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Document ID: 6502

PDF Downloads Configuring and Troubleshooting ATM Connection Configurations and Cisco BPX 8600 Series Switches

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More... Related Products/Technology • Cisco BPX 8600 Modules • Cisco IGX 8400 Series Switches • Cisco BPX/IGX/IPX WAN Software • Cisco BPX 8600 Series Switches

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Contents Introduction Prerequisites Requirements Components Used Conventions Background Information Leaky Buckets Policing Options Troubleshoot Connections Constant Bit Rate (CBR) CBR Introduction Connection Parameters Details Screen Shots dspchstats Detail Variable Bit Rate (VBR) Real Time and Non-real Time Connections Connection Parameters Details Screen Shots Available Bit Rate (ABR) ABR Introduction Resource Management (RM) Cells Connection Parameters Details Summary of ABR Connection Configuration Parameter Differences Summary of Differences Between ABR Standard With VS/VD and ABR With Foresight Screen Shots Changes for BXM Model F Firmware and Switch Software Release 9.2.x Unspecified Bit Rate (UBR) UBR Introduction Connection Parameters Details

Screen Shots References Leaky Bucket Colloquial, Industry Slang Terms Acronyms Concepts and Definitions Related Information Introduction This document is a configuration guide for ATM connections for the Cisco BPX 8600 Series Switch Broadband Switch Module (BXM) using switch software release 8.4.x and later. Configuring ATM connections on the Cisco BPX 8600 Series Switch has changed from switch software release 8.1.x to 9.2.x. The bulk of the changes occurred when the ATM Forum-compliant BXM card was introduced with switch software release 8.4. The predecessors to the BXM, the ASI and BNI cards used a proprietary ATM-like cell structure and policing mechanism. This document provides a broad overview of ATM service for 8.4.x and later networks using the BXM. Since the Cisco WAN Manager (formerly SV+) Connection Manager values for ATM connections are restricted in range, they are not addressed in this document. For additional information, see the References section of this document for: Leaky Bucket Colloquial, Industry Slang Terms Acronyms Concepts and Definition Prerequisites Requirements There are no specific requirements for this document. Components Used This document is not restricted to specific software and hardware versions. Conventions For more information on document conventions, refer to the Cisco Technical Tips Conventions. Background Information

Leaky Buckets When a customer purchases a service from an ATM service provider, a traffic contract is agreed on. This traffic contract specifies the expected network quality of service when the user's traffic is compliant with the predetermined parameters such as: Peak Cell Rate (PCR) Cell Delay Variation Tolerance (CDVT) Sustainable Cell Rate (SCR) Maximum Burst Size (MBS) Customer traffic compliance with the contract is performed at the ingress to the ATM network. Once the traffic is admitted to the ATM network, it expects to be transported to the destination. The traffic contract is enforced by the Broadband Switch Module (BXM) Routing Control, Monitor, and Policing (RCMP) chip. This chip performs the traffic policing, or screening function for all ATM connections. "Dual leaky bucket" is a colloquial term used to describe the algorithm used for conformance checking of cell flows against the set of parameters specified in the traffic contract. For additional definitions, see the Leaky Bucket Colloquial, Industry Slang Terms section. The rate that cells flow into the network is determined by the "leak rate" using PCR or SCR parameters. Cell bursts are determined by the "bucket depth" using CDVT or MBS parameters. The parameters for PCR, CDVT, SCR, and MBS are user-configurable using the cnfcon command and are used by switch software to derive Burst Tolerance (BT). Burst Tolerance is used to police the second leaky bucket. The relationship between BT and MBS is defined by BT = (MBS-1) * (1/SCR - 1/PCR). The parameter values for PCR, CDVT, SCR, and MBS should directly reflect those values specified in the traffic contract. If the parameter values for PCR, CDVT, SCR, and MBS exceed the values specified in the traffic contract, the traffic in excess of the specific values may be discarded due to service provider policing. For example, if a customer purchases a 10 Mbps CBR ATM service from a service provider, and they configure their equipment to provide 25 Mbps of CBR traffic to that service provider, then 15 Mbps of CBR traffic may be discarded by the service provider as non-compliant.

The first leaky bucket screens for traffic contract compliance. If a cell does not meet the terms of the traffic contract, the cell is discarded. No Cell Loss Priority (CLP) tagging is performed at the first leaky bucket. The CLP setting of the ATM cell determines the priority of the cell through the network. The CLP setting is one bit in the ATM cell header that can either be a 0 or a 1. Cells with the CLP bit set to 0 have higher priority in the network than cells with the CLP bit set to 1. The second leaky bucket evaluates cells from the first leaky bucket to determine whether or not CLP tagging must be performed. A cell that is 'tagged' has the CLP bit set to 1. Because CBR connections only have PCR and CDVT parameters, CBR traffic is policed only on the first Leaky Bucket. Another way to visualize the policing process is shown in the diagrams below. In the diagrams, Incoming Data represents ATM cells that come from customer premise equipment (CPE). Cells that comply with the terms of the contract are shown as having tokens. Cells with tokens are allowed to pass through the first Leaky Bucket. Any cell that does not have a token (whether the CLP bit is set to 0 or 1) is not compliant. All cells that pass through the second Leaky Bucket are guaranteed transport through the WAN Switching network as CLP=0 or CLP=1 traffic. Unexpected congestion caused by trunk failures or other outage may occur, resulting in some ATM cells being dropped inside the WAN Switching network. Cells that are tagged CLP=1 will be discarded before cells that are tagged CLP=0. Even for CLP=0 cells that have successfully passed the policing function and are allowed into the WAN Switching network, discards may occur due to unexpected congestion. Compliant cells can be discarded due to network events that are beyond customer and service provider control. There is no 'credit' scheme for ATM policing. If data is transmitted continuously in excess of PCR for 10 hours and the connection is then idle for 14 hours, no extra 'credit' is allocated to the connection during those 14 idle hours to 'make up' for the earlier. A common fallacy that has a negative impact on traffic throughput is the idea that manually setting the ATM cell CLP bit to 1 decreases the amount of time cells spend in the RCMP chip and increases their delivery rate to the network. Configuring the ATM cell CLP bit to 1 prior to entry to the Cisco BPX 8600 Series Switch only eliminates the requirement to evaluate the cell at the second Leaky Bucket. The ATM cell still traverses the BXM RCMP chip and does not get admitted to the network ahead of other traffic. ATM cells with the CLP bit set to 1 are more likely to be discarded in the network. Network discards typically occur at egress trunk queues or egress port

queues. Dual Leaky Bucket Functionality Based on ATM Traffic Management Specification Version 4.0

