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Aggregation Switches must finally also support Quality of Service (QoS) in order to uphold prioritization of the data
coming from the Access Switches, if QoS is also implemented on them. Priority guidelines ensure that audio and
video communication are guaranteed to receive enough bandwidth so an acceptable quality of service is ensured.
All switches which forward on data of this type must support QoS so as to ensure prioritization of voice data in the
entire network.
Product example from Cisco
3.3.4. Core Layer / Backbone
The Core Layer in the hierarchical design is the high-speed “backbone” of the network. This layer is critical for
connectivity between the devices in the Aggregation Layer, which means that devices in this layer must also have
high availability and be laid out redundantly. The core area can also be connected with Internet resources. It
combines the data from all aggregation devices and must therefore be able to quickly forward large volumes of data.
It is not unusual to implement a reduced core model in smaller networks. In this case, the Aggregation and Core
Layers are combined into one layer.
Core Switches are responsible for handling most data in a switched LAN. As a result, the forwarding rate is one of
the most important criteria when selecting these devices. Naturally, the Core Switch must also support Link
Aggregation so as to ensure that Aggregation Switches have sufficient bandwidth available.
Due to the severe load placed on Core Switches, they have a tendency to generate higher process heat than
Access or Aggregation Switches; therefore one must make certain that sufficient cooling is provided for them.
Many Core Switches offer the ability to replace fans without
having to turn off the switch.
Product example from Cisco
QoS (Quality of Service) is also an essential service component for Core Switches. Internet
providers (who provide IP, data storage, e-mail and other services) and company WANs (Wide
Area Networks), for example, have contributed significantly to a rise in the volume of voice and
video. Company- and time-critical data such as voice data should receive higher QoS guarantees
in the network core and at the edges of the network than data that is less critical, such as
files that are being transferred or e-mail.
Since access to high-speed WANs is often prohibitively expensive, additional bandwidth in the Core Layer may
not be the solution. Since QoS makes a software-based solution possible for data prioritization, Core Switches
can then provide a cost-effective option for using existing bandwidth in an optimal and diverse manner.
Page 56 of 156 © 08/2011 Reichle & De-Massari AG R&M Data Center Handbook V2.0