ATM or atm is an abbreviation which may refer to:

Asynchronous Transfer Mode ( ATM ) is, according to the ATM Forum, " a telecommunications concept defined by ANSI and ITU ( formerly CCITT ) standards for carriage of a complete range of user traffic, including voice, data, and video signals ," and is designed to unify telecommunication and computer networks.

Specifically, at speeds of OC-3 and above, the cost of segmentation and reassembly ( SAR ) hardware makes ATM less competitive for IP than Packet Over SONET ( POS ); because of its fixed 48-byte cell payload, ATM is not suitable as a data link layer directly underlying IP ( without the need for SAR at the data link level ) since the OSI layer on which IP operates must provide a maximum transmission unit ( MTU ) of at least 576 bytes.

When an ATM circuit is set up each switch on the circuit is informed of the traffic class of the connection.

ATM traffic contracts form part of the mechanism by which " quality of service " ( QoS ) is ensured.

The reference model given by the ITU-T and ATM Forum for UPC and NPC is the Generic Cell Rate Algorithm ( GCRA ), which is a version of the leaky bucket algorithm.

EPD and PPD work with AAL5 connections as they use the end of packet marker: the ATM User-to-ATM User ( AUU ) Indication bit in the Payload Type field of the header, which is set in the last cell of a SAR-SDU.

One application for SVCs is to carry individual telephone calls when a network of telephone switches are inter-connected using ATM.

In ATM this is called a virtual circuit ( VC ).

When available, cash out is convenient for the customer, who can bypass having to visit a bank branch or ATM.

Another area in which the ICAO is active is infrastructure management, including Communication, Navigation, Surveillance / Air Traffic Management ( CNS / ATM ) systems, which employ digital technologies ( e. g., satellite systems with various levels of automation ) in order to maintain a seamless global air traffic management system.

It is primarily used within network backbones and employs ATM.

The primary benefit is to eliminate dependence on a particular OSI model data link layer technology, such as Asynchronous Transfer Mode ( ATM ), Frame Relay, Synchronous Optical Networking ( SONET ) or Ethernet, and eliminate the need for multiple layer-2 networks to satisfy different types of traffic.

MPLS is able to work with variable length packets while ATM transports fixed-length ( 53 byte ) cells.

The biggest advantage that MPLS has over ATM is that it was designed from the start to be complementary to IP.

ATM can also use a Presentation ( PSAP ) and Session ( SSAP ) Access Point, but these may also be unspecified ; this is up to the application.

MPLS recognizes that small ATM cells are not needed in the core of modern networks, since modern optical networks () are so fast ( at 40 Gbit / s and beyond ) that even full-length 1500 byte packets do not incur significant real-time queuing delays ( the need to reduce such delays — e. g., to support voice traffic — was the motivation for the cell nature of ATM ).

Circuit switched networks, especially those intended for voice transmission, such as Asynchronous Transfer Mode ( ATM ) or GSM, have QoS in the core protocol and do not need additional procedures to achieve it.

In January 1997, the first distance lecture in Croatia was organized through the CARNet ATM core between the Rectorate of the Osijek University and the Faculty of Electrical Engineering and Computing in Zagreb.

Cut-through switching was one of the important features of IP networks using ATM networks since the edge routers of the ATM network were able to use cell switching through the core of the network with low latency at all points.

# For each serving exchange involved in providing end user access lines, a virtual path is provisioned to a BT ATM switch on BT's core network.

As with ATM Light for Macintosh, Adobe licensed to Microsoft the core code, which was integrated into Windows 2000 and Windows XP, making ATM Light for Windows obsolete, except for the special case of support for " multiple master " fonts, which Microsoft did not include in Windows, and for which ATM Lite still acts as a font driver.

While ATM did not live up to every expectation, it remained an important core network technology.

On slower or congested links ( 622 Mbit / s and below ), ATM does make sense, and for this reason most asymmetric digital subscriber line ( ADSL ) systems use ATM as an intermediate layer between the physical link layer and a Layer 2 protocol like PPP or Ethernet.

Most ATM networks supporting SPVPs, SPVCs, and SVCs use the Private Network Node Interface or Private Network-to-Network Interface ( PNNI ) protocol.

Many network engineers agree that ATM should be replaced with a protocol that requires less overhead, while providing connection-oriented services for variable-length frames.

Due to SONET / SDH's essential protocol neutrality and transport-oriented features, SONET / SDH was the obvious choice for transporting the fixed length Asynchronous Transfer Mode ( ATM ) frames also known as cells.

The proprietary protocol was based on Asynchronous Transfer Mode ( ATM ).

Other trunking protocols have been used but have become obsolete, including Inter-Switch Link ( ISL ), IEEE 802. 10 ( originally a security protocol but a subset was introduced for trunking ), and ATM LAN Emulation ( LANE ).

Depending on its device architecture and setup, a DSLAM aggregates the DSL lines over its Asynchronous Transfer Mode ( ATM ), frame relay, and / or Internet Protocol network ( i. e., an IP-DSLAM using PTM-TC Transfer Mode-Transmission Convergence ) protocol ( s ) stack.

The Point-to-Point Protocol over ATM ( PPPoA ) is a network protocol for encapsulating PPP frames in AAL5.

* Cells per second, bandwidth measurement unit for Asynchronous Transfer Mode ( ATM ) protocol.

* ITU-T Recommendation Q. 2110, B-ISDN ATM adaptation layer — Service specific connection oriented protocol ( SSCOP ).

* ITU-T Recommendation Q. 2111, B-ISDN ATM adaptation layer — Service specific connection oriented protocol in a multilink and connectionless environment ( SSCOPMCE ).

AAL 5 is a widely used ATM adaptation layer protocol.

* System Packet Interface or Utopia, an ATM protocol specification

The process is conceptually simple: an incoming packet from another protocol to be transmitted across the ATM network is chopped up into segments that fit into 48-byte chunks carried as ATM cell payloads.

Dynamic Bandwidth works by transmitting voice and data over a T1 connection using ATM as the underlying protocol.

ATM and Frame Relay, for example, are both examples of a connection-oriented, unreliable protocol.

The concept of CRC-based framing was developed by StrataCom, Inc. in order to improve the efficiency of a pre-standard Asynchronous Transfer Mode ( ATM ) link protocol.

Further improvements to the original APON standard – as well as the gradual falling out of favor of ATM as a protocol – led to the full, final version of ITU-T G. 983 being referred to more often as broadband PON, or BPON.

Q. 931 has more recently been used as part of the VoIP H. 323 protocol stack ( see H. 225. 0 ) and in modified form in some mobile phone transmission systems and in ATM.

Part of the reason for the failure of the IBM 473x to take hold in the ATM marketplace was the lack of a backwards compatibility to the 3624 protocol when it was introduced.