re usually not permitted to provide services between LATAs (interLATA), but could provide services within a LATA (intraLATA). 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. 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, bandwidth, 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 20-4 shows three locations: New York, Cleveland, and Los Angeles. There are two links: one T1 between New York and Cleveland, and one T1 between New York and Los Angeles. Both links have the same speed (1.54 Mbps), but it takes longer for packets to get from New York to Los Angeles than it does for them to get from New York to Cleveland. The discrepancy occurs because Los Angeles is a lot farther away from New York than Cleveland is. This form of latency is called propagation delay. Prop- agation delay is, to a large degree, a function of physics, and as such cannot be fixed, improved, or otherwise changed (no matter what your boss may want). To oversimplify, the speed at which electrons can transmit electrical impulses is limited. The speed at which photons can move in fiber is similarly limited. Processing delay Another form of latency is called processing delay, which is the time it takes for a device to process information. In contrast to propagation delay, which Chapter 20: Telecom Nomenclature New York Cleveland Angeles Figure 20-4. Different propagation delays usually cannot 