Table 3.1 (continued)
GUIDELINES AND
PRINCIPLES DESCRIPTION
Layering Considered Harmful The optimization for each layer must be done
separately. Introducing extra layers can lead to
violation of the simplicity principle and add
inefficiency caused by duplication of functions, such
as error control. See the section, “Middle-Age
Symptoms of the Internet,” later in this chapter.
Optimization Considered Optimization introduces complexity and tighter
Harmful coupling between components and layers, and
leads to less reliable systems.
Feature Richness Considered Feature richness in the network increases system
Harmful complexity and, therefore, has a higher risk for
failures and the certainty for higher cost.
Transport Efficiency for IP IP, Frame Relay, ATM, SONET and WDM are
examples of inefficiency often found in carrier
networks, without even mentioning cases of double-
layering (such as IP, ATM, and SONET).
Avoiding Interworking Interworking functions between networks increase
Functions complexity and degrade performance.
Avoid control plane interworking, such as that
between ATM and MPLS.
The payload of IP packets should (where possible)
be transmitted without modification.
IP is Quite Complex Packet switching may not be simpler than circuit
switching, and IP routers can be quite expensive.
Where possible, lower-layer switching (Ethernet)
and optical switching may be preferable.
The Myth of Overprovisioning Overprovisioning of IP networks that keeps
utilization under 50 percent is not much worse than
the efficiency of TDM networks, assures good
network performance, and can be considered a 1:1
protection service at the IP layer.
Quality of Service QoS is deployed when there is insufficient
bandwidth to support traffic. Packet drop may have
a more severe impact on TCP traffic than on voice.
QoS is better assured by avoiding congestion than
by complex software.46 Chapter 3