DAS
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direct attached storage
Disk drives and SSDs contained within the computer cabinet and connected to the CPU via PCI or some other peripheral bus. Desktop computers and most servers have direct attached storage (DAS). Contrast with "storage area network" (SAN), which extends direct attached storage to external storage arrays shared by many servers. Also contrast with "network attached storage" (NAS), which adds file storage on the network. See block level, SAN, NAS and RAID. |
distributed antenna system
Using multiple antennas in an area that might normally have only one antenna. Typically at lower power than a single antenna, a distributed antenna system (DAS) is commonly deployed for 4G cellular systems in urban areas. A distributed system may even be used in large apartment buildings. For example, an optical fiber might connect to the cellular carrier, and the signals are wired to antennas on every floor.Mandatory for 5G
Fifth-generation cellular networks require many more cell towers than LTE and previous systems (see 5G).
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| Three Antennas in One Block |
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| In San Francisco, distributed antenna systems are commonplace; witness these three small antennas within a couple hundred feet of each other. (Image courtesy of EMFanalysis.com.) |
FDDI
(Fiber Distributed Data Interface) Often pronounced "fiddy," it was a LAN and MAN access method that had its heyday in the mid-1990s. FDDI was an ANSI standard token passing network that transmitted 100 Mbps over optical fiber up to 10 kilometers. It included its own network management system and could optionally run over copper wire (CDDI) with distance limitations. FDDI II added circuit-switched service to this normally packet-switched technology in order to support isochronous traffic such as real-time voice and video.Dual Rotating Rings
FDDI provided an optional dual counter-rotating ring topology that contained primary and secondary rings with data flowing in opposite directions. If a line broke, the ends of the primary and secondary rings were bridged together at the closest node to create a single ring again.
Single Attached and Dual Attached
Nodes could be configured as Single Attached Stations (SAS) connected to concentrators or as Dual Attached Stations (DAS) connected to both rings. Groups of stations were typically wired to concentrators connected in a hierarchical tree to the main ring. Large networks could be configured as a "dual ring of trees," in which the dual ring provided the backbone to which multiple hierarchies of concentrators were attached.
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| MIC Connector |
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| FDDI used a dual-fiber MIC plug and socket for connection to devices. See fiber-optic connectors. |
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| MIC Connector |
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| FDDI used a dual-fiber MIC plug and socket for connection to devices. See fiber-optic connectors. |
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