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Table of Contents

ATM Connections

ATM Connections

This chapter describes how ATM connection services are established by adding ATM connections between ATM service interface ports in the network using ATM standard UNI 3.1 and Traffic Management 4.0. It describes BXM and ASI card operation and summarizes ATM connection parameter configuration

The chapter contains the following:

ATM Connection Services

ATM connection services are established by adding ATM connections between ATM service interface ports in the network. ATM connections can originate and terminate on the ASI (ATM Service Interface) cards, on BXM-T3/E3, BXM-155 (OC-3), and BXM-622 (OC-12) cards configured for port (service access) operation on the BPX, or on the AXIS shelf (using the AUSM card for the AXIS). Frame relay to ATM network interworking connections are supported between either BXM or ASI cards to the IPX, IGX, or AXIS. Frame relay to ATM service interworking connections are supported between either BXM or ASI cards to FRSM cards on the AXIS shelf.

Figure 10-1 is a depiction of ATM connections over a BPX network. It shows ATM connections via BXM-T3/E3, BXM-155, BXM-622, ASI-1, and ASI-155 cards, as well as over AXIS shelves. It also shows frame relay to ATM interworking connections over AXIS, IPX, and IGX shelves. For further information on the AXIS shelf, refer to the AXIS Reference document.


Figure 10-1:
ATM Connections over a BPX Network

.


SVCs

When an Extended Services Processor (ESP) is co-located with a BPX Extended Services Node, ATM and Frame Relay Switched Virtual Circuits (SVCs) are supported in addition to Permanent Virtual Circuits (PVCs). For further information on ATM SVCs, refer to Chapter 10, SVCs, ATM and Frame Relay and to the BPX Service Node Extended Processor Installation and Operation document.

Traffic Management Overview

The ATM Forum Traffic Management 4.0 Specification defines five basic traffic classes:

Table 10-1 summarizes the major attributes of each of the traffic management classes:


Table 10-1: Standard ATM Traffic Classes
Attribute CBR rt-VBR nrt-VBR UBR ABR

Traffic Parameters

PCR & CDVT

x

x

x

x

x

SCR & MBS

x

x

MCR

x

QoS Parameters

Pk-to-Pk CDV

x

x

Max CTD

x

x

CLR

x

x

x

nw specific

Other Attributes

Congestion Control Feedback

x

Traffic parameters are defined as:

QoS (Quality of Service) parameters are defined as:

Congestion Control Feedback:

Standard ABR notes:

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 (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.

VSVD Description

ABR sources and destinations are linked via bi-directional 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 10-2 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).

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, i.e., 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: Constant Bit Rate (CBR), Variable Bit Rate (VBR), Available Bit Rate (ABR with VS/VD, ABR without VS/VD, and ABR using Foresight), and Unspecified Bit Rate (UBR). ABR with VS/VD supports explicit rate marking and Congestion Indication (CI) control.


Figure 10-2: ABR VSVD Flow Control Diagram

ForeSight Congestion Control

ForeSight may be used for congestion control across BPX/IGX/IPX switches for connections that have one or both end points terminating on ASI-T3/E3 or BXM cards. 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. The BXM cards also support the VSVD congestion control mechanism as specified in the ATM Traffic Management 4.0 standards.

ATM Connection Requirements

There are two connection addressing modes supported. The user may enter a unique VPI/VCI address in which case the BPX functions as a virtual circuit switch. Or the user may enter only a VPI address in which case all circuits are switched to the same destination port and the BPX functions as a virtual path switch in this case. 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, and are translated by tables in the BPX to route the connection. Connections are automatically routed by the AutoRoute feature once the connection endpoints are specified.

ATM connections can be added using either the StrataView Plus Connection Manager or a node's command line interface (CLI). Typically, the StrataView Plus Connection Manager is the preferred method as 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.

When adding ATM connections, first the access port and access service lines connecting to the customer CPE need to be configured. Also, the trunks across the network need to configured appropriately for the type of connection. Following that the addcon command may be used to add a connection, first specifying the service type and then the appropriate parameters for the connection.

For example, when configuring a BXM for CPE connections, the BXM is configured for port mode, a line is upped with the upln command and configured with the cnfln command. Then the associated port is configured with the cnfport command and upped with the upport command. Following this, the ATM connections are added via the addcon command with the syntax.

