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Good news for token ring

Good news for token ring

The Tolly Group over the past year has evaluated 16Mbps token ring switches from seven vendors and has come to a firm conclusion: token ring users can rest easy.

Second-generation products are delivering switching to the desktop and offering a clear upgrade path to 100Mbps token ring and beyond for purists who don't relish wholesale migrations to ATM or EthernetWith The Tolly Group Token Ring Industry Study now in its second year, we've gathered enough information to assess the market. The intention here is not to say which switch is faster or to reveal who beat whom in head-to-head competition. Rather, we're out to provide an evaluation of where the product category stands to help token ring users make some important decisions about strategic direction.

In terms of performance, the news is good. Across the board, token ring switches have matured into high-performance offerings that forward frames at almost three times the rate of Ethernet switches. Token ring switches often approach maximum wire speed even with small packets, which are toughest to forward.

Token ring switches also now offer plenty of value-added features and functions that you'll need to consider, including support for Remote Monitoring (RMON) and fancy filtering techniques that conserve bandwidth and improve network performance.

Token ring purists should note that while all seven participating vendors have notched up the performance of their token ring switches, only IBM, Madge Networks and Olicom have pledged unequivocally to support the emerging IEEE 802.5 High-Speed Token Ring (HSTR) standard for running token ring switches at 100Mbps and ultimately 1Gbps.

Vendors including Cabletron Systems, Cisco Systems and 3Com, meanwhile, have prepared for a future without industry-standard token ring. They've invested significantly in what are, in effect, exit strategies aimed at convincing users of the merits of ATM, Gigabit Ethernet or proprietary offerings such as Cisco's InterSwitch Link. Each company intends to wait and see if market demand develops around HSTR before floating a product.

Single-stream performance

In terms of raw performance, any of the switches tested should meet the demands of a token ring infrastructure. What should impress users most about a token ring switch's frame-handling capability is how quickly the device can forward small (28B and 64B) frames, prevalent in interactive traffic such as e-mail and database transactions.

Most networks will rarely, if ever, see a surge of small frame traffic beyond 5000 frames per second. Yet in pure token ring to token ring testing using a stream of 28B frames, eight of the nine switches tested delivered an average of 46,000 frames per second. That's almost 75 per cent of the maximum theoretical throughput and two-and-a-half times faster than products available just 18 months ago, when switches pumped out anywhere from 8000 to 18,000 frames per second. Even the worst of the bunch reported throughput ranging from 37,000+ to 47,000 frames per second for 28B frame tests, far exceeding the 5000 frames per second peak you're ever likely to need.

With large frames of 512B and up (common to file transfer and WAN traffic streams), wire-speed throughput was the order of the day for all switches tested. In single-stream tests of 3972B frames, all nine switches tested were able to ship data at 15.85Mbps out of a possible 16Mbps, which amounts to better than 99 per cent bandwidth utilisation. The test demonstrates that the switches tested can handle any large frame that comes their way without hitting a performance barrier.

Multistream tests

While single-stream tests explore the pure throughput a token ring switch can deliver, multistream tests probe how efficiently the switches use ATM, FDDI, Fast Ethernet and Gigabit Ethernet backbones as switch-to-switch links.

Essentially, the multistream results echo the single-stream test findings: across the board, token ring switch throughput is just a shade below wire speed. In configurations ranging from two 16Mbps streams of 3972B frames to eight streams over an ATM link, throughput never dipped below 99 per cent of the maximum possible. For example, when handling 3972B frames delivered over two 16Mbps data streams, six of the nine switches clocked in with throughput of 31.9Mbps and the remaining switches delivered 31.7Mbps out of a maximum of 32Mbps. With the same size packets in an eight-stream test over an ATM link, where the maximum throughput was 128Mbps, seven of nine switches tested delivered throughput of 127Mbps or more. Ultimately, the multistream tests prove that the switches tested don't hit any performance walls or suffer from architectural limitations that affect their scalability.

RMONed and ready

Beyond throughput tests, we examined vendor support for the RMON standard. Every vendor in the study supports basic RMON groups such as history, statistics and alarms. But only Madge offers support for all 10 RMON groups.

"It's the difficult groups that provide the most functionality and power to users trying to troubleshoot their nets," said Simon Jones, product marketing manager for token ring switches at Madge. RMON groups such as hosts, hostTOPn, filters and capture are still largely unsupported on token ring switches.

One reason token ring switch vendors provide limited support for RMON is they would have to add memory and possibly on-board Application Specific Integrated Circuits (ASIC) in order to maintain the same level of performance. Tracing a LAN at wire speed, for instance, requires the switch to dedicate memory to store captured frames or use large buffers to cache the data until a probe calls for it. The additional memory and ASICs would jack up prices at a time when token ring vendors are trying to compete against already less expensive Ethernet switches.

Moreover, many token ring switches lack the multitasking operating systems needed to handle RMON processing alongside switching. "Our aim is to let the switch focus on switching and do the RMON analysis somewhere else," said Ed Harper, product line manager of 3Com's Token Ring Business Group. It's interesting that RMON has essentially replaced IBM's LAN Network Manager as the pre-eminent management tool for token ring nets. Aside from IBM, only Bay Networks supports LAN Network Manager.

