Thu, 09 Jun 88 12:29:01 PDT
>> Date: Thu, 09 Jun 88 09:33:04 EDT
>> From: Frank Kastenholz <KASTEN@MITVMA.MIT.EDU>
>> Subject: Re: Convert /etc/hosts to RR format pgm anyone?
>> To: der Mouse <firstname.lastname@example.org>
>> Cc: email@example.com
Good start! I've added some corrections to the heirarchy.
It strikes me that this kind of info would be reasonable in an intro
of some kind to IP.
>> This sounds to me like there is some confusion over the meaning of
>> some of the terms used (which, to the best of my limited knowledge,
>> have never been fully codified - perhaps an addendum to the Assigned
>> Numbers RFC is in order - "Assigned Abbreviations and Terms and Their
I'd recommend Douglas Comer's book 'Internetworking with TCP/IP, Principals,
Protocols, and Architecture' or Andrew Tanenbaum's book 'Computer Networks'.
Both include a glossary at the back with very succinct definitions of most
everything you mention below.
>> As I understand things the "hierarchy" of terms in use in the Internet
>> protocols (among others) are:
Here is perhaps a better set of definitions: (some of these are essentially
pulled from Comer's book).
FRAME - The unit of information encapsulated for transmission on physical
media or network.
FRAGMENT - a unit that the IP layer breaks a DATAGRAM into if necessary
for transmission across networks that can not handle the size
of the entire DATAGRAM. A FRAGMENT has essentially the same
IP header as the original DATAGRAM.
DATAGRAM - The basic unit of information dealt with by the IP layer. This
is what is sent across the TCP/IP Internet. It may be broken
into FRAGMENTS if a network can not handle the DATAGRAM's size.
SEGMENT - the basic unit that TCP deals with. A segment consists of a block
of bytes that arrive or are sent at one time. These bytes make up
part of stream of bytes. Information in the segment identifies
where in the stream these bytes exist. A segment will be
passed to the IP layer as one or more DATAGRAMS for transmission
by that layer.
PACKET - the basic unit of information sent across a packet-switching network.
It's exact meaning is dependent upon the context.
BUFFER - an implementation detail that is used for passing blocks of information
including DATAGRAMS to the layers for processing.
Eric B. Decker
Menlo Park, California
uSnail: 1360 Willow Rd., Menlo Park, CA 94025
Phone : (415) 326-1941
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