load area. As we continue our examination of the STS-1 frame, we note how certain bytes within the section overhead area func- tion as pointers to the actual location of a frame within the payload area shown in Figure 6.5. When illustrated in two dimensions, note that each row contains a series of 90 bytes, with the overhead repeating every 90 bytes. The STS-1 frame is depicted in two dimensions as nine rows, each containing 90 bytes. This is because the STS-1 frame is 810 bytes in length. This frame repeats at the 8000 frame-per-second rate of both T1 and E1 carriers. Thus, 810 bytes/frame X 8000 frames/s results in a line operating rate of 51.84 Mbits/s. In examining Figure 6.5, note that the first three columns in each row represent overhead. Thus, the actual gross payload of an STS-1 frame row/column Figure 6.5 Two-dimensional Section depiction of the STS- Overhead 1 frame. Gross Payload Area Overhead byte order of transmission row 1, columns 1 through 90, row 2, columns 1 through 90, row 9, columns 1 through 90, row 1, columns 1 through 90, Fiber in the WAN becomes 783 bytes/frame X 8000 frames/s X 8 bits/byte, or 50.112 Mbits/s. As we will note below, there are nine path overhead bytes that float within the gross payload area. Thus, the net payload is 774 bytes/frame X 8000 frames/s X 8 bits/byte or 49.536 Mbits/s. This net payload capacity is sufficient to transport a T3 or even an E3 payload. However, to do SO SONET uses special overhead bytes, referred to as payload pointers, which indicate where the payload begins within the SONET frame. This use of pointers permits different types of payloads to literally float within the frame to an applicable position. Through the use of pointers individual DS1 frames can be synchronized, permit- ting SONET frames to be synchronized and providing for the "S" in the acronym SONET. OVERHEAD As indicated in Fig. 6.5, the first three columns of each STS-1 frame are used for section layer and line layer overhead. The remaining 87 bytes in each row represent a gross payloa