TCP to X.25 POS Gateway software for APACS, ISO 8583 and other custom ePOS Transactions

Example use of the FarSync TCP-X25 POS Gateway interconnecting IP and X.25 networks

The highly versatile FarSync TCP-X25 POS (Point-Of-Sale) Gateway handles APACS, ISO 8583, HGEPOS and many other custom electronic money transfer transaction messages between TCP/IP and X.25 networks plus general purpose routing / data translation between TCP and X.25


Some modern Point-Of-Sale (POS) terminals, store controllers and other types of electronic money transfer processing (EFT (Electronic Funds Transfer), Payment Clearing and Electronic Payment) equipment connect via TCP/IP whilst many existing POS transaction processing Hosts, such as VISA, use X.25 interfaces, in some cases the reverse situation exists. The FarSync TCP-X25 POS Gateway provides a dependable means of inter-connecting POS equipment to electronic money transfer central processing systems where there is a requirement for a specialist Gateway between TCP/IP and X.25 networks.

The very versatile Gateway supports ISO 8583, APACS 30, APACS 40, HGEPOS plus CTL (Card Tech Ltd) Online message type support. There are 3 versions of the POS Gateway software providing scalable solutions, starting with a small scale single store version supporting up to 10 simultaneous transactions to the MAX version allowing up to 4,000 simultaneous transactions.

In addition the Gateway can be configured for general purpose TCP to X.25 data translation with flexible routing options, including fixed routes, dynamic routing, RFC 1006 and Cisco RBP compatibility.

The Gateway, which operates as a Windows service on Windows Server 2003, XP or 2000, is designed for non-stop operation. Almost all changes to the configuration are applied dynamically with no need for reloading.

The FarSync TCP-X25 POS Gateway will operate in conjunction with an IP dial platform to support remote POS terminals connected via PSTN or ISDN connections.

Two or more Gateways can be used in a load balanced, resilient configuration that has no single point of failure.

Where a standalone rack mountable appliance is preferred to a software solution the FarLinX X25 Gateway should be used.


  • Interconnection of X.25 POS Terminals to TCP/IP connected host/s
  • Interconnection of TCP/IP connected POS Terminals to X.25 connected host/s
  • TCP to X.25 support for EFT (Electronic Funds Transfer), Payment Clearing and Electronic Payment
  • General purpose Gateway to transfer data between TCP/IP and X.25 networks

POS Gateway Operation

The Gateway provides connection establishment and data packetisation services for APACS, ISO 8583, HGEPOS and other custom ePOS systems to allow POS terminals operating over TCP/IP to interface to X.25 connected hosts, flexible general purpose options for mapping and routing TCP to X.25 data are also provided.

A special configuration option is available to support connection to CTL (Card Tech Ltd) Host equipment where the POS terminals are connected by X.25 and the connection to the verifying host is by TCP/IP.

The Gateway provides routing facilities to select the appropriate Host from those available and maintains X.25 sessions to the Host as required. An X.25 session is established for the POS transaction when the TCP session for a transaction is established.

The Gateway can operate in conjunction with an IP dial-up platform device supporting autocommand telnet this permits support for remote POS terminals connected via PSTN or ISDN connections.

APACS Options

APACS connections over X.25 can operate in two different ways. The FarSync TCP-X25 POS Gateway supports each mode transparently.


APACS messages are sent without a LRC in PAD-HOST mode, no APACS control frames eg ACK, DLE EOT are required . The transaction consists of a pair of APACS messages. An X.25 call (virtual connection) is established by the Gateway at the start of each transaction and cleared by the Gateway at the end of the transaction.


APACS messages are sent complete with the LRC. APACS control frames are used to regulate the flow and termination of the APACS message, each message being acknowledged with an ACK frame. Completion of a transaction is indicated by DLE EOT. An X.25 call (virtual connection) is established by the Gateway at the start of each transaction and cleared by the Gateway at the end of the transaction.

General Purpose Options

The Gateway also can be configured for general purpose TCP to X.25 data translation, which includes the functionality of DRPD, SRPD and SRSD Personality Modules as provided with the general purpose FarSync TCP-X.25 Gateway, providing fixed routing between TCP and X.25 connections, dynamic routing, RFC 1006 and Cisco RBP compatibility.

