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Table Of Contents
Overview of Procedure to add ATM Connections
ATM Connection Flow through the BPX
Traffic Shaping for CBR, rt-VBR, nrt-VBR, and UBR
Configuring Connection Policing
Related Switch Software Commands
Available Bit Rate Connections
Available Bit Rate Standard Connections
Available Bit Rate Foresight Connections
Unspecified Bit Rate Connections
ATM-to-Frame Relay Network Interworking Connections
Frame Relay-to-ATM Foresight Network Interworking Connection
Frame Relay-to-ATM Transparent Service Interworking Connections
Frame Relay-to-ATM Foresight Transparent Service Interworking Connections
Frame Relay-to-ATM Translational Service Interworking Connections
Frame Relay-to-ATM Foresight Translational Service Interworking Connections
Dual-Leaky Bucket (An Analogy)
Variable Bit Rate Dual-Leaky Bucket Policing Examples
Configuring ATM Connections
This chapter explains how to establish ATM connection services by adding ATM connections between ATM service interface ports in the network using ATM standard UNI 3.1 and Traffic Management 4.0.
Contents of this chapter include:
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Setting Up an ATM Connection
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ATM Connection Services
You establish ATM connection services by adding ATM connections between ATM service interface ports in the network.
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Frame relay to ATM network interworking connections are supported between either BXM cards to:
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Figure 21-1 depicts ATM connections over a BPX switch network, through BXM-T3/E3, BXM-155, BXM-622, as well as over MGX 8220 switches. It also shows Frame Relay to ATM interworking connections over the MGX 8220 and IGX shelves.
For further information on the MGX 8220, refer to the Cisco MGX 8220 Reference.
For further information on the MGX 8800, refer to the Cisco MGX 8800 Reference.
Setting Up an ATM Connection
To set up an ATM connection, use the following procedure:
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Step 7
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Figure 21-1 ATM Connections over a BPX Switch Network
Traffic Management Overview
The ATM Forum Traffic Management 4.0 Specification defines five basic traffic classes:
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Table 21-1 summarizes the major attributes of each of the traffic management classes:
The standard ATM traffic parameters are defined in Table 21-2.
The Quality of Service (QoS) parameters are defined in Table 21-3.
For congestion control feedback, ABR provides a means to control flow based on congestion measurement.
Standard Available Bit Rate
Standard ABR uses RM (Resource Management) cells to carry feedback information back to the connection's source from the connection's destination.
ABR sources periodically interleave RM cells into the data they are transmitting. These RM cells are called forward RM cells because they travel in the same direction as the data. At the destination these cells are turned around and sent back to the source as Backward RM cells.
The RM cells contain fields to increase or decrease the rate (the CI and NI fields) or set it at a particular value. which is the explicit rate (ER) field. The intervening switches may adjust these fields according to network conditions. When the source receives an RM cell it must adjust its rate in response to the setting of these fields.
VS/VD Description
ABR sources and destinations are linked through bidirectional connections, and each connection termination point is both a source and a destination; a source for data that it is transmitting, and a destination for data that it is receiving. The forward direction is defined as from source to destination, and the backward direction is defined as from destination to source.
Figure 21-2 shows the data cell flow in the forward direction from a source to its destination along with its associated control loop. The control loop consists of two RM cell flows, one in the forward direction (from source to destination) and the other in the backward direction (from destination to source).
Figure 21-2 ABR VS/VD Flow Control Diagram
The data cell flow in the backward direction from destination to source is not shown, nor are the associated RM cell flows. However, these flows are just the opposite of that shown in the diagram for forward data cell flows.
A source generates forward RM cells which are turned around by the destination and returned to the source as backward RM-cells. These backward RM-cells may carry feedback information from the network elements and/or the destination back to the source.
The parameter Nrm is defined as the maximum number of cells a source may send for each forward RM cell, that is, one RM cell must be sent for every Nrm-1 data cells. Also, in the absence of Nrm-1 data cells, as an upper bound on the time between forward RM cells for an active source, an RM cell must be sent at least once every Trm msecs.
BXM Connections
The BXM-T3/E3, BXM-155, and BXM-622 cards support ATM Traffic Management 4.0.
The BXM cards are designed to support all the following service classes:
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ABR with VS/VD supports explicit rate marking and Congestion Indication (CI) control.
ForeSight Congestion Control
The ForeSight feature is a proprietary dynamic closed-loop, rate-based, congestion management feature that yields bandwidth savings compared to non-ForeSight equipped trunks when transmitting bursty data across cell-based networks.
ForeSight may be used for congestion control across BPX and IGX switches for connections that have one or both end points terminating on BXM cards. The BXM cards also support the VS/VD congestion control mechanism as specified in the ATM Traffic Management 4.0 standards.
ATM Connection Requirements
Two connection addressing modes are supported:
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The full ATM address range for VPI and VCI is supported.Virtual Path Connections are identified by an * in the VCI field. Virtual Circuit Connections specify both the VPI and VCI fields.
The VPI and VCI fields have significance only to the local BPX switch, and are translated by tables in the BPX switch to route the connection. Connections are automatically routed by the Automatic Routing Management feature once the connection endpoints are specified.
You can add ATM connections by using either the Cisco WAN Manager Connection Manager or a node's command line interface (CLI). Typically, the Cisco WAN Manager Connection Manager is the preferred method because it has an easy to use GUI interface. The CLI may be the method of choice in some special cases or during initial node setup for local nodes.
Overview of Procedure to add ATM Connections
In general, to add ATM connections, use the following procedure:
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For example, when configuring a BXM for CPE connections, use the following procedure:
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Connection Routing
ATM connections for a BXM card are identified by the following numbers:
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The slot and port are related to the BPX switch hardware.
