I am having a problem understanding the issues between canonical and
non-canonical addressing. I understand that the bits are flipped within the
byte. On page 32-33 of Interconnections Second Edition she gives the example
of the address a2-41-42-59-31-51.
Canonical:
10100010 01000001 01000010 01011001 00110001 01010001
Non-Canonical:
01000101 10000010 01000010 10011010 10001100 10001010
If you look at this you can clearly see that the address in canonical format
is not a group address (last bit of first byte is zero) but in non-canonical
format it is a group address. At this point I can see a big problem because
she also states:
".the group bit in addresses was defined not as "the most significant bit"
or the "least significant bit" but rather as "the first bit on the wire."
Thus, an address that was a group address on 802.3 would not necessarily
look like a group address when transmitted on 802.5 because a different bit
would be transmitted first."
Here is the confusion: In canonical format the least significant bit is
transmitted first and in non-canonical format the most significant bit is
transmitted first. So on the wire the 1's and 0's would be in the same
order. Here is an excerpt from RFC 2469:
The figure below illustrates the difference between
canonical and non-canonical form using the canonical form address
12-34-56-78-9A-BC as an example:
In memory, 12 34 56 78 9A BC
canonical: 00010010 00110100 01010110 01111000 10011010 10111100
1st bit appearing on LAN (group address indicator)
|
On LAN: 01001000 00101100 01101010 00011110 01011001 00111101
In memory,
MSB format: 01001000 00101100 01101010 00011110 01011001 00111101
48 2C 6A 1E 59 3D
This shows that no matter how the information is stored in memory it looks
the same on the wire. So if it looks the same on the wire wouldn't an
adapter pickup the packet and flip the bits in the byte if it needed to.
Since it on the wire it looks like the bits are in non-canonical format a
canonical format media would automatically take the first byte and flip the
bits and so on, or so I would think.
If anyone can figure out where I am going wrong please let me know. If it
would be best to talk, email me directly with a daytime phone number and I
will call you. Thanks.
Neil
___________________________________
UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html
FAQ, list archives, and subscription info: http://www.groupstudy.com
Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
