 8,192 The Transport Network Infrastructure E-Carrier: Separate Signaling Channels The E-carrier system is different from the T-carrier and J-carrier systems in an important way: In the E-carrier system, the framing and signaling information travels in separate channels from the voice and data traffic. Two of the 32 channels are devoted to carrying signaling and framing information, and the other 30 channels are available to carry cus- tomer payload at 64Kbps. In T-carrier and J-carrier, because the signaling information flows in the conversation channel, voice channels are 64Kbps, but data channels are 56Kbps, with the remaining capacity reserved for signaling. The SDH/SONET Infrastructure SDH/SONET, created in the mid-1980s, is the second generation of digital hierar- chy. Whereas PDH involves a lot of overhead because it includes three standards throughout the world, SDH/SONET uses one common standard that applies to net- works worldwide. SDH, originally defined by the European Telecommunication Standards Institute (ETSI) for Europe, is now the most common form, used every- where except for Japan and North America. Japan uses a version of SDH that varies slightly in some details. SONET is the American National Standards Institute (ANSI) standard, which is part of SDH, and it is used in North America. SDH/ SONET was created to be an industry standard for high-speed transmission over optical fiber. It was actually part of a much bigger standard in the works at that time-Broadband ISDN. Broadband ISDN was envisioned for use with advanced applications (e.g., tele-education, telesurveillance, telemedicine, the ability to col- laborate, HDTV). Two technologies were required in order to support such applica- tions: a transport infrastructure (SDH/SONET) that had the significant bandwidth needed to support the applications and a switching technology (ATM) that could ensure that latencies could be controlled and kept very low. Consequently, SDH/ SONET and ATM, as modern broadband technologies, were both born out of the