CPSC 3600 - DAY 19
APRIL 24, 2017

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				INTERNETWORKING AND UDP
				-----------------------

No single networking technology is best for all needs

Internetworking talks about how to connect multiple physical connections into
one large, uniform communication system.

LAN vs WAN, some organizations need multiple types of networks for each task.

The concept of Universal Service helps solve a big problem, i.e. companies in
the 1970's had to use different computers for tasks with different networks.

The hardware component used to connect heterogeneous networks is a router

Like a bridge, routers contain a processor and memory as well as seperate I/O
interface for each network it connects to.

A router can connect two LANs, a LAN and a WAN, or two WANs

Internet is a virtual network system because the communication system is an
abstraction.

Internet and Transport Layer

	Layer 3 (internet) specifies the format of packets sent across the
	the internet as well as the mechanisms used to forward packets from a
	computer through one or more routers to final destination.

	Layer 4 (Transport) specifies the messages and procedures that are used
	to insure reliable transfer.

Host computer - a computer that connects to the internet and runs applications

Any restrictions you can think of (low memory, slow CPU, etc.)

User Datagrm Protocol

End to end - UDP can distinguish among multiple application programs running on
a given computer.

Connectionless - The interface that UDP supplies to applications follows a 
connectionless paradigm

Message-oriented - An application that uses UDP sends and receives individual
messages

Best effort - UDP offers applications the same best-effort delivery semantics
as IP.

Arbitrary Interaction - UDP allows an application to send to many other
applications, receive from many other applications or communicate with exactly
one other application

Operating System Independent - UDP provides a means of identifying application
programs that does not depend on identifiers used by the local operating system

UDP packets, can be lost, delayed, duplicated.


0					16				     31
+---------------------------------------+-------------------------------------+
| UDP SOURCE PORT			|	UDP DESTINATION PORT	      |
+---------------------------------------+-------------------------------------+
| UDP MESSAGE LENGTH			| 	UDP CHECKSUM		      |
+---------------------------------------+-------------------------------------+
|		PAYLOAD (MESSAGE DATA)					      |
+-----------------------------------------------------------------------------+
|					...			              |
+-----------------------------------------------------------------------------+


Data Encapsulation
			+-----------+----------------------------------------+
			| UDP Header|		UDP Payload		     |
			+-----------+----------------------------------------+
			|
			V
	+---------------+----------------------------------------------------+
	| IP Header	|	IP Payload				     |
	+---------------+----------------------------------------------------+
	|
	V
+--------------+-------------------------------------------------------------+
| Frame Hdr.   |							     |
+--------------+-------------------------------------------------------------+


UDP datagram is encapsulated in an IP datagram for transmaission across the 
internet.