To support higher port densities in a smaller form factor, Cisco has introduced a Smart Serial cable. Cisco devices support the EIA/TIA-232, EIA/TIA-449, V.35, X.21, and EIA/TIA-530 serial standards. The WAN provider or the CSU/DSU usually dictates this cable type. The other end of the serial transition cable is available with the connector appropriate for the standard that is to be used. The router end of the shielded serial transition cable may be a DB-60 connector, which connects to the DB-60 port on a serial WAN interface card.
The cable for the DTE to DCE connection is a shielded serial transition cable. With a null modem connection, the transmit (Tx) and receive (Rx) lines are crosslinked as shown in the figure. A null modem is a communication method to directly connect two DTEs, such as a computer, terminal, or printer, using a RS-232 serial cable. In other words, the two devices can be connected without a modem. However, if you want to connect two DTEs, such as two computers or two routers in the lab, a special cable called a null modem eliminates the need for a DCE. The original RS-232 standard only defined the connection of DTEs with DCEs, which were modems. Procedural - Specifies the sequence of events for transmitting data Mechanical/physical - Number of pins and connector typeĮlectrical - Defines voltage levels for 0 and 1įunctional - Specifies the functions that are performed by assigning meanings to each of the signaling lines in the interface
The DTE/DCE interface for a particular standard defines the following specifications: These reasons are no longer significant, but we are left with two different types of cables: one for connecting a DTE to a DCE, and another for connecting two DTEs directly to each other. In the development of the RS-232 standard, there were reasons why 25-pin RS-232 connectors on these two types of equipment needed to be wired differently. Originally, the concept of DCEs and DTEs was based on two types of equipment: terminal equipment that generated or received data, and communication equipment that only relayed data.
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