7.2 Network Services
CDC's network facilities can be divided into the internal Local Area Network (LAN) and the connectivity to the Wide Area Network (WAN). Heavy reliance upon centralized computing resources, with minimal computing power on the individual's desktop, requires dependable, high-bandwidth networking to maintain user productivity. Access to remote computer systems at NCEP, NCAR, and GFDL and the importance of CDC on-line data sets and graphical web products to external users dictate that CDC also requires adequate connectivity to the Internet.
CDC is in the fortunate position of having considerable control over its internal LAN wiring. Although LAN equipment was provided to CDC as part of the move to the new David Skaggs Research Center (DSRC) in March 1999, it quickly became apparent that a mixture of Asynchronous Transfer Mode (ATM) and Ethernet protocols within the LAN and the use of edge switches in the role of core switches were not providing CDC the level of service needed. Consequently, with the advent of inexpensive copper-based Gigabit Ethernet technology, CDC completely replaced their LAN in 2000 for approximately $45,000. The new LAN (Fig. 7.2) features an Extreme Networks Summit 7i Gigabit Ethernet switch at its heart. The switch provides 28 1000BT (copper wire) ports and four 1000SX (fiber cable) ports. The 7i's backplane can handle all active ports at full wire speed. Most of CDC's Sun servers are connected directly into the 7i to provide high-bandwidth for the NFS (network file system) traffic between the user's running job and the user's data files. Other Gigabit links go to Fast Ethernet concentrators, the Extreme Networks Summit 24 and a Summit 48. The Summit 48 provides 48 Fast Ethernet ports for the desktop PC's, Mac's, and printers. The Summit 24 connects to our 12 Maxtor NAS devices, with plenty of room for expansion. Another Gigabit link from the 7i goes to a Sun Ultra 60 that serves as the gateway to our Compaq Alpha-cluster. This Sun gateway serves to shield the 7i from the Linux operating system on the Alphas. The Alphas are connected to the Ultra 60 using a Cisco Catalyst 5000, our only holdover from our former location on the CU east campus. Finally, two Gigabit links go from the 7i to the two SunRay servers. The SunRay architecture requires a private LAN for communication between the SunRay server and the SunRay desktop clients. CDC utilizes an Extreme Networks Summit 48 for this purpose. The Summit 48 has been configured so that if one of the SunRay servers fails, the SunRay users are still able to log on to the other SunRay server. In 1997, each office user had access to an Ethernet (10-Mbps) line shared with nine other users or devices. Today, each office user has a dedicated Fast Ethernet (100-Mbps) line.
For connections to the outside world, CDC takes advantage of the excellent connectivity provided by the DSRC's ATM backbone and the Boulder Research and Administrative Network (BRAN), a fiber-based metropolitan-area network that CDC helped create (see Fig. 7.3). The DSRC ATM backbone provides OC12 (622-Mbps) links between CDC and the other building tenants, including the Forecast Systems Laboratory (FSL), the Aeronomy Laboratory (AL), and the National Geophysical Data Center (NGDC). An OC3 (155-Mbps) link via BRAN connects the DSRC backbone both to the University of Colorado-Boulder and to NCAR. Both of these institutions are connected at OC3 speeds to the Front Range GigaPOP (FRGP), which provides connectivity to the commercial Internet via Qwest and to the Next Generation Internet (NGI) in the form of Abilene. If problems develop at the FRGP, the DSRC backbone can switch to a secondary route though FSL, albeit at fractional T3 (6-Mbps) speeds. A bottleneck for CDC is caused by the connection from the CDC Summit 7i to the DSRC ATM backbone. At present this is only a Fast Ethernet (100-Mbps) connection. Despite this, CDC, which represents only 5% of the DSRC's occupants, has accounted for 28% of the total network traffic through the DSRC's gateway to the outside world over the past year (Fig. 7.4). Most of this traffic has been outbound, meaning transfer of information from CDC to the rest of the scientific community and to the general public. Only FSL can equal CDC's network traffic through the DSRC gateway, but most of their traffic has been inbound on that link. In the near future, the DSRC network operations center is planning to upgrade our 100-Mbps bottleneck to a 1000-Mbps Gigabit Ethernet connection.
