Guides & Tutorials

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ATM OPERATIONS

SVCs (SWITCHED VIRTUAL CIRCUITS) AND PVCS (PERMANENT VIRTUAL CIRCUITS)

ATM networks sustain point-to-point links for direct connectivity, point-to-multipoint connections for broadcast and multicast services, and multipoint-to-multipoint connections for applications such as interactive videoconferencing and telecollaborative teleresearch. Path specifications for moving traffic across ATM networks are termed Switched Virtual Circuits (SVCs) and Permanent Virtual Circuits (PVCs).

SVCs are created virtually on a semi-permanent basis for enabling multimedia transmission. SVCs establish connections on a call-by-call basis for accommodating bursty transmissions and bandwidth on-demand. UBR (Unspecified Bit Rate) service for SVC (Switched Virtual Circuit) connections supports information delivery on a best-effort basis. SVC connections do not guarantee the availability of bandwidth for enabling QoS (Quality of Service) transmissions.

In comparison to SVCs, PVCs are static virtual connections between network endpoints that support always-available and assured bandwidth allocations for current and emergent network applications and services. As a consequence, PVCs enable stable, dependable, and reliable transmission of voice, video, and data traffic with QoS guarantees.


ATM SWITCHES

ATM networks consist of routers, servers, switches, and endpoint devices such as network nodes and stations. The ATM switch family includes workgroup, campus, enterprisewide, and next-generation switches that provide services in a variety of LAN, MAN, and WAN environments. For example, ATM switches enable LATMs (Local Area ATM Networks) to provision services to legacy workstations and support sophisticated network backbone operations for advanced academic and research networks.

ATM multiservice switches provide the underlying physical infrastructure for the network configuration and control network processing speed. These devices uniformly facilitate cell relay operations, sustain throughput and end-to-end network performance, interlink nodes on ATM networks, and route multiple cells concurrently to destination addresses. It is important to note that ATM switches also support diverse applications, services, and operations, and vary in structure, capacity, value-added capabilities, interoperability support, and traffic management functions in order to accommodate a wide range of E-government (electronic government), E-business (electronic businesses), telemedicine, teleresearch, and/or tele-education requirements.


User-to-Network Interfaces (UNIs), Network-to-Node and Network-to-Network Interfaces (NNIs), and Private Network-to-Node or Network-to-Network Interfaces (PNNIs)

ATM installations consist of a set of ATM switches or internetworking devices that are interconnected by point-to-point ATM interfaces. ATM interfaces or virtual connections include User-to-Network Interfaces (UNIs) and NNIs (Network-to- Node Interfaces or Network-to-Network Interfaces). UNIs are ATM protocols that define standard interfaces between customer premise equipment (CPE) and the network switch. For example, FUNI (Frame UNI) clarifies parameters for integrating legacy devices with ATM switching equipment in mixed-mode Frame Relay and ATM network configurations.

PNNIs (Private Network-to-Node or Private Network-to-Network Interfaces) are NNI protocols that define ATM interfaces within and between private networks. PNNIs determine approaches for routing ATM connection-oriented requests across an ATM network or between ATM networks.

Moreover, PNNIs employ signaling technologies to support SVCs and PVCs in multivendor environments, provision QoS guarantees, and foster distribution of reserved bandwidth. PNNIs also establish the format for the Broadband-Intercarrier Interface (B-ICI) between public networks for enabling seamless multicarrier multivendor multiservice ATM implementations.


ATM CLASS OF SERVICE (COS) AND QUALITY OF SERVICE (QOS)

ATM networks employ Classes of Service (CoS) for optimizing network performance and supporting applications with specified bandwidth or throughput requirements. ATM service classes resolve congestion problems and traffic management issues in order to ensure seamless transmission in multivendor environments. A Class of Service (CoS) refers to a category of ATM connections that features identical traffic patterns and resource requirements. Each class provisions a distinct level of service and associated QoS guarantees. Depending upon the format of the QoS service requested, the ATM network defines a series of CoS categories. The Variable Bit Rate (VBR) Class of Service consists of applications with specific requirements for delays and throughputs such as packetized voice and data applications. The real-time Variable Bit Rate (VBR-rt) Class of Service requires real-time support for provisioning applications such as video-on-demand (VOD) and voice-over-IP (VoIP). VBR-rt bandwidth requirements vary over time. However, delay and delay variance limits are clearly established.

