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Chapter 8

Digital Loop Start Protocols


8.1 Introduction
8.2 Signaling Overview
8.3 Parameters

8.1 Introduction

This chapter provides the following information:

Natural MicroSystems loop start protocols cover both analog and digital interfaces. The digital variations are implemented by the LPS8 and LPS9 TCPs.

The digital trunks are usually T1, connected to a private branch exchange (PBX) from within the private network, or directly to a network or a PSTN. The protocol is referred to as OPS (Off-Premise Station), and it comes in general in two types: FX (foreign exchange), and SA (special access). OPS-FX is covered by the LPS8 TCP, OPS-SA by the LPS9 TCP.

8.2 Signaling Overview

The following tables describe digital loop start signaling in two cases: OPS-FX and OPS-SA. Two tables are necessary because the protocol changes depending on which side started the call.

In general, digital variations of the loop start protocol represent the loop current of analog loop start with one bit, and the ring voltage with another bit. Only the A and B bits are used, with A representing the loop current presence or absence, and B the presence of absence of ring voltage.

The following table illustrates the case in which the switch presents the call to the terminal equipment.
State

Outbound switch AfBf

Line

Inbound terminal AbBb

Idle

01 (OPS-FX)

11 (OPS-SA)

\xdf

01 (OPS-FX)

00 (OPS-SA)

Ring on

00 (OPS-FX)

10 (OPS-SA)

01 (OPS-FX)

00 (OPS-SA)

Ring off

01 (OPS-FX)

11 (OPS-SA)

01 (OPS-FX)

00 (OPS-SA)

At this point, the incoming call is presented to the application. The application can answer or reject it. If it answers it, the line code changes to the conversation state code.

Answer - conversation state

01 (OPS-FX)

11 (OPS-SA)

\xdf

11 (OPS-FX)

10 (OPS-SA)

If the inbound side application rejects the call instead, the LPS TCP doesn't pick up the phone, and eventually the calling party will abandon the call.

If the switch side clears the call, a cleardown tone might be on the line. The terminal responds to this by hanging up the call.

Clear and idle

01 (OPS-FX)

11 (OPS-SA)

\xdf

01 (OPS-FX)

00 (OPS-SA)

The following table illustrates the case in which the terminal equipment places the call:
State

Outbound terminal AfBf

Line

Inbound switch AbBb

Idle

01 (OPS-FX)

00 (OPS-SA)

\xdf

01 (OPS-FX)

11 (OPS-SA)

Seizure

11 (OPS-FX)

10 (OPS-SA)

01 (OPS-FX)

11 (OPS-SA)

Seizure acknowledge

11 (OPS-FX)

10 (OPS-SA)

\xdf
Dial tone

01 (OPS-FX)

11 (OPS-SA)

Here the outbound side starts to send the address information. This can be done by means of DTMF tones, or by decadic pulses. If the method is decadic pulses, the loop Af bit is switched off (pulse on) and on (pulse off) repeatedly to signal the digits.

Call progress tones

11 (OPS-FX)

10 (OPS-SA)

\xdf
Ring tone

01 (OPS-FX)

11 (OPS-SA)

If the called switch rejects the call instead, the terminal will detect the busy tone on the line, and abandon the call. Or, if nobody answers, the terminal will abandon the call after a parameterized number of rings.

Answer - conversation state

11 (OPS-FX)

10 (OPS-SA)

\xdf
Voice

01 (OPS-FX)

11 (OPS-SA)

If the switch side clears the call, a cleardown tone might be on the line. The terminal responds to this by hanging up the call.

Clear and idle

01 (OPS-FX)

00 (OPS-SA)

01 (OPS-FX)

11 (OPS-SA)

8.3 Parameters

The parameters that program the LPS8 and LPS9 TCPs belong to the ADI.LPS category - the same used for the (analog) LPS0 TCP. However, some of the parameters in this category are not relevant to the digital loop start TCPs. The following table lists all the ADI.LPS parameters:
Field Name

Type/Unit

Default

Description

cleardownflag

mask

1

Selects whether to run the cleardown tone detector in the conversation state.

Value Definition
1 Cleardown enabled
0 Not enabled

qualloopoff

ms

10

Minimum duration of loop current interruption before a hang-up will be recognized.

ringdetectmode*

mask

0

Selects whether the ring detector is voltage-sensitive or frequency-selective.

