本文档旨在说明在使用DSL连接的Cisco 8xx路由器上可能测量到的异常延迟。
在这种情况下,有两个参数可能影响延迟:
流量整形
DSL参数
对于Cisco 8xx DSL路由器,ATM流量整形是使用软件完成的,因此不太准确。整形是通过在没有要发送的数据的时间和当PVC超过其PCR时发送空闲信元来实现的。从路由器执行ping测试时,通常会观察到延迟。由于ping不在持续流量中,因此当ping完成时会有额外延迟。由于连接处于空闲状态,因此一旦对已处于空闲状态的连接执行ping操作,就可能发送空闲信元。仅在发送这些空闲信元后,才会发送ping信元。
当线速非常小(如64k或128k)时,这种额外延迟更为主要。对于高上行速度,它并非非常主导。
另一方面,DSL参数也会由于它们带来的开销而增加延迟(FEC字节、交织等)。要降低此问题的影响,可以执行以下任务:
使用no atm traffic-shaping命令完全禁用流量整形。由于没有整形,因此不发送空闲信元。
使用no atm cell-clumping-disable命令减少延迟。此处执行整形,但数据单元可以在群中发送,而不是持续发送。如果在ATM交换机上执行管制,则可能需要调整CDVT。此外,在此场景中不发送空闲信元。
注意:但是,不建议使用此命令。
调整DSL参数,以减少由它们引起的开销。但是,此解决方案需要谨慎使用,因为如果DSL线路导致错误,可能会导致性能下降。
此行为已在Bug CSCdy44786中描述,该漏洞已关闭,因为这是8xx路由器的限制。
本文档包含几个说明此行为的性能测试。使用的设置如下:
ADSL路由器是运行12.2(8)YM的827路由器
Cisco Internetwork Operating System Software IOS (tm) C820 Software (C820-SV6Y6-M), Version 12.2(8)YM, EARLY DEPLOYMENT RELEASE SOFTWARE (fc1) Synched to technology version 12.2(11.2u)T TAC Support: http://www.cisco.com/tac Copyright (c) 1986-2002 by cisco Systems, Inc. Compiled Fri 23-Aug-02 00:53 by ealyon Image text-base: 0x80013170, data-base: 0x80C4FA74 ROM: System Bootstrap, Version 12.2(1r)XE2, RELEASE SOFTWARE (fc1) ROM: C820 Software (C820-V6Y6-M), Version 12.2(8)T5, RELEASE SOFTWARE (fc1) ADSL-router uptime is 7 weeks, 22 hours, 40 minutes System returned to ROM by power-on System image file is "flash:c820-sv6y6-mz.122-8.YM.bin" CISCO C827-4V (MPC855T) processor (revision 0xD01) with 31744K/1024K bytes of memory. Processor board ID JAD050767V4 (2609117246), with hardware revision 5916 CPU rev number 5 Bridging software. 4 POTS Ports 1 Ethernet/IEEE 802.3 interface(s) 1 ATM network interface(s) 128K bytes of non-volatile configuration memory. 16384K bytes of processor board System flash (Read/Write) 2048K bytes of processor board Web flash (Read/Write) Configuration register is 0x2102
有关文档规则的详细信息,请参阅 Cisco 技术提示规则。
本文档没有任何特定的前提条件。
本文档不限于特定的软件和硬件版本。
本文档中的信息都是基于特定实验室环境中的设备创建的。本文档中使用的所有设备最初均采用原始(默认)配置。如果您是在真实网络上操作,请确保您在使用任何命令前已经了解其潜在影响。
对于第一次测试,上行和下行速度将配置为128Kbps。我们将比较RTT时间:
VBR-nrt用作128kbps
未使用VBR-nrt
没有流量整形
ADSL-router#show dsl int atm 0 ATU-R (DS) ATU-C (US) Modem Status: Showtime (DMTDSL_SHOWTIME) DSL Mode: ITU G.992.1 (G.DMT) ITU STD NUM: 0x01 0x01 Vendor ID: 'ALCB' 'ANDV' Vendor Specific: 0x0000 0x0000 Vendor Country: 0x00 0x00 Capacity Used: 7% 31% Noise Margin: 29.0 dB 23.0 dB Output Power: 18.0 dBm 12.5 dBm Attenuation: 1.0 dB 7.0 dB Defect Status: None None Last Fail Code: None Selftest Result: 0x49 Subfunction: 0x02 Interrupts: 49941 (1 spurious) Activations: 41 Init FW: embedded Operartion FW: embedded SW Version: 3.8129 FW Version: 0x1A04 Interleave Fast Interleave Fast Speed (kbps): 128 0 128 0 Reed-Solomon EC: 0 0 0 0 CRC Errors: 0 0 0 0 Header Errors: 0 0 0 0 Bit Errors: 0 0 BER Valid sec: 0 0 BER Invalid sec: 0 0 <skip>
第一种情况是,通过如下所示显式配置ADSL路由器,确保vbr-nrt为128Kbps:
interface ATM0.100 point-to-point ip address 1.1.1.1 255.255.255.0 pvc 2/100 vbr-nrt 128 128 encapsulation aal5snap
对终端设备执行多次ping操作,测量RTT时间,然后取平均值,如下所示:
ADSL-router#ping 1.1.1.2 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 1.1.1.2, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 72/73/80 ms ADSL-router#ping 1.1.1.2 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 1.1.1.2, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 64/71/76 ms
