Question on ATM w/ FreeBSD

[Harti Brandt]

On Mon, 30 Aug 2004, Richard Hodges wrote:

RH>On Mon, 30 Aug 2004, Ted Mittelstaedt wrote:
RH>
RH>> Hi All,
RH>>
RH>>    Can I plug in an ATM DS3 into something like a Cisco Lightstream LS1010
RH>> with a DS3 card, then plug a PC running FreeBSD and Quagga, with a
RH>> Marconi Forerunner HE155 using the fatm() driver, into a OC3 card on
RH>> the LS1010, then define a VC, switch it through the switch,
RH>> and run data over that?
RH>
RH>I cannot answer for netgraph-atm (maybe Harti could help there), but I
RH>have some knowlege about the Fore/IDT LE155 card and HARP/ATM in the
RH>later versions of 4.x
RH>
RH>HARP supports RFC1483 routed packet encapsulation, and if your other end
RH>supports this, then you should be fine.  Many or most ATM/Ether switches
RH>prefer 1483 bridged encapsulation, so this is an important thing to check.
RH>LANE (LAN emulation) uses bridged, CLIP (classical IP) uses routed
RH>encapsulation, by the way.

With NgATM you can also use HE155 cards (nice if you need CBR shaped 
VCCs), IDT 77252 based cards (ProSum has these, they support also VBR) in
addition to the HARP supported cards. As for the protocols NgATM does only 
CLIP over PVCs at the moment, but you can use the card capabilities for 
shaping with this if you need to (see natmip(4) and atmconfig(8)).

RH>The LS1010 or any decent ATM switch should be fine to link your DS3 to
RH>OC3.  For the price, I would go for a Fore ASX-200BX or an ASX-200WG
RH>converted to a -BX (by upgrading the CPU board).  The -WG is usually very
RH>cheap on ebay.
RH>
RH>> We are looking into bringing in another feed this time via ATM DS3,
RH>> and I don't think that a DS3 ATM card exists for the PC that has a
RH>> FreeBSD (or Linux) driver.
RH>
RH>I think Imagestream sells one, but I would rather spend a couple hundred
RH>on an ATM switch than a thousand or more on a PCI card.
RH>
RH>> However I see a number of PCI ATM lan adapters for PC's.
RH>
RH>The Fore/IDT LE155 cards are cheap and functional.

Fore PCA200E and HE155 are also for 10$ on ebay.

RH>> It seems that an ATM switch, of which there are plenty
RH>> available, would be the way to get from one to the other.  However I
RH>> have not dealt yet with ATM switches, is there anything inherently different
RH>> about ATM on a lan adapter like the HE155, and ATM on a DS3?
RH>
RH>Not really.  Obviously the cell rate is different.  This _might_ be an
RH>issue if your host with the OC3 bursts packets to the point that your DS3
RH>bandwidth is exhausted and packets are discarded.  By the way, if you have
RH>an option for EPD (early packet discard), this can help reduce the damage
RH>in this case.  One ugly way to fix this would be to hack the IDT driver
RH>to force a lower cell rate.  On the other hand, if your traffic is TCP,
RH>flow control might not be an issue.

If the traffic goes over a single PVC you can configure this PVC to shape 
the traffic to a DS3 bandwidth. But that just moves the dropping point 
from the ATM switch to the host. As Richard said, TCP should take care 
itself.

harti

RH>I think the key is making sure that the other end can handle RFC1483
RH>routed encapsulation.
RH>
RH>You should have no trouble finding the LE155 card, the switch, and the OC3
RH>and DS3 modules on ebay, but feel free to contact me for parts if you
RH>wish.
RH>
RH>All the best,
RH>
RH>-Richard
RH>
RH>_______________________________________________
RH>freebsd-atm at freebsd.org mailing list
RH>http://lists.freebsd.org/mailman/listinfo/freebsd-atm
RH>To unsubscribe, send any mail to "freebsd-atm-unsubscribe at freebsd.org"
RH>
RH>
RH>