Chapter Objectives

  • 9-1 Outline the purpose of backbone networks.
  • 9-2 Summarize the design and use cases of a metropolitan area network (MAN).
  • 9-3 Describe the features of private and public wide area networks (WANs) and the types of WAN connections, including leased lines, broadband, and wireless.
  • 9-4 Compare the features and benefits  software-defined wide area network (SD-WAN) with traditional WAN technologies such as MPLS in terns of cost, performance, reliability, and efficiency.
  • 9-5 Discuss best practices for troubleshooting common WAN scenarios.

Backbone Networks

We ended the last chapter with virtual local area networks, or VLANs. As you recall, a VLAN groups devices together logically on one or more LANs so that the LANs can communicate as if they are on the same physical network, regardless of their physical location. VLANs are used to improve network performance, security, and scalability by allowing network administrators to group hosts together based on their resource needs, traffic characteristics, or other criteria.

A backbone network interconnects lower-speed distribution channels or clusters of dispersed user devices, connecting multiple networks together, and allowing them to communicate and exchange information over its high-capacity connectivity infrastructure.

While VLANs and backbone networks are both used to connect multiple networks together, they serve different purposes. A backbone network provides for the exchange of information between different LANs or subnetworks. Backbone networks can tie together diverse networks in the same building, in different buildings in a campus environment, or over wide areas.

Types of backbone networks include distributed backbones and collapsed backbones. A distributed backbone is a backbone network that consists of a number of connectivity devices connected to a series of central connectivity devices, such as hubs, switches, or routers, in a hierarchy. The routing and switching functions are decentralized at each location. In the case of a collapsed backbone, each location features a link back to a central location to be connected to the collapsed backbone. The collapsed backbone can be a cluster or a single switch or router. The topology and architecture of a collapsed backbone is a star or a rooted tree.

Backbone networks are used to link LANs together and to link other backbone networks to WANs. They are designed to provide high-speed connectivity and to ensure that data is transmitted efficiently and reliably across the network. The choice of backbone architecture depends on the specific needs of the organization, the size of the network, and the types of applications that will be running on the network. Backbone networks are operated by large telecommunications companies, internet service providers, and other organizations, and provide the high-speed data links that enable data to be transmitted quickly and efficiently between different parts of the internet. 

Backbone architectures often include the following components.