Frame Relay

Frame Relay. Frame Relay is a standardized wide-area network technology that specifies the physical and logical link layers of digital telecommunications channels using a packet switching methodology. Originally designed for transport across Integrated Services Digital Network interfaces, it became a popular service for connecting local area networks across wide area networks in the late 1980s and 1990s. It provides cost-efficient, streamlined data transmission by statistically multiplexing multiple logical connections over a single physical link.

Overview

The protocol was developed as a more efficient successor to the older X.25 protocol, eliminating much of the overhead associated with error correction and flow control. A primary application was to interconnect geographically dispersed corporate networks, such as linking a branch office in Chicago to a headquarters in New York City. Key service providers like AT&T Corporation, MCI Communications, and Sprint Corporation offered commercial Frame Relay services. The technology's simplicity and reliance on higher-layer protocols in end devices, like those from Cisco Systems or Juniper Networks, contributed to its rapid adoption during the expansion of business data networks prior to the widespread deployment of Internet Protocol-based solutions.

Technical details

Frame Relay operates at the data link layer of the OSI model, transmitting variable-sized data units called frames. These frames contain header information with crucial identifiers, primarily the Data Link Connection Identifier, which specifies the virtual circuit to which the frame belongs. The network uses Permanent Virtual Circuits, which are pre-configured paths, and Switched Virtual Circuits, which are established dynamically. Congestion is managed through explicit signals like the Forward Explicit Congestion Notification and Backward Explicit Congestion Notification bits within the frame header. Committed Information Rate and Committed Burst Size are key parameters defined in a service level agreement between the customer and a carrier like British Telecommunications or Deutsche Telekom, governing the guaranteed bandwidth.

Frame Relay versus other technologies

Compared to its predecessor X.25, Frame Relay offers significantly higher performance by assuming more reliable digital links, such as those using T-carrier or E-carrier systems, and moving complex error recovery to the network endpoints. When contrasted with the later Asynchronous Transfer Mode technology, Frame Relay is generally less suited for real-time, isochronous traffic like voice or video because it uses variable-length frames rather than fixed-length cells. The emergence of Multiprotocol Label Switching and ubiquitous Internet Protocol networks, supported by robust routers from vendors like Huawei and Nokia Networks, ultimately provided more flexible and scalable alternatives, leading to the decline of dedicated Frame Relay deployments for new installations.

Deployment and history

Frame Relay saw its major deployment phase begin in the early 1990s following standardization by the International Telecommunication Union and the American National Standards Institute. It became a cornerstone for enterprise networks, often used to build large private networks for institutions like NASA or major financial firms on Wall Street. The technology's popularity peaked in the late 1990s, coinciding with the growth of early corporate intranets. However, with the commercialization of the Internet and the advent of cost-effective Digital Subscriber Line and Metro Ethernet services from providers such as Verizon Communications and Comcast, migration away from Frame Relay accelerated in the early 2000s. Legacy Frame Relay networks still exist in some niche industrial or governmental applications, but most have been phased out in favor of IP/MPLS networks.

Standards and protocols

The foundational standards for Frame Relay were developed by the International Telecommunication Union Telecommunication Standardization Sector, originally published as the ITU-T I.122 recommendation. In the United States, the American National Standards Institute committee Accredited Standards Committee played a key role, with relevant specifications adopted by the Internet Engineering Task Force as well. Key protocol specifications include Q.922 for the core link access procedure, and management interfaces were often handled by the Local Management Interface. Interoperability with higher-layer protocols was ensured through standards like RFC 1490, which defined the encapsulation of multiprotocol traffic, such as from Internetwork Packet Exchange or AppleTalk networks, over Frame Relay. These standards were critical for ensuring multi-vendor interoperability between equipment from IBM, Digital Equipment Corporation, and other manufacturers.

Category:Network protocols Category:Wide area networks Category:Telecommunications standards