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ATM Vs Gigabit Ethernet: a Technical Perspective

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ATM Vs Gigabit Ethernet: a Technical Perspective White Paper Gigabit Ethernet and ATM A Technology Perspective Bursty, high-bandwidth applications are driving the need for similarly high-bandwidth campus backbone infrastructures. Today, there are two choices for the high-speed campus backbone: ATM or Gigabit Ethernet. For many reasons, business and technical, Gigabit Ethernet is selected as the technology of choice. This paper briefly presents, from a technical perspective, why Gigabit Ethernet is favored for most enterprise LANs. In the past, most campuses use shared-media backbones — such as 16/32 Mbps Token-Ring and 100 Mbps FDDI — that are only slightly higher in speed than the LANs and end stations they interconnect. This has caused severe congestion in the campus backbones when these backbones interconnect a number of access LANs. A high capacity, high performance, and highly resilient backbone is needed-one that can be scaled as end stations grow in number or demand more bandwidth. Also needed is the ability to support differentiated service levels (Quality of Service or QoS), so that high priority, time-sensitive, and mission-critical applications can share the same network infrastructure as those that require only best-effort service. 2 Gigabit Ethernet and ATM: A Technology Perspective White Paper Until recently, Asynchronous Transfer Interface, and Multiprotocol over ATM). Which is a “better” technology is no Mode (ATM) was the only switching This additional complexity is required in longer a subject of heated industry debate technology able to deliver high capacity order to adapt ATM to the connectionless, — Gigabit Ethernet is an appropriate and scalable bandwidth, with the promise frame-based world of the campus LAN. choice for most campus backbones. of end-to-end Quality of Service. ATM Meanwhile, the very successful Fast Many business users have chosen Gigabit offered seamless integration from the Ethernet experience spurred the development Ethernet as the backbone technology desktop, across the campus, and over the of Gigabit Ethernet standards. Within for their campus networks. An Infonetics metropolitan/wide area network. It was two years of their conception (June Research survey (March 1999) records thought that users would massively 1996), Gigabit Ethernet over fiber that 91 percent of respondents believe deploy connection-oriented, cell-based (1000BASE-X) and copper (1000BASE-T) that Gigabit Ethernet is suitable for LAN ATM to the desktop to enable new native standards were approved, developed, and backbone connection, compared with 66 ATM applications to leverage ATM’s rich in operation. Gigabit Ethernet not only percent for ATM. ATM continues to be a functionality (such as QoS). However, provides a massive scaling of bandwidth good option where its unique, rich, and this did not come to pass. The Internet to 1000 Mbps (1 Gbps), but also shares a complex functionality can be exploited Protocol (IP), aided and abetted by the natural affinity with the vast installed base by its deployment, most commonly in exploding growth of the Internet, rode of Ethernet and Fast Ethernet campus metropolitan and wide area networks. roughshod over ATM deployment and LANs running IP applications. Whether Gigabit Ethernet or ATM marched relentlessly to world dominance. Enhanced by additional protocols already is deployed as the campus backbone When no other gigabit technology existed, common to Ethernet (such as IEEE technology of choice, the ultimate ATM provided much needed relief as a 802.1Q Virtual LAN tagging, IEEE decision is one of economics and sound high bandwidth backbone to interconnect 802.1p prioritization, IETF business sense, rather than pure technical numerous connectionless, frame-based Differentiated Services, and Common considerations. campus LANs. But with the massive Open Policy Services), Gigabit Ethernet is The next two sections provide a brief proliferation of IP applications, new now able to provide the differential qualities description of each technology. native ATM applications did not appear. of service that previously only ATM could Even 25 Mbps and 155 Mbps ATM provide. One key difference with Gigabit Asynchronous Transfer to the desktop did not appeal to the Ethernet is that additional functionality Mode (ATM) vast majority of users, because of their can be incrementally added in a Asynchronous Transfer Mode (ATM) complexity, small bandwidth increase, non-disruptive way as required, compared has been used as a campus backbone and high costs when compared with the with the rather revolutionary approach of technology since its introduction in the very simple and inexpensive 100 Mbps ATM. Further developments in bandwidth early 1990s. ATM is specifically designed