Technical Spec´s X.25 Gateways to TCP/IP *

© Farsite Communication Ltd. • 2012 


The FarLinX X25 Gateway product range is the third generation of X.25 Gateway products from FarSite, providing a very flexible powerful gateway for your X.25 migration needs at a very affordable cost. It incorporates all the popular features of the previous product ranges with an improved browser interface and new comprehensive set of online statistics, connection logging, active session display and status change alert functions to put you in control.

Key Features

        • TCP to X.25 data translation with a very wide variety of modes including: RFC1006, Cisco RBP, header stripping and parity conversion and many others
        • TCP <-> X.25 and TCP <-> XOT routing including: fixed routes, dynamic routing and PAD routing
        • Optional software upgrade to support the POS protocols APACS, ISO 8583, HGEPOS and CTL (Card Tech Ltd)
        • Routing of calls between XOT (X.25 over TCP/IP) and multiple X.25 lines
        • X.25 to X.25 switching
        • XOT to TCP/IP Data Routing
        • X.28 PAD option supporting Telnet access and up to 17 async lines
        • X.25 Host PAD emulation support
        • Supports routing of OFTP/400 and protocols requiring ISO Transport such as FTAM and X.400
        • 6 Models, equipped with XOT and between 1 to 8 X.25 lines with X.25 line speeds up to 2 Mbits/s
        • Choice of X.25 Network interface connections E1, RS232C (V.24), V.35, RS530 (RS422) or X.21
        • Optional support for end to end authentication and data security over TCP/IP ensured by use of IPSEC encryption
        • High performance, non stop operation - over 3000 messages per second and over 2,000 SVC and PVC simultaneous connections
        • Dual Gateways with a shared IP address providing automatic switch over and backup for resilience
        • Easy and intuitive Graphical Configuration from your Browser
        • Current session activity display
        • Critical event SNMP alerts
        • Local or remote activity logs (syslog standard) with a configurable level of connection and data tracing
        • Local or remote Line Monitor application or use Wireshark to view and decode X.25 traffic for easy network problem diagnosis
        • Real time statistics of line performance, errors, connections and much more
        • Low power consumption, 1U high rack mountable all metal design
        • Gateway Firmware upgradeable in situ

The condition of the Gateway can be monitored from a browser with current line status, real time line and data statistics and real time active session activity available. There are also daily activity logs with a selectable level of detail, automatically archived on a daily basis or routed to a remote server using syslog. The SNMP support provides alerts for a number of different conditions including critical events such as line down and line up.

Dual Gateway support is available such that 2 Gateways can share a common IP address to provide automatic switch over support for a range of conditions including X.25 line down and Gateway failure. Any such failures and switchover events will generate SNMP alerts so the network operator can instantly know what's happened.

The product support protocols where the X.25 Host system treats the incoming X.25 data as a character stream. It can also convert the data when a header is used to describe the message payload within the TCP connections and remove this header on the X.25 virtual circuits. Data types supported include: RFC1006, Cisco RBP and special character delimiting. Dynamic routing is supported where the Client TCP application determines the X.25 address and call parameters used at the time the connection is established. XOT is supported so that the X.25 network can run over the top of an IP network. The Gateway can provide connectivity to several different Host systems at the same time with each having different data conversion configurations.

Some typical Applications

        • Replacing a complete X.25 and Triple-X PAD Network by using FarLinX X25 Gateways to manage the X.25 and X.28 connections over a TCP/IP network running XOT
        • Reduce line costs by replacing expensive X.25 lines with a TCP/IP connection and conversion to X.25 at each terminating node
        • Conversion of legacy X.25 connections and data for transfer over a TCP/IP network
        • 4 or 8 port X.25 switch with Telnet and async line PAD support with migration and selective routing of X.25 traffic to TCP/IP networks
        • ISO FTAM operation between TCP/IP and X.25, eg using Futjitsu OpenFT-FTAM
        • POS Gateway to allow TCP/IP and X.25 based Point of Sale systems to interoperate
        • Conversion of XOT traffic to TCP/IP connections eliminating the need for X.25 at that location
        • OFTP/400 (Odette File Transfer Protocol) conversion between TCP and X.25 used by car manufacturers, domestic appliance manufacturers, the chemical industry and many others
        • Provides an X.25 Gateway to interface with X.400 Servers

Functional Overview - XOT and X.25 Switching

The FarLinX X25 Gateway provides a reliable means of routing connections between X.25 and XOT (X.25 over TCP/IP). Connections can be routed between X.25 lines and over XOT which is treated as another connection path. The connection routing module supports default routes, hunt groups, X.25 address translation, and routing commands with NUA wildcards for maximum flexibility.

