Daniel: Sorry, for placing on discuss. I am still learning, where and what, for the lists.
I figured that I would not use the amount of download but curious.
You answered the implied question, however, the part that I am still wondering about, and, I realize that it doesnot matter a twit, is the calculation.
One part is in bits per second the other GB per month.
When most people refer to 8 bit bytes, they are just talking about the data, not the rest of the message, or envelope etc. That is what I would like to clear up in this fossilizing brain. Parity and/or check bits, header and trailer or envelope bytes, these must add another 15% to the size of the data.
ne c'est pas?
Chris
I'll take a stab at this, networking is my chosen profession.
There is really no fixed percentage that you can figure on for this. It depends on exactly where you want to start from and what kind of data you are transmitting.
Take this email message for example. I'm looking at a bunch of characters on a screen and I could count those characters and arrive at a byte count for the message. I have this set for plain-text, but if I had it set for html format, there would be additional characters in the message that I wouldn't directly see or be able to count. When I press "send" the e-mail program will prepend the e-mail header which you can view (in Mozilla, CNTL-U). That's the first layer of encapsulation - the Application layer.
Next is the Transport Layer. In this case, the TCP protocol. It will break the message up into appropriate sized pieces (generally between 600 to 1500 bytes), negotiate a connection with the other end, and encapsulate the bytes in a header with port numbers and sequencing numbers. This is called a datagram.
In some applications there can be an additional layer between the Transport and Application. An example is the Real Time Transport protocol that is used for streaming media such as Internet phone. This adds it's own header and sequencing information to the message.
After the Transport layer is the Internet layer. IPv4 adds at least 20 octets of IP addresses and various flag bits to the message. Different options can add to this overhead. This is now called a packet.
Overall, you are looking at about 32 to 40 bytes of overhead for every packet. In addition, it is possible that the packet can be further fragmented by routers in the path. Each fragment is a full-fledged IP packet in it's own right and the fragments aren't reassembled until they arrive at your machine. This doesn't happen so much anymore, but it is still possible.
The packets get further encapsulated at the Data Link and Physical layers into frames, but I think it's safe to assume that your ISP is measuring at the packet level.
Bottom line is that it depends a lot on what you're sending or receiving. An ftp download probably has around 1-2% overhead, while a short e-mail message may see closer to 100-200%. Web-surfing is probably in the 5% range give or take. Every message will be different.
There will be a quiz on Friday. :)
Rod
