Networking and Internetworking - Guide to Cloud Computing for Business and Technology Managers - page 44

TABLE 2.1
OSI Layers or Stack

Layer Description Examples

Application Protocols at this level are designed to meet the

communication requirements of specific
applications, often defining the interface to a
service.

HTTP, FTP, SMTP,
CORBA HOP

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.

TLS security, CORBA
data representation

Session At this level, reliability and adaptation measures

are performed, such as detection of failures and
automatic recovery.

SIP

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, LDP

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 signaling, using amplitude or
frequency modulation of electrical signals
(on cable circuits), light signals (on fiber optic
circuits), or other electromagnetic signals
(on radio and microwave circuits).

Ethernet baseband
signaling, ISDN

machine, that machine processes the packet; if the packet is intended for
some other machine, the packet is just ignored.
Broadcast systems usually also allow the possibility of addressing
a packet to all destinations by using a special code in the address field.
When a packet with this code is transmitted, it is received and processed
by every machine on the network. This mode of operation is called broad-
casting. Some broadcast systems also support transmission to a subset of
the machines, which is known as multicasting. An alternative criterion for
classifying networks is by scale. Distance is important as a classification
metric because different technologies are used at different scales. At the