The Future Railway Mobile Communication System (FRMCS) represents a critical replacement of the current Global System for Mobile Communications-Railway (GSM-R) system, transitioning the GB rail network to a future-proofed, 5G-enabled communications platform. This migration will strengthen mission-critical voice and data capabilities, whilst supporting existing operational railway systems. FRMCS rollout will comprise three core technical aspects: 1.Trackside civils - potentially 4,000 - 5,000 masts (including some potential re-use of existing GSM-R masts) and associated infrastructure 2.Train fitment - radio and associated equipment on all trains across the network 3.FRMCS active network - Core, RAN etc. Trackside civils is a critical focus area for FRMCS delivery & Network Rail is therefore issuing this Request for Information (RFI) to engage with the supply chain and inform potential future procurement of FRMCS trackside civils infrastructure. Please note that any content received via response to this RFI will be used for information purposes only and will not be deemed as forming part of any proposed bid now, or any potential future tender.