The non-real-time variable bit rate (VBR-nrt) Class of Service eliminates the need for guaranteed delivery of applications such as multimedia e-mail, bulk file transmissions, and business and educational database transactions with minimal service requirements. Bandwidth for VBR-nrt applications varies within a specified range. However, delay and delay variance requirements are not fully defined. The Available Bit Rate (ABR) Class of Service requires the use of flow control mechanisms for ensuring allocation of bandwidth on-demand for non-real-time, mission-critical applications. With ABR applications, guaranteed minimum transmission rates are specified for the duration of the connection. In addition, ABR also establishes peak transmission rates for data bursts when bandwidth is available. As a consequence, the ABR service class tolerates delay variations. Applications grouped into this category allow priority traffic to consume bandwidth first. ABR applications include LAN emulation (LANE), file and data distribution, and LAN interconnections.

The Unspecified Bit Rate (UBR) Class of Service is equivalent to best-effort delivery in IP networks. Delay-tolerant UBR applications include Web browsing and IP transmissions. Because UBR applications require minimal network support, QoS guarantees and pre-established throughput levels are not defined. The Constant Bit Rate (CBR) Class of Service (CoS) requires utilization of a virtual channel with constant bandwidth for seamlessly transporting applications in accordance with pre-defined response time requirements. CBR applications include videoconferencing, telephony services, and television broadcasts.

In conjunction with establishing a CoS, ATM networks define cell rates and burst size to facilitate seamless network performance. For example, Peak Cell Rate (PCR) indicates the maximum rate at which cells transit the network for brief time periods. Sustainable Cell Rate (SCR) refers to the cell rate that is sustained for a specified period of time. Maximum Burst Size (MBS) defines the maximum number of back-to-back cells that transit the network.

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IP-OVER-ATM

The popularity of IP (Internet Protocol) applications contributes to implementation of IP overlays on top of multiservice ATM networks. IP-over-ATM solutions employ protocols such as MPOA (MultiProtocol-over-ATM) and MPLS (MultiProtocol Label Switching) for leveraging IP enhancements. Moreover, IP packets can be mapped to ATM service classes to transport, for instance, IP-based voice and video traffic via CRC and VBR-rt. Additionally, IP-over-ATM implementations support VPNs (Virtual Private Networks) and ATM emulated LAN (ELAN) protocols that work in concert with the Network Layer or Layer 3 and the Transport Layer or Layer 4 of the OSI (Open Systems Interconnection) Reference Model. Sponsored by the ATM Forum, the ATM-IP Collaborative Working Group (AIC) develops specifications for coordinating the provision of IP services with ATM technology. Approaches for mapping ATM QoS to the IP DiffServ (Differentiated Services) protocol are also in development.

In order to interoperate with IP packet-switched services, ATM defines a framing structure for carrying IP packets as sets of ATM cells. ATM PVCs (Permanent Virtual Circuits) support virtual connections within an IP network. In provisioning IP integrated services over an ATM infrastructure, a portion of the available bandwidth is reserved for specified CoS transmissions. By employing fixed capacity virtual connections for designated CoS transmissions, the ATM infrastructure guarantees the availability of reserved bandwidth on-demand.


CIP-OVER-ATM (CLASSICAL IP-OVER-ATM)

Protocols for preserving in-place infrastructure investments in ATM environments include Classical IP-over-ATM (CIP-over-ATM). A CIP-over-ATM solution employs Permanent Virtual Circuits (PVCs) or dynamic Switched Virtual Circuits (SVCs) for transporting IP packets to ATM addresses. Moreover, CIP-over-ATM deployments enable access to ATM services and connectivity to legacy IP applications. CIP-over- ATM implementations require modification of the IP Address Resolution Protocol (ARP) in order to establish ATM connections that correspond to IP addresses.


MULTIPROTOCOL-OVER-ATM (MPOA) PROTOCOL

Endorsed by the ATM Forum, the MPOA (MultiProtocol over ATM) protocol defines Network Layer or Layer 3 services for enabling ATM implementations. IMPOA employs Next Hop Resolution Protocol (NHRP) for mapping IP packets to ATM cells at AAL5 of the ATM protocol stack. In addition, MPOA routes ATM traffic directly between ELANs (Emulated LANs) and employs SVCs (Switched Virtual Circuits) to ensure reliable and dependable voice, video, and/or data delivery to destination addresses. Robust transmissions are achieved by reducing the number of nodes participating in the internetwork transmission process.

With MPOA, network stations or nodes on different subnetworks establish Permanent Virtual Connections (PVCs) or shortcuts, thereby eliminating the need for intermediate cell segmentation and cell reassembly. In contrast to MPOA, LANE (LAN Emulation) and CIP protocols use intermediate routers for enabling intercommunications between subnetwork nodes. This process limits ATM transmission rates and the amount of voice, video, and data throughput transported via the network by requiring intermediate cell segmentation and reassembly.


