10 Gigabit Ethernet: Difference between revisions

Content deleted Content added

Inline

Revision as of 17:00, 29 April 2008

The 10 Gigabit Ethernet or 10GbE or 10 GigE standard was first published in 2002 as IEEE Std 802.3ae-2002 and is the fastest of the Ethernet standards. It defines a version of Ethernet with a nominal data rate of 10 Gbit/s, ten times as fast as Gigabit Ethernet.

Over the years the following 802.3 standards relating to 10GbE have been published: 802.3ae-2002 (fiber -SR, -LR, -ER and -LX4 PMDs), 802.3ak-2004 (-CX4 copper twin-ax InfiniBand type cable), 802.3an-2006 (10GBASE-T copper twisted pair), 802.3ap-2007 (copper backplane -KR and -KX4 PMDs) and 802.3aq-2006 (fiber -LRM PMD with enhanced equalization).

The 802.3ae-2002 and 802.3ak-2004 amendments have been consolidated into the IEEE 802.3-2005 standard. The other amendments will be consolidated into IEEE Std 802.3-2008 which has not yet been published.

10 Gigabit Ethernet supports only full duplex links which can be connected by switches. Half duplex operation and CSMA/CD (carrier sense multiple access with collision detect) are not supported in 10GbE.

File:Nortel-10G-ERS-8600.JPG

10 Gigabit Nortel Router

The 10 Gigabit Ethernet standard encompasses a number of different physical layer (PHY) standards. As of 2008 10 Gigabit Ethernet is still an emerging technology with only 1 million ports shipped in 2007, and it remains to be seen which of the PHYs will gain widespread commercial acceptance. A networking device may support different PHY types by means of pluggable PHY modules.

At the time the 10 Gigabit Ethernet standard was developed there was much interest in 10GbE as a WAN transport and this led to the introduction the concept of the WAN PHY for 10GbE. This operates at a slightly slower data-rate than the LAN PHY and adds some extra encapsulation. The WAN PHY and LAN PHY are specified to share the same PMDs (Physical Medium Dependent) so 10GBASE-LR and 10GBASE-LW can use the same optics. In terms of number of ports shipped the LAN PHY greatly outsells the WAN PHY.

Fiber

Optical transceivers are connected to a host by either a XAUI, XFI or SFI interface. XAUI (XGXS) uses a four-lane data channel and is specified in IEEE 802.3 Clause 48. XENPAK, X2, and XPAK modules use XAUI to connect to their hosts. XFI and SFI use a single lane data channel and the encoding specified in Clause 49. XFP modules use XFI and SFP+ (see SFP transceiver) modules use SFI.^[1]

It is hoped that the low cost SFP+ (see SFP transceiver) optical module developed by the ANSI T11 fibre channel group will enable lower cost 10GE optical modules to be produced.^[2] These only do optical to electrical conversion, no clock and data recovery, putting a higher burden on the host's channel equalization.

Optical modules are not specified in 802.3 but by multi-source agreements (MSAs). XENPAK was the first MSA for 10GE. X2 and XPAK were later competing standards to produce a smaller form factor module. X2 and XPAK have not been as successful in the market as XENPAK and XFP which is newer and has the smallest form factor.

There are two classifications for optical fiber: single-mode (SMF) and multi-mode (MMF). SMF is used for long distance communication and MMF is used for distances of less than 300m. SMF has a narrower core (6.3 µm) which makes it difficult to connect. MMF has a wider core (50 or 62.5 µm) and is more expensive than SMF. The advantage of MMF for short distances is that because of its wider core it can be driven by lower cost lasers and its connectors are cheaper and more reliable. Its disadvantage is that due to chromatic dispersion it can only work over short distances.^[3] To distinguish SMF from MMF cables, typically, SMF cables are yellow, while MMF cables are orange.^[4]

New structured wiring installations use OM3 50 µm MMF which has no center defect. OM3 cable can carry 10GBE 300m using low cost 10GBASE-SR optics or use 10GBASE-LX4 without a mode conditioning patch cord. See ISO 11801 and multi mode fibre.

Older installations use FDDI grade 62.5 µm MMF which has a center defect and is harder for the 10GBE optical modules to drive^[5]. For -LX4 a mode conditioning patch cord is needed that adds extra cost to an installation.

LAN PHY

The most common optical variety is referred to as LAN PHY, used for connecting directly between routers and switches. Although called LAN, this can be used with 10GBase-LR up to 10 km (6.2 mi) and -ER up to 40 km (25 mi). LAN PHY uses a line rate of 10.3125 Gbit/s and a 64B/66B encoding. The LAN PHYs use 10GBASE-R as the Physical Coding Sublayer, except for 10GBASE-LX4, which uses 10GBASE-X.

