WAN protocols

Frame Relay

A packet-switched technology that emerged in the early 1990s, Frame Relay is a Data Link and Physical layer specification that provides high performance. Frame Relay is a successor to X.25, except that much of the technology in X.25 used to compensate for physical errors (noisy lines) has been eliminated. Frame Relay can be more cost-effective than point-to-point links, and can typically run at speeds of 64Kbps up to 45Mbps (T3). Frame Relay provides features for dynamic bandwidth allocation and congestion control.

ISDN

Integrated Services Digital Network (ISDN) is a set of digital services that transmit voice and data over existing phone lines.  ISDN can offer a cost-effective solution for remote users who need a higher-speed connection than analog dial-up links offer. ISDN is also a good choice as a backup link for other types of links such as Frame Relay or a T-1 connection.

LAPB

Link Access Procedure, Balanced (LAPB)  was created to be a connection-oriented protocol at the Data Link layer for use with X.25. It can also be used as a simple data link transport. LAPB causes a tremendous amount of overhead because of its strict timeout and windowing techniques.

HDLC

High-Level Data-Link Control (HDLC) was derived from Synchronous Data Link Control  (SDLC), which was created by IBM as a Data Link connection protocol. HDLC is a protocol at the Data Link layer, and it has very little overhead compared to LAPB. HDLC wasn’t intended to encapsulate multiple Network layer protocols across the same link. The HDLC header carries no identification of the type of protocol being carried inside the HDLC encapsulation. Because of

this, each vendor that uses HDLC has their own way of identifying the Network layer protocol, which means that each vendor’s HDLC is proprietary for their equipment.

PPP

Point-to-Point Protocol (PPP) is an industry-standard protocol. Because all multi-protocol versions of HDLC are proprietary, PPP can be used to create point-to-point links between different vendors’ equipment. It uses a Network Control Protocol field in the Data Link header to identify the Network layer protocol. It allows authentication and multilink connections and can be run over asynchronous and synchronous links.

ATM

Asynchronous Transfer Mode (ATM) was created for time-sensitive traffic, providing  simultaneous transmission of voice, video, and data. ATM uses cells instead of packets that are a fixed 53 bytes long. It also can use isochronous clocking (external clocking) to help the data move faster.