SCS - structured cable network. Or, roughly speaking, "sockets in the wall." The most expensive in the SCS - not sockets, but huge kilometers of wires connecting the sockets with server and switching.



The layer of concepts that are hidden behind the SCS is very extensive. There are professionals who know when to organize switching on the floors, how to properly conduct a bundle of fibers between floors, etc. There are also their marketers, whose task is to convince you that you need to do this way, $ Xk more in the estimate, and not the way you wanted.



The very area of ​​SCS construction is closer to construction (engineering) work, rather than to the field of system administration.

')

But sometimes in the life of a sysadmin there is a situation when it depends on him what will be the SCS in the building (floor, room) of the company. In the worst case, the sysadmin drags her, at best, this task is outsourced (more precisely, to contractors). But what kind of SCS will be, usually two or three people decide. At the same time, the remaining two determine only the budget, and only a sysadmin can fight for quality. [on the other side is the representative of the contractor who drags the blanket to his side, and although he may seem to be a comrade-in-arms to the sysadmin in the battle for the quality of the SCS, in fact, he just wants to be more expensive and should be treated with caution].



Here I am writing the point of view of the administrator, as the "end user" of the SCS. If I lied somewhere, or forgot to write about something important - say, correct.



So, SCS.

Viewpoint of the owner (director)

Need wires with sockets. The cheaper the better. The admin once said that computer can be branched on the ground, so you can put them smaller, for it is expensive. By the way, that's where the people are sitting in a handful, they have enough of one outlet.

Contractor's point of view

The customer needs to sell the maximum. Maximum, this is a full-fledged SKS with switching on the floors, interfloor optics ... What? Does he want cheaper? Well, figs with him, let him what he wants, he does.

What do you need from SCS?

Speed

Write out for yourself the minimum that you need. Despite the stories of marketers, most modern applications have 10 megabits behind their eyes and ears. A rare application needs 100 megabits (mainly due to the transfer of large amounts of data). If the application needs gigabit, then maybe you made a mistake with the place of its installation (maybe better to get closer to the servers?). Write down everything that is usually done on the computer. It turns out that most of these tasks are not demanding on speed. If you have not found such applications, it means that the requirement of category 5e, rather than 6, is quite boldly written in TK, as you can be persuaded to start.

Telephony

Some companies use IP phones, they are not interested in this question. If your IP ends near the PBX or old telephony is used, then telephone jacks are needed. The question is how to do them?



Options:

• In one wire with ethernet
• Several telephone pairs in one wire
• Separately, a separate wire to each outlet.

The first option (ethernet + phone), formally, let's say (maybe two applications in one cable), but in my practice I met a cable in which packets started to get lost at the time of the call (call). The main advantage of this solution is saving on wires. The main disadvantage is the need to breed it all. It is not comfortable.



The second option (ethernet separately, telephony of 4 pairs in the wire) is slightly better, but is complicated by the problem of wiring in the wall from the outlet to the outlet. If your contractor is ready to do it without additional. Payment - this may be an option. The downside is the non-universality of the SCS (more on this below), the plus is a significant saving on the cable (1 cable instead of 4).



The third option (a separate cable for each outlet) is the most interesting and the most expensive. You have between the server (switching) and the outlet is strictly a set of wires. What to let through (ethernet or telephony) - you decide. The peak of universality is the sockets for RJ45 for both ethernet and telephony (telephone RJ11 are completely included in RJ45).



The third option is very important in terms of universality. Need two phones? (fax + telephone) - please, here are two sockets, you can use them. Do I need another print server instead of a phone? You are welcome.



This option is the easiest to switch (1 wire - 1 application), the most easily debugged and reliable. And the most expensive.



If you have a large building, then at 500 sockets for phones you will lose about 12 kilometers of cable (you can calculate the price yourself) compared to the first option and about 18 km of cable compared to the second.

How many sockets

The main stumbling block. Each outlet is MONEY. Each outlet without use - money down the drain. Usually, the directorate looks at the staffing plan, pokes the number of sockets, allows for a maximum of +2 to the reserve - that's all. And then it turns out that in a room for 10 people there are only 3 pairs of sockets. Because earlier it was thought that this would be a presentation, but now it is an accountants room. Oh, yes, you need two more network printers, here to that wall, and to this one. No power outlets? Who cares?



The solution to the problem is to place the sockets not by the number of employees, but by the MAXIMUM-POSSIBLE number of jobs. Those. by the floor space.



It turns out expensive. Approximately 1.5-4 times more expensive than if you do "under working." But at the same time, the SCS becomes universal, i.e. suitable for any number of employees in any location.



