Asynchronous Transfer Mode

Asynchronous Transfer Mode
Rjamorim at English Wikipedia · Public domain · source
Name	Asynchronous Transfer Mode
Invented	1980s
Developer	International Telegraph and Telephone Consultative Committee, Bell Labs
Initial release	1980s
Influence	Broadband Integrated Services Digital Network, Multiprotocol Label Switching

Asynchronous Transfer Mode Asynchronous Transfer Mode is a telecommunications switching technique developed in the 1980s for high-speed packet-switching that influenced broadband networking, integrated services, and carrier transport. Designed by standards bodies and researchers at institutions such as the International Telegraph and Telephone Consultative Committee and Bell Labs, ATM aimed to unify voice, video, and data across wide area and metropolitan networks and to interwork with systems like Broadband ISDN and optical transport.

History

ATM originated during standardization efforts involving the International Telegraph and Telephone Consultative Committee, the American National Standards Institute, and researchers at Bell Labs, with early work influenced by packet-switching research at RAND Corporation, Xerox PARC, and the University of California, Berkeley. Development in the 1980s and 1990s saw contributions from corporations such as IBM, AT&T, Siemens, and Nortel, and trials coordinated with national operators like British Telecom, Japan's NTT, and France Télécom. Debates over broadband services, work on Integrated Services Digital Network led by CCITT, and expectations set by the development of ISDN and SONET/SDH shaped ATM's adoption in backbone networks by carriers including Sprint and MCI. Later, competition from Ethernet standards advanced by the IEEE, and the emergence of IP routing improvements at Cisco and Juniper Networks, shifted deployment away from ATM in many enterprise contexts.

Architecture and principles

ATM's architecture combined fixed-size cell switching with virtual connection concepts inspired by earlier virtual circuit networks developed at Xerox PARC, SRI International, and ARPANET projects. The design separated control and user planes, reflecting principles seen in architectures from ITU-T and IEEE, and incorporated switching elements similar to those in telephone exchanges created by Bell Labs and Siemens. ATM defined concepts of Permanent Virtual Circuits and Switched Virtual Circuits, echoing callsign and session models used in telephony operations at British Telecom and interexchange carriers like AT&T. Integration with optical transport systems such as SONET, SDH, and Dense Wavelength Division Multiplexing was planned alongside interworking with MPLS initiatives from IETF working groups and carrier networks.

Cell structure and formats

ATM used small, fixed-length 53-octet cells with a 5-octet header and a 48-octet payload, a format resulting from compromise discussions among standards organizations including ITU-T and ANSI, and debated in industry consortia involving IBM, Motorola, and Ericsson. The header fields supported identifiers analogous to channel identifiers used in traditional telephony and signalling systems like Signalling System No. 7, and provided fields for Virtual Path Identifier and Virtual Channel Identifier used in switching fabric designs in hardware by vendors such as Cisco, Alcatel, and Nortel. ATM Adaptation Layers mapped services such as voice codecs from ITU-T Study Groups and video codecs from MPEG and ITU-T Video Coding Experts Group into cell payloads, reflecting interworking needs with multimedia work by Bell Labs and academic labs at MIT and Stanford.

Signalling and virtual connections

Signalling protocols for ATM included variants standardized by ITU-T, ATM Forum initiatives, and implementations interoperating with network management frameworks from ISO and IETF. Call and connection setup used protocols that paralleled features of telephony switching protocols at Ericsson and Siemens and incorporated aspects familiar from Signalling System No. 7 deployments by national carriers like Verizon and British Telecom. The control plane enabled connection-oriented services with RSVP-like resource reservation goals discussed in IETF and academic circles at Carnegie Mellon and UC Berkeley, while device vendors such as Lucent and Alcatel provided signaling stacks integrated with carrier OSS/BSS systems.

Quality of Service and traffic management

ATM provided multiple Quality of Service classes including Constant Bit Rate, Variable Bit Rate, and Available Bit Rate, concepts developed in coordination with telecommunication regulators and research groups such as ITU-T Study Groups and the ATM Forum. Traffic management features such as policing, shaping, and congestion indication (including Early Packet Discard ideas related to RED researched at MIT) were implemented in switches and routers by vendors like Cisco, Nortel, and Juniper. These QoS mechanisms were intended to support real-time voice and video from standards bodies like ITU-T and multimedia groups such as MPEG while coexisting with data traffic from enterprises using equipment from HP and Sun Microsystems.

Implementations and deployment

Operational ATM networks were deployed by carriers including British Telecom, NTT, France Télécom, and Sprint for backbone and metropolitan area services and by enterprises using equipment from vendors such as Cisco, Nortel, Lucent, and Alcatel. ATM was embedded in optical transport platforms from companies like Corning, Ciena, and Alcatel-Lucent and interfaced with SONET/SDH rings used by telecom operators and consortiums including ITU-T and ANSI. ATM Forum interoperability events and demonstrations at industry shows by IEEE, IETF, and major vendors facilitated multi-vendor deployments, while university testbeds at Stanford, MIT, and UC Berkeley evaluated performance and scaling.

Legacy and impact on modern networking

Although ATM declined in enterprise access and carrier cores as Ethernet advances from the IEEE and IP routing enhancements by Cisco and Juniper prevailed, its concepts influenced MPLS standardized by IETF, traffic engineering research at universities such as Carnegie Mellon, and QoS architectures in DiffServ and IntServ discussions at IETF. Hardware switching advances pioneered by ATM vendors informed modern ASIC design at Broadcom and Marvell, and ATM's integration with optical transport contributed to the evolution of SONET/SDH and DWDM systems by Ciena and Corning. Lessons from ATM's standardization and deployment continue to inform networking work at organizations like ITU-T, IEEE, and IETF and ongoing projects at research institutions including Stanford, MIT, and CMU.

Category:Telecommunications