Connection Routing

ATM connections for a BXM or ASI card are identified as follows:

The slot and port are related to the BPX 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 AutoRoute feature is standard with all BPX, IGX, and IPX nodes. The network automatically detects trunk failures and routes connections around the failures.

Addcon Command Syntax

The following parameters are entered for BXM addcon command. Depending upon the connection type, the user is prompted for the appropriate parameters as shown in the following:

addcon local_addr node remote_addr traffic_type....extended parameters

Field Value Description

local/remote_addr

slot.port.vpi.vci

desired VCC or VPI connection identifier

node

slave end of connection

traffic_type

Type of traffic, chosen from CBR, VBR, ABR, and UBR

extended parameters

The traffic management and performance parameters associated with an ATM connection.


Note The range of VPIs and VCIs reserved for PVC traffic and SVC traffic is configurable using the cnfport command. While adding connections, the system checks the entered VPI/VPC against the range reserved for SVC traffic. If there is a conflict, the addcon command fails with the message "VPI/VCI on selected port is reserved at local/remote end".

ATM Connection Configuration

The following figures and tables describe the parameters used to configure ATM connections:

The following figures list the connection parameters in the same sequence as they are entered when a connection is added:

The following figure shows the VSVD network segment and external segment options available when ABR Standard or ABR ForeSight is selected. ForeSight congestion control is useful when both ends of a connection do not terminate on BXM cards. At present, FCES (Flow Control External Segment) as shown in Figure 10-7 is not available for ABR with ForeSight.

The following figures list the connection parameters in the same sequence as they are entered when a connection is added:


Table 10-2: Traffic Policing Definitions
Connection Type ATM Forum TM spec. 4.0 conformance definition PCR Flow (1st leaky bucket) CLP tagging (for PCR flow) SCR Flow (2nd leaky bucket) CLP tagging (for SCR flow)

CBR

CBR.1

when policing set to 4 (PCR Policing only)

CLP(0+1)

no

off

n/a

CBR

When policing set to 5 (off)

off

n/a

off

n/a

UBR

UBR.1

when CLP setting = no

CLP(0+1)

no

off

n/a

UBR

UBR.2

when CLP setting = yes

CLP(0+1)

no

CLP(0)

yes

VBR, ABR, ATFR, ATFST

VBR.1

when policing set to 1

CLP(0+1)

no

CLP(0+1)

no

VBR, ABR, ATFR, ATFST

VBR.2

when policing set to 2

CLP(0+1)

no

CLP(0)

no

VBR, ABR, ATFR, ATFST

VBR.3

when policing set to 3

CLP(0+1)

no

CLP(0)

yes

VBR, ABR, ATFR, ATFST

when Policing set
to 4

CLP(0+1)

no

off

n/a

VBR, ABR, ATFR, ATFST

when Policing set
to 5 for off)

off

n/a

off

n/a

Note 1: - For UBR.2, SCR = 0

Note 2:


Table 10-3:

PARAMETER WITH [DEFAULT SETTING] BXM T3/E3, OC3 & OC12 RANGE ASI T3/E3 RANGE ASI-155 RANGE

PCR(0+1)[50/50]

50- T3/E3 cells/sec

50 - OC3

50 - OC12

T3: MCR - 96000

E3: MCR - 80000

Limited to MCR - 5333 cells/sec for ATFR connections.

OC3 (STM1): 0 - 353200

%Util[100/100]

for UBR [1/1]

0 - 100%

1 - 100%

1 - 100%

MCR[50/50]

cells/sec

6 - T3/E3OC3/0C12

T3: 0 - 96000 cells/sec

E3: 0 - 80000 cells/sec

N/A

FBTC (AAL5 Frame Base Traffic Control):

for VBR [disable]

for ABR/UBR [enable]

for Path connection [disable]

enable/disable

enable/disable

enable/disable

CDVT(0+1):

for CBR [10000/10000],

others [250000/250000]

0 - 5,000,000 usec

T3/E3 1 - 250,000 usecs.

OC3/STM1: 0 - 10000 usecs.

VSVD[disable]

enable/disable

enable/disable

Select disable, as only ABR w/o VSVD is supported.

