Asynchronous Transfer Mode (ATM) is a

telecommunications Telecommunication, often used in its plural form or abbreviated as telecom, is the transmission of information over a distance using electronic means, typically through cables, radio waves, or other communication technologies. These means of ...

standard defined by the

American National Standards Institute The American National Standards Institute (ANSI ) is a private nonprofit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States. The organiz ...

and International Telecommunication Union Telecommunication Standardization Sector (ITU-T, formerly CCITT) for digital transmission of multiple types of traffic. ATM was developed to meet the needs of the Broadband Integrated Services Digital Network as defined in the late 1980s, and designed to integrate telecommunication networks. It can handle both traditional high-throughput data traffic and real-time, low-latency content such as

telephony Telephony ( ) is the field of technology involving the development, application, and deployment of telecommunications services for the purpose of electronic transmission of voice, fax, or data, between distant parties. The history of telephony is ...

(voice) and video.ATM Forum, The User Network Interface (UNI), v. 3.1, , Prentice Hall PTR, 1995, page 2. ATM is a cell switching technology, providing functionality that combines features of

circuit switching Circuit switching is a method of implementing a telecommunications network in which two network nodes establish a dedicated communications channel ( circuit) through the network before the nodes may communicate. The circuit guarantees the full ...

and

packet switching In telecommunications, packet switching is a method of grouping Data (computing), data into short messages in fixed format, i.e. ''network packet, packets,'' that are transmitted over a digital Telecommunications network, network. Packets consi ...

networks by using

asynchronous Asynchrony is any dynamic far from synchronization. If and as parts of an asynchronous system become more synchronized, those parts or even the whole system can be said to be in sync. Asynchrony or asynchronous may refer to: Electronics and com ...

time-division multiplexing.McDysan (1999), p. 287. ATM was seen in the 1990s as a competitor to

Ethernet Ethernet ( ) is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 198 ...

and networks carrying IP traffic as, unlike Ethernet, it was faster and designed with quality-of-service in mind, but it fell out of favor once Ethernet reached speeds of 1 gigabits per second. In the Open Systems Interconnection (OSI) reference model

data link layer The data link layer, or layer 2, is the second layer of the seven-layer OSI model of computer networking. This layer is the protocol layer that transfers data between nodes on a network segment across the physical layer. The data link layer p ...

(layer 2), the basic transfer units are called '' frames''. In ATM these frames are of a fixed length (53

octets Octet may refer to: Music * Octet (music), ensemble consisting of eight instruments or voices, or composition written for such an ensemble ** String octet, a piece of music written for eight string instruments *** Octet (Mendelssohn), 1825 compos ...

) called ''cells''. This differs from approaches such as

Internet Protocol The Internet Protocol (IP) is the network layer communications protocol in the Internet protocol suite for relaying datagrams across network boundaries. Its routing function enables internetworking, and essentially establishes the Internet. IP ...

(IP) (OSI layer 3) or

(also layer 2) that use variable-sized packets or frames. ATM uses a connection-oriented model in which a

virtual circuit A virtual circuit (VC) is a means of transporting data over a data network, based on packet switching and in which a connection is first established across the network between two endpoints. The network, rather than having a fixed data rate reser ...

must be established between two endpoints before the data exchange begins. These virtual circuits may be either permanent (dedicated connections that are usually preconfigured by the service provider), or switched (set up on a per-call basis using signaling and disconnected when the call is terminated). The ATM network reference model approximately maps to the three lowest layers of the OSI model:

physical layer In the seven-layer OSI model of computer networking, the physical layer or layer 1 is the first and lowest layer: the layer most closely associated with the physical connection between devices. The physical layer provides an electrical, mechani ...

, data link layer, and

network layer In the seven-layer OSI model of computer networking, the network layer is layer 3. The network layer is responsible for packet forwarding including routing through intermediate Router (computing), routers. Functions The network layer provides t ...

.McDysan, David E. and Spohn, Darrel L., '' ATM : Theory and Application'', , McGraw-Hill series on computer communications, 1995, page 563. ATM is a core protocol used in the synchronous optical networking and synchronous digital hierarchy (SONET/SDH) backbone of the

public switched telephone network The public switched telephone network (PSTN) is the aggregate of the world's telephone networks that are operated by national, regional, or local telephony operators. It provides infrastructure and services for public telephony. The PSTN consists o ...

and in the

Integrated Services Digital Network Integrated Services Digital Network (ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the digitalised circuits of the public switched telephone network. ...

