In Mobility Load Balancing (MLB) as part of Self-Optimization feature of SON, there is the 'X2 Resource Update Response' and Update messages that come from eNB 2, when eNB1 sends an 'X2 Resource Update Request' message. As part of this message, S1 Transport Network Layer (TNL) Load indication is indicated. Standard says the implementation of this is vendor-dependent . So, what does S1 TNL Load indicate? Is it related to S1-U load?