In recent years, IP has emerged as the network-layer and service protocol of choice. IP is broadly deployed in the core of service-provider networks, as well as in business and even residential networks, putting it on both "sides" of the access network. Using IP in the local loop means greater efficiencies, as no conversions to intermediary protocols are needed. From the service perspective, a large number of IP-based applications covering the triple-play gamut are available, including VoIP, Internet access, virtual private networks (VPNs) and other data services, and broadcast video and VoD.

IP itself has been expanded over the years to encompass a broader set of network services. For example, the differentiated services (DiffServ) architecture defines a set of IP-based quality of service (QoS) mechanisms based on the classification and marking of packets for special handling within the network. Similarly, IP-based multicasting protocols allow for the efficient delivery of a given information stream to multiple recipients.

Ethernet has emerged as a viable alternative to the combination of SONET and ATM in the local loop. Until recently, TDM, SONET, and ATM have been the primary transport protocols in the access network. However, SONET/ATM gears have very low unit and port volumes compared to Ethernet/IP, and there is little room left for realizing significant further cost savings. Likewise, due to the complexity of these technologies, a SONET/ATM infrastructure carries heavy operations, provisioning, management, and maintenance costs. In addition, the service provider generally has the additional cost of training its workforce because the talent pool for experienced technicians is limited.

Another drawback to SONET/ATM in the access network is that the available feeder bandwidth has only recently upgraded to OC-3 (155 Mbps). These networks require other costly upgrades to get to OC-12 (622 Mbps), and even newly planned networks at OC-48 (2.4 Gbps) will be limited if VoD and higher-speed data services achieve their expected growth. The available bandwidth divided among all of the triple-play services and video services alone (as shown in Table 1) can quickly consume even this seemingly large amount of bandwidth in a moderate-sized access network.

Ethernet offers a variety of advantages over SONET/ATM. Like IP, Ethernet is a mature, well-understood technology. Due to its wide deployment and broad market support, Ethernet is a low-cost technology, both in terms of equipment costs and operations and management costs. Unlike SONET/ATM, Ethernet has a volume of commercial deployments driving its cost and technology evolution. Likewise, Ethernet and IP are easy to provision, and a large pool of technicians exists.

High bandwidth in scalable increments is another compelling advantage of Ethernet. During its more than 25-year life span, Ethernet's bandwidth has increased from 10 Mbps up to 10 Gbps, with 1 Gbps interfaces readily available. In addition, the Ethernet 802.3ad link aggregation standard allows operators to increase the bandwidth between connected devices by logically combining multiple links into a trunk. The BLC dynamically uses all of the available bandwidth for services delivery—increasing network efficiency and, ultimately, customer satisfaction.

Figure 4 provides a summary of the similarities and advantages of an Ethernet/IP infrastructure compared to a TDM/SONET/ATM infrastructure.

Figure 4 (table)