第二种情况是在PVC下不使用VBR-nrt。然后配置应如下所示:
interface ATM0.100 point-to-point ip address 1.1.1.1 255.255.255.0 pvc 2/100 encapsulation aal5snap
对终端设备执行多次ping操作,测量RTT时间,然后取平均值,如下所示:
ADSL-router#ping 1.1.1.2 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 1.1.1.2, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 40/40/44 ms ADSL-router#ping 1.1.1.2 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 1.1.1.2, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 40/41/44 ms
第三种情况是不使用ATM流量整形。要删除流量整形,请使用no atm traffic-shaping interface命令,如下所示。在这种情况下,配置如下:
interface ATM0 no atm traffic-shaping
对终端设备执行多次ping操作,测量RTT时间,然后取平均值,如下所示:
ADSL-router#ping 1.1.1.2 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 1.1.1.2, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 36/40/44 ms ADSL-router#ping 1.1.1.2 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 1.1.1.2, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 36/40/44 ms
在上述测试中,我们可以看到,ATM流量整形会增加ping的RTT,即使PVC整形的值等于线路带宽。
此测试重复测试1中执行的三种情况,但带宽较少。在本例中,我们仅使用64kbps上游。
ADSL-router#show dsl int atm 0 ATU-R (DS) ATU-C (US) Modem Status: Showtime (DMTDSL_SHOWTIME) DSL Mode: ITU G.992.1 (G.DMT) ITU STD NUM: 0x01 0x01 Vendor ID: 'ALCB' 'ANDV' Vendor Specific: 0x0000 0x0000 Vendor Country: 0x00 0x00 Capacity Used: 6% 14% Noise Margin: 31.0 dB 27.0 dB Output Power: 18.0 dBm 12.0 dBm Attenuation: 1.0 dB 7.0 dB Defect Status: None None Last Fail Code: None Selftest Result: 0x49 Subfunction: 0x02 Interrupts: 49948 (1 spurious) Activations: 42 Init FW: embedded Operartion FW: embedded SW Version: 3.8129 FW Version: 0x1A04 Interleave Fast Interleave Fast Speed (kbps): 64 0 64 0 Reed-Solomon EC: 0 0 0 0 CRC Errors: 0 0 0 0 Header Errors: 0 0 0 0 Bit Errors: 0 0 BER Valid sec: 0 0 BER Invalid sec: 0 0 <skip>
通过如下所示显式配置ADSL路由器,确保vbr-nrt为64Kbps:
interface ATM0.100 point-to-point ip address 1.1.1.1 255.255.255.0 pvc 2/100 vbr-nrt 64 64 encapsulation aal5snap
对终端设备执行多次ping操作,测量RTT时间,然后取平均值,如下所示:
ADSL-router#ping 1.1.1.2 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 1.1.1.2, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 104/113/120 ms ADSL-router#ping 1.1.1.2 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 1.1.1.2, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 104/113/120 ms
第二种情况是在PVC下不使用VBR-nrt。为此,请从接口使用no vbr-nrt 64 64配置命令。然后,配置如下所示:
interface ATM0.100 point-to-point ip address 1.1.1.1 255.255.255.0 pvc 2/100 encapsulation aal5snap
对终端设备执行多次ping操作,测量RTT时间,然后取平均值,如下所示:
ADSL-router#ping 1.1.1.2 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 1.1.1.2, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 56/64/80 ms ADSL-router#ping 1.1.1.2 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 1.1.1.2, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 56/60/72 ms
第三种情况是不使用ATM流量整形。在这种情况下,在步骤2中的配置中使用no atm traffic-shapingconfig命令。
对终端设备执行多次ping操作,测量RTT时间,然后取平均值,如下所示:
ADSL-router#ping 1.1.1.2 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 1.1.1.2, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 52/56/60 ms ADSL-router#ping 1.1.1.2 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 1.1.1.2, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 52/56/60 ms
如上例所示,64kbps的ping的RTT高于128kbps的RTT。
本测试将展示细胞聚集对整体RTT的影响。上行比特率为128Kbps,并且将使用64Kbps VBR-nrt PVC。
