54 lines
1.8 KiB
Markdown
54 lines
1.8 KiB
Markdown
# lec12
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Networkk Layer
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Here instead of datagrams, or segments, we are referring to chunks of data as _datagrams_.
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We concern ourselves with _host to host communication_.
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There are two major function to worry about:
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* forwarding
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* getting from an input to an output
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* routing
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* concerned with
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## Virtual Circuits
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_THIS SECTION IS BAREBONES_
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Datagram Service: network provides network-layer _connectionless_ service.
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Virtual Circuit: network provides network-layer _connection_ service.
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### Setup a connection
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Virtual Connections: before two end hosts start sending data to each other both must determine over which route they will communicate with.
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This means that we have to get routers between hosts involved with this initial setup.
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When the routers get involved they put an incoming vc number on an incoming bus, and an outgoing vc number on an outgoing bus.
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These entries are stored in the routers _forwarding table_.
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## VC Implementation
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1. Path from source to destination
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2. VC numbers one number for each link
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3. entries in forwarding table
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### Forwarding Table
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__pls clarify section__
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Each router has a forwarding table which allows for entries regarding data about it's incoming/outgoing buses.
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Router has has incoming/outgoing interface on these lines we see that datagram has a vc# when its incoming to the router.
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Upon exit we know that each vc# from the incoming interface corresponds to a vc# on some outgoing interface.
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## IP Addresses & Datagram forwarding tables
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> What is an ip address?
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Think of an adress of a variable in memory.
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Instead of a variable we have an end host.
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Instead of an address memory we have an address in some network.
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Usually we'll write a destination address in the header of a datagram so that we know where the data is meant to go.
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