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Network Layer (Layer 3)
(Page 2 of 2)
Network Layer Connection-Oriented and Connectionless Services
Network layer protocols may offer
or connectionless services for delivering
packets across the network. Connectionless ones are by far more common
at the network layer. In many protocol suites, the network layer protocol
is connectionless, and connection-oriented services are provided by
the transport layer. For example, in TCP/IP, the Internet Protocol (IP)
is connectionless, while the layer four Transmission Control Protocol
(TCP) is connection-oriented.
The most common network layer protocol
is of course the Internet
Protocol (IP), which is why I have already
mentioned it a couple of times. IP is the backbone of the Internet,
and the foundation of the entire TCP/IP protocol suite. There are also
several protocols directly related to IP that work with it at the network
layer, such as IPsec,
NAT and Mobile
is the main error-handling and control protocol that is used along with
IP. Another notable network layer protocol outside the TCP/IP world
is the Novell IPX protocol.
Key Concept: The OSI Reference Models third layer is called the network layer. This is one of the most important layers in the model; it is responsible for the tasks that link together individual networks into internetworks. Network layer functions include internetwork-level addressing, routing, datagram encapsulation, fragmentation and reassembly, and certain types of error handling and diagnostics. The network layer and transport layer are closely related to each other.
The network interconnection devices
that operate at the network layer are usually called routers,
which at this point should hopefully come as no surprise to you. They
are responsible for the routing functions I have mentioned, by taking
packets received as they are sent along each hop of a route
and sending them on the next leg of their trip. They communicate with
each other using routing protocols, to determine the best routes for
sending traffic efficiently. So-called brouters also reside
at least in part at the network layer, as do the rather obviously named
layer three switches. J
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The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005
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