The argument for the authorities: if we do the SCS by the number of jobs, then if you change the profile of the business or transplant employees, all the money goes to the cat, you have to redo it. If you make the SCS by the meter, then the SCS will not be an attribute of the current state of affairs in the company, but an element of the room (building), it becomes a capital investment in real estate, increasing its market value and versatility.

Switching

(this applies to the case when the SCS is on several floors).



We can drag all the wires to the server. They will be a lot. In one of the organizations in which I worked, this harness could hardly be wrapped around, almost a meter in diameter. The advantage of this is the very versatility - the wires go in a straight line (in the sense, without breaking the electrical connection), anything can be included in them - from the telephone to the video camera.



And we can do more cunning. We put the vertical part of the structured cabling system (interfloor connections), on each floor we allocate a corner in which the wires from the floors converge. In principle, there may even be more than one such corners on the floor.



SCS on the floor - universal. SKS interfloor - specialized.



Interfloor SCS: between the floors there is a gigabit, or even all ten, or even optics, or even ... (do not forget in this place about modesty, and stop at gigabit), a switch is placed. Telephony descends into a multi-multi-pair cable, which is routed to patch panels or crosses (cron66 or something like that). Further, the universal SCS of the floor, as you please, switches between the “telephony”, “ethernet”, “signaling”, etc. options.



The advantage of this solution is that several thick telephony wires converge to the server (which are routed to the PBX and you can no longer think about them), several gigabit (10 gigabit) cables converging to switches (apparently, to a distribution level, if you follow the tsisok scheme). The server is free of wires, all the "low" user rendered from the server. There is no need to look at non-essential personnel in order to break the wires for the transplanted employee, there is just everything Very Important.



However, from these pluses there are minuses. Moving a piece of equipment from the server to the switch (it’s understandable that in a good way it should be a small room, in reality it is usually a switch box under the ceiling, or even on the floor in one of the cabinets) leads to an increase in the SCS vulnerability. Dust, dirt is the first. The second is unauthorized access (you enable a person to carry out an ideal man-in-middle attack in a remote corner of the building) and hooliganism. Third - SCS loses its versatility. And what if there were not enough telephone pairs per floor? And below the floor is used 10 pairs of 200 ...

aggressive branching

(I do not know how this scheme is called officially)



Instead of a single switching room, we make many shelves. Relatively speaking, for every 1-2 rooms there is a separate switching shelf. It comes 1 ethernet and 1 how many a pair of telephone cable. This scheme is intermediate. On the one hand, you have less wires from the server room (not by the number of workplaces, but by the number of cabinets), on the other hand, the SCS of a separate room can be redone with little blood. These are pluses.



Cons - the same problem of imbalance of applications (if there is not enough telephony in the room, what are we doing?), A lot of places where the shelves are located (these places are not always obvious and well documented, I somehow found such switching in the middle of the room above the false ceiling) . The placement of electrical equipment (switches) requires electrical power (PoE can be partially smoothed, but this is expensive ...).



This solution has the “cheapest option” - this is a hub (switch) under your feet or in a corner. From the server goes a few wires to the switches, from these switches go wires to the neighboring switches ... So you can provide a couple of hundred outlets at the cost of 3-4 bays (300m * 4 = 1.2km) of wires, several desktop switches and patch cords, which are usually not patch cords and same twisted pair, but crimped. [Reference: monolithic twisted pair (in which each wire is monolithic copper) has the best characteristics, but low mechanical strength, the “real” patch cords have stranded fibers that are worse for data transmission, but survive the bends, advancing, pinching chairs and tables]. It is from this option that one should run like a devil from incense, because it delivers so many problems that it cannot be described with words (the switches will lose power, hang, the cables will get confused and get dirty ... I don’t even want to remember this).

Switching and shelves

The most radical option: a vertical cable network comes to the floor, a horizontal cable runs from the floor to the shelves in the rooms, from the shelves in the rooms there is an “in-room SCS” to outlets at work places.



Pros - the sum of the advantages of the previous ones.



The disadvantages are the same, but one more appears: the more switching occurs with the application, the worse the signal (this is not about switches, of course, although they also increase the delay, which can be unpleasant in some applications). 8 connectors from the phone to the PBX - quite a worthy reason for yourself, in a year or two to start hovering into the telephone receiver.



An interesting feature of this solution is that it fits perfectly on the core-distribution-access model. At the same time, the most important wires are interfloor, usually run in a box, there are few of them (this is important, because a small box is easier to make), they are well protected (perhaps inside walls).

