Cisco 10000-2P2-2DC Software Guide - Page 64

Line Card VC Limitations Chapter 2 Scalability and Performance Table 2-1 Parameter Priority ATM Service Categories CBR VBR-rt 0 1 VBR-nrt 2 Shaped UBR 3 Unshaped UBR None The number of SAR priority levels and the service categories supported at each priority level vary from line card to line card. For example, the 1-port OC-12/STM-1 line card supports the four levels of priority and the service categories listed in Table 2-2, but the 4-port OC-3 line card supports only two levels of priority and the service categories listed in the table. The ATM line cards support a maximum number of VCs per priority. That VC limit depends on the VC limit of the SAR (SAR limit) and the number of priority levels configured. Table 2-2 describes how to determine the VC limit per priority level per port for the specified line cards. Table 2-2 Maximum Number of VCs per Priority ATM Line Card SAR Priority Levels 1-Port OC-12/ 0 = CBR VCs STM-1 1 = VBR-rt VCs 2 = VBR-nrt VCs 3 = UBR VCs VC Rate Full line rate Half line rate and below 4-Port OC-3 0 = CBR, VBR-nrt VCs Half line rate 1 = UBR VCs and below 8-Port E3/DS3 0 = CBR VCs 0 = VBR-nrt VCs 1 = UBR VCs Half line rate and below Maximum Number of VCs per Priority SAR limit / 2 / number of priority levels 4 priority system: 65,536 / 2 / 4 = 8192 VCs per priority level SAR limit / number of priority levels 4 priority system: 65,536 / 4 = 16,384 VCs per priority level SAR limit / number of PHYs / number of priority levels 2 priority system: 65,536 / 4 / 2 = 8192 VCs per priority level per port SAR limit / number of PHYs / number of priority levels 2 priority system: 65,536 / 8 / 2 = 4096 VCs per priority level per port Configuring more channels or VCs than there are available priority locations can cause random channels or VCs to get stuck in the SAR. This occurs when an active channel tries to reschedule itself, but no priority locations are available. Therefore, the channel cannot find a place to reschedule itself, which results in a lost event for the channel, and the channel becomes stuck in the SAR. On the PRE2, when a VC becomes stuck in the SAR, the PRE2 scheduler stops forwarding traffic on only the VC that is stuck in the SAR; the other VCs still carry traffic. On the PRE3, the PRE3 scheduler stops forwarding traffic on all the VCs configured on that ATM line card. For example, suppose a 1-port OC-12 line card at full line rate is configured for four levels of priority and a 4-port OC-3 line card at half line rate is configured for two levels of priority. By calculating the maximum number of VCs as described in Table 2-2, you can configure 8192 VCs per priority level for Cisco 10000 Series Router Software Configuration Guide 2-2 OL-2226-23