FCES (Flow Control External Segment) [disable]

enable/disable

enable/disable

N/A

Default Extended Parameters[enable]

enable/disable

enable/disable

N/A

CLP Setting[enable]

enable/disable

enable/disable

enable/disable

SCR [50/50]

cells/sec

50 - T3/E3OC3/OC12

T3: MCR - 96000:T3

E3: MCR - 80000: E3

Limited to MCR - 5333 cells/sec for ATFR connections.

OC3/STM1: 0 - 353200

MBS [1000/1000]

1 - 5,000,000cells

T3/E3: 10 - 24000 cells

OC3 (STM1): 10 - 1000 cells

Policing[3]

For CBR: [4]

1 - VBR.1

2 - VBR.2

3 - VBR.3

4 - PCR policing only

5 - off

1 - VBR.1

2 - VBR.2

3 - VBR.3

4 - PCR policing only

5 - off

1 - VBR.1

2 - VBR.2

3 - VBR.3

4 - PCR policing only

5 - off

ICR:

max[MCR, PCR/10]

MCR - PCR cells/sec

MCR - PCR cells/sec

N/A

ADTF[1000]

62 - 8000 msec

1000 - 255000 msecs.

N/A

Trm[100]

ABRSTD: 1 - 100 msec

ABRFST: 3 - 255 msec

20 - 250 msecs.

N/A

VC QDepth [16000/16000]

For ATFR/ATFST [1366/1366]

0 - 61440 cells

Applies to T3/E3 only
ABR: 1 - 64000 cells
ATFR: 1 - 1366 cells

ATFR: 1 - 1366 cells

CLP Hi [80/80]

1 - 100%

1 - 100%

N/A

CLP Lo/EPD [35/35]

1 - 100%

1 - 100%

N/A

EFCI [30/30]

For ATFR/ATFST [100/100]

1 - 100%

1 - 100%

0 - 100%

RIF:

For ForeSight:

max[PCR/128, 10]

For ABR STD[128]

If ForeSight, then in absolute (0 - PCR)

If ABR then 2n

(1 - 32768)

If ForeSight, then in absolute (0 - PCR)

If ABR, then 2n

(1 - 32768)

N/A

RDF:

For ForeSight [93]

For ABR STD [16]

If ForeSight, then %

(0% - 100%)

If ABR then 2n

(1 - 32768)

If ForeSight, then %

(0% - 100%)

If ABR, then 2n

(1 - 32768)

N/A

Nrm[32], BXM only

2 - 256 cells

N/A

N/A

FRTT[0], BXM only

0 - 16700 msec

N/A

N/A

TBE[1,048,320], BXM only

0 - 1,048,320 cells

(different max range from TM spec. but limited by firmware for CRM(4095 only) where CRM=TBE/Nrm

N/A

N/A

IBS[1/1]

0 - 24000 cells

T3/E3 ABR: 0 - 24000 cells

ATFR: 1 - 107 cells

0 - 999 cells

Connection Parameters with Default Settings and Ranges

Table 10-4:
Parameter Description

PCR

Peak cell rate:

The cell rate which the source may never exceed

%Util

% Utilization; bandwidth allocation for: 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 non-compliant cell. This is used to set the Early Packet Discard bit at every node along a connection.

VSVD

Virtual Source Virtual Destination:

(see Meaning of VSVD and Flow Control External Segments, Figure 10-7)

FCES (Flow Control External Segments)

(see Meaning of VSVD and Flow Control External Segments, Figure 10-7)

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 definitions of Traffic Policing, Table 10-2)

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. For ASI cards, regardless of the FBTC setting, this is the CLP Lo 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, i.e., 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, i.e. 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

Connection Parameter Descriptions

CBR 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 10-3 in the sequence in which they occur during the execution of the addcon command. The CBR policing definitions are summarized in Table 10-5.


Figure 10-3: CBR Connection Prompt Sequence


Table 10-5:
Connection Type ATM Forum TM spec. 4.0 conformance definition PCR Flow (1st leaky bucket) CLP tagging (for PCR flow) SCR Flow (2nd leaky bucket) CLP tagging (for SCR flow)

CBR

CBR.1

when policing set to 4 (PCR Policing only)

CLP(0+1)

no

off

n/a

CBR

When policing set to 5 (off)

off

n/a

off

n/a

CBR Policing Definitions

VBR and ATFR Connections

VBR Connections

VBR (variable bit rate) connections may be classified as rt-VBR or nrt-VBR connections.

