My TN Connection

A question often raised is whether media converters can support large packets (jumbo frames), but before that question is answered let me explain large packets.

Historically, Ethernet was defined with a maximum packet size of 1518 bytes, where 4 bytes were used for the header (destination address, source address, type or length) 4 bytes were used for the trailer (checksum) and a maximum of 1500 bytes for the data payload.  As networks have developed so has the need for new features and speeds. Such features as VLAN, QoS, ToS, and others mean there is the need for additional header details.

The term commonly used today for these are Jumbo Frames. However, the term Jumbo Frame is also used in gig Ethernet, where to utilize the faster speeds the payload size has been increased 9000 bytes and sometimes the term Jumbo Frame is used in the same context.  Whereas, the features VLAN, QoS, ToS, etc add a few bytes to the packet size. For example, standard Ethernet packet plus VLAN, QoS, ToS, etc may increase the packet size from 1518 to 1536. So for the purpose of dealing with the issue raised I will use Jumbo Frames as the 9000 bytes for Gigabit Ethernet and for VLAN, QoS, ToS, etc features I will use the term Baby Giants.

Back to the question about large packets with media conversion. If you are using a pure media converter like 100mb on copper and 100mb on fibre then there is no issue as a media converter is a level one device and doesn’t look at the packet (whether it is a Standard packet, Baby Giant or Jumbo Frame).

The real issue and sometimes a problem can occur when using a media converter which has 10/100/1000 on the copper port and 100 or 1000 on the fibre port.  Technically this device is not a media converter but a switch, and being a switch it will investigate the Ethernet packet including the size of the packet.

So, when making your choice about the type of media converter you want to use,  be aware about the packet sizes you are using. Pure media converters  support standard, Baby Giants and Jumbo Frames. Switching media converters generally only support standard and Baby Giant Frames.  However, there are also some switching media converters which will support Jumbo Frames.

Questions? Comments? Leave a response below.

Keywords: About, Copper, Ethernet, Fiber, Fibre, Gigabit Ethernet, Jumbo Frames, LAN, media conversion, Media Converter, Media Converters, Networks, Packets, Port, QoS, Switching, ToS, VLAN

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