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1.0 INTRODUCTION The HDLC application decodes frames conforming to the HDLC format. High-level Data Link Control (HDLC) is the frame level definition of a number of modern protocols such as SDLC, BDLC, and X.25. Frames are delineated by special characters called flags. HDLC defines a zero-bit stuffing and removal technique that insures data will never appear as flag characters, so data in HDLC frames are always transparent. Each frame includes two CRC (error checking) bytes at the end. The first two bytes of each frame are defined as the address and control bytes. The HDLC application decodes the address and control bytes giving you a simple representation of their contents. The control byte can have up to four fields: 1-8 bits specifying the command or response, a poll/final bit, a 3 bit send frame number variable (0-7) and a 3 bit receive frame number variable (0-7.) 2.0 INSTALLING THE SOFTWARE The HDLC decode software module is named HDLC.OM4. The HDLC software is on a disk marked 5015-0029. You must copy this file to your working diskette or to the directory on your hard disk where the PC Comscope II files are kept. 1. Make a working copy of the diskette: 2. For non-hard disk systems: 3. For hard disk systems: The HDLC application will now appear in the APPLICATION PROGRAM menu when you run the PC Comscope II program. The HDLC.OM4 file is a standard .EXE format file. You can copy the HDLC.OM4 file to HDLC.EXE if you wish to use it with the resident option of the PC Comscope II program. Note, however, that if you try to run the HDLC program without the Omni/O resident the results are unpredictable. Your PC can possibly lock up. 3.0 RUNNING THE HDLC APPLICATION The HDLC application is started by selecting it from the APPLICATION PROGRAM menu as described in the user's manual for the PC Comscope II. The HDLC application can process live line data, captured data, or data from a journal file. The HDLC application does NOT automatically select the HDLC data mode, so you must do that before viewing live line data. The format of the screen that the HDLC application generates is described in section 4. Briefly, though, the top half of the screen is the standard datascope format while the bottom half is a mnemonic decode of the frames displayed in the top half. The HDLC application handles live and captured data slightly differently. In live mode the HDLC application continuously decodes the frames in real time. In captured mode (data in the capture buffer or from a journal file) the application decodes one frame each time the user hits a key. In captured mode you can move through the data with the arrow keys the same way you do when in Review Captured Data mode with no application program selected. When you hit one of the non-arrow keys the HDLC application will decode the next frame after the cursor. Note that the HDLE application will think the first bytes it sees are the address and control bytes, so you must move the cursor to the very beginning of a frame or else ignore the first decoded frame. 3.1 LIVE MODE In live mode the application is decoding live line data. There are three function keys active in live mode: 3.1.1 F2 Returns you to the PC Comscope II menus. 3.1.2 F3 Halts data capture and puts you into Captured mode. 3.1.3 F4 Toggles display from selected display code to hexadecimal and back again. 3.1.4 F10 same as F2 3.2 CAPTURED MODE In captured mode the application is decoding captured data, i.e. data in the capture buffer or data from a journal file. In captured mode you step through the data one frame at a time and you can move back and forth in the captured data. The following keys are active in captured mode: 3.2.1 Function key F2 Returns you to the PC Comscope II menus. 3.2.2 Function key F4 Toggles display from selected display code to hexadecimal and back again. 3.2.3 Function key F10 same as F2. 3.2.4 Arrow keys, Home, Pg Up, Pg Dn, End same as in Review Captured Data mode in your PC Comscope II User's Manual. 4.0 DISPLAY FORMAT When the HDLC application is running you will see a line across the middle of your screen that reads: LNT ADR TYPE PF R S/LNT ADR TYPE PF R S The left half (up to the '/' is for Transmit data, that is frames generated by the DTE. The right half of the screen is for receive data, frames generated by the DCE. A receive frame that appears on the same line as a transmit frame ended after the transmit frame, so the display reads left to right, top to bottom. Aborted frames, frames with CRC error, and overlong frames will be displayed in color. The decode information may be nonsense in colored frames since you don't know where the error(s) occurred. Underneath the 'LNT ADR TYPE...' line will be up to seven lines of frame decode information. These seven lines are scrolled upwards with each new line of information. The last decoded frame will be the one immediately preceding the cursor in the top half of the screen. The decode information appears directly underneath the heading mnemonic as detailed below: 4.1.1 LNT - Length Number of characters in the frame. The HDLC application supports frames of up to 500 characters. Longer frames will appear as two or more colored framed. 4.1.2. ADR - Address Hexadecimal value of the first byte in the frame, the address byte. 4.1.3 TYPE - Mnemonic for the type of command or response. The mnemonics are listed in section 5. 4.1.4 PF - Poll/final Value of the poll/final bit. 4.1.5 R - Receive variable Value of the receive variable (not present in all frames.) Can have values 0 - 7. 4.1.6 S - Send variable Value of the send variable (present in info frames only.) Can have values 0 - 7. 5.0 LIST OF MNEMONICS The following is a list of all possible mnemonics for command or response type. These mnemonics are used under the 'TYPE' heading as explained in section 4.
