APPLICATION

	GATEWAY
	general network access and error recovery is handled here.
	Interface to the end user.     

PRESENTATION

	data formatting is defined here.
	Provides the transformations on data to suuport the application interface.

SESSION LAYER

	Establishes , manages and terminates connections.
	name recogonition and security functions are defind
	NETBIOS is an API which operates here

TRANSPORT LAYER

	provides reliable transport between end points, end to end error recovery and flow control.
	data multiplexing is defined.

NETWORK LAYER

	BROUTERS
	datagrames are sent with aknowledgement
	define the path which data should take
	logical addressing for both nodes and network is defined
	IP, IPX and UDP operates at this layer
	Organizes data into packets Forwards and routes packets to their destination.

DATALINK LAYER

	Prepares the information so it can be placed on the transmission medium.
	BROUTERS
	BRIDGES

PHYSICAL LAYER

	Responsible for the mechical,electrical and procedural characteristics to establish and maintain connections.
	ANSI, RS232,V.42 are defined here
	media access methods are defined
	data merely is a stream of bits
        hub operates here

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GATEWAY
	APPLICATION LAYER	
	Protocol converters, able to strip off one protocol and apply another.
	Operate at Any layer of OSI/RM 
SWITCHES 
	Faster than traditional network devices, can give each sender/reciever pair the lines full bandwidth.
	Operates at Physical, Data-link, Network and Transport layers
ROUTER
	Direct data packets between networks based on IP address. Operates at the Network layer. 
BROUTERS
	Can route traffic to a variety of networks and can use non-routable protocols.
	Operates at Data-Link and Network layers
	NETWORK LAYER AND DATALINK LAYER
BRIDGES
	Filters frames by hardware address to determine if a specific frame belongs on a local segment or 
	another LAN segment. Operates at the Data-Link layer.
REPEATER
	Amplifies the elecronic signal. Operates at the Physical layer.
HUB
	Connects computers in a Star -configured network.Operates at the Physical layer.
	PHYSICAL
NIC
        Interface between the computer and the network. Operates at the Data-Link layer.
CSU/DSU
	Terminates physical connections, translates digital data into bipolar signals.
	Operates at the Physical layer.

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APPLICATION		GATEWAY (Operate at Any layer of OSI/RM)

PRESENTATION		GATEWAY 

SESSION LAYER		GATEWAY 

TRANSPORT LAYER		GATEWAY 	SWITCHES 

NETWORK LAYER		GATEWAY 	SWITCHES 	BROUTERS	ROUTER 		

DATALINK LAYER		GATEWAY 	SWITCHES 	BROUTERS	BRIDGES		NIC

PHYSICAL LAYER		GATEWAY 	SWITCHES 	HUB		CSU/DSU		REPEATER