Browse Prior Art Database

Data Synchronization in an Asynchronous Ring Network Environment Utilizing Variable-Length Data Packets

IP.com Disclosure Number: IPCOM000046991D
Original Publication Date: 1983-Sep-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 3 page(s) / 63K

Publishing Venue

IBM

Related People

Lanier, CS: AUTHOR

Abstract

In peer-to-peer ring networks it has been customary to provide a master timing station at one point in the ring to originate timing reference signals for the communications of all stations. A problem with such ring configurations is their dependency on the operativeness of the timing station. If the timing station fails, the ring becomes effectively incapacitated, and the stations on the ring may no longer be able to communicate with each other. In order to avoid this, it has been proposed to permit each station to time its transmissions independently (e.g., with reference to an internal quartz oscillator local clocking source), while developing reception clocking references from incoming data (data transferred from a preceding station on the ring).

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Data Synchronization in an Asynchronous Ring Network Environment Utilizing Variable-Length Data Packets

In peer-to-peer ring networks it has been customary to provide a master timing station at one point in the ring to originate timing reference signals for the communications of all stations. A problem with such ring configurations is their dependency on the operativeness of the timing station. If the timing station fails, the ring becomes effectively incapacitated, and the stations on the ring may no longer be able to communicate with each other. In order to avoid this, it has been proposed to permit each station to time its transmissions independently (e.g., with reference to an internal quartz oscillator local clocking source), while developing reception clocking references from incoming data (data transferred from a preceding station on the ring). A problem in this regard is that although the transmission timing oscillators at all of the stations nominally have a common frequency, they are nevertheless asynchronous. Therefore, they will inevitably drift slowly relative to each other, and there is always a possibility of the loss of data in passage through a station due to either overrunning or underrunning of the local clock. In one such asynchronous ring network, data arriving at a station is configured in variable-length frames (typically ranging from 7 to 1,007 bytes in length) prefixed by destination information determining that station's handling (receive/process locally only, pass through, or both receive/process locally and pass through in the case of special broadcast-type frames). At least a portion of each arriving frame must be buffered to hold the arriving data long enough to determine its routing/handling and to provide a stable platform for pass-through handling when required. Furthermore, a variable-depth insertion buffer (pass- through queue) is interposed between the staging buffers and the station's transmission circuits to allow for variable accumulation of pass-through data which begins to arrive while local origin data is being transmitted. The pass- through queue is operated on a first-in, first-out (FIFO) basis, and must have sufficient byte capacity to store at least a maximal length frame, in order to avoid the possibility of overrun when a pass-through frame starts to arrive shortly after the beginning of a local origin transmission and the relative clock drift mentioned above is such that the rate of byte arrival exceeds the rate of byte transmittal by a critical amount. In addition, the size of the pass-through queue and the configuration of the logical mechanism governing pass- through and local origin frame transmissions should be constrained to eliminate entirely the possibility of either overrun or underrun due to differences in reception and transmission clock rates (underrun occurs when the reception clock is slower than the transmission clock and the pass-through transmission of a frame is st...