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T1 connections subject to Multiplexing: In a carrier environment, carriers try to manage "few & big" circuits throughout their network. To accomplish this, any customer T1 connections will be multiplexed to the next level (DS3), and then combined into optical carriers (OC-1 / OC-3 / OC-12 / OC-192) as quickly as possible for management and restoral reasons. This helps to effectively manage T1 fiber utilization. Why combine into Higher Speed Circuits? Typical T1 copper connections will be multiplexed at neighborhood fiber vaults or SLC-96 devices. This enables the telephone company to mange copper facilities at the customer premises, and push "backbone" facilities closer and closer to the end user. This aids the carrier in several ways: 1) By pushing higher speed services closer to the user, the carrier can offer newer and higher speed services to a larger footprint. 2) Copper facilities are more prone to interference and outages due to storms (lightning and rain) than are fiber-based systems - neither is protected if a tree hits an aerial run. 3) Since fiber systems are inherently more reliable, carriers can improve MTBF (mean time between failure) statistics which help to boost customer loyalty and credibility. From T1 to Fiber Muxing Up (Carrier interconnects). As stated, T1s are copper-based circuits, and require 2 copper pairs. The next mux level is DS3, also requiring 2 pairs, but a DS3 can handle 28 times the traffic on the same number of pairs. As quickly as equipment placements and outside plant facilities can accommodate, the carrier will mux multiple copper DS3 connections to fiber-based optical carriers. DS3 connections to either carrier or campus fiber environments are typically handled by an FLC (Fiber Loop Converter). An FLC accepts a DS3 (44.736Mbs) electrical input signal and converts it to optical data by a laser driver/diode module for output as a light-wave signal. This light-wave signal is most typically at 2.4Gbs, yielding SONET restoration capabilities if the network is architected in a ring configuration. As with all typical multiplexing and terminating equipment, Fiber Loop Converters offer both local and remote loop-back options for testing and fault isolation. Sometimes referred to as a DS3 modem, Fiber Loop Converters convert a light-wave signal to an electrical signal, as well as provide remote testing and configuration. By multiplexing multiple DS3s into an OC-level circuit, a single fiber pair can carry hundreds of circuits. While carriers have been using this form of multiplexing to "build-up" routes prior to transport over their backbone routes, only recently have business applications warranted the huge amounts of bandwidth that OC-level circuits can provide. Reference sources regarding T1 fiber line:
Muxing Down. A DS3 Connection is typically made using either coaxial cable or copper wire to a multiplexer (mux), typically called an M13, is a Telecom term for the device required by either Telco's or large business users to break down the DS3 signal into DS1 (T1) level connections which are required by most PBXs and Routers. While each DS3 has a capacity to carry 28 DS1s, it is not required that it carry all 28. For termination, a DS3 mux is placed between the DS3 facility and those devices requiring DS1 (T1) connections, and a mux card is used to decode the DS3 time slot for each respective DS1 of service being carried by the DS3. If T1 output is not desired, a DS3 mux will be used to statistically divide (stat mux) the 45MB data stream into the desired bandwidth increments. Common Names / Muxing Levels: Electrical Circuits
Optical Circuits
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T1 Fiber
