CERN Accelerating science

The New Network Infrastructure for the CERN's Site

  Jacques Altaber IT/CS

The first CERN site-wide computer network was CERNET, a locally designed system used between 1978 and 1989. From 1984 onwards, CERNET was progressively replaced by multiple Ethernets running over shared co-axial cables. Since 1990, these Ethernets have been inter-connected by a high speed optical fibre network. Although this gave CERN an excellent basis for joining together several thousand personal computers, workstations, servers, and printers, it was not without problems. The fact that users were connected via coaxial cable, shared between many users, meant that interference and cable problems were common and network capacity was limited.

In 1994, the Management approved a major project - the Structured Cabling Project - to completely refurbish the site-wide office networks. This project started in 1995, and has recently been completed on schedule. By now the network connections in almost every office at CERN have been moved onto structured cabling. Instead of many users sharing each cable, there is a dedicated cable from a central point in each area to each "socket" in the office. These cables form a many-pointed star, so the central points are known as "star points", and there are about 60 of them in total. In each star point the network is connected to the optical fibre backbone.

The cables coming from the sockets in offices are connected to ports of hubs in the star point and this represents the "real" connection point onto the network. Not all cables are connected to hubs and, in fact, users will find that only the sockets in their offices which have computers attached to them will work. When an office socket is not used, it is not connected in the star points.

Because there is a separate cable to each office socket, the total capacity of the network in a building can be increased by installing extra equipment in the star point. The funding of the project includes the equipment in the star point for delivering 10baseT Ethernet, but the cabling itself is able to carry much higher bandwith. Indeed, for some high-speed requirements from physics experiments 100Mbits CDDI (FDDI on copper) and 100baseT (FastEthernet) have been installed. With such a powerful cabling infrastructure, we hope there will be no need for significant extra cabling work for the next ten years.

This major project has required about 1,200 km of cable which has been installed, within the buildings, by the contractor, Olivetti Oliservice, giving about 21,000 office connectors (we have used a standard office connector-density of one connector for 5 sqm). In addition, more than 28 km of optical fibre cable (in over 70 sections), containing many fibres, has been installed to interconnect the star points. More than 8000 user devices have been connected, fed by equipment supplied by HP (10baseT hubs), 3Com (100baseT switches), Schneider and Koch (CDDI concentrators), Cisco (routers and 10baseT switch) and DEC (FDDI backbone and Gigaswitches).

In parallel with the new cabling infrastructure activity, the architecture of the network has been changed from a bridged network to a routed network. The introduction of routing requires special care as it impacts every host on the network. Currently more than 40 star points and 7000 hosts have been connected to the new routed network. It is expected that, by mid 1998, all the hosts on the structured network will be routed. Before this migration the bridged architecture meant that the many thousand hosts were all on the same logical network, sharing the troubles, much in the same way as they shared their troubles when on coaxial cable. With the new routed network, hosts can be grouped in independent clusters with minimal interference between them, thus improving significantly the stability of the overall network.

The IT/CS networking team is managing all this effort as well as keeping the remaining parts of the old network alive. Results so far are exactly as expected, with generally better network performance and a significant reduction in the operational breakdowns. Users are now accustomed to requesting all changes to their network connections through the World-Wide Web. For any new installation, move or removal of a host, whether on the structured cabling or on the coaxial networks, please submit a request through the following Web page:

For further information, please consult the CS group Web pages at