gest provider of co-location and data center services worldwide. Connecting Smaller Providers and Competitors to Customers Telephone companies and Multiple System Operators (MSOs) rent various portions of their networks to smaller providers and to competitors that might have some of their own switches and/or long-haul networks, but no last-mile connections to customers. They offer access to their networks on a wholesale basis. For example, they offer connections between their POPs and their local central offices. These connections are considered transport networks. Smaller providers use these lines to transport traffic between their own switch (which might be located at the POP) and the local telephone company's switch. They also lease last-mile cabling infrastructure to reach each of their customers. Both large and small providers make these arrangements with one another and with large enterprises. For example, Verizon sells services to large enterprises that have offices throughout the United States and around the world. Often, these enterprises purchase nationwide networking services for all of their www.TechnicalPDF.com locations. Verizon rents transport services from providers such as AT&T in cities where it does not own the local cabling infrastructure. Providers make these types of arrangements with carriers in other countries as well. AT&T, in turn, leases these services for its own large customers' remote offices that are located in areas where AT&T does not have its own last-mile network. APPENDIX Table 4-2 SONET: A North American Standard for Multiplexing Streams of Traffic onto Fiber- Optic Cabling and Transporting It at Optical Carrier (OC) Speeds* Synchronou North American European S Digital Synchronous Synchronous Hierarchy Transport Signal Transfer Mode (SDH) (STS) Levels (STM) Levels Channels 52Mbps 28 DS1s or 1 DS3 21 E1s 155Mbp 84 DS1s or 3 63 E1s or 1 E4 622Mb 336 DS1s or 12 252 E1s or 4 2,488M 1,344 DS1s or 48 1,008 E1s or 16 9,953M 5,376 DS1s or 192 4,032 E1s or 64 39.812 21,504 DS1s or 16,1