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10 Gigabit Ethernet

The 10 gigabit ethernet standard is a computer networking standard that was first published in 2002. It is also known as 10GE, 10GbE or 10 GigE. This ethernet standard defines a version of ethernet with a nominal data rate of 10 Gbit/s (billion bits per second), which is ten times faster than gigabit ethernet. 10 gigabit ethernet defines  full-duplex point-to-point links, which are generally connected by network switches. Half-duplex operation, hubs, and CSMA/CD (carrier sense multiple access with collision detection), do not exist in 10GbE. 

10GbE encompasses a number of different physical layer (PHY) standards. A networking device may support different PHY types through pluggable PHY modules, like those based on SFP+. Market forces determine the most popular 10GE PHY types.

Interest in 10GbE as a wide area network (WAN) transport led to the introduction of a WAN PHY for 10GbE. 10 gigabit ethernet operates at a slightly slower data rate than the local area network (LAN) PHY and adds some extra encapsulation. They both share the same physical medium-dependent sublayers and can use the same optics.

10 Gigabit Ethernet Standards

The Institute of Electrical and Electronics Engineers (IEEE) 802.3 working group published several ethernet standards relating to 10GbE. They consist of, standard 802.3ae-2002 (fiber -SR, -LR, -ER and -LX4 PMDs), standard 802.3ak-2004 (-CX4 copper twin-ax InfiniBand type cable), standard 802.3an-2006 (10GBASE-T copper twisted pair), standard 802.3ap-2007 (copper backplane -KR and -KX4 PMDs), and standard 802.3aq-2006 (fiber -LRM PMD with enhanced equalization).

The 802.3ae-2002 and 802.3ak-2004 amendments were consolidated into the IEEE 802.3-2005 ethernet standard. The IEEE 802.3-2005 and the other amendments were consolidated into the IEEE Std 802.3-2008 ethernet standard.

10 Gigabit Ethernet Physical Layer Modules

In order to support different 10GbE physical layer standards, many interfaces consist of a standard socket to plug PHY modules into. Physical layer modules are not specified in an official standards body. PHY modules are specified by multi-source agreements (MSAs) that can be negotiated more quickly. Relevant MSAs for 10GbE include, XENPAK (and related X2 and XPAK), XFP, and SFP+.  Designers considers cost, reach, media type, power consumption, and size and form factors when designing MSAs.

XENPAK was the first MSA for 10GE with the largest form factor. X2 and XPAK have smaller form factors and were competing for standards. X2 and XPAK were not as successful in the market as XENPAK. XFP came after X2 and XPAK. Their form factor is also smaller.

SFP+

The newest module standard is the enhanced small form-factor pluggable transceiver, generally called SFP+. SFP+ is based on the small form-factor pluggable transceiver (SFP) and was developed by the ANSI T11 fiber channel group. It is smaller and lower power than XFP. SFP+ is the most popular socket on 10GE systems. SFP+ modules can handle optical to electrical conversion, not clock and data recovery, and that puts a higher burden on the host's channel equalization. SFP+ modules share a common physical form factor with legacy SFP modules, allowing higher port density than XFP and the re-use of existing designs for 24 or 48 ports in a 19" rack width blade.

Optical Modules

Optical modules are connected to a host by either a XAUI, XFI or SFI interface. XENPAK, X2, and XPAK modules, use XAUI to connect to their hosts. XAUI (XGXS) uses a four-lane data channel and is specified in IEEE 802.3 Clause 48. XFP modules use a XFI interface and SFP+ modules use an SFI interface. XFI and SFI use a single lane data channel and the 64b/66b encoding specified in IEEE 802.3 Clause 49.

SFP+ modules are grouped into two types of host interfaces, linear or limiting. Limiting modules are preferred, except when using old fiber infrastructure, which requires the use of the linear interface provided by 10GBASE-LRM modules.

Optical Fiber

There are two classifications for optical fiber. They are single-mode (SMF) and multi-mode (MMF). In SMF, light follows a single path through the fiber. With MMF light takes multiple paths resulting in differential mode delay (DMD). SMF is used for long distance communication and MMF is used for shorter distances of less than 300 m. SMF has a narrower core (8.3 µm), which requires a more precise termination and connection method. MMF has a wider core (50 or 62.5 µm). The advantage of MMF is that it can be driven by low-cost VCSEL lasers for short distances. Multimode connectors are cheaper and easier to terminate reliably in the field. The advantage of SMF is that it can work over longer distances.

