  The networking community continues to create new technologies and update
existing ones to improve the quality, reliability, and "tailorability" of data
networks. However, whenever Internet service providers attempt to productize
"tailorability" and sell it explicitly to end customers as a premium service
over best effort connectivity, they either fail to overcome net neutrality
concerns or struggle to gain market traction. For this article, we focus only
on those networking protocols, technologies, or standards whose goal is to
offer tailored connectivity to paying customers on a public network and refer
to them as differentiated QoS (D-QoS) standards. This article makes two
contributions. First, it explores the techno-economic market trajectory of
D-QoS standards to understand the factors that determine success. In doing
this, we acknowledge that while there is wide variation and dissimilarity in
their underlying technical properties, the expectation and goal for all D-QoS
standards is that they will be used to provide guaranteed connection for which
customers could be prepared to pay. As such, we consider Layer 2/3 technologies
(e.g., ATM, frame relay, MPLS), signaling technologies (e.g., RSVP), data
packet markers (e.g., IP ToS, DiffServ, WME, QCI), and end-to-end separation
solutions (e.g., leased lines, network slicing) as a single cohort and analyze
them together. Second, by exploring the parallels with 5G network slicing, we
argue that despite its inherent technical differences with other D-QoS
standards, the commercial performance of network slicing may end up resembling
that of previous D-QoS standards. Consequently, we seek to learn lessons from
previous D-QoS attempts and suggest that enterprise-focused 5G slices, running
within a single service provider's domain and with binding service level
agreements, will have the highest chance of success in the short/medium term.
