Network Warrior

Configuring DS3s

Recall that there are two flavors of DS3: clear-channel and channelized. Typically, clear-channel DS3s are used for data links, and channelized DS3s are used for voice links. The configurations in this section assume an integrated CSU/DSU in all cases. If you have an older router that requires an external CSU/DSU, you'll probably have a High-Speed Serial Interface (HSSI—pronounced hissy), which still looks like a serial interface within IOS. The difference will be that you cannot configure framing on a HSSI port. Additionally, because the CSU/DSU (which counts and reports these errors) is an external device, you won't be able to see DS3 errors on a HSSI port.

Clear-Channel DS3

Configuring a clear-channel DS3 is a pretty boring affair. Specify the framing with the framing interface command, then configure the interface like any other serial interface:

interface Serial3/1/0
 description DS3
 ip address 10.100.100.100 255.255.255.252
 framing c-bit

Showing the status of the interface is done the same as for any other interface. The errors and counters are generic, and not DS3-specific:

7304#sho int s3/1/0 Serial3/1/0 is up, line protocol is up Hardware is SPA-4XT3/E3 Description: DS3 Internet address is 10.100.100.100/30 MTU 4470 bytes, BW 44210 Kbit, DLY 200 usec, reliability 255/255, txload 1/255, rxload 1/255 Encapsulation HDLC, crc 16, loopback not set Keepalive set (10 sec) Last input 00:00:02, output 00:00:01, output hang never Last clearing of "show interface" counters ...