rrives in the United States from a European country, the receiving American carrier must convert the incoming E1 signal to T1. If a call originates from Canada and is terminated in Australia, the Canadian originating carrier must convert the call to E1 before trans- mitting it to Australia. Up the Food Chain: From T1 to DS3 Beyond When T1 and E1 first emerged on the telecommunications scene, they represented a dramatic step forward in terms of the bandwidth that ser- vice providers now had access to. In fact, they were so bandwidth rich Frame Bit Signaling Bit Figure 3-43 E1 framing Timeslots 2-15 Timeslots 17-32 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Telephony Telephony that there was no concept that a customer would ever need access to them. What customer, after all, could ever have a use for a million and a half bits per second of bandwidth? Of course, that question was rendered moot in short order as increas- ing requirements for bandwidth drove demand that went well beyond the limited capabilities of low-speed transmission systems. As T1 became mainstream, its usage went up, and soon requirements emerged for dig- ital transmission systems with capacity greater than 1.544 Mbps. The result was the creation of what came to be known as the North American Digital Hierarchy, shown in Figure 3-44. The table also shows the Euro- pean and Japanese hierarchy levels. From DS1 to DS3 We have already seen the process employed to create the DS1 signal from 24 incoming DSO channels and an added frame bit. Now we turn Hierarchy Europe United States Japan Figure 3-44 Level North 64 Kbps 64 Kbps 64 Kbps American Digital 1.544 Mbps 1.544 Mbps Hierarchy 2.048 Mbps DS-1c 3.152 Mbps 3.152 Mbps 6.312 Mbps 6.312 Mbps 8.448 Mbps 32.064 Mbps 34.368 Mbps 44.736 Mbps DS-3c 91.053 Mbps 139.264 Mbps 274.176 Mbps 397.2 Mbps Downloaded from Digital Engineerin