Telos Zephyr Xstream - Manual (Page 154)

USER’S MANUAL
Section 7: ISDN BASICS 142
7.4 Switched 56
Switched 56 is a transition technology, which is often available in areas of the USA & Canada
where ISDN is not available. As the name suggests, this is a service that permits a single bi‐
directional digital data stream to be sent at a 56kbps rate. It can use either one or two copper
pairs (“2 wire” and “4 wire”, respectively), depending upon the particular Central Office
configuration. Be sure to determine in advance which service will be provided.
Of course two Switched 56 circuits can be ordered, if transmission of stereo is desired.
In most areas, switched 56 and ISDN are “inter‐worked” within the Central Office switches, so
that subscribers of both services can connect to each other (at a 56kbps rate, of course).
The Xstream can be used with Switched 56 and other synchronous data services through the
optional V.35/X.21 interface and external CSU/DSU(s). We cover more about using the
V.35/X.21 interface to interface to Switched 56 CSU/DSUs in Section 9 (The V.35/X.21 Interface).