WAN Protocols

WAN Internet Protocols are used in conjunction with WAN routers to perform the task of distinguishing between a private LAN and the related public WAN. Several WAN protocols have been developed over the decades for this task, as well as other purposes, including:

Packet switching: A method of data transmission. In packet switching, messages are broken into multiple packets. Each packet contains a header that includes information on how to reassemble the packets, as well as the intended destination of the packets. As a measure to prevent data corruption, the packets are triplicated. The triplicated packets are sent separately over optimal routes through the internet. Then, once the packets reach their destination, they are reassembled. The triplicate copies are compared with one another to detect and correct any data corruption that occurred during transmission (at least two of the three copies should match). If the data cannot be reassembled and/or data corruption is evident in all three copies, the destination will make a request to the origin to resend the packet.
Frame relay: Also a method of data transmission. Frame relay is an older technology originally designed for use on Integrated Services Digital Network (ISDN) lines. However, the technology is now used in other network interfaces. Frame relays are used to transmit data between endpoints of a WAN through a packet switching method that works at the OSI data link and physical layers. A fast data communications network, called a Frame Relay Network, is used to transport data packets in frames. The reliability of Frame Relay Networks minimizes the need for error checking. The frames include routing address information for the destination.
- Permanent Virtual Circuits (PVCs) - Used for long-term data connections. Stays open even when data is not being transmitted.
- Switched Virtual Circuits (SVCs) - Used in temporary session connections for sporadic communications.
Asynchronous Transfer Mode (ATM): ATM is an older technology that encodes data using asynchronous time-division multiplexing. The encoded data is packaged into small, fixed-sized cells. ATM can send the cells over a long distance, which makes it useful for WAN communications. ATMs uses routers as end-points between ATM networks and other networks. ATM technology has been replaced for the most part by Internet Protocol (IP) technologies.
High Level Data Control (HLDC): An encapsulation or data link protocol that delivers data frames through a network. The frames include multiple fields that can hold information about start and end flags, controls, Frame Check Sequence (FCS), and protocol used. HLDC was developed to use multiple protocols to replace Synchronous Data Link Control (SDLC), which used only one protocol. HLDC includes error correction, flow control, and data transmission through polling. HLDC has three modes to define the relationship between two devices, or nodes, during communications:
- Normal Response Mode (NRM) - Primary node must give permission to the secondary node to transmit.
- Asynchronous Response Mode (ARM) - Primary node allows the secondary node to initiate communication.
- Asynchronous Balanced Mode (ABM) - Both nodes can act as either the primary or secondary nodes. They can each initiate communications without permission.
Packet over Synchronous Optical Network (SONET) or Synchronous Digital Hierarchy (SDH): A communication protocol used for WAN transport. The SONET or SDH communication protocols define how point-to-point links communicate over fiber optics cables.
Multiprotocol Label Switching (MPLS): A technique for optimizing network routing. MPLS replaces inefficient table lookups for long network addresses with short path labels. These labels direct data from node to node.