2BASE-TL is an IEEE 802.3-2008 Physical Layer (PHY

PHY

PHY is an abbreviation for the physical layer of the OSI model.An instantiation of PHY connects a link layer device to a physical medium such as an optical fiber or copper cable. A PHY device typically includes a Physical Coding Sublayer and a Physical Medium Dependent layer. The PCS encodes and...

) specification for a full-duplex long reach point-to-point Ethernet

Ethernet

Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....

 link over voice-grade copper wiring. 2BASE-TL is used in Ethernet in the first mile

Ethernet in the first mile

Ethernet in the first mile refers to using one of the Ethernet family of computer network protocols between a telecommunications company and a customer's premise. From the customer's point of view it is their "first" mile, although from the access networks' point of view it is known as the "last...

 applications.

Rates and Distances

Unlike 10BASE-T

10BASE-T

Ethernet over twisted pair technologies use twisted-pair cables for the physical layer of an Ethernet computer network. Other Ethernet cable standards employ coaxial cable or optical fiber. Early versions developed in the 1980s included StarLAN followed by 10BASE-T. By the 1990s, fast, inexpensive...

, 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

American wire gauge

American wire gauge , also known as the Brown & Sharpe wire gauge, is a standardized wire gauge system used since 1857 predominantly in the United States and Canada for the diameters of round, solid, nonferrous, electrically conducting wire...

, number of pairs if the link is aggregated, amount of crosstalk

Crosstalk (electronics)

In electronics, crosstalk is any phenomenon by which a signal transmitted on one circuit or channel of a transmission system creates an undesired effect in another circuit or channel...

 between the pairs, etc.), desired link parameters (such as desired SNR

Signal-to-noise ratio

Signal-to-noise ratio is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. It is defined as the ratio of signal power to the noise power. A ratio higher than 1:1 indicates more signal than noise...

 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 (8,858.3 ft), using ITU-T

ITU-T

The ITU Telecommunication Standardization Sector is one of the three sectors of the International Telecommunication Union ; it coordinates standards for telecommunications....

 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

PME Aggregation Function

PME Aggregation Function is a mechanism defined in Clause 61 of IEEE 802.3, which allows one or more Physical Medium Entities to be combined together to form asingle logical Ethernet link....

 (PAF).

For a single pair, the minimum possible link bitrate

Bitrate

In telecommunications and computing, bit rate is the number of bits that are conveyed or processed per unit of time....

 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

Decibel

The decibel is a logarithmic unit that indicates the ratio of a physical quantity relative to a specified or implied reference level. A ratio in decibels is ten times the logarithm to base 10 of the ratio of two power quantities...

 noise margin and no spectral limitations, the max bitrate can be achieved over distances of up to 1 kilometres (3,280.8 ft). At 6 kilometres (19,685 ft) the max achievable bitrate is about 850 kbit/s.

The throughput

Throughput

In communication networks, such as Ethernet or packet radio, throughput or network throughput is the average rate of successful message delivery over a communication channel. This data may be delivered over a physical or logical link, or pass through a certain network node...

 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
  Ethernet in the First Mile
  Ethernet in the first mile refers to using one of the Ethernet family of computer network protocols between a telecommunications company and a customer's premise. From the customer's point of view it is their "first" mile, although from the access networks' point of view it is known as the "last...
  
  
• PME Aggregation Function
  PME Aggregation Function
  PME Aggregation Function is a mechanism defined in Clause 61 of IEEE 802.3, which allows one or more Physical Medium Entities to be combined together to form asingle logical Ethernet link....
  
  
• 10PASS-TS
  10PASS-TS
  10PASS-TS is an IEEE 802.3-2008 Physical Layer specification for a full-duplex short reach point-to-point Ethernet link over voice-grade copper wiring, used in Ethernet in the first mile applications....
  
  
• G.SHDSL

External links

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