The Shielded twisted pair STP

In Twisted pair cables two conductor wires are twisted together for the purposes of canceling out electromagnetic interference (EMI) from external sources AC DC motors, generators, electric main supply lines of one phase or three phase carrying high current and crosstalk between neighboring pairs. Two basic types of twisted-pair cable exist: unshielded twisted pair (UTP) and shielded twisted pair (STP). Shielded twisted-pair (STP) cable combines the techniques of shielding, cancellation, and wire twisting. Each pair of wires is wrapped in a metallic foil.They have usually 150-ohm impedance. The use of STP is in Ethernet network installations, because STP reduces electrical noise both within the cable which may be due topair-to-pair coupling, or crosstalk and from outside the cable for example EMI and RFI. STP is installed with STP data connector, which is created especially for the STP cable. The Speed and throughput of STP cables may ranges in 10 to 100 Mbps with Maximum cable length is 100 m. The construction of STP cables has following four layers,

• Plastic cover - outer most layer
• Metal shield or metal grid or mesh
• Insulation of each individual copper wire
• Cooper wire

what are the cables used in Networking

THE Most of the Network are established with the use of UTP cables. UTP is the most common form of twisted pair wiring. It is less expensive and easier to work with than STP (Shielded Twisted Pair). UTP is used in Ethernet 10 Base-T and 100Base-T networks, as well as in home and office telephone wiring.The main advantage of use of UTP is that twist in UTP helps to reduce crosstalk interference between wire pairs.
Categories of UTP cables:
EIA has made some standards of UTP cables also. There are five major categories of UTP cables.
The categories of UTP cables is function of cable quantity with category 1 is less and category5 maximum quality.
Category 1 UTB cable (CAT 1) : It is suitable for voice communicatin thus mostly used in telephone line and less in data communication application, normally very low speed transmission is possible with CAT1 UTP.
Category 2 UTB cable (CAT 2) : This is of a little bit higher grad, but again recommended for voice communication and only for data transmission of equal or less than 4Mbps.
Category 3 UTB cable CAT 3) : The category3 or CAT3 UTP cables have at least 3 twist per foot in lenght. These can be used for data transmission of Up to 10MBps. Cat 3 UTP was the standard cable for use with Ethernet 10Base-T. But it is most standred cables used for Telephone industry.
Category 4 UTB cable CAT 4) : The category3 or CAT4 UTP cables must have at least 3 twist per foot in lenght. These can be used for data transmission of Up to 16MBps.
Category 5 UTB cable CAT 5) : The Cat5 UTP are used in data communication with speed of upto 100MBps and for ATM up to 155Mbit/s. Cat 5 UTP was the standard cable for use with Ethernet 100Base-TX.
Category 5e UTP cable (CAT 5e) : Category 5e UTP is an enhanced version of Cat 5 UTP. Cat 5e UTP is rated to carry data up to 1000Mbit/s. Cat 5e UTP is the standard cable for use with Ethernet 1000Base-T. Cat 5e can also be used to extend the distance of 100Base-TX cable runs up to 350 meters.

Modem standards

There are many modem standards used in world, but some of them are briefely described here for just review purposes.

1. Bell Modem standards
2. ITU-T modem standards
3. Intelligent modems

Bell Modem standards:

In the early 1970s, Bell Labs created carrier standards for use with Bell equipment and lines, to accommodate the networks. Bell Standards include the following:

Bell 103 - Asynchronous data transmission, full-duplex operation over 2-wire dialup or leased lines; 300-bps data rate, work on barb wire.

Bell 212 A - Synchronous/ asynchronous data transmission, full-duplex operation over 2-wire leased or dialup lines; 1200-bps data rate. This versatile standard provides for efficient full-duplex operation over 2-wire dialup lines.

Bell 201 B, Bell 201 C - 201 B: Synchronous data transmission, full-duplex operation over 4-wire leased lines and half-duplex operation over 2-wire leased lines; 2400-bps data rate. 201 C: synchronous data transmission, half-duplex operation over 2-wire dialup lines; 2400-bps data rate. Both are comparable to ITU V.26. Bell 201 B compatible modems are the first of the fast modems.

Bell 208 A, Bell 208 B - 208 A: Synchronous data transmission, full-duplex operation over 4-wire leased lines, half-duplex operation over 2-wire leased lines; 4800-bps data rate. 208 B: same as 208 A, but over 2-wire dialup lines. Comparable to ITU V.27. The first standards to enable higher-speed data transmission (4800 bps) over leased lines for multipoint networks.

ITU-T modem standards:

The International Telephone and Telegraph Consultative Committee (CCITT), known since 1990 as the International Telecommunication Union (ITU).
The goal of the ITU is to define international communications standards. Modem standards can be divided into 3 categories:
Modulation standards (e.g. CCITT V.21)
Error correction standards (e.g. CCITT V.42)
Data compression standards (e.g. CCITT V.42bis)

V.22; 600 baud (Hz), 1200 Bits Per Second, The same as the Bell 212A standard but different handshaking.

CCITT V.21: 300 bps, Full duplex, An international standard similar to the Bell 103 standard.

ITU V.22bis: 2,400 bps, Full duplex, An international standard that is an improved version of the V.22 standard (thus the name V.22bis).

ITU V.23
1,200 bps
Half duplex
An international standard that transmits data in half-duplex mode, i.e. data is transmitted in just one direction at a time. Optional 75 baud reverse channel.
ITU V.23
1,200 bps/75 bps
Full duplex
An international standard giving asymmetrical full duplex, i.e. it allows data transmission in one direction at 1,200 bps and at 75 bps in the other direction.
ITU V.29: 9,600 bps, Half duplex, An international standard that transmits data in half-duplex mode, i.e. data is transmitted in just one direction at a time. This standard was developed especially for fax machines.
ITU V.32: 9,600 bps, Full duplex, An international standard that transmits in full-duplex mode and incorporates error correction standards. Data transmission takes place according to an error correction technique called quadrature amplitude trellis-coded modulation. This technique consists in sending an additional bit for each group of 4 bits that are sent on the transmission line.

ITU V.32bis: 14,400 bps, Full duplex, An international standard that improves on the v.32 standard by allowing 6 bits per baud to be sent and a transmission speed of up to 14,400 bps.
ITU V.32fast: 28,800 bps, Full duplex, An international standard sometimes called V.FC (Fast Class) that allows data transmission at a speed of 28,800 bps.
ITU V.34: 28,800 bps, Full duplex, An international standard that allows data transfer at 28,800 bps. Thanks to a DSP processor (Digital Signal Processor), modems using this standard can attain a speed of up to 33,600 bps.
ITU V.90: 56,000 bps, Full duplex, An international standard that allows transmission speeds of up to 56,000 bps.