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It is also possible to use MPLS for many other purposes as well.
It can be used to perform fast restoration of MPLS forwarding paths, e.g., to reroute traffic over
a precomputed failover path in response to link failure [Kar 2000; Huang 2002; RFC 3469]. Finally,
we note that MPLS can, and has, been used to implement so-called virtual private networks
(VPNs).
In implementing a VPN for a customer, an ISP uses its MPLS-enabled network to connect together
the customer’s various networks. MPLS can be used to isolate both the resources and addressing
used by the customer’s VPN from that of other users crossing the ISP’s network; see [DeClercq
2002] for details. Our discussion of MPLS has been brief, and we encourage you to consult the
references we’ve mentioned.
We note that MPLS rose to prominence before the development of software-defined
networking, and that many of MPLS’ traffic engineering capabilities can also be achieved via SDN
and the generalized forwarding paradigm.
Only the future will tell whether MPLS and SDN will continue to co-exist, or whether newer
technologies (such as SDN) will eventually replace MPLS.

Introduction
We’ll begin by keeping our discussion general enough to cover a wide range of networks,
including both wireless LANs such as Wi-Fi and 4G and 5G cellular networks; we’ll drill down into
a more detailed discussion of specific wireless architectures in later sections.
We can identify the following elements in a wireless network:

• Wireless hosts. As in the case of wired networks, hosts are the end-system devices that run
applications.
A wireless host might be a smartphone, tablet, or laptop, or it could be an Internet of Things (IoT)
device such as a sensor, appliance, auto mobile, or any other of the myriad devices being
connected to the Internet. The hosts themselves may or may not be mobile.
• Wireless links.

A host connects to a base station (defined below) or to another wireless host through a wireless
communication link. Different wireless link technologies have different transmission rates and
can transmit over different distances. link transmission rates and coverage ranges, of the more
popular wireless network standards.

(The figure is only meant to provide a rough idea of these characteristics.

For example, some of these types of networks are only now being deployed, and some link rates
can increase or decrease beyond the values shown depending on distance, channel conditions,
and the number of users in the wireless network.)

We’ll cover these standards later in the first half of this chapter; we’ll also consider other
wireless link characteristics (such as their bit error rates and the causes of bit errors)

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