[ee122] hmwk problem Number 2.16

[Jonathan D. Ellithorpe]

Ah very interesting. That is why you and I are saying different things.

On page 339 of the textbook it says:

"The maximum amount of data that a link layer frame can carry is called 
the maximum transmission unit (MTU)."

Which conflicts directly with:

"MTU is the length of the largest link-layer frame that can be sent by 
the local sending host"



Nescio Nomen wrote:
> Is it defined for packets or for frames?  I'm finding conflicting 
> definitions on google.  The book says that the MTU is the "length of 
> the largest link-layer frame that can be sent by the local sending 
> host"-- hence my confusion since we're not provided any link layer 
> header info.  But, if I understand what you've said earlier, we're to 
> assume it's strictly going to only have IP header anyway.
>
> On 9/20/07, *Jorge Ortiz* <jortiz at cs.berkeley.edu 
> <mailto:jortiz at cs.berkeley.edu>> wrote:
>
>     The MTU is the largest sized packet that can be passed.  This includes
>     header information.
>
>
>     On 9/20/07, Nescio Nomen <nescionomen at gmail.com
>     <mailto:nescionomen at gmail.com>> wrote:
>     > Oh wait, I think I understand-- you're saying that MTU does not
>     include the
>     > link header size?
>     >
>     >
>     > On 9/20/07, Nescio Nomen < nescionomen at gmail.com
>     <mailto:nescionomen at gmail.com>> wrote:
>     > > I'm not sure I understand.  (in a real life problem) why
>     wouldn't we need
>     > to know the size of the frame header just because we are given
>     the MTU?
>     > Wouldn't we try to find the amount of 'real data' that could fit
>     by doing
>     > something along the lines of MTU - frame header size - IP header
>     size -
>     > Layer 4 header size?
>     > >
>     > >
>     > >
>     > > On 9/20/07, Jonathan D. Ellithorpe < jde at berkeley.edu
>     <mailto:jde at berkeley.edu>> wrote:
>     > > > I think the MTU is actually defined as being the maximum
>     amount of data
>     > > > that a link layer frame can encapsulate. Thus, we don't need
>     to consider
>     > > > the size of the frame, since we're just given the MTU of the
>     link-layer.
>     > > >
>     > > >
>     > > > Jorge Ortiz wrote:
>     > > > > On 9/20/07, Nescio Nomen <nescionomen at gmail.com
>     <mailto:nescionomen at gmail.com>> wrote:
>     > > > >
>     > > > >> For hmwk Problem #2, P16, do we know if the datagram will
>     have a TCP
>     > header
>     > > > >> inside?  (Is it necessarily the case that a datagram always
>     > encapsulated a
>     > > > >> TCP header?)
>     > > > >>
>     > > > >
>     > > > > If it's specified as only being a plane datagram (as it is
>     in the
>     > > > > problem), we only need to include the IP header.
>     > > > >
>     > > > >
>     > > > >> Also, when we are transmitting into the link, how big is the
>     > > > >> frame header?
>     > > > >>
>     > > > >
>     > > > > Treat the packet as having only an IP header and the data
>     you wish to
>     > send.
>     > > > >
>     > > > >
>     > > > >> We haven't really talked about this layer yet.  Does the
>     size
>     > > > >> of the frame header depend on the technology, i.e. optical?
>     > > > >>
>     > > > >
>     > > > > It may, yes.  Different mediums may have different header
>     definitions.
>     > > > >
>     > > > > jorge
>     > > > >
>     > > > >
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