6.0 HDLC STATISTICS The Model 903 PC Comscope II has the ability to determine line utilization in an HDLC or SDLC environment. This feature is called HDLC Statistics and is included with the optional HDLC Decode Software. Operation is described below. 1. Select the HDLC data mode from the Comscope menus. 2. Highlight or enter HDLCSTAT on the PROGRAM OPTION menu. Hit F9 to start the program. 3. The HDLCSTAT program will prompt you: Report file name (ENTER for none): If you want the program to generate a report file enter the name of the report file at this point. Simply hit the ENTER key if you don't want a report file. 4. The program will then prompt you: Seconds between reports: Enter the number of seconds in each report period. The program will copy the screen to the report file (if selected) after each report period. The report totals (see below) are reset after each report period. You must enter a report period even if you are not generating a report file. 5. The program will then prompt you: Minutes to run test (0 for continuous): Enter the number of minutes you want the test to run before stopping itself. If you want the test to run continuously enter a zero. 6. The test will then begin capturing and analyzing data. There are three groups of information presented: Line utilization, error rate information, and frame type summary. Each group is separated by a line '-------'s. 6.1 The top section details line utilization. The INFO frames in HDLC are what carry data, so the number of bits in these frames can be used to estimate line utilization. The 'bytes' figures used here include the data characters, the address, and control bytes, the two CRC bytes, and one flag character for each INFO frame. The 'bytes' figure is then multiplied by 8 (bits/byte) and divided by the number of seconds to produce an equivalent bits/sec figure. This number can be compared to the bit rate of the data line to estimate the utilization of the line. The figures under 'DCE INFO' are for data coming from the DCE (receive data) and those 'DTE INFO' are for data coming from the DTE (transmit data.) The figures on the 'Report' line are reset at the end of each report period, while those on the 'Cumulative' line are accumulated for the whole test. 6.2 The second section provides a measure of line quality. The program accumulates the number of good, errored, and aborted frames. The Block Error Rate (BLER) is the ratio of errored + aborted frames may be due to line errors or generated by the DTE or DCE. Note also that this program will probably only catch data errors in one direction, since errors that occur between the end being monitored and the remote end will not be seen by the Comscope. You will however have some indication of these errors in the frame summary (below.) 6.3 The frame summary can provide information about the overall performance of the protocol and data line. For instance: 7.0 FUNCTION KEYS F2 Freezes the display. The program does not update the screen until you hit F2 again, although the program continues to run. You may want to freeze the display when examining the accumulated numbers. F6 Resets all the figures. F6 is the same as starting the test over, except that the report file and report period remain the same. F10 Takes you back to the Comscope menus. COPYRIGHT Copyright (c) 1989 by Telebyte Technology, Inc., Greenlawn, NY 11740 PC Comscope II is a trademark of Telebyte Technology, Inc. This manual and the X.25 decode software are copyright Telebyte Technology, Inc. Telebyte Technology, Inc. grants to the original purchaser of this software the right to make several copies of the software for backup purposes only. You are also authorized to make such copies of this manual as are helpful to the use of the software so long as the manual is copied in its entirety with this notice as a permanent part of the copy. DISCLAIMER OF WARRANTY The HDLC decode package is sold without warranty of any kind. Telebyte Technology, Inc. makes no claims or guarantees concerning the accuracy, performance, or suitability of this product. You are given a period of thirty days from the purchase date to evaluate the suitability of this product for your purposes. If you determine that the product is not suitable you may return the software to the address below for a full refund. Any copies of the software must also be destroyed at that time. Please call before returning the software to insure proper receipt of your refund.
270 Pulaski Road Greenlawn, NY 11740 (516) 423-3232
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