10GBASE-SR

10GBASE-SR ("short range") uses 64B/66B encoding and 850 nm lasers. It is designed to support short distances over deployed multi-mode fiber cabling, it has a range of between 26 metres (85 ft) and 82 metres (269 ft) depending on cable type. It also supports 300 metres (980 ft) operation over new, 50 μm 2000 MHz·km OM3 multi-mode fiber (MMF). The transmitter can be implemented with a VCSEL (Vertical Cavity Surface Emitting Laser) which is low cost and low power. MMF has the advantage of having lower cost connectors than SMF due to its wider core. OM3 is now the preferred choice for structured optical cabling within buildings.

10GBASE-SR delivers the lowest cost, lowest power and smallest form factor optical modules.

10GBASE-LRM

10GBASE-LRM, (Long Reach Multimode) also known as 802.3aq, is a newly ratified standard^[6] which supports distances up to 220 metres (720 ft) on FDDI-grade 62.5 µm multi-mode fibre (using 1310 nm) originally installed in the early 1990s for FDDI and 100BaseFX networks and 260 metres (850 ft) on OM3. 10GBASE-LRM reach is not quite as far as the older 10GBASE-LX4 standard. However it is hoped that 10GBASE-LRM modules will be lower cost and lower power than 10GBASE-LX4 modules.

10GBASE-LR

10GBASE-LR is a Long Range Optical technology delivering serialized 10 gigabit Ethernet over a 1310 nm connection on single-mode fiber via IEEE 802.3 Clause 49 64B-66B Physical Coding Sublayer (PCS).

Single-mode optical cabling is used to interconnect transceivers at a distance spaced at 10 kilometres (6.2 mi), but it can often reach distances of up to 25 kilometres (16 mi) with no data loss.

Fabry-Perot lasers are commonly used in 10GBASE-LR optical modules. Fabry-Perot lasers are more expensive than VCSELs but their high power and focused beam allow efficient coupling into the small core of single mode fiber.

10GBASE-LR optical modules are now cheaper than 10GBASE-LX4 optical modules.

10GBASE-ER

10GBASE-ER ("extended range") supports distances up to 40 kilometres (25 mi) over single-mode fiber (using 1550 nm).

10GBASE-ZR

Recently, 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 and manufacturers have created their own specifications based upon the 80 km PHY described in the OC-192/STM-64 SDH/SONET specifications.

802.3 will not be amended to cover the ZR PHY.

10GBASE-LX4

10GBASE-LX4 uses coarse wavelength division multiplexing to support ranges of between 240 metres (790 ft) and 300 metres (980 ft) over legacy multi-mode cabling. This is achieved through the use of four separate laser sources operating at 3.125 Gbit/s in the range of 1300 nm on unique wavelengths. This standard also supports 10 kilometres (6.2 mi) over single-mode fiber.

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

10GBASE-LX4 is used by people who want to support both MMF and SMF with a single optical module. Because 10GBASE-LX4 uses four lasers it has a potential cost, size and power disadvantage compared to 10GBASE-LRM.

When used with legacy MMF an expensive mode conditioning patch cord is needed. The mode conditioning patch cord is a short length of SMF which connects to the MMF in such a way to move the beam away from the central defect in the legacy MMF. This is not needed with OM3.

WAN PHY

10GBASE-SW, 10GBASE-LW, 10GBASE-EW, and 10GBASE-ZW are varieties that use the WAN PHY, designed to interoperate with OC-192/STM-64 SDH/SONET equipment using a light-weight SDH/SONET frame running at 9.953 Gbit/s. WAN PHY is used when an enterprise user wishes to transport 10G Ethernet across telco SDH/SONET or previously installed wave division multiplexing systems without having to directly map the Ethernet frames into SDH/SONET. The WAN PHY variants correspond at the physical layer to 10GBASE-SR, 10GBASE-LR, 10GBASE-ER and 10GBASE-ZR respectively, and hence use the same types of fiber and support the same distances. There is no WAN PHY standard corresponding to 10GBASE-LX4 and 10GBASE-CX4 since the original SONET/SDH standard requires a serial implementation. The WAN PHYs use 10GBASE-W as the Physical Coding Sublayer.

Copper

10GBASE-CX4

10GBASE-CX4 — also known by its working group name 802.3ak — transmits over 4-lanes in each direction over copper cabling similar to the variety used in InfiniBand technology. It is designed to work up to a distance of 15 m (49 ft). This technology has the lowest cost per port of all 10Gb interconnects, at the expense of range. Each device capable of supporting a 10GbE module uses some MSA (Multi-Source Agreement) to provide the actual module connectivity within the device to the outside connector. XENPAK, X2, and XPAK connectors all fit into a standard MSA pinout. CX4 modules exist at least in the XENPAK, X2, and XFP variety, and possible XPAK, although the smaller size makes this configuration more difficult. Each lane of the copper carries 3.125 Gbaud of signaling bandwidth. It is the job of the 802.3ae Clause 48 protocol to manage and synchronize the data flowing between these 4 channels; this functionality is maintained in the PCS. Compare to 10GBASE-R devices, which use the Clause 49 protocol. Clause 48 uses an 8 to 10 bit conversion to accommodate better line signaling, but Clause 49 uses a 64 to 66 bit conversion for this accommodation, which leaves the actual overhead for signaling much tighter than the Clause 48.

