When the first Hermes network was installed in the early eighties, no standard protocols existed for levels 4 (transport) and 5 (session) of the OSI reference model. An international standard was available only for the network levels (1-3): X.25. Therefore the Hermes pioneers had to create proprietary (so-called UIC) high level communication protocols. Although they worked perfectly for many years, their support was expensive and later the UIC protocols started to block introduction of new services.
One of the great results of the Internet revolution were new de facto standards for all communication layers. Their existence led the Hermes railways in 1998 to approve a strategic decision to migrate their international applications from the UIC protocols to Hermes Open Systems Architecture (HOSA) protocols. Then the HIT Rail members decided in 1999 to replace the X.25 Hermes Plus network with an outsourced Virtual Private Network (VPN) using IP.
The aims for HOSA introduction were the following objectives and benefits:
- Allow new applications and services
- Provide flexibility (configurable per application)
- Connect new partners easy and cheap
- The same technology for internal and external use
- Ensure significant costs savings
The Hermes Open Systems Architecture (HOSA), developed by HIT Rail, includes:
- FILE TRANSFER PROTOCOL (FTP) proposed for file transfer applications
- MESSAGE QUEUING (MQ) proposed for interactive dialogue applications
- INTERNET E-MAIL for electronic mail
- HYPERTEXT TRANSPORT PROTOCOL (http) proposed for web applications access
- INTERNET PROTOCOL (IP) for networking (used for Hermes VPN)
The composition of the HOSA protocols suite is shown on the following picture:
The HOSA protocols are mostly based on Open Standards, more precisely Internet standards, which are de facto industry standards and market winners. It is true for IP, FTP, E-mail and HTTP. Only the MQ protocol for dialogue applications is not an Open Standard yet, although it is based on draft international standard ISO 10026, part 7. However, many of the main IT suppliers are already providing products which support MQ, also known as BQM (Business Quality Messaging). MQ is on the way to become an industry standard and market winner. Based on the market reality, the decision was to build a MQSeries network. The railways are free to use any MQ product, if its external interface interacts with the IBM's MQSeries Q-manager.
Scheme of the MQ model is shown on the following picture:
Detailed instructions for the Hermes implementation for the FTP and MQ protocols are given in respective Implementation Guidelines. Each document describes the target protocol: the standard, functionality, options and profiles to be supported, requirements for application programming interfaces (APIs) and conversion rules.
In order to save cost and ensure compatibility, specific Hermes FTP Client software module was developed along the FTP Implementation Guidelines.
Scheme of the FTP model is shown on the following picture:
It needs be noted, that also other protocols can run over the Hermes VPN. The only condition is that they are TCP/IP based and conform to the Hermes VPN Security Policy.