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7. Data Center Networking
Protocols
Introduction
Although this guide is focused on the structured cabling system, it is helpful to have a basic
understanding of the data protocols running over this passive infrastructure. We will discuss the more
common protocols and evaluate how each can affect the cabling requirements within the data center.
The OSI 7-layer model was developed to help standardize communication about computer
networking, and is provided here for reference. Data Cabling fits squarely within layer 1, or
the physical layer, and is required as the communication channel pathway for data to flow
through network devices. This chapter, however, focuses primarily on the data link layer. At
Layer 2, a received signal from the physical layer is interpreted before being passed up to
Layer 3. Or data from Layer 3 is translated into a physical format that can be sent out across
Physical Layer media.
Ethernet
Ethernet is a set of frame-based computer networking technologies designed for local area
networks (LANs). It defines a number of wiring and signaling standards for the Physical Layer
of the OSI networking model, through means of network access at the Media Access Control
(MAC) or Data Link Layer, and a common addressing format. IEEE 802.3 addresses the
requirements for all Ethernet data rates.
As shown below, Ethernet protocols range in data rate from 10 Mb/s to 10 Gb/s TODAY
and can run over a range of media types.
“Slow” Ethernet 10 Mb/s
“Fast” Ethernet 100 Mb/s
Gigabit Ethernet 1,000 Mb/s
10 Gigabit Ethernet 10,000 Mb/s
Gigabit Ethernet (GbE or 1 GigE) is a term for Ethernet transmission at a rate of 1 gigabit per
second, as defined by IEEE 802.3z. Although half-duplex links (one-way data transmission)
connected through hubs are allowed by the specification for lower data rate applications, the
marketplace has basically settled on full-duplex applications for 1 Gbe and higher. The 10
Gigabit Ethernet (or 10 GE or 10 GbE or 10 GigE) Standard is published as IEEE Std 802.3ae
and defines a data rate that is 10 times that of Gigabit Ethernet. 10 GbE supports only full
duplex links which can be connected by switches. Half Duplex operation and CSMA/CD
(carrier sense multiple access with collision detect) are not supported in 10 GbE.
10 GbE is no longer the highest speed that is planned for and system designers are trying to
ensure that networks installed today can support speeds of 40 and 100 GbE. It is expected that
the media required for data rates higher than 10G will be optical fiber. This will include multimode
fiber (OM3 or OM4) to 100 meters or more, and single-mode fiber for links of significant length.
Refer to Chapter 8 Transmission Media for more detail on the different fiber types.
Let’s examine how the structured cabling for a 40 G/s Ethernet system could be configured
using today’s OM3 fiber. To be able to use today’s 10 G/s VCSEL sources, the 40 G/s
transmit signal is required to be broken down into four lower data rate channels. Each
individual channel is now 10 G/s, which also matches the bandwidth of OM3 fibers,
requiring four fiber pairs to carry the four 10 G/s channels. As Ethernet is a duplex operation,
we must account for the receive path as well. At the electronics, the four channels are
recombined into the 40G signal. This solution of breaking up a high data rate signal into
multiple lower data rate signals for transmission is known as Parallel Optics.