1. Multiplexors
   • Function: Enable multiple signals to be sent out over a single physical circuit, optimizing the use of available bandwidth.
2. WAN Switches
   • Function: Multi-port networking devices used in carrier networks to connect private data over public data networks using digital signals.
   • Layer: Operate at the Data Link Layer.
3. Access Servers
   • Function: Provide dial-in and dial-out connections to the network, facilitating remote access for users.
4. Modems
   • Function: Transmit data over telephone lines, converting digital signals into analog signals and vice versa for communication.
5. Channel Service Unit (CSU) / Data Service Unit (DSU)
   • Function: Digital interface devices used to terminate the physical interface on a DTE (Data Terminal Equipment) device, connecting to the closest telephone company switch in a central office (CO).

These hardware components play critical roles in managing and facilitating network operations, especially in environments requiring efficient data transmission and connectivity.