Breaking of Ethernet frames

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Hi All,

I am very new to the Ethernet area.

I am trying to design and Implement an Ethernet switch or Multiplexer.

 so say if I am bridging between two 1-gbps channels with one 2-gbps
 when I think of designing a TDM switch between the 2 channels of 1
gbps my basic design will contain a MAC and a FIFO right...?

I was thinking that if the incoming data frame is long so that it will
cross the TDM slot for that channel of 1 gbps. then I will have to
break that frame store the remaining data in fifo and send it in the
next slot.

Here I am not getting is that how it will get reconstructed at the
receiving end .
So firstly is it allowed to break like this if yes then how to insert a
packet number etc in the frame.

Please Help...

Thanks & Regards.

Re: Breaking of Ethernet frames
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Do you have two networks that you need to connect?

A switch is a device that recieves a packet and find the correct channel
to forward it to.

Or do want to combine two 1 gbps networks in one 2 gbps transmission
line and then seperate the two lines in the other end of the
transmission line.

A multiplexer is a device that combines e.g. several telephone lines
into a high speed link.


Re: Breaking of Ethernet frames
yes I want to make an ethernet Multiplexer...
correct but 2 3 people gave me a responce saying Mux is same as switch.
so I concluded may be switch has more intelligent functionality than

but presently I want to implement a Mux combine 2 channels in one

so do you mean to say that at a receiving end of the mux transmitter a
demux is neccesory means the final 2 gbps line cannot be routed to a
general wan,lan etc it has to be a point to point connection between
mux and demux.

then what is the technique to break and combine frames as well giving
the channel number ....?

Thanks & Regards,


Re: Breaking of Ethernet frames
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If I understand you correctly then you have two 1 gbps ethernet networks
  that you want to route into one 2 gbps ???? network. What type of
connection is the 2 gbps? What will happen with the data when it reach
the other end of the 2 gbps connection?

The multiplexer will combine but keep the data as separate channels as
needed for telephone lines. In the other end there will be a demux to
split the lines up two the separate telephones.

The switch will combine and mix the channels together into one e.g. an
ethernet switch with eight 100Mbps channels and one 1 gbps channel. The
traffic from the different channels will be routed to the correct
channel based on reciever address. Some ethernet switches use a method
called "store and forward" where it stores the ethernet packet reads the
reciever address and by a table lookup it decides which channel the
ethernet packet should be forwarded to.

If the 2 gbps channel is a connection to the internet then your need to
follow a specific set of protocols because that is necessary in order to
communicate with the equipment placed at the ISP. Your ISP should then
provide you with equipment or with the protocols needed.

You will need some kind of equipment in both ends of the communication
line in order to send and recieve data packets. If you want to create a
backbone with a 2 gbps network then you will need some kind of equipment
to route the signals between the 2 gbps communication lines and that
equipment will use some kind of protocol in order to know where to
forward the data to. You will need to follow that protocol when you
route from the two 1 gbps ethernet channels to the 2 gbps network.

If you just want to mux the two 1 gbps channels into one 2 gbps channel
and in the other end of the 2 gbps channel demux into the same two 1
gbps channels then the easiest solution would be to create a protocol
that adds some information in front of the ethernet packet. That could
be length of the ethernet packet and which channel it came from. Then
you will be able to recreate the two original data streams. To be sure
that you don't mix up the channels remember to add a checksum to be sure
that the length and channel values are correct.

your protocol           ethernet packet
length channel checksum reciever sender data checksum


Re: Breaking of Ethernet frames
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Kedar -

There is nothing simple about what you want to do. The first thing you need
to do it learn about Ethernet - the frame structure, the CRC, how MACs work,
etc. You can't just split Ethernet frames to fit into TDM slots, especially
if you're operating at a point in the link where the data is 8B10B encoded.
You would need to do much more than just split frames. Even if you figure
out how to split frames, connecting two bidirectional 1Gbps links to one
2Gbps link is not as simple as a mux. It is relatively simple to combine the
1Gbps links into a 2Gbps link in the 1Gbps to 2Gbps direction. But in the
other direction, when you're trying to steer data from the 2Gbps link onto
one of the 1Gbps links you've got a 2:1 data rate mismatch. At a minimum you
need enough buffering to absorb a max-lengthed 2Gbps frame until you have
time to dribble it out onto the 1Gbps link. And then what happens if 2Gbps
frames keep coming, all destined for the same 1Gbps link? You can only have
so much buffering, so eventually your buffer will overflow and you need to
discard frames. Loss of data is not handled at the Ethernet level, so you
need to deal with that at a higher protocol level (e.g., TCP).

From what you've said so far it sounds like you're approaching a very
complicated problem with a very simple and inadequate solution. Nobody here
knows enough about your system to know what you can get away with, so you'll
have to figure the basics out for yourself. Then post specific questions
when you run into specific problems.


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