In LTE, a default EPS bearer is automatically established as part of the attach procedure, giving every connected UE an always-on IP data path. This is a fundamental shift from 3G, where the user had to explicitly activate a PDP context before data could flow. The default bearer creates a logical tunnel stretching end to end from the UE through the eNodeB and SGW all the way to the PGW, where the UE receives its IP address. This tunnel uses GTP (GPRS Tunneling Protocol) on both the S1-U and S5 interfaces.