Tieline Technologies

Overview of X.21

1. How Do X.21 Modules Connect to the Network?
2. How Does it Work?

3. Connecting Via X.21
4. X.21 over Leased Lines
5.Programming a Connection using the menu wizard
6. Programming the function of your codec in x.21 mode using Toolbox Software
7. C Signalling Mode
8. Permanent Link Mode

1. How Do X.21 Modules Connect to the Network?

X.21 modules use a D-15 connector to connect to leased line networks. The X.21 module has a male connector and it connects to a female version of the same connector. Click here to download the pin-outs for DB15 and DB25 connectors for X.21.

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2. How Does it Work?

First you need to insert a Tieline X.21 module in each of your codecs. Next, you will need to ensure that you have correctly connected the codecs to your leased line network. A diagram follows with an example of how this might look over a traditional X.21/ISDN interface.

x21 diagram

Figure 1: X.21 ISDN Interface Connection

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3. Connecting Via X.21

Install the X.21 module into your codec and when the codec is powered up the X.21 connection should appear in the root menu of the main codec LCD screen. For the procedure to connect over X.21, please see the Tieline Quick Start guide. Use the X.21 connection wizard to program X.21 settings.

4. X.21 over Leased Lines

With C/DTR call establishment, a ‘C’ (Control Signal) is used to enable and disable call control protocols. An ‘I Signal’ (incoming call signal) is used to indicate the presence of an incoming call.

When dialing from one codec to another, the dialing codec (DTE1) changes the C Signal from off to on to initiate an outbound call. At the codec (DTE2) receiving the call an ‘I Signal’ (‘Indication’ or incoming call signal) changes from off to on, indicating the presence of an incoming call. The codec receiving the call then initiates a C Signal state change, from off to on, and replies to the dialing codec, which receives the incoming signal and changes its I Signal state from off to on. This completes the call connection process over X.21.

To clear a call, press "HANG UP" on either codec to change the C Signal from on to off. This will terminate the connection between the codecs.

For more information on how to connect via X.21 using Tieline codecs, please see the X.21 or Quick Start section of your codec's reference manual or contact customer support at support@tieline.com for more info.

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5. Programming a connection using the menu wizard

The simplest way to program your codec is to use the X.21 connection wizard. To do this press SOFTKEY 3 "WIZ" on the codec when the square brackets on the screen surround the X.21 connection. Then program settings such as the algorithm, link type (ISDN or X.21), the bit rate of your X.21 service, and whether you have a permanent link or C Signal X.21 service. Once this is done simply dial to connect.

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6. Programming the function of your codec in x.21 mode using ToolBox software

When you click on the "X21" TAB in the "Profile Editor" menu there are several settings available for programming the function of your codec in X.21 mode. (Please note: Even if you don’t have ToolBox software connected to your codec, these functions are available by accessing your codec menu via the menu wizard using SOFTKEY 3.

x21 tabs

Select X.21 Interface
An i-Mix G3 has a single module slot and COMMANDER G3 codecs have two module slots. It is therefore possible to run two X.21 modules from a COMMANDER G3 codec. Using this menu you are able to select the X.21 module in a codec that you wish to configure. Simply click on the blue arrow to reveal the drop-down menu and make your selection.

X.21 Link Type
Tieline codec X.21 modules support connections via an ISDN or X.21 Terminal Adapter. Ensure that you select the correct setting for your particular network in this menu.

Bit Rate
Please select the bit rate you require from this menu and ensure that your DCE Device supports this bit rate. The bit rate setting of your codec must match that of your DCE Device.

Manual Default Algorithm
The Manual Default Algorithm setting in the X.21 menu relates to the Manual Default Profiles within ToolBox. The setting you choose here will relate to any Manual Default Profiles that utilize X21 connections. For example, if you select G.722 from the drop-down menu, any manual default profile using an ISDN connection will be programmed to use the G.722 algorithm.

Sample Ratex21 samplerate diagram
If you select one of the MPEG algorithms you can also select the sample rate you wish to use from the four available options. The Samplerate setting is for all manual default profiles and will also be used by custom profiles with connections that use the Any setting within the Algorithm drop-down menu in the Connection Setup menu TAB.

The sample rate you select will be dependent on the connection profile you are using. For example, if you are connecting using a stereo profile with a 64 kbps X.21 connection, you will not be able to use a Samplerate of 48,000bps. If you do connect at this Samplerate the quality will not be very good. The recommended maximum you should set it at is 32,000bps for this type of connection. The default Samplerate for MP2 algorithms is 32,000 bps.

X.21 Call Control Type
This menu configures whether you are connecting using X.21 in either C Signaling or Permanent Link modes.

x21 call control type

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7. C Signalling Mode

In C Signaling mode, a ‘C’ (Control Signal) is used to control the connection. An ‘I Signal’ (incoming call signal) is used to indicate the presence of an incoming call.

When dialing from one codec to another, the dialing codec (DTE1) changes the C Signal from off to on to initiate an outbound call. At the codec (DTE2) receiving the call an ‘I Signal’ (‘Indication’ or incoming call signal) changes from off to on, indicating the presence of an incoming call. The codec receiving the call then initiates a C Signal state change, from off to on, which causes the I signal at the calling end to change its state from off to on. This completes the call connection process over X.21.

To clear a call, press "HANG UP" on either codec to change the C Signal from on to off. This will terminate the connection between the codecs.

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8. Permanent Link Mode

In essence, X.21 connections in Permanent Link mode behave similarly to making a call in POTS leased-line mode.

Very Important Note: Session data is automatically turned off in Permanent Link mode. In this mode ensure that both codecs are pre-programmed to operate using X.21 and with the same algorithm and bit rate settings etc.

When dialing from one codec to another, the dialing codec (DTE1) changes the C Signal from off to on to initiate an outbound call. A call is initiated when a user presses the "ENTER/DIAL" button on the dialing codec. Unlike in C Signalling mode, the I (CTS) signal is ignored.

An operator must manually press the "ANSWER" button on the answering codec (DTE2) to accept the call. Please note that there is no auto-answering in this mode.

To clear a call, press "HANG UP" on both codecs. This will terminate the connection between the codecs.

If you require more information on session data and how it works, please see the section titled Data Transfer & Using 3rd Party Devices in the user manual on the codec.

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