Access 4000 X25 - TCP IP Gateway

Overview

The Access 4000 X.25 - TCP/IP Gateway offers comprehensive solutions for migrating legacy devices and X.25 networks to TCP/IP including:

X.25 – TCP/IP conversion
X.25 over TCP tunneling (XOT)
XOT to TCP conversion
X.25 switching for partial TCP/IP migration
HDLC/LAPB to TCP conversion
Async /serial to TCP conversion

Features

Dual serial ports individually configurable for X.25, async/serial, or HDLC/LAPB
Serial ports support speeds up to 2Mbps
Up to 1024 SVC and/or PVC logical channel connections per X.25 link
Encapsulation method configurable on a per connection basis
X.25 link sharing between X.25 and TCP/IP networks
No re-configuration of X.25 devices necessary
Easy to use web configuration GUI

X.25 to TCP Conversion

The X.25 to TCP conversion Gateway interfaces (bridges) between X.25 and TCP/IP devices by interconnecting X.25 logical channels to TCP sockets using one of the encapsulation methods. The Gateway connects directly to X.25 DTE devices or to X.25 packet networks (DCE).

An important function of gateway conversion is the preservation of application messages. X.25 implementations delineate messages using packet sequences and a “More-bit” to reconstruct long messages. TCP, on the other hand, delivers messages as a non-delimited byte stream, and so requires the addition of an encapsulation header on top of TCP to preserve the boundaries of the message. Supported encapsulation methods are:

XOT (RFC1613 - X.25 over TCP)
RFC1006 Encapsulation (ISO Transport Service on TCP)
Odette FTP Encapsulation on TCP (as per RFC5024)
2-byte length header
X.25 M-bit and Q-bit preservation header
LINE mode for terminal applications
RAW (when no encapsulation header is required)
Other encapsulation methods are available by request

X.25 over TCP Encapsulation (XOT)

An XOT gateway is typically used when the X.25 network or point-to-point connection between X.25 devices is being replaced with an IP network. By tunnelling the X.25 packets over TCP, transparency is maintained while providing X.25 to IP address mapping and end-to-end X.25 logical channel number translation. X.25 devices do not need to be re-configured.

XOT to TCP Conversion

When an IP host supports X.25 on top of TCP (XOT) and relies on an external X.25 gateway to convert back to X.25, a second X.25-TCP gateway would be required for conversion to a TCP/IP device. The Access 4000 Gateway goes one step further by combining XOT–X.25 de-encapsulation and X.25-TCP conversion internally, eliminating the X.25 physical interface and associated overhead or bottleneck.