector primarily used to connect telephone equipment.

RJ-11 Pin Signal Name

1 VCC (5 volts regulated)

2 Power Ground

3 One Wire Data

4 One Wire Ground

RJ-11 (Registered Jack)

RJ11 Connector


RJ11 Connector for RS 232 Communication

RJ11 Connector

Pin Signal Description I/O

1 NC --

2 +5V +5V power only for STU, left it unconnected when connect to a PC serial port /NC

O

3 TxD RS232 transmit. O

4 GND Ground. GND

5 RxD RS232 receive. I

6 NC --


The acronym for Registered Jack-45 is RJ-45. The RJ-45 connector is an eight-wire connector that is commonly used to connect computers to a local area network (LAN), particularly Ethernet LANs. Although they are slightly larger than the more commonly used RJ-11 connectors, RJ-45s can be used to connect some types of telephone equipment.

RJ45 Connector

RJ-45 (Registered Jack)


Difference Between RJ45 and RJ11• The main difference between these two is in where they are actually used.

RJ45 jacks are used in networking, where you connect computers or other network elements to each other. RJ11 is the cable connector that is being used in telephone sets.

• The number of cables that are accommodated in each connector. here are only four wires inside and RJ11 while there are eight wires inside an RJ45. As a consequence of having to accommodate more wires, RJ45 connectors are also a little bit bigger than RJ11s.

Summary1.RJ45 is used with ethernet cables in computer networking while RJ11 is used in connecting telephone units2.RJ45 contains more wires than RJ113.RJ45 is physically bigger than RJ11 to accommodate the extra wires


BNC Connectors

• The BNC (Bayonet Neill–Concelman) connector is a miniature quick connect/disconnect radio frequency used for coaxial cable.


BNC Tee connectors

Applications1. Originally designed for military use2. Has gained wide acceptance in video and RF applications to

2 GHz.3. The BNC connector is used for signal connections such as: i. analog and serial digital interface video signals ii. amateur radio antennas iii. aerospace electronics (avionics) iv. test equipment.4. Used for composite video on commercial video devices.5. Commonly used on 10base2 thin Ethernet network cables and

network cards.



Aspects to digital-to Analog conversion

• Bit Rate / Baud Rate– Bit rate is the number of bits per second. Baud rate is the number

of signal units per second. Baud rate is less than or equal to the bit rate.

– Bit rate is important in computer efficiency– Baud rate is important in data transmission.

• Baud rate determines the bandwidth required to send signal– Baud rate = bit rate / # bits per signal unit

– An analog signal carries 4 bits in each signal unit. If 1000 signal units are sent per second, find the baud rate and the bit rate• Baud rate = 1000 bauds per second (baud/s) Bit rate = 1000 x

4 = 4000 bps– The bit rate of a signal is 3000. If each signal unit carries 6 bits,

what is the baud rate?• Baud rate = 3000/6 =500 bauds/sec

MODEM• A modem (modulator-demodulator) is a network hardware device that

modulates one or more carrier wave signals to encode digital information for

transmission and demodulates signals to decode the transmitted information.

• The goal is to produce a signal that can be transmitted easily and decoded to

reproduce the original digital data.

• A common type of modem is one that turns the digital data of a computer into

modulated electrical signal for transmission over telephone lines and

demodulated by another modem at the receiver side to recover the digital data.


Classification of MODEM/ MODEM Standards

• Classified by the amount of data they can send in a given unit of

time, usually expressed in bits per second (symbol bit/s,

sometimes abbreviated "bps"), or bytes per second (symbol B/s).

• Classified by their symbol rate, measured in baud. The baud unit

denotes symbols per second, or the number of times per second

the modem sends a new signal.



Bit Baud comparison

Modulation Units Bits/Baud

Baud rate

Bit Rate

ASK, FSK, 2-PSK Bit 1 N N

4-PSK, 4-QAM Dibit 2 N 2N

8-PSK, 8-QAM Tribit 3 N 3N

16-QAM Quadbit 4 N 4N

32-QAM Pentabit 5 N 5N

64-QAM Hexabit 6 N 6N

128-QAM Septabit 7 N 7N256-QAM Octabit 8 N 8N


Phone modems

Classification of MODEM/ MODEM StandardsToday most of the modems are V-series standards published by the ITU-T.

1. V.32:Uses a combined modulation and encoding technique called Trellis-coded modulation.

2. V.32bis: First of the ITU-T standards to support 14400 bps transmission. Uses 128 QAM

transmission at a rate of 2400 baud. An additional feature provided by V.32bis, is inclusion

of an automatic fall-back and fall forward feature that enables the modem to adjust its speed

upward or downward depending on the quality of the line or signal.

3. V.34bis:Provides a bit rate of 28,800 with a 960-point constellation and a bit rate of 33,600

bps with a 1664-point constellation.

4. V.90: These modem with a bit rate of 56kbps are available, these are called 56K modems.

These modem may be used only if one party is using digital signaling(such as through an

internet provider).



V-series (ITU-T Standards)• V-32.

