A signaling method used in 100VG-AnyLan (100BaseVG) networks. Signals are transmitted over all four pairs of wire in voice-grade unshielded twisted-pair (UTP) cabling. Quartet signaling makes possible the transmission of data at a speed of 100 Mbps while using the same transmission frequencies that are used on standard 10BaseT networks. Quartet signaling also enables 100VG-AnyLan to leverage existing installations of category 3, 4, and 5 UTP cabling for 100-Mbps transmission.
10BaseT Ethernet networks use only two pairs of wires in a four-pair UTP cable - one pair for transmitting data and the other pair for receiving data and for detecting collisions on the network. 100VG-AnyLan uses a demand priority method for controlling access to the media, which prevents collisions from occurring. As a result, 100VG-AnyLan can use all four pairs of wires for data transmission - hence the term “quartet signaling.” In addition, quartet signaling uses a different line coding technique than the traditional Manchester coding method used in Ethernet networks. Quartet signaling uses the 5B/6B NRZ line coding method, while Manchester coding uses a 1B/2B scheme whereby 1 bit of data is encoded using two binary symbols. The 1B/2B algorithm is reliable and simple to implement but inefficient. The 5B/6B method encodes 5 bits using six binary symbols, which allows two and a half times as much information to be transmitted per wire compared to 10BaseT Ethernet (as shown in the following table).
| Manchester Coding | Quartet Signaling | |
| Line coding | 1B/2B | 5B/6B |
| Line frequency | 20 MHz | 30 MHz |
| Data rate per pair | (1/2) x 20 = 10 Mbps | (5/6) x 30 = 25 Mbps |
| Number of pairs used | 1 | 4 |
| Total data rate | 1 x 10 = 10 Mbps | 4 x 25 = 100 Mbps |
The 100BaseT4 form of Fast Ethernet also uses all four pairs of wire in twisted-pair cabling.