OpenVMS Cluster Systems - OpenVMS Systems - HP

Table F–5 SHOW PORT/VC Display
Field Description
Troubleshooting the NISCA Protocol
F.3 Using SDA to Monitor LAN Communications
! Msg Xmt (messages transmitted) Shows the total number of packets transmitted over the virtual circuit to the
remote node, including both sequenced and unsequenced (channel control)
messages, and lone acknowledgments. (All application data is carried
in sequenced messages.) The counters for sequenced messages and lone
acknowledgments grow more quickly than most other fields.
" ReXmt (retransmission) Indicates the number of retransmissions and retransmit related timeouts for
the virtual circuit.
• The rightmost number (106) in the ReXmt field indicates the number
of times a timeout occured. A timeout indicates one of the following
problems:
The remote system NODE11 did not receive the sequenced message
sent by UPNVMS.
The sequenced message arrived but was delayed in transit to
NODE11.
The local system UPNVMS did not receive the acknowledgment to
the message sent to remote node NODE11.
The acknowledgment arrived but was delayed in transit from
NODE11.
Congestion either in the network or at one of the nodes can cause the
following problems:
Congestion in the network can result in delayed or lost packets.
Network hardware problems can also result in lost packets.
Congestion in UPNVMS or NODE11 can result either in packet
delay because of queuing in the adapter or in packet discard
because of insufficient buffer space.
• The leftmost number (128) indicates the number of packets actually
retransmitted. For example, if the network loses two packets at the
same time, one timeout is counted but two packets are retransmitted.
A retransmission occurs when the local node does not receive an
acknowledgment for a transmitted packet within a predetermined
timeout interval.
Although you should expect to see a certain number of retransmissions
(especially in heavily loaded networks), an excessive number of
retransmissions wastes network bandwidth and indicates excessive
load or intermittent hardware failure. If the leftmost value in the
ReXmt field is greater than about 0.01% to 0.05% of the total number
of the transmitted messages shown in the Msg Xmt field, the OpenVMS
Cluster system probably is experiencing excessive network problems or
local loss from congestion.
# Msg Rcv (messages received) Indicates the total number of messages received by local node UPNVMS
over this virtual circuit. The values for sequenced messages and lone
acknowledgments usually increase at a rapid rate.
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Troubleshooting the NISCA Protocol F–11