RFC 1046 (rfc1046) - Page 2 of 11

Queuing algorithm to provide type-of-service for IP links

RFC 1046                Type-of-Service Queuing            February 1988


   satellite link introduces is less than the MGD, that link should be
   considered in the route.  If however, the MGD is less than the
   satellite link can provide, it should not be used.  For this
   discussion it is assumed that delay for individual links are low
   enough that a sending node can provide the MGD service.

   Low delay class of service is not the same as low Round Trip Time
   (RTT).  Class of service is unidirectional.  The datagrams responding
   to low delay traffic (i.e., Acking the data) might be sent with a
   high reliability class of service, but not low delay.

   The performance of TCP might be significantly improved with an
   accurate estimate of the round trip time and the retransmission
   timeout.  The TCP retransmission timeout could be set to the maximum
   delay for the current route (if the current route could be
   determined).  The timeout value would have to be redetermined when
   the number of hops in the route changes.

   High throughput class of service should get a large volume of data
   through the Internet.  Requesters of this class are less concerned
   with the delay the datagrams have crossing the Internet and the
   reliability of their delivery.  This type of traffic might be served
   well by a satellite link, especially if the bandwidth is high.
   Another attribute this class might have is consistent one way
   traversal time for a given burst of datagrams.  This class of service
   will have its traversal times affected by the amount of Internet
   load.  As the Internet load goes up, the throughput for each source
   will go down.

   High reliability class of service should see most of its datagrams
   delivered if the Internet is not too heavily loaded.  Source Quenches
   (SQ) should not be sent only when datagrams are discarded.  SQs
   should be sent well before the queues become full, to advise the
   sender of the rate that can be currently supported.

   Priority service should allow data that has a higher priority to be
   queued ahead of other lower priority data.  It is important to limit
   the amount of priority data.  The amount of preemption a lower
   priority datagram suffers must also be limited.

   It is assumed that a queuing algorithm provides these classes of
   service.  For one facility to be used over another, that is, making
   different routing decisions based upon the TOS, requires a more
   sophisticated routing algorithm and larger routing database.  These
   issues are not discussed in this document.






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