asppp supports asynchronous communications only. Solaris PPP 4.0 supports both asynchronous communications and synchronous communications.
Setting up asppp requires configuring the asppp.cf configuration file, three UUCP files, and the ifconfig command. Moreover, you have to preconfigure interfaces for all users who might log in to a machine.
Setting up Solaris PPP 4.0 requires defining options for the PPP configuration files, or issuing the pppd command with options. You can also use a combination of both the configuration file and command-line methods. Solaris PPP dynamically creates and removes interfaces. You do not have to directly configure PPP interfaces for each user.
Solaris PPP 4.0 features not available from asppp
MS-CHAPv1 and MS-CHAPv2 authentication
PPP over Ethernet (PPPoE), to support ADSL bridges
Data compression that uses Deflate or BSD compress
Microsoft client-side callback support