PDF of this tutorialEPONs offer many cost and performance advantages that enable service providers to deliver revenue-generating services over a highly economical platform. However, a key technical challenge for EPON vendors lies in enhancing Ethernet’s capabilities to ensure that real-time voice and IP video services can be delivered over a single platform with the same QoS and ease of management as ATM or SONET.
EPON vendors are attacking this problem from several angles. The first is to implement methods, such as differentiated services (DiffServ) and 802.1p, which prioritize traffic for different levels of service. One such technique, TOS Field, provides eight layers of prioritization to make sure that the packets go through in order of importance. Another technique, called bandwidth reserve, provides an open highway with guaranteed latency for POTS traffic so that it does not have to contend with data.
To illustrate some of the different approaches to emulating ATM/SONET service capabilities in an EPON, Table 2 highlights four key objectives that ATM and SONET have been most effective at providing: (1) the quality and reliability required for real-time services; (2) statistical multiplexing to manage network resources effectively; (3) multiservice delivery to allocate bandwidth fairly among users; (4) tools to provision, manage, and operate networks and services; and (5) full system redundancy and restoration.
In every case, EPONs have been designed to deliver comparable services and objectives using Ethernet and IP technology. Sometimes this has required the development of innovative techniques, which are not adequately reflected in literal line-by-line adherence to ATM or SONET standards and features.
| Objective | ATM/SONET Solution | Ethernet PON Solution |
| Real-time services | ATM service architecture and connection-oriented design ensure the reliability and quality needed for real-time service. | A routing/switching engine that offers native IP/Ethernet classification with advanced admission control, bandwidth guarantees, traffic shaping, and network resource management that extends significantly beyond the Ethernet solutions found in traditional enterprise LANs |
| Statistical multiplexing | Traffic shaping and network resource management allocates bandwidth fairly between users of non–real-time services Dynamic bandwidth allocation implementation needed. | Traffic-management functionality across the internal architecture and the external interface with the MAN EMS provides coherent policy based traffic management across OLTs and ONUs. IP traffic flow is inherently bandwidth conserving (statistical multiplexing). |
| Multiservice delivery | These characteristics work together to ensure that fairness is maintained among different services coexisting on a common network. | Service priorities and SLAs assure that network resources are always available for a customer-specific service. Gives service provider control of “walled-garden” services, such as CATV and interactive IP video. |
| Management capabilities | A systematic provisioning framework and advanced management functionality enhance the operational tools available to manage the network. | Integrating EMS with service providers’ OSSs emulates the benefits of connection-oriented networks and facilitates end-to-end provisioning, deployment, and management of IP services. |
| Protection | Bidirectional line-switched ring (BLSR) and unidirectional path-switched ring (UPSR) provide full system redundancy and restoration. | Counter-rotating ring architecture provides protection switching in sub 50 ms intervals. |
Table 2. Comparison of ATM, SONET, and EPON Service Objectives and Solutions
These techniques allow EPONs to deliver the same reliability, security, and QoS as more expensive SONET and ATM solutions.
- Guaranteed QoS using TOS Field and DiffServ
- Full system redundancy providing high availability and reliability
- Diverse ring architecture with full redundancy and path protection
- Multilayered security, such as VLAN closed user groups and support for VPN, IPSec, and tunneling