The XOT and X.25 support features particularly fast switching times, over 200 calls a second can be established. This is particularly useful where calls are frequent or the system is prone to bursts of calls.

A mix of over 2,000 SVC or PVC sessions can be handled simultaneously over XOT and X.25 lines.


This configuration shows the FarLinX X25 Gateway acting as the link between IP network with PCs
running XOT (FarSync XOT Runtime software) and an X.25 connected host.

This configuration shows a complete X.25 network simulated by FarLinX X25 Gateway's running XOT
over an IP network (4 X.25 lines in this example but could be hundreds or thousands).
This allows complete X.25 networks to be replaced while leaving hosts connected by X.25
to that network undisturbed.

Functional Overview - data packetization and routing between TCP/IP and X.25 or XOT

The Gateway provides connection establishment and data packetization services for general protocols to allow applications sending data over TCP/IP to interface to X.25 or XOT connected hosts. The Gateway provides routing facilities to select the appropriate Host from those available and maintains X.25 or XOT sessions to the Host as required.

Over 2,000 SVC or PVC sessions can be handled simultaneously between TCP/IP and X.25 or XOT.

Example network configuration using the FarLinX X25 Gateway
to interlink the TCP/IP and X.25 networks

The Gateway listens on a number of TCP ports – one port per configured X.25 Host. When a client establishes a TCP connection to the Gateway, the Gateway sets up an X.25 virtual circuit to the appropriate Host. Once the end-to-end connection is complete, the messages can be transferred.

At the end of the transaction, if the terminal disconnects, the Gateway will clear the X.25 virtual circuit. Alternatively, if the Host clears the X.25 virtual circuit first, the Gateway will disconnect the TCP connection to the terminal.

An X.25 Switch function can switch X.25 calls between X.25 connections and permit selective filtering of calls to TCP.

TCP to X.25 data translation functions

The Gateway supports a wide range of TCP to X.25 data translation and connection functions, these include:

        • Character stream
        • ETX terminated messages
        • Special character terminated messages (customisable)
        • Message header conversion - types available 2 or 4 byte ASCII or Binary length representation
        • Custom message header conversion
        • RFC1006 - ISO Transport Class 0 protocol data units, using the RFC-1006 encapsulation on the TCP connection
        • Cisco RBP - Record Boundary Preservation
        • X.25 Parity conversion - the Gateway performs any required parity adjustments and removal on the X.25 / XOT connection
        • POS Protocols APACS, ISO 8583, HGEPOS and CTL (Card Tech Ltd) - Requires the POS Option

Many of the functions can be configured for the same connection for maximum flexibility.

Connection Routing and Address Mapping

The FarLinX X25 Gateway can support routes to thousands of different X.25 / XOT hosts. Similarly, when using the called X.25 address as the routing key, incoming X.25 / XOT calls can be routed to thousands of different TCP/IP hosts.

When making connections to the X.25 network or XOT, the Gateway has the capability of mapping the source IP address to a calling X.25 address, thus allowing the destination X.25 / XOT host to identify the connection source uniquely.

The Dynamic routing options allow the X.25 address (NUA) and call parameters to be set by the remote application at the time each X.25 / XOT connection is established. These modes allow X.25 packetisation information to be passed to the application. Linux and Windows sample applications provided.
The main modes supported include:

        • Statically defined routing
        • XDRPD (eXtended Dynamic Routing Packetized Data) and DRPD - these formats allow TCP connected applications to dynamically setup and control the X.25 or XOT connection
        • X.25 Data Switching - allows X.25 devices to be interconnected via an IP network without the overheads associated with XOT
        • PAD Routing - PAD or Dynamic routing may be employed to allow the TCP client application to specify the X.25 call parameters

Functional Overview - PAD Features

X.28 Host Pad

The FarLinX X25 Gateway can be configured to act as an X.28 host PAD for remote terminals or applications connecting over X.25 and expecting a host that supports X.28. The host PAD sends X.28 PAD configuration commands over X.25 to the connecting terminals. The host PAD profile is configurable.

