System converts serial devices to TCP/IP

ISDNconnect provides Shell's wide area network with a low-bandwidth, always-on connection between terminal equipment and a central location.

Shell has been operating an onshore telemetry wide area network in Scotland since the mid 1980s.

The network, extending southwards from Shell's Saint Fergus Gas Terminal, is used to monitor and control onshore pipeline operations.

In 2002, Shell decided to carry out a review of this network and appointed Andrew Willder of AdRem Consulting to conduct the review.

The results of this review led to AdRem Consulting managing the migration of the network in 2004 to a BT packet-switched system, which resulted in savings in annual operating costs and improved reliability.

The security of the replacement network was also a key requirement, and this was independently reviewed and approved by Shell's own network specialists (SITI).

Originally, the telemetry network comprised 24 point-to-point analogue private leased lines from BT, with a hub-and-spoke topology and an average length of 100km.

Annual operating costs were significant for the combination of private circuit and PSTN line rental, and unreliability of telecoms equipment was consuming an inappropriate level of manpower.

Availability of the original solution was less than 99%.

The new network is based on a BT packet-switched service called ISDNconnect.

This solution, capable of supporting TCP/IP, utilises spare capacity on BT's ISDN2e channels, to provide a low-bandwidth, always-on connection between terminal equipment and a central location.

This type of service is used extensively in the financial services industry for ATM and card swipe authentication.

Up to 1000 such connections can be made to a central packet handler.

The connections are configured by BT as a closed user group thus providing the required security.

A standard option for the service provides automatic failover to a standby packet handler, over a geographically separate link, in the event of link failure to the primary packet handler.

AdRem Consulting carried out the network design and managed implementation of the migration.

Part of the migration required the existing telemetry, which was based upon serial Modbus communications, to be converted to Modbus TCP over TCP/IP for compatibility with the new packet-switched network.

Consequently AdRem Consulting needed to call upon an expert, to assist in the conversion of legacy industrial serial devices onto TCP/IP.

They approached specialist communications and automation supplier, MAC Solutions, for this service.

MAC Solutions provide a whole range of open Ethernet communications equipment for such purposes and recommended its Ethernet industrial device server from Lantronix, which would enable all of the existing, serial telemetry equipment to be left in place, whilst utilising the new packet-switched network.

This would save time, money and minimise downtime for Shell.

Around 80 device servers were required throughout the network.

Unlike the original serial Modbus network where only one master was permissible, the new device servers meant that multiple masters could potentially access data simultaneously.

This allowed AdRem to completely bypass the original master/standby switch-over system, which was complex and costly, and to allow both redundant masters to access all slaves concurrently.

Andrew Willder of AdRem Consulting comments: "We found MAC Solutions over the internet as a provider of Ethernet device servers".

"The reliability of the Lantronix device servers is excellent and the technical support provided by MAC Solutions was first class".

"We carried out a project at Shell first".

"Dave Hammond at MAC Solutions configured the first batch of device servers for us and kept us updated with firmware for the units".

Standard network components from Cisco were also used throughout the network, with the exception of the packet handlers, which were supplied by AdRem Consulting.

The packet handlers are required to interface with a European standard protocol that is not supported by Cisco or other mainstream data communications equipment suppliers, however, this requirement has been met by the use of a gateway device implemented in standard hardware and custom software with full Escrow assurance.

The gateways have run uninterrupted for more than two years without fault, and are implemented in a fully redundant configuration.

There are two, dual redundant Arcom masters per slave.

Since the device servers were installed, each slave can now communicate with multiple masters, so the master change over unit (used to control which of the two masters could communicate with each slave) is no longer required.

One advantage of the ISDNconnect service is that there are no geographical charges, so the ISDN2e subscriber could be located anywhere within the UK.

There are some small telephone exchanges that do not support the service, and a survey is therefore required to ensure that ISDN2e can be deployed to the required subscriber site, and also that the associated local exchange supports the ISDNconnect service.

A further advantage of the solution is that short-term extra bandwidth can easily be provided on demand to remote sites by means of the inherent ISDN2e B-channel service, which effectively operates over the public switched telephone service.

BT's incremental charges for additional users, including the ISDN2e line rental, amount to under GBP 1000 per annum/user.

A new user's service can be set up or removed at relatively short notice.

As a result of this migration, Shell's annual operating costs and support effort have been reduced, and system availability is well over 99.9%.

The telemetry system is remotely managed by AdRem Consulting.

The service is ideal for centralising corporate UK telemetry operations, and provides a level of security and redundancy that should meet all business continuity planning requirements.

Andrew Willder concludes: "Although the BT ISDNconnect service is being withdrawn in 2007, BT broadband-accessed VPN services are now available as replacements".

"This only has a minor impact on Shell's telemetry network due to Shell's adoption of Modbus TCP via the device servers which means that substitution of a WAN based on ISDNconnect with a WAN based on a broadband-accessed VPN will be straightforward".

"The use of TCP/IP across these WANs is effectively transparent, and migrating from one to the other simply involves some routing changes".

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