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BASIC TELECOMMUNICATIONS

BASIC TELECOMMUNICATIONS . High speed communication circuits. BASIC TELECOMMUNICATIONS . In the 70s and 80s the PSTN started evolving into packet switching and digital networks.

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BASIC TELECOMMUNICATIONS

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  1. BASIC TELECOMMUNICATIONS High speed communication circuits

  2. BASIC TELECOMMUNICATIONS • In the 70s and 80s the PSTN started evolving into packet switching and digital networks. • In the 70s packet switching or frame relay was developed to speed up information exchange using the existing analog voice lines connecting the COs • In the 80s B-ISDN (Broadband Integrated Digital Services Network) was implemented to provide voice, data and video services over the PSTN

  3. BASIC TELECOMMUNICATIONS The telecommunications industry uses trunk lines to interconnect the different central offices and to connect large business and corporations that require a large amount of bandwidthusually for a PBX (Private Branch Exchange)

  4. BASIC TELECOMMUNICATIONS It is over these trunk lines that the various carrier technologies (frame relay, ISDN and others) are delivered

  5. BASIC TELECOMMUNICATIONS • In modern communications, trunking is a concept by which a communications system can provide network access to many clients by sharing a set of lines or frequencies instead of providing them individually. • This is analogous to the structure of a tree with one trunk and many branches

  6. BASIC TELECOMMUNICATIONS In Telephony a trunk line is a circuit connecting telephone switchboards (or other switching equipment), as distinguished from local loop circuit which extends from telephone exchange switching equipment to individual telephones or information origination/termination equipment

  7. BASIC TELECOMMUNICATIONS • The phone company moves nearly all voice traffic as digital rather than analog signals • The process of converting analog to digital is called PCM (pulse code modulation) • PCM takes an analog wave form and produces a series of square waves that have pulse amplitudes corresponding to the analog signal amplitudes and then converts them to digital values

  8. BASIC TELECOMMUNICATIONS • The most common and popular trunk line used today in many businesses is the T-1 line (Transmission one) • A T-1 trunk uses two dry pair of wires for transmitting and receiving • A dry pair means that no idle condition exist on the pairs when they’re not being used (no voltage or grounds present) unlike your home phone line that always has a voltage present in the on-hook stage

  9. BASIC TELECOMMUNICATIONS A T-1 enclosure or NIU (Network Interface Unit) with the T-l cards showing green lights

  10. BASIC TELECOMMUNICATIONS • Today many T-1 trunks are delivered over fiber optic cabling and sometimes coax cable brought right into the customer’s premises • A T-1 transmits data at 1.544Mbps (1,544,000bps) • A standard T-1 trunk carries 24 channels of digital PCM voice or data over two pair STP (shielded twisted pair)

  11. BASIC TELECOMMUNICATIONS • It has a voice channel capacity equal to 24 separate analog trunk lines which makes it ideal for medium and large businesses that have a lot of phones • 1 analog channel is referred to as a DS0 running at 64Kbps • So a T-1 is 24 DS0s (digital signal level 0) NOTE: the L is dropped so as not to confuse it with a DSL loop

  12. BASIC TELECOMMUNICATIONS • Each voice or data channel in a T-1 runs at 64Kbps How many bits is 64K bits? How many bits in a Byte? What does a byte represent?

  13. BASIC TELECOMMUNICATIONS • Your analog line gets converted to a digital signal by sampling 8,000 times per second at 8 bit resolution 8 x 8,000 (64Kbps) (PCM) • The 8 bit code outputs for each of the 24 voice channels and then are combined into a single 192 bit stream (24 x 8) by using the TDM method • Also included in the T-1 bit stream is a 1, 8Kbps synchronization bit transmitted before the 24 channel voice or data packets

  14. BASIC TELECOMMUNICATIONS • Together they form a 193 bit composite, 1.544Mbps T-1 signal (24 channels x 64Kbps + one 8Kbps sync and control bit called the frame bit) • T-1s are combined into a super frame format for transmission called D4 framing. • D4 combines 12, 193bit T-1 frames, the framing bit identifies both the channel and the signaling frame

  15. BASIC TELECOMMUNICATIONS This is what constitutes frame relay circuits Condensed; missing frames not shown, total frames is 24 8000 frame bit 64K 8 x 8000=64K 24 8 bit channels x 64k = 153,600 + 1, 8K frame bit = 1,544,000

  16. BASIC TELECOMMUNICATIONS T-1 STP cable with the drain wires, this cable is typically red and listed as T-1 cable

  17. BASIC TELECOMMUNICATIONS There are several other “T” trunks available that provide more bandwidth: • T-1C 3.152Mbps • T-2 6.312Mbps • T-3 44.736Mbps • T-4 174.176Mbps All of these higher bandwidth Ts operate on the same frame relay principles as the T-1

  18. BASIC TELECOMMUNICATIONS • T-1 circuits are located at the d-marc and appear on a RJ-21X • There are usually two RJ-21Xs, 1 for the transmit pair (TX) and 1 for the receive pair (RX) • The separation of the TX and RX helps eliminate EMI (electromagnetic interference) amongst the pairs

  19. BASIC TELECOMMUNICATIONS The T-1 pin out on a RJ-48C (commonly referred to as a RJ-45): White/Orange 1 Orange/White 2 White/Blue 5 Blue/White 4 E-1 is the European equivalent to the T-1

  20. BASIC TELECOMMUNICATIONS • The smart jack is typically a box on the wall with some lights and at least one circuit board visible behind a clear plastic cover, has at least one RJ45 jack, and a cable going to either the RJ21x block or other D-marc. • This is the NIU and is used for the high speed circuits we have discussed

  21. BASIC TELECOMMUNICATIONS NIU used for T-1 and ISDN interfaces, notice the green lights….all is good in the telcom world

  22. BASIC TELECOMMUNICATIONS • There are other high speed digital circuits available such as the ISDN (Integrated Services Digital Network) interfaces that provide voice, data and video services • The two standard ISDN interfaces are : BRI (basic rate interface) PRI (primary rate interface) • Both circuits contain B channels for data signaling and a D channel as the control channel

  23. BASIC TELECOMMUNICATIONS • The smart jack converts the incoming 2 pair line to an RJ45 T1 or PRI line, you need a CSU/DSU between it and your equipment to handle the protocol translation. • The smart jack and the cable going to it are the phone company's property and their responsibility to fix

  24. BASIC TELECOMMUNICATIONS • The BRI interface is a small business application that consists of two B channels of 64Kbps and a D channel of 16Kbps for a total of 144Kbps • The PRI interface is a large corporation application that consists of 23 B channels of 64Kbps and a D channel of 64Kbps for a total of 1,544Kbps • The PRI interface is considered an enhanced T-1circuit

  25. BASIC TELECOMMUNICATIONS • BRI and PRI circuits are used to connect a PBX (Private Branch Exchange) to central offices, the D channel is used for sync, performance monitoring, error control and other functions • xDSL circuits have been replacing the use of BRI and PRI interfaces because xDSL circuits are faster, cheaper and easier to configure

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