remaining bits-all of the odd-numbered frame bits in the frame-are used as a 4 Kbps facility data link for end-to-end diagnostics and network management tasks. ESF provides one major benefit over its predecessors: the ability to do unintrusive testing of the facility. In earlier systems, if the user reported trouble on the span, the span would have to be taken out of service for testing. With ESF, that is no longer necessary because of the added func- tionality provided by the CRC and the facility data link. Figure 3-42 Extended Extended Superframe: Superframe 24x193 4,632 bits (ESF) framing 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 Chapter 3 The Rest of the World: E1 E1, used for the most part outside of the United States and Canada, dif- fers from T1 on several key points. First, it boasts a 2.048 Mbps facility, rather than the 1.544 Mbps facility found in T1. Second, it utilizes a 32- channel frame rather than 24. Channel 1 contains framing information and a four-bit cyclic redundancy check (CRC-4); Channel 16 contains all signaling information for the frame; and channels 1 through 15, and 17 through 31 transport user traffic. The frame structure is shown in Figure 3-43. There are a number of similarities between T1 and E1 as well: Chan- nels are all 64 Kbps and frames are transmitted 8,000 times per second. And whereas T1 gangs together 24 frames to create an extended super- frame, E1 gangs together 16 frames to create what is known as an ETSI multiframe. The multiframe is subdivided into two sub-multiframes; the CRC-4 in each one is used to check the integrity of the sub-multiframe that preceded it. A final word about T1 and E1: Because T1 is a departure from the international E1 standard, it is incumbent upon the T1 provider to per- form all interconnection conversions between T1 and E1 systems. For example, if a call a