10GBASE-Kx

Backplane Ethernet — also known by its working group name 802.3ap — is used in backplane applications such as blade servers and routers/switches with upgradable line cards. Kx implementations are required to operate in an environment comprising up to 1 metre (39 in) of copper printed circuit board with two connectors. The standard provides for two different implementations: 10GBASE-KR and 10GBASE-KX4. 10GBASE-KR uses the same coding as the 10GBASE-LR/ER/SR. It also defines an optional layer of Forward Error Correction, an autonegotiation protocol and link training where the receiver can set a three tap transmit equalizer. 10Gbase-KX4 is virtually identical with 10GBase-CX4. Implementations of both variants of 802.3ap are supposed to be backwards compatible with 1000Base-X serial implementations through autonegotiation.

10GBASE-T

10GBASE-T, or IEEE 802.3an-2006, is a standard released in 2006 to provide 10 gigabit/second connections over conventional unshielded or shielded twisted pair cables, over distances up to 100 metres (330 ft).^[7] As of 2007, products remain scarce, but new silicon is expected to make 10GBASE-T switches available in 2008 at a price of less than 500 USD per port.

Connectors

10GBASE-T uses 650 MHz versions of the venerable IEC 60603-7 8P8C connectors already widely used with Ethernet.

Cables

10GBASE-T will work up to 55 m (180 ft) with existing Category 6 cabling. In order to allow deployment at the usual 100 m (330 ft), the standard uses a new partitioned Category 6a (a.k.a "augmented Cat6") cable specification, designed to reduce crosstalk between UTP cables (formally known as "alien crosstalk").

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.

Notes and references

External links

[1] "Pictures of optical modules supplied by Merge Optics".

[2] "10GbE Optical Component and SFP+ Modules: This Time It's Different by Andrew Schmitt".

[3] "Why choose Multimode fiber? by Corning" (PDF).

[4] ttp://www.superwarehouse.com/10M_MMF_CABLE_SC_SC_62.5_125/09167/p/9102

[5] "10 Gigabit Ethernet over Multimode Fiber by John George" (PDF).

[6] "IEEE Standards Status Report for 802.3aq".

[7] "IEEE Standards Status Report for 802.3an".

[1]

[2]

[3]

[4]

[5]

[6]

[7]

@@ Line 16: / Line 16: @@
 ==Fiber==
 [[Image:Netiron xmr 16000.JPG|thumb|200px|right|A [[Router]] with 10 Gigabit Ethernet Optical Interfaces.  The yellow cables are for potentially long range, single mode fiber connections]]
-Optical transceivers are interconnected with a host device, by either an IEEE 802.3 Clause 48 4-lane [[XAUI]] (XGXS) channel or more recently by a Clause 49 encoded single lane [[XFI]] channel.  ([[XENPAK]]s, X2s, and XPAKs use the Clause 48 conversion and [[XFP]]s use a straight Clause 49).<ref>{{cite web|url=http://www.mergeoptics.de/overview.html|title=Pictures of optical modules supplied by Merge Optics}}</ref>
+Optical transceivers are connected to a host by either a [[XAUI]], [[XFI]] or SFI interface. [[XAUI]] (XGXS) uses a four-lane data channel and is specified in IEEE 802.3 Clause 48. [[XENPAK]], X2, and XPAK modules use XAUI to connect to their hosts. [[XFI]] and SFI use a single lane data channel and the encoding specified in Clause 49. XFP modules use XFI and SFP+ (see [[SFP transceiver]]) modules use SFI.<ref>{{cite web|url=http://www.mergeoptics.de/overview.html|title=Pictures of optical modules supplied by Merge Optics}}</ref>
 It is hoped that the low cost SFP+ (see [[SFP transceiver]]) optical module developed by the ANSI T11 [[fibre channel]] group will enable lower cost 10GE optical modules to be produced.<ref>{{cite web|url=http://www.nyquistcapital.com/2007/11/28/10gbe-and-sfp-this-time-its-different/|title=10GbE Optical Component and SFP+ Modules: This Time It's Different by Andrew Schmitt}}</ref> These only do optical to electrical conversion, no clock and data recovery, putting a higher burden on the host's channel equalization.