An MPLS based Metro Ethernet network uses MPLS in the Service Provider Network. The subscriber will get an Ethernet interface on Copper (ex:-100BASE-TX) or fiber (ex:-100BASE-FX). The customer's Ethernet packet is transported over MPLS and the service provider network uses Ethernet again as the underlying technology to transport MPLS. So, it is Ethernet over MPLS over Ethernet. Here, Label Distribution Protocol (LDP) signaling is used as site to site signaling for the inner label (VC label) and Resource reSerVation Protocol-Traffic Engineering (RSVP-TE) or LDP may be used as Network signaling for the outer label. One of the restoration mechanisms used in an MPLS based Metro Ethernet Networks is Fast Re Route-FRR (MPLS local protection) The main advantages of an MPLS-based Metro Ethernet against a pure Ethernet are:
Scalability: pure Ethernet MAN are limited to a maximum of 4,096 VLANs for the whole network, when using MPLS, Ethernet VLANs have local meaning only (like Frame Relay PVC). Same scalability considerations applies to the MAC addresses where in a pure Ethernet MAN all MAC addresses are being shared among the network while only having local meaning in the MPLS context.
Resiliency: pure Ethernet network resiliency relies on STP, RSTP or MSTP (30 to 1 sec convergence) while MPLS-based MANs use MPLS-based mechanism (i.e. MPLS Fast Reroute) to achieve SDH-like (50 msecs) convergence times.
Multiprotocol convergence: with the maturity on pseudowires standards (ATM Virtual Leased Line VLL, FR VLL, etc.) an MPLS-based Metro Ethernet can backhaul not only IP/Ethernet traffic but virtually any type of traffic coming from customer networks or other access networks (i.e. ATM aggregation for UMTS or TDM aggregation for GSM).
End to End OAM: MPLS-based MAN offers a wider set of troubleshooting and OAM MPLS-based tools which enrich Service Providers ability to effectively troubleshoot and diagnose network problems. These include for example, MAC ping, MAC traceroute, LSP ping etc.
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