Mark Smith <na...@85d5b20a518b8f6864949bd940457dc124746ddc.nosense.org> wrote:
> What about NAT, ATM cell tax, unnecessary addressing fields in PTP > protocols (including your beloved HDLC), SSAP, DSAP fields not being big > enough in 802.2 necessitating SNAP, IPX directly over 802.3, AAL1 > through AAL4, PPPoE "dumbell" MTUs and MSS hacks? Some of those are far > worse sins in my opinion. Hmm. PPPoE: this kludge is a direct fallout of abusing Ethernet for WAN/PTP. If all those xDSL users were willing to stick V.35 cards in their PCs and use "modems" that put out V.35 instead of Ethernet, the whole PPPoE kludge with all of its attendant MTU issues would have been completely unnecessary. Want PPP for authentication etc? Just run straight PPP (RFC 1662) over V.35 instead of Ethernet/PPPoE, HDLC has no fixed MTU unlike Ethernet (jogging my memory, all HDLC controllers which I recall working with allowed maximum frame size up to just a little under 2^16 octets or so), and one can thus have the standard MTU of 1500 octets on that PPP link! Oh, and yet another soapbox of mine, an xDSL modem that puts out V.35 instead of goddamn Ethernet would be a true modem: a modulator/demodulator that modulates/demodulates the bits at the electrical level without caring about what's in those bits. What everyone else in this fubared world calls an xDSL "modem" (a black box that puts Ethernet out) is not a modem at all (i.e., total misappropriation of the term), it is actually a bastardized router! These boxes forward packets between two network interfaces: the presented Ethernet interface and the internal (often horrendously non-standard and proprietary) HDLC or ATM interface on the actual line. A device that forwards packets between two different network interfaces is by definition a router, hence what everyone calls a "modem" is actually a bastardized router - bastardized because its routing (packet forwarding) function is something incomprehensible. The Ethernet-to-Ethernet NAT boxes that everyone else calls "routers" should be called "NATters" or something like that, anything but a router! A true router is a box with a few AUIs and a few V.35 ports sticking out of it, running some very capable, flexible and totally user-configurable packet forwarding software stack that supports all networking models: IP routing, MAC bridging, VC cross-connect. As for ATM... The part that totally baffles me about the use of ATM on xDSL lines is that I have never, ever, ever seen an xDSL line carrying more than one ATM VC. OK, there may be someone out there who has set up a configuration like that just for fun, but 99.999% of all ATM'd xDSL lines out there carry a single PVC at 0*35 or 0*38. So what then is the point of running ATM?!?! All the hyped benefits of ATM (a little cell can squeeze in the middle of a big packet without waiting for it to finish, yadda yadda yadda) are contingent upon having more than one VPI/VCI going across the interface! If every single non-idle cell going across that ATM interface is 0*35 or 0*38, the interface will never carry anything other a direct succession of cells making up an AAL5 packet, strictly in sequence and without interruption. So what's the point of ATM then? Why chop that packet up into cells only to transmit those cells in direct sequence one after another? Why not simply send that same packet in plain HDLC over the same copper pairs/fiber? OK, the backhaul network upstream of the DSLAM may be ATM and that one does have many VCs, so ATM *might* be of use there, but even in that case why not do FRF.8 in the DSLAM and keep the ATM strictly on the backhaul, sending HDLC down the copper pairs? <off the soapbox for the moment> MS
