AIT rides the bleeding edge of ATM

Auckland Institute of Technology has begun installation of its new state-of-the art ATM network. Calum Macleod, AIT's IS manager, is opting for a bold direction by implementing a network where the routing is performed by switches and where the underlying technology, MPOA (multiprotocol over ATM), is not yet ratified as a standard by the ATM Forum.

Auckland Institute of Technology has begun installation of its new state-of-the art ATM network.

Calum Macleod, AIT’s IS manager, is opting for a bold direction by implementing a network where the routing is performed by switches and where the underlying technology, MPOA (multiprotocol over ATM), is not yet ratified as a standard by the ATM Forum.

But Macleod is unfazed by the bleeding-edge aura surrounding his decision.

He finds confidence in the fact that Newbridge, the company providing the ATM switching equipment, has done extensive MPOA R&D and is the first to market with a product that supports the technology.

“I decided to go with Newbridge because they had been doing MPOA longer than anyone else. They’ve had it in the field at universities and businesses for the past two years, whereas a lot of the other manufacturers are just starting to release products with virtual routing,” he says.

Also, the ATM Forum is due to ratify the standard in June. Meanwhile, the crucial part of the technology is in the switch’s software, so any changes can be made there, he says.

Instead, Macleod focuses on the bene-fits of the new ATM MPOA 155Mbit/s backbone, which gives him multiprotocol control and bridging across the network. It will easily accommodate video streaming, which is because staff are already making queries about video on demand and video-conferencing.

“The ATM solution we’re installing will still have 10MHz Ethernet to the desktop but 155MHz from servers, between buildings and to the ATM ridge devices which connect to Ethernet hubs. With the ATM protocol most of the 155MHz is available for traffic so there is a lot more bandwidth. Bandwidth is to do with capacity, not speed, and effects the amount of data that can be handled without congestion which does cause delays. ATM is more than just bandwidth and includes quality of service.”

The overall upgrade of the network, planned for the next three years, will cost $1.8 million including cable, switches, hubs and routers (still needed at the edge of the network for Internet access).

“We’re just putting in the most critical areas for now,” says Macleod. “That will cover 70% of the backbone. Cost for the Newbridge equipment and hubs so far is about $300,000. It might be quite a high cost for the remaining 30% of the network because it is quite scattered.”

It’s a complex network that Macleod has under his domain.

Used by administration, teachers and students, it comprises 23 Novell servers, 10 Unix servers, 1800 workstations, a fibre-optic connection to Netlink for Internet access and two microwave links to other sites. There are roughly 1200 to 1500 staff accounts and 15,000 to 20,000 student accounts.

During its 18-year existence the network has grown ad hoc from an RS232 environment, through the addition of ArcNet to Ethernet on coaxial cable. About six years ago network usage took off and the old 10Mbit/s Ethernet, while adequate in most areas, began to hit restrictions about two and a half years ago, says Macleod.

“We had to start looking at technologies that could deliver more data to specific areas. We knew we would hit these problems, particularly in the commerce faculty.”

Commerce covers computer science and business studies and accounts for 25% of the entire network — including six file servers, about 700 workstations and 10,000 student accounts.

The problem was temporarily averted by installing Ethernet switches and the network was rearranged to contain classroom traffic to local segments off the file server. “That has got us through the past 18 months,” says Macleod.

When it came to the major upgrade AIT had three choices: Fast Ethernet switching, FDDI (fibre distributed data interface) and ATM (asynchronous transfer mode).

“Fast Ethernet, while probably the cheapest and easiest to implement, didn’t remove the technical problems of the Ethernet protocols, it just masked them. “The main disadvantage of the Ethernet protocol is that it is contentious, which means the error rate and re-tries increase as the utilisation increases. Ethernet works best if utilisation is kept below about 30% — that is, 3MHz of bandwidth on our 10MHz backbone or 30MHz for a 100MHz backbone.

“We seriously considered FDDI because it is more efficient but it would have meant a steep learning curve for staff and the technology wasn’t being developed at the same rate as ATM.

“So we looked at ATM, which is quite different again. It has a lot of features that we don’t need immediately but are likely to require in the future, such as quality of service, which supports video streaming.”

Macleod says one of the major issues with network traffic is how to make the best use of the network to control the traffic flow so that it only goes where it’s needed. “Traffic shaping”, if you like.

“That’s where the need for routers comes in. To implement any of those other technologies and to make the best use of the network we would have needed routers. Not only would that have put the cost up, but the throughput of a traditional router is about 10% of unrouted traffic. With ATM and MPOA (multiprotocol over ATM) in particular, the switch performs virtual routing which is done at the same speed as switching. That is seen as an advantage with ATM. We thought, why not go for the technology which is going to be around for as long as possible. Around the world companies are investing billions of dollars in ATM.”

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