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About Your DSU
1-33550-A2-GB20-10 February 1995
2-Port TDM/Flex
The 2-port TDM/Flex is a separate circuit card that
attaches to the Model 3550 DSU. It allows independent
ports to share one standard digital point-to-point facility.
The 2-port TDM/Flex provides the following features:
• Port capacity. This feature permits the DSU to
operate as a digital sharing device and provides two
independent ports. Port 1 is on the DSU and Port 2
is on the 2-port TDM/Flex. Either port can operate
as an EIA-232 or V.35 interface.
• Multiplexing. With this option, time division
multiplexing can be performed using two
independent ports to share one standard DDS
point-to-point circuit.
• Line speeds. The TDM/Flex operates at all line
speeds supported by the DSU: 2.4, 4.8, 9.6, 19.2,
38.4, and 56 kbps. For LADS operation, 64 kbps is
also supported.
• Port speeds. Each port can be set to 1.2, 2.4, 4.8,
9.6, 14.4, 19.2, 48, 56, or 64 kbps. In 2-port
TDM/Flex applications, the sum of the port speeds
cannot exceed the line speed.
• Asynchronous operation. Although the DSU
provides synchronous transmission through the
DDS network, any port can be configured for
asynchronous operation. When the 2-port
TDM/Flex is installed, asynchronous-to-
synchronous conversion can be performed.
Asynchronous data rates of 150, 300, 600, 1200,
and 1800 bps are supported, along with the
synchronous data rates.
• Digital sharing. With this feature, the ports can
share the same channel. All ports in a
digital-sharing group operate at the same speed, and
all receive the same data. When configured for
DSD (digital-sharing device) port contention, only
one port at a time is allowed to send.
• Elastic store per port. A transmit elastic store
buffer is provided for each port for the support of
extended circuits. Both digital and analog
extensions are supported.
• Switched-carrier emulation. In 2-port TDM/Flex
transmission, switched-carrier emulation is optional
for each port, for both the inbound (toward the
control DSU) and outbound (from the tributary
DSU) directions.
• NMS control. Control of a 3550 DSU with 2-port
TDM/Flex can be performed from a 6700 Series
NMS or the DSU’s DCP.
• Point-to-point backup. A 3550 DSU with 2-port
TDM/Flex can also have a DBM installed for
point-to-point dial backup. If backup is at a
different speed than the DSU’s speed, TDM/Flex
operation automatically changes to the lower
speed.
Upgrades Available
Although your DSU may not currently have a DBM or
2-port TDM/Flex installed, you can add these features at a
later time. Both the DBM and 2-port TDM/Flex features
are available as upgrades.
You can order the option you want and install it
yourself (referred to as a field installation). Refer to the
Equipment List in Appendix F for the feature number to
order.
Technical Specifications
Tables 1-1 through 1-4 list the technical specifications
for the following:
• General specifications that apply to all Model 3550
and 3551 circuit cards (Table 1-1)
• Specifications for the Model 3550 and 3551 DSU
only (Table 1-2)
• Specifications for the V.32 DBM (Table 1-3)
• Specifications for the 2-port TDM/Flex
1-4