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    Understanding Business Ethernet Services

    Multi Site Connectivity Using Multipoint EVC
    Figure 2: Multi-site Connectivity using Multipoint EVC

    Figure 2 illustrates multi-site connectivity using a multipoint EVC. With this type of connectivity, the Ethernet Service Provider performs all the switching enabling every site to communicate with every other site. This WAN connectivity is very similar to LAN connectivity inside a building.

    If you anticipate a large number of sites to be interconnected, multipoint connectivity enables additional sites to be more easily added to the WAN. Multipoint connectivity also allows for simple traffic prioritization and can effectively support IP telephony (VoIP) and data traffic over the same WAN. Finally, a multipoint EVC is better suited for applications requiring significant amounts of any-to-any site communication. However, if sites are geographically dispersed over large distances, a multipoint EVC may not be available nor be able to provide acceptable service performance for demanding applications to those long distance sites.
    Multi Site Connectivity Using Point To Point EVC
    Figure 3: Multi-site Connectivity using Point-to-Point EVC

    Figure 3 illustrates multi-site connectivity using multiple point-to-point EVCs in a hub and spoke arrangement. With this type of connectivity, the hub site router or Ethernet switch perform all the switching between the spoke sites. Therefore, for any spoke site to communicate with another spoke site, the traffic must first go over the EVC to the hub site and then get switched to the EVC of the other spoke site. This type of connectivity is very similar to a typical Frame Relay or Private Line WAN deployment.

    Multiple point-to-point EVCs for multi-site connectivity is better suited for applications where most of the WAN traffic is between spoke sites and a hub site. The bandwidth and performance requirements between sites are simpler to engineer with this type of WAN architecture.

    Ethernet Service Bandwidth

    Ethernet service bandwidth defines the amount of traffic you can send to or receive from the network. The service bandwidth can be specified to be the bandwidth of an entire Ethernet port speed or the port speed could be subdivided into the amount of bandwidth needed for a given application. Service bandwidth could also be specified for each service or Class of Service (CoS).

    Ethernet service bandwidth is specified using a Committed Information Rate (CIR). The CIR, specified, in Mbps, articulates the amount of service bandwidth that will be subject to the service performance objectives in the product specifications.

    Service providers may offer an Excess Information Rate (EIR) or a CIR and EIR for a given service. An EIR-based service (service with no CIR, i.e., CIR=0) is a best effort service with no assurance that any traffic will get through the network. A service with a CIR and EIR will assure that traffic conformant to the CIR will meet the specifications. Traffic bandwidth that exceeds the CIR is considered excess traffic and is provided no bandwidth assurances. EIR traffic may get through the network if there is no congestion.

    At a minimum you want your Ethernet service to have a CIR to assure service bandwidth

    Having an EIR improves what is called “Goodput” which enables you to get more of your traffic through the network at times when the network is not congested. Compare an EIR to residential broadband service bandwidth where sometimes you receive better application performance, e.g., watching a streaming video uninterrupted, and when the network is congested and your video stutters as video packets are lost due to congestion and must be retransmitted.

    Service bandwidth increments are often related to the port speed. While any bandwidth increment can be offered at any port speed, service providers typically provide bandwidth in the increments listed in Figure 4.
    Service Bandwidth Increments By Port Speed
    Figure 4: Service Bandwidth increments by Port Speed

    When multiple EVCs are delivered on a single Ethernet UNI, a CIR (and/or EIR) can be defined for each service. The MEF has defined a "bandwidth profile" which includes the CIR and EIR values. Figure 5 lists the different types of bandwidth profiles and use cases. As you can see, there are many options which create complexities.
    Ethernet Service Performance Metric

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