Beyond network backbones, connectivity is needed to connect smaller towns and villages to the backbone and provide links in and around metropolitan areas. These links are sometimes called the “middle mile.” Such links can be provided by satellite, microwave, or fiber optic cable, with the latter becoming increasingly common due to its high capacity. Metropolitan area networks are often established for high-traffic locations such as major cities by routing traffic along high-capacity fiber optic rings. This part of the broadband supply chain also includes links used to transport traffic from distant points, such as a wireless base station, to an aggregation point in the network, such as a mobile telephone switching office or other network node (United States, FCC n.d.). This particular function in wireless networks is often referred to as “backhaul” (that is, hauling traffic back to the network).

5.6.1 Regional and Metropolitan Links

In many cases, as governments develop policies to encourage backbone development or the rollout of local access networks, the metropolitan portion of the broadband supply chain can be forgotten. But building out the two ends of the network—backbone and last mile—will be ineffective unless capacity exists in the middle to tie all the pieces together. Hence policies to address middle-mile and backhaul problems, such as promotion of facilities-based competition or open-access requirements, are just as important as policies in other parts of the network.* See, for example, numerous comments filed generally in a U.S. Federal Communications Commission proceeding that was established to develop the National Broadband Plan (United States, FCC 2009).

Metropolitan ring networks are a special case worth noting. In most countries, the majority of broadband traffic is generated in urban areas. Initial links are typically point-to-point, but over time this architecture can become increasingly complex and inefficient. The topology of a ring network is highly practical for metropolitan areas where a significant amount of traffic is destined for other users in the area. A ring network simplifies network architecture by connecting premises in central business areas together over fiber optic cable. Traffic flows along the ring, with each node examining every data packet (Figure 5.7). The standard for metropolitan ring networks is Institute of Electrical and Electronics Engineers (IEEE) 802.17.* IEEE Standards, “IEEE 802.17™: Resilient Packet Rings,” http://standards.ieee.org/about/get/802/802.17.html.

One of the dangers with ring networks is that if a node goes down or the fiber optic cable breaks, the whole ring could fail. This can be overcome by transmitting the information in two directions (clockwise and counterclockwise) or by building in other types of redundancy. Rings have tended to use Synchronous Optical Network/Synchronous Digital Hierarchy (SONET/SDH) technology for transport. Wavelength Division Multiplexing (WDM) is emerging as a transport standard because of its efficiency and integration with gateways to national and international backbones.

5.6.2 Implementation Issues for Metropolitan Connectivity

Many of the implementation issues associated with the middle mile are the same as those involved with backbone development, namely cost and competition. However, the choices of where such links should be built (or, perhaps more accurately, upgraded, since lower-capacity links may exist) and how the network should be designed can be more difficult, both politically and technically. Government interventions are usually part of a plan to connect rural areas and are combined with other measures to roll out networks to those areas as well as part of metropolitan government initiatives. Even if broadband networks reach rural areas, most countries have a significant gap in broadband speeds between rural and urban areas. For instance, in Europe most of the lowest broadband download speeds (256–512 kbit/s) are found in rural areas.

In the context of limited funds for network build-out, choices will have to be made that balance the government’s desire to spread the benefits of broadband widely with the reality that not all areas can be served right away. In Australia in 2009, for example, the government announced a $A 250 million “blackspots” program designed to bring high-capacity links to regional centers without adequate connectivity, holding a consultation to determine which regions should receive new links (Australia, Department of Broadband, Communications, and the Digital Economy n.d.).

Network design issues can also be difficult. In most developed countries and in countries with a liberalized telecommunications framework, competing alternative carriers use the dominant carrier’s network through leases or open-access requirements and build their own networks around the dominant carrier’s physical facilities. But as new broadband links are installed at the metropolitan level, an important issue to resolve is determining how many points of interconnection will be offered to the new broadband facilities and where the points will be located. In Australia there has been a strong debate over how many points of interconnection should be offered, with the government and the National Broadband Network Company originally suggesting 14, while the competition authority states that 120 interconnection points are needed.