Re: Question on HDLC and raw access to T1/E1 serial streams.

From: Ben Greear
Date: Sat Sep 30 2006 - 18:01:36 EST

Krzysztof Halasa wrote:
Ben Greear <greearb@xxxxxxxxxxxxxxx> writes:

I am looking for a way to bridge a T1/E1 network by reading a raw
bitstream from one T1 interface and writing it out to the other. The
application is adding delay and/or bit corruptions for impairment

I have been using Sangoma's drivers and NICs, but I'm having no luck
getting their latest stuff to work so I was hoping to use in-kernel
drivers (even if that means writing or hiring someone to write new ones.)

Is there currently a way to read/write the raw bitstream for a full T1
or E1 or a subset of channels?

Well, my generic HDLC works with HDLC framing only, T1/E1 is
a layer lower than that... I think Cyclades have (had?) a version
of PC300 card with T1/E1 interface. It at least doesn't require
any "binary blobs", though I think the driver would need some work.

Which line interface do you need? G.703?
Do you need to bridge multiple streams (not slots) over one
interface (internal (de)multiplexer - I mean "more than one
subset of channels")?
For protocols running HDLC as transport, I can just bridge HDLC frames. I would want
to be able to select the channel(s) for the HDLC frames.

For bridging something like voice, I think if I could break out an individual channel into
a bit-stream interface, I could just read bits off on one T1 channel and write to the other.
Preferably, I could also bond multiple channels (including an entire T1 or E1) and bridge
it as raw bits too.

I think if I could support these scenarios below, I would have everything I need:

* Configure T1 as unchannelized bitstream, bridge entire thing to second T1.

* Configure channels 1-5 as a bitstream and bridge that to channels 1-5 of a second T1. (random proprietary bit-streaming protocol,
would probably bridge HDLC just fine, but handling HDLC as frames would be more efficient I think.)
channels 6-10 configured as an HDLC interface, bridged as HDLC frames to channels 6-10 of a second T1. (PPP & other protocols over HDLC)
channels 10-24 each configured as a separate bit-stream, bridged to channels 10-24 on the second T1. (Voice)

* Configure entire T1 as HDLC transport, bridge HDLC frames from one T1 to the other.

Does that make sense?


Ben Greear <greearb@xxxxxxxxxxxxxxx> Candela Technologies Inc

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