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The following traffic management functions are supported on the PNNI node:
The following service categories as defined in ATM Forum Traffic Management 4.0 are supported:
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Note ABR is currently only supported in SPVCs. ABR will be supported in SVCs when UNI 4.0 is supported. |
| Attribute | CBR | rt-VBR | nrt-VBR | UBR | ABR |
|---|---|---|---|---|---|
PCR, CDVT | yes | yes | yes | yes | yes |
SCR, MBS | N/A | yes | yes | N/A | N/A |
MCR (UNI 4.0) | N/A | N/A | N/A | N/A | yes |
RAIG CLP (PNNI 1.0) | Yes | yes | yes | N/A | N/A |
peak-to-peak CDV (UNI 4.0) | yes | yes | no | no | no |
max CTD (UNI 4.0) | yes | yes | no | no | no |
CLR (UNI 4.0) | yes | yes | yes | no | network specific |
Each connection between an ATM CPE (ATM end user) and the WAN switching network establishes a contract with the network based on Quality of Service (QoS) parameters. This contract specifies an envelope that describes the intended traffic flow, including values for peak bandwidth, average sustained bandwidth, and burst size.
The ATM CPE device is responsible for adhering to the contract by means of traffic shaping. Traffic shaping is the use of queues to constrain data bursts, limit peak data rate, and smooth jitter so that the traffic complies with the criteria specified in the envelope.
The SES PNNI nodes have the option of using traffic policing to enforce the networking contract. The SES PNNI node uses the following two methods to police traffic from ATM CPE into the network:
Connection Admission Control (CAC) verifies that sufficient network resources are available to accept the call. The desired ATM traffic contract is specified in the Bearer Capability, the Traffic Descriptor, and Quality of Service (QoS) information elements of the Setup message. These UNI signaling Setup message elements are mapped to Usage Parameter Control (UPC) parameters in the SES PNNI node.
CAC functions are performed on each individual node. G-CAC (Generic CAC) is performed by the routing protocol when it selects a routing path for a call. The PNNI routing protocol needs to make sure that the routing path it selected will satisfy the basic traffic parameter requirement specified by the call. The checking performed by the routing protocol at border node is called G-CAC. For G-CAC description, refer to "ATM Forum PNNI 1.0 Spec. af-pnni-0055.000". A routing path which satisfied the G-CAC checking may not guarantee the call will have traffic resource on each node of its routing path. This is attributed to the routing data base synchronization delay in the network. To ensure a call has traffic resource it requested on each node of its routing path, a local CAC (A-CAC) must be performed when the call arrived on the node. A call will be released or cranked back if it fails on A-CAC. A-CAC performance is described in the section below.
Both resource-related criteria and policy-related criteria are used for CAC. And the CAC is performed per service category. The CAC is applied to all types of interfaces, UNI, NNI, and IISP.
For resource-related CAC, the CAC algorithm calculates the Equivalent Cell Rate (ECR) of a connection prior to establishing the connection, and ensures high efficiency of network resources in accordance with the following criteria:
When a call is admitted with the ECR, the requested QoS for the connection is guaranteed even under the worst scenario as described by the traffic descriptors of the connection.
For policy-related CAC, the following parameters are configurable per service category.
BPX/SES support per CoS queuing. The BXM supports 16 qbin for each port. Qbin 0 to Qbin 9 are reserved for AutoRoute. Qbin 10 to Qbin 15 are reserved for VSI applications such as PNNI and MPLS service. For detail Qbin description and configuration, refer to Appendix D, Virtual Switch Interface, and Chapter 10, Configuring ATM SVCs, PNNI Routing, and SPVCs.
Prior to SES Release 1.0.10, the control VCs share the same Qbin as the connection VCs for data traffic. For example, the SSCOP VC shares the Qbin of nrtVBR traffic. In case of congestion, switchcc, massive reroutes or resetcd, signalling messages may be dropped either due to lack of Qbin resource or due to policing done by a switch on the path. Although the control messages are handled by reliable message delivery mechanisms, dropping control cells can lead to trunks/ports going down and connections get rerouted. Without having a dedicated Qbin for control VCs, control VC messages are subject to being dropped as are other data messages with the same service type when the network is congested.
