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X21 Operation
X.21 is a protocol that runs over subscriber networks (i.e. leased line connections).
X.21 can operate as a full duplex connection with data rates from between 9,600 bps
to 2 megabits.
X.21 is an ITU-T data interface standard for connecting a DTE to a DCE and
transferring synchronous serial data. The properties of X.21 define the physical,
electrical and call control procedures for interfacing using this standard. The basic
interface signals performed in most X.21 signalling include transmit, receive, control,
indicate and timing. X.21 connections use balanced data, clock and control signal
lines. X.21 connections have been fully integrated into Tieline codecs.
64 – 384 kbps connections are most common and Tieline codecs support X.21 leased
line mode connections from 64 – 2,048 kbps. Ensure that the bit rate setting in your
codec is matched to that of your ISDN TA/X.21 DCE device. If you are unsure of the
bit rate of your ISDN TA/X.21 DCE device, please check its user manual to discover
the correct setting.
The physical interface to a Tieline
codec is via a DB15 connector (ISO 4903). The pin-outs for D-15
X.21 module connections are displayed in the Connector Wiring section
of this reference manual. A straight-through cable is required from
the male D15 connector on the X.21 module to a female DB15 connector,
which will attach to an X.21 DCE Device (such as an ISDN Terminal
Adaptor/TA). The connection profiles supported are mono, stereo,
dual mono and mono/IFB.
Once a call has been made successfully between two codecs that are programmed to
use the X.21 protocol, any data can be transferred over the connection. In Tieline
codecs, choose from G.711, G.722, MPEG 2 Layer 2 (MP2), and
Tieline Music Algorithms (Tieline Music is capable of 15 kHz mono or stereo over
64kbps or 128kbps with 70ms delay) as standard.
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.
2. How Does it Work?
First you will require 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.
Figure 1: X.21 ISDN Interface
Connection
3. Connecting Via X.21
First install the X.21 module into
your codec. The connection should then appear in the root menu of
the main codec LCD screen. For the procedure to connect over X.21,
please see the Quick Start section of this reference manual. This
will display the menu wizard for X.21 module connections and explain
the Quick Start connection procedure to get you connected.
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 the reference manual or contact
customer support at support@tieline.com for more info.
Programming the function of
your codec in x.21 mode
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 SOFTKEY 4 Menu. Next select
Configuration and select the X.21 connection you wish to configure. Now scroll
through the menu and adjust the settings you wish to change. See the Configuration
menu diagram for details of this menu structure.)
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 currently only support connections via an ISDN
Terminal Adapter (TA). Ensure that you select X21 < - > ISDN in this menu.
Bit Rate
Please select the bit rate you require from this menu and ensure that your ISDN
TA/X.21 DCE Device supports this bit rate. The bit rate setting of your codec will
need to match that of your ISDN TA/X.21 DCE Device.
Manual Default Algorithm
The Manual Default Algorithm setting in the X21 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.
Important Algorithm Selection Information
The manual default profile algorithm settings in the POTS, GSM LL/GSM, X21
and ISDN menus of the ToolBox Profile Editor, select which algorithm will be the
default for manual default profiles using these connections. For example, if Music
is selected in the Man Dflt Algorithm setting in the POTS menu, all manual
default profiles connecting via a POTS connection will use the Music algorithm.
This can be overridden in two ways. If you are using the Connection Setup
(Advanced) menu to set your connections, you will note that a Connection Type’s
Algorithm setting can be changed. If Any is the selected algorithm, the algorithm
for each Connection Type will be the one selected for manual default profiles, i.e.
the default ones selected in the POTS, GSM LL/GSM, and ISDN menus. Any
other algorithm selections here will override default algorithm settings in the
POTS, GSM LL/GSM, X21 and ISDN menus.
Secondly, you can reset the algorithm using the codec itself by accessing the
algorithm selections in the G3 codec menus. |
Sample Rate
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.
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.
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.
Last updated 16th April 2007
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