U1911: small and medium-sized branches, providing services for less than 100 users.
U1960: local access gateway in midsize branches, providing services for 300–1000 users.
U1980: Works as a voice PBX in large-sized enterprises or as a local access gateway
in large-sized branches, providing services for 1000–10000 users.
U1981: Works as a voice PBX in large-sized enterprises or as a local access gateway in large-sized branches, providing services for 1000–20000 users.
