PPP over T1/E1 and SHDSL
Jonathan Goodchild
whole bandwidth is available as a single link - is it simply PPP within
synchronous HDLC frames as per RFC 1661 & 1662?
Or is PPPoE or PPPoA used instead?
How about PPP over SHDSL?
Thanks very much,
Jonathan Goodchild
James Carlson
> Can anyone tell me how PPP is typically carried over T1/E1 links, when the
> whole bandwidth is available as a single link - is it simply PPP within
> synchronous HDLC frames as per RFC 1661 & 1662?
Yes. More precisely, you have T1/E1 framing on the link, and some set
of the DS0s (not necessarily all) are concatenated to provide a
synchronous bit pipe. Synchronous HDLC is then run over that pipe.
There are a couple of options here, depending on whether you're using
fractional services (some of the DS0s are either not configured or are
D&I'd out to a different device) or there's some old equipment on the
path that (at least for T1) can't deal with B8ZS and forces you to use
56K DS0s instead of 64K.
A fairly common set-up has a CSU/DSU that does all that framing work
and provides a simple synchronous V.35 port for the router (or host)
running PPP.
> Or is PPPoE or PPPoA used instead?
No.
> How about PPP over SHDSL?
As long as it looks like a DS1 pipe, it ought to be straight HDLC.
PPPoE is a bit of a aberration that exists because ADSL seems to have
been originally defined in terms of ATM.
ATM for small bit pipes _might_ be more common in Europe, though, and
that'd be a fair reason for PPPoA. I'm not sure about that.
--
James Carlson, IP Systems Group <james.d...@sun.com>
Sun Microsystems / 1 Network Drive 71.234W Vox +1 781 442 2084
MS UBUR02-212 / Burlington MA 01803-2757 42.497N Fax +1 781 442 1677
Jonathan Goodchild
>> How about PPP over SHDSL?
>
> As long as it looks like a DS1 pipe, it ought to be straight HDLC.
> PPPoE is a bit of a aberration that exists because ADSL seems to have
> been originally defined in terms of ATM.
>
> ATM for small bit pipes _might_ be more common in Europe, though, and
> that'd be a fair reason for PPPoA. I'm not sure about that.
We're currently attempting to do some interoperability testing against a
Cisco router, and it seems it doesn't do PPP over straight HDLC on its SHSDL
interface (or not by default, anyway - I suppose it might be possible to
reconfigure it).
Instead, it does seem to be doing some ATM stuff, which, according to one of
my colleagues, makes some sense as seems to be compatible with the way PPP
is used on ADSL.
(The trouble is that, although I know quite a bit about the PPP protocol
itself, and HDLC in general, I don't really know much about xDSL, nor ATM
for that matter, so apologies if I'm somewhat clumsy in expressing myself.)
Anyway, there's support for PPPoA in Linux, isn't there?
Given that we have a SHSDL card and a driver which is capable of sending and
receiving HDLC frames, where's the best place to get information on how the
various software components need to be configured and plumbed together?
Thanks,
Jonathan
James Carlson
> > ATM for small bit pipes _might_ be more common in Europe, though, and
> > that'd be a fair reason for PPPoA. I'm not sure about that.
>
> We're currently attempting to do some interoperability testing against a
> Cisco router, and it seems it doesn't do PPP over straight HDLC on its SHSDL
> interface (or not by default, anyway - I suppose it might be possible to
> reconfigure it).
>
> Instead, it does seem to be doing some ATM stuff, which, according to one of
> my colleagues, makes some sense as seems to be compatible with the way PPP
> is used on ADSL.
Yes, that makes sense. Seems unfortunate, but it makes some sense.
> (The trouble is that, although I know quite a bit about the PPP protocol
> itself, and HDLC in general, I don't really know much about xDSL, nor ATM
> for that matter, so apologies if I'm somewhat clumsy in expressing myself.)
>
> Anyway, there's support for PPPoA in Linux, isn't there?
So I've heard, provided that you have ATM hardware. You'll need to
hunt around the Linux groups instead to read more about that.
ATM doesn't use HDLC at all. It has its own framing structure. You
need a card that can do ATM UNI framing with AAL-5.
> Given that we have a SHSDL card and a driver which is capable of sending and
> receiving HDLC frames, where's the best place to get information on how the
> various software components need to be configured and plumbed together?
For Linux? I'm not really sure. (Check that email address again.
;-})
I'd probably start here:
http://sourceforge.net/projects/linux-atm/
http://sourceforge.net/projects/pppoa-udsl/
Not sure what to make of those ...