X.28 Triple-X PAD

Triple-X PAD (X.28, X.3 and X.29) support is included with the Gateway, accessible over TCP/IP via Telnet or using the single permanent async port. Additional RS232C async ports (9 pin D type) can be ordered with options for 4, 8 or 16 async ports. The connecting terminal is presented with a Triple-X PAD service and can be used to make X.25 connections over the physical X.25 line(s) or via XOT connections to remote hosts. The initial PAD profiles for each async port and for the Telnet access are fully configurable.

Encryption over TCP/IP (IPSEC)

The FarLinX X25 Gateway supports the option of selecting IPSEC to provide communications security in IP networks. It can be especially important when public Internet connections are used for part of the communications path.

IPSEC operates between a pair of devices. Each must know details of the remote device in order to authenticate communications and successfully encrypt/decrypt data being sent and received. In the FarLinX X25 Gateway, the details of multiple partner Gateways can be configured. The pre-shared key used to authenticate is unique for each remote partner. Once authentication has completed an exchange of encryption keys takes place under the pre-shared key. The session key is used only for a single session.

FarLinX Gateway models without IPSEC can be supplied to any country. Models with IPSEC capability can be
exported without a special export licence to some countries. Where IPSEC is required and the destination country is not on the pre-approved list, FarSite will apply for an export license for that customer. See Order Information for more details.

Resilience Options

To permit network line redundancy, a FarLinX X25 Gateway may operate with two or more X.25 lines acting as a hunt group. Calls can optionally be routed over any active line connected to the Gateway so that if one line goes out of operation then the other lines can continue to be used automatically. Backup X.25 lines can also be configured.

Two Gateways can be used together as an Active and Standby pair sharing a single IP address. Should the active Gateway fail, the standby Gateway will automatically take over.

Statistics, Event Logging and SNMP


The gateway maintains a comprehensive set of statistics and activity counts. This information can be used to indicate the total loads on the Gateway and also to give early warning of line performance problems even misconfigured systems elsewhere in the network. See a sample screen of some of the stats available on the right.


All connections setup through the Gateway can be logged. The logs are automatically saved on a daily basis, old logs can be displayed as required. Log events can also be routed to syslog to allow logging centrally.

The connection status of active connections / most recent connections / disconnections are displayed in a browser window.


The Gateway supports SNMP alerts with 3 configurable levels. Alerts can be issued for SVCs connecting and disconnecting, PVC errors, connection routing errors, line up and line down events and many more events.

Built in Line Monitor

The Gateway includes on the CD Line Monitor software installable on a PC that allow the X.25 traffic to be recorded and displayed in real time. Multiple channels from multiple Gateways can be monitored simultaneously. Support to allow the popular Wireshark line monitor to record and display the X.25, TCP/IP and XOT line traffic is also included.

Line Monitor showing a trace of an X.25 line

This very useful feature allows Network Managers and System Installers to locally or remotely analyse and rapidly diagnose problems that may occur on the X.25 lines without the need for expensive external line monitors.

The line traces can be saved and viewed later, for example in a customer support situation.


The Gateway is configured from a Browser, IE, Firefox and Chrome are supported. Access to the configuration is secured through a user name and password.

The Configuration Application allows all the features of the Gateway to be managed. The majority of configuration changes to the Gateway are made dynamically so continuous operation of the Gateway can be maintained. For example, where the configuration for one line is changed, only that line is restarted; other lines remain operational.

Configurations can be saved for later use.

The sample configuration screen on the right shows configuration of a remote host.

System Upgrades

Upgrades to the firmware can be remotely and securely uploaded to the device so that the latest revision levels can be used.

