R&M Data Center Handbook

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3.8. Transmission Protocols
In order to be able to transfer information from a transmitter to one or more recipients, the
data must be packed properly for transmission, in accordance with how it is transmitted. This
is the job of transmission protocols in data communication. A connection-oriented protocol
first establishes a connection, then sends the data, has this confirmed and finally ends the
connection when the transmission is finished. By contrast, a connectionless protocol entirely
omits the steps of establishing and ending the connection and confirming the transmission,
which is why such a transmission is less secure but faster. Protocols therefore establish
different rules.
A protocol is an agreement on how a connection, communication and data transfer between two parties must be
executed. Protocols can be implemented via hardware, software, or a combination of the two.
Protocols are divided up into:
• Transport-oriented protocols (OSI layer 1–4) & application-oriented protocols (OSI layer 5–7)
• Routable and non-routable protocols (ability to forward through routers, IP = routable)
• Router protocols (path selection decision for routers, e.g. RIP, OSPF, BGP, IGRP, etc.)
A transmission protocol (also known as a network protocol) is a precise arrangement by which data are exchanged
between computers or processors that are connected to one another via a network (distributed system).
This arrangement consists of a set of rules and formats (syntax) which specifies the communication behavior of
the instances which are communicating in the computers (semantics).
The exchange of messages requires an interaction of different protocols, which assume different tasks. The individual
protocols are organized into layers so as to control the complexity associated with the process. In such an
architecture, each protocol belongs to a specified layer and is responsible for carrying out specific tasks (for
example, checking data for completeness – layer 2). Protocols at higher layers use the services from protocols at
lower layers (e.g. layer 3 relies on the fact that all data arrived in full). The protocols structured in this way together
form a protocol stack (this is currently typically a TCP/IP protocol stack).
3.8.1. Implementation (OSI & TCP/IP, Protocols)
The OSI reference model was drafted starting in 1977 by the International Organization for Standardization as a
basis for developing communication standards, and published in 1984 (ISO 7498). The goal of Open Systems
Interconnection (OSI) is a communication system within heterogeneous networks, especially between different
computer worlds, that is based on basic services supported by applications. These basic services include, for
example, file transfer, the virtual terminal, remote access to files and the exchange of electronic mail. In addition to
the actual application data, these and all other communication applications require additional structural and
procedural information that are specified as OSI protocols.
7- Application Layer
Application
6- Presentation Layer
5- Session Layer
4- Transport Layer
3- Network Layer
2- Data Link Layer
1- Physical Layer
Computer
Active components
Passive components
R&M Data Center Handbook V2.0 © 08/2011 Reichle & De-Massari AG Page 95 of 156