When you are putting together a data centre, everything has to be connected together; most good data centres will have enough data flowing to completely overwhelm a typical wireless router, and wired data speeds are always faster than wireless, hence the emphasis on cable runs.
Planning how your networking topology will run is a large part in setting up your data centre. You need to set space for the cables to be run, and it helps to know what kind of cable you plan on using.
The lowest grade of twisted pair cable is plain old telephone cable, such as is used to hook up your phone to the wall socket; this has serious bandwidth issues, and the signal drops off rapidly over time. In terms of the standards bodies that rate these, this is CAT 3 cable, and is all but unheard of in any kind of new built network architectures, though in legacy configurations where low bandwidth is acceptable, many installations of CAT 3 were never pulled and upgraded to CAT 5.
CAT-2 was used for an older architecture type called Token Ring (promulgated by IBM with the PS/2 systems). CAT 4 is an updated version of CAT 2 with better shielding and transmission properties.
The most basic of the modern cable types used in networking is Category 5, or Cat-5. This twisted pair cable is shielded, and has a grounding line, allowing it to go for much longer runs than the CAT-3 cables that preceded it; it originally hit the scene in the mid ’90s, and while more expensive at the time, quickly supplanted the prior cable types for anything driven by the TCP/IP networking stack.
Incremental improvements were made in both the protocols and the network adapters that used CAT 5, and its capacity has gradually increased as networking standards have grown; each increase in the capacity of the cable has resulted in a greater need for shielding to prevent packet loss and other interference artefacts; this has resulted in a partial upgrade to the standard called CAT5E. CAT-5E is also called Gigabit Ethernet cabling, and is the likeliest cable that you would be buying for a consumer networking connection.
On the horizon (meaning it’s primarily used for high end connectivity at this point) is CAT 6 cabling, which offers significant cross talk reduction from CAT5E, and has about a fivefold increase in bandwidth. This standard has also been extended by some cable vendors, who have created 10 Gigabit Ethernet, and the cables they use are commonly called CAT-6E. The CAT-6E standard was codified in February of 2008.
CAT 7 is a future standard, and is still being worked on; there are some facilities using pre-release versions of this standard for high data bandwidth apps, mostly for use in full motion video transfers, and radiology departments. Up until the CAT-6E standard, CAT7 was the only 10GBASE-T implementation that could handle the full bandwidth for a full hundred meters; it’s uncertain whether it will be supplanted by CAT-6E, or, as is likely, it will become the baseline for future extensions of bandwidth.