ATM - alive and kicking

The vast majority of the world's telephone and data connections pass over ATM networks. But does the exuberance over ADSL mean...

The vast majority of the world's telephone and data connections pass over ATM networks. But does the exuberance over ADSL mean ATM is about to be put out to grass?

There is a great deal of excitable talk about the next generation of broadband services. ADSL, Gigabit Ethernet, cable and satellite modems all promise high data rates for much lower costs per megabyte.

There are many compelling reasons to purchase these newer technologies. Most use the existing infrastructure to provide better performance, from a backbone to a local area network. That all important backbone technology used by international telecommunications carriers and big business has also seen new contenders, such as Nortel's ground breaking OPTera, which provides between 1600Gbps and 1.6 terabits using an optical D-WDM system. Yet, despite all this innovation, the most common form of carrier class communications system is still ATM.

With over $3 billion worth of equipment already installed worldwide, ATM is vital to the global data communications infrastructure. According to a recent Dataquest study, the market for ATM backbone products is likely to grow to $4.7 billion in 2001. Among the biggest spenders in this sector are companies wanting to connect branch offices to a central office.

Another indirect factor making ATM such a strong technology is the prevalence of ISDN-B. The symbiotic relationship between ISDN and ATM stems from the initial installation most telcos established when data first looked like becoming as important as voice. Back in the 1980s, the primary data transmission standard was SDH. SDH offered fast data transmission but with very little provision for switching between sender(s) and receiver(s). A harmonised switching technology called cell relay emerged around this time and together, these were the basis of ATM. For the telcos, the existing infrastructure was easily adaptable to ATM and the ISDN services were a great way to divide up these new 155Mbps and 622Mbps pipes for commercial use.

Many business users have some misconceptions regarding ATM. The biggest is that ATM needs fibre cabling. This is incorrect. At lower speeds, 155Mbps can easily be transported over copper. In fact, ATM isn't sensitive to its mode of physical transport - twisted pair, fibre or coaxial. The overriding problem with ATM in an office environment is the comparatively high cost of network cards, hubs and switches.

ATM also has built-in QoS standards, unlike Ethernet, which - up until the recent 802.3p standard - had very shaky QoS support. Even today, making an Ethernet network QoS compliant requires a major overhaul. However, though QoS is built into ATM, it can be much more complex to implement and configure.

Some critics claim that ATM is not a modern enough standard to support the demands of multimedia. Chris Hornsey, UK sales director for General Datacomm, disagrees. " Bringing innovations such as the MAC 500 to the market place, GDC provides end-to-end provisioning for a wide range of multimedia services. The MAC 500 (ATM) multimedia access concentrator distinguishes itself as one of the most forward thinking and useful products in the voice/video/data convergence field.

"The Internet explosion means that people use more video - and they expect high quality... The product features a modular, scalable architecture that grows with customers' needs and it conforms to the latest LAN, WAN and multimedia standards to ensure interoperability across an entire network."

The entry level ATM market is starting to become more attractive due to the big players - such as Nortel, Cisco, and Lucent - acquiring smaller companies while pushing up bandwidth on high-end solutions. The prospect of OC-768 switching fabric delivery up to 40Gbps can make the current ATM installation more effective, reducing the cost per megabyte even further. With these larger dedicated pipes, providers are now able to offer better bandwidth, both in terms of value and capacity.

ATM does have some problems. When used in a local or campus network, it is expensive when compared with some of the high-end Ethernet solutions. However, ATM is quite capable of transporting IP, so the skill sets required to implement and manage an ATM solution are not beyond the scope of most IT managers familiar with Ethernet, Token Ring or Frame Relay.

Ethernet offers highly effective connectivity along the boundary and is simple and inexpensive. As applications have grown, Ethernet has been scaled up over the years. From 10Mbps speeds, Ethernet first increased to 100Mbps and then to the modern 1000Mbps Gigabit Ethernet. Many organisations are providing power users with dedicated Fast Ethernet connectivity for faster access to server farms and client/server applications, and, as a result, are relying on the bandwidth of Gigabit Ethernet to aggregate data-intensive workgroups into building backbones.

The temptation is to spread this Gigabit Ethernet structure to the whole WAN environment, but Ethernet has some major problems when compared with ATM. Gigabit Ethernet lacks ATM's resilience and does not support load sharing. Without load sharing, even 1000Mbps backbones can become overwhelmed when supporting multiple Fast Ethernet connections. Nor does Gigabit Ethernet support true, end-to-end QoS. Although Class of Service (CoS) traffic prioritisation schemes can be added to the technology, they increase the cost and complexity of Gigabit Ethernet and do not provide the performance and latency guarantees of ATM.

As examples, the Institute of Electrical and Electronic Engineers (IEEE) 802.1p draft standard and the Internet Engineering Task Force (IETF) Resource Reservation Protocol (RSVP) Internet draft, when ratified, will provide only prioritisation and bandwidth reservation respectively. The 802.1p standard will work only on a packet-by-packet basis at Layer 2; and RSVP, if it ever comes to fruition, will work only at Layer 3 and will not enforce the quality of the packet flow. ATM, on the other hand, was designed from the ground up with the ability to provide full QoS and traffic management guarantees on end-to-end connections, for the duration of flows, and without regard to the protocol layer.

ATM has its place within both the enterprise and carrier markets. Understanding the benefits it brings to tasks which require high prioritisation or reliability is key. The skill set is not so complex and ATM isn't sensitive about which transport method it is used on. Far from being a dead technology, ATM is very much alive and kicking.

Will Garside

This was first published in April 2000



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