The rt-VBR (real-time variable bit rate) category is used for connections that transmit at a rate varying with time and that can be described as bursty, often requiring large amounts of bandwidth when active. The rt-VBR class is intended for applications that require tightly constrained delay and delay variation. An example of rt-VBR is video conferencing which 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 nrt-VBR (non-real time variable bit rate) category is used for connections that are bursty but are not constrained by delay and delay variation boundaries. For those cells in compliance with the traffic contract, a low cell loss is expected. Non-time critical data file transfers are an example of an nrt-VBR connection. A nrt-VBR connection is characterized by PCR, SCR, and MBS.

Configuring VBR connections. The characteristics of rt-VBR or nrt-VBR are supported by appropriately configuring the parameters of the VBR connection.

The parameters for a VBR connection are shown in Figure 10-4 in the sequence in which they occur during the execution of the addcon command. The VBR policing definitions are summarized in Table 10-6.


Figure 10-4: VBR Connection Prompt Sequence


Table 10-6:
Connection Type ATM Forum TM spec. 4.0 conformance definition PCR Flow (1st leaky bucket) CLP tagging (for PCR flow) SCR Flow (2nd leaky bucket) CLP tagging (for SCR flow)

VBR, ABR, ATFR, ATFST

VBR.1

when policing set to 1

CLP(0+1)

no

CLP(0+1)

no

VBR, ABR, ATFR, ATFST

VBR.2

when policing set to 2

CLP(0+1)

no

CLP(0)

no

VBR, ABR, ATFR, ATFST

VBR.3

when policing set to 3

CLP(0+1)

no

CLP(0)

yes

VBR, ABR, ATFR, ATFST

when Policing set
to 4

CLP(0+1)

no

off

n/a

VBR, ABR, ATFR, ATFST

when Policing set
to 5 for off)

off

n/a

off

n/a

VBR Policing Definitions

ATFR Connections

An ATFR (ATM to Frame Relay) 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 10-5 in the sequence in which they occur during the execution of the addcon command.


Figure 10-5: ATFR Connection Prompt Sequence

ABR Notes

The term ABR is used to specify one of the following:

ABR and ATFST Connections

ABR 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.

Policing for ABR connections is the same as for VBR connections which are summarized in Table 10-6.

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 10-6 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 VSVD congestion flow control.

VSVD and flow control with external segments are shown in Figure 10-7.


Figure 10-6: AB
R Standard Connection Prompt Sequence

Figure 10-7:
Meaning of VSVD and Flow Control External Segments

ATFST Connections

The 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 10-8 in the sequence in which they occur during the execution of the addcon command.


Figure 10-8: ABR ForeSight Connection Prompt Sequence

An ATFST connection is a frame relay to ATM connection 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 10-9 in the sequence in which they occur during the execution of the addcon command.


Figure 10-9: ATFST Connection Prompt Sequence


UBR 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 10-10 in the sequence in which they occur during the execution of the addcon command.

The UBR policing definitions are summarized in Table 10-7.


Figure 10-10: UBR Connection Prompt Sequence



Table 10-7:
Connection Type ATM Forum TM spec. 4.0 conformance definition PCR Flow (1st leaky bucket) CLP tagging (for PCR flow) SCR Flow (2nd leaky bucket) CLP tagging (for SCR flow)

UBR

UBR.1

when CLP setting = no

CLP(0+1)

no

off

n/a

UBR

UBR.2

when CLP setting = yes

CLP(0+1)

no

CLP(0)

yes

UBR Policing Definitions

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:

If the cells are clumped too closely together, they are non-compliant 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)

A GCRA viewpoint is as follows:

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 a connection is added, a VPI.VCI address is assigned, and the UPC parameters are configured 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:

The CBR connection may be configured 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 10-11. 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 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 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 10-11: CBR Connection, UPC Overview


Figure 10-12 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 10-12: CBR.1 Connection with Bucket Compliant


Figure 10-13 shows a CBR connection policing example, with policing =4, where the CDVT(0+1) of the single leaky bucket is exceeded and non-compliant cells are discarded. The leaky bucket only discards cells; it does not tag them


Figure 10-13: CBR.1 Connection, with Bucket Discarding non-Compliant Cells


.

