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Wide Area Network - What is a WAN?

A Wide Area Network (WAN) connects smaller networks over large distances. Its architecture, protocols and technologies are constantly evolving - to its latest manifestation, the Software Defined WAN.


Without Wide Area Networks (WAN), telecommunications as we know it today would be impossible. There would be neither uniform networks for companies with widely scattered locations nor the possibility to communicate with each other via video calls. But fortunately there are WANs, which have been constantly developed for decades to meet the demands for ever more and, above all, faster data traffic.

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Wide Area Network - Definition and History

A wide area network is a network that uses various channels such as closed direct connections, multiprotocol label switching (MPLS), virtual private networks (VPNs), wireless networks and the Internet to connect smaller local networks into a single network. The sites that a wide area network connects can be a few kilometres apart or scattered halfway around the globe. In companies, a WAN can be used to connect branches all over the world, as well as individual employees, with the head office or data centre in order to share company resources and communication.

Wide Area Networks have been around since the beginning of computer networks. Wide Area Networks used to be based on telephone lines and modems until they were replaced by today's connectivity options such as leased lines, wireless, MPLS, broadband internet and satellite. As the technologies changed, so did the transmission rates. The initial 2400 bit/s modems have now become 40 Gbps and 100 Gbps lines. These speed increases have allowed more and more devices to connect to networks, enabling the explosion of connected devices. This ranges from computers, phones and tablets to machines, home appliances and millions of sensors and devices in the Internet of Things (IoT).

In addition, speed improvements have meant that applications can use greater bandwidth to transmit large amounts of data at high speeds over WANs. This has enabled businesses to hold video conferences and run large backups over the network. No one would have thought of holding a video conference over a 28 kbps modem, but now employees can sit at home and participate in global company meetings via video.

WAN vs. LAN - differences

A wide area network is often compared to a local area network (LAN). LANs are networks that usually cover a single building or a small campus. They are limited to a single organisation or even person and can already be set up with relatively inexpensive means, such as a Wi-Fi router. Your Wi-Fi network at home, for example, is a LAN.

However, the technologies and protocols that LANs use are limited in terms of distance as well as the number of endpoints. So WANs were created because of the technical limitations of LANs, to connect small networks across larger geographical distances. Another difference to Local Area Networks are the network technologies and protocols that Wide Area Networks use to transmit information.

Strictly speaking, the internet is a WAN. However, when we talk about Wide Area Networks, we usually mean private or semi-private networks that connect LANs that are distant from each other. For example, branch offices of companies in different cities can share internal company resources via a WAN. While LANs are usually built and maintained by a company's own IT staff, wide area networks often rely, at least in part, on external physical connections provided, for example, by telecommunications providers. Deciding what type of connections or communication protocols to use and how to deploy them is critical to building the WAN architecture.

Wide Area Network - Protocols

Let's start with Wide Area Network protocols - the rule sets that define network communications over a WAN. One of the first protocols used to carry WAN traffic is X.25, which uses Packet Switching Exchanges (PSE) for the hardware that distributes traffic onto the lines between sites. It includes standard packets that are delivered in a specific order and include error correction. Physical connections include leased lines, telephone dial-up services or ISDN connections. However, X.25 is almost no longer used today.

Frame Relay is a successor to X.25. The protocol divides the data into frames of different sizes and leaves the error correction and retransmission of missing packets to the endpoints. This speeds up data throughput. Frame Relay also requires fewer dedicated connections to create distributed networks. This means fewer physical circuits, saving companies money. Frame Relay, while once popular, has largely disappeared from the scene.

Asynchronous Transfer Mode (ATM) is similar to Frame Relay, but has one big difference: data is divided into packets of standard sizes called "Cells". These cells make it possible to mix different types of traffic on a single physical line while ensuring good quality of service. The disadvantage of ATM is that due to the use of relatively small cells, the headers, i.e. the description of the content, take up a relatively large proportion of the total volume of transmissions. Therefore, the overall bandwidth utilisation of ATM is less efficient than that of Frame Relay. ATM is also rather unpopular with business users.

Today, Multi-Protocol Label Switching is used to transmit a lot of enterprise data over wide area network links. Within an MPLS network, short header segments called labels allow MPLS routers to quickly decide where to forward packets. In addition, labels are used to define a specific class of service, which further increases the efficiency of timely distribution. In this way, it is possible to run different protocols within MPLS packets while giving appropriate priority to different applications. The Internet Protocol (IP), which became ubiquitous in the 1990s, is a protocol that is often carried in MPLS.

