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From ATM to IP/Ethernet.

Ravi Mali, regional director, MENA Region at Tellabs outlines three approaches for enterprises to migrate from ATM to MPLS. Depending on the existing customer base and service mix, as well as individual business strategies, service providers have three basic options when it comes to an ATM-to-MPLS migration strategy. They can migrate to IP/MPLS using: Approach 1: ATM/FR service migration Service providers can use IP enabled ATM or FR to migrate legacy services to MPLS-based services like IP-VPN or Ethernet, for example. The Layer 3 MPLS-based IP-VPN approach has one major advantage over legacy Layer 2 ATM and FR VPN services: ease of connecting new IP/Ethernet-based customer sites. While MPLS-based IP-VPNs can deliver cost-competitive, scalable and flexible services, using them to migrate ATM/FR services to MPLS is not the best option for all end-customers. For one, many customers cannot and will not share their IP routing information for customer-specific routes with their service provider -- a requirement when implementing MPLS-based IP-VPNs. This is often the case for route-sensitive customers like government agencies or financial institutions. Secondly, the service provider will need to maintain the existing ATM network and the IP/MPLS network in parallel for some time as this transition from ATM to IP/MPLS takes place. Finally, all of a given customer's endpoints connected and communicating using a common service need to be migrated simultaneously in a flash cut, adding both planning complexity and inflexibility. Advantages: - Ease of connecting new IP/Ethernet-based customer sites Disadvantages: - Requires supporting parallel ATM and IP/MPLS networks throughout a long migration - Migration to IP/MPLS network requires an operationally complex customer-by-customer service cutover - Potential revenue loss from customers that do not want to migrate away from ATM/FR - MPLS-based services like IP and Ethernet lack the end-to-end OAM, QoS and security of the ATM networks Approach 2: ATM/FR Data tunneling over MPLS Service providers that do not want to share their customer specific IP routes can be migrated to an IP/MPLS core if the service provider constructs pseudowire-based Layer 2 VPNs. The pseudowire solution enables legacy services, such as ATM and FR, to traverse new high-speed packet networks while maintaining original attributes. However, the downside of the pseudowire migration strategy, especially for larger service providers, is that pseudowires lack dynamic setup or signaling of ATM/FR connections over MPLS, limiting large-scale deployments. As the number of customer sites grow, the number of pseudowires needed to provision is going to grow by orders of magnitude. In addition, like the IP-VPN approach, all of a given customer's endpoints connected and communicating using a common service need to be migrated simultaneously in a flash cut, adding planning complexity. The pseudowire solution works well for operators with fewer ATM/FR connections on an MPLS core. But, to simplify provisioning with dynamic connection setup, or to link multiple regional ATM networks over an MPLS core, a more scalable approach is required. Advantages: - No sharing of IP routing information needed Disadvantages: - Requires intensive manual provisioning of a large number of point-to-point ATM or FR pseudowires to connect customer sites - Requires supporting parallel ATM and IP/MPLS networks throughout a potentially long migration period - Migration to IP/MPLS network requires an operationally complex customer-by-customer service cutover - Limited to data plane tunneling only; no support of the ATM control plane - Lacks the end-to-end OAM, QoS and the security of the ATM networks Approach 3: Converged IP/MPLS network supporting native ATM/FR control and data planes A third option is to converge ATM, IP and Ethernet onto a single MPLS network supporting native ATM switching and PNNI. By preserving the dynamic provisioning capabilities of ATM, this migration scenario enables service providers to connect multiple ATM networks over IP/MPLS while enabling new IP and Ethernet services over one network. A converged network also minimises the impact on end user customers by allowing them to continue using their existing ATM service and CPE with no service disruption or to CPE. Advantages: - Does not require supporting parallel ATM - IP/MPLS networks throughout a migration - Enables graceful and independent circuit-by-circuit migration versus simultaneously cutting all endpoints of a given customer to a parallel network - Continues supporting existing native ATM/FR transparently; migration to IP/Ethernet when customer dictates - Continue to support end-to-end ATM OAM capability and predictability of ATM/FR QoS Additional PNNI-to-MPLS Interworking Benefits: - Decouples the ATM and MPLS control planes, allowing them to operate separately enabling continued support of legacy services with no disruptions/changes for end-users. - Preserves the routing and signaling information in the ATM control plane, end-to-end across the MPLS core, which maintains ATM security because there is no need to exchange IP addressing or network topology with vendors. - Employs pseudowire technology for data-plane encapsulation, enabling service providers to retain Layer 2 operations and offer VPN-type security without sharing routing information. - Uses MPLS fast reroute in the MPLS core to restore the tunnel Label Switched Path (LSP) and ensure carrier-class reliability. - Limits the need to pre-establish and manage large numbers of E-LSPs by aggregating ATM SVCs or SPVCs connected to the same remote network into the same E-LSP.

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Publication:ITP.net
Date:Dec 10, 2012
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