Smoothing filter

• US 5,018,171 A
• Filed: 08/09/1989
• Issued: 05/21/1991
• Est. Priority Date: 08/09/1989
• Status: Expired due to Term

• Current Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Original Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Inventors: Perloff, Ronald S., Garverick, Timothy L.
• Primary Examiner(s): Olms, Douglas W.
• Assistant Examiner(s): Chin, Stephen
• Application Number:
  US07/391,439
• Time in Patent Office: 650 Days
• Field of Search: 375/106, 375/121, 370/85.15, 370/94.3, 370/85.4, 370/85.6, 370/94.1, 370/85.1, 370/100.1, 370/85, 370/85.5, 340/825.5
• US Class Current: 375/377
• CPC Class Codes: H04L 12/433 with asynchronous transmission, e.g. token ring, register insertion

Abstract

Preamble smoothing for information character transmissions in a data transmission network is accomplished as follows. First, the smoothing filter identifies the start of a new preamble. If the start of a new preamble is identified and a previously received preamble has been extended, then the preamble is contacted by deleting an IDLE byte or, if the frame received prior to the initial IDLE byte was a frame fragment, then the information character preceding the initial IDLE byte is deleted. Following the contraction of the preamble, a determination is made as to whether next received byte is an IDLE byte. If it is not, then the preamble is extended by inserting an IDLE byte and the smoothing filter begins searching for the start of a new preamble. If it is, then a counter is incremented. If the counter has not yet reached its preset threshold, then the next byte is checked to determine whether it is an IDLE byte. If it is, then the counter is again incremented. This iterative process continues until the counter threshold is reached. At that point, the smoothing filter again begins searching for the start of a new preamble.

Claims

1. In a data transmission network wherein an information frame is transmitted from a transmit station in the network to a receive station in the network, the information frame comprising a series of information characters including a sequence of a plurality of preamble information characters, a method of controlling the number of preamble information characters included in the transmitted sequence, the method comprising the sequential steps of:

(a) identifying an information character as an initial preamble information character;

(b) in the event that the preamble of a previous frame has been extended, deleting the initial preamble information character;

(c) in the event that the next information character is a preamble information character, incrementing a counter;

(d) iteratively repeating step (c) to identify a sequence of preamble information characters until the counter reaches a preset threshold, indicating that a continuous sequence of a preselected number of preamble information characters has been transmitted.

2. A method as in claim 1 wherein, in the event that the counter does not reach the preselected number, indicating that less than a continuous sequence of the preselected number of preamble information characters has been transmitted, inserting a preamble information character.

3. In a Fiber Distributed Data Interface network wherein information frames are transmitted from a transmit function to a receive function, the information frames comprising a series of information bytes including an initial preamble comprising a continuous sequence of a plurality of IDLE bytes, a method of expanding or contracting the transmitted preamble, the method comprising the sequential steps of:

(a) identifying an information byte as an initial IDLE byte, indicating the start of a new preamble;

(b) in the event that the preamble of a previous frame has been extended, contracting the new preamble by deleting the initial IDLE byte;

(c) when the next subsequent information byte is an IDLE byte, incrementing a counter;

(d) iteratively repeating step (c) to identify a sequence of IDLE bytes until the counter reaches a preset threshold, indicating that a continuous sequence of a preselected number of IDLE bytes has been transmitted.

4. A method as in claim 3 wherein, in the event that the counter does not reach the preset threshold, indicating that less than a continuous sequence of the preselected number of IDLE bytes has been transmitted, extending the transmitted preamble by inserting an IDLE byte.

5. In a data transmission network wherein an information frame is transmitted from a transmit station in the network to a receive station in the network, the information frame comprising a series of information characters including a sequence of a plurality of preamble information characters, apparatus for controlling the number of preamble information characters included in the transmitted sequence, the apparatus comprising:

(a) means for identifying an information character as an initial preamble information character;

(b) means for deleting the initial preamble information character when the preamble of a previous frame has been extended;

(c) means for examining the next subsequent information character to identify whether it is a preamble information character;

(d) a counter;

(e) means for incrementing the counter when the next subsequent received information character is a preamble information character; and

(f) means for iteratively examining information characters to identify a sequence of preamble information characters until the counter reaches a preset threshold indicating that a continuous sequence of a preselected number of preamble information characters has been transmitted.

6. Apparatus as in claim 5 and further comprising means for inserting a preamble information character in the event that the counter does not reach the preset threshold, indicating that less than a continuous sequence of the preselected number of preamble information characters has been transmitted.

