Outubro 2008
Prof. Ismael H. F. Santos
- ismael@tecgraf.puc-rio.br
2
OSI protocol summary
Layer
Description
Examples
Application
Protocols that are designed to meet the communication requirements of
specific applications, often defining the interface to a service.
HTTP,
FTP
,
SMTP,
CORBA IIOP
Presentation
Protocols at this level transmit data in a network representation that
is
independent of the representations used in individual computers, which
may
differ. Encryption is also performed in this layer, if required.
Secure Sockets
(
SSL),CORBA Data
Rep.
Session
At this level reliability and adaptation are performed, such as
detection of
failures and automatic recovery.
Transport
This is the lowest level at which messages (rather than packets) are
handled.
Messages are addressed to communication ports attached to processes,
Protocols in this layer may be connection-oriented or connectionless.
TCP,
UDP
Network
Transfers data packets between computers in a specific network. In a
WAN
or an internetwork this involves the generation of a route passing
through
routers. In a single LAN no routing is required.
IP,
ATM virtual
circuits
Data link
Responsible for transmission of packets between nodes that are directly
connected by a physical link. In a WAN transmission is between pairs of
routers or between routers and hosts. In a LAN it is between any pair
of hosts.
Ethernet MAC,
ATM cell transfer,
PPP
Physical
The circuits and hardware that drive the network. It transmits
sequences of
binary data by analogue signalling, using amplitude or frequency
modulation
of electrical signals (on cable circuits), light signals (on fibre
optic circuits)
or other electromagnetic signals (on radio and microwave circuits).
Ethernet base- band
signalling,
ISDN