Those are SFP slots for gigabit optical links. They're Ethernet, but they require an SFP plug-in module typically used for a fiber-optic connection
Two of them are shared with the two copper RJ-style gigabit interfaces, in other words you can use a copper UTP connection to the conventional plug, or an optical SFP plug-in module, but not both.
The other two are stand-alone gigabit modules for optical Ethernet links.
There are a number of SFP modules available for different types of fiber-optic cables, and there's even a RJ-style SFP if you need four gigabit copper connections. These aren't for T-1 connections, however.
The 1234 switch has very limited IP routing capability and doesn't support T1 connections.
The 1335 series switch/router has a NIM slot capable of accepting a variety of modules including those that will support one or two T1 lines as well as full router/firewall/VPN functionality. This would be a good choice for an integrated 24-port switch, router, firewall, and NAT appliance in a 1U space.
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