How many bits in a network "packet?"

[Hulk]

Always wondered...

 

[gaidin123]

It varies based on the size of the payload in the packet. I'm not sure what the absolute minimum size for a payload-less packet is but in general the max packet size for standard networks is 1500 bytes, or 12000 bits. The max packet size is also your MTU.

Gaidin

 

[ScottMac]

An Ethernet FRAME (layer two) is max @ ~1500 bytes (actually a little larger than 1500). The minimum Ethernet FRAME size is 64 bytes.

A one byte IP PACKET (layer three) with generate a 64 byte Ethernet frame (the packet, plus the rest of the space padded out to 64 bytes).

FWIW

Scott

 

[spidey07]

A one byte IP PACKET (layer three) with generate a 64 byte Ethernet frame (the packet, plus the rest of the space padded out to 64 bytes).

layer2 header, plus layer3 header, plus one byte of payload and then padded at layer2 to 64 bytes. Then pre-amble applied to front end.



But I think scott was trying to say "it can be anywhere between 64 and 1512 bytes"

 

[ScottMac]

Yeah yeah yeah ....encapsulation, headers, all that .... blah blah blah ....

Preamble (I'm pretty sure) is not really considered part of the frame ... it's just there to sync up the receiver. Typically, some preamble bits are lost as the frame passes through a ----> HUB <----- or other repeater. In a series of Hubs, the preamble tends to shorten because a few bits are lost at each synchronization.

Not that *I'D* nitpick about something like that.....

Thanks for the catch ... I was in a hurry this morning.

Take care, Top O' the holidays to ya.

Scott

 

[spidey07]

heh, its just fun sometimes to remember the size/layout of each and every layer.

to Scott.

 

[cmetz]

Hulk, most network technologies support variable length packets/frames/PDUs/whatever. There is one exception I know of, the ever-retarded technology ATM, which decided that every cell shall be 53 bytes long, requiring an ugly adaptation to provide variable-length packet service on top of that. So how many bits (or bytes) is in a packet is normally a variable thing and not a simple one-number answer.

IP packets in the wild statistically spike at around 24 bytes (IP header + TCP header = pure TCP ACK), 576 bytes (minimum reassembly buffer size also often mistaken as the minimum MTU), and 1500 bytes (standard Ethernet MTU). Lesser spikes are seen at somewhere in the 40s for DNS, and 4096 & 4352? for the HPC guys.

Depending on your L2 technology, add some overhead. Standard Ethernet adds a 14 byte header to an IP packet, but there is also sometimes VLAN tagged framing adding yet another 4. PPP I believe adds 2 bytes normally, but there are a whole lot of different things PPP can do and some modes add more.

 

[Garion]

*cough* Geeks *cough*..

To make it simple.. A packet has a certain maximum size, usually 1500 bytes and a certain minimum size, usually 64 bytes. The rest of it is filled with your actual network data.

If your data ends up being longer than one packet it will get split among several - That's normal.

Think of it this way - Your request to a web server "get http://www.cnn.com/index.html" might only result in a 300 byte packet going TO CNN, but the response of the index page will be ~50,000 bytes long and split up among ~35 full size 1500 byte packets.

- G

 

[ScottMac]

Yeah, ATM sucks so much that in another couple years, Ethernet will catch up to where ATM was YEARS AGO in terms of end-to-end Quality of Service, Traffic Management, and traffic control.

Cells are fixed length for a good reason. It allowed for high-speed switching in hardware with the technology of the day for pretty much any service available and in-use at the time.

(This should be a good to get some discussion goin' .... )

Ethernet is to L2 communication what Microsoft is to Network Operating Systems: Loaded down with strap-ons and adaptations in an attempt to keep up with systems that were (and are) superior by design from day one.

ATM was (and is) a wonderful thing. Ethernet is MaryAnn, ATM is Ginger (please don't connect the "strap on" comment to this line of the discussion).

Gotta get to work ....

Seeya

Scott