Talk:Packet (information technology)
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I decided to put the definition in this page, instead of Datagram, since a lot more pages link here, so we can avoid a redirect if a reader hits the "packet" link. Noel 09:12, 24 Aug 2003 (UTC)
I'm torn about the IP packet area. I just fixed some typos for 'length' and also realised that a) the description is very long-winded and might benefit from a graphic representation, and b) the idiom 'next XX bits is YY' is used. I personally would use 'next XX bits are YY' instead, but I can see the point of treating the group of bits as a single non-plural. What do people think? TheMoog 11:34, 16 February 2006 (UTC)
- Yes. I've cleaned up the section and made it an ordered list, but I'm still not too happy with it. Maybe it's better to remove the section and link to the IPv4 packets/IPV6 packets sections instead? Ddfreyne 12:56, 29 April 2006 (UTC)
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[edit] FYI Packets vs Datagrams
I feel inclined when removing a chunk of existing definition to explain what is going on. The definition tried to use the notion of "connections" to define datagrams. This is not correct - the generally accepted definition is that datagrams are unreliable while packets might-or might not-be, depending of if they are datagrams. While connections are related to reliable transmission on the Internet (TCP), there are clear examples of networks that did not support connections per se, but attempted to provide reliable transmission (Arpanet, SDLC, and probably everything else predating Aloha). The network does not need to have a notion of "connections" in order to have reliable transmission. Rick Smith 16:55, 14 June 2006 (UTC)
- It is my understanding that datagrams are created in the network layer, particularly by IP. This is supported by RFC 791 which states, "The internet protocol provides for transmitting blocks of data called datagrams from sources to destinations." It is also supported by RFC 793 which states, "TCP assumes it can obtain a simple, potentially unreliable datagram service from the lower level protocols." (emphasis mine) There are other statements in the RFCs to support this. It appears to me that the notion that datagrams are unreliable is a misunderstanding of the roll of the network layer. It is usually the transport layer that determines whether a block is reliable or unreliable (TCP or UDP). Therefore, a datagram may be reliable or unreliable depending on how the segment was formated in the transport layer.
- My observation is that the word "packet" is used, generically, to mean any block of data, whether it be a segment (transport layer), a datagram (network layer) or frame (data link layer) but often is used synonymously with "datagram". The term "datagram" is most often used to refer to packets created in the network layer. The use of the term "datagram" in the transport layer for UDP appears to be a rather loose and unique exception. Rsduhamel (talk) 21:01, 28 February 2008 (UTC)
[edit] end-to-end principle
Is there a name for "networks that forward packets several hops from one node to the next, but occasionally drop packets and immmediately forget about them"? I suppose I could call them "dumb networks that follow the end-to-end principle", but is there a better name?
What other kinds of networks are there? --65.70.89.241 21:19, 21 August 2006 (UTC)
My understanding is that email is sent using some sort of ARQ system ...
It's called an unreliable network. Learjeff 19:57, 10 August 2007 (UTC)
[edit] preamble
I am considering adding this to the article:
- In some radio communications, a fixed preamble is transmitted before the rest of the packet.
- This helps the automatic gain control and clock recovery in the reciever settle to reasonable values.
Is the preamble considered "the first part of" the header, or "comes before" the header? --65.70.89.241 21:19, 21 August 2006 (UTC)
Is a one-byte preamble the same as a "sync byte"? A "sync byte" is mentioned in Transport_stream#Packet (0x47) and Binary_Synchronous_Communications#Framing (what value?) and Local_Interconnect_Network#Header (0x55).
--65.70.89.241 16:18, 25 August 2006 (UTC)
Ethernet also uses a preample. Preambles are common to protocols that use a broadcast medium, regardless of the particular broadcast medium. For Ethernet, the preample provides collision detection.
