Specifications

Table Of Contents
3-4
Cisco AS5800 Operations, Administration, Maintenance, and Provisioning Guide
DOC-7810814=
Chapter 3 Operations
Verifying Modem Performance
EIA/TIA-232 in Cisco IOS Software
The Cisco IOS software variation of asynchronous EIA/TIA-232 is shown in Figure 3-3. The variation
exists between the Cisco IOS line (DTE) and the NAS modem (DCE).
Six EIA/TIA-232 pins exist between each NAS modem and Cisco IOS line. One or more grounding
wires also exist on physical EIA/TIA-232 lines; however, these wires do not convey signaling.
Each pin controls a different EIA/TIA-232 signal.
The arrows in Figure 3-3 indicate the signal transmission direction.
Figure 3-3 Cisco IOS EIA/TIA-232
Tips In Figure 3-3, notice that the DSR signal is the DCD signal for the modem. In the scheme
of Cisco IOS software, the DCD pin on the DCE is strapped to the DSR pin on the
Cisco IOS DTE side. What the Cisco IOS software calls DSR is not DSR; it is DCD. The
DCEs actual DSR pin and ring ignore (RI) pin are ignored by the Cisco IOS software.
Table 3-1 describes how Cisco uses its EIA/TIA-232 pins. The signal direction in the table is from the
perspective of the DTE (IOS line):
Data signals (TxD, RxD)
Hardware flow control signals (RTS, CTS)
Modem signals (DTR, DSR, DCD, RI)
33178
TxD
RxD
RTS
CTS
DTR
DCDDSR
RI
DCE
(NAS modem)
DTE
(IOS line)
Inside a Cisco
network access server