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

[Ben Greear <greearb@candelatech.com>]

Krzysztof Halasa wrote:
> Ben Greear <greearb@candelatech.com> 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
>> testing.
>>
>> 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?

Thanks,
Ben

-- 
Ben Greear <greearb@candelatech.com> 
Candela Technologies Inc  http://www.candelatech.com