Filtering fuss

RMON support may help users monitor what data rides over the network, but filtering features can help prevent unwanted data from traversing the network in the first place, conserving bandwidth and improving overall network performance in the process.

Evaluating token ring switch support for filtering can be a tedious task. You'll be faced with a mountain of filtering options, but the main ones you need to consider are broadcast type (including single- and all-route broadcasts), Layer 3 IP address filtering and media access control address filtering.

All the top vendors will probably support these features; depending on the level of customisation offered and the resulting payback. Pay attention to factors such as how many filters the switch supports per port, and examine the type of bit patterns the filters can recognise. The Bay 5525HD, for example, supports up to 90 different filters per port and can filter broadcast, NetBIOS and unknown unicast traffic, among other types. Check, too, the level of integration between filters and RMON management. Some switches, such as Cabletron's SmartSwitch 9000, enable you to set high and low thresholds via an RMON application.

As for broadcast filtering, the IEEE 802.5 standards committee has not yet tackled broadcast management, so the implementations by definition are proprietary. But because broadcast management is done switch by switch, there are no interoperability issues to worry about when combining switches from different vendors onto the same campus LAN. Here, Madge's Smart Ringswitch seems to have the most developed broadcast throttling mechanism with its Active Broadcast Control (ABC). ABC provides a battery of eight broadcast management grooming facilities, including advanced filtering and caching techniques. The software, which resides on any of Madge's Smart Ringswitches, reduces the amount of broadcast traffic sent to rings. Additionally, ABC converts All-Routes Explorer (ARE) frames to Spanning Tree Explorer frames, which produce a fraction of the broadcast frames ARE churns out.

ABC also filters Novell's IPX Routing Information Protocol (RIP) and Server Advertisement Protocol (SAP) frames. Smart Ringswitch software learns which rings contain devices that need to receive RIP and SAP frames and forwards data as needed. Madge has even inserted facilities in ABC to control NetBIOS traffic.

Token ring endures

The Tolly Group's examination of leading token ring switches reveals that vendors have gone a long way toward extending the life of token ring LANs by improving switch performance and outfitting their products with advanced filtering and monitoring techniques. Clearly, token ring purists who wish to maintain their token ring environment now have a migration path to a high-speed 100Mbps backbone option with the evolution of HSTR. What's less clear, though, is whether some of the industry's more formidable vendors, including Cisco, Cabletron and 3Com, will eventually come around and support the IEEE 802.5 HSTR standard.

By all appearances, HSTR will survive because of the diligence of vendors such as IBM, Madge, Olicom and possibly Bay. But if users want HSTR to endure - along with the benefits of large frame sizes, data prioritisation and source routing - they must send a clear message to suppliers that HSTR is their preferred option. HSTR detractors claim products won't emerge for at least a year, but vendors, including IBM, demonstrated prototypes earlier this month at NetWorld + Interop 98. Other vendors are planning initial shipments as early as next quarter. At this point in the ongoing Token Ring Industry Study, our conclusion is that HSTR is alive and well.

About the Token Ring Industry Study

by Charles Bruno

Token ring switching has undergone a metamorphosis, with the throughput of most switches nearly tripling. At the same time vendors have packaged an abundant array of value-added services. In an effort to demonstrate product differences and provide network managers with the comprehensive data required to make purchasing decisions, The Tolly Group has applied its Industry Study model to token ring switches.

We evaluated key aspects of token ring switches including throughput, filtering support and traffic management capabilities such as buffering and other advanced features. We also looked at signalling and ATM routing, support for legacy LAN services such as LAN Emulation and Classical IP, and several management features including Remote Monitoring support.

To conduct single-stream performance tests, we used nearly a dozen Wandel & Goltermann DA-320 DominoLAN analysers, specifically to take advantage of their frame-generation and traffic monitoring capabilities. For the 28Kbps token ring frame tests, the DA-320 was the only tool capable of pushing the devices being tested. The DA-320s each connected to a token ring multistation access unit, which connected to the token ring switch operating at 16Mbps in half-duplex mode. The DA-320s also generated various traffic loads for uplink testing. For tests with high-density port traffic, The Tolly Group also employed Netcom Systems's SmartBits traffic generators.

Invitations to participate in the testing were sent to all ATM switch vendors. The participating vendors funded this project, although The Tolly Group conceived and executed all tests independent of the vendors. Complete test results are available worldwide at no cost and will be updated during 1998 as additional products are evaluated.

High-Speed Token Ring: vendor directionsby Charles BrunoWhen it comes to High-Speed Token Ring (HSTR), switch vendors are falling into one of two camps. One group is steadfastly behind HSTR and plans to offer a clear-cut upgrade path. Members of the other camp are adopting a wait-and-see approach, in the interim coaxing users to migrate their existing token ring networks to other high-speed alternatives.

