Control Plane for Carrier Grade Ethernet


Originally designed for Local Area Networks, Ethernet is moving toward Metro Area Networks, and is now considered by many carriers as a future transport network technology.
This paper studies the latest standardization effort toward a control plane for carrier-grade Ethernet, in the light of carrier-grade Ethernet data plane and management plane.

I. Introduction

Ethernet as a transport network technology is a very attractive solution for carriers. The Metro Ethernet Forum (MEF) provides good material about why this is the case.
Because most business offices traffic originates from Ethernet LANs anyway, it simply makes sense for Ethernet to extend its reach inside the metropolitan network.
Ethernet is a widely deployed solution, making Ethernet equipments relatively cheaper to buy and to operate, thus allowing CAPEX and OPEX savings, compared to other predominant metropolitan technologies such as ATM or SONET/SDH.
Last, but not least, Ethernet is a packet-switching technology that provides the right flexibility to carry the ever-growing IP-based traffic. The existing SONET/SDH infrastructure for instance, lacks the ability to provide the right granularity or to easily adapt to traffic bursts - although the VCAT/LCAS capabilities implemented in latest MSPPs somehow mitigate this statement.

On the other hand, until recently, Ethernet itself did not meet transport-network requirements. Among the most significant issues were:

  • Scalability of Ethernet Provider bridges (IEEE 802.1ad). Only 4094 VLANs can be supported by a carrier. And every carrier switch must learn about all its customers' MAC addresses, which may potentially be a huge number.
  • Legacy Ethernet control plane and its Spanning-Tree Protocol (STP), Rapid-STP or Multiple-STP, do not provide optimal paths, especially in some topologies such as rings.
  • There is no mechanism to ensure end-to-end QOS.
  • Ethernet lacks the support of traditional protection mechanisms provided by transport-network technologies such as SONET/SDH or OTN.
  • Ethernet OAM features did not match those of other transport-network technologies, for instance regarding fault isolation and detection.

In the past few years however, several standardization bodies have tackled these issues, in order to provide transport-network capabilities to Ethernet, thus allowing for a kind of "connection-oriented" Ethernet data plane.
Significant efforts have also been carried out for the associated management plane, and the control plane specification is now under way.

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