T-Carrier Systems

F-bit per framing channel (SF) [formula]

(n Kbps/x fbits) * (12 Fbits/8 kbps)

F-bit per framing channel (ESF) [formula]

(n Kbps/x fbits) * (24 Fbits/8 kbps)

System Clock [formula]

(n channels/frame) * (8 bits/channel) * (8000 frames/second)

# of Time Slots for Europe

32

FPS for ESF

001011

Framing bits in even-numbered frames

001110 repeating

Maximum Transmission Distance without a Repeater

1 mile (600 ft)

Transmission Rate for T1

1.544 Mbps

Framing bits in odd-numbered frames

101010 alternating

# of Time Slots for USA

24

Robbed Bit Signaling

5 of 6 frames have an 8-bit resolution, while 1 of 6 frames has a 7-bit resolution; used in D-4 Framing

Voice Rate is _______, resulting in the suffering of _____________.

56 kbps; voice quality

CRC-6

6 bits in an ESF used for error detection (1,5,9,13,17,21); short version of CRC-16

Signaling Channel rate is ____, which is too small, resulting in ________.

8 kbps; Bandwidth waste

Channel bit rate (bps) [formula]

8000 * (n/m) where n is the number of bits every m frames

Line Speed for T1 Digital Carrier System [formula]

=(193 bits/frame0 * (8000 frames/second) = 1.544 Mbps = 1.536 Mbps + 8000 bits = 1.544 Mbps

T1 Digital Carrier

A carrier system that uses digital pulses rather than analog signals to encode information

Multiframe Alignment Bit

Added to the transmit signal of each frame as an overhead; occurs once per frame (8kbps rate) and is recovered in the receiver

AMI Format

Alternate Mark Inversion Format (Unipolar - Bipolar); Alternates polarity of each 1 = Mark

BSRF

Basic System Reference Frequency; used by the master clock; an atomic clock located in Hillsboro, Missouri; most accurate clocking device available for T1 circuits; STRATUM 1 CLOCK

B8ZS

Bipolar 8 Zero Substitution; overcomes bit stuffing limitation; overrides 00000000 with 00011011, creating Bipolar violation when sending 11 and 11; receiver recognizes BPV and interprets 8 zero's; 64 kbps transmission rate remains

BPV

Bipolar Violation; Occurs when two consecutive ones have the same polarity

CPE

Customer Premises Equipment; terminate T1 with a RJ-48C jack

CRC

Cyclic Check Redundancy

ESF

Extended Super Frame

D5 Channel Banks

Extended Super Frames; 24 frames; each frame has 24 DS-0 64 Kbps channels; frame = 193 bits; ESF = 4632 bits (193 * 24); 6 of 24 F-bits used for synchronization (4, 8, 12, 16, 20, 24)

FDL

Facilities Data Link; 12 remaining F-bits in an ESF provide for this management channel

Bit Robbing

Fine method for voice data; humans cannot detect sound change in 125 usec; not appropriate for pure data (ASCII File Transfer)

DS-1

First level digital signal; processed by T1 line driver

Bit Stuffing

For a sequence of eight zeros, the eight bit will be replaced with a 1

For T1 to operate correctly, the transmitter and receiver is _____ ___________.

Frame synchronized

D4 Framing

Frames 1-6 (A-highway) and 7-12 (B-highway), where 6 and 12 are the signaling frames

ESF Channels

Framing (6 bits) Error checking channel (6 bits) Management Channel (12 bits)

FPS

Framing Pattern Sequence

Synchronization is realized through the usage of _______ ____.

Framing bits

E1 Carrier

Gross data rate of 2.048 Mbps; 32 8-bit channels send in a 256 bit frame; two channels for signaling, other 30 for data; does not support bit robbing

Both SF and ESF used __-____ Signaling

In-band

Master/Slave Timing

Loop Timing; slave takes its timing from the T1 loop

T1 Repeaters

Maintain clocking of original signal; use incoming 1's to maintain the clock timing (clock recovery)

Zero Constraint Rule

Need to average at least one 1 every eight bits and cannot transmit more than 7 0's in a row; easy with voice transmission, difficult with data transmission

Bit Stuffing Limitation

No De-stuffing, when bit stuffing is applied, data is modified (56 kbps)

Clear Channel

No bit robbing data transfer

Bell System

North American Telephone Standard recognized by CCITT (ITU-T)

Framing bits are referred to an ________

Overhead

Master/Slave Clock Relationship

Relationship where the master provides the clock, the slave derives the clock (clock recovery) from the master.

Stratum Clock Accuracies

STRATUM 1 = .001 PPM STRATUM 2 = .200 PPM STRATUM 4 = 50 ppm (used by channel banks)

Transmitter and receiver must be clock synchronized, in a method called...

Sample Synchronization

SS7

Signal System 7; telephone signaling network with packet-switching and out-of-band signaling; lots or redundancy

S-Bit

Signaling bit; used for inband signaling (7 bits voice, 1 bit signaling); used for flash-hook, on hook, off hook, dial pulsing, ringing

In-Band Signaling

Signaling information is carried in the same bandwidth (channel) as the voice and data messages

T1 Line Driver

Sits between TDM (DS1) and the External interface; Conditions T1 bit stream electrical characteristics to meet specifications, converts to AMI format

SF

Superframe; group of 12 frames

Regenerative Repeaters

T1 Repeaters; necessary since a digital signal is still electrical in nature

Out of Band Signaling

Telephony signaling carried over separate network from telephone calls; allows for signaling between any switches, signaling during call, higher than voice data rate signaling; in band tone signaling helps phone phreaksl out of band signaling more secure

T1 Physical Layout

Two balanced pairs of copper wire (twisted pair); full-duplex; no clock signal

Payload

User data

T1 Carrier System

Uses PCM-TDM; Multiplexes 24 voice-band channels (1 Frame) each frame separated by a framing bit