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FEATURE OPTICAL TRANSPORT


Data Center


Tere are essentially four segments of data centre operators, which vary in terms of business models, services provided, and transport


network requirements: l


Internet content providers (ICP)– are focused on the creation, storage and delivery of content. ICPs may build their own inter data centre transport network, or lease fibre or connections from carrier service providers (CSP). Delivery of an ICP service to the end customer usually takes place over a network provided by a CSP. Services and applications provided by ICPs are oſten referred to as over-the-top (OTT) services. Examples include Google, Amazon, and Facebook.


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Carrier service providers (CSP)– in addition to data centre services, CSPs provide a broad range of communications and networking services. Tey own fibre infrastructure and build transport networks for both their data centres and for other data centre operators. CSPs are also the main provider of connections from end-users to all data centre service providers. Examples include NTT, Verizon, AT&T, and Comcast.


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Data Center


Data Center 1G/10G Enterprise N x 100G wavelengths


ROADM-based data center


Data Center interconnect (DCI) Data Center N x 100G wavelengths


N x 10G/ 100G wavelengths


ROADM-based


end user data center interconnect (EDCI)


Residential


Mobile


N x 100G ROADM Transport wavelengths ROADM Transport Figure 1. ROADM optical layer switching in data centre transport enables better network resiliency,


Figure 1. ROADM optical layer switching in Data Center transport enables better network resiliency, provides a flexible programmable network infrastructure and can lower transport costs for DCI, EDCI and combined applications.


provides a flexible programmable network infrastructure and can lower transport costs for DCI, EDCI and combined applications


Carrier neutral providers (CNP)– provide data centre infrastructure, power, colocation and interconnection for other ICPs, CSPs and enterprises. Examples include Equinix, 365 Data Centers, Dupont Fabros, and EdgeConneX.


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Enterprise verticals (EV) – are enterprises that build their own private data centre networks or use another entity like a CNP or CSP to host their applications and/or provide the networking. Examples include financial institutions and hospital networks.


No matter the type of operator, there are two kinds of transport interconnections required for cloud services – those between data centres and those connecting the end customer to the data centre. Interconnection into the cloud of data centres must also connect to a specific data centre, but applications or services may move within the cloud. At the same time, the end user’s entrance point may also move. An adaptable end user access transport network or flexibility within the data centre to data centre transport network is required to support all these connections. We will come back to this more advanced requirement later, but for now delve into some basic requirements for both types of transport connections.


The other data centre interconnect What primarily defines data centre interconnect (DCI) is the requirement for very-high bandwidth connections between the data centres. (Since there is some potential for ambiguity on whether DCI also refers to the connections between end users


30 FIBRE SYSTEMS Issue 9 • Autumn 2015


and the data centre, for the purpose of this article, DCI is only used to refer to data centre to data centre connections.) Depending on the data centre operator, the scale of the cloud-based services provided, and the number of data centres, the bandwidth required between data centres can range from multiple 10G to multiple 100G connections. In the case of hyperscale data centres, the DCI


In the future more focus will be placed on building greater resiliency into cloud services


bandwidth has already transitioned to multiple 100G connections and will continue to increase, both in number, and in rate, to 400G and beyond in the future. How many data centres that need to be


interconnected is another important factor that drives the type of transport network. For ICPs, the number of interconnected data centres can be small. A good example is Google. As of July 2015 the firm has 12 large global data centres with an additional two announced, but not yet active, that support search, Gmail and YouTube cloud applications, according to the company’s website. Contrast this with Verizon, a CSP that currently has 43 global data centres providing ‘hosting, colocation, cloud, and IT infrastructure solutions’ as per the company’s website. Given all of the requirements discussed above,


fibre-based DWDM solutions are the primary transport technology used to implement DCI transport networks. Many of these networks are built today using point-to-point DWDM


connections between the data centres, especially for long-haul interconnections. In the case of metro DCI where there are more interconnected data centres that support connections to content, internet peering and also connect to end-user networks, ROADM deployments have gained traction. In the future, bandwidth requirements will


continue to grow and more focus will be placed on building greater resiliency into cloud services and DCI transport networks. Tis resiliency, both in terms of the data centre service functions and the DCI network, is not only to protect against the failure of individual fibre connections, but also against other potential catastrophic, natural or man-made events that may have a more far reaching impact to the ability to maintain service. To improve the service experience, especially for


services that require high bandwidth, the distribution of data centres closer to the end user is under evaluation to improve factors like latency, but also to reduce the overall transport bandwidth that is required in the aggregation part of network. Tis would have far reaching effects on the DCI network and would put a strain on building point-to-point DWDM networks that will not have the flexibility, manageability, low power consumption, and required cost profile as the number of meshed data centres increases.


Connecting end users with EDCI While less high profile than the interconnections between data centres, end user to data centre interconnect (EDCI) is just as important since, without the right connection, users cannot exploit the benefits of cloud services to their fullest extent. One of the key differences in connecting enterprise and consumer end users to the cloud is that in most cloud-based applications there are many more user connections to data centres than connections


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