Virtual path connections (VPCs) are identified by a "*" for the VCI field.
Virtual circuit connections (VCCs) are identified by both a VPI and VCI field.
Connections added to the network are automatically routed once the end points are specified. This Automatic Routing Management feature is standard with all BPX and IGX switches. The network automatically detects trunk failures and routes connections around the failures.
addcon Command Syntax
Enter the following parameters for the BXM addcon command. Depending upon the connection type, you are prompted for the appropriate parameters as shown in the following example:
addcon local_addr node remote_addr traffic_type/class number....extended parametersEXAMPLESaddcon 2.2.11.11 pubsbpx1 2.3.12.12 3addcon 2.3.22.22 pubsbpx1 2.2.24.24 abrstd 50/50 100/100 50/50 25000/* e e e d 50/50 * 3 * 80/* 35/* 20/* 50/* * 100 128 16 32 0 *The field descriptions are described in Table 21-4.
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addcon Example
The following example shows the initial steps in adding a connection with the addcon command, and the addcon prompt requesting the user to enter the ATM type of service.
pubsbpx1 TN silves BPX 8620 9.2.2G July 21 1999 21:32 PDTLocal Remote Remote RouteChannel NodeName Channel State Type Avoid COS O2.2.1.4 pubsbpx1 2.3.5.7 Ok nrt-vbr2.2.1.5 pubsbpx1 2.3.5.8 Ok rt-vbr2.2.1.6 pubsbpx1 2.3.5.9 Ok rt-vbr2.3.5.7 pubsbpx1 2.2.1.4 Ok nrt-vbr2.3.5.8 pubsbpx1 2.2.1.5 Ok rt-vbr2.3.5.9 pubsbpx1 2.2.1.6 Ok rt-vbrThis Command: addcon 2.2.11.11 pubsbpx1 2.3.12.12Enter (nrt/rt-VBR,CBR,UBR,ABRSTD,ABRFST,ATFR,ATFST,ATFT,ATFTFST,ATFX,ATFXFST)or class number:Instead of entering a class of service, you can instead enter a class number to select a pre-configured template, for example, class 4 for ntr-VBR, and class 3 for rt-VBR. You can modify the class of service templates as required by using the cnfcls and cnfatmcls commands and displaying them by using the dspcls and dspatmcls commands.
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An example of a cnfcls and cnfatmcls commands and response is shown in the following example:
pubsbpx1 TN silves:1 BPX 8620 9.2.2G July 16 1999 10:42 PDTATM Connection ClassesClass: 2 Type: nrt-VBRPCR(0+1) % Util CDVT(0+1) AAL5 FBTC SCR1000/1000 100/100 10000/10000 n 1000/1000MBS Policing1000/1000 3Description: "Default nrt-VBR 1000 "This Command: cnfcls atm 2Enter class type (rt-VBR, nrt-VBR, CBR, UBR, ABRSTD, ABRFST, ATFR, ATFST, ATFT,ATFTFST, ATFX, ATFXFST):ATM Connection Flow
This section describes the ATM connection flow.
ATM Connection Flow through the BPX
The BPX supports the standard ATM service types, CBR, rt-VBR, nrt-VBR, ABR, and UBR. When adding a connection by using the addcon command, you select these service types by entering one of the CLI service type entries listed in Table 21-5 when prompted.
The BPX also supports ATM to Frame Relay Network Interworking and Service Interworking connections. When adding a connection by using the addcon command, you select these service types by entering one of the CLI service type entries described in Table 21-6 when prompted.
Advanced CoS Management
Advanced CoS management provides per-VC queueing and per-VC scheduling. CoS management provides fairness between connections and firewalls between connections. Firewalls prevent a single noncompliant connection from affecting the QoS of compliant connections. The noncompliant connection simply overflows its own buffer.
The cells received by a port are not automatically transmitted by that port out to the network trunks at the port access rate. Each VC is assigned its own ingress queue that buffers the connection at the entry to the network. With ABR with VS/VD or with Optimized Bandwidth Management (ForeSight), the service rate can be adjusted up and down depending on network congestion.
Network queues buffer the data at the trunk interfaces throughout the network according to the connection's class of service. Service Classes are defined by standards-based QoS. Service Classes can consist of the five service classes defined in the ATM standards as well as multiple subclasses to each of these classes. Service Classes can range from constant bit rate services with minimal cell delay variation to variable bit rates with less stringent cell delay.
When cells are received from the network for transmission out a port, egress queues at that port provide additional buffering based on the Service Class of the connection.
CoS Management provides an effective means of managing the quality of service defined for various types of traffic. It permits network operators to segregate traffic to provide more control over the way that network capacity is divided among users. This is especially important when there are multiple user services on one network.
Rather than limiting the user to the five broad classes of service defined by the ATM standards committees, CoS management can provide up to 16 classes of service (service subclasses) that can be further defined by the user and assigned to connections. Some of the CoS parameters that may be assigned include:
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These class of service parameters are based on the standards-based Quality of Service parameters and are software programmable by the user. The BPX switch provides separate queues for each traffic class.
Connection Flow Example
The example shown in Figure 21-3 shows the general ATM connection flow through BXM cards in BPX switches. The cnfport, cnfportq, cnfln, cnftrk, and cnftrkparm commands are used to configure resources affecting the traffic flow of a connection. For examples, see the Traffic Shaping for CBR, rt-VBR, nrt-VBR, and UBR section.
Ingress from CPE 1 to BXM 3
ATM cells from CPE 1 that are applied to BXM 3, Figure 21-3, are processed at the physical level, policed per individual VC based on ATM header payload type, and routed to the applicable one of 15 per card slot servers, each of which contains 16 CoS service queues, including ATM service types CBR, rt-VBR, nrt-VBR, ABR, and UBR.
