onnections to storage area networks (SANs) that hold backup files. Access to the backup files is via either Internet or private lines. Carrier Ethernet over Copper in the First Mile The availability of high-speed carrier services for business and commercial customers in Europe, Latin America, and the Middle East has been held back by low availability of fiber-optic cabling. This is also generally true worldwide outside of metropolitan areas; however, this is starting to change. Ethernet in the first mile (EFM) is now avail- able at speeds from 2Mbps up to 100Mbps over copper cabling. Using existing copper cabling increases the availability of Ethernet by eliminating the expense and delays deploying new fiber-optic cabling. Ethernet over Copper is based on an Institute of Electrical and Electronics Engi- neers (IEEE) standard 803.ah, which was ratified in 2004. This standard specifies bonded pairs of copper cabling. Bonding is the use of equipment called inverse mul- tiplexers to increase bandwidth by combining two or more circuits or pairs of copper cabling such that they act as a single circuit. Figure 5-6 presents an example of bonding on Ethernet over Copper. The inverse multiplexing function is included in Ethernet- over-copper gear. Bonding requires the availability of extra pairs of copper cabling at the customer's buildings. High-Speed Access via Carrier Gigabit Ethernet Ethernet over Copper device with inverse Ethernet over Copper device multiplexing at with inverse multiplexing at ISP customer site Internet ######## Two pairs of copper cabling Figure 5-6 Bonding two or more pairs of copper cabling together increases capacity. Ethernet over Copper overcomes cabling impairments. Extra pairs of copper cabling are often available because telephone companies commonly deploy cabling it in bundles of 25, 50, or 100 pairs upon installation. This is done to avoid the expense of adding new cabling later if customers want more lines. Adding additional cabling afterward can involve labor and material for digging tre