Standing behind HSTR

IBM, Olicom and Madge Networks make no bones about it - they're unwavering in their support for High-Speed Token Ring (HSTR) products based on the emerging IEEE 802.5 standard. All three vendors - along with, to a lesser extent, Bay Networks - are positioning HSTR as a frame-based high-speed backbone alternative. At the same time, the vendors are offering high-speed backbone products based on ATM as their cell-based backbone option.

Token ring users need HSTR because it provides support for large frame sizes, prioritisation and source routing services, says Jeff King, Madge's product line manager for switching products. ATM, meanwhile, offers benefits over standard frame-based options, including its quality-of-service and class-of-service features, says Greg Wong, IBM's product line manager for token ring switches. ATM is also better suited to blending voice and data than token ring. Jorgen Hog, vice president of Network Products Marketing at Olicom, also points to the reliability of ATM. Olicom's ClearSession software, for example, enhances fault tolerance in the ATM core by detecting network failures and redirecting traffic in three seconds or less.

HSTR can likewise serve as a backbone technology, with the caveat that it is not as scalable as ATM, Wong said. "We think HSTR, since it is standards-based, will have the best shot at minimising migration concerns for token ring users," he said. "IBM will deliver an HSTR blade for its 8270 Nways LAN Switch Model 800, as well as HSTR server cards." However, he offers no definitive timetable for delivery. At a recent token ring conference, an IBM spokesman said a triple-speed 4/16/100Mbps network interface card will arrive in September and switch upgrades will be generally available by year-end.

Madge will roll out a four-port HSTR module in September for its Ringswitch Plus and Ringswitch Express products, King said. Madge's Active Broadcast Control, its hallmark broadcast management facility, will be supported on HSTR modules running in the Ringswitch line, he added.

Olicom plans to offer HSTR support for its OC-8600 CrossFire Token ring Switch and HSTR server adapters in July or August, Hog says. Each OC-8600 will be able to support four HSTR ports along with 20 4/16Mbps ports. Customers could stack up to eight switches, making 32 HSTR ports, he says.

Bay's strategy largely revolves around support for ATM, but the vendor is developing an HSTR proof-of-concept board and can churn out a product if customer demand materialises, according to Jeff Clowers, Bay's product line manager for token ring. Any packet that touches Bay's 5525HD TR Switch Host's backplane gets converted internally to an ATM cell. "We can merge token ring, Ethernet and ATM in the same box," he said. As for HSTR, "we won't discount it as a backbone technology, but we'd rather see it as a server link", Clowers said.

Token ring supporters exit here

Despite pledging support for HSTR a year ago, Cabletron Systems, Cisco Systems and 3Com are now taking a wait-and-see attitude. At the same time, they are aggressively pushing alternative, and sometimes proprietary, solutions. It seems unlikely that these companies will ever support HSTR unless customers threaten to take their business elsewhere. "Our customer base doesn't have time to wait for such a standard to come to fruition," said Finn Nielsen, Cabletron's product marketing manager.

Their implementations may differ, but each of the vendors is touting a switch that can meld Ethernet and token ring into a single switch fabric. Cabletron's big push is translational switching, what the vendor likes to call "any-to-any switching". Basically, the SmartSwitch 9000 converts any incoming packet to an internal common frame format. It is converted back to the appropriate format as it hits an egress port. "This is a full translation, so I can have a token ring client today talk to an Ethernet server," Nielsen said. "We give token ring stations access to higher speed technologies, whether Fast Ethernet, Gigabit Ethernet, FDDI or ATM."

Cisco is taking a more proprietary approach. The company has served up the InterSwitch Link, which offers 100Mbps performance and allows token ring to tunnel through Fast Ethernet. Cisco also supports ATM as a backbone choice. "In no way are we refuting or moving away from HSTR," said Randall Campbell, product line manager for token ring switching at Cisco.

Cisco takes proprietary route

Cisco, however, objects to the High-Speed Token Ring Alliance's use of token ring media access control (MAC) technology instead of the Ethernet version, arguing it amounts to reinventing the wheel. Network interface cards and Application Specific Integrated Circuits supporting the Ethernet MAC format already exist; coming up with new versions for token ring will drive up development costs and, ultimately, prices. In addition, Cisco contends HSTR lacks adequate support for Ethernet, a point hotly contested by Jeff King, product line manager for switching products at Madge. One of the provisions of the HSTR standard is the 802.1q tagging standard that permits HSTR to carve out tunnels for pockets of Ethernet, King says. "If you try to do that the other way around [carry token ring in Ethernet], you have this fundamental crunch with 1518B Ethernet packets trying to support the longer token ring frames," King said.

3Com isn't going the proprietary route like Cisco, but instead is rallying around its traditional Ethernet strengths. 3Com offers three avenues for users to adopt high-speed backbone alternatives to token ring: ATM (via token ring LAN Emulation), FDDI and token ring tunnelling within Fast Ethernet. "Our main strategy is to help large customers make a smooth migration as they add Fast Ethernet and help them move in that direction," said Ed Harper, product line manager of 3Com's Token Ring Business Group. 3Com will support IEEE 802.5 HSTR only if customer demand warrants it, Harper said.


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