Ethernet physical layer
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| 1. Physical layer |
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The Ethernet physical layer is the name given to component of TCP/IP which makes use of the Ethernet standard.
The Ethernet physical layer evolved over a considerable time span and encompasses quite a few physical media interfaces and several magnitudes of speed. The speed ranges from 3 Mbit/s to 10 Gbit/s in speed while the physical medium can range from bulky coaxial cable to twisted pair to optical fiber. In general, network protocol stack software will work identically on most of the following types.
The following sections provide a brief summary of all the official Ethernet media types (section numbers from the IEEE 802.3-2002 standard are parenthesized). In addition to these official standards, many vendors have implemented proprietary media types for various reasons—often to support longer distances over fiber optic cabling.
Many Ethernet adapters and switch ports support multiple speeds, using autonegotiation to set the speed and duplex for the best values supported by both connected devices. If auto-negotiation fails, a multiple speed device will sense the speed used by its partner, but will assume half-duplex. A 10/100 Ethernet port supports 10BASE-T and 100BASE-TX. A 10/100/1000 Ethernet port supports 10BASE-T, 100BASE-TX, and 1000BASE-T.
Contents |
[edit] Physical layers
[edit] Xerox experimental Ethernet
| Name | Description |
|---|---|
| Xerox Ethernet | The original, 3 Mbit/s Ethernet implementation, which had a frame format different from the production forms of Ethernet. |
[edit] Early implementations (10 Mbit/s and 1 Mbit/s)
| Name | Standard | Description |
|---|---|---|
| 10BASE5 | 802.3 (8) | 10 Mbit/s, Manchester coded signaling, copper RG-8X (expensive) coaxial cabling, bus topology with collision detection (aka Thick Ethernet) |
| 10BASE2 | 802.3 (10) | 10 Mbit/s, Manchester coded signaling, copper RG-58 (cheap) coaxial cabling, bus topology with collision detection (aka Thin Ethernet) |
| 10BROAD36 | 802.3 (11) | 10 Mbit/s, scrambled NRZ signaling modulated (PSK) over high frequency carrier, broad bandwidth coaxial cabling, bus topology with collision detection |
| 1BASE5 | 802.3 (12) | 1 Mbit/s, Manchester coded signaling, copper twisted pair cabling, star topology |
| StarLAN 10 | 10 Mbit/s, Manchester coded signaling, copper twisted pair cabling, star topology - evolved into 10BASE-T | |
| 10BASE-T | 802.3 (14) | 10 Mbit/s, Manchester coded signaling, copper twisted pair cabling, star topology - direct evolution of 1BASE-5 |
| FOIRL | Fiber-optic inter-repeater link; the original standard for Ethernet over fiber | |
| 10BASE-F | 802.3 (15) | (also called 10BASE-FX) -- A generic term for the family of 10 Mbit/s Ethernet standards using fiber optic cable: 10BASE-FL, 10BASE-FB and 10BASE-FP. Of these only 10BASE-FL is in widespread use. 10 Mbit/s, Manchester coded signaling, fiber pair |
| 10BASE-FL | 802.3 (15) | an updated version of the FOIRL standard |
| 10BASE-FB | 802.3 (15) | intended for backbones connecting a number of hubs or switches; it is now obsolete |
| 10BASE-FP | 802.3 (15) | a passive star network that required no repeater, it was never implemented |
[edit] Fast Ethernet (100 Mbit/s)
-
For more details on this topic, see Fast Ethernet.