ATM cells undergoing traffic shaping, for example, ABR cells are applied to traffic shaping queues before going to one of the 15 per card slot servers. ATM cells applied to the traffic shaping queues receive additional processing, including congestion control by means of VS/VD or ForeSight and virtual connection queuing.
Cells are served out from the slot servers via the BPX backplane to the BCC crosspoint switch. The cells are served out on a fair basis with priority based on class of service, time in queue, bandwidth requirements, and so forth.
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Egress to Network via BXM 10
In this example, ATM cells destined for BPX 2 are applied via the BCC crosspoint switch and BPX backplane to BXM 10 and out to the network. The cells are served out to the network via the appropriate trunk Qbin, CBR, rt-VBR, nrt-VBR, ABR, or UBR.
Ingress from Network via BXM 5
ATM cells from the network that are applied to BXM 5 in BPX 2 are processed at the physical level and routed to one of 15 per card slot servers, each of which contains 16 CoS service queues, including ATM service types CBR, rt-VBR, nrt-VBR, ABR, and UBR.
Cells are served out from the slot servers via the BPX backplane to the BCC crosspoint switch. The cells are served out on a fair basis with priority based on class of service, time in queue, bandwidth requirements, etc.
Egress from BXM 11 to CPE 2
In this example, ATM cells destined for CPE 2 are applied via the BCC crosspoint switch and BPX backplane to BXM 11 and out to CPE 2. The cells are served out to CPE 2 via the appropriate port Qbin, CBR, rt-VBR, nrt-VBR, or ABR/UBR.
ATM cells undergoing traffic shaping, for example ABR cells are applied to traffic shaping queues before going to one of the 15 per card slot servers. ATM cells applied to the traffic shaping queues receive additional processing, including congestion control by means of VS/VD or ForeSight and virtual connection queuing.
Figure 21-3 ATM Connection Flow via BPX Switches
Traffic Shaping for CBR, rt-VBR, nrt-VBR, and UBR
With the introduction of traffic shaping for CBR, VBR, and UBR, you have the option to provide traffic shaping for these connections types on the BXM. Previously, only ABR utilized traffic shaping. Traffic shaping involves passing CBR, VBR, or UBR traffic streams through VC queues for scheduled rate shaping.
Traffic shaping is performed on a per port basis. When traffic shaping is enabled, all traffic exiting the port (out to the network) is subject to VC scheduling based on the parameters you configure for the connection.
Figure 21-4 shows an example of traffic shaping. In this example, port 1 is configured to perform traffic shaping.
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Figure 21-4 shows port 2 is not configured for traffic shaping, and only the ABR traffic with FCES (flow control external segment) passes through the VC queues.
Figure 21-4 Traffic Shaping Example
Traffic Shaping Rates
Traffic shaping rates are listed in Table 21-7.
Table 21-7 Traffic Shaping Rates
CBR
PCR
PCR
rt-VBR and nrt-VBR
SCR * %Util
PCR
UBR
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ABR
MCR * %Util
PCR
Configuration
To configure traffic shaping, use the following procedure:
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No connections should be enabled on the port prior to changing the port traffic shaping parameter. If there are existing connections when the port is toggled, the connections are not updated unless the card is reset, connections are rerouted, a switchcc occurs, or you modify the connection parameters.
The following is an example of the cnfln command:
pubsbpx1 TN silves BPX 8620 9.3 Aug. 1 2000 14:41 PDTLN 2.2 Config OC3 [353208cps] BXM slot: 2Loop clock: No Idle code: 7F hexLine framing: --coding: --CRC: --recv impedance: --E1 signalling: --encoding: -- cable type: --T1 signalling: -- length: --HCS Masking: YesPayload Scramble: Yes56KBS Bit Pos: -- Frame Scramble: Yespct fast modem: -- Cell Framing: STS-3CVC Shaping: NoLast Command: cnfln 2.2Next Command:The following is an example of the cnfport command:
pubsbpx1 TN silves BPX 8620 9.3 Aug. 1 2000 15:12 PDTPort: 2.2 [ACTIVE ]Interface: LM-BXM CAC Override: EnabledType: UNI %Util Use: DisabledShift: NO SHIFT (Virtual Trunk Operation)SIG Queue Depth: 640 Port Load: 28 %Protocol: NONE Protocol by Card: NoLast Command: cnfport 2.2Next Command:The following is an example of the cnftrk command:
pubsbpx1 TN silves BPX 8620 9.3 Aug. 1 2000 14:43 PDTTRK 2.4 Config OC3 [353207cps] BXM slot: 2Transmit Rate: 353208 Line framing: STS-3CProtocol By The Card: No coding: --VC Shaping: No CRC: --Hdr Type NNI: Yes recv impedance: --Statistical Reserve: 1000 cps cable type: --Idle code: 7F hex length: --Connection Channels: 256 Pass sync: NoTraffic:V,TS,NTS,FR,FST,CBR,NRT-VBR,ABR, T-VBR clock: NoSVC Vpi Min: 0 HCS Masking: YesSVC Channels: 0 Payload Scramble: YesSVC Bandwidth: 0 cps Frame Scramble: YesRestrict CC traffic: No Virtual Trunk Type: --Link type: Terrestrial Virtual Trunk VPI: --Routing Cost: 10 Deroute delay time: 0 secondsThis Command: cnftrk 2.4Transmit Rate [ 1-353208 ]:Configuring VBR Connections
The characteristics of rt-VBR or nrt-VBR are supported by appropriately configuring the parameters of the VBR connection. For a description of the rt-VBR and nrt-VBR classificaitons, see the Variable Bit Rate Connections section.
