 entire T1 or E1 network for frame alignment loss, 4 HP stands for Hewlett-Packard, a well-known manufacturer of electronics test equipment. HP spun off the test equipment line to Agilent Technologies. NETWORK MANAGEMENT errored seconds, and severely errored seconds. One can "look" at each link and examine its performance in 15-minute windows for a 24-hour period. The Newbridge equipment can also monitor selected other data services such as frame relay, which, in our example above, rides on E1 aggregates. Such equipment can be a most important element in the network management suite. The E1 digital network hierarchy also provides capability of in-service monitoring and test. We remember from Chapter 8 that E1 has 32 channels or time slots: 30 are used for the payload and 2 channels or time slots serve as support channels. The first of these is channel (or time slot) 0, and the second is channel (time slot) 16. This latter is used for signaling. Time slot (channel) 0 is used from synchronization and framing. Figure 21.2 shows the E1 multiframe structure. The sequence of bits in the frame alignment (TSO) signal of successive frames is illustrated in Figure 21.2. In frames not containing the frame alignment signal, the first bit is used to transmit the CRC multiframe signal (001011) that defines the start of the sub-multiframe (SMF). Alternate frames contain the frame alignment word (0011011) preceded by one of the CRC-4 bits. The CRC-4 remainder is calculated on all the 2048 bits of the previous sub-multiframe (SMF), and the 4-bit word is sent as C1, C2, C3, C4 of the current SMF. Note that the CRC-4 bits of the previous SMF are set to zero before the calculation is made. At the receive end, the CRC remainder is recalculated for each SMF, and the result is compared with the CRC-4 bits received in the next SMF. If they differ, then the checked SMF is in error. What this is telling us is that a block of 2048 bits had one or more errors. One thousand CRC-4 block error checks are made every second. It should be noted t