Subject: Re: Nr in data packets

From: Vernon Schryver <[email-masked]>
Date: Fri, 21 Jan 2000 12:53:57 -0700 (MST)

> From: David Chen <[email-masked]>

> Another related topic is "PPP over ethernet" that
> the underline layer is not lossless and not serial transmission.

Most layers beneath PPP can suffer losses.  PPP itself is supposed to
throw away packets.  That's the purpose of the FCS in async framed PPP.

I do not know what is meant by "serial transmission".  Ethernet or
IEEE-802.3 seems pretty serial to me.  Even if you throw in bridges,
re-ordering is very rare, as required by many non-IP protocols.  The only
network media that I can think of off hand that are not serial as I
understand the word are old-style HIPPI (i.e. not the new fangled
serial-HIPPI) and some of the memory-to-memory and bus extension schemes.
Some people might object that the latter are not network media.  They are
certainly very short range, but some of them have carried TCP/IP.

If "serial transmission" is intended to mean "preserves order," then of
course, there are many networks (but that are not link layer media) that
fit that bill.

> Also, MP has to re-ordering frames anyway when fan-in (reverse multiplexing)
> all individual links.
> ...

No, MP as defined in RFC 1990 does not re-order frames.  MP is required
to deliver packets in the order implied by the MP fragment sequence
numbers, but the multilink protocol assumes the layers beneath each link
in the MP bundle delivers packets to the receiver in the same order as
the packets were put on the link by the transmitter.
Consider the implications of the non-decreasing sequence number rule
for receivers in RFC 1990.

Vernon Schryver    [email-masked]

---

From: David Chen <[email-masked]>
Date: Fri, 21 Jan 2000 15:39:48 -0500

Why PPP demanding the lower layer be serial transmission? (frame in sequence)
when its encapsulate IP(X)...that do not demand this.
If PPP needs this other then its encapsulate protocol then
it can use RFC1663.
--- David

>Vernon Schryver    [email-masked]

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David Chen
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