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Gigabit Ethernet and 10 Gigabit Ethernet Fundamentals

What is Gigabit Ethernet?

Operating 10 times faster than fast Ethernet, Gigabit Ethernet uses CSMA/CD—the same frame format and frame size as the other versions of Ethernet ─ and it can support full duplex operation. The biggest differences between Ethernet and Gigabit Ethernet (GigE) are in the cabling and signaling used.

 

Using the 8B/10B encoding method, fiber-optic support offers several options, but all based on the Fibre Channel technology that is already in use.

1000BASE-LX (long wavelength, 1300 nm) can be used by singlemode fiber (9 m) from 2 m up to 5 km, and multimode fiber (62.5 or 50 m) from 2 m up to 550 m.

1000BASE-SX (short wavelength, 780 nm) can be used by 62.5 m multimode fiber from 2 m to 275 m and 50 m multimode fiber from 2 m to 550 m.

Under 1000BASE-X using 8B/10B encoding, there is 1000BASE-CX media, which is based on four-pair Category 5 UTP cable and operates over short distances up to 25 m. The gigabit media independent interface (GMII) came about because the above specification could not accommodate the 100 m four-pair Category 5 UTP that is in common use today.

 

To allow four-pair Category 5 UTP to be used up to 100 m (or networks with a diameter of 200 m) it was necessary to develop new technology that is not based on Fibre Channel. So the MAC layer was split to allow two different encoding methods. 1000BASE-T uses all four pairs to transmit/receive and a five-level coding scheme. It may also be necessary to test current cabling to see if it is able to carry a gigabit per second.

Summary of GigE Characteristics:

  • 1000 Mbit/s data rate
  • Preserves 802.3 frame format
  • Switched point-to-point (initially)
  • Half and full duplex (only FDX being deployed)
  • Shared and half duplex will use CSMA/CD
  • Flow control for switched operation
  • Fiber- (multimode, singlemode) or copper-based transmission media
  • Modified MAC layer protocol

The Gigabit Ethernet Specifications

1000BASE-T is one of the four physical layers (or transceivers) defined by the two GigE standards: IEEE 802.3z (1000BASE-X) and IEEE 802.3ab (1000BASE-T).

1000BASE-X supports multimode and singlemode fiber media and a 25-meter copper jumper. The IEEE 802.3 1000BASE-T standard supports GigE operation over Category 5 cabling systems.


 

1000BASE-T works by using all four of the Category 5 pairs to achieve 1000 Mbit/s operation over the installed Category 5 copper cabling. 1000 Mbit/s data rates are achieved by sending and receiving a 250 Mbit/s data stream over each of the four pairs simultaneously (4 X 250 Mbit/s = 1 Gbit/s). 

What is 10 Gigabit Ethernet?

The fastest and most recent of the Ethernet standards is 10 GigE or IEEE 802.3ae.

There are a number of different media types for 10 GigE LANs, MANs and WANs.

10GBASE-SR (short range): This uses multimode cabling over short distances and has a range of between 26 m and 82 m depending on cable type. Supports 300 m operation over the 2000 MHz•km multimode fiber.
10GBASE-CX4: This is a copper interface using Infiniband cables for short-reach applications (such as aggregation switch to router).
10GBASE-LX4: This uses wavelength-division multiplexing (WDM) to support ranges of between 240 m and 300 m over multimode cabling. Also supports 10 km over singlemode fiber.


10GBASE-LR and 10GBASE-ER (long range and extended range): These standards support 10 km and 40 km respectively over singlemode fiber. Several manufacturers have introduced 80 km-range ER pluggable interfaces.


10GBASE-LRM: 10 Gbit/s on FDDI-grade 62.5 m multimode cable
10GBASE-SW, 10GBASE-LW and 10GBASE-EW: These varieties use the WAN PHY, designed to interoperate with OC-192/ STM-64 SONET/ SDH equipment. They correspond at the physical layer to 10GBASE-SR, 10GBASE-LR and 10GBASE-ER respectively, and hence use the same types of fiber and support the same distances.
The IEEE is developing a standard for 10 GigE over twisted pairs (10GBaseT), using Category 6 or Category 7 cable.

10 GigE InterfaceData Rate
/Gbit/s
Operating
Wavelength
Fiber
Interface
Operating Trans-
mission Range
10GBASE-SR 10.3125 850 nm Multimode 50 µm
Multimode 62.5 µm
2 to 300 m
2 to 33 m
10GBASE-LR 10.3125 1310 nm Singlemode 2 m to 10 km
10GBASE-ER 10.3125 1550 nm Singlemode 2 m to 40 km
10GBASE-SW 9.95328 850 nm Multimode 50 µm
Multimode 62.5 µm
2 to 300 m
2 to 33 m
10GBASE-LW 9.95328 1310 nm Singlemode 2 m to 10 km
10GBASE-EW 9.95328 1550 nm Singlemode 2 m to 40 km

The Function of the 10 GigE LAN PHY

In order to understand the reasoning behind the definition of both a 10 GigE LAN and 10 GigE WAN, we need to recall the compatibility interests of data and telecom networking.

 

Ethernet dominates the LAN and SONET/SDH dominates the MAN/WAN. Ethernet was designed for bursty, high-bandwidth unpredictable data, while SONET/SDH was originally designed for voice traffic that is predictable and low bandwidth.


The IEEE has created guidelines to support Ethernet both across the LAN and the WAN. 10 GigE LAN interfaces are commonly deployed where distances are shorter and direct router connections can be made without being part of traditional telecom networks.
10GBASE-R (LAN PHY) interfaces offer an effective line rate of 10.3125 Gbit/s (10 Gbit/s of data traffic encoded in a 64B/66B protocol).


The 10GBASE-X interface utilizes 8B/10B encoding, providing a four-wavelength (each at 3.125 Gbit/s) version of the LAN PHY.

10GigE Interfaces

10GBASE-LR and 10GBASE-LW are long-wavelength interfaces (1310 nm) using singlemode fiber (SMF) from 2 m to 10 km.


10GBASE-LR and ER interfaces are designed for use over dark fiber and the 10GBASE-LW and EW interface are designed to connect to SONET/SDH. 
10GBASE-ER and 10GBASE-EW interfaces are for use over (1550 nm) singlemode fiber (SMF) from 2 m up to 40 km (131,233 feet).


The 10GBASE-LX4 interface uses wavelength-division multiplexing (WDM) technology and operates at 1310 nm over multimode fiber (MMF) from 2 m up to 300 m or from singlemode fiber (SMF) dark fiber 2 m up to 10 km.