What is a WAN? Wide-area network definition and examples

WANs connect smaller networks across long distances, and their architecture, protocols and technologies have evolved to their latest incarnation, SD-WAN.

Wide-area networks: What WANs are and where they’re headed

If it weren't for wide-area networks (WAN) it wouldn't be possible to telecommute, to create unified networks for organizations with far-flung locations, or to do online anything. But WANs do exist, constantly evolving to carry more and more traffic faster as demands increase and technology becomes more powerful.

What is a WAN?

A WAN is a computer network that uses various links-private lines, Multiprotocol Label Switching ( MPLS ), virtual private networks ( VPNs ), wireless ( cellular ), the Internet-to connect smaller campus and metropolitan area networks in diverse locations into a single, distributed network covering a large geographical area. The sites could be a few miles apart or halfway around the globe. Enterprise uses of a wide area network include connecting regional and branch offices and individual remote workers with centralized resources.

WANs vs. LANs: What's the difference?

A WAN is often contrasted with a local area network or LAN. LANs are networks generally limited to a single building or small campus. Your home Wi-Fi network is a LAN.

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The technologies and protocols that make LANs easy to set up don't scale beyond a certain limited distance or to truly massive numbers of endpoints. Dealing with those scales is the purpose of a WAN: connecting one or more LANs. The networking technologies and protocols a wide area network uses to transmit information are different from those used within a local area network.

When we talk about WANs, we usually mean private or semi-private networks connecting far-flung LANs. Branch offices in different cities might share private internal corporate resources over a WAN, for instance.

WAN architecture

While LANs are usually maintained by an organization's own IT staff, WANs are often at least in part reliant on physical connections provided by telecommunications carriers. Decisions on what kind of connections or communications protocols to use and how to deploy them will guide the creation of your WAN architecture.

WAN protocols

Today, multi-protocol label switching is used to carry much corporate data across WANs. Within an MPLS network, brief header segments called labels allow MPLS routers to decide quickly where to forward packets and to treat them with the class of service indicated by the labels. This makes it possible to run different protocols within MPLS packets while giving different applications appropriate priority as traffic travels between sites.

Internet protocol (IP), which became more ubiquitous in the 1990s, is one protocol commonly carried within MPLS.

Other protocols popular earlier include X.25, frame relay and ATM.

X.25 uses packet-switching exchanges (PSE) for the hardware that drops traffic onto the wires connecting sites. It includes standard-sized packets delivered in order and includes error correction.

Frame relay cuts data into different-sized frames and leaves error correction and retransmission of missing packets up to the endpoints. These differences speed up the overall data rate. Because it is a switched service, it can save money by using fewer circuits.

Asynchronous Transfer Mode (ATM) is similar to frame relay with one big difference: it uses standard-sized packets called cells, making it possible blend multiple classes of traffic onto a single physical circuit and guarantee qualities of service. The downside is ATM is inefficient because cells are relatively small so their headers eat up about 10% of the cell.

Types of WAN connections

Initially, WANs were built with meshed webs of private lines bought from telecommunications carriers, but now packet-switched services such as MPLS, frame relay and ATM dominate. Using a single WAN connection to a site, a service-provider can connect it to many other sites via switching within the carrier's network. For certain types of traffic, the internet can also be woven into the mix to provide less expensive WAN connections.

What is tunneling? What is a VPN?

WAN connections that operate over the internet or some other public network generally use a technique known as tunneling. In a tunneled connection, the private-network data and protocol information are encrypted and encapsulated in IP packets that are routed over the open internet. When those packets arrive at the destination, the IP headers are stripped away, the payload is decrypted and private-networking features come back into play.

The most common tunnel is the virtual private network ( VPN ). VPN connections encrypt data in order to keep it private as it travels over public networks. VPN s are frequently used to allow home office workers to connect to private corporate WANs.


WANs today may use multiple types of connections and protocols simultaneously, which adds complexity. As a result, the use of software-defined technology to manage WANs is gaining momentum. Software-defined WAN (SD-WAN) takes software-defined networking concepts, and brings the to the WAN.

SD-WAN software monitors the performance of all WAN connections-MPLS, dedicated circuits, the internet-and chooses the most appropriate connection for each traffic type. So teleconferencing might run over a dedicated circuit, but email might use the internet. In making its decisions, SD-WAN software takes into account how well each link is performing at the moment, the cost of each connection, and the needs of each application.

Initially SD-WAN aimed at creating hybrid WANs and using policies to mix MPLS and internet connections in order to improve efficiency and lower costs. SD-WAN connections proved invaluable as office workers scattered to their homes during the coronavirus pandemic, and the market is expected to increase by 168% by 2024 , according to the Dell'Oro Group.

A subset of SD-WAN called SD-Branch is helping reduce the need for hardware within branch offices. Offerings from big vendors including Aruba and Juniper can replace many physical devices with software running on off-the-shelf servers. Mobile backup across an SD-WAN can provide a failover for broadband connections as wireless WAN technology (4G, LTE , 5G , etc.) costs decrease.

WAN management and optimization

Because data transmission still relies on the rules of physics, the greater the distance between device A and device B, the longer it takes for data to travel between them. Network congestion and dropped packets can also introduce performance problems.

Some of this can be addressed using WAN optimization, which makes data transmissions more efficient. WAN links can be expensive, so technologies have sprung up that reduce the amount of traffic crossing WAN links and ensure it arrives efficiently. These WAN optimization methods include abbreviating redundant data (known as deduplication), compression, and caching (putting frequently used data closer to the end user).

Traffic can be shaped to give time-sensitive applications such as VoIP a higher priority over other, less urgent traffic such as email, which in turn helps improve the overall WAN performance. This can be formalized into quality-of-service settings that define classes of traffic by the priority each class receives relative to others, the type of WAN connection that each traffic type will travel, and the bandwidth that each receives.

Once a separate category, WAN optimization is being absorbed by SD-WAN.

WAN security

A WAN connection represents a potential vulnerability that an attacker could use to gain access to a private network. A virtual private network (VPN) overlaying the underlying physical network can provide security including authentication, encryption, confidentiality, and non-repudiation.

In addition to networking features, many SD-WAN offerings provide security services as well, which need to be kept top of mind during deployment.

History of WANs

WANs have been around since the early days of computer networks. WANs were based on circuit-switched telephone lines and modems but now connectivity options also include leased lines, wireless, MPLS, broadband internet, and satellite.

As technologies changed, so did transmission rates. The early days of 2400bps modems evolved to 40Gbps and 100Gbps connectivity today. These speed increases have allowed more devices to connect to networks, enabling the explosion of connected computers, phones, tablets, and smaller connected devices that make up the Internet of Things.

In addition, speed improvements have allowed applications to utilize larger amounts of bandwidth, enabling videoconferencing and large-file data backup.

Interplanetary internet

WAN technologies aren't just limited to Earth. NASA and other space agencies are working to create a reliable "interplanetary internet," which aims to transmit test messages between the International Space Station and ground stations. The Disruption Tolerant Networking (DTN) program is the first step in providing an internet-like structure for communications between space-based devices, including communicating between the Earth and Moon, or other planets. But barring any dramatic breakthroughs in physics, network speeds would likely top out at the speed of light.

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