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TelecommunicationSystems
Chapter 12 Telecommunication Systems What we cover Telephony Telecommunications Lines one can buy What we covered POTS Technologies for WAN access What we did not cover – Digital Wireless Data Communications and Computer Networks Chapter 12 Leased Line Services Many home computer users use POTS lines and conventional modems to connect to other computer systems. What if you need a faster service, or need one that is always on? You can get a leased line service. A basic leased line, or tie line, gives you a 56 Kbps data transfer rate. A T-1 (or T1) service gives you a 1.544 Mbps rate and is used by businesses to connect their in-house telephone systems (PBX) and data networks to the outside world. Data Communications and Computer Networks Chapter 12 T-1 Service A T-1 service is a digital, synchronous TDM stream used by businesses and telephone companies. A T-1 service is always on and always transmitting. One T-1 service can support up to 24 simultaneous channels. These channels can be either voice or data (PBX support). A T-1 service can also be provisioned as a single channel delivering 1.544 Mbps of data (LAN to ISP connection). Data Communications and Computer Networks Chapter 12 T-1 Service A T-1service requires 4 wires, as opposed to a 2-wire telephone line. A T-1 can be either intra-LATA (local) which costs roughly $300-$700 per month, or inter-LATA (long distance) which can cost thousands of dollars per month. A customer may also be able to order a ? T-1 or a ? T-1. Data Communications and Computer Networks Chapter 12 T-1 Service A T-1constantly transmits frames (8000 frames per second). Each frame consists of one byte from each of the 24 channels, plus 1 sync bit (8 * 24 + 1 = 193 bits). 8000 frames per second * 193 bits per frame = 1.544 Mbps. If a channel is used for voice, each byte is one byte of PCM-encoded voice. If a channel is used for data, ea
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