Several years ago backhaul was considered just an ancillary part of mobile base stations and did not get much attention from the industry. Microwave was not an exception, with large infrastructure vendors (Ericsson and Nokia Siemens for instance) including microwave equipment within their deployment proposals and a number of heavyweights playing their specialization card (such as NEC and Aviat). Microwave equipment was clearly classified into divisions such as PDH, Super PDH and SDH, and its performance was dependent on the frequency resources available and regulatory restrictions.

However, the debate that the radio access network has housed for years has expanded inwards onto the backhaul segment. As happens with any new technological evolution, things are getting more complex with the hype surrounding all-IP backhaul. This hype has been increased by mobile carriers’ awareness of operating cost savings of Ethernet microwave compared to expensive leased lines. Since there is always a race to get to the market as soon as possible, Ethernet-capable microwave equipment has been commercially available for years, but is it ready for carrier deployment? As I explain later, not ready enough to have a future-proof solution that would not present scalability problems as data demand continues to rise.

If we analyze the evolution of the amount of research and investment around backhaul, we will see we are just at the top of a Gauss bell. Fortunately the industry has already agreed microwave and fiber complement each other. Microwave is better suited for improved cost-effectiveness and fast deployment in last mile and some aggregation parts of the network, while increased capacity of fiber is required for the rest of aggretation, metro and core networks. However, the need to deploy all those small base stations for 4G services has led to several new wireless backhaul technologies: unlicensed 60 GHz, semi-licensed 80 GHz and free space optics. Furthermore, the enhancement of layer 1 to take advantage of packet transport has brought new features such as pure packet microwave, adaptive code and rate modulation, Ethernet compression and new topologies such as ring and mesh.

The Microwave Gauss Bell. Source: Maravedis Wireless Backhaul Report

The hype I mentioned above is now climbing the protocol stack to layer 2. Ethernet is a great technology for small deployments, but when you have a cellular network with thousands of network devices that require predictable performance and resiliency, “naked” Ethernet is not enough. Two are the Carrier Ethernet technologies fighting for the gold: Provider Backbone Bridges Traffic Engineered (PBB-TE) and MPLS-TP (Transport Profile). The first one consists in turning Ethernet into a carrier-grade technology, solving scalability problems and replacing the classical packet flooding and address learning mechanisms by an NMS-controlled path configuration. In turn MPLS-TP is a simplification of MPLS to make it affordable for the backhaul but still preserving compatibility with the mother technology. This way MPLS-TP offers a more uniform approach, but perhaps less cost-optimized than Ethernet’s unbeatable cost effectiveness.

Although the debate around backhaul was foreseeable, it will not be around forever. Eventually microwave backhaul will slide back down the other side of the bell to a more mature state, as it was before the Ethernet revolution. Vendors such as Nokia Siemens, Alcatel-Lucent and NEC are somewhat advancing the situation by integrating their microwave offerings into a more general backhaul solution where microwave, fiber and all upper-layer protocols are implemented. Furthermore, in order to accelerate this technological convergence, these vendors are integrating complementary microwave equipment such as 80 GHz links from partners instead of developing their own solutions. When will the bottom of the bell be reached? When network managers start to consider microwave as simply another kind of Ethernet interface for any network equipment. However, since we are still at the top of the Gauss bell, Maravedis’ coming Wireless Backhaul Report takes an approach that guides carriers and equipment vendors towards safely descending the curve.

MARAVEDIS is a leading analyst firm focusing on disruptive technologies including smart networks using WiMAX, IEEE, and 3GPP/LTE. Maravedis works with system and service providers, vendors, regulators, and institutional investors. Learn more at www.maravedis-bwa.com.

Author: Esteban Monturus, Market Analyst - Europe & Backhaul