The rules in the WAN Router

Standards and protocols or the main function of the WAN is operating at the physical layer and data link layer. That means another layer 5 is not found in the WAN. In other words, standard and protocol layer 1 and layer 2 WAN different from a standard and protocol layer 1 and layer 2 of the LAN.

WAN physical layer describes the interface between data terminal equipment (DTE) and data circuit-terminating equipment (DCE). Generally, DCE is on the provider and the DTE is on the device. In this model, communication through the DTE with the help of a modem or CSU / DSU.
The main function of a router is to send data using a 3-layer address. This process is called routing. Routing occurs at the network layer, or Layer 3. If the WAN operates at Layer 1, 2 and 3, if the router is a device for LAN or WAN? the answer is both.
Router in the WAN is to deliver packets at layer 3, but he also could be used in a LAN. At the time of the router using a standard protocol and physical layer and data link layer it operates as WAN equipment. For example, a router may have to have an ISDN interface that uses PPP encapsulation, and a serial interface that is connected to T1 lines using Frame Relay encapsulation. Router must be able to change the bit stream from a single service type to another type, in this case, T1 and ISDN to modify the data link encapsulation from PPP to Frame Relay.

Below is a list of standards and protocols on the WAN physical layer:
- EIA/TIA-232
- EIA/TIA-449
- V.24
- V.35
- X.21
- G.703
- EIA-530
- ISDN
- T1, T3, E1 and E3
- XDSL
- SONET (OC-3, OC-12, OC-48, OC-192)

Below is a list of standards and protocols on the WAN data link:
- High-level data link control (HDLC)
- Frame Relay
- Point-to-Point Protocol (PPP)
- Synchronous Data Link Control (SDLC)
- Serial Line Internet Protocol (SLIP)
- X.25
- ATM
- LAPB
- LAPD
- LAPF