In the 802.3 standard, they refer to FDDI-grade MMF fiber. This fiber has a 62.5 µm core and a minimum modal bandwidth of 160 MHz*km at 850 nm. It was originally installed in the early 1990s for FDDI and 100BaseFX networks. The 802.3 standard also references ISO/IEC 11801, which specifies OM1, OM2, OM3 and OM4 MMF fiber types. OM1 has a 62.5 µm core while the others have a 50 µm core. At 850 nm, the minimum modal bandwidth of OM1 is 200 MHz*km, the minimum modal bandwidth of OM2 500 MHz*km, the minimum modal bandwidth of OM3 2000 MHz*km, and the minimum modal bandwidth of OM4 4700 MHz*km. FDDI-grade cable is now obsolete. New structured cabling installations use either OM3 or OM4 cabling. OM3 cable can carry 10GbE 300 meters using low-cost 10GBASE-SR optics (OM4 can manage 400 meters).

SMF and MMF

SMF and MMF cables are distinguished by color. SMF cables are usually yellow, while MMF cables are orange (OM1 & OM2) or aqua (OM3 & OM4); however, it must be noted that in fiber optics there is no agreed color for any specific optical speed or technology, with the exception being angular physical connector (APC), which is green and is an agreed upon color.

There are also active optical cables (AOC). These cables have the optical electronics already connected which eliminates the connectors between the cable and the optical module. The cables plug into standard optical module sockets. This makes AOC lower cost than other optical solutions because the manufacturer can match the electronics to the required length and type of cable.

10GBASE-SR

10GBASE-SR, also called short range, is a port type for multi-mode fiber that uses 850 nm lasers. Its Physical Coding Sublayer 64b/66b PCS is defined in IEEE 802.3 Clause 49 and its Physical Medium Dependent PMD in Clause 52. It delivers serialized data at a line rate of 10.3125 Gbit/s.

Over obsolete FDDI-grade 62.5 micron multi-mode fiber cabling, it has a maximum range of 26 meters. Over 62.5 micron OM1 it has a range of 33 meters. Over 50 micron OM2 it has a range of 82 meters. Over OM3 it has a range of 300 meters. And over OM4 it has a range of 400 meters. OM3 and OM4 are the preferred choices for structured optical cabling within buildings. MMF connectors are less expensive because of its wider core, which gives it the advantage compared to SMF.

The 10GBASE-SR transmitter is implemented with a vertical-cavity surface-emitting laser (VCSEL), which is low cost and low power. OM3 and OM4 optical cabling is sometimes described as laser optimized because they have been designed to work with VCSELs. 10GBASE-SR delivers the lowest cost, lowest power, and smallest form factor optical modules.

There is also a non-standard, lower cost, lower power variant referred to as 10GBASE-SRL (10GBASE-SR lite). This is inter-operable with 10GBASE-SR but only has a reach of 100 meters.

10GBASE-LR

10GBASE-LR (long reach) is a port type for single-mode fiber. LR uses 1310 nm lasers. Its Physical Coding Sublayer 64b/66b PCS is defined in IEEE 802.3 Clause 49 and its Physical Medium Dependent PMD is defined in Clause 52. It delivers serialized data at a line rate of 10.3125 Gbit/s.

10GBASE-LR has a specified reach of 10 kilometers (6.2 mi); however, 10GBASE-LR optical modules can often manage distances of up to 25 kilometers (16 mi) with no data loss.

The 10GBASE-LR transmitter is implemented with a Fabry–Pérot or Distributed Feedback Laser (DFB). DFB lasers are more expensive than VCSELs. Their high power and longer wavelength allow efficient coupling into the small core of single mode fiber over greater distances.

10GBASE-LRM

10GBASE-LRM(Long Reach Multimode) is a port type for multi-mode fiber using 1310 nm lasers. It is specified in IEE 802.3aq. The Physical Coding Sublayer 64b/66b PCS is defined in IEEE 802.3 Clause 49 and its Physical Medium Dependent PMD is defined in Clause 68. It delivers serialized data at a line rate of 10.3125 Gbit/s.

