While the cabling standards specify the bandwidth of the installed cabling, the actual rate at which data can be transmitted over a cabling system depends on the design of the electronic equipment attached to it. The bandwidth of the cabling system is specified in megahertz (MHz). However, the data rate is specified in bits per second – today, that is usually millions (megabits per second – Mb/s) or billions (billions of bits per second – Gb/s).
While the category of the cabling system will determine the maximum bandwidth that it offers, the maximum data rate actually transported by the cable is determined by the electronic equipment connected to the cabling system. Standardized data rates tend to increase by powers of ten. For example, 100 megabits per second (100 Mb/s) is the next standard data rate for Ethernet above 10 megabits per second provided by original Ethernet. Consequently, standards may not be developed to take advantage of the theoretical maximum capacity of some cable categories. The chart "Maximum Data Rates" below indicates the maximum data rates (by cabling category) for which standards have been developed.
Why is this important? For one thing, note that the maximum data rate is the same for Category 5e and Category 6. Both are capable of transporting 1 gigabit per second or 1,000 megabits per second (1 Gb/s or 1,000 Mb/s). So, even though Category 6 cabling has a theoretical maximum capacity that is 2.5 times that of Category 5e, there are no standards for electronic systems that take advantage of it, nor are any standards being developed. As noted above, standard data rates tend to increase by powers of 10, so the next step above 1 Gb/s is 10 Gb/s. Newly-standardized augmented Category 6 (Category 6a) is required to carry this data rate.
Therefore, users must question why they would pay a premium for a Category 6 cabling system (that in reality provides no increase in performance over Category 5e) rather than installing less-costly Category 5e.
While Category 5 cabling is no longer recognized by standards, there are many Category 5 cabling systems installed. As discussed in "Cable Categories", both Category 5 and Category 5e cables are intended to support a bandwidth of 100 MHz. However, the Category 5e standard includes measurements of some parameters that are not required by the Category 5 standard. It is probable that a high-quality Category 5 system will meet the requirements of these additional parameters required for Category 5e. If it does, it will not be limited to a maximum data rate of 100 megabits per second (normally considered to be the limit of Category 5) and will actually be capable of supporting the same data rates as Category 5e (i.e. 1 Gb/s). This can be determined by testing the installed Category 5 system against the Category 5e requirements. It will usually be sufficient to test a sample of installed cables rather than the entire system.
This chart is also useful to determine if an installed cabling system can be re-used by a subsequent occupant. For example, while both Category 5e and Category 6 will support 1 Gb/s (1000 Mb/s), no department is known to run more than 100 Mb/s to the work area. Hence, a Category 5 system should meet the actual requirements of virtually all departments and need not be replaced.
A few departments are using old 3270 terminals – so-called "dumb terminals". Most of these operate at data rates of only approximately 19 kb/s (0.19 Mb/s) although some components do operate at up to 2.5 Mb/s. Accordingly, even a Category 3 system will suffice.
Note: While the theoretical maximum data rate is roughly 2.4 billion bits / second (2.4 gigabits per second), no standards are being developed for equipment operating at this data rate. Next highest standard data rate is 10 gigabits / second and equipment operating at this speed requires augmented Category 6 (Category 6a) cabling.
Note: Category 5 is no longer standard. Many Category 5 systems will support 1 billion bits / second (1 gigabit / second. Testing will verify.