Orbitor 3000 Reference Manual— 3-1
Section 3 — Link Interfaces Reference
Pinout Information
Each link interface available is described with detailed information on pin designation. Standard interface cables will
provide correct connections to modems, datasets, or DSU/CSUs.
V.35 links are provided as DB25 connectors on the back of the bridge/router, so an interface converter is needed to
convert to the standard V.35 connectors.
When connecting two bridge/routers back-to-back without modems, a null-modem cable is required to crossover the pins
on the links. Crossing over the pins allows two bridge/routers both configured as DTE interfaces to be connected
together. With this configuration, both bridge/routers will provide clocking for the links, and each bridge/router must
have a link speed defined.
Link Clocking Information
All of the link interfaces on the Orbitor act as DTE devices, this means that they may be directly connected to DCE
devices (modems, etc.) with the DCE devices providing the clocking for the link. The link speed is controlled by the
DCE device. Setting the link speed on the Orbitor will not result in a speed change on the link.
Some DCE devices allow the DTE devices connected to them to supply a clock signal which is then routed back to the
transmit clock pins on the DCE interface. This clock is then received by the Orbitor link interface. By using this
method, the Orbitor may be in control of the link speed. The link speed may also be controlled by the Orbitor when a
null-modem cable is used to connect two Orbitors in a back-to-back configuration.
Changing the link speed within the menu system of the Orbitor changes the clock output speed that is generated on the
DTE Terminal Timing pins on the link interfaces.
CSU/DSU Link Module Information
The CSU/DSU link module is normally configured to receive clock from the connected network. When two CSU/DSU
link modules are to be used on a leased line in a back-to-back set-up, one of the modules must provide the clock.
Switch number 1 determines whether the CSU/DSU link module will generate clocks or receive clocks. When switch 1
is down, the normal position, the module receive clocks from the connected network. When switch 1 is up, the module
will generate clocks. When a pair of Orbitor bridge/routers are connected back-to-back with CSU/DSU link modules one
module must be set to generate clocks and one module must be set to receive clocks.
On 64 Kbps units only, switch number 3 determines the mode of the CSU/DSU. When switch 3 is down, the CSU/DSU
is in DDS (Digital Data Service) mode for normal connection to the 64 Kbps digital service. When switch 3 is up, the
CSU/DSU is in LDM (Limited Distance Modem) mode for back-to-back connection with a null-modem cable.
Figure 3—1 Rear View of CSU/DSU Link Module
