Visara LINCS Central Control - Manual (Page 166)

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LINCS Central Control
707024-002
• The first two bytes represent the SDLC frame portion, which includes the SDLC address
(first hex byte) followed by the SDLC command byte (second hex byte).
• The remaining bytes represent the information portion of an information frame, usually
the SNA frame. When an SNA frame is present, only the TH, RH, and first couple of
bytes of the RU are displayed. The rest of the RU is truncated to allow more room in the
monitor for link level frames. For a complete display of the RU, you must observe the
corresponding Host Monitor trace.
Display Monitor Forward LINCS C8.2 Central Control
> 1591
< 15D1
> 25D1
< 25F1
·
·
·
> 1591
< 15D1
PF1-Menu PF7-Back PF8-Forw
Line Monitor - X.25 Trace
The X.25 Line Monitor facility displays the entire link level data packet, including the entire
information area (SNA) data. Note that the entrees into the Line Monitor are not a true
representation of the traffic over the link in reference to time, but are a close approximation.
Data that LINCS transmits is placed in the monitor just prior to sending. Data received is
entered into the monitor upon receiving the entire packet. Therefore, a packet that LINCS
begins to receive prior to one that is being transmitted may in fact be entered into the monitor
after the one that was transmitted. Note too, the nature of a Full-Duplex packet protocol such
as X.25 allows for packets to pass each other in the network due to different routing paths.
Therefore, the sequence that the packets are received in may not be the same in which they
were sent. The trace shows the packets in the order in which they were received. The example
panel presents a typical trace. The format of the data is as follows:
• Greater than or less than symbol to indicate direction of SDLC frame. Traffic received
by LINCS uses the greater than symbol (>), while traffic being sent uses the less than
symbol (<).
• The first two bytes represent the X.25 link layer and are very similar to SDLC. Address 03
always represents a Network command or a LINCS response. Address 01 always represents
a LINCS command or a Network response. The second byte is the Control byte.
• The next three bytes represent the X.25 packet layer. The first two of the three bytes
represent the logical channel number that is being used (high order bit is a Q bit and
may change with the frame type). Each PU has its own LCN in a multihost circuit
environment.
• For PSH protocol only, the next two bytes represent the PSH header. For QLLC protocol,
there is no 2-byte header.
• The remaining bytes represent the information portion of an information frame, usually
the SNA frame. The SNA frame may be divided among multiple packets. The X.25 header
will give an indication of which order the packets should be reassembled to restore the
SNA frame. Refer to the corresponding SNA Host Monitor trace to view the SNA data.