49 lines
2.0 KiB
Markdown
49 lines
2.0 KiB
Markdown
# lec13
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## Datagram Forwarding
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Prefix matching: instead of branching on ranges with a given destination address and our address ranges, we can do a depth-first search to determine where our given address should go.
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This means it will fall into one of our address ranges and we can determine which interface to forward that datagram to.
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Essentiall: Instead of branching we'll do a depth first search to see where each datagram must go.
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_We search the binary values._
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## Output ports
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This is more or less the point where packets can be dropped along its route.
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The reason why is because if the queue for that router is full and we try to add more stuff in the queue from fabric.
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We detect that the queue is full, and our incoming bus is full, so we drop that datat before anything else happens so that we dont mix data arbitrarily.
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Those output ports will each have their own queue buffers.
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However inputs can also have their own issues.
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## Input ports
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Just like first we read from a bus off the wire to determine where that data is meant to go.
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This process takes time however so sometimes we have to drop datagrams from memory completely if our queue gets too full.
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## Scheduling
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Now we'll look at which packet to drop.
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### Priority
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Send highest priority packets first.
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Say we have to decide about two packest: which goes into queue first?
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In this case higher priority goes in first, then the lower.
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### Weighted Fair queueing
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* Generalized Round Robin
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Each class gets weighted amount of service in each cycle.
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## IP Datagram Format
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Let's start with the header data.
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Each datagram is given an ip header which tells other nodes in a network where that datagram is meant to finally end up at.
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If a datagram is large however, we might fragment that datagram giving each _chunk_ their own header that tells the other routers where it's supposed to go and if that datagram is part of a larger datagram.
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When the pieces finally arrive to their destinatino they can be reassembled using the previous header information.
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