10GBASE-LRM supports distances up to 220 meters (720 ft) on FDDI-grade multi-mode fiber. It supports the same 220m maximum reach on OM1, OM2 and OM3 fiber types. 10GBASE-LRM reach does not extend as far as the older 10GBASE-LX4 standard.

To ensure that specifications are met with FDDI-grade, OM1 and OM2 fibers; the transmitter should be coupled through a mode conditioning patch cord. Mode conditioning patch cord is required for applications over OM3 or OM4.

Some 10GBASE-LRM transceivers also support distances up to 300 meters (980 ft) on standard single-mode fiber (SMF, G.652); however, this is not part of the IEEE or MSA specification.

10GBASE-LRM uses electronic dispersion compensation (EDC) for receive equalization.

10GBASE-LRM has been a failure in the market.

10GBASE-ER

10GBASE-ER (extended reach) is a port type for single-mode fiber and uses 1550 nm lasers. Its Physical Coding Sublayer 64b/66b PCS is defined in IEEE 802.3 Clause 49 and its Physical Medium Dependent PMD in Clause 52. 10GBASE-ER delivers serialized data at a line rate of 10.3125 Gbit/s.

The 10GBASE-ER transmitter is implemented with an externally modulated laser (EML).

10GBASE-ER has a reach of 40 kilometers (25 mi) over engineered links and 30 km over standard links.

10GBASE-ZR

Several manufacturers have introduced 80 km (50 mi) range ER pluggable interfaces under the name 10GBASE-ZR. This 80 km PHY is not specified within the IEEE 802.3ae standard. Manufacturers created their own specifications based upon the 80 km PHY described in the OC-192/STM-64 SDH/SONET specifications.

The 802.3 standard will not be amended to cover the ZR PHY.

10GBASE-LX4

10GBASE-LX4 is a port type for multi-mode fiber and single-mode fiber. It uses four separate laser sources operating at 3.125 Gbit/s and coarse WDM with four unique wavelengths around 1310 nm. Its Physical Coding Sublayer 8B10B PCS is defined in IEEE 802.3 Clause 48. Its Physical Medium Dependent PMD in Clause 53.

It supports a range of 300 meters (980 ft) over FDDI-grade, OM1, OM2 and OM3 multi-mode cabling (all these fiber types are specified to have a minimum modal bandwidth of 500 MHz*km at 1300 nm).

10GBASE-LX4 also supports a range of 10 kilometers (6.2 mi) over SMF.

For MMF links, the WDM output needs to be coupled through a SMF offset-launch mode-conditioning patch cord. This is explained in subclauses 53.6 and 38.11.4 of the IEEE 802.3 spec.

Until 2005 10GBASE-LX4 optical modules were cheaper than 10GBASE-LR optical modules.

10GBASE-LX4 was used by people who wanted to support both MMF and SMF with a single optical module.

10GBASE-LX4 is now an obsolete technology and has no significant market presence.

Copper

10G ethernet can also run over twin-ax cabling, twisted pair cabling, and backplanes.

10GBASE-CX4

10GBASE-CX4 was the first 10G copper standard published by 802.3 (as 802.3ak-2004). It uses the XAUI 4-lane PCS (Clause 48) and copper cabling similar to that used by InfiniBand technology. It is specified to work up to a distance of 15 m (49 ft). Each lane carries 3.125 G baud of signaling bandwidth.

10GBASE-CX4 offers the advantages of low power, low cost and low latency. It does, however, have a bigger form factor and more bulky cables than the newer single lane SFP+ standard. It also has a much shorter reach than fibre or 10GBASE-T.

Shipments of 10GBASE-CX4 today are very low.

SFP+ Direct Attach

SFP+ Direct attach are also known as 10GSFP+Cu, 10GBase-CR, or 10GBase-CX1, SFP+, or 10GbE Cu SFP cables. Direct Attach uses a passive twin-ax cable assembly and connects directly into an SFP+ housing. SFP+ Direct Attach has a fixed-length cable. Those cables are 3, 5 or, 7m in length, and, like 10GBASE-CX4, are low power, low cost, and low latency. They have the added advantage of using less bulky cables and of having the small form factor of SFP+. SFP+ Direct Attach tremendously popular today, with more ports installed than 10GBASE-SR.