Policing Options For CBR, VBR, and ABR ATM connection types, policing can be configured for Types 1, 2, 3, 4, or 5. The CBR, VBR, and ABR policing algorithms are summarized in this table. For UBR ATM connections, policing is configured using the CLP setting. "cnfcon" Policing Description Type BPX BXM ATM TM 4.0 Connection Conformance Type Definition

1

Policing and discards on both leaky VBR, ABR buckets for CLP=0+1 traffic. Policing and discards on the first leaky bucket for CLP=0+1 traffic; VBR, ABR policing and discards on the second leaky bucket for CLP=0 traffic. Policing and discards on the first leaky bucket for CLP=0+1 traffic; VBR, ABR policing and tagging on the second leaky bucket for CLP=0 traffic. Policing and discards on the first leaky bucket for CBR, VBR, CLP=0+1 traffic. ABR No policing on the second leaky bucket. Policing is CBR, VBR, disabled. Use ABR only for troubleshooting

VBR.1

2

VBR.2

3

VBR.3

4

CBR.1

5

as one misbehaving (noncompliant) connection can affect others. The policing types are illustrated in these five diagrams. Policing Option 1

Policing Option 2

Policing Option 3

Policing Option 4

Policing Option 5

Troubleshoot Connections To aid in troubleshooting, the BXM trunk offers dspchstats functionality similar to the BXM line. BXM model F firmware introduces changes to the output of the dspchstats command. Due to an enhancement request for the BXM model F, resource management (RM) cells in the From Network field are no longer registered or displayed. The From Network counter only registers and displays user data cells received from the crosspoint switch. RM cell discards have also been removed from the TX Clp 0+1 Dscd and the TX Clp 0 Dscd registers. For switch software release 9.2.x and later, the TX Clp 0+1 Dscd, TX Clp 0 Dscd, and the

TX Clp 1 Dscd counters have been removed from the dspchstats screen and replaced with these counters: Receives CLP 0 user cells discarded due to a VC_Q overflow (Ingress). Receives CLP 1 user cells discarded due to a VC_Q overflow (Ingress). Non-Compliant CLP 0 user cells discarded by the policer (Ingress). Non-Compliant CLP 1 user cells discarded by the policer (Ingress).

Oflw CLP0 Dscd

Oflw CLP1 Dscd

NCmp CLP0 Dscd

NCmp CLP1 Dscd

The ingress virtual source/virtual destination allowed cell rate (Igr VSVD ACR) and egress virtual source/virtual destination allowed cell rate (Egr VSVD ACR) counters apply only to ABR connections that have VSVD enabled. To configure VSVD, refer to Available Bit Rate. To obtain dspchstats information for a target connection, issue the StrataCom-level dcct <connection_number> command and scroll to the last screen. Use the This Chan value to complete the dspchstats <trunk_slot.trunk_port.This_Chan> command.

Constant Bit Rate (CBR) CBR Introduction CBR connections are used for delay- and jitter-sensitive Time Division Multiplex (TDM) traffic such as voice, video, and circuit emulation services in an ATM network. The CBR service category is used by connections that request a static amount of bandwidth that is continuously available during the connection lifetime. This amount of bandwidth is characterized by the Peak Cell Rate (PCR). Due to the TDM nature of the traffic, CBR service is typically the most expensive service offered by commercial carriers. For WAN Switching equipment, CBR connections are the simplest to configure and troubleshoot. There is no ingress VC_Queue used for CBR service; BXM QBINs are used. If VC Shaping (for example, traffic shaping) is enabled per line, egress VC_Queues are used. For WAN switch software release 9.1 and 9.2, do not enable VC Shaping on trunks unless VC Shaping functionality has been verified. CBR connections are policed on the first Leaky Bucket and, if traffic does not comply, it is discarded. All non-compliant cells (whether CLP=0 or CLP=1) are discarded at the first Leaky Bucket. As CBR service is guaranteed at PCR, the second Leaky Bucket is not used to evaluate CBR traffic. Please refer to the Policing Option 4 diagram for an illustration. Connection Parameters The parameters listed here are in the order that they appear in the cnfcon display. PCR(0+1): This is the Peak Cell Rate for all traffic: CLP=0 and CLP=1.

% Util: This is the amount of time the connection is expected to be transmitting at PCR (0+1) into the network. CDVT(0+1): This is the CDVT for all traffic: CLP=0 and CLP=1 Policing: The algorithm used to determine conformance to traffic contract. Trunk Cell Routing Restrict: Whether switch software routes the connection across a non-cell-based trunk. Details PCR(0+1): (PCR (0+1)) * (% Util) = the amount of bandwidth allocated in the network for a CBR connection. This is expressed in load units on a trunk and can be inspected using the dspload <trunk_number> command. % Util: For CBR traffic, it is recommended to leave % Util at 100. CDVT(0+1): The amount of 'clumping' between ATM cells. Some routers require high Cell Delay Variation Tolerance (CDVT) values (250,000 microseconds) due to performance issues. For voice, video, or circuit emulation services CDVT values such as 5,000 microseconds or less is desired to ensure constant play-out of cells. When a CBR connection is used to provide a Virtual Trunk, the CDVT should be configured to accommodate all traffic streams that use the Virtual Trunk (for example, CBR, VBR, ABR, and UBR). Configuring a CBR connection that carries a Virtual Trunk with a small CDVT value such as 500 microseconds may result in traffic drops on the different data streams that ride over the Virtual Trunk. The load model does not use CDVT to calculate bandwidth through the network. If CDVT is configured to be the maximum of 250000 for 1000 connections, the actual load on the network is significantly understated. Policing: Can only be configured to 4 (CBR.1) or 5 (disabled) for CBR connections. For troubleshooting, it is recommended to disable policing by selecting 5 from the cnfcon command. After policing has been disabled, always remember to re-enable policing since one misbehaving connection can affect all connections of the same type on a port. Trunk Cell Routing Restrict: This setting determines whether the connection can be routed across a non-cell-based trunk such as an NTM. For example, if Trunk Cell Routing Restrict is set to Y, then the connection will not route across an NTM trunk. The default setting for the Trunk Cell Routing Restrict parameter can be set from cnfnodeparm Trk Cell Rtng Restrict parameter 41. This parameter is not applicable and is not displayed for local (for example, DACs-type) connections. For troubleshooting,

verify the Trunk Cell Routing Restrict setting at both ends of a connection using the dspchcnf command. Screen Shots This is a sample CBR connection with incoming traffic set to 1000 CPS, PCR of 500 CPS, and policing option 4. Note the NonCmplnt Dscd is approximately one-half the offered rate of traffic.

