Evolution of Enterprise WAN and SD‑WAN: Concepts, Scenarios, and Challenges

Abstract: This paper introduces the evolution of enterprise WAN technologies, SD‑WAN application scenarios and solutions, the current state of SD‑WAN, and its challenges. Keywords: WAN, SD‑WAN, broadband access, Internet Download link: "SD‑WAN Beginner's Guide"

1. Overview

Continuous growth of broadband access and Internet backbone capacity drives transformation of enterprise WAN technologies. Building on existing leased lines, SD‑WAN offers a low‑cost, rapid solution that is gaining industry attention. This article covers enterprise WAN evolution, SD‑WAN scenarios, solutions, current status, and challenges.

2. Evolution of Enterprise WAN Technologies

Traditional enterprise applications (e‑mail, file sharing, web apps) are centrally deployed, with data centers at headquarters connected to branches via leased carrier lines (SDH, OTN, Ethernet, MPLS, etc.). Carriers guarantee SLA metrics such as bandwidth, latency, jitter, and packet loss. Traditional leased lines suffer from poor accessibility, long deployment cycles, high cost, and inflexible ordering.

To improve utilization, WAN optimization and acceleration technologies (QoS flow control, TCP optimization, protocol proxy, caching, compression) emerged.

Figure 1: Traditional Enterprise WAN Network

With widespread Ethernet, carriers now offer Ethernet services (E‑Line, E‑Tree, E‑LAN) with more flexible bandwidth ordering. Carrier‑side SDN deployment (SDN controllers and orchestrators) further improves provisioning efficiency, as shown in Figure 2.

Figure 2: Carrier SDN‑WAN Network

Internet capacity continues to grow, making branch‑to‑headquarter connectivity over the public Internet feasible and cost‑effective. Internet links (xPON, xDSL, Ethernet) cost roughly one‑third to one‑half of MPLS and have shorter provisioning cycles. Enterprises can connect headquarters and branches via the Internet (Hybrid‑WAN), as illustrated in Figure 3.

Figure 3: Hybrid‑WAN Network

With mobile work and cloud adoption, enterprise traffic patterns shift dramatically toward public cloud services (Office 365, Salesforce, Skype for Business, Box, off‑premise storage). Cloud traffic traverses the Internet, where quality cannot be guaranteed, potentially degrading user experience.

Figure 4: Enterprise Applications on Public/Private Cloud

SDN concepts have permeated the ICT sector and are now being applied to enterprise WAN, giving rise to SD‑WAN.

Virtual WAN

Virtual WAN leverages existing public WAN (Internet, LTE, public WLAN) to create a private WAN for enterprises, reducing capital and operational expenses compared with traditional MPLS connections.

Key considerations for Virtual WAN include:

Security – traffic traverses public networks, so SSL/TLS encryption is used to protect data.

Performance – Internet bandwidth may not match MPLS QoS; aggregating multiple Internet links and dynamic load‑balancing mitigates this.

Stability – public networks are less stable; multi‑link aggregation and load‑balancing improve reliability.

SD‑WAN

SD‑WAN builds on Virtual WAN and adds an overlay layer. Its four core functions are:

Multi‑connectivity support (MPLS, frame‑relay, LTE, public Internet, etc.).

Dynamic path selection for load‑balancing and elasticity.

Centralized management interface (controller‑based policy, monitoring, CLI/GUI).

Integrated services such as VPN, firewall, gateway, and WAN optimization.

Typical SD‑WAN operation routes critical traffic (e.g., VoIP) over MPLS while sending less‑sensitive traffic (e.g., file transfers) over Internet, and can use Internet as a backup for MPLS failures.

SD‑WAN Products

SD‑WAN can be delivered as physical appliances, virtual instances, or WAN‑as‑a‑Service (WaaS). Devices are placed alongside or replace WAN edge routers, ensuring all branch traffic passes through the SD‑WAN layer. Cloud‑based SD‑WAN deployments are increasingly common.

Two main vendor models exist: (1) appliances (dedicated or integrated into existing hardware) and (2) WaaS providers that supply both the WAN transport and SD‑WAN functionality. Aryaka, for example, operates a global WAN with 26 points of presence, offering sub‑30 ms latency for 95 % of enterprises and reducing deployment time from months to hours, cutting costs by over 50 %.

According to a 2017 Q1 report, Viptela held 21 % of the SD‑WAN market, while VeloCloud held 14 %.

Related Technologies

Comparisons with adjacent technologies help clarify SD‑WAN's value:

Hybrid WAN – uses multiple WAN links (MPLS + Internet) without software‑defined control; SD‑WAN adds centralized control and intelligent routing.

WAN Optimization – focuses on improving data transfer efficiency over existing links; can be combined with SD‑WAN.

WAN Edge Router – traditional routers may embed SD‑WAN functions; newer vendors provide dedicated SD‑WAN appliances.

MPLS – provides guaranteed QoS; SD‑WAN can complement or replace MPLS for less‑critical traffic.

NFV – network functions virtualization enables SD‑WAN to host VPN, firewall, and optimization VNFs.

SDN – SD‑WAN shares the software‑defined principle but operates at the WAN edge rather than the data‑center core.

3. SD‑WAN Use Cases and Solution Analysis

SD‑WAN addresses three primary scenarios: Hybrid‑WAN, public‑cloud access, and BYOD. A typical Hybrid‑WAN deployment introduces a centralized controller that manages branch CPE devices, automates configuration for both Internet and leased‑line links, and provides real‑time WAN monitoring and intelligent routing.

Figure 5: Hybrid‑WAN Scenario

New CPE devices can be plug‑and‑play, automatically connecting to the SD‑WAN controller and receiving configuration. Cloud‑based value‑added services (e.g., security, optimization) can be delivered from edge cloud nodes.

Figure 6: Cloud‑Based Value‑Added Services Deployment

4. SD‑WAN Current Status and Challenges

IDC predicts SD‑WAN can reduce WAN costs by at least 20 % and that the market will exceed $6 billion by 2020. Gartner lists SD‑WAN as a hot technology expected to see large‑scale commercial adoption within 2‑5 years.

Operators (e.g., DT, Verizon, SingTel, NTT) are piloting SD‑WAN services, leveraging their data‑center and edge‑cloud resources to offer firewall, acceleration, and security as value‑added services. Third‑party providers also build their own WAN backbones and sell SD‑WAN as a service.

The market is fragmented, with no unified standards, making vendor selection difficult. SD‑WAN solutions are primarily optimized for Hybrid‑WAN; integration with existing LAN, data‑center, and private‑cloud environments remains a challenge, as does the need for unified operations and monitoring systems.

5. Conclusion

Increasing Internet and backbone capacity is reshaping the traditional WAN market. SD‑WAN provides a rapid, low‑cost deployment model that is gaining traction among enterprises and carriers. Ongoing innovation makes SD‑WAN an attractive arena for startups, and open, interoperable solutions are a key focus for all stakeholders.

Download link: "SD‑WAN Beginner's Guide"