TOLLY. Premise: Buyers of multi-port. BayStack T Switch Fast Ethernet Switch Competitive Evaluation Backplane Capacity.

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1 Preise: Buyers of ulti-port switches need to know the actual capacity of the backplane (switching fabric) used to interconnect ports. To assure a non-blocking environent i.e., all ports can run at wire-speed the rated capacity should equal or exceed the nuber of ports ultiplied by the port speed. T H E TOLLY G R O U P No Septeber 1998 Bay Networks, Inc. BayStack T Switch Fast Ethernet Switch Copetitive Evaluation Backplane Capacity Test Suary Test Highlights Deonstrates a peak backplane capacity of 2.4 Gbit/s Delivers up to double the backplane capacity of the SuperStack II Switch 3300 Delivers five ties the backplane capacity of the Express 510T Switch Bay Networks, Inc. has developed the BayStack T, a 24-port Fast Ethernet workgroup switch with a generous 2.5 Gbit/s backplane capacity. The BayStack T s aple backplane capacity supports sufficiently high frae rates for its 24 full-duplex Fast Ethernet ports. Bay Networks coissioned The Tolly Group to benchark the actual backplane capacity of the BayStack T against two 24- port Fast Ethernet switches: 3Co Corp. s SuperStack II Switch 3300 and Intel Corp. s Express 510T Switch. Testing was perfored in July The Tolly Group bencharked the backplane capacity of each product in a single switch configuration. Engineers subjected each switch under test to the sae traffic patterns. Test results show the Bay- Stack T outperfored the Backplane capacity (Gbit/s) Backplane Capacity Benchark 24 Full-Duplex Fast Ethernet Ports 1,518-byte Fraes Intel Express 510T Switch 3Co SuperStack II Switch 3300 Bay BayStack T Switch Theoretical axiu Source: The Tolly Group, Septeber 1998 Figure The Tolly Group Page 1

2 copetitive products in all scenarios tested. In the best-case test scenario, the BayStack T was able to transport 2.4 Gbit/s of traffic or 100% of the theoretical axiu throughput with streas of large 1,518-byte fraes. The SuperStack II Switch 3300 and Express 510T Switch deonstrated only 58% and 18% of the theoretical axiu throughput. Results Backplane Capacity The Tolly Group tested the backplane capacity of the BayStack T Switch versus the SuperStack II Switch 3300 and Express 510T Switch. First, the backplane capacity was tested using the easiest-to-forward frae size (1,518 bytes) in order to show the axiu backplane capacity supported by each switch. In this best case scenario, the BayStack T deonstrated a peak backplane capacity of 2.4 Gbit/s. Even in the best case scenario, the copetitive switches were not able to deonstrate near the theoretical backplane capacity of 2.4 Gbit/s. The SuperStack II Switch 3300 and Express 510T deonstrated peak backplane capacities of 1.4 Gbit/s and 0.4 Gbit/s respectively. See figure 1. The Tolly Group tested the steady state (no loss) throughput to deterine the actual backplane capacity of the device by generating bidirectional traffic with a Netco Systes, Inc. SartBits Backplane capacity (Gbit/s) Backplane Capacity Benchark 24 Full-Duplex Fast Ethernet Ports 64-byte Fraes Intel Express 510T Switch between 24 full-duplex Fast Ethernet ports. 3Co SuperStack II Switch 3300 Testing was conducted by increasing traffic rates until no ore than 2% of the fraes were lost. Tests eployed 64- and 1,518-byte fraes. Those frae sizes were chosen to deonstrate throughput with sall fraes, which are characteristic of interactive traffic (the worst case scenario because it is ore taxing to the switch fabric) and large, file transfer-type fraes (the best case scenario). For 64-byte fraes, the worstcase test scenario, the test results show that the BayStack T supports an actual backplane capacity of 2.0 Gbit/s versus the theoretical axiu of 2.4 Gbit/s. The SuperStack II Bay BayStack T Switch Theoretical axiu Source: The Tolly Group, Septeber 1998 Figure 2 Switch 3300 deonstrated a 0.9 Gbit/s backplane capacity and the Express 510T deonstrated 0.4 Gbit/s. Once again, the copetitive products were not able to deonstrate a capacity near the theoretical axiu throughput. See figure 2. The copetitive products were tested with and without flow control enabled to deonstrate that their actual backplane capacity reains roughly the sae. Flow control does not increase throughput; it virtually eliinates frae loss once port congestion occurs. Results with and without flow control were within 1% of each other for both the Super-Stack II Switch 3300 and the Express 510T. See figure 3 for a coplete set of results for all test cases The Tolly Group Page 2

