TCP and IP are STREAMS modules in the Solaris 7 system. The command strconf < /dev/tcp shows you all the modules. STREAMS is not supported in SunOS 4 system TCP/IP.
Solaris 7 system DLPI provides both connection-oriented and connectionless services, and multicast features. See the dlpi(7P) man page.
IP multicast is a standard supported feature in the Solaris 7 system. In the SunOS 4 system, multicasting is not supported. But, it is available using anonymous FTP from gregorio.stanford.edu in the file vmtp-ip/ipmulti-sunos41x.tar.Z.
IP is a STREAMS module in the Solaris 7 system, and any module or driver interface with IP should follow the STREAMS mechanism. There are no specific requirements for the interface between IP and network drivers.