(ISDN) but has largely been superseded in favor of

next-generation network The next-generation network (NGN) is a body of key architectural changes in telecommunication core network, core and access networks. The general idea behind the NGN is that one network transports all information and services (voice, data, and al ...

s based on IP technology. Wireless and mobile ATM never established a significant foothold.

Protocol architecture

To minimize

queuing delay In telecommunications and computer engineering, the queuing delay is the time a job waits in a queue until it can be executed. It is a key component of network delay. In a switched network, queuing delay is the time between the completion of si ...

and

packet delay variation In computer networking, packet delay variation (PDV) is the difference in end-to-end one-way delay between selected packets in a flow with any lost packets being ignored. The effect is sometimes referred to as packet jitter, although the de ...

(PDV), all ATM cells are the same small size. Reduction of PDV is particularly important when carrying voice traffic, because the conversion of digitized voice into an analog audio signal is an inherently real-time process. The decoder needs an evenly spaced stream of data items. At the time of the design of ATM,

synchronous digital hierarchy Synchronous Optical Networking (SONET) and Synchronous Digital Hierarchy (SDH) are standardized protocols that transfer multiple digital bit streams synchronously over optical fiber using lasers or highly coherent light from light-emitting diod ...

with payload was considered a fast optical network link, and many plesiochronous digital hierarchy links in the digital network were considerably slower, ranging from 1.544 to in the US, and 2 to in Europe. At , a typical full-length 1,500 byte

Ethernet frame In computer networking, an Ethernet frame is a data link layer protocol data unit and uses the underlying Ethernet physical layer transport mechanisms. In other words, a data unit on an Ethernet link transports an Ethernet frame as its paylo ...

would take 77.42

μs A microsecond is a unit of time in the International System of Units (SI) equal to one millionth (0.000001 or 10−6 or ) of a second. Its symbol is μs, sometimes simplified to us when Unicode is not available. A microsecond is to one second, ...

to transmit. On a lower-speed T1 line, the same packet would take up to 7.8 milliseconds. A queuing delay induced by several such data packets might exceed the figure of 7.8 ms several times over. This was considered unacceptable for speech traffic. The design of ATM aimed for a low-jitter network interface. Cells were introduced to provide short queuing delays while continuing to support

datagram A datagram is a basic transfer unit associated with a packet-switched network. Datagrams are typically structured in header and payload sections. Datagrams provide a connectionless communication service across a packet-switched network. The de ...

traffic. ATM broke up all data packets and voice streams into 48-byte pieces, adding a 5-byte routing header to each one so that they could be reassembled later. Being 1/30th the size reduced cell contention jitter by the same factor of 30. The choice of 48 bytes was political rather than technical. When the

CCITT The International Telecommunication Union Telecommunication Standardization Sector (ITU-T) is one of the three Sectors (branches) of the International Telecommunication Union (ITU). It is responsible for coordinating standards for telecommunicat ...

(now ITU-T) was standardizing ATM, parties from the United States wanted a 64-byte payload because this was felt to be a good compromise between larger payloads optimized for data transmission and shorter payloads optimized for real-time applications like voice. Parties from Europe wanted 32-byte payloads because the small size (4 ms of voice data) would avoid the need for

echo cancellation Echo suppression and echo cancellation are methods used in telephony to improve voice quality by preventing echo from being created or removing it after it is already present. In addition to improving subjective audio quality, echo suppression i ...

on domestic voice calls. The United States, due to its larger size, already had echo cancellers widely deployed. Most of the European parties eventually came around to the arguments made by the Americans, but France and a few others held out for a shorter cell length. 48 bytes was chosen as a compromise, despite having all the disadvantages of both proposals and the additional inconvenience of not being a

power of two A power of two is a number of the form where is an integer, that is, the result of exponentiation with number 2, two as the Base (exponentiation), base and integer as the exponent. In the fast-growing hierarchy, is exactly equal to f_1^ ...

in size. 5-byte headers were chosen because it was thought that 10% of the payload was the maximum price to pay for routing information.

