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Mechanism for Sending Fill Characters During the SDLC Frame Sending Periods When Data Are Not Available

IP.com Disclosure Number: IPCOM000100851D
Original Publication Date: 1990-Jun-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 2 page(s) / 55K

Publishing Venue

IBM

Related People

Calvignac, J: AUTHOR [+5]

Abstract

In a transmission system, handling SDLC (Synchronous Data Link Control) frames separated by flags, when a frame transmission is started, there is no overrun avoidance possibility and the complete data must be made available by the transmitter for the entire frame duration, until the ending flag. This entails constraints in the design of the transmitter, especially for the long frame transmissions over high speed links.

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This is the abbreviated version, containing approximately 61% of the total text.

Mechanism for Sending Fill Characters During the SDLC Frame Sending Periods When Data Are Not Available

       In a transmission system, handling SDLC (Synchronous Data
Link Control) frames separated by flags, when a frame transmission is
started, there is no overrun avoidance possibility and the complete
data must be made available by the transmitter for the entire frame
duration, until the ending flag. This entails constraints in the
design of the transmitter, especially for the long frame
transmissions over high speed links.

      This article relates to a mechanism which allows the
transmissions of long frames on the high speed links to be improved
without suppressing any SDLC function.

      The transmitter will send time fill characters having the
configuration 01111110 until the next data are ready to be sent, and
a complete fill character will be sent before resuming the sending of
the next data.

      An example of a frame sent by the transmitter is shown below. F
represents the flag byte, and D represents the data bytes.
  FDDDDDDDD111111101111111011111110DDDDDD..D011111110DDDDD....DF
  --------T1------------------T2-----------T3----T4------------->

      At T1 and T3, the data are no more available and fill
characters are sent, as for the flags, and the zero may be shared by
two fill characters.

      At T2 and T4, the data are available, so that the sending of
the frame data resumes after the complete fill character.

      If...