Subject: Re: Nr in data packets

From: Vernon Schryver <[email-masked]>
Date: Mon, 24 Jan 2000 10:46:37 -0700 (MST)

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

> The design principle of the state machine is that
> if you are in state that have seen packet #1,2 and not seeing #3 then you
> goto other state otherwise goto yet another state.
>
> The rational here is that PPP state machine does not differentiate the 
> difference of ....
> unless the flow control is implemented in PPP.

That so called design principle is how all state machines work.  It's
the definition of a state machine.

How did flow control get into this discussion?  We were talking about
the fact that the PPP state machine, which is used in at most slightly
modified form in all PPP protocols assumes control packets are not
re-ordered by the lower layers.

> As far as TCP, one of its design drawback is that it does not handle out of 
> sequence packet.
> The L2tp or any underlining layers of (TCP) are not obligated to make up 
> its design deficiency.

I do not understand any of that.  TCP throughput and latency suffer
significantly should the lower layers re-order packets.  However, the
primary design goal and description of TCP is to transport a reliable,
sequenced stream of bytes.  If TCP "does not handle out of sequence
packet," then the world needs to know.

Anyone who wants to run L2TP or any other underlining (underlying?) layers
just for their own sake is welcome to do so.  However, most people won't
use L2TP except to move TCP/IP.  If L2TP does not cater to the whims of
TCP/IP or otherwise allows TCP/IP to not do well, then people will blame
L2TP instead of TCP/IP.

Vernon Schryver    [email-masked]

---

From: David Chen <[email-masked]>
Date: Tue, 25 Jan 2000 10:45:04 -0500

IP service does not guarantee packet delivery in sequence.
Clearly, UDP/IP does not neither and
TCP treat out of sequence packet as if loss of packet. -
as appose to buffering and re-ordering (packets).
(therefore, TCP provides in sequence no-loss packet delivery)
As for L2tp, a packet such as PAYLOAD/TCP/IP/PPP/L2TP/UDP/IP on the 
protocol stack,
is clearly that L2TP does not need keeping the packet sequence and dropping 
the packet for
the same reason (keeping packet sequence).
--- David