Cell structure

An ATM cell consists of a 5-byte header and a 48-byte payload. ATM defines two different cell formats:

user–network interface In telecommunications, a user–network interface (UNI) is a demarcation point between the responsibility of the service provider and the responsibility of the subscriber. This is distinct from a network-to-network interface (NNI) that defines a si ...

(UNI) and network–network interface (NNI). Most ATM links use UNI cell format. ;GFC :The generic flow control (GFC) field is a 4-bit field that was originally added to support the connection of ATM networks to shared access networks such as a distributed queue dual bus (DQDB) ring. The GFC field was designed to give the User-Network Interface (UNI) 4 bits in which to negotiate multiplexing and flow control among the cells of various ATM connections. However, the use and exact values of the GFC field have not been standardized, and the field is always set to 0000. ;VPI :

Virtual path identifier Asynchronous Transfer Mode (ATM) is a telecommunications standard defined by the American National Standards Institute and International Telecommunication Union Telecommunication Standardization Sector (ITU-T, formerly CCITT) for digital trans ...

(8 bits UNI, or 12 bits NNI) ;VCI : Virtual channel identifier (16 bits) ;PT :Payload type (3 bits) ::Bit 3 (msbit): Network management cell. If 0, user data cell and the following apply: ::Bit 2: Explicit forward congestion indication (EFCI); 1 =

network congestion Network congestion in data networking and queueing theory is the reduced quality of service that occurs when a network node or link is carrying more data than it can handle. Typical effects include queueing delay, packet loss or the blocking of ...

experienced ::Bit 1 (lsbit): ATM user-to-user (AAU) bit. Used by AAL5 to indicate packet boundaries. ;CLP :Cell loss priority (1-bit) ;HEC : Header error control (8-bit CRC, polynomial = X⁸ + X² + X + 1) ATM uses the PT field to designate various special kinds of cells for operations, administration and management (OAM) purposes, and to delineate packet boundaries in some ATM adaptation layers (AAL). If the

most significant bit In computing, bit numbering is the convention used to identify the bit positions in a binary numeral system, binary number. Bit significance and indexing In computing, the least significant bit (LSb) is the bit position in a Binary numeral sy ...

(MSB) of the PT field is 0, this is a user data cell, and the other two bits are used to indicate network congestion and as a general-purpose header bit available for ATM adaptation layers. If the MSB is 1, this is a management cell, and the other two bits indicate the type: network management segment, network management end-to-end, resource management, and reserved for future use. Several ATM link protocols use the HEC field to drive a CRC-based framing algorithm, which allows locating the ATM cells with no overhead beyond what is otherwise needed for header protection. The 8-bit CRC is used to correct single-bit header errors and detect multi-bit header errors. When multi-bit header errors are detected, the current and subsequent cells are dropped until a cell with no header errors is found. A UNI cell reserves the GFC field for a local flow control and sub-multiplexing system between users. This was intended to allow several terminals to share a single network connection in the same way that two ISDN phones can share a single basic rate ISDN connection. All four GFC bits must be zero by default. The NNI cell format replicates the UNI format almost exactly, except that the 4-bit GFC field is re-allocated to the VPI field, extending the VPI to 12 bits. Thus, a single NNI ATM interconnection is capable of addressing almost 2¹² VPs of up to almost 2¹⁶ VCs each.

Service types

ATM supports different types of services via AALs. Standardized AALs include AAL1, AAL2, and AAL5, and the rarely used AAL3 and AAL4. AAL1 is used for constant bit rate (CBR) services and circuit emulation. Synchronization is also maintained at AAL1. AAL2 through AAL4 are used for

variable bitrate Variable bitrate (VBR) is a term used in telecommunications and computing that relates to the bitrate used in sound or video encoding. As opposed to constant bitrate (CBR), VBR files vary the amount of output data per time segment. VBR allows ...

(VBR) services, and AAL5 for data. Which AAL is in use for a given cell is not encoded in the cell. Instead, it is negotiated by or configured at the endpoints on a per-virtual-connection basis. Following the initial design of ATM, networks have become much faster. A 1500 byte (12000-bit) full-size

takes only 1.2 μs to transmit on a network, reducing the motivation for small cells to reduce jitter due to contention. The increased link speeds by themselves do not eliminate jitter due to queuing. ATM provides a useful ability to carry multiple logical circuits on a single physical or virtual medium, although other techniques exist, such as Multi-link PPP, Ethernet

VLAN A virtual local area network (VLAN) is any broadcast domain that is partitioned and isolated in a computer network at the data link layer ( OSI layer 2).IEEE 802.1Q-2011, ''1.4 VLAN aims and benefits'' In this context, virtual refers to a ...