This is a sample CBR connection with incoming traffic set to 1000 CPS, PCR of 500 CPS, and policing option 5.

dspchstats Detail For switch software release 9.2.x and later, the Tx Clp 0+1 Dscd, TX Clp 0 Dscd, and the TX Clp 1 Dscd counters have been removed from the dspchstats screen and replaced with these counters: Oflw CLP0 Dscd Oflw CLP1 Dscd NCmp CLP0 Dscd NCmp CLP1 Dscd The counters for dspchstats, including the four fields added in switch software release 9.2.x, are described in this table. Field Name Description Connection Type VBR/ABR/UBR. AAL5 is

Rx Frames

Number of ingress ATM SAR PDU

Rcv

frames received. required as This is calculated in EOF marker is the RCMP using the used. ATM cell PTI field EOF marker.

Depth (in cells) of the connection TX Q Depth All Egress Queue Engine on the BXM. Ingress VSVD ACR. The allowed cell rate (in cells) for ingress ABR traffic. This is nonconfigurable and varies based on whether any congestion is experienced at the local end. PCR>ACR>MCR. ACR=ICR at T0

Igr VSVD ACR

ABR only. Field is used for ABR standard and ABR Foresight.

Rx Clp0+1 Port

Number of cells marked with CLP=0 and CLP=1 received at the port (for example, from CPE). All This indicates whether cells are received with CLP=1 from the other device. CLP=0 cells dropped due to ingress Queue Engine (QE) All overflow. This statistic is derived

Oflw CLP0 Dscd

from the difference between the number of CLP=0 cells that arrive at the QE and the number of departing CLP=0 cells. This is not reliable for ABR connections because RM cells are sourced/terminated to/from the data stream by the QE. The statistics used to derive this counter are collected from the QE for each connection. All cells (CLP=0 and CLP=1 traffic) dropped due to policing at the ingress of the connection. The NonCmplnt policing depends All upon which option Dscd has been selected for the connection (policing option 1, 2, 3, 4 or 5). This statistic is collected from the RCMP. The number of cells marked CLP=0 All received at the port (for example, from

Rx CLP0

CPE). This can be used to determine the number of cells that are received with CLP=1 from the other device. Egress VSVD ACR. The allowed cell rate for egress ABR traffic. This is nonconfigurable and varies based on whether the external device sends information to the BPX BXM port. PCR>ACR>MCR. ACR=ICR at T0

Egr VSVD ACR

ABR only.

CLP=0 cells dropped due to policing at the ingress of the connection. The policing depends NCmp CLP0 upon which option All has been selected Dscd for the connection (policing option 1, 2, 3, 4 or 5). This statistic is collected from the RCMP. CLP=1 cells dropped due to ingress Queue Engine (QE) All overflow. This statistic is derived from the difference between the

Oflw CLP1 Dscd

number of CLP=1 cells that arrive at the QE and the number of departing CLP=1 cells. This is not reliable for ABR connections because RM cells are sourced/terminated to/from the data stream by the QE. The statistics used to derive this counter are collected from the QE for each connection whether it is CBR, VBR, ABR, or UBR. Depth (in cells) of Rx Q Depth ingress connection queue. Number of cells received from the network (trunk) with CLP=0. Number of cells transmitted to the port (for example, from CPE) with CLP=0.

All

Rx Nw CLP0

All

TX Clp0 Port

All

CLP=1 cells dropped NCmp CLP1 due to policing at All Dscd the ingress of the connection. The

policing depends upon which option is selected for the connection (policing option 1, 2, 3, 4 or 5). This statistic is collected from the RCMP. Variable Bit Rate (VBR) Real Time and Non-real Time Connections VBR connections are classified into real time and non-real time categories. Real time VBR connections are used to transport delay sensitive applications that may also exhibit bursty behavior, such as Voice Activity Detection (VAD) voice and data traffic in an ATM network. Non-real time VBR connections are used to transport bursty data that is not sensitive to variation in delay in an ATM network. The amount of bandwidth required for VBR connections is characterized by PCR, SCR, and MBS. Due to the delay-sensitive nature of the traffic, rt-VBR service is typically more expensive than nrt-VBR, ABR, and UBR service offered by commercial carriers. For WAN switching equipment, VBR connections are simple to configure and troubleshoot. There is no VC_Queue used for VBR service except on the egress direction when traffic shaping is enabled. BXM QBINs are also used. VBR connections are policed on both Leaky Buckets. Connection Parameters These parameters are in the order that they appear in the cnfcon display. PCR(0+1): This is the Peak Cell Rate for all traffic (CLP=0 and CLP=1). % Util: This is the amount of time the connection is expected to be transmitting at PCR (0+1) into the network. CDVT(0+1): This is the CDVT for all traffic (CLP=0 and CLP=1). AAL5 FBTC: ATM Adaptation Layer type 5 Frame-Based Traffic Control. SCR: This is the Sustainable Cell Rate for all traffic (CLP=0 and CLP=1). MBS: Maximum Burst Size

Policing: The algorithm used to determine conformance to traffic contract. Trunk Cell Routing Restrict: Whether switch software routes the connection across a non-cell-based trunk. Details PCR(0+1): (PCR (0+1)) * (% Util) = the amount of bandwidth allocated in the network for a VBR connection. This is expressed in load units on a trunk and can be inspected using the dspload <trunk_number> command. CDVT(0+1): The amount of 'clumping' between ATM cells. Some routers require high CDVT values (250,000) due to performance issues. This type of bursty traffic is suitable for nrt-VBR connection types. For the voice, video, or circuit emulation services, carried by rt-VBR connections, CDVT values such as 10,000 or less are desired to ensure rapid play-out of cells. AAL5 FBTC: If this option is enabled, it is assumed that the connection carries AAL5 frames. The term frame means the AAL5 PDU. AAL5 cells contain information to indicate the start and end of frame. FBTC enables Early Packet Discard (EPD) on all via trunks for a specific connection. EPD is a mechanism to discard all the ATM cells associated with a frame before they are admitted to the network. Without EPD, parts of an ATM frame may be transmitted through the network consuming bandwidth and resources. EPD is configured using thresholds based on connection Queue depth. If Queue depth exceeds the configured threshold (CLP Low), the new data frame is not accepted when the Start-of-Frame AAL5 cell arrives. For VBR traffic, EPD is allowed for rt-VBR and is configured per port using the cnfportq <slot_number.port_number> command. For purposes of this document, AAL5 FBTC is turned off to accommodate the traffic provided by the test set. The test set generates a constant stream of AAL1 traffic (no EOF flag). This traffic type causes inconsistent discards when AAL5 FBTC is Enabled. For AAL5 traffic, it is recommended to Enable AAL5 FBTC. SCR: The sustained cell rate used with the maximum burst size for policing on the second Leaky Bucket. SCR is used as the average rate for traffic and service contracts are typically sold using the SCR as the defined rate. The service is typically guaranteed by configuring PCR to be greater than SCR as PCR is used to reserve network resources. MBS: The maximum burst of cells that may be transmitted at the peak rate and not discarded or tagged. MBS is determined using burst tolerance, SCR, and the configured policing option. Policing: Can be configured to 1 (VBR.1), 2 (VBR.2), 3 (VBR.3), 4 (CBR.1), or 5 (disabled) for VBR connections. For VBR traffic, valid policing types are 1, 2, 3, and 5. Policing

