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I have been trying to teaching myself about internet protocols, and I learned how to calculate the end to end delay for a packet switched network from this website (1c): http://www.ics.uci.edu/~keldefra/teaching/spring2013/uci_cs132/problemsets/CS132_EECS148_ProblemSet2_Solution.pdf

However, what happens if h bytes is added to each packet when it is being transmitted? In the example WITHOUT adding a header each packet size is (message size / number of packets) bits, so do I just do everything the same, except considering each packet size to be ((message size + header size)/ number of packets) ?

I'm essentially just not sure if the header is added only ONCE by the initial sender, or if it is added by each link, can you guys clarify this for me ?

(If this is not the right stack exchange site to post it on, could someone refer me to an applicable site?)

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Since you mention "Internet protocols", I have to assume you are talking about Layer 3 protocol data units like IP packets (discounting the Layer 2 frame the packet is contained in).

An IP header has a max length of 60Bytes, per RFC791. Any modifications an intermediary device makes to the Layer 3 header must fit within that space. As such, it would be unusual in the extreme to accumulate data on each hop. Generally speaking, a device would only alter traffic as is pertinent to a networking purpose, like reencapsulating a packet in a new frame as it enters a new network, but changes like those are only meaningful to the network the packet is currently passing through, so the data is completely replaced at each hop, not accumulated. It is possible for a network of specially designed devices to alter the message in the packet, adding or changing information in the Layer 4 or above protocol data units, such that data is accumulated at each hop, but that seems like a silly thing to do.

  • Bits in the header can and are flipped as a packet moves through a network. The Time To Live counter and thus, Header Checksum bits change as a packet moves through the network. When a NAT gateway is encountered, Source or Destination IP addresses (and again, Header Checksum) are re-written. Also, routers can toggle DSCP (Differentiated Services Code Point) and ECN (Explicit Congestion Notification) bits, and even, rarely, add Options to the header. However, each router handling the packet along the way re-writes the header, if only to modify TTL and checksum, but not cumulatively. – Nevin Williams Jan 26 '18 at 20:20

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