VxLAN Virtual eXtensible LAN (VXLAN) is a network virtualization technology that uses a VLAN-like encapsulation technique to encapsulate OSI model, OSI layer 2 Ethernet frames within layer 4 User Datagram Protocol, UDP datagrams, using 4789 as the defau ...

MPLS Multiprotocol Label Switching (MPLS) is a routing technique in telecommunications networks that directs data from one node to the next based on labels rather than network addresses. Whereas network addresses identify endpoints, the labels identi ...

, and multi-protocol support over SONET.

Virtual circuits

An ATM network must establish a connection before two parties can send cells to each other. This is called a

(VC). It can be a permanent virtual circuit (PVC), which is created administratively on the end points, or a switched virtual circuit (SVC), which is created as needed by the communicating parties. SVC creation is managed by signaling, in which the requesting party indicates the address of the receiving party, the type of service requested, and whatever traffic parameters may be applicable to the selected service. '' Call admission'' is then performed by the network to confirm that the requested resources are available and that a route exists for the connection.

Motivation

ATM operates as a channel-based transport layer, using VCs. This is encompassed in the concept of the virtual paths (VP) and virtual channels. Every ATM cell has an 8- or 12-bit virtual path identifier (VPI) and 16-bit virtual channel identifier (VCI) pair defined in its header.Cisco System
''Guide to ATM Technology''
(2000). Section "Operation of an ATM Switch". Retrieved 2 June 2011. The VCI, together with the VPI, is used to identify the next destination of a cell as it passes through a series of ATM switches on its way to its destination. The length of the VPI varies according to whether the cell is sent on a user-network interface (at the edge of the network), or if it is sent on a network-network interface (inside the network). As these cells traverse an ATM network, switching takes place by changing the VPI/VCI values (label swapping). Although the VPI/VCI values are not necessarily consistent from one end of the connection to the other, the concept of a circuit ''is'' consistent (unlike IP, where any given packet could get to its destination by a different route than the others).Cisco System
''Guide to ATM Technology''
(2000). Section "ATM Cell Header Formats". Retrieved 2 June 2011. ATM switches use the VPI/VCI fields to identify the virtual channel link (VCL) of the next network that a cell needs to transit on its way to its final destination. The function of the VCI is similar to that of the data link connection identifier (DLCI) in

Frame Relay Frame Relay (FR) is a standardized wide area network (WAN) technology that specifies the Physical layer, physical and data link layers of digital telecommunications channels using a packet switching methodology. Frame Relay was originally devel ...

and the logical channel number and logical channel group number in

X.25 X.25 is an ITU-T standard protocol suite for Packet switched network, packet-switched data communication in wide area network, wide area networks (WAN). It was originally defined by the CCITT, International Telegraph and Telephone Consultative Co ...

. Another advantage of the use of virtual circuits comes with the ability to use them as a multiplexing layer, allowing different services (such as voice, Frame Relay, IP). The VPI is useful for reducing the switching table of some virtual circuits which have common paths.

Types

ATM can build virtual circuits and virtual paths either statically or dynamically. Static circuits (permanent virtual circuits or PVCs) or paths (permanent virtual paths or PVPs) require that the circuit is composed of a series of segments, one for each pair of interfaces through which it passes. PVPs and PVCs, though conceptually simple, require significant effort in large networks. They also do not support the re-routing of service in the event of a failure. Dynamically built PVPs (soft PVPs or SPVPs) and PVCs (soft PVCs or SPVCs), in contrast, are built by specifying the characteristics of the circuit (the service ''contract'') and the two endpoints. ATM networks create and remove switched virtual circuits (SVCs) on demand when requested by an end station. One application for SVCs is to carry individual telephone calls when a network of telephone switches are interconnected using ATM. SVCs were also used in attempts to replace

local area network A local area network (LAN) is a computer network that interconnects computers within a limited area such as a residence, campus, or building, and has its network equipment and interconnects locally managed. LANs facilitate the distribution of da ...

s with ATM.