VBR Dual-Leaky Bucket Policing Examples

The contract for a variable bit rate 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 10-14.

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, is based on:

The policing options, selected by entering 1-5 in response to the policing choice prompt, are as follows for VBR connections:

VBR.1

VBR with policing set to 1.

CLP(0+1) cells compliant with leaky bucket 1 are passed to leaky bucket 2; non-compliant cells are discarded. CLP(0+1) cells compliant with leaky bucket 2 are admitted to the network; non-compliant cells are discarded.

VBR.2

VBR with policing set to 2.

CLP(1) cells compliant with leaky bucket 1 are admitted to the network; non-compliant CLP(0+1) cells are dropped. CLP(0) cells compliant with leaky bucket 1 are applied to leaky bucket 2; non-compliant cells are dropped. CLP(0) cells compliant with leaky bucket 2 are admitted to the network; non-compliant cells are dropped.

VBR.3

VBR with policing set to 3.

VBR.3. CLP(1) cells compliant with leaky bucket 1 are admitted to the network; non-compliant CLP(0+1) cells are dropped. CLP(0) cells compliant with leaky bucket 1 are applied to leaky bucket 2; non-compliant cells are dropped. CLP(0) cells compliant with leaky bucket 2 are admitted to the network; non-compliant cells are tagged and admitted to the network.

VBR with policing set to 4.

CLP(0+1) cells compliant with leaky bucket 1 are admitted to the network; non-compliant cells are dropped. Leaky bucket 2 is not active.

VBR with policing set to 5.

Policing is off, so there is no policing of cells on ingress.


Figure 10-14: 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:

Examples

Figure 10-15 shows a VBR connection policing example, with policing set to 4, leaky bucket 1 compliant, and all cells being admitted to the network


Figure 10-15: VBR Connection, Policing = 4, Leaky Bucket 1 Compliant

.

Figure 10-16 shows a VBR connection policing example, with the policing set to 4, and leaky bucket 1 non-compliant which indicates that the connection has exceeded the PCR for a long enough interval to exceed the CDVT (0+1) limit. Non-compliant cells with respect to leaky bucket 1 are discarded


Figure 10-16: VBR Connection, Policing = 4, Leaky Bucket 1 Non-Compliant

.

Figure 10-17 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 10-17: VBR.2 Connection, Policing = 2, with Buckets 1 and 2 Compliant


Figure 10-18 shows a VBR.2 connection policing example, with policing set to 2, and leaky bucket 2 non-compliant. 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 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 10-18: VBR.2 Connection, Leaky Bucket 2 Discarding CLP (0) Cells


Figure 10-19 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 CDVT plus maximum burst size MBS (as specified by BT), and for compliance with SCR sustained cell rate.


Figure 10-19: VBR.1 Connection, Policing = 1, with Buckets 1 and 2 Compliant


Figure 10-20 shows a VBR.3 connection policing example, with policing set to 3, and Leaky bucket 2 shown as non-compliant. 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 10-20: 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 VSVD 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 10-21.

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 % utilization default of 1%.

Leaky Bucket 2

When CLP=Yes (UBR.2), CLP(0) cells that are compliant with leaky bucket 1 are sent to leaky bucket 2. Since 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 10-21: UBR Connection, UPC Overview


LMI and ILMI Parameters

The following is a listing of the LMI and ILMI parameters for the ASI and BXM:

For ILMI information, refer to Table 10-8:


Table 10-8:
Parameter Description

VPI.VCI

VCCI for ILMI signaling channnel equal 0.16

Polling Enabled

Keep-alive polling

Trap Enabled

VCC change of state traps

Polling Interval

Time between GetRequest polls

Error Threshold

Number of failed entries before ILMI link failure is declared.

Event Threshold

Number of successful polls before ILMI link failure is cancelled.

Addr Reg Enab

SVC Address Registration procedures enabled.

ILMI Parameters

For the LMI information, refer to Table 10-9.


Table 10-9:
Parameter Description

VPI.VCI

VCCI for LMI signaling channel equal 0.31

Polling Enable

Keep-alive polling

T393

Status Enquiry timeout value

T394

Update Status timeout value

T396

Status Enquiry polling timer

N394

Status Enquiry retry count

N395

Update Status retry count

LMI Parameters


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Posted: Thu Jan 18 12:25:10 PST 2001
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