All of these protocols operate over different types of network connections. Originally, WANs were built with linked networks of direct lines purchased from telecommunications providers. However, wide area network architectures have since evolved to include packet-switched services. This allows a single connection to a site to switch between many different service provider networks. These types of connections provide direct communication paths between different LANs. This brings speed and security - but it is not cheap. For certain types of traffic, the internet can also be woven into the mix to provide cheaper WAN connections.

WAN and SD-WAN - Tunneling and VPN

Wide-area network connections that run over the Internet or another public network use a technique called tunneling. In such a tunneled connection, the transmitted data and protocol information are encrypted and encapsulated into IP packets that are routed over the open Internet. When these packets arrive at the destination LAN, the IP headers are removed, the data is decrypted and the usual network features come back into play. From the point of view of the LAN users at both ends, the packets behave as if they were travelling over a private WAN. The name for this technique comes from the metaphorical tunnel through which the private data packets travel.

The most commonly used "tunnel" is the Virtual Private Network. VPN connections encrypt data to keep it secret as it travels over public networks. VPNs are often used to provide home office employees with a secure connection to private company networks. A VPN user's internet traffic is routed through the WAN network to which they are connected. This allows the user to receive an IP address that does not correspond to their actual physical location. This makes VPNs a popular tool for streaming content whose use may be geographically restricted.

Today's wide area networks can use multiple types of connections and protocols simultaneously, but this also adds complexity. Therefore, the use of software-defined technology to manage WANs is becoming increasingly important. Software-defined WANs (SD-WAN) use software concepts for building a wide area network that are based on decoupling the physical data plane from the control and management plane. In particular, they transfer the decoupling of the control plane from the data plane to the WAN.

SD-WAN uses special software to continuously monitor the performance of mixed wide area network connections - MPLS, dedicated circuits, Internet - and select the most appropriate connections for each type of traffic. For example, video conferencing can run over a high-bandwidth dedicated line, while email is sent over the Internet. In making its decisions, the SD-WAN software takes into account how well each connection is performing at the moment, the cost of each connection and the requirements of each application, for example in terms of response times or data throughput.


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Originally, SD-WAN aimed to create hybrid wide area networks and mix MPLS and internet connections using policies to increase efficiency and reduce costs. The next phase of development is to improve management and monitoring and provide more security, according to Lee Doyle of Doyle Research. SD-WAN connections proved essential when workers were sent to the home office during the coronavirus pandemic in 2020/2021. Due to the high demand for SD-WAN connections, Dell'Oro Group expects this market to grow 168 per cent by 2024.

A subset of SD-WAN, called SD-Branch, is expected to help reduce the need for hardware in corporate offices. Offerings from major vendors such as Aruba and Juniper can replace many devices with software running on commodity servers. Mobile backup over an SD-WAN can provide failover for broadband connections as the cost of wireless wide area network technology (4G, LTE, 5G, etc.) comes down.

Wide Area Network - Management and Security

Since data transmission is still subject to the rules of physics, the greater the distance between two devices, the longer the data transmission takes. The greater the distance, the greater the delay. Network congestion and packet loss can also cause performance problems.

Some of these problems can be solved by wide area network optimisation, which makes data transmission more efficient. This is important because WAN links can be expensive. Because of these high costs, technologies have emerged to reduce the amount of traffic over WAN links and ensure that it arrives efficiently. These optimisation methods include filtering out redundant data (known as deduplication), compression and caching (storing frequently used data closer to the end user).

Traffic can be prioritised so that time-critical/essential applications such as VoIP are given higher priority than other, less urgent data such as email. This prioritisation can be captured in quality-of-service settings. The settings define, for example, the priority of data classes, the type of wide area network connection, and the bandwidth each class receives.

Traffic between WAN sites can be protected by VPNs, which provide underlying physical network security through, authentication, encryption, confidentiality and reliability of information. In general, security is a critical component of any wide area network deployment, as any WAN connection is a potential vulnerability. A potential attacker could use the wide area network to gain access to a corporate network. Especially in branch offices of companies, the issue of security is often treated somewhat stepmotherly. As a result, a hacker who has penetrated the branch office network could gain access to the company's main WAN - including the data treasures located there.

WAN Future - Interplanetary Internet

Wide-area network technologies are not limited to Earth. NASA and other space companies are already working to create a reliable "interplanetary internet" to transmit test messages between the ISS and ground stations. The Disruption Tolerant Networking (DTN) programme is the first step in creating an internet-like structure for communication between devices in space. This includes communication between Earth and the Moon as well as communication between other planets. But unless there is a dramatic breakthrough in physics in the near future, network speeds will probably end up at the speed of light. (ba/fm)

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