Backplane

Backplane ethernet is also known by its task force name 802.3ap. It is used in backplane applications such as blade servers and routers/switches with upgradable line cards. 802.3ap implementations are required to operate in an environment of up to 1 meter (39 in) of copper printed circuit board with two connectors. The standard definition is two port types for 10 Gbit/s (10GBASE-KX4 and 10GBASE-KR) and a 1 Gbit/s port type (1000BASE-KX). It also defines an optional layer for FEC, a backplane autonegotiation protocol, and link training for 10GBASE-KR where the receiver can set a three tap transmit equalizer. The autonegotiation protocol selects between 1000BASE-KX, 10GBASE-KX4, and 10GBASE-KR or 40GBASE-KR4 operation. 40GBASE-KR4 is defined in clause 802.3ba.

New backplane designs use 10GBASE-KR instead of 10GBASE-KX4.

10GBASE-KX4

10GBASE-KX4 operates over four backplane lanes and uses the same physical layer coding (defined in IEEE 802.3 Clause 48) as 10GBASE-CX4.

10GBASE-KR

10GBASE-KR operates over a single backplane lane and uses the same physical layer coding (defined in IEEE 802.3 Clause 49) as 10GBASE-LR/ER/SR.

10GBASE-T

10GBASE-T, or IEEE 802.3an-2006, is a standard released in 2006 that provides 10 Gbit/s connections over unshielded or shielded twisted pair cables and over distances up to 100 meters (330 ft).10GBASE-T cable infrastructure can also be used for 1000BASE-T. This allows a gradual upgrade from 1000BASE-T using autonegotiation to select which speed to use. 10GBASE-T has latency in the range 2 to 4 microseconds. That compares to 1 to 12 microseconds on 1000BASE-T. As of 2010, 10GBASE-T silicon is available from several manufacturers, with claimed power dissipation of 3-4 W, at structure widths of 40 nm. with 28 nm in development, power will continue to decline.

10GBASE-T uses the IEC 60603-7 8P8C (commonly known as RJ45) connectors already widely used with ethernet. Transmission characteristics are now specified to 500 MHz. Category 6A or better balanced twisted pair cables, specified in ISO/IEC 11801 amendment 2 or, ANSI/TIA-568-C.2, are needed to carry 10GBASE-T up to distances of 100 m. This allows them to reach the 500 MHZ frequency. Category 6 cables can carry 10GBASE-T for shorter distances, when qualified, according to the guidelines in ISO TR 24750 or TIA-155-A.

Electrical Characteristics

The 802.3an standard defines the wire-level modulation for 10GBASE-T as a Tomlinson-Harashima precoded (THP) version of pulse-amplitude modulation with 16 discrete levels (PAM-16), encoded in a two-dimensional checkerboard pattern known as DSQ128. Several proposals were considered for wire-level modulation, including PAM with 12 discrete levels (PAM-12), 10 levels (PAM-10), or 8 levels (PAM-8), both with and without Tomlinson-Harashima Precoding (THP). PAM-5 is what is used in the older 1000BASE-T gigabit ethernet standard.

WAN PHY (10GBASE-W)

The WAN PHY uses the 10GBASE-S, 10GBASE-L and 10GBASE-E optical PMDs and is designated as 10GBASE-SW, 10GBASE-LW or 10GBASE-EW. Its Physical Coding Sublayer 64b/66b PCS is defined in IEEE 802.3 clause 49. Its Physical Medium Dependent PMDs is defined in clause 52. It also uses a WAN Interface Sublayer (WIS) which is defined in clause 50 and adds extra encapsulation to format the frame data to be compatible with SONET STS-192c.

The WAN PHY was designed to interoperate with OC-192/STM-64 SDH/SONET equipment using a light-weight SDH/SONET frame running at 9.953 Gbit/s.

10GbE NICs

10GbE network interface cards are available from several manufacturers. These plug into ordinary computer servers using PCI express and connect to the LAN with a choice of PHY modules.

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