T1/E1 ports on the 4-port T1/E1 and RS-232 Combination module (supported on the 7705 SAR-H) support channelization down to the DS0 level. To change port types, all ports must first be shut down. The ports can be configured for DS1 (T1) or E1 operation. All ports on the module must be either T1 or E1; there cannot be a mix of the two types. When the first port is configured on a module, all other ports on the card must be set to the same type.