Ethernet has a long history as a durable, flexible LAN technology. Its history doesn’t look to come to an end any time soon with the advent of connection-oriented Ethernet (COE).

Originally developed to connect on-campus computers and peripheral devices within a relatively small area, Ethernet has been continuously reinvented through a series of improved standards. Today, it serves as a full transport solution that provides the benefits of both Ethernet’s inherent connection-less technology and of traditional circuit-based solutions such as SONET.

Also known as IEEE 802.3, Ethernet owes its against-the-odds resilience to several attributes. It is an inexpensive, flexible and simple way to network latency-insensitive traffic within a single, well-bounded administrative domain. It’s also an open, as opposed to a proprietary, standard. These attributes have amounted to an open, collaborative and freely competitive soil in which the original Ethernet seed has flourished through a multi-stage evolution.

As Bob Metcalfe, Ethernet’s original creator, insightfully commented, “When something rises up to defeat Ethernet, it’s very likely that they’re going to call it Ethernet.”

Today, Ethernet is everywhere. Most of the data traffic on the Internet originates or terminates over an Ethernet connection, and the technology’s bandwidth potential has increased from 10 Mbps to 10 Gbps, with technologies being introduced today, and in the near future, to handle 40 and 100 Gbps Ethernet connections. Ethernet’s ability to reinvent itself and keep up with the times has made it the hottest thing going in metro networking.

With broadband data loads exploding faster than anticipated, the metro optical network must be efficiently utilized in order to meet the demand of new and emerging Ethernet and IP applications. The current version of Ethernet is challenged to support the stringent performance and reliability required by applications such as voice and video. Thus, this long-lived technology is evolving into connection-oriented Ethernet.

COE is intended to be the foundation for service providers to deliver profitable high-bandwidth applications to mobile, enterprise and residential users.


Ethernet is a packet networking technology, in contrast to the circuit technologies, such as SONET, on which the traditional telecom carriers have based their networks. Packet networking is connection-less, whereas circuit-based networking is connection-oriented. Connection-oriented technologies enable carriers to deliver much better and more consistent standards of customer service, as well as to differentiate their services by priority, capacity and other characteristics.

However, connection-based technologies are costly in comparison to their simple and price-friendly packet-based cousin. Service providers have traditionally delivered enormously profitable TDM services by creating a single aggregation and transport infrastructure based on connection-oriented SONET/SDH technology. But the price, flexibility and simplicity benefits of Ethernet have been too compelling to ignore.

Manufacturers and service providers therefore decided it was a worthy goal to capture the benefits – and eliminate the disadvantages – of both circuit and packet types of network.

COE - High-Performance - Carrier Ethernet

Pursuit of this goal has resulted in the deployment of a wide variety of Ethernet technologies, as well as “beefed-up” enterprise-class Ethernet hardware and software platforms. Among these developments is carrier Ethernet, a group of extensions to the IEEE 802.3 standard. Carrier Ethernet was designed to enable telecommunications companies to leverage the benefits of Ethernet and to bring Ethernet service to their customers.

The Metro Ethernet Forum defined three Carrier Ethernet service types – E-Line, E-LAN and E-Tree – but it did not specify how these services were to be carried across the network. This meant that carrier Ethernet services could be encapsulated into circuit-based, connection-oriented technologies like SONET. These services were developed to create a market for standardized service types, in response to demand for bandwidth and for guaranteed service levels (in contrast to “best-effort” services). In essence, carrier Ethernet has focused on extending the classic connectionless Ethernet “LAN” protocol into a service provider environment.

Carrier Ethernet is often transported using other technologies, such as SONET or IP/MPLS. But it is difficult for Ethernet services to achieve the 99.999 percent availability and deterministic performance of a traditional carrier network without imposing penalties in terms of cost and complexity.

It is also important to point out that Carrier Ethernet, in either its connection-oriented or connection-less variants, does not replace the IP service layer, but optimizes it by fully utilizing connections into that domain. COE is able to coexist with existing legacy/TDM applications, along with emerging optical transport solutions such as OTN.

In general, carrier Ethernet brings attractive benefits to the metro network. Therefore, while the benefits of carrier Ethernet are valuable to metro service providers, these limitations and the proliferation of varied technologies and applications have created impetus to go further and develop a single, general-purpose Ethernet infrastructure.

This new infrastructure must deliver the best of both circuit-based, connection-oriented and packet-based connectionless worlds. It must combine the flexibility and cost-efficiency of Ethernet with the determinism, quality control and reliability of the connection-oriented protocols used in traditional carrier networks.

The MEF defines carrier Ethernet with five attributes: standardized services, reliability/protection, QoS, service management/OAM and scalability. Connection-oriented Ethernet is a high-performance implementation of carrier Ethernet optimized for aggregation infrastructure and for high-performance, MEF-defined services: EVPL, EPL and E-Tree. COE uses the five carrier Ethernet attributes and adds a sixth attribute: addressing security.

Through these new high-performance services, COE actually achieves the determinism of TDM while retaining the flexibility and low cost of Ethernet. Deterministic COE connections deliver guaranteed bandwidth – in addition to the lowest possible latency and jitter performance – 50 ms protection switching and precision fault management.

While COE was designed for performance, it also allows for statistical multiplexing and oversubscription, something not achievable with TDM networks, or even Ethernet over SONET implementations.

Single, General-Purpose COE Infrastructure

Three essential functions make Ethernet into a connection-oriented network environment. These are:

  • Predetermined (provisioned) Ethernet Virtual Connections (EVCs)
  • Resource reservation and admission control
  • Per-connection traffic engineering and traffic management

These three functions together ensure that consistent levels of connection performance and failure protection are maintained as and when requested, by controlling the route, resources and priority associated with individual flows of network traffic. In sum, they enable delivery of “carrier-class” services – on par with SONET/SDH – on an Ethernet foundation. It’s carrier Ethernet with full traffic engineering.

In practical terms, this means that some services, such as low-cost residential broadband offerings, can be oversubscribed, while premium-priced services that support delay-sensitive traffic such as 4G mobile backhaul or video services, are assigned guaranteed, predictable levels of transmission speed and availability.

The best implementation path for COE infrastructure is packet optical networking platforms (Packet ONPs). These platforms enable Ethernet and TDM services to be delivered on the same physical network infrastructure. They incorporate the advances of optical and WDM networking into plug-in modules instead of having separate network elements, and they facilitate a cost-effective migration path to pure packet-based optical networks.

COE deployment is being driven by several important applications. Among these are 4G wireline and residential broadband (DSLAM) backhaul, triple-play network infrastructure, enterprise Ethernet-based metro and wide area networks, and private line equivalent services.

COE provides high-quality, connection-based Ethernet services with the highest availability; native Layer 2 aggregation and statistical multiplexing for network optimization; and advanced, flow-based traffic management.

COE is a critical piece of the Packet ONP solution; it allows network providers to revolutionize their services and applications through an evolutionary approach that doesn’t adversely affect any existing applications. Additionally, Packet ONP solutions leverage DWDM and OTN optical networking to allow for a cost-effective and standard means of transporting large quantities of bandwidth on a single fiber pair.

The aggregation infrastructure to support the many new and emerging applications will require a general-purpose infrastructure where COE, conceptually speaking, mirrors traditional SONET/SDH infrastructure, yet provides all of the benefits of a packet-switched network. As demand for Ethernet continues to grow, and as service providers are faced with demand for higher-quality Ethernet networking for all applications, this universal aggregation and transport foundation will connect all types of end users to one another and to every type of service.