2BASE-TL

2BASE-TL is an IEEE 802.3-2008 Physical Layer (PHY) specification for a full-duplex long reach point-to-point Ethernet link over voice-grade copper wiring. 2BASE-TL is used in Ethernet in the first mile applications.

Rates and Distances

Unlike 10BASE-T, 100BASE-T and 1000BASE-T PHYs, providing a single rate of 10, 100 or 1000 Mbit/s respectively, 2BASE-TL link rate can vary, depending on the copper media characteristics (such as length, wire diameter or gauge, number of pairs if the link is aggregated, amount of crosstalk between the pairs, etc.), desired link parameters (such as desired SNR margin, Power Back-Off, etc.), and regional spectral limitations.

2BASE-TL PHYs deliver a minimum of 2 Mbit/s over distances of up to 2.7 kilometres (8,900 ft), using ITU-T G.991.2 (G.SHDSL.bis) technology over a single copper pair. These PHYs may also support an optional aggregation or bonding of multiple copper pairs, called PME Aggregation Function (PAF).

For a single pair, the minimum possible link bitrate is 192 kbit/s (3 x 64 kbit/s) and the maximum bitrate is 5.7 Mbit/s (89 x 64 kbit/s). On a 0.5 mm wire with 3 dB noise margin and no spectral limitations, the max bitrate can be achieved over distances of up to 1 kilometre (3,300 ft). At 6 kilometres (20,000 ft) the max achievable bitrate is about 850 kbit/s.

The throughput of a 2BASE-TL link is lower than the link's bitrate by an average 5%, due to 64/65-octet encoding and PAF overhead, both factors depend on packet size.

See also

• Ethernet in the First Mile
• PME Aggregation Function
• 10PASS-TS
• G.SHDSL

External links

• IEEE 802.3ah - Ethernet in the First Mile Task Force archive
• Metro Ethernet Forum