types can be selected based on level of service. For VBR service advertising guaranteed SCR, policing option 3 is the most beneficial to the customer. Policing type 3 tags all cells above SCR (evaluated at the second leaky bucket) and only discards at the first leaky bucket. Policing types 1 and 2 support discards at the second leaky bucket, but policing type 2 avoids reevaluating CLP=1 cells. For troubleshooting, it is recommended to disable policing by selecting 5 using the cnfcon command. After policing has been disabled, always re-enable policing since one misbehaving connection can affect all connections of the same type on a port. Screen Shots Sample rt-VBR connection with incoming traffic set to 1000 CPS (AAL1), PCR of 1000 CPS, and policing option 3.

Sample nrt-VBR connection with incoming traffic set to 1000 CPS (AAL1), PCR of 1000 CPS, and policing option 3.

This is a sample rt-VBR connection with incoming traffic at 1000 CPS (AAL1), PCR of 500 CPS, and policing option of 3. Note the NonCmplnt Dscd and NCmp CLP0 Dscd fields indicate CLP=0 discards at the first leaky bucket.

This is a sample nrt-VBR connection with incoming traffic at 1000 CPS (AAL1), PCR of 500, and policing of 3. Note the NonCmplnt Dscd and NCmp CLP0 Dscd fields indicate CLP=0 discards at the first leaky bucket.

Available Bit Rate (ABR) ABR Introduction ABR connections are used for bursty, non-real time traffic such as file transfer in an ATM network. The ABR service category is used by connections that do not require a static amount of bandwidth that is continuously available during the connection lifetime. For ABR service, available bandwidth varies in the network, and feedback is used to control the source rate in response to bandwidth changes. The feedback is conveyed to the source through specific Resource Management (RM) cells. ABR connections use peak cell rate (PCR) and minimum cell rate (MCR) to vary the source rate as necessary. For WAN Switching equipment, ABR connections are complex to configure and troubleshoot. There is a VC_Queue and QBIN used for ABR service. ABR connections are policed using the generic algorithm illustrated in the Dual Leaky Bucket diagram. Two types of ABR connections can be configured on WAN switches; ABR standard (abrstd) and ABR with Foresight (abrfst). Both ABR connection types use compliant ATM cells, but they use different mechanisms to implement traffic management.

ABR standard is the default ABR connection type when neither Foresight nor ABR standard with virtual source/virtual destination (VS/VD) have been enabled using cnfswfunc. ABR standard with VS/VD builds on the ABR standard connection by adding virtual endpoints for increased congestion control. ABR standard connection parameters are a subset of the ABR standard with VS/VD parameters, and are not addressed separately. The Foresight or ABR standard with VS/VD feature only needs to be enabled on one BPX to propagate to all nodes. These are the only two software features that behave like system parameters configurable using the cnfsysparm command. The Foresight software feature is billable and the ABR standard with VS/VD software feature is offered free of charge. There are significant differences between ABR standard with VS/VD and Foresight connection parameters and performance measurements. The summary of differences is discussed in the Summary of ABR Connection Configuration Parameter Differences table. Resource Management (RM) Cells RM cells are used to provide network feedback to the end-system. RM cells are used only for ABR connections. CBR, VBR, and UBR connections do not use RM cells. RM cells for an ABR Standard (ABRSTD) connection are generated differently than the RM cells for an ABR with Foresight connection. See the Summary of ABR Connection Configuration Parameter Differences table for more information. Using RM cells for feedback results in increased values for the To Network and From Network fields in the dspchstats screen for switch software release 9.1.x and earlier. For information on later releases, refer to Changes for BXM Model F Firmware and Switch Software Release 9.2.x. The end-system Customer Premise Equipment (CPE) is expected to adapt to variation in network resources as communicated by RM cells. CPE adaptation is required to minimize cell loss. RM cells do not go through the VC-Queue, and are served directly by the QBIN. For ABR standard with VS/VD (ABRSTD VS/VD) connections that have asymmetrical load, rate-based RM cells can present a problem as a different rate of BRM cells is generated for every FRM cell. Increasing the OOR RM cells on ABR standard with VS/VD connections (cnfcon Nrm value) mitigates this problem. It is important to note that ABRSTD VS/VD connections generate RM cells from both endpoints towards the opposite end point. The RM cells generated using the default connection parameters add overhead of 6%. This percentage is calculated by adding the 3% overhead generated from each connection terminating point. The additional 6% of RM cells consume some of the allocated bandwidth budget for the connection

and reduce the amount of available bandwidth for user traffic. For example, an ABRSTD connection with a PCR of 1000 cells per second (CPS) and all other parameters left to default limit the user traffic to approximately 940 CPS. The available bandwidth for user traffic may vary due to the granularity of the BXM. The equation used to calculate user traffic throughput for an ABRSTD VS/VD connection with a PCR of 1000 CPS is: 1000 CPS - (1000 CPS * 6%) = 1000 - 60 = 940 CPS If user traffic is required to run at a PCR of 1000 CPS, the connection PCR must be increased by at least 7% to allow user traffic to reach peak throughput. For example, if the peak user traffic throughput required is 1000 CPS and RM cell overhead is 6%, then the connection PCR should be configured for 1064 CPS. The equation used to calculate user traffic throughput of 1000 CPS for an ABRSTD VS/VD connection is: PCR (user cells and RM cells) = PCR (user cells) / 94% = 1000 / 0.94 = 1064 CPS The percentage of RM cells with respect to user cells is controlled by two PVC parameters (RTRM and RNRM are variables): If Trm = 100, then every 100 milliseconds (msec) an FRM cell is generated. TRM is time-based FRM cell generation that is most effective for low speed connections. Can be one of 8 distinct values based on the following formula: Trm = 100 / 2RTRM msec. Where RTRM is between 0 and 7. Can be one of 8 distinct values based on the following formula: Nrm = 2 * 2RNRM cells. Where RNRM is between 0 and 7.

Trm

Nrm

If Nrm = 32, then for every 32 user data cells, an FRM cell is generated. NRM is rate-based FRM cell generation that is most effective for high speed connections.

