R&M Data Center Handbook

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Layer 1 – Physical Layer / Bit Transmission Layer
This layer is responsible for establishing and ending connections as well as for the protocol information pattern.
This specifies, among other things, what logical information “1” or “0” is represented by what voltage level.
Cables and plugs, electrical and optical signals can be assigned to this layer.
Layer 2 – Data Link Layer
The bitstream is examined for transmission errors in the Data Link Layer, and error-correcting functions are used if
necessary. This layer is also therefore called the Security Layer. It is also responsible for flow control, in case data
is arriving faster than it can be processed. In cell transfers like ATM, cells are numbered so the recipient can put
cells, which sometimes arrive unordered due to the use of different transmission paths, back into their original
order.
In LAN applications, this layer is subdivided into the sublayers called Logical Link Control (LLC) and Media Access
Control (MAC). The MAC Layer assigns transmitter rights. The best known transmission protocol defined by the
IEEE is Ethernet (IEEE 802.3).
3
IEEE
802.1
Network (Internet/IP)
IEEE 802.2 Logical Link Control
2
1
OSI -
Layer
Architecture Übersicht
Management
Architektur
Management
Overview
IEEE 802.3
Ethernet
10Base...
100Base...
1000Base..
10GBase...
usw.
IEEE 802.11
Wireless LAN
FrequencyHopping
Direct Sequence
Infrared
802.11a 5 GHz
802.11b/g 2.4GHz
802.11n
usw.
IEEE 802.1 MAC Bridging
Media Access Control
Physical
Network adapters as well as switches (layer 2) can be assigned to this layer.
Layer 3 – Network Layer
This layer is responsible for routing information that is transported over multiple heterogeneous networks. This
model assumes that the data from the Data Link Layer (layer 2) is correct and free of errors. IP network addresses
are read and evaluated, and the information is passed to the next stages (networks) through the use of routing
tables. In this process, routing parameters like tariff rates, maximum bit transmission rates, network capacities,
thresholds and information on service quality are reported to routers by means of appropriate configurations.
In addition to routers, Layer 3 switches are also part of this layer.
Layer 4 – Transport Layer
This layer is responsible for controlling end-to-end communication. This information is therefore not evaluated in
the intermediate stations (switches or routers). If there is information in this layer on whether a connection is unstable
or has failed, this layer takes care of re-establishing the connection (handshake). In addition, this layer is
sometimes responsible for address conversions.
In the meantime, devices indicated as layer 4 switches are provided. This is intended to stress the fact that certain
protocol functions from this layer are integrated into these devices.
Layer 5 – Session Layer
The primary task of the Session Layer is to fundamentally implement and complete a session from the Application
Layer. In the process, this layer also specifies whether the connection is full-duplex or half-duplex.
This layer is also responsible for monitoring and synchronizing the data stream as well as other tasks.
Page 96 of 156 © 08/2011 Reichle & De-Massari AG R&M Data Center Handbook V2.0