Perle Systems Case Study
Mercury Communications Limited is one of the UK's biggest success stories of the last decade. Mercury was the first company to offer an alternative service to British Telecom and now provides a wide range of national and international services to both residential and business customers. With business line sales up 20% on last year, and over 100 direct routes to other countries, Mercury has become the 16th largest international traffic carrier in the world.
In the UK, Mercury had 44 regional telephone exchanges (or "switches"). An interactive connection had to be maintained to each switch in order to configure individual user requirements (customer datafill), monitor traffic, and collect statistics.
Previously, this switch management was performed from 14 regional centers by Mercury support staff. These centers were connected to their switches using a variety of hardware systems: terminal servers, modems, and X.25.
In order to improve the service and reduce the workload, Mercury decided to rationalize switch management into three centralized systems: CDMS, SIC and SAC.
Each system required its own dedicated server. Mercury was then faced with two serial connectivity problems to overcome: how to connect each system to all 44 switches, and, in the case of CDMS, how to connect the 200-plus people who logged in and used the system.
Mercury chose the Perle RIO product to solve both problems. RIO is a sophisticated serial I/O solution with support for 512 high-speed connections, flexible configuration and a data security features unrivalled in the serial I/O market.
Each switch management system required four serial connections to each of the 44 switches - a total of 156 connections per server - with room for expansion as more switches were added to the system.
In each server, Mercury use two RIO Host serial cards and 21 8-port Remote Terminal Adapters (RTAs) to connect to its switches. Each 8-port RTA connects to two switches, four ports to each. Connection to the switches is via 64K X.21 leased lines.
RIO's unique fault tolerance enables additional, standby links to be installed between RTAs. If any link cable fails or is accidentally disconnected, a connection is maintained via one of the standby fault tolerant links. This way no switch can become isolated.
A further RIO host serial card installed in the CDMS server and another seven RTAs provide access for 200-plus users. Five of the RTAs handle users in the same building - all using Apple Macs. RIO's modular and flexible nature means that they can locate each RTA within actual workgroups. And using RTA/P modules, which provide seven serial ports and one parallel port, means that each workgroup can have its own parallel printer. The sixth RTA is connected to a pool of modems for dial-in access by homeworkers, and the seventh RTA is installed via LDM on another London site.
One of the reasons for choosing RIO was its performance. Mercury's SIC system, in particular, had to be able to cope with a very high volume of traffic. All 44 switches download half a megabyte of data each every 15 minutes. That's 22 megabytes suddenly arriving on the server at the same time. The data takes three to four minutes to download, but because RIO handles so much of the workload, the host CPU can collate and store all the data in real-time.
"RIO handles it like a dream," enthused John Sizeland, Chief Engineer at Mercury's Hardware and Communications center in London. "We did our best to break it...in fact we spent a whole weekend trying to overload the system, but gave up once we had reached twice our worst case scenario."
The Ethernet and X.25 solutions that Mercury looked at just couldn't handle this level of traffic. Sizeland described them as "cumbersome".
This is due to RIO's award-winning use of transputer technology. The RIO host serial card and each RTA employ a RISC-based Inmos T225 Transputer. The transputer provides four highspeed RS422 communications channels (RIO "Links"). Thus, each RIO system runs off an impressive 10Mbit/s serial backbone - as fast as Ethernet but sustainable for greater distances.