Two NCBs per Session Based on Need Declining as Traffic Climbs (104510)
This article was previously published under Q104510
SUMMARY
The recommended ratio of two network control blocks (NCBs) per
session seems to contradict the fact that an NCB setting of 254 is
suggested when there are 128 or more sessions.
An extra NCB per session is generally recommended because at any one
time there can be at least one asynchronous NCB posted per session,
and it can be useful to have another NCB available. For example, a
second NCB can be used for raw I/O, where an asynchronous RECEIVE is
posted on the session then a SEND is issued on the same session while
the RECEIVE is pending. In addition to cases of this sort, the system
also requires overhead NCBs such as the auxiliary RECEIVE_ANY and the
RECEIVE_DATAGRAMS that are always pending for computername, domain,
otherdomains, and so on.
But as the number of active sessions increases, the likelihood that
there will actually be a pending asynchronous NCB posted on every
session decreases radically, which means that the likelihood of two
pending NCBs per session decreases even more. In short: when there
are lots of sessions, the need for an extra NCB per session
decreases sharply.
The recommended ratio of two NCBs/session (not three or more) takes
into account that the redirector and server utilize the interface
in such a way that it's unlikely that more than two NCBs will ever
be pending on a single session.
Modification Type: |
Major |
Last Reviewed: |
7/30/2001 |
Keywords: |
KB104510 |
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