Connection Points for Physical Transmission between Digital Trunk Board & PBX

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This file aims at introducing the essential points related to the connection for physical transmission and the way to perform a corresponding test to ensure the safety of physical transmission.


This file is applicable to those who use Synway products at the first time, and those who use Synway products to carry out projects, as well as those who come across troubles in the use of Synway products.

Connection Points for Physical Transmission

Ensure Good Grounding of Industrial Computer (often skip)

No or improper grounding may cause instability in operation and noises in call as well as decrease in lightning resistance. Refer to the file Grounding of Industrial Computer& Grounding Test for details.

Ensure Correct Settings of Grounding Jumpers

If it is a 120Ω twisted pair cable, all the jumper caps on the board need to be unpinned.
If it is a 75Ω coaxial cable, refer to the section on how to configure the impedance jumper in the corresponding hardware manual. In most situations, it is not necessary to adjust the jumper caps. However, when both the transmitting and receiving shield layers of the E1 trunks at the remote end are common grounded, all the jumper caps on the board need to be unpinned. The way to test common grounding is as follows: Use the multimeter for resistance measurements. Connect the two pointed probes respectively to the transmitting and receiving shield layers of the E1 trunks. If the result is less than 10Ω, the two shield layers are regarded as common grounded.

Ensure Correct Settings of Board Clock

Incorrect settings of board clock will cause problems in synchronization. Refer to the file Board Clock Management-- Configuration Instruction for details.

Ensure Consistent CRC-4 Settings with PBX

CRC-4 is a form of cyclic redundancy checking (a method of checking for errors in transmitted data) that is used on E1 trunk lines. To check if the control switch for CRC-4 verification is consistent with the central office, refer to the chapter on how to configure CRC-4 in the document SynCTI Programmer's Manual.

Ensure Successful Initialization of Board

Run the test program Test.exe supplied by Synway. If no errors are reported, it means the board has been initialized successfully. Only if the board is successfully initialized can it guarantee the normal physical transmission.

Ensure Proper Connection of E1 Trunk from PBX and Board

If it is a single E1 line, check if the pins in it are connected in a right order.
For a 75Ω coaxial cable from PBX, check if the pins for receiving and transmitting in the E1 lines from the remote PBX are connected to those at the interfaces on the Synway board in a right order.
For a 120Ω twisted pair cable, check if the E1 lines from the remote PBX are connected to the interfaces on the board in a right order. Refer to the corresponding hardware manual for details.
Verification Method
Run the test program test.exe supplied by Synway. For a correct connection, the sync indicator for the corresponding E1 will light on and the value of SsmGetPcmLinkStatus will show the synchronization is in a normal state; inversely, the sync indicator will not light on and SsmGetPcmLinkStatus will return the information telling the synchronization is abnormal. Refer to the document SynCTI Programmer's Manual for more about
If there are multiple E1 lines, besides ensuring the right order in pin connection of each E1, you have to check if all the E1 lines are connected properly to the corresponding E1 interfaces on the board so as to prevent the cross connection of transmit and receive lines.
Connection in Wrong Order
Each pair of E1 Lines from PBX has a number to locate its physical position which should not be mistaken. (Especially for SS7, which pair of E1 lines the signaling links are located on and which CIC the pair of E1 lines corresponds to are both fixed. For detailed information about signaling links and CIC, please consult the PBX manufacturer.) See below for the corresponding relationship of logical number and physical position of E1 lines on the board: From the board stator or the screws fixing the computer, up to down, they are respectively the 1st, 2nd, …, nth E1 lines. Also, you can refer to the digits marked on the board.
Cross Connection of Transmit & Receive Lines
Once two or more than two PCM trunks are connected with their transmit and receive lines crossed, single pass may occur. Such situation often appears in adding or removing a trunk.
In the two troubles mentioned above, the channels may fail to go into the idle state, or the call may fail to connect, or single pass may occur. The way to verify such problems is similar to that for a single E1. However, as the verification method for a single E1 can be used only to examine the synchronization data on the direction from PBX to Board, we perform an extra pullout test for multiple E1 lines. For example, pull out the trunk at a PCM and let the remote PBX to check if something goes wrong with the corresponding E1 in the synchronization status.