Optical Transceivers for 10 Gigabit Ethernet

Just as 10 gigabit Ethernet (10GbE) technologies have changed, so have the cabling technologies that support them and the devices that connect the cabling to their network. Optical transceivers provide the interface between the equipment sending and receiving data and the cabling transporting it. Just as there are distinct cabling technologies that coincide with 10 gigabit technologies, various transceivers are also available to match each cabling standard. 10 gigabit Ethernet has mainly four defined optical transceiver types. These optical transceivers are the result of multi-source agreement (MSA) which enables vendors to produce 802.3ae-compliant pluggable transceivers. This post will give a brief introduction to these four types of transceivers—XENPAK, X2, XFP, and SFP+.

XENPAK

XENPAK, the first 10 gigabit Ethernet pluggable transceivers on the market to support the 802.3ae standard transmission optics. They are large, bulky and used mainly in LAN switches. These transceivers are “hot pluggable” and support the new 802.3ak copper standard with vendors now producing transceivers to connect CX4 cables. XENPAK is a highly integrated, serial optical transponder module for high-speed, 10Gbit/s data transmission and offers a wide variety of 10 gigabit Ethernet connectivity options for data center, enterprise wiring closet, and service provider transport applications. It is designed to transmit and receive optical data of link length of 300m, 10km, 20km, 40km, up to 80km. XENPAK 10GB solution include dual fiber XENPAK, CWDM XENPAK and DWDM XENPAK modules which enable high port densities for 10 gigabit Ethernet systems.

X2

X2, the smaller brother of the XENPAK pluggable transceiver, is about 2/3 the size of the XENPAK transceiver module. With the same “hot pluggable” specifications and supporting all the 10 gigabit Ethernet standards (including copper), the X2 form factor allows for more port density on switches. X2 fiber optic transceiver module is used in datacom optical links only (not telecom). Its electrical interface to the host board is also standardized and is called XAUI (10 Gigabit attachment unit interface). X2 uses the same 70-pin electrical connector as XENPAK and supports implementations of XENPAK’s four lane XAUI at both Ethernet (3.125 Gbit/s) and/or Fiber Channel (3.1875 Gbit/s) rates. X2 will also support serial electrical interfaces as they may emerge in XENPAK, as well as ongoing maintenance. There are 300m, 10km, 20km, 40km, 80km X2 optical modules, like Cisco X2-10GB-SR, X2-10GB-ER and X2-10GB-ZR, which provides customers with a strong sense of assurance that this technology is a good choice and will have strong vendor support. The picture below shows a XENPAK transceiver and an X2 transceiver.

XENPAK and X2

XFP

XFP modules are hot-swappable and protocol-independent. They typically operate at near-infrared wavelengths (colors) of 850 nm, 1310 nm or 1550 nm. Principal applications include 10 gigabit Ethernet, 10 Gbit/s Fibre Channel, synchronous optical networking (SONET) at OC-192 rates, synchronous optical networking STM-64, 10 Gbit/s optical transport network (OTN) OTU2, and parallel optics links. They can operate over a single wavelength or use dense wavelength-division multiplexing techniques. They include digital diagnostics that provide management added to the SFF-8472 standard. XFP modules use an LC fiber connector type to achieve higher density. The positive aspect of the XFP form factor is it will allow switch vendors to increase port density in a smaller area for cost savings. A drawback of the XFP will be its inability to support the current copper (802.3ak) or the 10GBASE-LX4 standards.

SFP+

SFP+, the enhanced version of the SFP, supports data rates up to 16 Gbit/s. It is a popular industry format supported by many network component vendors. In comparison to earlier XENPAK or XFP modules, SFP+ modules leave more circuitry to be implemented on the host board instead of inside the module. Consideration has to be given to whether the module is linear or limiting. Linear SFP+ modules are most appropriate for 10GBASE-LRM; otherwise, limiting modules are preferred. SFP+ also introduces direct attach for connecting two SFP+ ports without dedicated transceivers. SFP+ supports 8 Gbit/s Fibre Channel, 10 Gigabit Ethernet and Optical Transport Network standard OTU2. Although the SFP+ standard does not include mention of 16G Fibre Channel, it can be used at this speed. The picture below shows an XFP transceiver and an SFP+ transceiver.

XFP and SFP+

Fiberstore is a professional manufacturer and supplier for good quality optical transceivers products. They offer these four kinds of optical transceiver modules for 10 gigabit Ethernet cabling applications. For example, Cisco XFP-10G-MM-SR, FTLX8512D3BCL XFP and FTLX8571D3BCL SFP+ branded by Finisar are for 10GBASE-SR; Cisco XFP-10GLR-OC192SR and HP 455886-B21 SFP+ are for 10GBASE-LR.

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