The Metro Ethernet Forum (MEF) is an industry organization dedicated to furthering the deployment of carrier Ethernet services. Ethernet began life as a LAN then expanded to the MAN and is now truly a WAN with many carriers offering services that span the globe. The MEF specifies the Ethernet user network interface (E-UNI) and the network services (E-Line, E-LAN and E-Tree). The E-UNI is the service demarc and is defined to be a standard Ethernet interface. The access technology and core network technology is not defined by the MEF, allowing the carrier to select the right technology for its network. Service attributes are defined for each service, so carrier offerings can be compared even though different technology may be used to implement the service.
There are many technologies that can be used by carriers to implement Ethernet services. There are a wide variety of technologies used in the first mile connection (access), some of which may be used to implement E-Line services in a network core. Additionally, the core network may use Ethernet or IP/MPLS technology to implement the service. Many carriers use a variety of technologies within their network that balance their requirements for capital and operational expenditures.
Access to Ethernet services can be implemented using copper, fiber and wireless technologies. For copper there are a variety of technologies available: Ethernet over Copper (EoCu) , Ethernet over Hybrid Fiber Coax (EoHFC), Ethernet over TDM (EoTDM). A carrier will select the appropriate technology option for their network. For example, a cable company is likely to use EoHFC, whereas a CLEC may use (EoCu). Fiber options include native Ethernet, Ethernet over SONET (EoS), Ethernet over Wavelength Division Multiplexing (EoWDM) and some proprietary solutions. Often fiber access is used for access to higher speed services. Finally, Ethernet over Wireless is an option where wired infrastructure is scarce or the connection is going to be temporary.
In the core of a carrier network we will also find a variety of technologies in common use. For E-Line services EoS and EoWDM may be used. In shared networks the options are to use Ethernet-based or IP/MPLS-based technologies.
Ethernet standards have been expanded to incorporate capabilities to enable Ethernet to scale to the size required by carriers and to offer survivability and management capabilities. The Ethernet technology evolution is an extension of the bridging and virtual LAN (VLAN) capabilities found in enterprise networks. The first step in evolution of Ethernet was the development of the IEEE 802.1ad specifications, which are known as Provider Bridging (PB). PB adds the ability to support two VLAN identifiers (VID) in the frame, enabling a carrier to separate customer connections through the use of a service provider VID (S-VID). As the popularity of carrier Ethernet services has grown it has been realized that PB does not scale to the level required by large network operators. This led to the development of IEEE 802.1ah, referred to as Provider Backbone Bridging (PBB). In PBB the customer Ethernet frame is encapsulated in an Ethernet frame that is used in the providers backbone network. This approach allows for significant scaling and separates the carrier network from the customer network. The final development in Ethernet for carrier cores came with the development of IEEE 802.1Qay, know and Provider Backbone Bridging with Traffic Engineering (PBB-TE). PBB-TE is also sometimes referred to as Provider Backbone Transport (PBT) after the technology developed by Nortel that led to development of IEEE802.1Qay.
Today many carriers have built extensive IP/MPLS networks to support IP-based services. Rather than build a new network to support Ethernet services in the WAN, a carrier may opt to implement Ethernet services using the IP/MPLS core. There are two specification from the IETF to implement Ethernet virtual private networks (VPNs). The first option is Virtual Private Wire Service (VPWS) for delivering point-to-point E-Line services. The second is Virtual Private LAN Service (VPLS) for multipoint-to-multipoint services.
While it may seem there are many technology options open for carriers to implement Ethernet services, work is still underway to further define options for carriers building larger networks to support Ethernet. Ongoing efforts include the expansion of the operation, administration and management (OAM) capabilities and integration of 802.1ah and 802.1Qay with VPLS. Stay tuned!
|<mp3>http://podcast.hill-vt.com/tHAWT/tHAWT_091109.mp3%7Cdownload</mp3> | tHAWT #171 Carrier Ethernet|