Case Study 3: Design Scenario - C

One of the many advantages of Metro Ethernet is that the customer can use a standard 10/100-Mbps Ethernet interface, or a Gigabit or 10-Gbps interface, to access the service provider’s network. The customer can set up virtual circuits to reach other sites and to reach an ISP. Metro Ethernet supports a copper or fiber-optic interface, but uses fiber-optic cabling inside the provider’s network. It can use a variety of transport protocols, including SONET, ATM, dense-mode wavelength-division multiplexing (DWDM), and Multiprotocol Label Switching (MPLS).

Metro Ethernet service providers allow subscribers to add bandwidth as needed. Compared to adding WAN bandwidth, adding bandwidth to a Metro Ethernet service can happen extremely quickly, sometimes as quickly as a few minutes or hours. Metro Ethernet providers offer a wide range of bandwidth options. In addition to the standard Ethernet speeds, many providers offer a 1-Mbps service and allow customers to add bandwidth in 1-Mbps increments.

Some Metro Ethernet implementations use what is called an Ethernet virtual circuit (EVC). An EVC is similar to a Frame Relay PVC. An EVC is an association of two or more User-Network Interfaces (UNI), where a UNI is a standard Ethernet interface at a customer’s site. Three basic service types use EVCs:

· Ethernet line service (E-line service) provides a point-to-point EVC between two UNIs.

· Ethernet LAN service (E-LAN service) provides multipoint connectivity. It can connect two or more UNIs. It is also known as Virtual Private LAN Services (VPLS) or Transparent LAN Services (TLS).

· Ethernet tree service (E-Tree service) provides point-to-multipoint connectivity.

Metro Ethernet is a blending of WAN and LAN technologies. It supports virtual circuits like a WAN and also provides support for a committed information rate (CIR), committed burst size, peak information rate (PIR), and peak burst size, like a WAN often does. In a similar fashion to a LAN, Metro Ethernet also supports VLANs, 802.1X port authentication, and the Spanning Tree Protocol. Metro Ethernet also supports many QoS features to optimize the forwarding of latency-sensitive traffic. Cisco routers and switches that implement Metro Ethernet, for example, support advanced queuing techniques, traffic shaping, and Random Early Detection (RED).

Metro Ethernet is used to connect intranet and extranet sites. ISPs are also starting to use Metro Ethernet. The ISP typically multiplexes multiple subscribers over a high-speed Ethernet UNI. An ISP’s customer uses an EVC to connect to the ISP’s local point of presence (POP).

The most common method for using Metro Ethernet for dedicated Internet access is to use the E-line service. If the customer wants to use the same UNI to support both Internet access and an intranet or extranet connection, this is also possible with the use of separate EVCs. A customer can also use multiple EVCs to access multiple ISPs for redundancy, thus multihoming the Internet connection.