can be deployed Traditional SONET Architectures at a building or at an intermediate location for consolidating traffic from widely separated neighborhoods. An ADM can also be configured as a sur- vivable ring. Drop and Repeat SONET enables drop and repeat (also known as drop and continue). With drop and repeat, a signal terminates at one node, is duplicated (repeated), and is then sent to the next node in the ring. The next node repeats this process. This is a useful capability in telephony, cable TV, and perhaps Ethernet applications. In high-availability applications, drop and repeat provides alternate routing for traffic passing through intercon- necting rings in a matched-node environment. If the connection cannot be made via one of the nodes, the signal is repeated and passed to the com- panion node; this node has an alternate route to the destination node. Broadband Digital Crossconnect (DXC) A SONET crossconnect device accepts various OC rates, accesses the STS-n signals, and switches the signals at this level. (It is the synchronous equivalent of a DS3 DXC and supports hubbed network architectures.) A key difference between a crossconnect and an ADM is that a crossconnect may be used to intercon- nect a much larger number of STS-n signals, whereas the latter typically only drops off a single STS-n. The broadband crossconnect can be used for grooming (consolidating or segregating) STS-n signals or for broadband traffic management. 3.2.4 Synchronization Traditionally, telco transmission systems have been asynchronous. This means that each device in the network runs on its own free-running clock.8 Because these clocks are not synchronized, variations occur in the clock rate; this in turn impacts the signal bit rate. For example, a DS3 signal specified at 44.736 Mbps +20 parts per million (ppm) can produce a varia- tion of up to 1,789 bps between one incoming DS3 and another. Traditional asynchronous multiplexing uses multiple stages. Signals such as asynchro- nous DS1s are multiplexed. Extra bits are added t