Hello Luis
First of all, it is important to understand what it is that specific terms are referring to. Some terms refer to a specific technology, others to the physical infrastructure, and others to Datalink (Layer 2) or even Network (Layer 3) functionalities, but all are involved, in some way, with the WAN.
The term WAN is most often used for two things.
- It refers to the connection to the Internet from the enterprise network
- It refers to the network that connects remote sites
Now the various terms that you have mentioned in your post exist at different layers of the OSI model, so some of these may actually co-exist in a particular implementation. I’ll try to clarify the role of each one below.
Physical WAN connections, like all network connections, can take one of three forms: copper, fiber, or wireless. Strictly on the physical layer, for each of these we have:
Copper
- Physical layer - typically two-wire connections come into the customer premises, although eight wire UTP connections are rare but not unheard of. Coaxial cable is also prevalent. Technologies that typically use copper include xDSL, Cable (DOCSIS) and Serial.
Fiber
- Physical layer - Fiber Optic cables can be terminated on the customer premises. These cables are most often single mode fibers that employ Dense Wavelength Division Multiplexing (DWDM) which is strictly a physical layer technique for fiber optic cables, that allows multiple carrier signals to run over a single fiber, thus increasing data capacity.
Wireless
- Physical Layer - Technologies such as microwave, Wi-MAX, and broadband cellular are all physical layer wireless technologies that use different frequencies and encoding techniques.
The Data Link layer is a place where some more commonly heard WAN terms live. These are technologies which, with very few exceptions, can run over any of the above physical layer WAN infrastructures. These include:
- Ethernet - Even though Ethernet was designed to be a LAN technology, it is so well designed, that it has the flexibility to be expanded into a WAN technology. Specifically, Metro Ethernet is the “type” of Ethernet that is used for WAN. Metro Ethernet can run over copper, fiber, as well as wireless technologies.
- PPP is typically used over, and has traditionally been associated with, a serial connection. But PPP is used over many types of physical networks including serial cable, phone lines, trunk line, cellular telephone, specialized radio links, and fiber optic links such as SONET. Its authentication mechanisms are used especially for xDSL and Cable (and dialup in the past) in specific arrangemements such as PPPoE. For more info about PPPoE, take a look at the related lesson.
- Frame Relay is a Layer 2 technology that can run over various types of physical infrastructure, but most commonly over copper. It is most often used to interconnect remote sites, rather than connect a site to the Internet.
- ATM was developed for high speed transfer of video, voice, and data, but never took off.
Somewhere between the Data Link and Network Layers, is MPLS. This is a technology primarily used to interconnect remote sites. It can run over various combinations of physical and data link layer technologies.
At the Network layer we have technologies such as DMVPN which is essentially a technology that allows for a hub and spoke topology over any combination of the above mentioned WAN technologies.
Are there any other WAN technologies? The only ones I can think of at this time are X.25, ISDN, dialup, and satellite.
VoIP doesn’t need a particular WAN technology to function, its primary requirement is a steady rate of transmission, something that can be achieved over any WAN technology, as long as QoS mechanisms are employed. Fiber channel storage across WANs can use what is called Fiber Channel over IP to overcome the distance limitations that fiber channel has. FCoIP can be routed over any WAN technology described above. More about this can be seen at RFC3821
I hope this has been helpful!
Laz