8
CSU/DSU MS/DBU
2.3 Introduction to 4-Wire Switched 56
This dial-up 4-wire Digital Data Service allows customers to pay for data
connection only for the time the unit is active. The regional operating
companies provide the 4-wire local loop service to SW56 customers. Switched
56 service is supplied by AT&T, U.S. Sprint, and other interexchange carriers.
In SW56 mode, the CSU/DSU MS/DBU supports DTE rates of 2.4, 4.8, 9.6,
19.2, 38.4 (asynchronous or synchronous), and 56 Kbps (synchronous). The
additional DTE rate of 57.6 Kbps is available in async modes.
2.4 The Front Panel
Fig. 2-1. CSU/DSU MS/DBU Front View.
The Light Emitting Diodes (LEDs) are identified as follows:
• RS—Request to Send
• CS—Clear to Send
• TD—Transmit Data
• RD—Receive Data
• CD—Carrier Detect
• ALM—Alarm Indication
• TST—Test Mode
CSU/DSU MS/DBU
RS
CS
TD
RD
CD
ALM TST
SHIFT
D
A
E
B
QUICK
F
C
7
4
1
ENTER
CANCEL
8
5
2
9
6
3
0
#
*
Summary of Contents for CSU/DSU MS/DBU
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