This is the timestamp, as a string up to 21 characters, recording when this specific switched virtual call's connection came up. An admin uses this to calculate how long a given active call has actually been connected, which is useful both for spotting an unusually long-lived call tying up node resources and for billing duration calculations. For example, a call whose ConnectionUPTime shows it's been up for many hours longer than typical for this type of traffic would be a candidate to investigate as a stuck or forgotten session.