Value Definition
0 Voltage-sensitive
1 Frequency-selective

qualringon

ms

6

For voltage-sensitive ring detection, the minimum duration of detected voltage to be recognized as the start of a ringing signal.

qualringoff

ms

100

For voltage-sensitive ring detection, the minimum duration of loss of detected voltage to be recognized as the end of a ringing signal.

freqringlow*

Hz

16

For frequency-selective ring detection, the minimum frequency recognized.

freqringhigh*

Hz

54

For frequency-selective ring detection, the maximum frequency recognized.

freqringperiods*

count

4

For frequency-selective ring detection, number of periods of the ring frequency needed to qualify. Range is 1-8.

freqdeglitchtime*

count

26

For frequency-selective ring detection, deglitch time in 1/8 ms. Range is 2-80 (.25 to 10 ms).

freqtolerance*

percent

10

For frequency-selective ring detection, frequency tolerance in percent.

ringsigmintime

ms

100

The minimum duration of a detected ring signal before the ring signal is considered valid.

ringsigmaxtime

ms

3000

The maximum duration of a detected incoming ringing signal before the ringing is considered to be invalidly long.

interringmaxtime

ms

8000

The maximum length of an incoming ring period (on time + off time) that can elapse before the call is considered to be abandoned.

numrings

count

0

Number of rings to detect for an incoming cal.:
Value Definition
0 1st ring begin
1 1st ring end
n after n rings
Note that if caller ID is enabled (cidsupport = 1) then the incoming call is reported after at least one ring.

dialtonewaittime

ms

5000

For outgoing calls, the maximum time to wait for initial dial tone.

dialtonemintime

ms

1000

For outgoing calls, the minimum duration of non-precise dial tone required before dialing will begin.

Set this to 0 to disable non-precise dial tone detection. (Precise dial tone detection is controlled by ADI_START_PARMS.)

nodialtoneaction

integer

0

Selects what to do if no dial tone detected.

Value Definition
0 Hang up and abandon the
call
1 Proceed to dial anyway
2 Generate an incoming call
event

xfersupport

mask

1

Flag to select whether PBX transfer is allowed.

Value Definition
0 Transfer commands are
disabled
1 Transfer commands are
allowed

cidsupport

mask

0

Flag to enable caller ID detection.

Value Definition
0 No caller ID detection
1 Caller ID detection enabled

For AG boards, the AG configuration file must include the DSP file adsir.dsp when caller ID is enabled.

reversalmode*

integer

0

Selects a loop current reversal detection mode for the AG 2000 board.

Value Definition
0 Disable detection
1 Reversal indicates remote
answer
2 Reversal indicates remote
hang up

3 Reversal indicates answer
and hang up

releaseguardtime

ms

1000

If the host specifies to place a call immediately after releasing a call, the line is not taken off-hook until this time has elapsed. This ensures that the CO considers the line idle.

CIDtype

integer

0

Type of Caller ID protocol, if CID is enabled.

Value Definition
0 BellCore CID Protocol
1 NTT Japan CID Protocol
2 ETSI Ringing Pulse Alerting
Signal CID Protocol

CIDmaxwaittime

ms

0

Maximum time to wait for Caller ID to arrive before concluding the caller has hung up (if CID is enabled).

xferstring

String[6]

"!;"

Prefix of feature code for transfer operation. The default string "!;" generates a flash hook, then waits for a dialtone.

connstring

String

"!"

Dial string for reconnect.

CIDalertmaxtime

ms

0

Maximum duration of an alert signal in Caller ID protocol (if CID is enabled).

qualreversal*

ms

200

Qualification time for loop current reversal event on the AG 2000 board.

polaranswertime*

ms

0

Wait time after going off-hook answering a call before you start detecting the loop current polarity reversal on far-end disconnect
(if reversal mode = 2 or 3).

polardialtime*

ms

0

Wait time after dialing before starting the loop current polarity reversal detection
(if reversal mode = 1 or 3).

relaytype*

integer

0

Obsolete. Kept for applications runtime compatibility.

CIDminmarktime

ms

100

Minimum duration of the "mark" signal of the caller ID protocol that is interpreted as such.

* Indicates parameters that are not applicable to the LPS8.TCP and LPS9.TCP



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