When configuring a rt-VBR connection, the trunk cell routing restriction prompt does not display, because rt-VBR connection routing is automatically restricted to ATM trunks.
With Release 9.2.20 and later, you specify rt-VBR and nrt-VBR connections separately when adding a connection by using the addcon command. To do this, enter either rt-vbr or nrt-vbr to select the rt-VBR or nrt-VBR connection class, respectively. Each connection is assigned the applicable associated default parameters for its type of service.
For rt-VBR an additional queue, referred to as the rt-VBR queue, is used at a BXM port. At BXM or BNI trunks, voice and rt-VBR traffic share a queue, referred to as the rt-VBR queue.
The rt-VBR and nrt-VBR service queues are configured differently from each other at both port ingress and port egress queues. The rt-VBR typically uses smaller queues for low delay, whereas the nrt-VBR queues are typically larger in size for more efficient bandwidth sharing with other nonreal time service types.
The rt-VBR connections are configured per class 3 service parameters. The nrt-VBR connections are configured per class 2 service parameters.
You can configure the connection classes to whatever service and parameters you want by:
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For a new node running software release 9.2.20 or later, the rt-VBR connection class number is 3. However, an upgraded node will retain existing connection classes. Therefore, it won't have the rt-VBR connection class 3.
For nrt-VBR connections in a new node, running 9.2.20, a number of connection classes are preconfigured, including 2, 4, 5, and 6.
The following is an example of cnfcls 3, for rt-VBR:
pubsbpx1 TN silves:1 BPX 8620 9.2.20 July 16 2000 10:42 PDTATM Connection ClassesClass: 3 Type: rt-VBRPCR(0+1) % Util CDVT(0+1) AAL5 FBTC SCR4000/4000 100/100 10000/10000 n 4000/4000MBS Policing1000/1000 3Description: "Default rt-VBR 4000 "This Command: cnfcls atm 3Enter class type (rt-VBR, nrt-VBR, CBR, UBR, ABRSTD, ABRFST, ATFR, ATFST, ATFT,ATFTFST, ATFX, ATFXFST):The following is an example of cnfcls 2, for nrt-VBR:
pubsbpx1 TN silves:1 BPX 8620 9.2.2G July 16 1999 10:42 PDTATM Connection ClassesClass: 2 Type: nrt-VBRPCR(0+1) % Util CDVT(0+1) AAL5 FBTC SCR1000/1000 100/100 10000/10000 n 1000/1000MBS Policing1000/1000 3Description: "Default nrt-VBR 1000 "This Command: cnfcls atm 2Enter class type (rt-VBR, nrt-VBR, CBR, UBR, ABRSTD, ABRFST, ATFR, ATFST, ATFT,ATFTFST, ATFX, ATFXFST):Connection Criteria
The following are the requirements for connection criteria:
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Configuring Connection Policing
The BPX Command Line Interface (CLI) and Cisco WAN Manager accept the same connection policing and bandwidth parameters as in previous releases for both rt-VBR and nrt-VBR service.
The displayed addcon parameter prompts for both rt-VBR and nrt-VBR connections are the same:
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There is no change in CDVT usage and the previous policing system.
When using the addcon command without the extended parameters, rt-VBR connections automatically use the parameters provided by connection class 3 which contains pre-determined values. Similarly, nrt-VBR connections use connection class 2.
To modify the values of a connection class, use the commands cnfcls and cnfatmcl.
To display these values, use the commands dspcls and dspatmcls.
Figure 21-5 rt-VBR and nrt-VBR Connection Prompt Sequence
Configuring Resources
Qbin values on both ports and trunks used by rt-VBR connections and nrt-VBR connections can be configured separately.
Trunk Queues for rt-VBR and nrt-VBR
A rt-VBR connection uses the rt-VBR queue on a trunk. It shares this queue with voice traffic. The rt-VBR and voice traffic shares the default or user configured parameters for the rt-VBR queue. These parameters are queue depth, queue CLP high and CLP low thresholds, EFCI threshold, and queue priority.
A nrt-VBR connection uses the nrt-VBR queue on a trunk. The configurable parameters are queue depth, queue CLP high and CLP low thresholds, EFCI threshold, and queue priority.
You can configure the the following Qbin values separately for rt-VBR and nrt-VBR classes on trunks by using the cnftrkparm command:
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The following example shows the cnftrkparm screen and the parameters that can be configured for the various service type queues:
pubsbpx1 TN silves:1 BPX 8620 9.2.2G July 16 1999 10:50 PDTTRK 2.4 Parameters1 Q Depth - rt-VBR [ 885] (Dec) 15 Q Depth - CBR [ 600] (Dec)2 Q Depth - Non-TS [ 1324] (Dec) 16 Q Depth - nrt-VBR [ 5000] (Dec)3 Q Depth - TS [ 1000] (Dec) 17 Q Depth - ABR [20000] (Dec)4 Q Depth - BData A [10000] (Dec) 18 Low CLP - CBR [ 60] (%)5 Q Depth - BData B [10000] (Dec) 19 High CLP - CBR [ 80] (%)6 Q Depth - High Pri [ 1000] (Dec) 20 Low CLP - nrt-VBR [ 60] (%)7 Max Age - rt-VBR [ 20] (Dec) 21 High CLP - nrt-VBR [ 80] (%)8 Red Alm - I/O (Dec) [ 2500 / 10000]22 Low CLP/EPD-ABR [ 60] (%)9 Yel Alm - I/O (Dec) [ 2500 / 10000]23 High CLP - ABR [ 80] (%)10 Low CLP - BData A [ 100] (%) 24 EFCN - ABR [ 20] (%)11 High CLP - BData A [ 100] (%) 25 SVC Queue Pool Size [ 0] (Dec)12 Low CLP - BData B [ 25] (%)13 High CLP - BData B [ 75] (%)14 EFCN - BData B [ 30] (Dec)This Command: cnftrkparm 2.4Port Queues for rt-VBR and nrt-VBR
The rt-VBR and nrt-VBR connections use different queues on a port, these are the rt-VBR and nrt-VBR queues, respectively. You can configure these separately by using the cnfportq command.
