The Choice of Two Data Link Protocols
As mentioned earlier in this section, the two point-to-point
WAN data link protocols used most often are HDLC and PPP. Both protocols work
well but, of course, there are differences; otherwise, you wouldn't need both of
them. The most important things to remember about these two protocols are their
similarities:
-
You use HDLC and PPP on point-to-point WAN links.
-
You don't need to worry about data link layer addresses.
-
There's an FCS field so that the receiver can discard frames
that have errors.
The differences between the two protocols are mainly an
outgrowth of when they were created, with HDLC being defined by the ITU in the
1970s, and PPP being defined in RFC 1661 during the 1990s. As a simple result of
being designed later, PPP has several advanced features, some of which have to
do with security, as covered in Chapter
17, "Accepting the Right People and Rejecting the Wrong People." Cisco uses
a nonstandard version of HDLC, mainly to add features to the relatively old
HDLC. Because Cisco's HDLC implementation is proprietary, both routers on each
end of the link must be Cisco routers if you use HDLC. However, Cisco conforms
to the standard for PPP, so when you use PPP, you could have a Cisco router on
one end of a link, and another vendor's router on the other end of the
link.
Sections
Comments (0 posted)
Syndication