If Trm is set to 100 msec, then one RM cell is generated every 100 msec when user

traffic is present. An interval rate of 100 msec equates to an RM cell rate of 10 CPS. If Nrm is set to 32 cells, then one RM cell is generated for every 32 user data cells. The Broadband Switch Module (BXM) uses either the Nrm or Trm threshold based on the quantity of user traffic. For the values specified in the table, the Trm is the dominate factor for user data rates up to 320 CPS. At a user data rate of 320 CPS, Nrm also generates RM cells at 10 CPS. As the user data cell rate increases over 320 CPS, Nrm becomes the dominate factor and governs RM cell generation. RM cell generation is equivalent for Trm and Nrm at 320 user data cells per second. The equation used to calculate equivalent RM cell generation for Trm and Nrm is provided here given these assumptions: A default Trm value of 100 msec gives an RM cell rate of 10 CPS. A default Nrm value generates RM cells at 10 CPS when the user data traffic reaches 320 CPS. User traffic rate = 32 (user cells per RM cell) * 10 RM CPS (default Trm rate) = 320 (user data cells per second) The examples above utilize the Cisco default values for TRM and NRM. Each default value was chosen based on the ATM Forum recommendation. Connection Parameters The parameters that are listed here are in the order that they appear in the cnfcon display. PCR(0+1): This is the Peak Cell Rate for all traffic: CLP=0 and CLP=1. % Util: This is the amount of time the connection is expected to transmit at PCR (0+1) into the network. MCR: Minimum Cell Rate CDVT(0+1): This is the CDVT for all traffic: CLP=0 and CLP=1 AAL5 FBTC: ATM Adaptation Layer type 5 Frame-Based Traffic Control. VSVD*: Virtual Source Virtual Destination FCES: Flow Control External Segment SCR: This is the Sustainable Cell Rate for all traffic: CLP=0 and CLP=1 MBS: Maximum Burst Size Policing: The algorithm used to determine conformance to traffic contract.

VC Qdepth: Virtual Connection Queue Depth. Used only for VSVD connections. CLP Hi: Cell Loss Priority Tag High Threshold CLP Lo/EPD: Cell Loss Priority Tag Low Threshold/Early Packet Discard EFCI: Explicit Forward Congestion Indication ICR: Initial Cell Rate ADTF: ACR Decrease Time Factor Trm: Terminal RM cells RIF: Rate Increase Factor RDF: Rate Decrease Factor Nrm*: Maximum Number of cells between RM-cell generation FRTT*: Fixed Round-Trip Time TBE*: Transient Buffer Exposure Trunk Cell Routing Restrict: Whether switch software routes the connection across a non-cell-based trunk. * ABR standard (abrstd) with VS/VD connections only. Not displayed for abrfst connections. Details PCR (0+1): This is the Peak Cell Rate for all traffic: CLP=0 and CLP=1. % Util: This is the amount of time the connection is expected to transmit at PCR (0+1) into the network. MCR: (MCR (0+1)) * (% Util) is the amount of bandwidth allocated in the network for an ABR connection. This is expressed in load units on a trunk and can be inspected using the dspload <trunk_number> command. CDVT(0+1): The amount of 'clumping' between ATM cells. Some routers require high CDVT values (250,000) due to performance issues. AAL5 FBTC: If this option is enabled, it is assumed that the connection carries AAL5 frames. The term frame means the AAL5 PDU. AAL5 cells contain information to indicate the start and end of frame. Frame-Based Traffic Control (FBTC) enables Early Packet Discard (EPD) on all trunks for a specific connection. EPD is a mechanism to

discard all the ATM cells associated with a frame before they are admitted to the network. Without EPD, parts of an ATM frame may be transmitted through the network consuming bandwidth and resources. EPD is configured using thresholds based on connection Queue depth. If Queue depth exceeds the configured threshold, the new data frame is not accepted when the Start-of-Frame AAL5 cell arrives. For ABR traffic, EPD is configured per port using the cnfportq <slot_number.port_number> command. When enabled, FBTC uses the CLP Lo/EDP value for ABR connections. For purposes of this paper, AAL5 FBTC is turned off to accommodate the traffic provided by the test set. The test set generates a constant stream of ATM Adaptation Layer (AAL1) traffic (no EOF flag). This traffic type causes inconsistent discards when AAL5 FBTC is Enabled. For AAL5 traffic, it is recommended to Enable AAL5 FBTC. VSVD*: This option allows the BXM to provide virtual management endpoints in a network. It cannot be configured for abrfst-type connections. FCES: This option allows the BXM to provide congestion information to non-Cisco products using a standard interface. FCES extends ABR flow control to the external segment. Note: Do not enable if the attached equipment does not support FCES. SCR: This is the Sustainable Cell Rate for all traffic: CLP=0 and CLP=1. MBS: The maximum burst of cells that may be transmitted at the peak rate and not be discarded or tagged. MBS is determined using burst tolerance, SCR, and the configured policing option. Policing: Can only be configured to 1-4 (ABR.1) or 5 (disabled) for ABR connections. For troubleshooting, it is recommended to disable policing by selecting 5 from the cnfcon command. VC Qdepth: Connection threshold that allows the maximum number of cells queued per VC. This buffer is provided after cells have been through the policing stage. Separate VC_Queues are provided using the Schedule and ABR Engine (SABRE) chip for ABR connections. These VC_Queues are provided in addition to connection queues used for the CBR, VBR, and UBR traffic types. CLP Hi: Connection threshold that indicates when CLP=1 cells will start being discarded. This is performed in the VC_Queue after policing. CLP Hi is expressed as the percentage of VC_Queue depth. CLP Lo/EDP: Connection threshold that indicates when CLP=1 cells will stop being

discarded. If FBTC is enabled, it is the EDP threshold setting. This is performed in the VC Queue after policing. CLP Lo/EDP is expressed as the percentage of VC_Queue depth. EFCI: Connection threshold that uses the EFCI bit in the data cell to indicate congestion for abrfst connections. EFCI uses the CI bit in the RM cell to indicate congestion for abrstd connections. It is recommended to set EFCI threshold lower than CLP Lo/EPD. EFCI is expressed as the percentage of VC_Queue depth. ICR: Rate at which connection is allowed to transmit at if connection is idle. ADTF: ADTF is the idle time-out factor in milliseconds. If no RM cell is received within the time specified, the connection rate is ramped down to ICR. The BXM currently only supports these ADTF values: 62.5 msec 125 msec 250 msec 500 msec 1 sec 2 sec 4 sec 8 sec Trm: Refer to the summary table. RIF: Refer to the summary table. RDF: Refer to the summary table. Nrm*: Refer to the summary table. FRTT*: Refer to the summary table. TBE*: Refer to the summary table. * ABR standard (abrstd) with VS/VD connections only. Not displayed for abrfst connections. Summary of ABR Connection Configuration Parameter Differences

ABR Standard with VS/VD TRM is the minimum FRM interval. If TRM=100, then every 100 milliseconds an FRM are generated. RIF is an integer value. A large RIF means a small rate of increase. ACR1 = ACR0 + (ACR0/RIF) RDF is an integer value based on ACR. A large RDF means a slower rate of decrease. ACR1 = ACR0 - (PCR/RDF) NRM is the RM cell generation rate (for example, the number of RM cells in a block of cells). The default is 32 or 6% (for example, out of every 32 cells, an RM cell is issued).