Overview of Resilient Operation

The FarSync TCP-X25 POS Gateway can be deployed in a wide variety of ways to achieve the level of resilience required by the application. The level will depend on the value of the data traffic and the acceptable degree of user intervention required to rectify any problem. The aim with resilience is to remove single points of failure. Resilient configurations using more than one POS Gateway also allow improved performance by sharing the traffic load between several machines.

Network Line Redundancy

To achieve network line redundancy, a single FarSync TCP-X25 POS Gateway may operate with two or more X.25 lines. It can route data over any active line connected to the Gateway so that if one line goes out of operation then the second line continues to be used automatically. Your network provider may also support a number of additional resilient offerings. Examples include diverse routing of cabling into your premises or even connection of network lines to geographically dispersed network nodes.

Communications Equipment Redundancy

To further improve on Network Line Redundancy, multiple FarSync X.25 cards may be used in a single POS Gateway machine. This will allow the Gateway to continue operation even if there were a hardware or software fault within one of the communications adapters that prevented it handling calls.

Gateway Redundancy and Load Balancing

For fully resilient operation, two or more FarSync TCP-X25 POS Gateways may be deployed. This can be either with simple failover from a primary to a backup machine or in a load balancing configuration.

The FarSync TCP-X25 POS Gateway operates in conjunction with Windows Network Load Balancing (NLB), an integral feature of Windows Server 2003 (also Windows 2000 Advanced Server). NLB provides failover support for IP based applications and services that require high scalability and/or availability and is ideally suited to improving the availability of the FarSync TCP-X25 POS Gateway. Load balancing these services ensures there is no single point of failure and that there is no performance bottleneck.

FarSync Gateway Supervisor

The FarSync TCP-X25 POS Gateway utilises the FarSync Gateway Supervisor application to integrate tightly with NLB to extend its basic LAN resilience to also cover the service level as well as the LAN access level. The Gateway Supervisor checks the state of the X.25 network lines and as these change state between fully operational and faulty it selectively enables/disables the server from the NLB pool for the FarSync TCP-X25 POS Gateway service, thus managing the availability of that particular POS Gateway machine. Events such as the connections established are logged on a rotating log file, key events such as loss of an X.25 line are also logged on the Windows event log.

Performance and Expandability

The FarSync TCP-X25 POS Gateway easily handles very high transaction loads. Support for large numbers of X.25 lines and multiple Gateways provides enormous scalable expansion capability and resiliency. The main performance and expansion capabilities of the Gateway are:

  • Up to 500 POS transactions per second on each Gateway (MAX version)
  • Multiple load balancing Gateways, up to 32 sharing a single IP address
  • X.25 line speeds from 2,400 baud to 8 Mbits/s
  • From 1 to 16 X.25 lines per Gateway
  • X.25 network, leased line and X.25 dial-up connections supported
  • Up to 2,000 connections per X.25 line (MAX version)
  • 3 versions - 10 session, 20 session and MAX (up to 4,000 )
  • Up to 4,000 simultaneous connections on the MAX version of the POS Gateway

Connection Routing and Address Mapping

The FarSync TCP-X25 POS Gateway is typically used to route connections to a single acquiring host. It can, however, support routes to 2,000 different X.25 hosts. Similarly, when using the called X.25 address as the routing key, incoming X.25 calls can be routed to thousands of different TCP/IP hosts.

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

The Dynamic routing option allows the X.25 address (NUA) and call parameters to be set by the remote application at the time each X.25 connection is established. X.25 packetisation information is passed to the application.

Configuration Application

Configuration Application screen showing the config parameters for an APACS 30 connection

The Configuration Application for the POS Gateway allows the TCP interface, X.25 connection, and POS protocol types and the event log levels to be selected. Almost all changes to the configuration are made dynamically so continuous operation of the Gateway can be maintained.

The sample screen shot taken from the Configuration Application shows the configuration parameters for an APACS 30 X.25 to TCP/IP connection

Configuration by Text Files

As an alternative to using the Gateway Configuration program, the POS Gateway configuration can be defined in text files. This approach is more scalable, allowing hundreds of routing definitions to be easily configured. As with the Configuration Application changes to the text files can be applied dynamically allowing continuous operation to be maintained.

