Cisco 6130 NI-2 DSLAM System ATM Addressing Guidelines

This appendix describes network provider guidelines for setting up Cisco 6130 system ATM virtual path connection (VPC) and virtual channel connection (VCC) addresses. We assume that you have a working knowledge of ATM switching, in a permanent virtual circuit (PVC) provisioning setting.

When you are determining the optimal Cisco 6130 6130 NI-2 system ATM address space within the network provider ATM network, consider the following:

ATM UNI Version 3.1 specification restrictions
Cisco 6130 NI-2 system VPC and VCC connection capacity
Number of subscribers and connections per subscriber
Evolution to switched virtual circuits (SVCs)
Subtend connection mapping
Symmetry for application programming interface (API) design

C.1 ATM UNI Version 3.1 Specification Restrictions

The following address usage constraints are imposed by the ATM Forum UNI Version 3.1 specification :

Up to 65,536 virtual channel identifiers (VCIs) per physical UNI are permitted.
VCIs can be mapped in up to 256 virtual paths (VPs).
VCIs 0 to 31 on each VP are reserved for future use and are typically not used for user traffic.

Note Each ATM network element vendor comprises the full VPC and VCC space as defined by the ATM Forum.

ATM Forum specifications are designed for a scalable evolution and do not take into consideration the price and performance attributes of memory technology at given points in time.

C.2 Cisco 6130 NI-2 DSLAM System VPC and VCC Connection Capacity

The following ATM address space type (VPC and VCC) and ranges are supported in Cisco IOS Release 12.0(5)DA1:

Virtual path identifier (VPI) 1 supports up to 1600 VCIs, from VCI 0 to VCI 1599.
VPI 0, 227 each support up to 400 VCIs, from VCI 0 to VCI 399.
The remaining 228 VPs (allowed within the ATM UNI Version 3.1 standard) are usable for VPC switching only. Within the Cisco 6130 NI-2 system, VPCs are intended for use when you are mapping subtended Cisco 6130 NI-2 system connections through a higher level Cisco 6130 NI-2 system to the edge switch connection.

The ATM address space type (VPC and VCC) and ranges are further conditioned into actual capacities per the following constraints. Each successive constraint is explained in detail to show the difference between theoretical and actual maximums.

Theoretical maximum network-side VPI and VCI address space = 1600 + 27(400) = 12,400.

: This represents the maximum number of VPI and VCI addresses that you can switch across the DSLAM (the host multiplexer, for example, the DSLAM that is physically connected to the ATM bearer service without any ATM UNI specification or subtending constraints).

Theoretical maximum network-side VPI and VCI address space, while observing VCIs 0 to 31 reservation guidelines = 1568 + 27(368) = 11,504.

: This represents the maximum number of VPI and VCI addresses that you can switch across the host DSLAM, taking into consideration the ATM UNI Version 3.1 specification of reserving VCIs 0 to 31 on each VPI. This maximum does not take into consideration subtending port constraints.
: Due to the need for contiguous use of address space within the Cisco 6130 NI-2 system ATM chipset, if VCIs 0 to 31 are reserved for each VP, then 1600 - 32 = 1568 VCIs can be mapped across VPI 1, and 400 - 32 = 368 VCIs can be mapped across VPIs 0, and 2 to 27.

Theoretical maximum subscriber-side VPI or VCI address space (assuming 6 subtended Cisco 6100s, and utilizing VPC switching from subtended Cisco 6100s) = 7 DSLAMs x 400 subs x 4 VCCs = 11,200.

: This represents the maximum number of VPI or VCI addresses required (out of the above possible 11,504), assuming a full subtended tree of six DSLAMs and one host DSLAM, with 4 VCCs allocated per subscriber. Because of a VCC address space constraint on the subtend port (discussed below), the assumption is made here that VPC switching is utilized across subtend ports.

The actual VPI or VCI address space maximum depends on whether VCIs traverse intermediate DSLAMs, on their way to the ATM bearer service, as VCCs or across virtual paths (VPCs). You can address a maximum of 4000 VCCs to any one subtend port. This means that in a full subtend tree, the host DSLAM can be assigned only 8000 VCCs. So the maximum number of VCCs that can be supported on a fully subtended Cisco 6130 NI-2 system network is 1600 + 8000 = 9600. If VPCs are used to traverse intermediate DSLAMs on their way to the ATM bearer service, then 7 x 400 subs x 4 VCCs per sub = 11200 virtual circuits (VCs) can be supported.

