Physical layer

When first established in 1996, our network consisted of several different physical media, including optical fiber, satellite stations, and microwave antennae, as illustrated in Figure 1. The network consists of three major segments: the ground network in California, the satellite link across the Pacific Ocean, and the ground network in Hawaii.

The ground network in California connects Caltech with JPL, the site of the satellite ground station. This portion of the network was established as part of Pacific Bell's extant fiber optic network. The only work required to establish this physical connection was the installation of a fiber optic line from the Caltech backbone to the remote observing room. This portion of the network has also been the most static, remaining essentially the same for the past year of operation.

The ground network in Hawaii has been somewhat more complex in its evolution, primarily due to the relative inexperience of GTE Hawaiian Telephone, as compared to PacBell in California, and a lack of infrastructure in Hawaii. Initially, the network consisted of undersea optical fiber for a portion of its length, from the satellite ground station in Honolulu to the GTE Hawaiian Telephone office on the big island of Hawaii. (This fiber had been installed less than a year before our project began.) The network then utilized microwave antennae to reach Hale Pohaku, at the 9,000-foot level on Mauna Kea, as fiber optical cable had not yet been installed in these remote areas. The final portion of the network, from Hale Pohaku to the telescope dome on the summit of the mountain, again employs fiber optic cable.

 

Figure 2: A schematic of the high-speed terrestrial network in Hawaii used for the Keck remote observing project. The network is shown in its initial and final (all-fiber) states.  

In January of 1997, the portion of the ground network in Hawaii consisting of microwave antennae was finally upgraded to optical fiber (see Figure 2). The improved performance for high-speed data transfers resulting from the lower bit error rates (BER) of the final all-fiber network was immediately noticed.