Packet calculation

mooney1111mooney1111 Member Posts: 5 ■□□□□□□□□□
in Off-Topic
hey guys i was wondering if anyone could shed some light on this subject of calculating the amount of ip packets needed to send a document.


size of file is 438,954 bytes

any help would be great.
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  • DevilWAHDevilWAH Member Posts: 2,997 ■■■■■■■■□□
    Well is just work out what the MTU of the link is ? are you using standard or jumbo frames or some other size.

    then whats the overheads are for a packet, this can be various depending what kind of network the packet is going across or if it has encryption.

    Once you have these figures you can easly calculate how much "user" data can be transferred in a single packet and just device the value above by this.

    Oh you need to know the TCP MSS of the host as this might be less than the MTU of the link.

    Its just a case of finding out the max packet size on the link, then taking away any header information so you have payload size and dividing through. ll of that can easly be found in google.

    Post what you think is the solution and we will be happy to help you correct it if needed. but i'm not posting the actual answer :)

    http://packetpushers.net/tcp-over-ip-bandwidth-overhead/
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  • DevilWAHDevilWAH Member Posts: 2,997 ■■■■■■■■□□
    Oh remember to consider both Layer 3 (IP packet) and layer 2 (frame) over head
    • If you can't explain it simply, you don't understand it well enough. Albert Einstein
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  • SimridSimrid Member Posts: 327
    As above. Please correct me if i'm wrong.

    The size of an IP packet can be defined or varies depending on what protocol is being used. I believe the largest size for an IP packet is 65535 (2^16) bytes. Therefore 438,954/65535 = 6.69 packets > Rounding to 7?

    That's not gospel but give that a go.
    Network Engineer | London, UK | Currently working on: CCIE Routing & Switching

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  • DevilWAHDevilWAH Member Posts: 2,997 ■■■■■■■■□□
    To elaborate on this correct response :) the 65535 comes from the length value in the header of an IP packet that is a 16bit field that holds the size of the packet. 16bits can hold the maximum number 65535.


    However that is a theoretical limit that a Packet could be, seeing as Ethernet uses an MTU of 1500bytes or if you have jumbo frames up to 9000bytes. So both of these are well below the theoretical limit.

    I think Simrid answer is as correct as any other unless you know what infrastructure you are passing the data over. And you could send a 64K packet across a link with and MTU of 1500, it would get fragmented.
    • If you can't explain it simply, you don't understand it well enough. Albert Einstein
    • An arrow can only be shot by pulling it backward. So when life is dragging you back with difficulties. It means that its going to launch you into something great. So just focus and keep aiming.
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