Posted on Jul 26, 2009 in Knowledge Base

XENPAK is a Multisource Agreement (MSA), instigated by Agilent Technologies and Agere Systems, that defines a fiber-optic or wired transceiver module which conforms to the 10 Gigabit Ethernet (10GbE) standard of the Institute of Electrical and Electronics Engineers (IEEE) 802.3 working group. The MSA group received input from both transceiver and equipment manufacturers during the definition process. XENPAK has been replaced by more compact devices providing the same functionality.


XENPAK modules were supplied for physical layer interfaces supporting multi-mode and single mode Fiber Optic Cables and InfiniBand copper cables with connectors known as CX4. Transmission distances vary from 100 metres (330 ft) to 80 kilometres (50 mi) for fiber and up to 15 metres (49 ft) on CX4 cable. Newer XENPAKs using the 10GBase-LX4 standard operated using multiple wavelengths on legacy multi-mode fibres at distances of up to 300 metres (980 ft), eliminating the need to reinstall cable in a building when upgrading certain 1 Gbit/s circuits to 10 Gbit/s.

Replacement form factors

The XENPAK form factor was initially supported by numerous network equipment manufacturers and module makers. However, advances in technology led to more compact form factors for 10 Gigabit Ethernet applications. Soon after the standard was introduced in 2001, two related standards emerged: XPAK and X2. These two standards have the same electrical interface as XENPAK (known as XAUI) but different mechanical properties.

The XPAK group was announced on March 19, 2002, first published their specification on May 24, 2002, and version 2.3 on August 1, 2003.

The X2 group was announced on July 22, 2002, and published their specification on February 13, 2003. Issue 3.0 of the XENPAK MSA was transferred to the Small Form Factor committee as document INF-8474 on September 18, 2002. The XENPAK MSA website existed through the end of 2008.