– Uses a combined modulation and encoding technique: Trellis coded Modulation.

– Trellis = QAM + a redundant bit– 5 bit (pentabit) = 4 data + 1 calculated from data.– A signal distorted by noise can arrive closer to an adjacent point than the

intended point (extra bit is therefore used to adjust)– Less likely to be misread than a QAM signal.

2400 baud • 4 bit = 9600 bps


V-series (cont.)• V-32.bis

– First ITU-T standard to support 14,400 bps transmission.– Uses 128-QAM

• (7 bits/baud with 1 bit for error control) • at a rate 2400 baud 2400 * 6 = 14,400 bps

– Adjustment of the speed upward or downward depending on the quality of the line or signal

• V-34 bis– Bit rate of 28,800 bps with 960-point constellation to 1664-point

constellation for a bit rate of 33,600 bps.


Constellation Diagram

Constellation diagram for V.32 Constellation diagram for V.32bis


V-series (cont.)• V-90

– Traditionally modems have a limitation on data rate (max. 33.6 Kbps)

– V-90 modems can be used (up to 56Kbps) if using digital signaling.• For example, Through an

Internet Service Provider (ISP)

– V-90 are asymmetric • Downloading rate (from ISP

to PC) has a 56 Kbps limitation.

• Uploading rate (from PC to IST) has a 33.6 Kbps limitation.


V-90/92 (cont.)• V-90

– In uploading, signal still to be sampled at the switching station. Limit due to noise sampling.

– Phone company samples at 8000 times/sec with 8 bits (including bit error)• Data rate = 8000 * 7 =

56Kbps– In download, signal is not

affected by sampling.• V-92

– Speed adjustment– Upload data at 48Kbps.– Call waiting service


Cable Modem• A cable modem is a device that enables you to hook up your PC to

a local cable TV line and receive data at about 1.5 Mbps. • A cable modem can be added to or integrated with a set-top box

that provides your TV set with channels for Internet access. In most cases, cable modems are furnished as part of the cable access service and are not purchased directly and installed by the subscriber.

• A cable modem has two connections: one to the cable wall outlet and the other to a PC or to a set-top box for a TV set.

Motorola SURFboard SBV6120E EuroDOCSIS 3.0 cable modem


TYPES OF MODEMConnection Modulation Bit rate(Kbps)

110 baud Bell 101 modem FSK 0.1300 baud (Bell 103 or V.21) FSK 0.3

1200 modem (1200 baud) (Bell 202) FSK 1.2

2400 modem (600 baud) (V.22bis) QAM 2.4

2400 modem (1200 baud) (V.26bis) PSK 2.4

4800 modem (1600 baud) (V.27ter) PSK 4.8

9600 modem (2400 baud) (V.32) QAM 9.6

14.4k modem (2400 baud) (V.32bis) trellis 14.4

19.2k modem (2400 baud) (V.32terbo) trellis 19.2

28.8k modem (3200 baud) (V.34) trellis 28.8

33.6k modem (3429 baud) (V.34) trellis 33.6

56k modem (8000/3429 baud) (V.90) digital 56.0/33.6

56k modem (8000/8000 baud) (V.92) digital 56.0/48.0

https://en.wikipedia.org/wiki/Baud

https://en.wikipedia.org/wiki/Bell_101


https://en.wikipedia.org/wiki/ITU_V.21


https://en.wikipedia.org/wiki/V.22bis


https://en.wikipedia.org/wiki/V.27ter

https://en.wikipedia.org/wiki/V.32


https://en.wikipedia.org/wiki/V.32terbo

https://en.wikipedia.org/wiki/V.34_(recommendation)



https://en.wikipedia.org/wiki/V.92

NULL MODEM• When we need to connect two DTE, in same building or when a terminal &

the host computers in vicinity(less than 15m apart), we don’t use MODEM.

• We need an interface to handle the exchange or an intermediary device which

has DCE ports on both sides that face DTE’s. This device is called “Null

Modem”, because it may not contain any electronic device or modem.

• A Null Modem provides the DTE-DTE interface without the DCE’s.

• Null modem is a communication method to directly connect two DTEs

(computer, terminal, printer, etc.) using an RS-232 serial cable.

• With a null modem connection the transmit and receive lines are cross linked.



• The null modem cable is frequently called a crossover cable.

• For this to happen, the Transmit (TXD) pin of one device needs to be

connected to the Receive (RXD) pin of the other device.

• To enable handshaking between the two devices, the Request to Send

(RTS) pin of one device must be connected to the Clear to Send (CTS) pin

of the other device. Because these pins are "crossed" on the two cable

terminals, the name crossover cable is used.


Simple Null Modem Cable

Null Modem Cable with Handshaking


Null Modem• Direct connection between two DTEs, e.g., terminal

and computer, or two computers directly

DTE

DSRDTR

CTSRTS

RCVXMIT

GND

Shield

DTE

DSRDTR

CTSRTS

RCVXMIT

GND

Shield

Physical layer interface & standards

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