background image
A Comparison of WAN Options 591
The product selection phase on any design project can and should necessarily include key
individuals from the organization that will be purchasing or leasing the hardware, Cisco (or the
reseller), and any contracted service companies participating in the future deployment of the
new equipment. (Some of you probably fall into each of those categories, and possibly into
several.) When choosing products, having the vendor or reseller involved can help avoid the
problem of trying to be aware of all possible products and options, particularly for new or
impending products.
To combat some of the challenges of choosing products from a widely varied product line,
Cisco developed the use of three key words to describe the type of product deployed in a typical
enterprise network: Core, Distribution, and Access. Figure 8-32 provides a basic network, and
Table 8-34 summarizes the meaning behind these three categorizations.
Table 8-33
Comparison of Leased Versus Packet Switching
Type of WAN
Service
Data Link
Protocols
Strengths and Weaknesses
Leased
Delivers pervasive availability. Can be expensive for long
circuits. Is more expensive for providers to engineer than are
packet services.
PPP
Can improve speed of routing protocol convergence. Allows
multivendor interoperability. Has available error recovery
option.
HDLC
Is the IOS default. Requires Cisco router on each end.
LAPB
Provides error recovery, but this also can result in throttling
(slowing) the data rate.
Packet-switched
Allows addition of new sites to be made quickly. Typically
involves a lower cost.
Frame Relay
Allows bursting past CIR, giving perception of "free"
capacity. Is pervasive in the United States.
ATM
As a WAN technology, is not as pervasively available as
Frame Relay. Has an attractive built-in Quality of Service
feature.
X.25
Is available pervasively in some parts of the world. Offers
beneficial error-recovery features when links have higher
error rates. Typically is the third choice of these three if all
are available to all connected sites.
ch08.fm Page 591 Monday, March 20, 2000 5:17 PM