A dedicated Qbin for all control VC traffic is supported in SES Release 1.0.10. The control VC Qbin on BXM use two previously unused Qbins, 0 and 4, to queue the control VC traffic. The data on the control VC Qbin has higher priority for servicing. This will guarantee that control traffic does not get dropped when the trunk is congested.
A new VC_Type, SIG, is defined to represent control VC traffic. It behaves like a NRT_VBR type VC, but it will not share the same queue with other NRT_VBR type VCs. The default CDVT for control VC is based on UNI 3.1 recommendation. When UNI 4.0 is available in later release, the default value may get changed based on UNI 4.0 standard.
In BPX, a user should load the latest FW in BXM first and then load the new SW in BCC, after that, setrev in PXM1 to use the new image. A user can configure bandwidth for SIG type VCs. No bookfactor is supported for the SIG type traffic and it is always set to be 100%.
Usage Parameter Control (UPC) may be performed at the ingress of network edge nodes only, or alternatively may be performed at every intermediate node. UPC is enabled on a per interface basis as specified by a service class template on the switches. The traffic contracts are defined in the ATM Forum Traffic Management Specification 4.0 and UNI 3.x, and are summarized in the following table.
| Service Category | CBR | CBR | rt, nrt, VBR | rt, nrt VBR | CBR | rt, nrt VBR | UBR | UBR | ABR |
|---|---|---|---|---|---|---|---|---|---|
| UNI 4.0 Conform-ance | 1 CBR.2 | CBR.3 | VBR.2 | VBR.3 | CBR.1 | VBR.1 | UBR.1 | UBR.2 | ABR |
| Parameters |
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PCR (0+1) | x | x | x | x | x | x | x | x | x |
PCR (0) | x | x |
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CDVT(0+1) | x | x | x | x | x | x | x | x | x |
CDVT(0) | x | x |
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SCR (0+1) |
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SCR (0) |
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| x | x |
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MBS (0+1) |
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MBS(0) |
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Tagging |
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Best Effort |
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MCR |
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Transmit ATC2 | 5 | 5 | 9, 10 | 9, 10 | 7 | 19, 11 | 10 | 10 | 12 |
ILMI Traffic Descriptor Type | NoClpNoScr | NoClpNoScr | ClpNoTaggingScr | ClpTaggingScr | NoClpNoScr | NoClpScr | NoClpNoScr | NoClpNoScr | ClpNoTagi-Mcr |
ILMI Best Effort Indicator | false | false | false | false | false | false | true | true | false |
Specification | 3.x
| 3.x
| 3.x 4.0 | 3.x 4.0 | 3.x 4.0 | 3.x 4.0 | 3.x 4.0 | 4.0 | 4.0 |
| 1This traffic definition applies to the CBR traffic sets specified in TM 3.x. 2Transmit ATC is defined in TM 4.0, which is not supported in the current release. |
Available Bit Rate (ABR) can operate in the following modes, all of which are supported by the
BPX switch:
EFCI marking and VS/VD control are configured by the service template for an interface. SPVC supports VS/VD on a per connection basis. Relative Rate marking (CI control) and Explicit Rate marking are configured on a per slot basis, and this configuration applies to both AutoRoute and
PNNI ABR connections on the slot.
The ABR closed loop virtual source/virtual destination (VS/VD) control is set up between the originating and terminating UNIs which are set up as VSVD endpoints. An interface is provisioned so that ABR endpoints on that interface operate as a VSVD endpoints.
