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Minimum Data that can be transmitted on an Ethernet Segment

Hi Experts,

I know that the minimum data that could be transmitted on a Ethernet segment is 64 Bytes..

out of the 64 bytes of data, 20 bytes are for the Ethernet Header does it mean that the data could be 46 bytes.

somewhere I read that 46 is the minimum data but just wondering from layers 7 to 3 all of them would be adding their headers..20  bytes for TCP, IP 8 byte header so the data can be 64-20-20-8 = 16 Considering the header for L7 then actual data could be much below 46 bytes,

please correct me if I techincally go wrong.

Thanks,

-Vijay

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4 REPLIES
Silver

Re: Minimum Data that can be transmitted on an Ethernet Segment

Ethernet 802.3 payload/data could be as little as 46 bytes. The complete Ethernet frame has to be minimum 64 bytes.

All of the following fields are fixed length except payload:

Dest Addr    = 6 B

Source Addr = 6 B

Type/Length = 2 B

Payload    = 46 to 1500 B

Checksum   = 4 B.

All add up to 64 bytes. The user data need not be a TCP/IP packet. 

Thanks.

Hall of Fame Super Silver

Minimum Data that can be transmitted on an Ethernet Segment

Hello Vijay,

in addition to what Rais has written:

IPv4 header is 20 bytes, TCP header is 20 bytes.

So a minimum size ethernet frame can carry a TCP ACK message.

An IPv6 header has a minimum size of 40 bytes.

Also in TCP/IP implementation we cannot see distinct headers for all seven OSI layers.

TCP fits in L4-L5 and is a service of reliable transport of a byte stream ( full duplex bidirectional between endpoints)

As noted when referring to ethernet frame the payload is variable in size with minimum size of 46 bytes regardless of what is contained.

Hope to help

Giuseppe

New Member

Minimum Data that can be transmitted on an Ethernet Segment

Thank you.

so if i understand it right the minimum data that is required to be tranmistted on a ethernet wire is 46  byte and it may be inclusive of the upper layer headers as well (starting from IP).

Any idea how did they arrive at the 46 bytes as the minimum data required for transmission?

Thanks.

-Vijay

Silver

Minimum Data that can be transmitted on an Ethernet Segment

It's the CSMA/CD governed limit.

The 64 byte minimum frame-size for Ethernet was derived from the fact that it took that many bytes of transmission/time for statoins on the farthest side of Ethernet span to realize someone is transmitting - so they can back off and wait for their turn later. So in a nutshell to avoid collisions.

HTH.

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