For those of you just starting out in the field of network administration, the wide area network (WAN) can be a confusing area. Understanding the various methods, protocols and costs involved in setting up a WAN isn't easy. In this blog, I'll describe the five most popular WAN connectivity options. I'll note the differences between the various choices and explain why you might choose one option over another in certain situations.
Connecting remote sites using dark fiber provides the greatest amount of flexibility and control. The term dark fiber essentially means fiber optics that have been run, but aren't currently in use. If, as an organization, you own the dark fiber between remote sites, this is an ideal situation as it provides completely private transport using whatever speeds you can run given the type of cabling between the two sites. However, if you don't own the fiber running between two locations, it's possible that a carrier or municipality has dark fiber that you can lease. Just keep in mind that the cost to lease fiber is usually more expensive than any other WAN option available today. So it's typically only leased when speed and security are of utmost importance.
Multi-Protocol Label Switching (MPLS) is a widely used WAN solution that intelligently routes packets through a service provider network using a four-byte MPLS header that uniquely identifies each customer. MPLS allows customers to forgo complex WAN routing and quality of service (QoS) policies and instead places that burden on the service provider. From the customer's perspective, you simply need to route the appropriate internal networks across the link.
Carriers typically offer several throughput options, often ranging from 1 Mbps for very small sites all the way up to thousands of Mbps. MPLS provides dedicated and symmetrical bandwidth, which includes strict service-level agreements to ensure you're getting what you pay for. MPLS supports point-to-point and point-to-multipoint depending on your traffic-flow needs. MPLS also scales tremendously well and can stretch the globe. So, if you have a large WAN that spans multiple geographical regions and require dedicated throughput and latency times, MPLS is likely a great option as long as you can afford it.
If your remote sites are in a relatively close proximity, then your carrier may offer Metro Ethernet as a cheaper option compared to MPLS. But as the name implies, the service is limited to specific geographic regions. So, if your remote site falls outside of the Metro Ethernet boundary, you're going to have to look at a different WAN connectivity option. Metro Ethernet is scalable up to hundreds of remote sites although not as scalable as MPLS, which can easily handle thousands of sites. Metro Ethernet also is tremendously easy to manage as the carrier's handoff looks and acts just like a standard Ethernet link on your LAN.
Carriers typically offer various throughput options, often ranging between speeds a low as 5 Mbps all the way up to gigabit speeds. Since Ethernet operates at layer 2 of the OSI model, you can use your own IP space for routing purposes. This is also true for QoS as you can simply extend your internal LAN QoS policies across Metro Ethernet. From a data transport point of view, all sites look as if they are connected to the same Ethernet switch inside the service provider cloud. Therefore, all sites are on a single multi-access network and each site can communicate directly with all others on the WAN.
Some organizations may choose to leverage lower cost broadband Internet connectivity and then create a secure overlay using some form of VPN technology. Broadband connectivity could be wired such as DSL or cable, or it could be wireless such as 3G/4G or satellite internet services. While the cost savings compared to other WAN options are great, the primary disadvantage is that you have no control over latency or QoS. Therefore, if you need to transmit/receive latency-sensitive data across your WAN, you may have to look at other leased services or leverage SD-WAN technologies combined with multiple broadband connectivity options to intelligently choose the fastest path from point A to point B. In terms of broadband throughput, there are usually several options from which to choose. One thing to watch for is whether your bandwidth is symmetrical or asymmetrical in nature.
If you have a WAN site in a remote location, geography may limit your WAN connectivity choices.. If that's the case, your best bet might be to utilize a legacy T1 that provides a dedicated, point-to-point connection at symmetric 1.5 Mpbs up/down speed. If that's not enough, your telco may offer the option to bond multiple T1's together to provided added throughput. The cost of legacy T1s have gone down somewhat over the past decade, but they are still far more expensive compared to broadband and in many cases comparable Metro Ethernet options. So, choose the T1 only as a last resort when no other WAN connectivity options are available.