And what for all these wires?

And here another interesting scheme is drawn, it is wifi and dect. If, instead of SCS, rooms have wifi hotspots and dect phone bases inside the rooms, the number of wires will be significantly reduced.



However, it still does not solve the problem of bringing the wire to the floor (room), and wifi quality / speed with good ethernet is not comparable (both in delay and in probability of packet loss).

What to choose?

Back to the first punt. First you must decide how the sockets will be distributed. In humans, or in square meters.



Next, you need to count how many wires there will be. If there are less than a couple of hundred (and if the length of the wires is within the 100m limit), you should not mess around with switching. If there are a lot of wires, or long distances, it is worth thinking about switching. If there is even the slightest opportunity to win over the premises, and not cabinets - you need to fight for the premises. No windows, no batteries, no walk-through doors. Just a closet.



Which wire to choose? In fact, any, the cheapest, on which the contractor is willing to vouch for quality. The cheapest certification wires (capable of certification) work no worse than silver twisted pair of oxygen-free copper with ferrite piercing.



But with sockets and patch panels, everything is much worse. Bad sockets - an eternal torment to the administrator.



So which socket is good?

1. The core should hold well. If the screws - great. Auto-snapping often breaks and dangles in a worm inside the box.
2. Tilt down or lid - a small plus (less dust)
3. Crimped twisted pair should be using a hammer, and not with a plastic cover with teeth. These teeth compress the pair worse than the drummer.
4. Durable (sorry for the banality): it should normally hold the wire, not squeak when moving the wire inside the outlet. It works for years, and no one promises that the wires will turn on / out carefully.

Telephony patch panels are a place for holivars. For a start: should telephony be placed on patch panels or on crowns? If on crowns - it is compact, very compact. If the patch panel - switching can be done without a drummer and power impact.



Similar holivary around the patch panels for ethernet. Are they needed or not? After all, wires can come "directly" and stick into switches. In this case, less mechanical contact and unwinding, i.e. the path is more reliable. On the part of the supporters: the patch panels allow you to organize the economy correctly . As experience shows, if there are a lot of units, then a patch panel is installed. If there are few units, they usually get tired.



Which option to choose - you decide.

Numbering

Less wires, the second (and maybe even the first) value of the SCS is its scheme. The diagram should show which socket goes where and how it goes (that is, the places where the wires go through must be clearly drawn on the floor plan). More important is the availability of outlet numbers both on the outlets themselves, and from the “server” side (i.e., from the side that is divorced on a patch panel or in a switching board). If there are no numbers, you can throw out the SCS (or start a long, painful numbering procedure). Numbers should be written so that they are easy to read (i.e., handwritten numbers are not very), and so as to remain for years. Those. the pencil is definitely no.



Do I need to number patch cords between patch panels and equipment when switching? I used to think so. Now, I doubt it, because in the proper SCS these wires are obviously visible and easy to find.

Patch cords

Well, the last. Patch cords MUST be with a cap, cap, reverse tongue ... Anything that will protect the jack latch from kicking for the wires when pulling the wire through the neighbors. IT IS IMPORTANT. Believe me, I personally suffered with 400+ wires WITHOUT caps. This is HELL. Instead of simply “pulling and pulling out”, you have to manually unravel each wire from your neighbors, the process of unraveling cleaves neatly laid wires, prevents you from pulling out other wires ... A cap (or at least a plug at the back) is MANDATORY.

Additions

Thanks for commenting. Moments that are not described.

• Switching log. How he looks “good” in theory, I don’t know, in my work he looked like a tabular file, in which there was a list of sockets and an indication of “who is assigned” this or that outlet. There was an attempt to number the patch cords, but it gradually stalled due to the general laziness. Apparently, in theory, for each switch there should be a magazine in which it says “so-and-so-so-so-so-so” (port of such-and-such a device).
• If the patch cords are already purchased without caps, as an emergency solution - electrical tape. Although she gets dirty and interferes. Caps better
• It is good to have organizers under the patch panels. Priceless units are spent on this, however, the SCS acquires accuracy and completeness.
• If you give the contractor SCS, do not skimp on the payment of the TZ. They (contractors) will make it more reasonable. Agree on their (rational) project, making adjustments and explaining what you want better than ... m ... the invention of your TK
• Standards for further guidance: EN 50173, ISO / IEC 11801
• For those who want to look at beautiful racks with beautifully laid wires: royal.pingdom.com/2008/01/24/when-data-center-cabling-becomes-art