Introduction
Server and network virtualization, coupled with the consolidation of enterprise networks, is driving significant change in the datacenter
infrastructure. Not only are datacenters getting bigger and faster, but the architecture is becoming increasingly complex especially at the
physical layer. The high-speed traffic exchange among servers, storage and networking devices consumes an ever-larger amount of fiber.
Maintaining high availability with the diagnostic tools currently available is an almost impossible job. To ensure that fiber in datacenters
is reliable, network professionals need a more accurate and faster methodology for assessing the integrity of the infrastructure. Such a shift
in requirements renders most existing testing equipment obsolete and instead demands a new class of Optical Time Domain Reflectometer
(OTDR) capable of characterizing and certifying enterprise fiber.
This white paper helps fiber installers and network technicians understand the key parameters for selecting a new OTDR. Choosing theright
device not only solves this new generation of datacenter testing requirements, but also helps professionals work efficiently, and increase
the reliability and value of the enterprise fiber network. We begin with a high-level overview of the changes datacenters are undergoing
and the implications of these changes on fiber testing requirements. Then we’ll offer the criteria for selecting an OTDR to satisfy evolving
requirements.
What is Driving Change in Fiber Technology?
Modular cabling systems
With its plug-and-play capability, modular or pre-terminated fiber cabling is gaining acceptance because it’s simpler and less costly to
install than field-terminated cable. The challenge is that pre-terminated fiber is only guaranteed “good” as it exists in the manufacturer’s
factory. It must then be transported, stored, and later bent and pulled during installation in the datacenter. All kinds of performance
uncertainties are introduced before fiber cables are deployed. Proper testing of pre-terminated cables after installation is the only way to
guarantee performance in a live application.
High-density and high-speed equipment in the datacenter
As datacenters grow larger, most enterprise IT departments look for ways to minimize power consumption and reduce expensive floor space.
One strategy for reigning in operational expenses is datacenter consolidation using faster and higher-density networking and storage
equipment. These new-generation devices are usually equipped with 10Gbps or faster fiber links to transport traffic. This shift is driving a
significant uptick in the use of fiber in datacenters.
Datacenter owners responsible for keeping critical enterprise IT services available must now ensure that the fiber infrastructure is
hardened.
With thousands of fibers being installed, they must be able to:
1 – Fully certify and document that all fibers are installed correctly and for maximum efficiency.
2 – Minimize fiber network downtime with the fastest possible problem resolution time.
Virtualization presents challenges along with advantages
The adoption of server and network virtualization dramatically affects datacenter networks. The implication is two-fold. First, virtualization
consolidates multiple server resources onto fewer physical platforms. This creates much greater data traffic to and from virtualized
platforms. Second, this traffic may pass to direct-attached storage or through a switch to network-attached storage, other servers, or to
the greater enterprise network. Datacenters adapted to the requirements of virtualization by using End-of-Row (EoR) and Top-of-Rack (ToR)
network topologies.
• EoR – topology places a switch at the logical end of a row of racks, replacing a single tier of home-run connections with two tiers
of switches. Adding a second tier makes the network more adaptable. EoR shortens the length of the cables in the lower tier to
the length of a row of racks. Shorter cables are generally easier to install and easier to change. EoR topology confines the impact
of asset reconfiguration to a row of racks, rather than across an entire datacenter. EoR may reuse some elements of the existing
physical network, however major upgrades are common.
• ToR – topology dedicates an Ethernet switch to every rack. The ToR switch interconnects server, storage and networking assets in
each rack and provides a trunk connection to an aggregation point in the datacenter. ToR also divides the physical connections into
two tiers, but provides greater modularity inside a rack than the EoR topology.
Both EoR and ToR topologies support the bandwidth demands of virtualization and drive new cabling requirements. Intra-rack fibers in ToR
configurations are typically less than 6 meters. To reduce clutter and improve equipment access, patch panels with short patch cords are
usually employed to connect server, storage, and networking assets. This creates new problems:
1. A high concentration of fibers connecting the equipment to the patch panels can confuse installers regarding fiber polarity.
2. Short patch cords quality and workmanship defects are invisible to most fiber test equipment.
As virtualization marches forward, datacenter networks will fundamentally change. To deliver bandwidth to virtualized assets, 10Gbps,
40Gbps or 100Gbps links will be employed throughout the datacenter. Any uncertainty in the fiber links will jeopardize the stability and
reliability of the network connected to those virtual servers. It is critical to have these fibers certified with channelized information and
properly documented.