ate is derived, namely, 56 kbps or 8000 X 7. Four subrate or submultiple data rates are also available: 2.4, 4.8, 9.6, and 19.2 kbps. However, when these rates are implemented, an additional bit must be robbed from the basic byte to establish flag patterns to route each substrate channel to its proper demultiplexer port. This allows only 48 kbps out of the original 64 kbps for the transmission of user data. The 48 kbps composite total may be divided into five 9.6-kbps channels, ten 4.8-kbps, or twenty 2.4-kbps channels, or two 19.2-kbps channels plus a 9.6-kbps channel. The subhierarchy of DDS signals is illustrated in Figure 10.19. 10.9.7.2 Transmitting Data on the Digital Network Based on CCITT Rec. V.110. This CCITT recommendation covers data rate adaption for standard rates up DATA COMMUNICATIONS Direction of transmission Serving central office* Customer premises Interoffice Intraoffice circuits circuits* Interface Interface Multiplex stage Customer Converts Converts loop DSO signal; Converts DS1 signal; signal customer duty cycle, signal to 64 kbps, intraoffice 1.544 Mbps, signal to bipolar format bipolar, DS0 signal format RZ signal required on to interoffice duty cycle, required at customer intraoffice duty cycle, DS1 signal RZ signal on loop service speed circuits NRZ signal Figure 10.19 Subhierarchy of DDS signals. Note: Inverse processing must be provided for the opposite direction of transmission. Four-wire transmission is used throughout. (From Ref. 19. Copyright American Telephone and Telegraph Company.) through 19.2 kbps by means of a two-stage process. It also includes adaptation for 48 kbps and 56 kbps to the 64 kbps E0 or clear DSO channel.¹3 13 In the two-step case, the first conversion is to take the incoming data rate and convert it to an appropriate intermediate rate expressed by 2k X 8 kbps, where k = 0, 1, or 2. The second conversion takes the intermediate rate and converts it to 64 kbps. Simple division of 64,000 bps by standard data rates shows that as a minimum, a lot of bit stuffing wou