on of spaces will result in a loss of synchronization. With no marks in the signal, the receiving end will eventually lose track of where bits begin and end. The risk of an all zeros signal exists, SO AMI sets every eighth bit to a 1, regardless of its original value. This ensures there are enough signal transitions in the line (i.e., that the ones density of the signal stream is sufficiently high to ensure synchronization). As few as 16 zeros in a row can cause the remote end to lose synchronization. Voice signals can easily absorb having every eighth bit set to 1. The human ear can't hear the difference if a single bit in the stream is changed. Data signals, though, can- not tolerate having any bits changed. If one bit is different in a TCP packet, the Cyclic Redundancy Check (CRC) will fail, and the packet will be resent (CRCs are not performed for UDP packets). Because of this limitation, AMI is not an accept- able encoding technique for use on data T1s. B8ZS encoding was introduced to resolve the shortcomings of AMI. The idea behind B8ZS is that if eight zeros in a row are detected in a signal, those eight zeros are converted to a pattern including intentional BPVs. When the remote side sees this well-known pattern, it converts it back to all zeros. Encoding Figure 20-3 shows how long strings of zeros are converted on the wire. The top sig- nal consists of a one, followed by nine zeros, then three ones. B8ZS takes the first eight zeros and converts them to a pattern including two BPVs. This pattern would not be seen on a normal, healthy circuit. When the remote side receives the pattern, it converts it back into eight zeros. This technique allows data streams to contain as many consecutive zeros as necessary while maintaining ones density. Nine spaces (zeros) 10000000011 Original signal B8ZS converted signal 1011011011 Bipolar violation Bipolar violation Figure 20-3. B8ZS zero substitution Framing Phone audio is sampled 8,000 times per second (i.e., at 8 kHz). Each sample is con- verted to an 8-bit value, wi