Physical Layer

Following 6 months of installation of optical fiber, satellite stations, and microwave antennae, our network began end-to-end testing in February of 1996. 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 (see Figure 2).

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. Due to the integrated nature of Caltech and JPL, the only infrastructure required to establish this physical connection was the installation of a fiber optic line from the Caltech backbone to the remote observing room in the astronomy building. Existing available bandwidth between Caltech and JPL well exceeded our requirements. This segment of the network has been extremely stable, remaining reliable and unchanged for the duration of our experiment.

 

Figure 3: Hawaiian network infrastructure: a. A microwave relay station at Hale Pohaku, at the 9,000-foot level on Mauna Kea. Before the completion of a fiber network up the mountain in January of 1997, several dishes such as this one relayed data between Hale Pohaku and the base of the mountain. b. The ATM switch installed on the summit of Mauna Kea, in the Keck Telescope building. The switch is a Newbridge 36150 MainStreet ATMnet, provided by GTE Hawaiian Telephone. Two single-mode DS-3 cards are installed in the left end of the switch.  

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 prior infrastructure in Hawaii. The first segment of the Hawaii network consisted of undersea optical fiber connecting the satellite ground station in Honolulu to the GTE Hawaiian Telephone office on the big island of Hawaii. Although already in existence, this fiber had been installed less than a year before our project began. The next segment of the network utilized microwave antennae to reach across the big island of Hawaii to Hale Pohaku, at the 9,000-foot level on Mauna Kea (see Figure 3a.). At that time, fiber optic cable had not yet been installed in these relatively remote areas. As we shall show, the introduction of the higher bit error rates (BER) of this non-fiber segment produced noticeable instability in the end-to-end network. Fortunately, in January of 1997 this portion of the ground network in Hawaii was upgraded to optical fiber. The improved performance for high-speed data transfers of the final all-fiber network was immediately apparent. The final segment of the Hawaii network, from Hale Pohaku to the telescope dome on the summit of Mauna Kea, employed pre-existing fiber optic cable. Figure 4 illustrates the final network configurations in Hawaii and California.

 

Figure 4: Schematics of the final terrestrial networks in Hawaii and California, as used for the Keck remote observing project. The Hawaii network connects the Keck Observatory to the ACTS HDR station in Honolulu, at DS-3 (45 Mbit/sec) speeds. The California network connects the Caltech campus to the ACTS HDR at JPL, at OC-3 (155 Mbit/sec) speeds. Black dots denote ATM switches.