Re: IP & TCP Precedence

John Lekashman (
Tue, 5 Jan 88 14:24:33 PST

        2 Questions about IP & TCP Precedence:

        (1) The IP Request For Comments (RFC-791) and IP Military Standard
        (MIL-STD-1777) specify that Type Of Service (TOS) including
        precedence is a parameter that can be passed from the upper layer
        protocols to IP during a SEND operation and can be passed from IP to
        the upper layer protocols during a RECEIVE operation.

        How many IP implementations support this?

        How many people actually use this?

I did a socket option to the kernel to allow a user program
to set different values for the type of service. Currently
this only consists of allowing it to set the value of that
byte in the header. My feeling is that this should have some sort
of abstraction of what sort of service is desired, and the
TCP will cause the IP layer to set this byte value appropriately.
The exact details of what sorts of service one might ask for,
and appropriate TOS byte settings for such are not worked out.

One major reason is attempting to figure out authentication
mechanisms in a connectionless environment, ie preventing
every random who feels like it setting his own personal
workstation to get high bandwidth, low delay, high reliability,
which then results in lossages to those who do the 'right thing'
whatever that happens to be. Still, the setting allows us
to send ftp data traffic over satellite channels, and telnet,
acks and such over terrestrial lines. (with appropriate software
switches in gateways and bridges.

Maybe we'll even use it beyond the lab one day, if we get
smart enough TCP's everywhere, which deal with satellites well.


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