Issue link: https://www.e-digitaleditions.com/i/1219491
20 I ICT TODAY cable is installed. In Europe, the Construction Products Regulation (CPR) has a defined process to guarantee that the cables installed within a jurisdiction are compliant to the specified flame and smoke performance levels. In China, IEC flame tests are the most popular and the performance levels are self-certified by the cable manufacturers. These varying requirements make it difficult to globally source the same trunk cable. While one cable designed to meet all applications would be convenient, cost considerations typically discourage that develop- ment process. For that reason, flame retardant cables are often provided by manufacturers based in the same region as the data center. It is interesting to note that many of the largest U.S.- based data center operators have been using singlemode optical fiber (SMF) as the primary cable plant media. In Europe and China, multimode optical fiber (MMF) is still the preferred choice (at least up to 100 GB/s), even at the hyperscale level. Part of the reason that MMF is still more popular in those regions is due to the physical size of the data centers, which puts limits on the cabling distances. However, it is also a design choice to maximize the use of multimode optics so that they can take advantage of the lower price point. Both SMF and MMF choices are compli- ant to the standards, but the performance requirements are clearly different. CABLING REQUIREMENTS The performance needed from the cabling goes beyond simply sending the signal from Point A to Point B. The cabling needs to be cost effectively sourced and installed. It needs to be able to perform in the environment in which it is installed. It also needs to maintain its perfor- mance over the expected lifetime of the data center. Here are some selected criteria that have varying levels of importance for different data center owners: Transmission characteristics Criteria such as attenuation rate, insertion loss, band- width and return loss constitute the transmission char- acteristics of the cabling. As part of the Layer 1 link, the cabling needs to match the requirements of the selected transceivers. Economic decisions must be made based on the price and availability of various component technologies. Data rates Typically, one would consider faster speeds to be better. However, newer and faster data rates tend to be signifi- cantly more expensive than older, slower data rates. The decision on data rates is often based on "how fast is fast enough?" The fewer layers and connections that there are in the data center, the lower the data rate needs to be. Installation methods Will the cable only be installed in overhead tray? Will it pass through underground conduits to link different data halls? Are the installation technicians fluent in all of the various termination techniques? What code compliance requirements exist in the municipality where the data center is located? Answers to these questions can influ- ence product and design decisions. Latency Certain networks require low latency connections (e.g., financial transactions). However, sometimes it is not low latency per se, but it is the relative latency among vari- ous paths that the connection may be made. In larger data centers with all-to-all connections, latency can become important even if the underlying application does not require it. Density If beauty is in the eye of the beholder, then appropriate density is in the eyes of the handler. There needs to be sufficient connections for the number of ports planned for the data center; they need to fit in the available real estate. While real estate is expensive, there are times when In China, IEC flame tests are the most popular and these the performance levels are self-certified by the cable manufacturers.