ABR with Foresight

Minimum rate adjust interval for RM cells (40 milliseconds). On BXM cards Foresight RTD is not supported. RIF is a decimal value. Switch software calculates the RIF based on PCR. RDF is a percentage based on ACR. If RDF=93%, then 93% of the ACR is the current rate decrease factor.

Not applicable per connection. Use cnffstparm.

FRTT is the Fixed Round Not applicable per Trip Time in connection. Use microseconds. To cnffstparm. disable, use a value of 0. TBE is the Transient Buffer Exposure. The Not applicable per negotiated number of connection. Use cells (0 - 1,048,320 cells) cnffstparm. that the network would like to limit the source to

sending during startup periods, before the first RM cell returns. Summary of Differences Between ABR Standard With VS/VD and ABR With Foresight ABR Standard With VS/VD ABR With Foresight

FRM cells. The SABRE chip uses the CI bit of the FRM to generate the BRM.

No FRM cells. BCM cells are generated by destination every Rate Adjust Interval. The SABRE chip uses the EFCI bit of the data cell to set the CI bit of the BCM. Less overhead due to the time-based congestion control mechanism.

More overhead due to rate-based congestion control mechanism.

RM cells typically increase the dspchstats To Network and From Network cell counts by 6%. These fields have higher cell counts than the 'From Port' and 'To Port'. For networks with limited resources, the connection PCR may need to be increased to account for the additional 6% of RM cells Quicker response to Rate Adjust messages (ATM Forum is rate-

RM cells typically increase the dspchstats To Network and From Network cell counts.

Slower response to the Rate Adjust messages. Rate adjustment is time

based so RM cells are released in accordance with the rate). Explicit Rate congestion control provides an accurate and immediate new rate.

based (cnffstparm command).

Rates are adjusted by rate up and rate down parameters (cnffstparm command).

TBE, FRTT, ICR, CRM improve avoidance of Ignores ERS transient cell loss (initial start up of traffic flow). Distributes buffers at Relies on a few large each of the VS/VD loops buffers for greater efficiency. Screen Shots This is asample abrfst connection with incoming traffic at 1000 CPS, PCR of 1000, and a policing option of 3.

This is a aample abrfst connection with incoming traffic at 1000 CPS, PCR of 500, and a policing option of 3. Note the NonCmplnt Dscd, NCmp CLP0 Dscd, Igr VSVD ACR, and Rx Q Depth.

This is a sample abrfst connection with incoming traffic at 1000 CPS, PCR of 500, and a policing option of 5. Note the Oflw CLP0 Dscd, NonCmplnt Dscd, NCmp CLP0 Dscd, Igr VSVD ACR, and Rx Q Depth.

This is a sample abrstd connection with incoming traffic at 1000 CPS, PCR of 1000, and a policing option of 3.

This is a sample abrstd connection with incoming traffic at 1000 CPS, PCR of 500, and a policing option of 3. Note the NonCmplnt Dscd, NCmp CLP0 Dscd, Igr VSVD ACR, and Rx Q Depth.

Changes for BXM Model F Firmware and Switch Software Release 9.2.x BXM model F firmware introduces changes to the output of the dspchstats command. BXM model F firmware is available for registered Cisco.com users. Due to an enhancement request for the BXM model F, RM cells in the From Network field are no longer registered or displayed. The From Network counter only registers and displays user data cells received from the crosspoint switch. RM cell discards have also been removed from the Tx Clp 0+1 Dscd and the TX Clp 0 Dscd registers. For switch software release 9.2.x and later, the TX Clp 0+1 Dscd, TX Clp 0 Dscd, and the TX Clp 1 Dscd counters have been removed from the dspchstats screen and replaced with these counters: Receive CLP 0 user cells discarded due to a VC_Q overflow (Ingress).

Oflw CLP0 Dscd

Oflw CLP1 Dscd

Receive CLP 1 user cells discarded due to a VC_Q overflow (Ingress). Non-Compliant CLP 0 user cells discarded by the policer (Ingress). Non-Compliant CLP 1 user cells discarded by the policer (Ingress).

NCmp CLP0 Dscd

NCmp CLP1 Dscd

sbpx1 TN StrataCom BPX 8620 9.2.31 July 13 2000 08:46 GMT Channel Statistics for 1.6.1.100 Cleared: July 13 2000 07:46 (\) Snapshot MCR: 500/500 cps Traffic Cells Collection Time: 0 day(s) 00:03:55 Avg CPS 0 --0 495 495 528 495 99 0 Rx Q Depth : 0 Corrupted: NO

CLP

%util Chan Stat Addr: 30F68BD0 99 OAM Cell RX: Clear 105 99

From Port : 116432 To Network : 124195 From Network: 116433 To Port : 116433 0

Rx Frames Rcv : TX Q Depth :

0 NonCmplnt Dscd: 0 Rx CLP0

: 116432 Rx Nw CLP0 : 116433 0 TX Clp0 Port : 116433 0 NCmp CLP1 Dscd: 0

Igr VSVD ACR : 535 Egr VSVD ACR :

