10-Gigabit Ethernet Switch Performance Testing - Ixia

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Table 1. Maximum packet arrival rates over 10-Gigabit Ethernet. Look-ups and performance. Classification table information is typically stored in a look-up table, usually held in a large TCAM or equivalent technology. When processing encapsulated packets or packets with multiple L2/L3 headers (i.e., IPv6 over IPv4, or MPLS stacks with Ethernet header, IP header, and TCP) the classification process might require multiple accesses to the look-up table for each packet. Table 1 shows the worst-case performance packet arrival rate for small packets. Depending on the packet arrival rate and number of required look-ups per packet, the packet processor or the classification device could become a resource bottleneck. For example, a back-to-back Ethernet packet with an IPv6 datagram requiring ACL and flow look-up might require 7–8 look-ups per packet. With 12 million packets arriving per second, this will require handling ~96 million look-ups/ sec. Stress Point 3: Traffic management The traffic management function provides advanced queuing, congestion management, and hierarchical scheduling of network traffic for large numbers of flows. It forwards traffic according to a user-defined set of rules pertaining to priority levels, latency and bandwidth guarantees, and varying congestion levels. It also provides the packet buffering required to work with any queuing mechanisms used to manage traffic flow Wire rate LAN throughput for minimum-size packet Ethernet IPv4 14.88 million packets/sec Ethernet IPv6 12.02 million packets/sec Ethernet Over MPLS IPv4 12.25 million packets/sec Ethernet Over MPLS IPv6 10.25 million packets/sec across the switch fabric. It may also include the SERDES function. Communication from line card to switch fabric requires additional flow control information, creating overhead and increased bandwidth. This additional bandwidth is called speedup. See "Speedup." on page 14. The architecture of a switch/router can affect how the network behaves in times of heavy demand. An important concern is how packets are queued as they enter the switching fabric, that is, how traffic prioritization is handled and how different traffic flows are merged through the fabric. Some products forward all high-priority packets before any lower-priority packets; this is called strict priority queuing. Other products use mechanisms such as Weighted Fair Queuing (WFQ) to statistically multiplex packets into the fabric. On the ingress line card, WFQ allows packets from lower priority queues to be interleaved with higher priority traffic into the switch fabric. This prevents the higher priority traffic from completely blocking the lower priority traffic, since the queues are guaranteed access to the switch fabric for a predefined proportion of the time. Packet discarding is also part of traffic management. During times of congestion, the traffic manager may need to make discard decisions based on the availability of queue space, priority, or destination port, using a packet discard algorithm like 10-Gigabit Ethernet Switch Performance Testing Copyright © 2004, Ixia 13
Random Early Detection (RED) or Weighted RED (WRED) for IP traffic. Some routers and switches are fundamentally limited by the small number of queues they have for QoS. Small numbers of queues are common for classbased queuing, which limits prioritization and fairness. Class-based queuing typically prioritizes traffic based on the Layer 2 header (virtual LAN and source or destination MAC address, for example), rather than on higher level information such as application or protocol type. Systems with large numbers of queues facilitate more granular prioritization and greater fairness. Queues established on a per-flow basis provide the possibility for each user session to get its own queue. However, a large number of CoS and QoS policies requires large amounts of memory and hierarchical schedulers capable of handling hundreds of thousands of flows. Stress Point 4: Crossbar switch and backplane interconnect Although most switch architectures for modern systems are non-blocking, three types of blocking can limit performance when multiple ingress ports are contending for an egress port: Head-of- Line (HOL) blocking, input blocking, and output blocking. HOL blocking can waste nearly half a crossbar switch's bandwidth if the cells waiting at each input are stored in a single First-In, First-Out (FIFO) queue. Modern switch architectures employ Virtual Output Queuing (VOQ). VOQ, in conjunction with a scheduling algorithm, eliminates most blocking issues. These scheduling algorithms require the traffic manager device and the switch fabric to exchange information, including requests for permission to transmit, granting of permissions to transmit, and other information. Speed-up. The additional bandwidth required to support VOQ and related scheduling algorithms is called speed-up. A 10GE line card that supports 15 Gbps to the switch fabric offers 50 percent speedup. Speed-up is a common way to reduce input and output blocking by running the crossbar switch faster than the external line rate. For example, if the crossbar switch runs twice as fast as the external line, the traffic manager can transfer two cells from each input port, and two cells to each output port during each cell time. The advantage of speed-up is obvious — it offers more predictable delay and jitter across the switch ports by delivering more cells per cell time, and thus reducing the delay of each cell through the switch. In fact, sufficient speed-up can guarantee that every cell is immediately transferred to the output port, where its departure time can be precisely scheduled. Stress Point 5: Multicast replication and queues The biggest challenge in handling multicast packets is packet replication. Packet replication is generally accomplished in two stages. The first stage handles the branch replications from one ingress line card to multiple egress line cards. The second stage handles the leaf replications, and is typically accomplished on the egress line card. Depending on the switch architecture, the packet replication function could cause resource starvation in memory and CPU processing, as well as contention with unicast packets, as it accesses the data plane to forward the replicated packets. New generation switches take advantage of the natural multicast properties of a crossbar switch and perform cell replication within the fabric by closing multiple cross points simultaneously. This method relieves the ingress line card from performing packet replication. However, the second-stage replication on the egress line card can still cause resource starvation and congestion. 14 Copyright © 2004, Ixia 10-Gigabit Ethernet Switch Performance Testing
Page 1 and 2: Enabling a Converged World 10-Giga
Page 3 and 4: Copyright © 1998-2004 Ixia. All ri
Page 5 and 6: 4 Copyright © 2004, Ixia 10-Gigabi
Page 7 and 8: 10-Gigabit Ethernet LAN The biggest
Page 9 and 10: What Happens to a Packet When It En
Page 11 and 12: Metering and statistics recording P
Page 13: performing key searches in a matter
Page 17 and 18: Developing the Right Test Methodolo
Page 19 and 20: Anticipating the behavior of the 10
Page 21 and 22: Ixia’s Test Solution Ixia provide
Page 23 and 24: Appendix: 10GE Testing Examples The
Page 25 and 26: 2. Testing for Latency: RFC 2544 La
Page 27 and 28: Methodology 1. Packets will be sent
Page 29 and 30: Results. The test results provide a
Page 31: Ternary Content Addressable Memory

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