The following example shows the configuration parameters available for a port queue:
Port Queue Parameters, cnfportq
pubsbpx1 TN silves:1 BPX 8620 9.3 July 16 2000 10:47 PDTPort: 2.2 [ACTIVE ]Interface: LM-BXMType: UNISpeed: 353208 (cps)SVC Queue Pool Size: 0CBR Queue Depth: 600 rt-VBR Queue Depth: 0CBR Queue CLP High Threshold: 80% rt-VBR Queue CLP High Threshold: 80%CBR Queue CLP Low Threshold: 60% rt-VBR Queue CLP Low/EPD Threshold: 60%CBR Queue EFCI Threshold: 60% rt-VBR Queue EFCI Threshold: 80%nrt-VBR Queue Depth: 5000 UBR/ABR Queue Depth: 20000nrt-VBR Queue CLP High Threshold: 80% UBR/ABR Queue CLP High Threshold: 80%nrt-VBR Queue CLP Low Threshold: 60% UBR/ABR Queue CLP Low/EPD Threshold:60%nrt-VBR Queue EFCI Threshold: 60% UBR/ABR Queue EFCI Threshold: 20%This Command: cnfportq 2.2Related Switch Software Commands
The following are the commands related to the process of adding and monitoring ATM connections:
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For additional information on CLI command usage, refer to the Cisco WAN Switching Command Reference and Cisco WAN Switching SuperUser Command Reference.
ATM Connection Configuration
The following figures and tables describe the parameters used to configure ATM connections:
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The following figures list the connection parameters in the same sequence as they are entered when a connection is added:
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The following figures list the connection parameters in the same sequence as you would enter them when adding a connection:
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CLP(0) means cells that have CLP = 0
CLP(1) means cells that have CLP = 1
CLP(0+1) means both types of cells: CLP = 0 & CLP = 1
CLP(0) has higher priority than CLP(1)
CLP tagging means to change CLP = 0 to CLP = 1, where CLP= 1 cells have lower priority
Table 21-10 Connection Parameter Descriptions
PCR
Peak cell rate: The cell rate which the source may never exceed
%Util
% Utilization; bandwidth allocation for: rt/nrt-VBR, CBR, UBR it's PCR*%Util, for ABR it's MCR*%Util
MCR
Minimum Cell Rate: A minimum cell rate committed for delivery by network
CDVT
Cell Delay Variation Tolerance:
Controls time scale over which the PCR is policed
FBTC (AAL5 Frame Basic Traffic Control)
To enable the possibility of discarding the whole frame, not just one noncompliant cell. This is used to set the Early Packet Discard bit at every node along a connection.
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VS/VD
Virtual Source Virtual Destination: (See Meaning of VS/VD and Flow Control External Segments, Figure 21-9).
FCES (Flow Control External Segments)
See Meaning of VS/VD and Flow Control External Segments, Figure 21-9.
SCR
Sustainable Cell Rate: Long term limit on the rate a connection can sustain
MBS
Maximum Burst Size: Maximum number of cells which may burst at the PCR but still be compliant. Used to determine the Burst Tolerance (BT) which controls the time scale over which the SCR is policed
Policing
See the definitions of Traffic Policing in Table 21-8.
VC QDepth
VC Queue Depth
CLP Hi
Cell Loss Priority Hi threshold (% of VC QMax)
CLP Lo/EPD
Cell Loss Priority Low threshold (% of VC QMax)/Early Packet Discard. If AAL5 FBTC = yes, then for the BXM card this is the EPD threshold setting.
EFCI
Explicit Forward Congestion Indication threshold (% of VC QMax)
ICR
Initial Cell Rate:
The rate at which a source should send initially and after an idle period
ADTF (ATM Forum TM 4.0 term)
The Allowed-Cell-Rate Decrease Factor: Time permitted between sending RM-cells before the rate is decreased to ICR
Trm (ATM Forum TM 4.0 term)
An upper bound on the time between forward RM-cells for an active source, that is, RM cell must be sent at least every Trm msec
RIF (ATM Forum TM 4.0 term)
Rate Increase Factor: Controls the amount by which the cell transmission rate may increase upon receipt of an RM cell
RDF (ATM Forum TM 4.0 term)
Rate Decrease Factor: Controls the amount by which the cell transmission rate may decrease upon receipt of an RM cell
Nrm (ATM Forum TM 4.0 term), BXM only.
Nrm: Maximum number of cells a source may send for each forward RM cell, that is, an RM cell must be sent for every Nrm-1 data cells
FRTT (ATM Forum TM 4.0 term), BXM only.
Fixed Round Trip Time: the sum of the fixed and propagation delays from the source to a destination and back
TBE (ATM Forum TM 4.0 term), BXM only.
Transient Buffer Exposure: The negotiated number of cells that the network would like to limit the source to sending during start-up periods, before the first RM-cell returns.
IBS
Initial Burst Size
Trunk cell routing restriction (Y/N) [Y]
The default (Y) restricts ATM connection routes to include only ATM trunks. Selecting (N) allows the network to route these connections over non-ATM trunks (such as Fastpacket trunks).
