Geiser, Joe ([log in to unmask]) wrote:
: ----------
: From:   Alan AMBERS
: Sent:   Thursday, July 18, 1996 6:48 AM
: To:     Multiple recipients of list HP3000-L
: Subject:        Re: VT-MGR, Packet Sizes, WANs...
 
: On the other hand, I too would be interested to see if packet size is
: settable anyplace.  Eero - Are you still out there? or is someone else
: from  HP (or in the know) out there on this issue?
 
- Ocassionally... not full time anymore.  Anyway, the short answer is that
  VT on the HP3000 will talk to the VT client using the maximum packet size
  the VT client negotiated with it in the connection establishment phase
  (VT negotiation messages, 4 first VT packets (note: not TCP packets) on
  the connection.  There are additional TCP packets, SYN, SYN/ACK etc...).
 
  Also, not all VT packets require an acknowledgement.  Some of them
  do require a reply.  However, what we are talking about here is HP3000
  write data packets to the PC client.  Those *DO NOT* require any kind
  of reply from the PC at VT protocol level.  The only kind of write from
  the HP3000 side that requires a reply is a "critical write".  What this
  means is that the application has to specifically request a critical write
  and the system is not supposed to complete it to the application before
  it receives a reply confirming the data was received.  Applications using
  critical writes are rare and (personally), I've never seen one.
 
  It is another story if the PC uses too small TCP window size and thus
  forces a TCP level ack or a window update before the 3k is allowed to
  send more data.  On the HP3k side your packet size for VT is not
  configurable and VT uses anything up to 12020 bytes if the client
  allows it.  TCP packet size on the 3k is configurable (indirectly) -
  i.e.  the TCP packet size will be set to the NI outbound buffer size you
  have configured for your WAN NI (Network Interface) in NMMGR.
  For the PC side, you'll have to consult PC specialists.. I'm not one
  of those.
 
  VT packets that do require a reply are those who either request some
  terminal driver setting or change some setting, expecting a reply with
  status whether the change succeeded or not.  Also, an abortio request
  needs a reply.
 
 
Hope this helps,
Eero Laurila - HP CSY Networking lab - (ex) NS/VT lab engineer