Rx Clp0+1 Port: 116432 NCmp CLP0 Dscd: Oflw CLP0 Dscd: 0 Oflw CLP1 Dscd: 0

Last Command: dspchstats 1.6.1.100 1 Unspecified Bit Rate (UBR) UBR Introduction UBR connections are used for bursty data, non-real time traffic (low priority file transfer) in an ATM network. The UBR service category is used by connections that do not require a static amount of bandwidth that is continuously available during the

connection lifetime. There is no network bandwidth guaranteed for UBR service. UBR traffic is transported through the WAN Switching network on a best effort basis. Due to the best effort delivery of UBR traffic, it is typically the least expensive service offered by commercial carriers. For WAN Switching equipment, UBR connections are simple to configure and troubleshoot. There is no VC_Queue used for UBR service; only the BXM ABR QBIN. Since UBR traffic uses the same QBIN as ABR traffic and can be misconfigured, the two traffic types should not be mixed on the same BXM port. UBR traffic must be configured for CLP=Y (UBR.2) if the ABR QBIN is shared with ABR traffic. Otherwise, UBR traffic looks like ABR traffic and can "starve out"' the ABR traffic in the QBINs. UBR connections are policed using the Dual Leaky Bucket algorithm with the second leaky bucket sustainable cell rate (SCR) value hard coded in the BXM to 0. Only the first leaky bucket parameters can be configured for UBR connections. Connection Parameters These parameters are in the order that they appear in the cnfcon display. PCR(0+1): This is the Peak Cell Rate for all traffic (CLP=0 and CLP=1). % Util: This is the amount of time the connection is expected to be transmitting at PCR (0+1) into the network. CDVT(0+1): This is the cell delay variation tolerance (CDVT) for all traffic (CLP=0 and CLP=1). AAL5 FBTC: ATM Adaptation Layer type 5 Frame-Based Traffic Control. CLP Setting: Cell Loss Priority Setting. Can be set to Yes (UBR.2) or No (UBR.1). The tagging limit is only the first 50 cells per second that are not tagged. Trunk Cell Routing Restrict: Whether switch software routes the connection across a non-cell-based trunk. Details PCR(0+1): (PCR (0+1)) * (% Util) = the amount of bandwidth allocated in the network for a UBR connection. This is expressed in load units on a trunk and can be inspected using the dspload <trunk_number> command. % Util: UBR traffic is treated with low priority as the default % utilization setting is 1%. Therefore, minimum network bandwidth and resources are reserved for UBR connections.

CDVT(0+1): The amount of 'clumping' between ATM cells. Some routers require high CDVT values (250,000) due to performance issues. For voice, video, or circuit emulation services, CDVT values of 10,000 or less are desired to ensure rapid play-out of cells. AAL5 FBTC: If this option is enabled, it is assumed that the connection carries AAL5 frames. The term 'frame' means the AAL5 PDU. AAL5 cells contain information to indicate the start and end of the frame. FBTC enables Early Packet Discard (EPD) on all trunks for a specific connection. EPD is a mechanism to discard all the ATM cells associated with a frame before they are admitted to the network. Without EPD, parts of an ATM frame may be transmitted through the network consuming bandwidth and resources. EPD is configured using thresholds based on connection Queue depth. If Queue depth exceeds the configured threshold, the new data frame is not accepted when the Start-of-Frame AAL5 cell arrives. For UBR traffic, EPD is configured per port using the cnfportq <slot_number.port_number> command. For purposes of this document, AAL5 FBTC is turned off to accommodate the traffic provided by the test set. The test set is generating a constant stream of AAL1 traffic (no EOF flag). This traffic type will cause inconsistent discards when AAL5 FBTC is Enabled. For AAL5 traffic, you should enable AAL5 FBTC. CLP Setting: If set to No, all cells that are compliant with the first leaky bucket are allowed into the network. This can be a problem if ABR and UBR connections share the same port and the Policing Options are similar. If ABR policing is set to 3, and UBR CLP is set to N (UBR.1), ABR and UBR traffic 'appears' the same to the network, and low priority UBR traffic is treated the same as higher priority ABR traffic. If ABR and UBR connections must share the same port, set CLP to Yes for the UBR connections. If set to Yes, then all CLP=1 cells that are compliant with the first Leaky Bucket are admitted to the network and all CLP=0 cells that are compliant with the first Leaky Bucket are evaluated at the second Leaky Bucket (see Policing Option 3). Since SCR is hardcoded in the BXM to 0, the second Leaky Bucket is essentially always full, and all the CLP=0 cells are "tagged" (CLP is set to 1). This allows the network to recognize UBR cells as lower priority cells and available for discard in the event of network congestion. Screen Shots This is a sample UBR connection with incoming traffic at 1000 CPS, PCR of 1000, and CLP=Y.

This is a sample UBR connection with incoming traffic at 1000 CPS, PCR of 500, and CLP=Y. Note the NonCmplnt Dscd, NCmp CLP0 Dscd, Igr VSVD ACR, and Rx Q Depth. The results are the same for CLP=N.

References Leaky Bucket Colloquial, Industry Slang Terms Colloquial, Industry Slang Term Definition

Dual Leaky Bucket

The algorithm used for conformance checking of cell flows against the set of parameters specified in the traffic contract. Screens for traffic contract compliance. If a cell does not meet the terms of the traffic contract, the cell is discarded.

First Leaky Bucket

Evaluates cells from the first leaky bucket to determine whether CLP Second Leaky Bucket tagging must be performed. A cell that is 'tagged' has the CLP bit set to 1. The rate that cells flow into the network. Function that determines cell bursts.

Leak Rate

Bucket Depth Acronyms Acronym

Definition ATM Adaptation Layer (traffic types are AAL1 for circuit emulation and AAL5 for data). Available Bit Rate (ABR standard and ABR Foresight types). Allowed Cell Rate. ACR Decrease Time Factor. Asynchronous Transfer Mode. International standard for cell relay in which multiple service types (such as voice, video, or data) are conveyed in fixedlength (53-byte) cells. Fixedlength cells allow cell processing to occur in hardware, thereby reducing transit delays.

AAL

ABR

ACR ADTF

ATM

Bc Be

committed Burst size. excess Burst size. Backward Congestion Management (cell type used for ABR Foresight connections). Backward Resource Management (cell type used for ABR standard connections). Constant Bit Rate (no VC_Queue only QBIN). Current Cell Rate. Cell Decrease Factor. Cell Delay Variation Tolerance. This is a mandatory parameter for any ATM connection type (CBR, VBR, ABR, and UBR). Congestion Indication. Cell Loss Priority (equivalent to FR Discard Eligibility bit). Cell Loss Ratio. Customer Premise Equipment (for example, Cisco 7200 router) Missing RM Cell count (CRM limits the number of FRM sent in the absence of received BRM).

BCM

BRM

CBR

CCR CDF

CDVT

CI

CLP

CLR

CPE

CRM

CTD

Cell Transfer Delay. Explicit Forward Congestion Indication (equivalent to FR FECN; configured per port queue for the BXM). Egress. End Of Frame. Early Packet Discard (part of FBTC; per-VC parameter; only apply to AAL5 traffic as AAL5 traffic has an EOF cell). Explicit Rate. Explicit Rate Stamping. Frame-Based Traffic Control (entire AAL Protocol Data Unit or 'frame' is discarded). Flow Control External Segment (must be enabled on both ends of a connection or not at all. Available only for ABR Standard with VS/VD or ABR ForesSight connections). Forward Explicit Congestion Notification. Frame-Generic Cell Rate Algorithm (proprietary extension to GCRA used for ASI cards).