| Name | Standard | Description |
|---|---|---|
| 100BASE-T | A term for any of the three standards for 100 Mbit/s Ethernet over twisted pair cable up to 100 meters long. Includes 100BASE-TX, 100BASE-T4 and 100BASE-T2. All of them use a star topology. | |
| 100BASE-TX | 802.3 (24) | 4B5B MLT-3 coded signaling, CAT5 copper cabling with two twisted pairs. |
| 100BASE-T4 | 802.3 (23) | 8B6T PAM-3 coded signaling, CAT3 copper cabling (as used for 10BASE-T installations) with four twisted pairs (uses all four pairs in the cable). Now obsolete, as Cat-5 cabling is the norm. Limited to half-duplex. |
| 100BASE-T2 | 802.3 (32) | No products exist. PAM-5 coded signaling, CAT3 copper cabling with two twisted pairs, star topology. Supports full-duplex. It is functionally equivalent to 100BASE-TX, but supports old telephone cable. However, special sophisticated digital signal processors are required to handle encoding schemes required, making this option fairly expensive. |
| 100BASE-FX | 802.3 (24) | 4B5B NRZI coded signaling, two strands of multi-mode optical fiber. Maximum length is 400 meters for half-duplex connections (to ensure collisions are detected) or 2 kilometers for full-duplex. |
| 100BASE-SX | TIA | 100 Mbit/s Ethernet over multi-mode fiber. Maximum length is 300 meters. Unlike 100BASE-FX using lasers as light sources, 100BASE-SX uses LEDs, so it is cheaper. |
| 100BASE-BX10 | 802.3 | 100 Mbit/s Ethernet bidirectionally over a single strand of single-mode optical fiber. A multiplexer is used to split transmit and receive signals into different wavelengths allowing them to share the same fiber. Supports up to 10 km. |
| 100BASE-LX10 | 802.3 | 100 Mbit/s Ethernet up to 10 km over a pair of single mode fibers. |
| 100Base-VG | 802.12 | Standardized by a different IEEE 802 subgroup, 802.12, because it used a different, more centralized form of media access ("Demand Priority"). Championed by only HP, 100VG-AnyLAN (as was the marketing name) was the earliest in the market. It needed four pairs of Cat-3 cables. Now obsolete (802.12 has been "inactive" since 1997). |
[edit] Gigabit Ethernet
-
For more details on this topic, see Gigabit Ethernet.
All of these use a star topology.
| Name | Standard | Description |
|---|---|---|
| 1000BASE-T | 802.3 (40) | PAM-5 coded signaling, CAT5/CAT5e/CAT6 copper cabling with four twisted pairs (used in both directions) |
| 1000BASE-TX | TIA 854 | over only Cat-6 copper cabling. Unimplemented. |
| 1000BASE-SX | 802.3 | 8B10B NRZ coded signaling, multi-mode fiber (up to 550 m). |
| 1000BASE-LX | 802.3 | 8B10B NRZ coded signaling, multi-mode fiber (up to 550 m) or single-mode fiber (up to 2 km; can be optimized for longer distances, up to 10 km). |
| 1000BASE-LH | multi-vendor | over single-mode fiber (up to 100 km). A long-haul solution. |
| 1000BASE-CX | 802.3 | 8B10B NRZ coded signaling, balanced shielded twisted pair (up to 25 m) over special copper cable. Predates 1000BASE-T and rarely used. |
| 1000BASE-BX10 | 802.3 | up to 10km. Bidirectional over single strand of single-mode fibre. |
| 1000BASE-LX10 | 802.3 | Up to 10 km over a pair of single-mode fibres. |
| 1000BASE-PX10-D | 802.3 | downstream (from head-end to tail-ends) over single-mode fiber using point-to-multipoint topology (supports at least 10 km). |
| 1000BASE-PX10-U | 802.3 | upstream (from a tail-end to the head-end) over single-mode fiber using point-to-multipoint topology (supports at least 10 km). |
| 1000BASE-PX20-D | 802.3 | downstream (from head-end to tail-ends) over single-mode fiber using point-to-multipoint topology (supports at least 20 km). |
| 1000BASE-PX20-U | 802.3 | upstream (from a tail-end to the head-end) over single-mode fiber using point-to-multipoint topology (supports at least 20 km). |
[edit] 10 gigabit Ethernet
 |
It has been suggested that Physical Media Dependent be merged into this article or section. (Discuss) |
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For more details on this topic, see 10 gigabit Ethernet.
| Name | Standard | Description
|
|---|---|---|
| 10 GBASE-SR | 802.3ae | designed to support short distances over deployed multi-mode fiber cabling, it has a range of between 26 m and 82 m depending on cable type. It also supports 300 m operation over a new 2000 MHz.km multi-mode fiber. |
| 10 GBASE-LX4 | 802.3ae | uses wavelength division multiplexing to support ranges of between 240 m and 300 m over deployed multi-mode cabling. Also supports 10 km over single-mode fiber. |
| 10 GBASE-LR | 802.3ae | supports 10 km over single-mode fiber |
| 10 GBASE-ER | 802.3ae | supports 40 km over single-mode fiber |
| 10 GBASE-SW | 802.3ae | A variation of 10 GBASE-SR using the WAN PHY, designed to interoperate with OC-192 / STM-64 SONET/SDH equipment |
| 10 GBASE-LW | 802.3ae | A variation of 10 GBASE-LR using the WAN PHY, designed to interoperate with OC-192 / STM-64 SONET/SDH equipment |
| 10 GBASE-EW | 802.3ae | A variation of 10 GBASE-ER using the WAN PHY, designed to interoperate with OC-192 / STM-64 SONET/SDH equipment |
| 10 GBASE-CX4 | 802.3ak | designed to support short distances over copper cabling, it uses InfiniBand 4x connectors and CX4 cabling and allows a cable length of up to 15 m. |
| 10 GBASE-T | 802.3an | Uses unshielded twisted-pair wiring. |
| 10 GBASE-LRM | draft 802.3aq | Extend to 220 m over deployed 500 MHz.km multimode fiber |
- 10 gigabit Ethernet is still fairly new and it remains to be seen which of the standards will gain commercial acceptance in consumer markets. 10 GBASE-LR/ER are the most common usage in the Carrier/ISP market.
