tands for interexchange carrier. An IXC is a telephone company that sup- plies connections between local exchanges provided by local exchange carriers. Connecting between LATAs may involve IXCs. J-carrier The J-carrier hierarchy is much closer to the U.S. T-carrier hierarchy (in terms of speed) than the European hierarchy, though the values change as the rates get faster. While J-carrier circuits may still be seen, most of the circuits I've worked on in Japan have actually been Els or T1s. The Japanese J-carrier hierarchy is shown in Table 19-3. Table 19-3. Japanese J-carrier hierarchy Designator Transmission rate Voice channels 64 Kbps 1.544 Mbps 6.312 Mbps 32.064 Mbps 397.200 Mbps 5,760 LATA (pronounced lat-ah) is short for local access and transport area. LATAs are geographically defined areas in which a telecom provider can provide local service. The Regional Bell Operating Companies (RBOCs), for example, were usually not permitted to provide services between LATAs (inter-LATA), but could provide services within a LATA (intra-LATA). LATAs come into play when point-to-point circuits like T1s are ordered. When a T1 starts and ends within the same LATA, the cost for the circuit is usually much lower than if the circuit starts in one LATA and ends in another. This is because IXCs must be involved to connect LATAs. To further complicate things, LATAs are geographic, and often do not mirror political boundaries such as county or state lines. Chapter 19: Telecom Nomenclature Latency Latency is the term used to describe the amount of time it takes for data to be processed or moved. Latency has nothing to do with the throughput, band- width, or speed of a link. Latency has to do with distance, the speed of light, and the amount of time it takes for hardware to process data. Latency on networks links is a combination of propagation delay and processing delay: Propagation delay Figure 19-4 shows three locations: New York, Cleveland, and Los Angeles. There are two links: one T1 between New York and Cleveland, and one T1 