Wireshark-bugs: [Wireshark-bugs] [Bug 9427] Dissector for T1-channels-over-raw-Ethernet protocol
Comment # 11
on bug 9427
from brett.meyer@bt.com
(In reply to comment #10)
> (In reply to comment #9)
> > Guy is now stuck in a good place, same place I am, I think. See the
> > attached comment from the bug please, I believe questioning the map of
> > router layer 2 frame with payload is delivered to the T1, and of course how
> > to extract it.
>
> Actually, I'm questioning how the 24 channels of your T1/DS1 are
> encapsulated into an Ethernet frame.
>
> Now that I look at it, I'll also ask what "The Packet contains a total of
> 40-T1's" means. Does it mean "40 T1 frames of 24 bits each"? It sounds from
>
> Src_router--T3--ch_16_T1>
>
> as if "ch_16_T1" mean mean T3 channel 16 is carrying a single T1; is that
> correct?
>
> Once I know that, the next question is "so is this T1 carrying nothing but
> one Frame Relay line", so that it's not multiplexing multiple bitstreams?
> And, if so, does that mean the first bit of the Frame Relay bit stream is in
> channel 0 of a T1 frame, the second bit is in channel 1 of that frame, ...
> the 24th bit is in channel 24 of that T1 frame, the 25th bit is in channel 0
> of the next T1 frame, etc.?
*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*
T3 channel 16 is a single T1.
Didn't see the following hit this bug, it may help answer your question above.
From: Mike
Subject: RE: [Bug 9427] Dissector for T1-data-over-TCP protocol from Guisys
wanted
Guy,
The T1 payload (data) is mapped to the Ethernet in the identical format or
structure in which it is carried in the T1. This means the 1st 8-bits are the
1st 8-bits of channel-1, the 2nd 8-bits are Channel-2, etc. the 24-octet is
Channel 24 and the end of that T1's payload. The next T1's payload continues
after that so the 'serial' stream of data from the T1 is mapped in identical
order and structure (as it is on the T1) to the Ethernet frames.
Each Ethernet Frame's payload consists of 40 T1's. If the Bridging mode is
activated after the T1 is installed - the Bridging system waits for the 1st bit
of Channel-1 and begins to map the data into the Ethernet Frame payload. So
the 1st octet (at 0010) is the DS0 Channel-1 data and so on. In this manner 40
T1's with 24 bytes of data = "" bytes. First T1: Chan-1, Chan-2...Chan-24,
2nd T1: Chan-1, Chan-2....Chan-24, ....until 40th T1: Chan-1 -> Chan-24. In
this manner full T1-frame payload integrity is maintained in the
Bridge-to-Ethernet process.
Note; if the Bridging is enabled prior to insertion and frame up of the
incoming T1, the 1st 8-bits may not be Channel-1. However the 'channelization'
stream will be maintained such that the payload 'stream' is maintained so
decoding and analysis of errors in the (Frame-Relay) payload can still be
monitored and captured. (ie I do not believe it is critical for this
application precisely where Channel-1 is located - as I believe that the
incoming data stream loaded into the T1 utilized the full bandwidth (is not
channelized). The maintenance of Channel synchronization is provided as a
future means to analyze those circuits where perhaps only one or two channels
may be carrying traffic of interest (DS0 or Frac-T1 operating modes).
Hope this helps clarify.
Mike
As an aside, our Ethernet test system is utilized by the Carriers (AT&T, etc.)
for installation, validation and collection of metrics of raw Copper or Optical
Ethernet spans (raw Layer-2 Opt-E-MAN, Gig-E-MAN services). The system does
support future addition of Layer-3 (IP).
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