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ALMA MEMO #420
Digital Transmission System Signaling Protocol
Robert W. Freund (National Radio Astronomy Observatory)
2002/09/06
Keywords: signaling protocol, digital protocol, digital transmission, parallel data
transmittion, optical fiber communication, data scrambling, virtual parallel
bus, OC-192, VPB
The ALMA Digital Transmission System (DTS) transmits digitized IF signals
from an antenna to the correlator at the central location. The digitized
data is divided equally across four identical transmission elements. Each
element formats the parallel data for serial transmission over three 10 Gb/s
optical fiber channels and converts it back into parallel data at the receiver.
This Virtual Parallel Bus (VPB) system is defined by the channel signaling
protocol. The protocol is based upon a 160-bit frame structure using line
coding employing scrambling techniques. The frame consists of a synchronization
word, a sequence word, payload, and a checksum. Modulo-2 addition of the frame
with a pseudo random pattern scrambles the data to provide adequate recovery
timing information and a reduction of low frequency content.
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Last modified: 2002-09-12
alma-memos@nrao.edu