Migrating to an Ethernet-centric Infrastructure

Yes, there are a number of ways in which you can provide SONET/SDH transport reliability in an Ethernet fibre access network. One is the ITU G.709 OTN standard that provides for a mapping of asynchronous services such as Ethernet and fibre channel into an OTU payload. The G.709 standard allows for overhead bytes that provide for SONET/SDH-like performance monitoring and protection switching on a per link basis.

Second is by using extensions to the 802.3 standard itself at Layer 1 and adding SONET/SDH-like performance monitoring and switching capability directly to Ethernet without having to map into another protocol. This is known as ‘Carrier-grade Optical Ethernet’. These extensions pioneered by Ciena utilize the inter-packet gap (IPG) between Ethernet packets to insert OAM&P overhead for performance monitoring, embedded signaling, and secure embedded communications without ever touching, processing, or modifying the data packets. This embedded overhead has a similar function and is similar in character to the transport overhead of SONET/SDH framing, which is likewise independent and separate from the data payload. No link bandwidth is used for this additional functionality. By utilizing these extensions, the network elements can also transparently pass every packet received on an ingress port—including 8B10B configuration codes—without MAC-layer termination or modification and with fixed, deterministic latency and jitter.

Third is via link aggregation that is fully Ethernet-standards compliant (IEEE 802.3ad). This method of logically bonding multiple physical links is the type of protection most supported by Ethernet clients that may attach to an Ethernet fibre access network. A LAG, link aggregation group, is treated just like any other physical port in the system, and traffic is “load balanced” among the group members (actual physical ports). Link aggregation can be used in 1-to-1 and 1-to-N configurations. The simplest form of link aggregation, which has two physical links in the LAG, can be used to protect the electronics on the equipment at both ends of the link, as well as the facilities (fiber) used to connect the equipment. If any one of the two links goes down, LACP (Link Aggregation Control Protocol), running on equipment at both ends, will negotiate the affected link to be temporarily out of the LAG, thus traffic avoids the broken link. In such a condition, alarms are sent to the NOC, and when the problem is resolved, the physical link can be negotiated back into the LAG. Compared to many other types of protection, link aggregation has the added benefit of providing twice the bandwidth of other protection methods under normal operating conditions. Failover times are similar to SONET APS requirements.