Routing

Most ATM networks supporting SPVPs, SPVCs, and SVCs use the Private Network-to-Network Interface (PNNI) protocol to share topology information between switches and select a route through a network. PNNI is a

link-state routing protocol Link-state routing protocols are one of the two main classes of routing protocols used in packet switching networks for computer communications, the others being distance-vector routing protocols. Examples of link-state routing protocols include ...

like OSPF and IS-IS. PNNI also includes a very powerful route summarization mechanism to allow construction of very large networks, as well as a call admission control (CAC) algorithm which determines the availability of sufficient bandwidth on a proposed route through a network in order to satisfy the service requirements of a VC or VP.

Traffic engineering

Another key ATM concept involves the

traffic contract If a network service (or application) wishes to use a broadband network (an ATM network in particular) to transport a particular kind of traffic, it must first inform the network about what kind of traffic is to be transported, and the performan ...

. 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 Quality of service (QoS) is the description or measurement of the overall performance of a service, such as a telephony or computer network, or a cloud computing service, particularly the performance seen by the users of the network. To quantitat ...

(QoS) is ensured. There are four basic types (and several variants) which each have a set of parameters describing the connection. # CBR Constant bit rate: a Peak Cell Rate (PCR) is specified, which is constant. # VBR Variable bit rate: an average or Sustainable Cell Rate (SCR) is specified, which can peak at a certain level, a PCR, for a maximum interval before being problematic. # ABR Available bit rate: a minimum guaranteed rate is specified. # UBR Unspecified bit rate: traffic is allocated to all remaining transmission capacity. VBR has real-time and non-real-time variants, and serves for bursty traffic. Non-real-time is sometimes abbreviated to vbr-nrt. Most traffic classes also introduce the concept of cell-delay variation tolerance (CDVT), which defines the ''clumping'' of cells in time.

Traffic policing

To maintain network performance, networks may apply traffic policing to virtual circuits to limit them to their traffic contracts at the entry points to the network, i.e. the

s (UNIs) and

network-to-network interface In telecommunications, a network-to-network interface (NNI) is an interface that specifies signaling and management functions between two networks. An NNI circuit can be used for interconnection of signalling (e.g., SS7), Internet Protocol (IP) ( ...

s (NNIs) using usage/network parameter control (UPC and NPC).ITU-T, ''Traffic control and congestion control in B ISDN'', Recommendation I.371, International Telecommunication Union, 2004, page 17 The reference model given by the ITU-T and ATM Forum for UPC and NPC is the generic cell rate algorithm (GCRA),ITU-T, ''Traffic control and congestion control in B ISDN'', Recommendation I.371, International Telecommunication Union, 2004, Annex A, page 87.ATM Forum, The User Network Interface (UNI), v. 3.1, , Prentice Hall PTR, 1995. which is a version of the leaky bucket algorithm. CBR traffic will normally be policed to a PCR and CDVT alone, whereas VBR traffic will normally be policed using a dual leaky bucket controller to a PCR and CDVT and an SCR and maximum burst size (MBS). The MBS will normally be the packet ( SAR- SDU) size for the VBR VC in cells. If the traffic on a virtual circuit exceeds its traffic contract, as determined by the GCRA, the network can either drop the cells or set the Cell Loss Priority (CLP) bit, allowing the cells to be dropped at a congestion point. Basic policing works on a cell-by-cell basis, but this is sub-optimal for encapsulated packet traffic as discarding a single cell will invalidate a packet's worth of cells. As a result, schemes such as partial packet discard (PPD) and early packet discard (EPD) have been developed to discard a whole packet's cells. This reduces the number of useless cells in the network, saving bandwidth for full packets. 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.

Traffic shaping

Traffic shaping Traffic shaping is a bandwidth management technique used on computer networks which delays some or all datagrams to bring them into compliance with a desired ''traffic profile''. Traffic shaping is used to optimize or guarantee performance, improv ...

usually takes place in the

network interface controller A network interface controller (NIC, also known as a network interface card, network adapter, LAN adapter and physical network interface) is a computer hardware component that connects a computer to a computer network. Early network interface ...

(NIC) in user equipment, and attempts to ensure that the cell flow on a VC will meet its traffic contract, i.e. cells will not be dropped or reduced in priority at the UNI. Since the reference model given for traffic policing in the network is the GCRA, this algorithm is normally used for shaping as well, and single and dual

leaky bucket The leaky bucket is an algorithm based on an analogy of how a bucket with a constant leak will overflow if either the average rate at which water is poured in exceeds the rate at which the bucket leaks or if more water than the capacity of th ...

implementations may be used as appropriate.

