Information Technology Reference
In-Depth Information
Task 2: Cable the Serial Link Between the R1 and R2 Routers
In a real-world WAN connection, the customer premises equipment (CPE), which is often a router, is
the data terminal equipment (DTE). This equipment is connected to the service provider through a
data communications equipment (DCE) device, which is commonly a modem or channel service unit
(CSU)/data service unit (DSU). This device is used to convert the data from the DTE into a form
acceptable to the WAN service provider.
Unlike the cables in the academy lab setup, the serial cables in the real world are not connected back
to back. In a real-world situation, one router might be in New York, while another router might be in
Sydney, Australia. An administrator located in Sydney would have to connect to the router in New
York through the WAN cloud to troubleshoot the New York router.
In the academy labs, devices that make up the WAN cloud are simulated by the connection between
the back-to-back DTE-DCE cables. The connection from one router serial interface to another router
serial interface simulates the entire WAN cloud.
Create a null serial cable to connect the R1 router to the R2 router.
Step 1.
In the academy labs, the WAN connection between routers uses one DCE cable and one
DTE cable. The DCE-DTE connection between routers is referred to as a null serial cable.
The labs will use one V.35 DCE cable and one V.35 DTE cable to simulate the WAN con-
nection. The V.35 DCE connector is usually a female V.35 (34-pin) connector. The DTE
cable has a male V.35 connector. The cables are also labeled as DCE or DTE on the router
end of the cable.
The DTE and DCE V.35 cables must be joined. Holding one of the V.35 ends in each
hand, examine the pins and sockets as well as the threaded connectors. Note that there is
only one proper way for the cables to fit together. Align the pins on the male cable with
the sockets on the female cable and gently couple them. Very little effort should be
required to accomplish this. When they are joined, turn the thumbscrews clockwise and
secure the connectors.
Connect the DCE end of the null serial cable to the Serial 0/0/0 interface of the R1 router,
and the DTE end of the null serial cable to the Serial 0/0/0 interface of the R2 router.
Step 2.
Review the following information before making these connections.
Before making the connection to one of the routers, examine the connector on the router
and the cable. Note that the connectors are tapered to help prevent improper connection.
Holding the connector in one hand, orient the cable and router connecters so that the
tapers match. Now push the cable connector partially into the router connector. It probably
will not go in all the way because the threaded connectors need to be tightened for the
cable to be inserted completely. While holding the cable in one hand and gently pushing
the cable toward the router, turn one of the thumbscrews clockwise, 3 or 4 rounds, to start
the screws. Now turn the other thumbscrew clockwise, 3 or 4 rounds, to get it started. At
this point, the cable should be attached sufficiently to free both hands to advance each
thumbscrew at the same rate until the cable is fully inserted. Do not overtighten these con-
nectors.