Minimum SCR and PCR
The minimum Sustainable Cell Rate (SCR) and Peak Cell Rate (PCR) of a connection supported by the BXM card used to be 50 cells per second (cps) or 19.2 Kbps. These values were set to maintain a policing accuracy with 1% when policing is performed on a BXM or UXM card. Because of this limitation, it was impossible to offer and differentiate connection services on the BXM at speeds less than 19.2 Kbps
(50 cps).The BPX supports connection policing with SCR and PCR values as low as 12 cps on the BPX switch, with certain card limitations.
Use the dspcd command to determine if this feature is supported on a given slot.
Use the addcon command to set the minimum SCR and PCR values.
If these values are less than the minimum values supported on a given card, the command line interface will not allow you to set them until you have disabled policing.
Note
The cards supported by the minimum SCR and PCR values and their performance specifications are listed in Table 21-11.
Table 21-11 Supported Cards and Performance Specifications
BPX-BXM
T3/E3
12 cps
BPX-BXM
OC3/STM-1
50 cps
BPX-BXM
OC12/STM-4
50 cps
Note
Policing must be disabled to support 6 cps minimum for all BXM card types.
Constant Bit Rate Connections
The CBR (constant bit rate) category is a fixed bandwidth class. CBR traffic is more time dependent, less tolerant of delay, and generally more deterministic in bandwidth requirements.
CBR is used by connections that require a specific amount of bandwidth to be available continuously throughout the duration of a connection. Voice, circuit emulation, and high-resolution video are typical examples of traffic utilizing this type of connection.
A CBR connection is allowed to transmit cells at the peak rate, below the peak rate, or not at all. CBR is characterized by peak cell rate (PCR).
The parameters for a CBR connection are shown in Figure 21-6 in the sequence in which they occur during the execution of the addcon command. The CBR policing definitions are summarized in Table 21-12.
Figure 21-6 CBR Connection Prompt Sequence
Variable Bit Rate Connections
Variable Bit Rate (VBR) connections can be classified as either:
•
For example, video conferencing requires real-time data transfer with bandwidth requirements that can vary in proportion to the dynamics of the video image at any given time. The rt-VBR category is characterized in terms of PCR, SCR (sustained cell rate), and MBS (maximum burst size).
•
The characteristics of rt-VBR or nrt-VBR are supported by appropriately configuring the parameters of the VBR connection.
Note
Connection Criteria for real-time VBR and nonreal-time VBR Connections
The following are the requirements for rt-VBR and nrt-VBR connections:
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•
•
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•
•
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•
The parameters for a VBR connection are shown in Figure 21-7 in the sequence in which they occur during the execution of the addcon command. The VBR policing definitions are summarized in Table 21-13.
Figure 21-7 rt-VBR and nrt-VBR Connection Prompt Sequence
Available Bit Rate Connections
The ABR (available bit rate) category utilizes a congestion flow control mechanism to control congestion during busy periods and to take advantage of available bandwidth during less busy periods. The congestion flow control mechanism provides feedback to control the connections flow rate through the network in response to network bandwidth availability.
The ABR service is not restricted by bounding delay or delay variation and is not intended to support real-time connections. ABR is characterized by PCR and MCR.
The term ABR is used to specify one of the following:
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•
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–
•
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–
–
Policing for ABR connections is the same as for VBR connections which are summarized in Table 21-12.
The ABR connections are configured as either ABR Standard (ABRSTD) connections or as ABR ForeSight (ABRFST) connections.
The parameters for an ABRSTD connection are shown in Figure 21-8 in the sequence in which they occur during the execution of the addcon command.
The ABRSTD connection supports all the features of ATM Standards Traffic Management 4.0 including VS/VD congestion flow control.
VS/VD and flow control with external segments are shown in Figure 21-9.
Available Bit Rate Standard Connections
The Available Bit Rate Standard (ABRSTD) connection uses VS/VD congestion control.
The parameters for an ABRSTD connection are shown in Figure 21-10 in the sequence in which they occur during the execution of the addcon command
Figure 21-8 ABR Standard Connection Prompt Sequence
Figure 21-9 Meaning of VS/VD and Flow Control External Segments
Available Bit Rate Foresight Connections
The Available Bit Rate Foresight (ABRFST) connection uses the propriety ForeSight congestion control and is useful when configuring connections on which both ends do not terminate on BXM cards.
The parameters for an ABRFST connection are shown in Figure 21-10 in the sequence in which they occur during the execution of the addcon command.
Figure 21-10 ABR ForeSight Connection Prompt Sequence
Unspecified Bit Rate Connections
The unspecified bit rate (UBR) connection service is similar to the ABR connection service for bursty data. However, UBR traffic is delivered only when there is spare bandwidth in the network. This is enforced by setting the CLP bit on UBR traffic when it enters a port.
Therefore, traffic is served out to the network only when no other traffic is waiting to be served first. The UBR traffic does not affect the trunk loading calculations performed by the switch software.
The parameters for a UBR connection are shown in Figure 21-11 in the sequence in which they occur during the execution of the addcon command.
The UBR policing definitions are summarized in Table 21-14.
Figure 21-11 UBR Connection Prompt Sequence
ATM-to-Frame Relay Network Interworking Connections
An ATM-to-Frame Relay (ATFR) connection is a Frame Relay to ATM connection and is configured as a VBR connection, with a number of the ATM and Frame Relay connection parameters being mapped between each side of the connection.
The parameters for an ATFR connection are shown in Figure 21-12 in the sequence in which they occur during the execution of the addcon command.
