T1, E1 Cable Bus description

T1 Bus

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T1/E1 Description

T-carrier is generic designator for any of several digitally multiplexed telecommunications carrier systems. T-x trunks are used mostly between Central Offices [CO] and Private Automatic Branch Exchanges (PABX). T1 lines represent the physical layer in the 7 layer OSI model.

Analog voice leaves your phone over two wires and heads to the Central Office [CO]. Once at the CO the signal is sampled at a 8kHz rate and digitized into 8 bits producing 64kbps per separate phone line. The 64kbps speed is defined as DS0 [Digital Signal 0]. When 24 DS0s are combined together the result is DS1 [T1]. Tn [T1, T2, T3 ....] defines the carrier or physical format. T1 lines are formed when 24 digitized phone lines are combined into a single digital data stream. The resulting data stream has a rate of 1.544Mbps [24 * 64,000 = 1.536Mbps plus a framing bit]. The T1 data stream is Time Division Multiplexed [TDM] by channel; 8 bits [one sample] of channel 1 followed by 8 bits of channel 2 and so on. T1 trunks are bi-direction, one twisted pair for transmit and one twisted pair for receive. The frames consists of one 8 bit sample for each of the 24 channels, or 24 [channels] x 8 [data bits] + 8 bit [frame] = 193 bits. Then 193 bits x 8K samples = 1.544 Mbps.

The pulse width is 648nS +/- 15nS

E1 lines which are used in Europe are formed when 32 digitized phone lines are combined into a single digital data stream.
The resulting data stream has a rate of 2.048Mbps. Europe does not use the DS designation.

**Common T1/E1 Rates**
Hierarchy	Speed	Digital Signal	US Carrier	European Carrier	# DSO's	# T1's

---	64kbps	---	---	---	1	---
First Level	1.544Mbps	DS1	T-1	---	24	1
First Level	2.048Mbps	---	---	E-1	32	---
Intermediate Level	3.152Mbps	DS1c	T-1c	---	48	2
Second Level	6.312Mbps	DS2	T-2	---	96	4
Second Level	8.448Mbps	---	---	E-2	128	---
Third Level	34.368Mbps	---	---	E-3	512	---
Third Level	44.736Mbps	DS3	T-3	---	672	28
Fourth Level	139.268Mbps	---	---	E-4	2048	---
Fourth Level	274.176Mbps	DS4	T-4	---	4032	168
Fifth Level	400.352Mbps	DS5	T-5	---	5760	240
Fifth Level	565.148Mbps	---	---	E-5	8192	---

The table shows the most common T-1 [US] and E-1 [Europe] transmission rates, there are other rates. Other countries use additional rates which are not shown in the table. The Primary US rate is: 1544kbps [24 [64kbps] channels plus framing data]. The Primary Europe rate is: 2048kbps [30 channels plus framing data]. In many cases transmission rates above level 3 are optical rather than electrical. Optical rates are shown on the SONET / SDH page.

Electrical Characteristics of the 64 kbps Interface

T1 uses alternate mark inversion [AMI], all adjacent marks have an opposite polarity. A bipolar violation [BPV] occurs if adjacent marks have the same polarity. Because repeaters require a minimum ones density in order to recover timing information. One pulse in at least every 8 bits may be forced to a one [1]. So instead of 64kbps on a DSO, 56kbps is seen; [8 bits - 1 bit] * 8000 samples. Which is why we have a 56k Modem as the top speed over a phone line.

PDH [Plesiochronous Digital Hierarchy] Plesiochronous Definition
PCM [Pulse Code Modulation]
TDM [Time Division Multiplexing ]
DTM [Digital Time-Domain Multiplexing]
ISDN: Integrated Services Digital Network. ISDN devices and standard descriptions are listed on it's own page.
AMI: Alternate Mark Inversion

T1 Standards Info

ITU; International Telecommunication Union [www.itu.int]

T1 Interface IC manufacturers

Telecom Device Manufacturers {Digital/Specialized Logic}

DS0; 64kbps has a symbol rate of 256kbaud: Low = 0v +/-0.1v; High 1.0v at 120 ohms
T1; 1544kbps: Low = 0v; High 2.4v to 3.6 volts at 100 ohms

Line Framing: T1: uses D4, or ESF, SLC-96, E1: uses G.704 [Electrical G.703]
Line Coding: T1: uses B8ZS or AMI, E1: uses HDB3

AKM Semiconductor {Codec/Transceiver IC for ISDN}

Cirrus Logic {T1/E1}

Cologne Chip {ISDN controller IC Manufacturer}

Conexant {T1/E1-T3/E3 ICs}

Infineon {ISDN-DDA-T1 ICs}

Maxim Integrated Products {T/E Carrier and Packetized Products. Single Chip Transceivers, Framers, Line Interface Units}

Mindspeed Technologies {DS3/E3 Line Card-on-a-Chip (LoC), T1/E1 LIUs/Framers}

PMC-Sierra Inc. {T1/E1 ICs}

STMicroelectronics {ISDN ICs}

TranSwitch Corp. {DS3/STS1-E1/E2/E3-T1 Frame Grabber}

Integrated Circuit Manufacturers {For other functions}

T1 Inductor Manufacturers