quartet signaling

Definition of quartet signaling in The Network Encyclopedia.

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What is Quartet Signaling?

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.

How It Works

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).

Calculations for Line Coding Data Rates

  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
NOTE

The 100BaseT4 form of Fast Ethernet also uses all four pairs of wire in twisted-pair cabling.

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