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According to the definition from wikipedia, I found processing delay to be the delay caused by router processing the packet header. I am just wondering are TCP, IP, and Data link Headers all encapsulated in the same packet or 3 individual ones?
夢のの夢
Posted 2016-02-25T04:33:02.123
Reputation: 105
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It depends what level you are looking at. For example, if you're looking at a packet on an Ethernet network that encapsulates a TCP packet, you'll find the TCP header inside the Ethernet packet. By the time it gets to the IP layer, the Ethernet packet header has been removed.
David Schwartz
Posted 2016-02-25T04:33:02.123
Reputation: 58 310
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They are all part of the same Protocol Data Unit. The Data link Frame holds in its data region an IP Packet, which itself holds a TCP Segment. It appears wikipedia's article does state "packet", but the linked definition of packet describes a generic protocol data unit at layer 2, not an IP packet as the ISO's OSI model or DARPA ARPANET stack defines it. This may be part of the source of your confusion.
it also may help you to know that routers and switches have a few differant modes for how they buffer and forward frames out bound (Cut-through vs Store-and-Forward), including whether they wait for the whole frame to come in and calculate its Frame check Sequence before making any real decisions about the frame and its interior protocol data. That will potentially dramatically affect the processing delay you are asking about.
Frank Thomas
Posted 2016-02-25T04:33:02.123
Reputation: 29 039
You don't have it quite right. The layer-2 (ethernet) frame encapsulates the layer-3 (IP) packet, which then encapsulates the layer-4 (TCP) segment. The router strips off the layer-2 frame and routes based on the resulting layer-3 packet, which still contains the layer-4 segment. Your description makes it sound like the layer-2 frame directly encapsulates the layer-4 segment. – Ron Maupin – 2016-02-25T04:45:39.777
I'm not really trying to explain the relationship of IP to TCP because TCP isn't used any other way other than on top of IP. – David Schwartz – 2016-02-25T04:46:29.807