Networks Chapter 4

Network layers
	Link layer
	Getting data from one point to another point
	Network layer
	Forwarding data through intermediate nodes to reach the destination
	End-to-end layer
	Everything else
	Message multiplexing/de-multiplexing across layers
	Network delay
	Propagation + Transmission+ Processing + Queuing

Link layer
	Bit framing-
	Manchester encoding
	Packet framing
	Bit stuffing
	Error handling
	Error detection and correction
	Retransmissions
	Link MTU
	Message fragmentation and reassembly

Network layer 
(getting packets to the destination)
	Routing
	Dynamic Vs Static
	Sample routing algorithm
	Exchange path vectors
	Routing tables can be huge
	Hierarchical addressing and routing
	Use TTL to prevent infinite loops

Network layer
	Control protocols
	To detect MTU
	Echo request/reply
	Hop-limit exceeded
	Properties
	Best effort delivery (discards packets)
	Duplicate packets
	Segmentation 
	Reordered delivery 

End to end layer
	Transport protocols
	TCP,UDP,RTP
	At least-once/at most-once delivery
	Timers
	Two generals problem (duplicate detection and termination)
	Flow control
	Lock step
	Sliding window

Congestion control
	Congestion collapse
	Do not add packets or work when congested
	Discard packets
	Exponential back off
	TCP congestion control
	Slow start (at the beginning)
	Packet loss ?> cut by half
	Increase slowly
	Timer expires -> enter slow start 


End-to-end argument
	A function can completely and correctly be implemented only at the 
	end points.
	Examples:
	Delivery guarantees
	Secure data transmission
	Duplicate message suppression
	Guaranteed FIFO message delivery
	Transaction management


Wide-area Unicast Internet Routing
	A path vector based routing algorithm
	Use of hierarchy to reduce routing complexity
	Transit Vs Peer relationship
	Various policies resulting in non-optimal routes