Migrating to an Ethernet-centric Infrastructure

Thanks for touching base again, Michael.

The topic of ROADM and ASON is an interesting one. The ASON architecture includes both an internal and external network node interface definition (I-NNI and E-NNI, respectively). The E-NNI ASON interface is compatible with optical networks that contain ROADMs, as the E-NNI is able to make use of an abstract view of a network domain. In a sense, the E-NNI never needs to know there is a ROADM inside the domain; it just needs to learn what connectivity the domain can establish.

In the case of an I-NNI, the status is quite different for ASON standards concerning a network domain including network nodes that are ROADMs. Although the ASON architecture encompasses photonic network elements and all-optical network reconfiguration, no standards yet exist for a photonic layer I-NNI, and I am not aware of any standards under active development. This is also the case in the I-ETF, in the GMPLS drafts.

There are significant technical difficulties in obtaining and interpreting necessary analog parameters for a photonic layer path computation. Additionally, vendors of optical networking equipment use different technologies, with significantly different propagation performance. Therefore, the practical application of multi-vendor photonic layer interworking is not near, at least not for the general networking case. There will always be specific situations where distances are short and nonlinear effects small, where photonic interworking will be achievable without a great deal of difficulty.

In summary, the emphasis of standards work in the ITU is on developing an E-NNI, and this seems to be a good solution for the electronic layer as well as the photonic layer, where ROADMs are included.

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.

This is not an apples-to-apples comparison, as WiMax—from a standards perspective—has both fixed and mobility versions. In addition to WiMax, “fixed wireless” can include other technologies such as microwave. It is usually point-to-point but can include point-to-multipoint varieties. For this discussion, we will focus on the differences between the fixed versus mobility versions of WiMax. In general, the differences revolve around range, bandwidth or channel size and market timing.

The WiMax 2004 standard (802.16-2004) is commercially available and deployable. This WiMax can be used in either point-to-point up to 50 kilometers or point-to-multipoint cell configurations from 7-10 km. The bandwidth is up to 75 Mbps per channel dependent on spectrum used and distance.

The WiMax 802.16e standard and is designed for mobility purposes. It is new as of the end of 2005, and therefore products are not yet widely available. In this standard, the bandwidth is up to 15 Mbps per channel (again dependent on the same factors) and the range is from 2-5 km.

In terms of the pros and cons of each, this is all relative to your specific application needs and requirements for bandwidth, range and mobility as described above.