7. In a Fiber Distributed Data Interface network wherein information frames are transmitted from a transmit function to a receive function, the information frames comprising a series of information bytes including an initial preamble comprising a continuous sequence of a plurality of IDLE bytes, circuitry for expanding or contracting the transmitted preamble, the circuitry comprising:

(a) means for identifying a information byte as an initial IDLE byte, indicating the start of a new preamble;

(b) means for contracting the new preamble by deleting the initial IDLE byte when a preamble of the previous frame has been extended;

(c) means for examining the next subsequent information byte to identify whether it is an IDLE byte;

(d) a counter;

(e) means for incrementing the counter when the next subsequent information byte is an IDLE byte; and

(f) means for iteratively examining information bytes to identify a sequence of IDLE bytes until the counter reaches a preset threshold indicating that a continuous sequence of a preselected number of IDLE bytes has been transmitted.

8. Circuitry as in claim 7 and further including means for extending the preamble by inserting an IDLE byte in the event that the counter does not reach the preset threshold indicating that less than a continuous sequence of the preselected number of IDLE bytes has been transmitted.

9. In a data transmission network wherein an information frame is transmitted from a transmit station in the network to a receive station in the network, the information frame comprising a series of information characters including a sequence of a plurality of preamble information characters, a method of controlling the number of preamble information characters included in the transmitted sequence, the method comprising the sequential steps of:

(a) identifying an information character as an initial preamble information character;

(b) in the event that the frame prior to the

preamble information character was a frame fragment, deleting the information character preceding the initial preamble information character;

(c) when the next subsequent information character is a preamble information character, incrementing a counter;

(d) iteratively repeating step (c) to identify a sequence of preamble information characters until the counter reaches a preset threshold, indicating that a continuous sequence of a preselected number of preamble information characters has been transmitted.

10. A method as in claim 9 wherein, in the event that the counter does not reach the preselected number, indicating that less than a continuous sequence of the preselected number of information characters has been transmitted, inserting a preamble information character.

11. In a Fiber Distributed Data Interface network wherein information frames are transmitted from a transit function to a receive function, the information frames comprising a series of information bytes including an initial preamble comprising a continuous sequence of plurality of IDLE bytes, circuitry for expanding or contracting the transmitted preamble, the circuitry comprising:

(a) a counter;

(b) means for holding the counter reset while not identifying IDLE bytes;

(c) means for releasing the counter upon identification of an initial IDLE byte;

(d) means for determining whether the previous frame was a frame fragment;

(e) means for deleting the initial IDLE byte in the event that the preamble of a previous frame has been extended and the previous frame was not a frame fragment;

(f) means for deleting the last information character of the frame fragment in the event that the preamble of a previous frame has been extended and the previous frame was a frame fragment;

(g) means for incrementing the counter of the next subsequent information character is an IDLE byte; and

(h) means for iteratively examining information

characters to identify a sequence of IDLE bytes until the counter reaches a preset threshold indicating that a continuous sequence of a preselected number of IDLE bytes has been transmitted.

12. Circuitry as in claim 11 and further including means for extending the preamble by inserting an IDLE byte in the event that the counter does not reach the preselected threshold, indicating that less than a continuous sequence of the preselected number of IDLE bytes has been transmitted.

13. In a data transmission network wherein an information frame is transmitted from a transmit station in the network to a receive station in the network, the information frame comprising a series of information characters including a sequence of a plurality of preamble information characters, apparatus for controlling the number of preamble information characters included in the transmitted sequence, the apparatus comprising:

(a) means for identifying a information character as an initial preamble information character;

(b) means for deleting the information character preceding the initial preamble iniormation character when the prior frame was a frame fragment;

(c) means for examining the next subsequent information character to identify whether it is a preamble information character;

(d) a counter;

(e) means for incrementing the counter when the next subsequent information character is a preamble information character; and

(f) means for iteratively examining information characters to identify a sequence of preamble information characters until the counter reaches a preset threshold indicating that a continuous sequence of a preselected number of preamble information characters has been transmitted.

14. Apparatus as in claim 13 and further comprising means for inserting a preamble information character in the event that the counter does not reach the preset threshold, indicating that less than a continuous sequence of the preselected number of preamble information characters has been transmitted.

