The network layer
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Network layer - packets
References:J. Postel, RFC 791 INTERNET PROTOCOL J. Postel, RFC 793
TRANSMISSION CONTROL PROTOCOL clear=all>Networking is structured in a layered architectures (the OSI model) in
which the upper level relies on the lower level to send/receive data.
The bottom level is the physical leyer, with network boards, switches,
cables, or radiowave, or whetever else;
Immediately above it is the data-link layer. This puts the datagrams in
packets and transmits them via the network interface. It adds start and end
flags and bit error checking (CRC or parity).
Above it is the network layer. This layer is responsible for routing the
packets so that they can reach their destination. It may split the segment in
fragments. It sends/receives datagrams.
Next there is the transport leyer. This layer breaks the data in
small-size chunks (segments) that can be send to the network. It also
reassembles incoming packets into a stream. It provides also error checking.
Above is the session leyer. This layer manages the logical control: source
and destination, startup and shutdown of a session.
Above is the presentation layer. This layer translates data from the
network in a format usable by the application, and viceversa from application
format into network format. Below this point bytes are a stream of octets.
At the top there is the application layer, which interacts with the user
and with other programs.
clear=all>The network implementation does not strictly follow this model. TCP
provides initialization of a connection (three way handshake), finilazation
(FIN-ACK), and control. TCP is session aware (logical ports). IP provides
fragmentation of long segments, and machine to machine routing with the IP
address system. Finally ethernet encapsulates packets with their physical (MAC)
address.
Marco Corvi - 2003
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