MPICH-CM: A communication library design for a P2P MPI implementation. The paper presents MPICH-CM -- a new architecture of communications in message-passing systems, developed for MPICH-V -- an MPI implementation for P2P systems. MPICH-CM implies communications between nodes through special Channel Memories introducing fully decoupled communication media. Some new properties of communications based on MPICH-CM are described in comparison with other communication architectures, with emphasis on grid-like and volunteer computing systems. The first implementation of MPICH-CM is performed as a special MPICH device connected with Channel Memory servers. To estimate the overhead of MPICH-CM, the performance of MPICH-CM is presented for basic point-to-point and collective operations in comparison with MPICH p4 implementation.