APS Computer Networks: Designed to Address Future CAT Needs

The currently planned APS networks, which are consistent with requirements posed by the CAT Beamline Controls and Data Acquisition Committee chaired by Mark Rivers, should support the needs of APS CATs and users. The design, in addition, also supports expected upgrades and reconfigurations that may be required by the CATs as their activities grow in the future. The system can be divided into three basic parts: the fiber-optic network infrastructure; the current network and capabilities; and the equipment to be installed to implement the future configurations.

The Fiber-Optic Cable Plant: The fiber-optic cable plant installed several months ago consists of a "star-geometry" FDDI (Fiber Distributed Data Interface) network. It was installed as a dual-attached, dual-homing set of fibers and interfaces. Dual-attachment and dual-homing means that fibers are provided so that all data are sent simultaneously over two separate routes to and from the central network hub. In case of a fiber break or electronic failure, the network will continue to function at its full performance capability. The star geometry was chosen so that a future higher performance Asynchronous Transfer Mode (ATM) network will be possible. The ATM network has point-to-point geometry, whereas the FDDI is a ring geometry. In the APS network, each LOM is an FDDI (later ATM) node. The FDDI operates at data rates of 100 M-bits/sec., while the ATM will provide rates from 155 M-bits/sec. to more than 1 G-bit/sec. ATM was not installed immediately because its standards have not been firmly established and components tend to be company-specific (and very expensive). Extra optical fibers were installed with the initial FDDI plant, and these fibers are available as spares or to support special CAT needs until any needed private fibers are installed. (Such extra fibers are sometimes called "dark fibers".)

The Network Equipment: The network equipment being installed now consists of a network router for each LOM and a hub chassis for CAT-specific modules. The router and hub will provide a minimum set of performance and network-separation capabilities. The initial performance will be a match for the Category-5 (CAT-5) wiring installed in the office and lab areas of the LOMs. Each CAT (actually, each quarter-LOM) will be assigned a 24-channel ethernet module to be patched into the CAT-5 wiring system. This will allow immediate use of the APS network at ethernet speeds. Different or additional modules could be installed by a CAT to provide other types of ethernet physical media-thin-wire, thick-wire, or fiber ethernet (all within the limits imposed by the 8-slot hub chassis). The router will be set up to provide a separate subnet for each CAT. This separation will insure that one CAT's network traffic will not appear on any other CAT's network. This separation will be very important later as data traffic increases and secure transmission becomes important. The Class-B network authorization obtained for the APS will allow for four subnets per quarter-LOM (more for special cases), allowing separate subnets for beamlines and the office area if desired.

Future Configurations: In view of the needs expressed by the Beamline Controls and Data Acquisition Committee, adequate provisions have been made for expansion space, network management, and higher performance through the provision of a separate hub for each CAT. This will allow modules to be installed for both ethernet and FDDI (or CDDI, its copper-based implementation), and for management of the CAT's subnets. The management module installed initially will enable a network manager to remotely disable misbehaving ethernet network components. A management module to enable management of FDDI or CDDI components can be installed later if needed. The router will allow full FDDI data rates for each CAT's hub.

As-Needed Installation: The components described above (router, hubs, and management modules) will be provided by the APS when and where they are needed. The reason for this policy is twofold. Fully equipping all LOMs immediately will be expensive, especially in view of the trend for prices to drop over time as technology improves and quantity production lowers costs. Additionally, newer and higher speed technology and standards may become available before all LOMs are occupied. Thus, all CATs should examine their network needs and inform the APS as to when they will need data bandwidth above ethernet speeds, when they will need network management, and when they will need subnet separation within their sectors. As soon as the APS receives these requests (by contacting Dave Wallis, e-mail: wallis@aps.anl.gov), the appropriate equipment will be purchased and installed by the APS.

Special Needs: Some CATs may require special network services, either in terms of data rates or security or both. One such CAT, the Structural Biology Center (SBC) CAT, has installed a fiber-optic wiring plant in their quarter-LOM and is planning an ATM link to the Building 202, the Biological and Medical Research building at Argonne. They will initially be using "dark fiber" (spare fibers of the APS plant) until their own fibers are installed.

-M. Knott, Accelerator Systems Division


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