The 1900 series switch supports only Inter-Switch Link (ISL) trunking. The 2900 series switch supports both ISL and Dot1Q trunking. The 2950 series switch supports only Dot1Q trunking.
1900 Series Switch
2900 Series Switch
Trunking can only occur on a Fast Ethernet port. A 1900 series switch has only two Fast Ethernet portsports A and B. These are defined as fa 0/26 and FA 0/27 in the command-line interface (CLI).
For any series switch, you must set trunk mode at both ends of the link for the trunk to become active.