Thedefacto standard Application Program Interface （API） for TCP/IP applications is the “so

ckets” interface. Although this API was developed for __（71）__ in the early 1980s it has also been implemented on a wide variety ofnon-Unix systems。 TCP/IP __（72）__ written using the sockets API have in the past enjoyed a high degreeof portability and we would like the same __（73）__ with IPv6 applications。 But changes are requiredto the sockets API to support IPv6 and this memo describes these changes。These include a new socket address structure to carry IPv6 __（74）__，new address conversion functions，and some new socket options。These extensions aredesigned to provide access to the basic IPv6 features required by TCP and UDPapplications，including multicasting， while introducing aminimum of change into the system and providing complete __（75）__ for existing IPv4 applications。

A.Windows

B.Linux

C.Unix

D.DOS@@@SXB@@@A.applications

B.networks

C.protocols

D.systems@@@SXB@@@A.portability

B.availability

C.capability

D.reliability@@@SXB@@@A.connections

B.protocols

C.networks

D.addresses@@@SXB@@@A.availability

B.compatibility

C.capability

D.reliability