Providing ubiquitous connectivity to the passengers of public transportation vehicles is an important goal of the communication system designers in the context of fast development of the intelligent transportation systems and of Future Internet communication technologies. Efficient usage of transmission resources available in the heterogeneous networking environment, characteristic to today's wireless networks, and effective routing over these networks with minimal involvement of the operator's core networks are some of the requirements for a fast and cost effective deployment. This paper proposes the architecture of an ubiquitous connectivity system for public transportation, the architecture design being considered on three distinct levels: system, functional and platform level. The proposed system architecture specifies a minimal set of entities required to implement envisaged connectivity solution and based on a functional analysis the subsystems and modules are derived. By mapping the functional architecture on the hardware components intended to be used the platform architecture is developed.