y 30 of them are used for the transport of E-Os. The remain- ing 2, occupying the sixteenth and thirty-second time-slot positions, are used for the transport of signaling and for synchronization of the E-1 frame, respectively. Both DS-1s and E-1s can be further multiplexed up to higher bit rates. The DS pro- tocol hierarchy is shown in Table 13.2. 3 The European E-0 links are similarly grouped into their higher-rate packages, as shown in Table 13.3. 4 Alas, these are not compati- ble with the North American standards. 3The DS-0 channel can be one voice channel, one 64-kbps data channel, or even a collection of subrate channels. 4Both DS-2 and E-2 links exist in the world of telephony specifications, but like the L-2, neither is used in practice. In all three cases, the leap is from 1 to 3. 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. Telephone Transport Key Telephony Concepts TABLE 13.2 North American Digital Service Transport Protocols Signal Speed Channels 64 kbps 1.544 Mbps 44.736 Mbps 274.176 Mbps 13.2 Wireless System Transport Wireless systems have their own specific transport needs both within a single mobile switching center (MSC) service area and between or among MSC regions. Now that we have explained the fundamentals of telephone transport, let us look at the four kinds of telephone transport in a wireless telephone system: from the base station to the MSC, signaling using ANSI-41, MSC to MSC, and from the MSC to the PSTN. 13.2.1 Base station to MSC (backhaul) Base-station-to-MSC transport is outside the realm of conventional telephony for sev- eral reasons: The voice channels use low-bit-rate speech coding. The voice channels use nonstandard data rates. A single pipe carries voice and data connections with differing rates. This transport network has many thin pipes. The network grows by adding nodes and pipes to those nodes, not