3 Analysis The steady-state perforance test eployed by The Tolly Group in this benchark allowed engineers to gauge the level of traffic that could be handled by all ports siultaneously before any fraes were dropped. That level provides a highwater ark for capacity at the given frae size. The theoretical axiu backplane capacity that can be deonstrated in a given test is deterined by the nuber, speed and duplex ode of the switch ports. In the current test, the configuration of 24, full-duplex 100 Mbit/s ports allows for a axiu of 2.4 Gbit/s (24 * 100 Mbit/s) of aggregate throughput. (Note: Had the ports been half duplex, this nuber would be divided by two since only 12 input-output streas would be possible.) While actual network traffic is a coplex ixture of variously-sized fraes, The Tolly Group chose to benchark backplane capacity using best-case and worst-case scenarios. In the best case scenario, all ports are offered 1,518-byte fraes. This reduces the frae processing load and should axiize a product s perforance by allowing it to strea the large data loads. Offering streas of 64-byte fraes constitutes the worst case scenario. Sending the sallest legal frae forces the switch to handle a very high frae rate of up to 148,810 fps per port. In the best-case scenario, Bay Networks delivers 100% of theoretical axiu throughput. In the worst-case, throughput is still 83% of that value. It should be noted that Fast Ethernet s axiu allowable frae rate of 148,810 fps per strea, rather than 100 Mbit/s, creates the upper liit boundary in this test. In the case of 3Co s Super- Stack II Switch 3300, 1.4 Gbit/s appeared to be the bestcase backplane capacity. In the worst-case, throughput is 900 Mbit/s. The Tolly Group s benchark of the SuperStack II Switch 3300 is accurate, according to Stephen Collinson, a arketing engineer with 3Co. However, Charles Gallagher, 3Co s product line anager of High Speed Switching, says that the backplane capacity etric is isleading because it does not account for port over-subscription or conforance to standards. Instead, 3Co favors easuring the percentage of offered traffic delivered on a nuber of devices connected together. In the case of Intel s Express 510T Switch, 400 Mbit/s appeared to be the upper liit of backplane capacity regardless of whether large or sall fraes were processed. The Tolly Group s 400 Mbit/s benchark of the Express 510T is accurate, according to Rayond Sit, a technical arketing engineer with Intel. However, the Express 410T backplane supports eight data streas, four of which are reserved for inter-switch counications, since the switch Bay Networks, Inc. BayStack T Switch Backplane Capacity Benchark Bay Networks, Inc. BayStack T Switch Product Specifications* 1998 The Tolly Group Page 3 Maxiu 10/100 Mbit/s port per unit: 28 Maxiu ports per stack: 224 Frae forwarding throughput: 3 illion packets per second Failsafe stackability Switch backplane speed: 2.5 Gbit/s Extendable backplane bandwidth: 2.5 Gbit/s IEEE 802.1p Priority Queuing IEEE 802.1Q VLAN Trunking VLAN support 12,000 MAC addresses supported Gigabit Ethernet and ATM support Redundant power supply support For ore inforation contact: Bay Networks, Inc Great Aerica Parkway Santa Clara, CA (408) URL: *Vendor-supplied inforation not verified by The Tolly Group

4 Steady State Layer 2 Switch Throughput Aggregate Throughput for 64 byte fraes Aggregate throughput for 1,518 byte fraes Product under test Flow control status Fraes per second Gbit/s Percentage of theoretical axiu Fraes per second Gbit/s Percentage of theoretical axiu Bay BayStack T not supported 2,996, % 195, % 3Co SuperStack II Switch 3300 disabled 1,318, % 112, % 3Co SuperStack II Switch 3300 enabled 1,332, % 112, % Intel Express 510 T Switch disabled 597, % 34, % Intel Express 510 T Switch enabled 597, % 34, % Source: The Tolly Group, Septeber 1998 Figure 3 is designed as a stackable unit, he says. So, in effect, data passing across the bus is liited to four other streas, he says. Moreover, the Express 510T is designed as a desktop switch, eaning it connects PC users to a backend workgroup switch, uch like a repeater or wiring concentrator would connect devices. Unlike workgroup or segent switches, the Express 510T does not support a connection to a backbone, Sit says. Intel does offer the Express 550E and 550F as viable workgroup or segent switches, Sit says. Based on the best-case backplane capacity results and retail syste prices, The Tolly Group calculated the cost per gigabit of throughput. The BayStack T Switch costs $1,498 per Gbit of throughput versus $2,578 and $5,998 per Gbit of throughput for the 3Co SuperStack II Switch 3300 and Intel Express 510T respectively. The calculations show the BayStack T offers ore throughput per dollar than copeting products tested. Related Tests Several onths before the current test, The Tolly Group conducted a test of Fast Ethernet switches, coissioned by 3Co, that included 3Co and Bay products entitled 3Co Corporation SuperStack II Switch 3300 and 1100 Fast Ethernet/Ethernet Switch Copetitive Evaluation Layer 2 Switch-to- Switch and Standalone Switch Perforance, docuent nuber The findings in the current test do not contradict earlier results because the ai of the previous test was to deonstrate the percentage of fraes delivered in a switch-to-switch configuration. Furtherore, the Bay product in that test was an earlier generation switch The Tolly Group Page 4