- Note that both IEEE 802.2ae and IEEE 802.3ak have been incorporated into IEEE 802.3-2005.
[edit] 100 gigabit Ethernet
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For more details on this topic, see 100 gigabit Ethernet.
| Name | Standard | Description |
|---|---|---|
| 100 GBASE-? | 802.3 HSSG | Higher Speed Study Group. 100 Gbit/s up to 100 m or 10 km using MMF or SMF optical fiber respectively |
[edit] Ethernet over twisted-pair cable
Several varieties of Ethernet were specifically designed to run over 4-pair copper structured cabling already installed in many locations. ANSI recommends using Category 6 cable for new installations [citation needed].
| Pin | Pair | Color | telephone | 10BASE-T | 100BASE-TX | 1000BASE-T | PoE mode A | PoE mode B |
|---|---|---|---|---|---|---|---|---|
| 1 | 3 |  white/green |
- | TX+ | z | bidi | 48V out | - |
| 2 | 3 |  green |
- | TX- | z | bidi | 48V out | - |
| 3 | 2 |  white/orange |
- | RX+ | z | bidi | 48V return | - |
| 4 | 1 |  blue |
ring | - | - | bidi | - | 48V out |
| 5 | 1 |  white/blue |
tip | - | - | bidi | - | 48V out |
| 6 | 2 |  orange |
- | RX- | z | bidi | 48V return | - |
| 7 | 4 |  white/brown |
- | - | - | bidi | - | 48V return |
| 8 | 4 |  brown |
- | - | - | bidi | - | 48V return |
Combining 10Base-T (or 100BASE-TX) with "IEEE 802.3af mode A" allows a hub to transmit both power and data over only two pairs. This was designed to leave the other two pairs free for analog telephone signals[citation needed][1].
The pins used in "IEEE 802.3af Mode B" supplies power over the "spare" pairs not used by 10BASE-T and 100BASE-TX.
In a departure from both 10BASE-T and 100BASE-TX, 1000BASE-T uses all four cable pairs for simultaneous transmission in both directions through the use of echo cancellation. (Telephones also use echo cancellation to simultaneously transmit in both direction over a single cable pair).
[edit] Ethernet Minimum Cable Lengths
All copper Ethernet segments that run the Collision Detect (CD) portion of CSMA/CD have a minimum cable length to function properly because of reflections[1]. This applies only to 10BASE-T and 100BASE-TX standards; The 1000BASE-TX standard is covered at the end of this section.
Fiber connections have minimum cable lengths due to level requirements on received signals[2].
Fiber ports designed for long-haul wavelengths require a signal attenuator if used within a building[3].
Industrial Ethernet applications uses a star topology with no collisions, therefore no minimum cable length is required[4].
1000BASE-TX supports half-duplex mode, making collisions possible. Consequently, the 1000BASE-TX standard requires a minimum cable length for collision detection to function properly; to avoid this in Gigabit Ethernet, small frames are padded into the transmission in half-duplex mode[5].
[edit] See also
[edit] References
- ^ Computer Technology Documentation Project, undated, URL retrieved on 1 June 2007
- ^ Cisco 100BASE-FX SFP Fast Ethernet Interface Converter on Gigabit SFP Ports, undated, URL retrieved on 1 June 2007
- ^ Extreme Network Consolidated Hardware Guide, undated, URL retrieved on 1 June 2007
- ^ Contemporary Controls Ethernet Media Converter Manual, undated, URL retrieved on 1 June 2007
- ^ Intel Network Connectivity Solutions Guide, undated, URL retrieved on 1 June 2007