EFCI

Egr EOF

EPD

ER ERS

FBTC

FCES

FECN

FGCRA

FR FRTT

Frame Relay. Fixed Round-Trip Time. Generic Cell Rate Algorithm (ATM Traffic Management Specification Version 4.0 policing algorithm). Generic Flow Control (field of ATM UNI cell). Initial Burst Size (equivalent to Frame Relay Cmax). Initial Cell Rate (equivalent to Frame Relay QIR). Ingress (ingress is always with respect to the backplane). Interim Inter-Switch Protocol (interim protocol to PNNI). Interim Local Management Interface (equivalent to FR LMI on ATM UNI). Maximum Burst Size (equivalent to FR Be). Minimum Cell Rate (equivalent to FR MIR). Network Node Interface. Maximum Number of cells between RM-cell generation.

GCRA

GFC

IBS

ICR

Igr

IISP

ILMI

MBS

MCR

NNI

NRM

nrt-VBR Oflw

Non-real time VBR. Overflow. Out-Of-Rate (applies to RM cell generation). Peak Cell Rate (equivalent to Frame Relay PIR). This is a mandatory parameter for any ATM connection type (CBR, VBR, ABR, and UBR). Protocol Data Unit. Private Network Node Interface (used for Network-toNetwork communication). Partial Packet Discard (part of FBTC; per-VC parameter; only apply to AAL5 traffic as AAL5 traffic has an EOF cell). Payload Type Indicator (ATM cell field used to specify AAL1 or AAL5 traffic types and congestion). Operations, Administration and Maintenance. Queue Engine. BXM subsystem that manages all VC and Class of Service queues (QBINs) and maintains connection and port statistics. Routing Control, Monitor, and Policing subsystem (BXM

OOR

PCR

PDU

PNNI

PPD

PTI

OAM

QE

RCMP

policing function) that resides on a chip developed by PMC/Sierra. The RCMP implements the Dual Leaky Bucket algorithm , manages ATM layer OAM flows, and determines the connection ID from Cell Header. RDF RIF Rate Decrease Factor. Rate Increase Factor. Resource Management cells (apply only to ABR connections). Relative Rate. Real time VBR (ATM trunk QBIN type used for VAD voice). Segmentation And Reassembly (one of the two sublayers in the ATM Adaptation Layer. The SAR sublayer divides information to be carried by the ATM layer into segments suitable for carrying in the 48octet information field of the ATM cell and vice versa). Sustainable Cell Rate (equivalent to FR CIR). StrataCom Trunk Interface (proprietary ATM-like cell used on legacy cards such as the ASI, BNI, ALM, and BTM).

RM

RR

rt-VBR

SAR

SCR

STI

TBE TDM TRM

Transient Buffer Exposure. Time Division Multiplex. Terminal RM. Unspecified Bit Rate (traffic type that uses ABR queues. This is due to inherent unfairness in queuing design that do not configure UBR and ABR connections over the same port). User Network Interface. Usage Parameter Control. Voice Activity Detection (used to reduce bandwidth required for voice traffic). Variable Bit Rate. Virtual Connection. Virtual Channel Connection (connection with the format x.x.x.x). Virtual Path Connection (connection with the format x.x.x.*). Virtual Source/Virtual Destination (ABR connections only).

UBR

UNI UPC

VAD

VBR VC

VCC

VPC

VS/VD

Concepts and Definitions Congestion is the increase in cell rate to the network until throughput is negatively

impacted. Congestion results in discarded traffic. For WAN Switching equipment, congestion indicators are set in the: VC_Queue (EFCI bit) Port Queue (EFCI bit) Trunk Queue (EFCI bit) Congestion occurs on WAN Switching network trunks that route more connections than they have bandwidth to support. Foresight is a Cisco, proprietary, closed-loop, congestion-prevention algorithm for Available Bit Rate (ABR) traffic. Foresight increases or decreases the service rate for a VC_Queue to control the speed (or rate) of a connection. Overbooking is the practice of routing more connections over a trunk than a trunk can support by adjusting one or more connection parameters. For example, a T3 (44.736 Mbps) trunk can be overbooked by reducing the %util parameter on all connections routed over the T3 trunk. Overbooking allows carriers to route many times the traffic supported by a T3 over the T3 trunk. For example, carriers may route 60 Mbps of connection bandwidth over a 44.736 Mbps (T3) trunk. Overbooking results in network congestion if all connections routed over the T3 trunk are in use and actively transmitting data at the same time. Policing is the function implemented at the 'edge' of the WAN Switching network in BXM line cards that enforces the compliance of every ATM connection to the negotiated traffic contract. Policing is often used as a substitute for Usage Parameter Control (UPC). Policing is independent of the congestion-related discards that may happen to a connection once it has been admitted into the network. PTI Field is the 3-bit field of an ATM cell that is used to indicate data or management cell payload type, cell congestion, and EOF of an AAL5 PDU. QBIN is a shared class-of-service FIFO buffer that services ATM and legacy connections like CBR, VBR, ABR/UBR. For example, all CBR connections on a BXM virtual interface (VI) share the same QBIN. There are 16 QBINs per VI. Token Bucket is a formal definition of a rate of transfer. It has three components: a burst size, a mean rate, and a time interval (Tc). A token bucket is used to manage a device that regulates the flow's data. VC_Queue is a FIFO buffer that is created for each connection when the connection is

added. VC_Queue has configurable thresholds for EFCI, CLP Hi, CLP Lo. For ABR connections, cells move from VC_Queues to QBINs at the Allowed Cell Rate as determined by the ATM Forum ABR algorithm or the Cisco Foresight algorithm. VS/VD is an ATM Forum standard-based closed-loop congestion prevention algorithm for ABR traffic. Usage Parameter Control (UPC) is implemented in the BPX BXM card as specified by ATM Traffic Management Specification Version 4.0. UPC represents a set of actions taken by the network to monitor and control traffic offered by the end user. Related Information BPX 8600 Architecture and Performance Virtual Trunking and Traffic Shaping on BPX 8600 Series BPX Congestion Avoidance Cisco BPX 8680 IP+ATM Wide-Area Switch SONET Automatic Protection Switching (APS) on the BPX 8600 Series Policing and Shaping Overview ATM Connections Cisco WAN Switching Solutions - Cisco Documentation Guide to New Names and Colors for WAN Switching Products Downloads - WAN Switching Software (registered customers only) Technical Support - Cisco Systems

Updated: Apr 17, 2009

Document ID: 6502

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