The ABR parameters (Table 3-3) are obtained from the following SETUP message information:
| Bearer Class must be set to ABR and User Plane Connection Configuration must be point-to-point. |
|---|---|
| IE contains the forward and backward MCR and PCR values. |
| Mandatory IE contains the forward and backward ICR, TBE, RIF and RDF values, and the CRM value. |
| Optional IE contains the forward and backward Nrm, Trm, CDF and ADTF parameters. |
If ABR parameters are not supplied in the SETUP message then default values are used.
| Parameter | Default | Value Range | Units | Description | IE |
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PCR | mandatory | 50 - Line Rate | cells/s | Peak Cell Rate | Traffic Descriptor |
MCR | 0 | 50 - Line Rate | cells/s | Minimum Cell Rate | Traffic Descriptor |
ICR | PCR | MCR - PCR | cells/s | Initial Cell Rate | ABR Setup Parameters |
RIF | 1/16 | Power of 2: 1/32768 - 1 | - | Rate Increase Factor | ABR Setup Parameters |
RDF | 1/16 | Power of 2: 1/32768 - 1 | - | Rate Decrease Factor | ABR Setup Parameters |
TBE | 16777215 | 0 - 16777215 | cells | Transient Buffer Exposure | ABR Setup Parameters |
FRTT | - | 0 - 16777215 | usec | Fixed Round Trip Time | ABR Setup Parameters |
Nrm | 32 | Power of 2: | cells | Maximum cells per forward RM-cell | ABR Additional Parameters |
ADTF | 0.55 | 0.01-10.23 | sec | ACR Decrease Time Factor | ABR Additional Parameters |
Trm | 100 | 100 times power of 2: 100*2-7 - 100*20 | msec | Time between Forward RM-cells | ABR Additional Parameters |
CDF | 1/16 | Power of 2: 1/64 - 1 | - | Cutoff Decrease Factor | ABR Additional Parameters |
CRM | TBE/Nrm | 1 - 4095 | cells | Cumulative RM-cell Count | Computed |
When the SES node receives a Setup message, the following processing, which includes Connection Admission Control (CAC), occurs:
BPX/SES support frame discard for AAL5 on PNNI 1.0 signaling to support SPVC applications. This can be configured per SPVC. Frame discard for SVC is configured on per port basis (on or off). Control of frame discard for individual SVC will be supported in later release when UNI4.0 is supported.
PNNI Controller supports both overbooking and underbooking when it sets up a port's CAC policy parameters. The CLI to change booking factor is cnfpnportcac portid service_category -bookfactor utilization-factor. The Service Category Utilization Factor (SCUF) is in the range of 1 to 200. The default is 100. An SCUF = 1 means the controller book 1% of requested bandwidth (i.e. request 100M BW on a call, the controller records only 1 M of bandwidth is reserved). This is an overbooking. On other hand, an SCUF = 200 means the controller book 200% of requested bandwidth. This is an underbooking.
A different connection BW is used for the GCAC and ACAC algorithms to deal with booking factor. For GCAC, the booking factor is considered at the time link BW is advertised to the network. For ACAC, the booking factor is considered at the time a connection is added to a link. With that in mind, here are some examples of how over and undersubscription works:
1. No overbooking or oversubscription
Suppose a user has a 100 MB link and the booking factor is 100.
2. Overbooking/Oversubscription
Suppose for the same 100MB link, the booking factor is 10.
3. Underbooking/Undersubscription
Suppose for the same 100 MB link, the booking factor is 200.
PNNI advertises the effective link BW by taking into consideration the actual link BW and the booking factor. Therefore, GCAC will always CAC the configured connection BW w/o considering the booking factor.
The ATM interface is configured for the actual link BW, so in its ACAC, it adjusts the connection BW as required by the booking factor.
Booking factors less than 100% result in link oversubscription since the BW booked for each connection is less than the configured BW for the connection. This is also referred to as overbooking.
Booking factors greater than 100% result in link undersubscription, and the BW booked for a connection is greater than the connection's configured BW. This is also referred to as underbooking.
We should also note that the policing BW is still based on the configured bandwidth, not book factor. That is, for a 10MB connection, no matter what the booking factor is, the policing is still 10MB.
Infinite oversubscription is not currently supported in PNNI since the booking factor can not be set to zero (range 1-200).
Posted: Thu Sep 28 15:17:24 PDT 2000
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