Timing Options
Timing Option Descriptions
D-4
SpectraComm 553 Fractional T1 DSU
076R155-000
Installation and Operation Manual
Issue 7
Internal Timing
With Internal Timing, illustrated in
, the SC 553 CSU/DSU provides the send timing
source
(1)
for T1 data output from the transmit buffer
(2)
to the network. This clock satisfies the
requirements of a Stratum 4, Level II clock, as defined in AT&T Technical Reference 62411. The
remote CSU/DSU uses this as its timing reference and loops it back to the local CSU/DSU. The
local CSU/DSU recovers the receive T1 clock from the network receive T1 data and uses it to clock
T1 data into the receive buffer
(3)
. The CSU/DSU also translates
(4)
the receive T1 clock to provide
the channel transmit and receive clock signals on the appropriate interface leads for each channel.
Select Internal Timing when using the SC 553 CSU/DSU in a private network that does not provide
timing (e.g., a non-DACS based service).
Figure D-2
Internal Timing
Note
A.Configure only one CSU/DSU in your network for Internal Timing, and configure the others
for Slave Timing.
B.Select the appropriate timing option for the customer equipment: The CSU/DSU provides
transmit timing on the channel's Tx Clk lead.
Receive
Buffer
Transmit
(Send)
Buffer
SC553 CSU/DSU
Network Receive T1 Data
Clock
Translator
CH. Receive Data
CH. Rcv Clk
Network Send T1 Data
Recovered
Receive
T1 Clock
CH. Send Data
CH. Tx Clk
S1
Timing
Source
1
3
2
4