Hi,
You skipped the a) clause! This is from the 1998 version I've got laying
around:
7.2 Support of the Internal Sublayer Service by IEEE Std 802.3 (CSMA/CD)
a) Use the procedure as described in IS/IEC 15802-3, 6.5.1. This can
result in tagged frames of less than 68 octets (but at least 64 octets)
being transmitted; or
So at least 64 octets on the wire, either with or without VLAN tag.
Sorry,
Jaap
Wed, 18 Jan 2006 Ran.Shenhar (AT) ecitele (DOT) com wrote:
K, thanks for the clarification.
However, in the meantime I also conducted another search, and I found two
sources -
1. IEEE 802.1Q (2003), see pg 39 (actual page, including all prefaces etc),
look near the end (specifically at the sentence "Include additional octets
before the FCS field in order for the transmitted frame length for such
frames to be 68 octets. This results in a minimum tagged frame length of 68
octets.")
(the file can be found here:
_(VLAN).pdf)
2. According to CISC - 68 bytes (
#frame2
)
Now, my problem is that I got a bet with R&D guys around here, and it seems
my sources say that it's 68 bytes, and you're saying it's 64 or have I
misunderstood the IEEE doc?
TnX
>
>
>
Jaap Keuter
<jaap.keuter@xs4a
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Re: [Ethereal-users] (Slightly T)
18/01/2006 13:34 Ethernet length question
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Hi,
What you should decouple is the minumum 64 octet Ethernet requirement
from the actual use of these octets.
The 802.1Q spec only tells you that if the Ethernet II header contains a
type value of 0x8100 the next two octets are to be interpreted as VLAN
tag. That defines use.
When a frame is present on the wire it needs to be minimum 64 octets,
whatever the use of these octets.
These are seperate things.
Hope it helps,
Jaap
>
>
>
Wed, 18 Jan 2006 Ran.Shenhar (AT) ecitele (DOT) com wrote:
TnX Jaap,
I know the CSMA/CD principles behind the 64 byte minimum requirement.
However, my question is really focused on the 802.1Q change (or no
change)
in that demand, and I didn't understand the answer for that issue from
your
answer.
Could you please try to clarify?
TnX
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Jaap Keuter
<jaap.keuter@xs4a
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Re: [Ethereal-users] (Slightly T)
18/01/2006 11:54 Ethernet length question
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Hi,
The layer protocol model is the best reference you can take in mind.
The minimum ethernet frame length (that is bits on the wire) is 64*8.
Together with the wirespeed this gives a minimum amount of transmission
time. This time is needed for the other endpoint (in a point-to-point
link) or other stations (on a shared medium) to assure recognition of the
frame and collision avoidance. All this is Physical layer stuff.
Then comes the meaning of the bits in the frame. If the ethernet header
says that it's a VLAN tag that is following then the next 2 octets are to
be interpreted that way. From there on the next protocol layer starts.
That is the true meaning of VLAN, a VIRTUAL LAN. It's not a real one, as
seen on the wires, but on a layer above that.
Hope it helps,
Jaap
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Wed, 18 Jan 2006 Ran.Shenhar (AT) ecitele (DOT) com wrote:
Hi All,
I need help with a non-ethereal specific - I know that an ethernet
frame
is
of minimum length = 64 bytes, including FCS.
However, what is the minimum length of a VLAN tagged ethernet frame? Is
it
64+4, or is it still 64?
I tried looking in IEEE 802.3q 2003 edition, however I was not able to
find
a definite answer.
If you could also point me to a reference about the answer, it'd be
even
better.
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