In Packet Tracer this is how we draw a WAN link, or a T1 link:
Does the "red line" here literally means there is a single cable connecting the two routers in real life?
If no, then what are the exact devices and their topology in a T1 link?
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No. There may be a dedicated circuit between the routers and the nearest telco central office, but between offices they are switched and multiplexed onto other, higher capacity circuits.
Today, most T1 circuits are emulated over a packet-switched (IP) network. They are rapidly becoming obsolete, and are being replaced by SIP over the IP network.
Literally? No. Unless the devices were very close, it's very unlikely they would ever have been directly connected. Even 20-30 years ago, in the era of T1's, there were repeaters, digital cross-connects, and multiplexing into larger T-carriers.
As Ron has said, today the T1 is a relic. It will be emulated and carried as packets like every thing else "internet". In fact, the 4-wire T1 interface is all but extinct. Every T1 I've seen for decades is physically an HDSL circuit -- single pair to the smartjack where it becomes the 4-wire T1. At the CO, it's packetized and routed to the destination end, where the process is reversed -- fully (back to a 4-wire T1, like the two router example pictured), or partially (channelized high bitrate interface [T3, OC3, etc.])