I understand that an HDMI cable contains essentially 4 shielded twisted pairs, along with additional control lines. Each of the twisted pairs is specified, to my understanding, to be a balanced transmission line with a characteristic impedance of 100Ω.
Now, since (ISO 11801) category 6/7 (shielded) twisted pairs are also balanced transmission lines, with a characteristic impedance of 100Ω, I'd assume that such a cable (or two), given enough (shielded) twisted pairs to carry all of the signals, can serve as an alternative medium to the standard HDMI cable (with the proper connectors at the end).
However, it seems that an "HDMI over Cat. 5/6/7" solution requires a device which is called a "balun" on both ends, at the interface between the proper HDMI and the ISO 11801 cable.
I understand baluns and transformers have a role at the interface of cables with different impedances, or when one is balanced and the other isn't. However, in this case, the lines in both standards are specified to be balanced 100Ω lines.
Why then are "baluns" required in this case? Are they really baluns, or do they provide some other function?
Thanks in advance.