5 Test Configuration and Methodology The Tolly Group tested the switches at the following code levels: Bay s BayStack T (hardware revision B, firware revision 1.02, software version ), Intel s Express 510T Switch (hardware version 0, software version 2.10) and 3Co s SuperStack II Switch 3300 (hardware version 1, software version 1.03). The switches under test were connected to two Netco Systes SartBits Advanced Perforance Tester/Siulator/ Analyzers, consisting of an SMB-2000 and SMB-10 chassis (running SartWindows version 6.24) via a total of 24 10/100 Mbit/s Ethernet/Fast Ethernet SartCards (odel SX-7410). (See figure 4.) All SartCards were configured to run at 100 Mbit/s Fast Ethernet in full-duplex ode. The Sart-Bits was configured to generate bidirectional traffic between port pairs for at least one inute. To deterine steady state (no loss) throughput, axiu frae generation rates were adjusted so that no ore than 2% frae loss occurred. Throughput was recorded in fraes per second. For all tests, the switch under test was first set to the factory default configuration. Then Spanning Tree and BOOTP were disabled as is custoary in throughput tests. Port autonegotiation was disabled and the ports were anually configured for 100 Mbit/s, fullduplex operation. For those products that offered flow control, tests were run ultiple ties with flow control enabled and disabled as indicated in the test results. Copetitive Issues: Equipent Acquisition, Support and Verification The Intel and 3Co switches were acquired through noral distribution channels. The Tolly Group contacted executives at both copanies and invited the to provide a higher level of support than available to custoers through noral channels. Both Intel and 3Co accepted The Tolly Group s invitation. The Tolly Group verified product release levels and shared test configurations with the vendors in order to give the an opportunity to optiize their devices for the test. Both Intel and 3Co approved their switch configurations. Results were shared with the copetitive vendors and the vendors acknowledged their accuracy. For a ore coplete understanding of the interaction between The Tolly Group, 3Co and Intel, check out the Technical Support Diary for Copetitive Products Tested posted on The Tolly Group s World Wide Web site at (see docuent 8286). The Role of Flow Control When a switching atrix reaches its axiu capacity and input traffic continues to arrive, the default action is for the switch to discard those fraes it cannot process. Unfortunately, even discarding one out of every 100 or 1,000 fraes while statistically insignificant can cause severe degradation for the application whose strea was interrupted, due to protocol resynchronization. The IEEE coittee created a flow control specification to allow switches to signal back to ports that the traffic flow should be slowed since axiu capacity has been reached. Flow control allows a graceful degradation. All fraes eventually are processed (rather than dropped) though the sender ay need to wait longer before sending the. Flow control does not increase or decrease the axiu capacity of a switch s backplane. This is evidenced in the results in this test. Flow control only kicks in when a device has reached its capacity for handling traffic. Bay Networks does not ipleent flow control in the BayStack T. By designing a high-capacity backplane that can effectively handle all ports at or near wire-speed, congestion of the switch fabric is not an issue and flow control logic is unnecessary The Tolly Group Page 5

6 Test Bed Netco Systes SartBits 24 full-duplex Fast Ethernet links Switch Under Test Source: The Tolly Group, Septeber 1998 Figure 4 The Tolly Group gratefully acknowledges the providers of test equipent used in this project: Vendor Product Web address Netco Systes, Inc. SartBits Since its inception, The Tolly Group has produced high-quality tests that eet three overarching criteria: All tests are objective, fully docuented and repeatable. We endeavor to provide coplete disclosure of inforation concerning individual product tests, and ultiparty copetitive product evaluations. As an independent organization, The Tolly Group does not accept retainer contracts fro vendors, nor does it endorse products or suppliers. This open and honest environent assures vendors they are treated fairly, and with the necessary care to guarantee all parties that the results of these tests are accurate and valid. The Tolly Group has codified this into the Fair Testing Charter, which ay be viewed at Project Profile Sponsor: Bay Networks, Inc. Docuent nuber: 8286 Product Classification: Workgroup switches Products under test: l BayStack T Switch l Intel Express 510T Switch l 3Co SuperStack II Switch 3300 Testing window: July 1998 Software versions tested: l Bay: Hardware version B, firware version 1.02, software version l Intel: Hardware version 0, software version 2.10 l 3Co: Hardware version, software version 1.03 Software status: All software is generally available. Additional inforation available: l Technical Support Diary: (see docuent 8286 at For ore inforation on this docuent, or other services offered by The Tolly Group, visit our World Wide Web site at send E-ail to info@tolly.co, call (800) or (732) Internetworking technology is an area of rapid growth and constant change. The Tolly Group conducts engineering-caliber testing in an effort to provide the internetworking industry with valuable inforation on current products and technology. While great care is taken to assure utost accuracy, istakes can occur. In no event shall The Tolly Group be liable for daages of any kind including direct, indirect, special, incidental, and consequential daages which ay result fro the use of inforation contained in this docuent. All tradearks are the property of their respective owners. Tolly Group doc rev. ck 01Septeber The Tolly Group Page 6