MULTIPROTOCOL LABEL SWITCHING (MPLS)

Developed by the IETF (Internet Engineering Task Force), the MPLS (MultiProtocol Label Switching) protocol enables the provision of merged IP and ATM services within the same networking environment. To accomplish this objective, the MPLS protocol interlinks the IP Layer and the ATM Layer and interconnects IP routers and ATM switches, thereby enabling IP transmissions to take advantage of ATM traffic management capabilities in provisioning CoS assurances. IP also benefits from ATM broadband transmission rates for enabling high-speed and dependable multimedia delivery.

MPLS technology enables operations at the Data-Link Layer or Layer 2 of the OSI Reference Model, supports connection-oriented switching based on IP routing and control protocols, and employs fixed-length labels for rapidly routing transmissions to destination addresses. The MPLS protocol works in concert with its own LDP (Label Distribution Protocol) in establishing links and shortcuts in accordance with IP addresses, ATM CoS requirements, and ATM QoS guarantees.

MPLS implementation requires development of a Label-Switching Path (LSP) for handling volume-intensive traffic that takes a specific destination route over the network and supporting identification of a communications channel with high capacity and minimal congestion to accommodate application bandwidth requirements. MPLS solutions optimize network performance, control network operating costs, minimize congestion, decrease the number of information packets dropped as a consequence of network instability, and provision preferential service for delivery of priority transmissions. The MPLS protocol works in concert with IPv4 (Internet Protocol version 4) and supports migration to IPv6 (Internet Protocol version 6) operations. In addition to ATM, the MPLS protocol optimizes performance of network configurations based on POS (Packet over SONET/SDH), Frame Relay, Ethernet, Fast Ethernet, and Gigabit Ethernet technologies.

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ATM LAN EMULATION (LANE)

ATM LANE FUNDAMENTALS

ATM LAN emulation (LANE) enables virtual LAN (VLAN) implementations across ATM backbone networks that reflect the logical associations of workgroups regardless of the physical location of workgroup participants. Modifications in virtual ATM LANE topologies are accomplished by redefining workgroups in the network management system and reconfiguring software in ATM switches. MPOA (MultiProtocol-over-ATM) enables direct transmission of virtual ATM LANE traffic over the ATM Physical Layer or Layer 1 of the OSI Reference Model. The Cells-in-Frames (CIF) Alliance supports implementation of ATM desk area networks (DANs) that operate in concert with the virtual ATM LANE infrastructure. ATM LANES are also called ATM ELANs (Emulated LANs).


ATM EMULATED LANS (LANES) IN ACTION

ATM LANEs are scalable and flexible, feature sophisticated network management and control capabilities, and perform functions equivalent to those supported by conventional Ethernet and Token Ring VLANs (Virtual LANs). ATM LANES enable each participant in a logical workgroup to take part in collaborative networking activities. Internetworking devices such as bridges and routers support voice, video, and data exchange between participants in enterprisewide ATM LANEs.

In an ATM LANE, local networking applications access an ATM network con- figuration via IP protocols. IP packets are transported in ATM cells. ATM LANEs use LAN Emulation User-to-Network Interfaces (LUNIs) and LAN Emulation Network- to-Node or Network-to-Network Interfaces (LNNIs) to provision QoS guarantees, Internet telephony, and connectionless unicast and multicast delivery. ATM LANEs support MAC (Medium Access Control) operations at the Data-Link Layer or Layer 2 of the OSI Reference Model.

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ATM IMPLEMENTATION CONSIDERATIONS

In the academic arena, ATM technology facilitates fast, reliable, and dependable access to an expanding array of Web initiatives and institutional resources. ATM enables tele-education, telementoring, and real-time interactions with subject experts in remote locations; multimedia applications; and curricular enhancement and enrichment. ATM also promotes deployment of virtual schools, virtual universities, virtual museums, and virtual communities.

ATM pilot trials and initiatives support the design and implementation of extendible, reliable, and scalable ATM configurations to accommodate current and anticipated network requirements. In addition, the ATM platform delivers high-capacity, high-speed multimedia services and applications. However, it is also important to note that major regulatory, technical, logistical, and economic issues associated with ATM deployment remain unresolved. As a consequence, the ATM acronym also stands for “All That Money.”

ATM is an evolving technology. As a consequence, standards and testing methods are still in development. Congestion on ATM networks can lead to cell loss before traditional network tools detect problems. Problems associated with providing effective traffic management, seamless network performance, and network-level security for information integrity and high-speed interactive data, video, and voice delivery must be resolved through further research. ATM functions are also constrained by the lack of cross-vendor support.

Migration to an ATM solution typically requires acquisition of ATM products and services from a single vendor. The majority of ATM switches in use by early adopters of ATM technology are expected to be incompatible with next-generation ATM switches. As a result, replacement of expensive in-place ATM switches with costly next-generation ATM switches appears to be necessary for enabling ATM services.

