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Physical Layer and T-Carrier Overview and Testing

Market Environment. Typical uses for the T1Voice ConnectionsData Connections (Wide Area Network)T1 is a commodity resource with numerous carriers able to provision T-Carrier service. Voice Applications. . T1 Facility. ChannelBank. PBX. . . . . . . . . . . . . . . . . . . . . . . . . 24 Voice Tru

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Physical Layer and T-Carrier Overview and Testing

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    1. Physical Layer and T-Carrier Overview and Testing UEN Network Operations Center

    2. Market Environment Typical uses for the T1 Voice Connections Data Connections (Wide Area Network) T1 is a commodity resource with numerous carriers able to provision T-Carrier service

    3. Voice Applications

    4. Multiplexer (MUX) Aggregates numerous voice or data input streams into a T1 Often uses proprietary channel assignments De-Multiplexer (DEMUX) necessary to break out individual channels from the T-Carrier.

    5. Data/Hybrid Applications

    6. CSU - Channel Service Unit Interface between the customer and the carrier circuit. Regenerates the signal Provides or recovers timing Passes a T1 signal (DS1-X) to customer premise equipment (CPE)

    7. DSU - the Data Service Unit Receives a T1 signal from the CSU Converts the signal to a “short-haul” interface format RS-232 V.35 RS-422 Can access and “break out” individual channels.

    8. The North American Digital Carrier System The Basic channel is a DS0 = 64kbps DS1 = 24 x DS0 plus framing = 1.544Mbps DS3 = 28 x DS1

    9. Definitions T1 and DS1 are synonymous To the end-user, a T1 represents either A digital transmission path of 1.536Mbits/sec, or 24 “channels”, with each channel capable of carrying a voice call or digital data up to 56kbits/sec. Channels are 64kbits/sec “wide”, more about that later…

    10. Restrictions on the T1 signal In the bit stream, there must never be more than 15 consecutive “0”s. Over short periods of time, there must be at least 12.5% “1”s in the signal.

    11. Synchronous Transmission

    12. What does a “raw” T1 Signal Look Like (AMI coding)?

    13. Signaling in a T1 At the T1 level “Superframe” signaling uses groups of 12 T1 frames to create timing and signaling patterns “Extended Superframe” signaling uses 24 T1 frames to create timing, error detection, and signaling capabilities

    14. Signaling in a T1 cont… Inside each channel Voice channels use signaling bits to indicate on-hook and off-hook conditions Data channels may include signaling bits and bits that enforce the “1”s density.

    15. SF and ESF Signaling

    16. What is a channel, and how do channels make up a T1? A “Frame” consists of 8 bits for each channel, strung one after the other 8 bits/channel times 24 channels = 192 bits One “Framing Bit” is added to each frame Total frame length is 193 bits 8000 frames are sent per second 8000 times 193 = 1,544,000

    17. The T1 Frame (D4 Format)

    18. Trends T1 facilities will continue to be in wide-spread use. T1 is being used to carry “Frame Relay” data traffic. UEN has viewed IMA (Inverse Multiplexing over ATM) aggregating multiple T1’s as the next logical step to provide additional bandwidth short of a DS3. At approximately 14 DS1’s it becomes cost (and management effective) to increase capacity to a DS3 (45Mbit/sec) that can be delivered clear channel, over ATM or SONET.

    19. The SONET Hierarchy Synchronous Optical Network STS-n is the electrical standard, OC-n the optical one Basic channel STS-1 = about 52Mbps OC-3 = about 155Mbps OC-12 = about 600Mbps OC-48 = about 2500Mbps, etc.

    20. UEN Bandwidth Benchmarks PTP T1 (1.544Mbps) - typical “last mile” connection” Clear Channel DS3 (45Mbps) – CVDS Connections to UEN Distribution System ATM DS3 (45MB) – Leased line service to SLCC for example Channelized DS3 (45Mbps) – Aggregation point at DO’s for multiple DS1’s from Elementary Schools and Secondary Schools. OC3 (155Mbps) – ATM or Sonet handoff for services such as Sprint/Qwest Internet OC-12 (600Mbps) – Typically ATM trunk connections in HUB and Core (LS1010 to MGX/Router) OC-48 (2500Mbps) – Approximate bandwidth of the entire CVDS backbone.

    21. European Digital Carrier Basic North American channel: DS0 = 64kbps Basic European Channel: E1 = 30 x DS0 + 2 x 64kbps for signaling = 2,048Mbps No signaling embedded in the user channels.

    22. DCS - the Digital Crossconnect Used by carriers and large end-users Electronically connects T1s to each other, or Connects channels from one T1 to channels in another T1.

    23. Types of Telco Tests QRSS – Is a basic T1 test. One’s density of 50%. Simulates traffic and tests timing recovery 1:7 (also written 1 in 8) – Used to reveal timing problems on B8Zs circuits ALL ONES – Causes circuit to consume max power tests pulse power. Also an alarm mode frequently encountered in initial installation. ALL ZEROS – Confirms that the circuit is optioned for B8ZS (use on ESF-B8ZS circuits only) Bridget Tap – Tests for unterminated cable on a line that can cause impedance mismatch

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