An examination of advantages, disadvantages and applications associated with the possibility of bringing fiber all the way to the user.
By Andrey B. Semenov, IT-SCS for IT Co. and Igor G. Smirnov, Signamax Inc.
It is no secret that operating efficiency of a contemporary organization in any branch enhances significantly if it has an information technology (IT) system. Such technical objects are implemented according to the known open system model, while their physical level may be built under different principles. To this end, with due regard of the entire set of features crucial for practical application, in an overwhelming majority of cases cable-based communication channels are used. At this stage of technological development their linear part formation is assisted by the so-called structured cabling system facilities.
Structured cabling is a complex technical object, created at the building stage with significant financial, material and human resources. The natural aspiration of cost minimization leads to an immediate necessity to consider a great number of various factors at the same time, as early as the basic designing stage. This peculiarity brings about a number of tasks. One of them—actually having a problem status, among other things, due to a large number of possible solutions—is transmission media type selection in a horizontal subsystem. Transition of a seemingly engineering task in a brand new status is conditional upon the fact that building a structured cabling horizontal subsystem requires an overwhelming share (about 85 percent) of all resources required for the entire IT cabling implementation. Besides, horizontal subsystem cable represents the key cabling system component in terms of required financial expenditures, which is the most resource-intensive at the installation stage.
One of the causes for the problem is that currently structured cabling technologies are widely used in various fields, drastically different from each other, owing to their high consumer qualities. Thus, there are several types of structured cabling, which can be initially adapted to the field of application to consider all peculiarities thereof. The cable types permitted for use in various types of structured cabling are given in the first table that appears in this article. However, the regulatory documents merely fix permitted cable types, irrespective of their application. Except for the maximum allowed channel length, perhaps, there are no unambiguous recommendations in the common official publications, even for preferred fields of their application, which are so desirable for designers and engineers.
Cable-type selection task
For obvious reasons, a system that has only one cable type is the easiest and most convenient to design, implement and operate, because in this case there is no way for the cable-type selection task to arise. However, to get this advantage, one must resolve an equally important task of a substantiated definition of this single type among a rather vast majority of its possible competitors.
It goes without saying, that providing variable conditions of actual projects one can observe in practice, there is no perfect cable type for every occasion. The evidence of this simple statement emanates from the fact that there are several competing standard types of products in the market. In this regard the cable-type selection problem is getting noticeably complicated and actually comes down to answers to the two largely complementary questions: 1) Does a certain structure have any advantages under the given specific conditions? and 2) Do its disadvantages under the given conditions have any significance?
Additionally, selection results are largely influenced by the boundary condition, which is rather far from engineering, but nonetheless important. That condition can be summarized as: What is the importance of the field in which this specific solution is the best under the general criterion of technical and economic efficiency, for end-user transfer and distribution services? In other words, should we differentiate it as a separate independent direction, or is it better to use well accessible insights from adjacent areas, that are in addition, of no difficulty for a wide range of experts, familiar with such insights owing to their occupation?
Examining optical fiber
Optical fiber is the first candidate for the perfect product for an IT cabling development. It is hardly viable to repeat in this article the impressive transmission-distance and transmission-rate figures for optical fiber that are well known. Using standard optical hardware components, circuits can be implemented directly to the subscriber in access networks, and directly to the user in office environments.
When considering optical cabling as a transmission medium, it has many advantages. However, for the purpose of selecting the preferred type of cabling components, optical fiber does also have some noticeable disadvantages that often result directly from its advantages.
It should be pointed out that optical-fiber equipment is inhomogeneous. Multimode solutions are preferable for short distances, including structured cabling backbone subsystems and horizontal subsystems. They can support the same transmission speeds as their singlemode counterparts, but provide cost advantages when short link lengths are implemented. It is viable to use singlemode equipment on extended interbuilding backbone links, owing to lower dispersion distortions. Singlemode and multimode cables must be considered separately, owing to the fact that during the composite channels’ development, they may not be connected directly without intermediate active equipment, such as a media converter or more-sophisticated piece of equipment.
Specific computations show that the viability border for transition from multimode to singlemode technology lies within the range of approximately 600 meters (2,000 feet) to 1,200 meters (4,000 feet); while with the transmission rate increases, the critical length shows a reducing trend. The latter results from both the higher values of higher-data-rate electronics and noticeably growing adoption of Om3 and Om4 multimode optical fibers.
Data center’s impact
Other factors may have a significant impact on component-type selection, and it is worth taking account of these factors. As an example, data center environments have grown rapidly in recent years, and top the list of factors that determine technology directions and may significantly impact component selection.
The following objective factors have a significant impact on the application scope of optical technologies in data centers.
A) A data center as a technical object does not provide services to end users, i.e. it lacks well-known man-machine system restrictions, primarily conditioning the ultimate data transmission lines.
B) Provision of operational support for the enterprise telephone network is not the top-priority objective in a data center, and thus, there is little or no demand for PoE technology. In this case the task of supply voltage delivery to the active networking equipment is resolved by completely different means.
