Gigabit and 10 Gigabit Ethernet

Compared with previous Ethernet standards Gigabit Ethernet has removed many limitations, such as network size, that were associated with shared media, shared bandwidth and half duplex. The aim is to provide reliable and high speed services. The new Gigabit topologies rely on switches that connect stations using dedicated and, generally, full duplex optical links. The exception is 1000BASE-T which was designed to provide a migration path for existing UTP Ethernet installations. The rest specifically address the metropolitan (MAN) and wide area network (WAN) markets.

Gbps Ethernet

The standard for 1000Mbps Gigabit Ethernet was standardized in 1998 under the name IEEE 802.3z/ab which describes two Ethernet architectures 1000BASE-X (which defines three versions: CX, LX and SX) and 1000BASE-T to run over UTP Cat 5 cable or better (see Figure 1.20).

 

Figure 1.20 1 Gigabit Ethernet defines several transmission media: 802.3z (1000BASE-X) based on the existing fibre Channel technology and covers three different types of media, and 802.3ab (1000BASE-T) which uses the popular UTP.

Gbps Ethernet and Beyond

There are two main differences between 10 Gigabit Ethernet and previous Ethernet versions. First is the inclusion of a long-haul (40+ km) optical transceiver for single mode fibre that can be used to build MANs. The second is the WAN option, which allows 10 Gigabit Ethernet to be transparently transported across existing SDH/SONET infrastructures.

Future of Ethernet

Manufacturers have recently been working on a higher-speed version of SONET (Synchronous Optical Network), boosting its capacity from 10G bps to 40G bps, which may have an impact on Ethernet's future. One group of manufacturers wants to piggyback on this work and develop a 40G bps version of Ethernet based largely on the STM-256/OC-768 specification.

 

Figure 1.21 Ethernet layers. MII and Auto-negotiation are optional.

However, other groups want to maintain the multiple of 10 strategy which would see 100 Gbps Ethernet as the next logical step. There is also a suggestion that vendors are more interested in putting 10 Gigabit Ethernet into the local telephone exchanges in order to obtain better returns, than investing in higher-speed Ethernet. Faster Ethernet definitely has a future, but its placement and timescale are very uncertain at the moment.