n and the channel group assigned in the controller configuration: interface Serial2/0/1:1 description T1 #1 ip address 10.220.110.1 255.255.255.252 interface Serial2/0/2:1 description T1 #2 ip address 10.220.120.1 255.255.255.252 interface Serial2/0/3:1 description T1 #3 ip address 10.220.130.1 255.255.255.252 interface Serial2/0/4:1 description T1 #4 ip address 10.220.140.1 255.255.255.252 You cannot create a serial interface larger than a T1 within a channelized DS3. If you need multimegabit speeds, you'll need to create multiple T1s, and either bundle them with Multilink-PPP or load-balance them using CEF or a routing protocol. This router (a 7304) has both channelized and clear-channel interface cards. When you do a show version on a router like this, the output can be confusing because the number of serial interfaces includes the clear-channel DS3s and any Tls you've configured from your channelized DS3s. This router contains four channelized DS3s and four clear- channel DS3s. If a channelized DS3 is not configured at the controller level, it does not appear in the output of the show version command. Because we have four clear-channel DS3s, which are serial interfaces by default, and we've configured 10 T1s to be serial interfaces out of one of the channelized DS3s, the router reports a total of 14 serial interfaces: 7304#sho ver [ Text Removed - ] 1 FastEthernet interface 2 Gigabit Ethernet interfaces 14 Serial interfaces4 Channelized T3 ports Configuring DS3s Here, we can see the individual serial interfaces on the router. Ten of them are logical (s2/0/1:1 - s/2/0/10:1), and four of them are physical (s3/1/0 - s3/1/3): - 7304#sho ip int brie Interface IP-Address OK? Method Status Protocol FastEtherneto unassigned YES NVRAM administratively down down GigabitEtherneto/a 10.220.11.1 YES NVRAM GigabitEthernet0/1 10.220.12.1 YES NVRAM Serial2/0/1:1 10.220.110.1 YES NVRAM up Serial2/0/2:1 10.220.120.1 YES NVRAM up Serial2/0/3:1 10.220.130.1 YES NVRAM up Serial2/0/4:1 10.220.140.1 YES NVRAM up Serial2/0/5:1 unass