FarSync X.25 card

The FarSync TCP-X25 POS Gateway uses the FarSync X25 T-Series or M-Series cards to provide the X.25 connection. One or more of these high performance PCI-X / PCI / PCMCIA cards are required to connect to the physical X.25 line/s that connect to the Host's X.25 network. See FarSync X.25 cards

Maintenance Contract

FarSite recognises that this product is often used as a key component in POS transaction systems and as such a guaranteed response to unexpected problems is required. A maintenance contract is available for the FarSync TCP-X25 POS Gateway and FarSync X.25 cards for priority service and rapid problem resolution.

Technical Specifications
Product Name FarSync TCP-X25
POS Gateway-10
FarSync TCP-X25
POS Gateway-20
FarSync TCP-X25
POS Gateway-MAX
Product code FS9103 FS9203 FS9003
Maximum simultaneous transactions 10 20 4,000+
Product Features
POS transaction protocols APACS 30, APACS 40, APACS 70, ISO 8583 (various options), HGEPOS
APACS protocol variants handled PAD-HOST - just APACS messages, no LRC
HOST-T/T - APACS messages with LRC plus control frames (ENQ, AK, DLE EOT, etc)
HPAD Conversion - HOST-T/T Mode to PAD-HOST Mode conversion
TPAD Conversion - PAD-HOST Mode to HOST-T/T Mode conversion
Miscellaneous data options Parity conversion for the X.25 datastream
CTL (Card Tech Ltd) Online message type
Cisco RBP message header format
RFC 1006
Minimal PAD for operation
TCP to X.25 translation modes

Yes, Fixed and Dynamic Routing (compatible with the DRPD module on the FarSync TCP-X25 Gateway). Mode list:

  • Character Stream
  • APACS CTL-Online
  • ISO 8583 Hdr2
  • ISO 8583 Hdr4
  • ISO 8583 (CTL)
  • Cisco RBP
  • ETX-Terminated
  • CR-Terminated
  • Conv Hdr 2-bin
  • Conv Hdr 2-ascii
  • Conv Hdr 4-bin
  • Conv Hdr 4-ascii
  • RFC1006
  • Plus other special modes
Transactions per second Up to 500 per second (MAX version)
Maximum simultaneous transactions Up to 2,000 on each X.25 line to total of 4,000 across all lines (MAX version)
Resilient configuration Yes, from 2 to 32 Gateways using Windows 2000 Advanced Server or Windows Server 2003 configured for NLB and the FarSync Gateway Supervisor application
Load balancing Yes, from 2 to 32 Gateways using Windows 2000 Advanced Server or Windows Server 2003 configured for NLB and the FarSync Gateway Supervisor application
TCP/IP connections to the POS Gateway Standard PC LAN cards
FarSync WAN cards for leased line / internet / intranet connections using E1, X.21 and V.35 network connections
Logging key events The Windows event log is used to log key operational events, eg X.25 call fails, X.25 line down, X.25 line up
Maximum X.25 lines Up to 16 lines per POS Gateway
Types of X.25 connection X.25 network, leased line, X.25 dial-up
X.25 cards supported One of more FarSync X25 cards must be used with this product, further info on FarSync X.25 cards
Summary of X.25 features
supported by FarSync X25 cards
X.21, V.35, EIA530, RS449 and V.24 network interfaces
254 SVC and/or PVCs per port, 2000 per port with the expansion pack
Speeds up to 8.448 Mbits/s
X.25 CCITT Compliance 1980, 84 and 88
Data packet sizes up to 4096 bytes
Reverse charging, Closed User Groups (CUG), Network User Identification (NUI),
Fast Select, Throughput Class Negotiation,
Built in Line Monitor
Rack mountable appliance solution See the FarLinX X25 Gateway
Operating systems supported Windows Server 2003, Windows XP Professional,
Windows 2000 Professional, Windows 2000 Server, Windows 2000 Advanced Server, Windows 2000 Datacenter Server

Information in this document is subject to change without notice.

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