C) Optical-fiber cables have much better weight-dimensional parameters when compared to balanced twisted-pair cables, facilitating the creation of a cooling system of active networking equipment.
D) When operated on long links, optical-fiber interfaces provide for much lower power consumption, i.e. building of “green” or energy-efficient data centers becomes easier.
Further analysis, however, causes us also to take into consideration the several additional factors. First, based on statistical data it should be concluded that owing to the focal application of a data center and its purpose, an expected market size of this type of structured cabling shall not exceed one-third of the office structured cabling market.
Second, in an earlier-published article (see “Considerations to make before investing in Category 6A cabling,” October 2010, page 5) we provided statistical data on some completed projects, showing that the average horizontal subsystem link length in a data center does not exceed 30 meters (100 feet), which is explained by the small size of this object owing to the natural intention to save an expensive area with complex engineering “stuffing” (uninterruptible power supply systems, precision air-conditioning/cooling systems, and others). The network interface based on balanced twisted-pair cable functions in a “short-reach” mode at such distances. It means that the length of most links is such that the optical technologies have no significant power-consumption advantages.
Third, 40-Gbit/sec transmission data rate is highly demanded in the data center, with the focal application area of server-to-server links. Current such transmission data rates may be confidently implemented on modern twisted-pair equipment, which still is less expensive than the optical equipment. Actually, until recently the lack of official standards was the basic restraining factor for its practical application.
Thus, despite a larger possible application niche for optical solutions in a data center, the classical office structured cabling shall remain unsurpassed either now or in the foreseeable future in terms of the application scope.
Access networks must be considered within the scope of this discussion, because they seemingly link up with the enterprise IT system owing to the current predominance of Ethernet technology.
Access networks may be built on various principles. For example, it may be implemented in the existing infrastructure. In terms of the scope and depth of coverage of existing housing stock, balanced twisted-pair cables and xDSL technology are beyond competition. Solutions based on overlaying of hybrid optical-fiber/coaxial CATV networks with such networks have certain prospects.
The newly built access networks are mostly based on optical-fiber equipment. The average link length in this part of a communication network may be assessed at a first approximation as 1 km (0.6 miles) size of order. In this situation advantages of singlemode technologies are fully expressed (in the form of Passive Optical Network or common Ethernet). In both cases a link is implemented through a single-fiber pattern. It provides for enhancement of the project’s economic features as a whole. At any rate, this very feature makes it difficult to link up an access network with an enterprise IT system, which traditionally uses classical dual-fiber links.
The number of access network users may be much higher than the number of IT system users, if only on the grounds that an individual access to the services of the latter is required preeminently for the corporate or government executives. The workers to officers’ ratio among the economically active population (including industrial and non-productive sectors) may be taken as 4:1. To assess the number of links in completed access networks at a first approximation, one may take as a premise that they approximately correspond to the number of households. Therefore, even disregarding the fact that in the context of overall engagement one household has two possible users of the IT system resources, we shall get that the number of access network links may be manifold higher than the number of structured cabling links, yet this difference can hardly reach the degree of order.
To assess the impact of an access-network technology on structured cabling, one should bear in mind that the basic volume of traffic generated and received by the IT system users is kept within this system. These are internal phone calls, local server addresses, e-document flow and some other services. Consequently, as a result of efforts for the structural optimization, it is viable to connect the whole IT system to an access network instead of an individual user, similar to use of PBX in telephony subsystems.
The aforesaid assumptions lead us to the conclusion that peculiarities of access networking, irrespective of the scope of their coverage, do not and cannot have any material impact on engineering solutions used in the general-purpose structured cabling.
From all this information, we reach four general conclusions about the prospects for all-optical structured cabling systems, which are described below.
1) In any foreseeable future all-optical networks shall neither prevail nor have material impact in office structured cabling. They will be used only in case of special requirements for resistance to external electromagnetic interference and protection against an unauthorized access to confidential information, i.e. those niche situations in which optical-fiber communication technology has no competitors whatsoever.
2) The scope of application of optical-fiber communication instrumentalities in the structured cabling projects shall grow. The data centers are objectively the driving force of this trend, where the parameter value may be even higher than 50 percent. The said growth will be evolutionary, and the data center shall not exceed percentage units by its annualized tempos even in the unsaturated market conditions.
3) Providing that the data center cabling market is relatively small compared to the similar office systems, the relative share of optical-fiber solutions in structured cabling technologies can hardly exceed 30 to 40 percent even at the extreme.
4) The impact of access networks on the scope of application of optical-fiber solutions in development of office structured cabling, which are the most important for the telecommunications industry, may be considered negligible.
Dr. Andrey B. Semenov is director of business development of IT-SCS (IT Structured Cabling System) for IT Co. He also heads the structured cabling systems faculty at the Moscow Technical University of Communications and Informatics (www.mtuci.ru/eng). Igor G. Smirnov is product manager for Signamax Inc. (www.signamax.com).
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