Differences Between SLIP and PPP
While we've said that SLIP and PPP are largely similar, there are some
key differences. PPP is a newer protocol, better designed, and more
acceptable to the sort of people who like to standardize protocol
specifications. More information about PPP can be found in the PPP FAQ.
Multi-Protocols
PPP has some additional benefits. Unlike SLIP (which can only transport
TCP/IP traffic), PPP is a multi-protocol transport mechanism. This means
that PPP not only transports TCP/IP traffic, but can also transport
IPX and Appletalk traffic, to name just a few. Better yet, PPP lets you
transport all of these protocols at the same time - on the same
connection.
This is often not a concern for most users since their purpose of either
using SLIP or PPP is to connect to the internet and the internet uses
TCP/IP only. Therefore, there is no need to transport other protocols.
Configuration Negotiation
With SLIP, you have to know the IP address assigned to you by your service
provider. You also need to know the IP address of the remote system you
will be dialing into. If IP addresses are dynamically assigned (depends on
your service provider), your SLIP software needs to be able to pick up the
IP assignments automatically failing which you have to setup them up
manually. You may also need to configure such details as MTU (maximum
transmission unit), MRU (maximum receive unit), use of VJ compression
header (ie., CSLIP), etc. All these can get confusing pretty fast.
PPP addresses this problem by negotiating configuration parameters at the
start of the connection. This can greatly simplify the configuration of
your PPP connection.
Automatic Login
Most SLIP/PPP software can dial-up and automatically login for you.
However, they often depend on your service provider's system sending out
standard prompts (eg, "login:" to get the login name and "password:" to
get the password). If they are any way non-standard, you either need to
write a script to automate the login process yourself or login manually
in the terminal emulation mode of your SLIP/PPP software.
PPP provides two methods with which logins can be automated - PAP
(Password Authentication Protocol) and CHAP (Challenge-Handshake
Authentication Protocol). Both provide the means for your system to
automatically send your login userid/password information to the remote
system.
Putting it all together...
The most significant advantage PPP can offer is the automatic login and
configuration negotiation. With these features, your PPP software only
needs to know your login userid/password and the telephone number of
your service provider. The software can then dial-up into your service
provider and figure out everything else on its own.
At this present point in time, PPP is generally not as widely available
as SLIP. It should gain more acceptance in the time to come, but in the
meanwhile, don't worry if you can only use SLIP. Once connected, PPP
doesn't give you more of the internet than SLIP already can.
One last note: Some users believe SLIP is faster because the protocol format
calls for a packet size that is 3 bytes smaller than a PPP packet. In
practice, this difference is too small to be of any significance. See
Morning Star's write-up on SLIP
vs PPP Performance Comparison.
[Previous] [Next]