Many envisioned applications of ad hoc networks involve only small scale networks that we term Vicinity Ad-hoc Groups (VAGs). Distributed coordination services, instead of pairwise communications, are primary requirements of VAGs. Existing designs for distributed services in ad hoc networks apply either a layered structure or a vertical integration. While the former approach is efficient for protocol development, the latter improves runtime efficiency. In this paper, we argue that, since distributed services require group-oriented communications, both design and runtime efficiency of protocols can be achieved in VAGs, provided that a dedicated network layer service is designed in place of unicast routing protocols. Based on these arguments, we propose NASCENT as a general network layer service for VAGs. NASCENT provides a light-weight VAG membership management along with a routing structure for message passing, and supports concurrent execution of various distributed algorithms. NASCENT is also tailored to cope with the transiency of VAGs. We demonstrate how smoothly distributed algorithms can be built on top of NASCENT. With a complexity-based analysis, we also show that NASCENT greatly improves the runtime efficiency of these distributed algorithms. Finally, through simulations with ns-2, we confirm the ability of NASCENT to support the envisioned VAG applications.