Reference model

The ATM network reference model approximately maps to the three lowest layers of the OSI reference model. It specifies the following layers: *At the physical network level, ATM specifies a layer that is equivalent to the OSI

. *The ATM layer 2 roughly corresponds to the OSI

. *The OSI

is implemented as the ATM adaptation layer (AAL).

Deployment

ATM became popular with telephone companies and many computer makers in the 1990s. However, even by the end of the decade, the better

price–performance ratio In economics, engineering, business management and marketing the price–performance ratio is often written as cost–performance, cost–benefit or capability/price (C/P), refers to a product's ability to deliver performance, of any sort, for i ...

-based products was competing with ATM technology for integrating real-time and bursty network traffic. Additionally, among cable companies using ATM there often would be discrete and competing management teams for telephony, video on demand, and broadcast and digital video reception, which adversely impacted efficiency. Companies such as FORE Systems focused on ATM products, while other large vendors such as

Cisco Systems Cisco Systems, Inc. (using the trademark Cisco) is an American multinational corporation, multinational digital communications technology conglomerate (company), conglomerate corporation headquartered in San Jose, California. Cisco develops, m ...

provided ATM as an option. After the burst of the

dot-com bubble The dot-com bubble (or dot-com boom) was a stock market bubble that ballooned during the late-1990s and peaked on Friday, March 10, 2000. This period of market growth coincided with the widespread adoption of the World Wide Web and the Interne ...

, some still predicted that "ATM is going to dominate". However, in 2005 the ATM Forum, which had been the trade organization promoting the technology, merged with groups promoting other technologies, and eventually became the

Broadband Forum The Broadband Forum is a non-profit industry consortium dedicated to developing broadband network specifications. Members include telecommunications networking and service provider companies, broadband device and equipment vendors, consultants and ...

Wireless or mobile ATM

Wireless ATM, or mobile ATM, consists of an ATM core network with a wireless access network. ATM cells are transmitted from base stations to mobile terminals. Mobility functions are performed at an ATM switch in the core network, known as a ''crossover switch'',Book on Wireless ATM Networks
- Chai Keong Toh, Kluwer Academic Press 1997 which is similar to the mobile switching center of GSM networks. The advantage of wireless ATM is its high bandwidth and high-speed handoffs done at layer 2. In the early 1990s,

Bell Labs Nokia Bell Labs, commonly referred to as ''Bell Labs'', is an American industrial research and development company owned by Finnish technology company Nokia. With headquarters located in Murray Hill, New Jersey, Murray Hill, New Jersey, the compa ...

and

NEC is a Japanese multinational information technology and electronics corporation, headquartered at the NEC Supertower in Minato, Tokyo, Japan. It provides IT and network solutions, including cloud computing, artificial intelligence (AI), Inte ...

research labs worked actively in this field.WATMnet: a prototype wireless ATM system for multimedia personal communication
D. Raychaudhuri, et al. Andy Hopper from the

University of Cambridge The University of Cambridge is a Public university, public collegiate university, collegiate research university in Cambridge, England. Founded in 1209, the University of Cambridge is the List of oldest universities in continuous operation, wo ...

Computer Laboratory also worked in this area. There was a wireless ATM forum formed to standardize the technology behind wireless ATM networks. The forum was supported by several telecommunication companies, including NEC, Fujitsu and

AT&T AT&T Inc., an abbreviation for its predecessor's former name, the American Telephone and Telegraph Company, is an American multinational telecommunications holding company headquartered at Whitacre Tower in Downtown Dallas, Texas. It is the w ...

. Mobile ATM aimed to provide high-speed multimedia communications technology, capable of delivering broadband mobile communications beyond that of GSM and WLANs.

Notes

References

External links

* *
ATM ChipWeb - Chip and NIC database
* * * * * {{cite web , url=http://www.cisco.com/web/psa/technologies/index.html?c=268435599 , archive-url=https://web.archive.org/web/20071029234552/https://www.cisco.com/web/psa/technologies/index.html?c=268435599 , archive-date=2007-10-29 , title=Asynchronous Transfer Mode (ATM) , publisher=Cisco Systems ITU-T recommendations Link protocols Networking standards