Technical Specifications

Product Name

FarLinX XOT Gateway

FarLinX X25 Gateway-1

FarLinX X25 Gateway-2

FarLinX X25 Gateway-4

FarLinX X25 Gateway-8

FarLinX X25 Gateway-E1

Product code







X.25 Line count


1 line

2 lines

4 lines

8 lines

1 E1 line

POS Upgrade available (FL2610)







Gateway Features

XOT <-> X.25 connection routing

PVCs and SVCs; SVC routing is flexible with support for wild-cards and address translation

TCP/IP <-> XOT   connection routing

PVCs and SVCs; SVC routing is flexible with support for wild-cards and address translation

X.25 switching

X.25 connection routing between up to 8 X.25 lines and XOT

Data packetization

Includes Customisable Message Header Conversion, Cisco RBP, RFC-1006 and packetisation of messages terminated by specific characters (ETX,   Carriage Return etc), X.25 parity conversion

POS Protocols

Optional software upgrade to support Point of Sale protocols APACS, ISO 8583, HGEPOS and CTL (Card Tech Ltd)

TCP <-> X.25 / XOT   call routing modes

Statically defined routing, Dynamically configured routing, PAD Routing, X.25 data switching

X.28 PAD

X.28 Host PAD and X.28 PAD terminal support. PAD support is available through Telnet and the built in async port. The PAD is also supported with   the 4, 8 and 16 port async expansion cards

Secure connections over   TCP/IP

IPSEC option selectable for support of authenticated and encrypted data connectivity over TCP/IP

Data packets per second

Over 3,000 messages per second

Calls per second

Over 200 calls per second in XOT and TCP to X.25 modes

Maximum simultaneous connections

Over 2,000, can be any mix of SVCs and PVCs

Logging key events

Events log maintained for events such as the connections and disconnections, X.25 call failures, X.25 line down, and X.25 line up. Log   auto archived daily. The most recent events are displayed in real time on a scrolling display in the Browser. Can   be routed to syslog for remote logging

Line Monitor

Line monitor application included for display of frames and packets on X.25 connections, can be run locally or remotely. Wireshark supported.


Securely configured by a Browser and Java applets using XML, login required. Configurations can be   saved.

SNMP Alerts

Configurable levels, generated for events such as X.25 line down, X.25 line up, connections established and disconnections and gateway failures   (when in dual operation).


Statistics provided for line activity, line errors, protocol problem, Gateway activity. Resetable on demand.

X.25 network connectors

Connections for E1 (G.703, G.704), RS232C (V.24), X.21, V.35, RS530 (RS422) and RS449 available.
Line speeds up to 2 Mbits/s; internal and external generated line clocks.

Types of X.25 connection

X.25 network, leased (fixed) line

Types of PAD connection

Async lines, Telnet

X.25 feature summary

Data packet size up to 4096 bytes
SVC and PVC logical connections
X.25 CCITT Compliance 1980, 84 and 88
DCE and DTE operation
Reverse charging, Closed User Groups (CUG), Network User Identification   (NUI), Fast Select, Throughput Class Negotiation
Hunt groups, backup lines
Compatible with all known X.25 networks including for example: Datex-P, BT X.25 Direct, Eirpac, Austpac, Transpac, Iberpac and Itapac

XOT Specification

Complies with RFC 1613 - X.25 over TCP (XOT)


10/100 BaseT LAN port,   RJ45.


CE: EN55022:2006+A1:2007 Class B, EN55024:1998+A1:2001+A2:2003, EN61000-3-2:2006, EN61000-3-3:1995+A1:2001:A2:2005. FCC part 15 Class B. UL. Safety: EN 60950-1: 2006. RoHS compliant.

Power Requirements

100 to 240 VAC, 50/60 Hz or -48 VDC version available
1 Amp, 60 Watts.


1U height all metal case, rack mounting ears supplied. Software selectable power down. Reset to factory defaults switch. Temperature   controlled fan operation. 
Dimensions: metric - 430(W) x 234(D) x 43(H) mm - imperial - 16.9”(W) x 9.2”(D) x 1.7"(H) inches
Weight: 3.4 kg (7.5 lbs).
Operating Temperature range: 5 to 40°C (41 to 104°F), Humidity: 20% to 95% RH (non-condensing)
Storage Temperature range: 0 to 70°C (32 to 158°F), Humidity: 5% to 95% RH (non-condensing)


36,267 hours (FarLinX X25 Gateway-2)

Warranty period

1 year

* All specifications are subject to change