C.3 Number of Subscribers and Connections per Subscriber

Each network provider must determine expected subscriber demand per Wire Center. Demand can be met in a variety of Cisco 6130 NI-2 system configurations, ranging from a dedicated (64 subscribers per Cisco 6130 NI-2 system) to fully concentrated (400 subscribers per Cisco 6130 NI-2 system).

The network provider should also consider the number of PVCs required per subscriber.

C.4 Evolution to SVCs

The network provider should consider the point when, due to either network design goals or the need for sheer volume connection deployment, SVCs begin to supersede PVCs as a means of establishing connections. One of the biggest drivers for SVCs is to remove the need for service providers to discretely map thousands or even millions of PVC segments to enable end-to-end ATM connections across an ATM bearer service. SVCs also reduce the strain on the connection space limits imposed by various network elements, because connection space is only required for active connections.

Established PVCs should be able to be preserved with the advent of SVCs. The signaling stack manages selection of an available VCC for each user call. Customers shifting from PVC service to SVC service would have their PVCs deleted by the network provider. Reservation of VCCs VPIn/VCI 0 to 31 protects appropriate space per VP for signaling purposes. SVC functionality is not available yet, and therefore Cisco makes no guarantee that some PVC address space reprovisioning might not be required. A Cisco goal is to minimize this. Utilities are being investigated to remap these PVCs in an automated fashion.

C.5 Subtend Connection Mapping

To decide whether or not you should map subtended connections through to the ATM bearer service network as VPCs or VCCs, consider the following:

The greater the desire to minimize connection configuration time, the more attractive VP switching becomes. However, VPC switching has the disadvantage of not offering support for early packet discard (EPD).
If you want a fully concentrated (400 subs x 4 VCCs per DSLAM) DSLAM and a fully subtended network (7 DSLAMs per edge switch connection), set up VPC switching to support all subscriber-side connections. Otherwise, the subtend address space VCC capacity might be exceeded.
VCC switching for subtended DSLAMs can be supported, up to the maximums defined in the "Cisco 6130 NI-2 DSLAM System VPC and VCC Connection Capacity" section.
Use the subtending hierarchy to three levels deep at most (total of seven DSLAMs in a fully configured subnetwork). This is not a hard limit, but it provides reasonable statistical bandwidth per subscriber. Even if bandwidth or connection space did not present subscriber density limitations, the network provider should address the potential impact on customers by a single failure (at the bearer service network edge).

C.6 Symmetry for API Design

For support of automated provisioning through an EMS/API and subtending, deploy DSLAMs using a standard "template." This template allows each DSLAM to power up in a state in which all the DSLAM requires to provide service is for a Cisco 605 or 675 to be attached to an incoming line, and an ATM connection to be made through the network at the edge switch attached to the network interface (NI) module.

To simplify API design

Identically configure each DSLAM.
Ensure that the configuration supports the DSLAM location anywhere in a subtended hierarchy.
Ensure that the configuration supports the Cisco 6130 NI-2 system outside of a subtended hierarchy.
VCIs = 0 to 31 support is not used in any VP.
1600 VCIs are available in VPI = 1.
400 VCIs are available in each of the other VPs (ignoring UNI Version 3.1 constraints for simplicity, a few less if VCIs 0 to 31 are reserved).
256 VPs are available on the network interface (per the UNI Version 3.1 standard).

Table of Contents

Cisco 6130 NI-2 DSLAM System ATM Addressing Guidelines

Cisco 6130 NI-2 DSLAM System ATM Addressing Guidelines

C.1 ATM UNI Version 3.1 Specification Restrictions

C.2 Cisco 6130 NI-2 DSLAM System VPC and VCC Connection Capacity

C.3 Number of Subscribers and Connections per Subscriber

C.4 Evolution to SVCs

C.5 Subtend Connection Mapping

C.6 Symmetry for API Design