# Payload size of IP packet?



## DonChoudhry (Dec 1, 2003)

Hi,

What is the size of the header and what is the size of the payload in an IP packet?

In reference to my query I am quoting a few lines from an article Measuring network throughput on Wikipedia.

People are often concerned about measuring the maximum data throughput rate of a communications link or network access. A typical method of performing a measurement is to transfer a 'large' file and measure the time taken to do so. The throughput is then calculated by dividing the file size by the time to get the throughput in megabits, kilobits, or bits per second.

Unfortunately, the results of such an exercise will result in the goodput which is less than the maximum throughput, leading to people believing that their communications link is not operating correctly. In fact, there are many overheads in transmission that mean the calculated goodput does not reflect the maximum throughput. [http://en.wikipedia.org/wiki/Measuring_network_throughput]

Thanks in advance


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## JohnWill (Oct 19, 2002)

Here's a reference that describes the header overhead for various TCP/IP packets: www.sans.org/resources/tcpip.pdf

Here's another treatment of the topic: http://en.wikipedia.org/wiki/Transmission_Control_Protocol


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## DonChoudhry (Dec 1, 2003)

Thanks allot for a very comprehensive answer.

In a senario where a fast ethernet is providing an IP bandwidth from a switch to an ATM network, what would it be called? Would ethernet be encapsulating PPP or PPPoE or something else? How much be the size of the header and the size of the payload then?

Thanks allot for your concern


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## JohnWill (Oct 19, 2002)

I honestly can't say, don't know enough about ATM to give an answer. I suspect there will be additional overhead for the ATM packet, but I have no idea how much.


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## O111111O (Aug 27, 2005)

Depends on the ATM encapsulation.

http://www.protocols.com/pbook/atmenca.htm#IP

You'll see various methods of encapsulation for frames into ATM cells. All horribly inefficient.


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## DonChoudhry (Dec 1, 2003)

ATM is not of any concern here. I just want to ask what is the header and the payload size of the IP packets that gets dropped on ATM Network. The transportation of IP packets are done by fast ethernet. Please refer to the attached diagramI just made for you guys to understand what I am saying.

Thanks in advance


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## JohnWill (Oct 19, 2002)

Well, the header size of IP packets is well known, and the references I provided should tell you what you want to know. Of course, you'll need to know what the MTU size is on that network, 1500 is the maximum, but it could be smaller.


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