15. In a Fiber Distributed Data Interface network wherein information frames are transmitted from a transmit function to a receive function, the information frames comprising a series of information bytes including an initial preamble comprising a continuous sequence of a plurality of IDLE bytes, circuitry for expanding or contracting the transmitted preamble, the circuitry comprising:

(a) means for identifying an information byte as an initial IDLE byte, indicating the start of a new preamble;

(b) means for deleting the information byte preceding the initial IDLE byte when the prior frame was a frame fragment;

(d) means for examining the next subsequent information byte to identify whether it is an IDLE byte;

(e) a counter;

(f) means for incrementing the counter when the next subsequent information byte is an IDLE byte; and

(g) means for iteratively examining information bytes to identify a sequence of IDLE bytes until the counter reaches a preset threshold indicating that a continuous sequence of a preselected number of IDLE bytes has been transmitted.

16. Circuitry as in claim 15 and further including means for extending the preamble by inserting an IDLE byte in the event that the counter does not reach the preset threshold, indicating that less than a continuous sequence of the preselected number of IDLE bytes has been transmitted.

17. In a data transmission network wherein information frames are transmitted from a transmit station in the network to a receive station in the network, an information comprising a series of information characters including a sequence of a plurality of preamble information characters, a method of controlling the number of preamble information characters included in the transmitted sequence, the method comprising the steps of:

(a) holding a counter reset while not identifying preamble information characters;

(b) releasing the counter upon identification of an initial preamble information character;

(c) determining whether the previous frame was a frame fragment;

(d) in the event that the preamble of a previous frame has been extended and the previous frame was not a frame fragment, deleting the initial preamble information character;

(e) in the event that the preamble of a previous frame has been extended and the previous frame was a frame fragment, deleting the last information character of the frame fragment;

(f) in the event that the next subsequent information character is a preamble information character, incrementing the counter;

(g) iteratively repeating step (f) to identify a sequence of preamble information characters until the counter reaches a preset threshold, indicating that a continuous sequence of a preselected number of preamble information characters has been transmitted.

18. A method as in claim 17 wherein, in the event that the counter does not reach the preset threshold, indicating that less than a continuous sequence of the preselected number of information characters has been processed, inserting a preamble information character.

19. In a Fiber Distributed Data Interface network wherein information frames are transmitted from a transmit function to a receive function, an information frame comprising a series of information bytes including an initial preamble comprising a continuous sequence of a plurality of IDLE bytes, a method of expanding or contracting the transmitted preamble, the method comprising the steps of:

(a) holding a counter reset while not identifying IDLE bytes;

(b) releasing the counter upon identification of an initial IDLE byte;

(c) determining whether the previous frame was a frame fragment;

(d) in the event that the preamble of a previous frame has been extended and the previous frame was not a frame fragment, deleting the initial IDLE byte;

(e) in the event that the preamble of a previous frame has been extended and the previous frame was a frame fragment, deleting the last information character of the frame fragment;

(f) in the event that the next subsequent information character is an IDLE byte, incrementing the counter;

(g) iteratively repeating step (f) to identify a sequence of IDLE bytes until the counter reaches a preset threshold, indicating that a continuous sequence of a preselected number of IDLE bytes has been transmitted.

20. A method as in claim 19 wherein, in the event that the counter does not reach the preset threshold, indicating that less than a continuous sequence of the preselected number of IDLE bytes has been transmitted extending the preamble by inserting an IDLE byte.

21. In a data transmission network wherein an information frame is transmitted from a transmit station in the network to a receive station in the network, the information frame comprising a series of information characters including a sequence of a plurality of preamble information characters, apparatus for controlling the number of preamble information characters included in the transmitted sequence, the apparatus comprising:

(a) a counter;

(b) means for holding the counter reset while not identifying preamble information characters;

(c) means for releasing the counter upon identification of an initial preamble information character;

(d) means for determining whether the previous frame was a frame fragment;

(e) means for deleting the initial preamble information character in the event that the preamble of a previous frame has been extended and the previous frame was not a frame fragment;

(f) means for deleting the last information character of the frame fragment in the event that the preamble of a previous frame has been extended and the previous frame was a frame fragment;

(g) means for incrementing the counter when the next subsequent information character is a preamble information character; and

(h) means for iteratively examining information characters to identify a sequence of preamble information characters until the counter reaches a preset threshold indicating that a continuous sequence of a preselected number of preamble information characters has been transmitted.

22. Apparatus as in claim 21 and further comprising means for inserting a preamble information character in the event that the counter does not reach the preset threshold, indicating that less than a continuous sequence of the preselected number of preamble information characters has been processed.