be changed, processing delay is a function of the speed of the equipment in use. Figure 20-5 shows two links: the top link is a direct connection between two modern Cisco 7609 routers, involving only the latest hardware; the bottom link connects the same two routers, but with a very old Cisco 2501 router in the middle. Although the total distance between the two Cisco 7609s is the same from point to point in both cases, adding a Cisco 2501 in the middle of the second link increases the processing delay dramatically. Another example of increasing processing delay occurs when you're using multilink PPP. Taking three 1.54 Mbps T1s and bonding them to form one logical 4.5 Mbps link sounds great, and it can be, but the added processing delay when you do SO can be enormous. As an example, notice the delay parameter in this show interface output from a T1 interface: Router#sho int s0/1 I inc DLY MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, Compare that with the output from the same show interface command for a multilink interface: Router#sho int multilink 1 I inc DLY MTU 1500 bytes, BW 100000 Kbit, DLY 100000 usec, The delay for a multilink interface is five times that of a serial T1 interface. Telecom Glossary Cisco 7609 Propogation delay about the same Cisco 7609 Cisco 2501 Cisco 7609 Cisco 7609 Added latency in the form of processing delay Figure 20-5. Processing delay The bandwidth and delay values shown for an interface are repre- sentative of the actual bandwidth and delay, provided they have not been modified. The bandwidth and delay values are configu- rable in IOS. The default values reflect the propagation delay well enough to illustrate the impact of multilink PPP. LEC (pronounced leck) is short for local exchange carrier. A LEC is a phone com- pany that provides local service, as opposed to an IXC, which interconnects LECs to provide long-distance service. Most of the largest LECs are RBOCs. Local loop The local loop (also referred to as the last mile) is the copper handoff for a circuit from the telecom fa