Successful ATM deployment requires the use of carefully executed measures to manage traffic flows and accommodate application requirements. Inasmuch as ATM support of multiple QoS parameters contributes to difficulties in managing ATM configurations, development and implementation of network management policies are indispensable in facilitating realization of the full potential of ATM technology.

An understanding of ATM technical capabilities is essential in order to effectively address pedagogical challenges associated with ATM implementation. Although ATM supports multifaceted options for information delivery to the desktop, SOHO venues, and local and wider area environments, deployment of ATM technology does not automatically guarantee its effective utilization in the educational domain. In implementing ATM applications and services in school and university environments, the capabilities of the proposed infrastructure must be determined. Requirements for a high-performance ATM infrastructure that is modular, reliable, secure, expandable, and available to accommodate bandwidth demands over time must be clarified. Effective ATM implementation in the tele-education milieu also involves developing ATM telelearning paradigms for supporting problem-solving skills and accomplishment of learning goals and objectives. Effective ATM deployment in the telelearning environment ultimately depends on its ability to foster knowledge-building competencies and exploratory learning, quality education, and focused research and facilitate instructional innovation and creativity. Future research involving ATM deployment in school and university settings must also focus on the practical design and deployment of pedagogical strategies and collaborative instructional activities for optimizing student skills in broadband tele-education environments.

In the broadband networking arena, ATM’s major competitor is Gigabit Ethernet technology. Gigabit Ethernet technology is compatible with the installed base of Ethernet and Fast Ethernet solutions in local area and wider area network environments. In comparison to ATM, Gigabit Ethernet does not provision information transport with QoS guarantees. However, Gigabit Ethernet leverages capabilities of newer technologies and protocols such as the Resource Reservation Protocol (RSVP) and the MultiProtocol Link Aggregation (MPLA) protocol to support scalable bandwidth, fault tolerance, network resiliency, and streamlined packet transmission for provisioning higher-level networking services. In addition, Gigabit Ethernet implementations are more affordable and easier to implement than complex ATM solutions.


SUMMARY

There is a growing consensus that ATM reliably and dependably accommodates requirements for high-speed, high-performance networking operations while also enabling a seamless migration path to the network of the future. Increasing numbers of ATM field trials and full-scale implementations demonstrate ATM capabilities in providing access to worldwide learning resources and supporting innovative telelearning activities and applications.
Distinctive attributes of major national and international ATM initiatives and research efforts that contribute to establishing a global ATM infrastructure are examined. ATM systems featuring a mix of wireline and wireless technologies for enabling transborder interdisciplinary research and global connectivity to innovative instructional programs are explored.

ATM technology is uniquely suited for supporting error-free multimedia transport in high-speed network configurations. Moreover, ATM is an enabler of network traffic consolidation, thereby streamlining network management operations and optimizing utilization of high-speed network connections. In addition, ATM provisions networking services via twisted copper pair, optical fiber, and hybrid optical fiber and coaxial cable (HFC) wireline media and wireless technical solutions. National and international standards organizations such as the ITU-T, the Institute of Electrical and Electronic Engineers (IEEE), the American National Standards Institute (ANSI), and the European Telecommunications Standards Institute (ETSI) endorse ATM specifications.

ATM solutions are designed to function in multiservice, multivendor environments. However, debate persists about the suitability of ATM technology in accommodating mission, goals, and requirements economically and effectively in the academic arena. Potential barriers to ATM deployment include high costs, lack of universally accepted standards, restricted geographical availability, equipment incompatibilities, and insufficient research data on the capabilities of ATM in provisioning Quality of Service (QoS) guarantees.

Despite these constraints, ATM is regarded as a key enabler for tele-education, telebusiness, E-government, and telemedicine applications. ATM provisions dependable Internet, intranet, and extranet connectivity; facilitates implementation of Virtual Reality (VR) applications; and supports reliable access to broadband multimedia services.

ATM networks resolve problems associated with internetwork congestion and enable seamless voice, video, and data transmission over wireless, wireline, and hybrid wireline and wireless network configurations. In the distance education domain, ATM enables access to new student populations in remote locations, promotes transborder research and telecollaboration, and facilitates curricular enrichment. Globally, ATM technology supports development and deployment of major research and education networks such as Abilene, vBNS+, Internet2, ESnet, CA*net II, and SuperJANET4. Moreover, ATM promotes incorporation of emergent network architectures, protocols, and transmission technologies into an integrated infrastructure. Continued research on the design and implementation of pedagogical approaches and methods for supporting student learning and achievement in ATM instructional settings is essential for achieving effective ATM implementation in school and university environments.