interface ATM0 no atm cell-clumping-disable ! interface ATM0.100 point-to-point ip address 1.1.1.1 255.255.255.0 pvc 2/100 vbr-nrt 64 64 encapsulation aal5snap ADSL-router#show dsl int atm 0 ATU-R (DS) ATU-C (US) Modem Status: Showtime (DMTDSL_SHOWTIME) DSL Mode: ITU G.992.1 (G.DMT) ITU STD NUM: 0x01 0x01 Vendor ID: 'ALCB' 'ANDV' Vendor Specific: 0x0000 0x0000 Vendor Country: 0x00 0x00 Capacity Used: 7% 32% Noise Margin: 30.0 dB 23.0 dB Output Power: 18.0 dBm 12.0 dBm Attenuation: 1.0 dB 7.0 dB Defect Status: None None Last Fail Code: None Selftest Result: 0x49 Subfunction: 0x02 Interrupts: 50011 (1 spurious) Activations: 50 Init FW: embedded Operartion FW: embedded SW Version: 3.8129 FW Version: 0x1A04 Interleave Fast Interleave Fast Speed (kbps): 576 0 128 0 Reed-Solomon EC: 0 0 0 0 CRC Errors: 0 0 0 0 Header Errors: 0 0 0 0 Bit Errors: 0 0 BER Valid sec: 0 0 BER Invalid sec: 0 0 <skip>
对终端设备执行多次ping操作,测量RTT时间,然后取平均值,如下所示:
ADSL-router#ping 1.1.1.2 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 1.1.1.2, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 40/42/44 ms ADSL-router#ping 1.1.1.2 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 1.1.1.2, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 40/43/44 ms
删除单元格集合并见证对RTT的影响:
interface ATM0 atm cell-clumping-disable
对终端设备执行多次ping操作,测量RTT时间,然后取平均值,如下所示:
ADSL-router#ping 1.1.1.2 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 1.1.1.2, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 76/79/84 ms ADSL-router#ping 1.1.1.2 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 1.1.1.2, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 76/80/88 ms
上述测试表明,显着启用聚集可以降低RTT。但是,不建议使用集聚。由于信元以集群形式发送,如果连接的ATM交换机/DSLAM正在执行策略管制,则某些信元可能会因违反合同而被丢弃。
本最终测试将显示DSL开销对整体RTT的影响。对于此测试,已配置DSLAM,因此线路使用0个检查字节(在DSLAM的配置文件中配置)。 路由器上使用的配置如下:
interface ATM0.100 point-to-point ip address 1.1.1.1 255.255.255.0 pvc 2/100 vbr-nrt 64 64 encapsulation aal5snap ADSL-router#sh dsl int atm 0 ATU-R (DS) ATU-C (US) Modem Status: Showtime (DMTDSL_SHOWTIME) DSL Mode: ITU G.992.1 (G.DMT) ITU STD NUM: 0x01 0x01 Vendor ID: 'ALCB' 'ANDV' Vendor Specific: 0x0000 0x0000 Vendor Country: 0x00 0x00 Capacity Used: 7% 27% Noise Margin: 26.5 dB 21.0 dB Output Power: 18.0 dBm 12.0 dBm Attenuation: 1.0 dB 7.0 dB Defect Status: None None Last Fail Code: None Selftest Result: 0x49 Subfunction: 0x02 Interrupts: 50025 (1 spurious) Activations: 52 Init FW: embedded Operartion FW: embedded SW Version: 3.8129 FW Version: 0x1A04 Interleave Fast Interleave Fast Speed (kbps): 576 0 128 0 Reed-Solomon EC: 0 0 0 0 CRC Errors: 0 0 0 0 Header Errors: 0 0 0 0 Bit Errors: 0 0 BER Valid sec: 0 0 BER Invalid sec: 0 0 <skip> ADSL-router#ping 1.1.1.2 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 1.1.1.2, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 56/62/68 ms ADSL-router#ping 1.1.1.2 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 1.1.1.2, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 56/59/68 ms
如您所见,降低DSL开销也可改善整体RTT。但是,通过减少DSL开销,您会增加DSL线路产生错误时数据丢失的可能性。这是因为DSL链路上发生的错误无法纠正。因此,应仔细调整DSL参数。
从以上所有数据中都可以看出,延迟较低,而在高上游速度下,当流量整形时,ping RTT保持相对相同。但是,上游带宽越小,带流量整形和不带流量整形的差异就越大。
此外,即使信元聚集由于信元以群形式发送而改善了RTT,但如果CDVT配置过紧,所连接的ATM交换机/DSLAM可能会丢弃信元。因此,不建议使用此配置。
版本 | 发布日期 | 备注 |
---|---|---|
1.0 |
14-Dec-2007 |
初始版本 |