Figure 21-12 ATFR Connection Prompt Sequence
Frame Relay-to-ATM Foresight Network Interworking Connection
A Frame Relay-to-ATM Foresight (ATFST) connection is a that is configured as an ABR connection with ForeSight. ForeSight congestion control is automatically enabled when connection type ATFST is selected. A number of the ATM and Frame Relay connection parameters are mapped between each side of the connection.
The parameters for an ATFST connection are shown in Figure 21-13 in the sequence in which they occur during the execution of the addcon command.
Figure 21-13 ATFST Connection Prompt Sequence
Frame Relay-to-ATM Transparent Service Interworking Connections
A Frame Relay-to-ATM Transparent Service Interworking (ATFT) connection is configured as a VBR connection with a number of the ATM and Frame Relay connection parameters being mapped between each side of the connection.
The parameters for an ATFT connection are shown in Figure 21-14 in the sequence in which they occur during the execution of the addcon command.
Figure 21-14 ATFT Connection Prompt Sequence
Frame Relay-to-ATM Foresight Transparent Service Interworking Connections
A Frame Relay-to-ATM Foresight Transparent Service Interworking (ATFTFST) connection is configured as an ABR connection with ForeSight. ForeSight congestion control is automatically enabled when connection type ATFTFST is selected. A number of the ATM and Frame Relay connection parameters are mapped between each side of the connection.
The parameters for an ATFTFST connection are shown in Figure 21-15 in the sequence in which they occur during the execution of the addcon command.
Figure 21-15 ATFTFST Connection Prompt Sequence
Frame Relay-to-ATM Translational Service Interworking Connections
A Frame Relay-to-ATM Translational (ATFX) Service Interworking connection and is configured as a VBR connection, with a number of the ATM and Frame Relay connection parameters being mapped between each side of the connection.
The parameters for an ATFX connection are shown in Figure 21-16 in the sequence in which they occur during the execution of the addcon command.
Figure 21-16 ATFX Connection Prompt Sequence
Frame Relay-to-ATM Foresight Translational Service Interworking Connections
A Frame Relay-to-ATM Foresight (ATFXFST) Translational Service Interworking connection that is configured as an ABR connection with ForeSight. ForeSight congestion control is automatically enabled when connection type ATFXFST is selected. A number of the ATM and Frame Relay connection parameters are mapped between each side of the connection.
The parameters for an ATFXFST connection are shown in Figure 21-17 in the sequence in which they occur during the execution of the addcon command.
Figure 21-17 ATFXFST Connection Prompt Sequence
Traffic Policing Examples
Traffic Policing, also known as Usage Parameter Control (UPC), is implemented using either an ATM Forum single or dual-leaky bucket algorithm. The buckets represent a GCRA (Generic Cell Rate Algorithm) defined by two parameters:
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If the cells are clumped too closely together, they are noncompliant and are tagged or discarded as applicable. If other cells arrive on time or after their expected arrival time, they are compliant, but three is no accrued credit.
Dual-Leaky Bucket (An Analogy)
The following are the generic cell rate algorithm viewpoints:
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CBR Traffic Policing Examples
CBR traffic is expected to be at a constant bit rate, have low jitter, and is configured for a constant rate equal to Peak Cell Rate (PCR). The connection is expected to be always at peak rate.
When you add a connection, you assign a VPI.VCI address, and configure the UPC parameters for the connection. For each cell in an ATM stream seeking admission to the network, the VPI.VCI addresses are verified and each cell is checked for compliance with the UPC parameters. The CBR cells are not enqueued, but are processed by the policing function and then sent to the network unless discarded.
For CBR, traffic policing is based on:
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You may configure CBR connection with policing selected as either 4 or 5.
With policing set to 5, there is no policing.
With policing set to 4, there is single leaky bucket PCR policing as shown in Figure 21-18. The single leaky bucket polices the PCR compliance of all cells seeking admission to the network, both those with CLP = 0 and those with CLP =1. Cells seeking admission to the network with CLP set equal to 1 might have either encountered congestion along the user's network or might have lower importance to the user and have been designated as eligible for discard in the case congestion is encountered. If the bucket depth CDVT (0+1) limit is exceeded, it discards all cells seeking admission. It does not tag cells. If leaky bucket 1 is not full, all cells (CLP =0 and CLP=1) are admitted to the network.
Figure 21-18 CBR Connection, UPC Overview
Figure 21-19 shows a CBR.1 connection policing example, with policing set to 4, where the CDVT depth of the single leaky bucket is not exceeded, and all cells, CLP(0) and CLP(1) are admitted to the network.
Figure 21-19 CBR.1 Connection with Bucket Compliant
Figure 21-20 shows a CBR connection policing example, with policing =4, where the CDVT(0+1) of the single leaky bucket is exceeded and noncompliant cells are discarded. The leaky bucket only discards cells; it does not tag them
Figure 21-20 CBR.1 Connection, with Bucket Discarding nonCompliant Cells
Variable Bit Rate Dual-Leaky Bucket Policing Examples
The contract for a variable bit rate (VBR) connection is set up based on an agreed upon sustained cell rate (SCR) with allowance for occasional data bursts at a Peak Cell Rate (PCR) as specified by maximum burst size (MBS).
When a connection is added, a VPI.VCI address is assigned, and UPC parameters are configured for the connection. For each cell in an ATM stream, the VPI.VCI addresses are verified and each cell is checked for compliance with the UPC parameters as shown in Figure 21-21.
The VBR cells are not enqueued, but are processed by the policing function and then sent to the network unless discarded.
For VBR, traffic policing, depending on selected policing option, are based on the following:
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The policing options for VBR connections, selected by entering 1 to 5 in response to the policing choice prompt, are shown in Table 21-15.