Fast Ethernet. and distance scalability will see 10 Gbps to transport multiple traffic types — On the other hand, Fast Ethernet, with its Ethernet over local (10G-BASE-T) and data, voice and video, real-time or auto-sensing, auto-negotiation capabilities, wide area (10G-BASE-WX) networks. non-real-time — with inherent QoS integrated seamlessly with the millions Thus, the promise of end-to-end seamless for each traffic category. of installed 10 Mbps Ethernet clients integration, once only the province of To enable this and other capabilities, and servers. Although relatively simple ATM, will be possible with Ethernet additional functions and protocols are and elegant in concept, the actual and all its derivations. added to the basic ATM technology. implementation of ATM is complicated Today, there are two technology choices Private Network Node Interface (PNNI) by a multitude of protocol standards for the high-speed campus backbone: provides OSPF-like functions to signal and specifications (for instance, LAN ATM and Gigabit Ethernet. While both and route QoS requests through a Emulation, Private Network Node seek to provide high bandwidth and hierarchical ATM network. Multiprotocol differentiated QoS within enterprise LANs, these are very different technologies. Gigabit Ethernet and ATM: A Technology Perspective White Paper 3 The main reason for this success is that Gigabit Ethernet provides the functionality that meets today’s immediate needs at an Interface, LAN Emulation Network- affordable price, without undue complexity Network Interface, and a multitude of and cost. Gigabit Ethernet is complemented additional protocols, signaling controls, by a superset of functions and capabilities and connections (point-to-point, point- that can be added as needed, with the to-multipoint, multipoint-to-point, and promise of further functional enhancements multipoint-to-multipoint). and bandwidth scalability (for example, over ATM (MPOA) allows the establish- IEEE 802.3ad Link Aggregation, and 10 Until recently, ATM was the only ment of short-cut routes between Gbps Ethernet) in the near future. Thus, technology able to promise the benefits communicating end systems on different Gigabit Ethernet provides a simple of QoS from the desktop, across the LAN subnets, bypassing the performance scaling-up in bandwidth from the 10/100 and campus, and right across the world. bottlenecks of intervening routers. There Mbps Ethernet and Fast Ethernet LANs However, the deployment of ATM to the have been and continue to be enhancements that are already massively deployed. in the areas of physical connectivity, desktop, or even in the campus backbone Simply put, Gigabit Ethernet is Ethernet, bandwidth scalability, signaling, routing LANs, has not been as widespread as but 100 times faster! and addressing, security, and management. predicted. Nor have there been many native applications available or able to Since Gigabit Ethernet uses the same While rich in features, this functionality benefit from the inherent QoS capabilities frame format as today’s legacy installed has come with a fairly heavy price tag in provided by an end-to-end ATM solution. LANs, it does not need the segmentation complexity and cost. To provide backbone Thus, the benefits of end-to-end QoS and reassembly function that ATM connectivity for today’s legacy access have been more imagined than realized. requires to provide cell-to-frame and networks, ATM — a connection-oriented frame-to-cell transitions. As a connection- technology — has to emulate capabilities Gigabit Ethernet as the campus backbone less technology, Gigabit Ethernet does not inherently available in the predominantly technology of choice is now surpassing require the added complexity of signaling connectionless Ethernet LANs, including ATM. This is due to the complexity and control protocols and connections broadcast, multicast, and unicast and the much higher pricing of ATM that ATM requires. Finally, because QoS- transmissions. ATM must also manipulate components such as network interface capable desktops are not readily available, the predominantly frame-based traffic on cards, switches, system software, Gigabit Ethernet is no less deficient in these LANs, segmenting all frames into cells management software, troubleshooting providing QoS. New methods have been prior to transport, and then reassembling tools, and staff skill sets. There are also developed to incrementally deliver QoS cells into frames prior to final delivery. interoperability issues, and a lack of and other needed capabilities that lend Many of the complexity and interoperability suitable exploiters of ATM technology. themselves to much more pragmatic and issues are the result of this LAN cost-effective adoption and deployment. Emulation, as well as the need to provide Gigabit Ethernet resiliency in these emulated
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