Figure 21-21 VBR Connection, UPC Overview
Leaky Bucket 1
Leaky bucket 1 polices for the PCR compliance of all cells seeking admission to the network, both those with CLP = 0 and those with CLP =1.
For example, cells seeking admission to the network with CLP set equal to 1 may have either encountered congestion along the user's network or may have lower importance to the user and have been designated as eligible for discard in the case congestion is encountered. If the bucket depth in the first bucket exceeds CDVT (0+1), it discards all cells seeking admission. It does not tag cells.
With policing set to 1 (VBR.1), all cells (CLP=0 and CLP=1) that are compliant with leaky bucket 1, are sent to leaky bucket 2.
With policing set to 2 (VBR.2) or to 3 (VBR.3), all CLP=1 cells compliant with leaky bucket 1 are admitted directly to the network, and all CLP=0 cells compliant with leaky bucket 1 are sent to leaky bucket 2.
Leaky Bucket 2
For VBR connections, the purpose of leaky bucket 2 is to police the cells passed from leaky bucket 1 for conformance with maximum burst size MBS as specified by BT and for compliance with the SCR sustained cell rate. The types of cells passed to leaky bucket 2 depend on how policing is set:
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BT + CDVT of leaky bucket 2. If not compliant, the cells are discarded. There is no tagging option.Examples
Figure 21-22 shows a VBR connection policing example, with policing set to 4, leaky bucket 1 compliant, and all cells being admitted to the network.
Figure 21-22 VBR Connection, Policing = 4, Leaky Bucket 1 Compliant
Figure 21-23 shows a VBR connection policing example, with the policing set to 4, and leaky bucket 1 noncompliant which indicates that the connection has exceeded the PCR for a long enough interval to exceed the CDVT (0+1) limit. Noncompliant cells with respect to leaky bucket 1 are discarded.
Figure 21-23 VBR Connection, Policing = 4, Leaky Bucket 1 nonCompliant
Figure 21-24 shows a VBR.2 connection policing example, with policing = 2, and both buckets compliant. Leaky bucket two is policing the CLP(0) cell stream for conformance with maximum burst size MBS (as specified by BT), and for compliance with the SCR sustained cell rate.
Figure 21-24 VBR.2 Connection, Policing = 2, with Buckets 1 and 2 Compliant
Figure 21-25 shows a VBR.2 connection policing example, with policing set to 2, and leaky bucket 2 noncompliant. Leaky bucket 2 is shown policing the CLP(0) cell stream for conformance with maximum burst size MBS (as specified by BT), and for compliance with SCR (sustained cell rate).
In this example (policing set to 2), CLP tagging is not enabled, so that the cells that have exceeded the BT + CDVT limit are discarded. In the example, either the sustained cell rate could have been exceeded for an excessive interval, or a data burst could have exceeded the maximum allowed burst size.
Figure 21-25 VBR.2 Connection, Leaky Bucket 2 Discarding CLP (0) Cells
Figure 21-26 shows a VBR.1 connection policing example, with policing set to 1, and both buckets compliant.
Leaky bucket 1 is policing the CLP (0+1) cell stream for conformance with the PCR limit.
Leaky bucket 2 is policing the CLP (0+1) cell stream for conformance with CDVT plus maximum burst size MBS (as specified by BT), and for compliance with SCR sustained cell rate.
Figure 21-26 VBR.1 Connection, Policing = 1, with Buckets 1 and 2 Compliant
Figure 21-27 shows a VBR.3 connection policing example, with policing set to 3, and Leaky bucket 2 shown as noncompliant.
Leaky bucket 2 is shown policing the CLP(0) cell stream for conformance with maximum burst size MBS (as specified by BT), and for compliance with SCR sustained cell rate.
For the policing = 3 selection, CLP tagging is enabled, so the cells that have exceeded the
BT + CDVT(0+1) limit are tagged as CLP=1 cells and admitted to the network.In this example, either the sustained cell rate could have been exceeded for an excessive interval, or a data burst could have exceeded the maximum burst size allowed.
Figure 21-27 VBR.3 Connection, Policing = 3, with Bucket 2 non-Compliant
ABR Connection Policing
Available Bit Rate (ABR) connections are policed the same as the VBR connections, but in addition use either the ABR Standard with VS/VD congestion flow control method or the ForeSight option to take advantage of unused bandwidth when it is available.
UBR Connection Policing
The contract for a unspecified bit rate connection is similar to the ABR connection service for bursty data. However, UBR traffic is delivered only when there is spare bandwidth in the network.
When a connection is added, a VPI.VCI address is assigned, and UPC parameters are configured for the connection. For each cell in an ATM stream, the VPI.VCI addresses are verified and each cell is checked for compliance with the UPC parameters as shown in Figure 21-28.
Leaky Bucket 1
Leaky bucket 1 polices the UBR connection for PCR compliance. When CLP=No (UBR.1), all cells that are compliant with leaky bucket 1 are applied to the network. However, these cells are treated with low priority in the network with a percentage utilization default of 1 percent.
Leaky Bucket 2
When CLP=Yes (UBR.2), CLP(0) cells that are compliant with leaky bucket 1 are sent to leaky bucket 2. Because SCR=0 for leaky bucket 2, the bucket is essentially always full, and all the CLP(0) cells sent to leaky bucket 2 are therefore tagged with CLP being set to 1. This allows the network to recognize these UBR cells as lower priority cells and available for discard in the event of network congestion.
Figure 21-28 UBR Connection, UPC Overview
ATM Command List
The commands used for ATM connection are listed in Table 21-16. For more information, refer to the Cisco WAN Switching Command Reference, Release 9.3.30.
Posted: Tue May 10 21:20:39 PDT 2005
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