The vast majority of broadband users today access the internet by sharing the "last mile" with existing telephone or cable television networks, with both services using the same physical medium. This results in upload speeds between 128 Kbps and 1 Mbps and download speeds of up to a theoretical 20 Mbps. The problem is that users are demanding higher speeds (even up to 100 Mbps), and achieving these bandwidth levels will require a major technological shift. There are numerous technical alternatives that could provide universal high-speed access. However, the biggest obstacle is cost. Additionally, any new network access method will need to support existing services.
Current and Future Applications
Private Homes.
Home network connectivity is the dominant application due to the large number of users it involves. The wide range of applications it covers includes email, internet access, telephone, cable television, etc. But new applications will demand much greater bandwidth. One frequently proposed application is video on demand. This involves, for example, downloading an HDTV video to a set-top box or decoder for later viewing. This type of service would require at least tens of megabits per second; however, hundreds of megabits per second would be much more efficient. It is also possible to envision IP television as the dominant medium for television signal distribution.
However, it is not just about entertainment. Increasingly, users are working from home.
Large Enterprises and SMEs
: Traditionally, businesses have been characterized by a large number of users, a relatively small volume of transactions, and high demands for network access speed. This characteristic has already necessitated very high-speed access. Consequently, more and more real-time graphical applications, video telephony, and videoconferencing, among others, are being developed.
Universities, schools, and hospitals:
These types of users have very similar needs to large companies, with the exception that they are often pioneers in adopting data visualization applications. In medicine, remote diagnosis and consultations require the transmission of diagnostic images (e.g., X-rays) at extremely high resolution and high-definition video to clearly observe the patient during a remote consultation. The use of content visualization applications in classrooms is also expanding rapidly.
Mobile infrastructure:
Cellular mobile telephony and data networks must be interconnected. As mobile networks continue to expand, especially to provide mobile internet access, base stations will need a connection to the backbones of very high-speed fixed networks.
Existing Access Solutions: Telephony and Cable.
Broadband Access over Existing Telephone Infrastructure (xDSL).
The Digital Subscriber Line (DSL) concept refers to a generic service encompassing a range of technologies that allow existing telephone lines to carry high-bandwidth data transmissions.
There are many DSL protocols. The "x" indicates that it is a member of the generic protocol family. The most widely used is ADSL (Asymmetric Digital Subscriber Line). In several countries, this is the predominant technology for broadband internet access. It was initially developed for residential broadband access. The maximum bandwidth specified in the standard is 6 Mbps download and 640 Kbps upload, although equipment manufacturers tend to offer higher speeds. In reality, the available bandwidth is usually reduced from its maximum potential due to distances or the quality of the installed lines.
Cable Television Networks:
The standard network for providing cable television is called "Hybrid Fiber-Copper" (HFC). Dedicated fiber optic cable connects the nodes to area cabinets installed in the street using a pair of single-mode optical fibers. In the area cabinet, the signal is recovered from the fiber, amplified, and injected into a coaxial cable. This coaxial cable, used to connect users to the HFC network, is a very high-quality medium capable of supporting a very large bandwidth. The main problem to be solved is that these cables are "buses." This means that all users connected to the bus operate on a shared medium with capped speeds. Although these capped speeds are often referred to as 30 Mbps, what it actually means is that the maximum capacity of the shared medium is this speed, and all users connected to the "bus" have access to this speed. To ensure availability, the upload speed is usually limited to very low speeds of approximately 128 Kbps.
The key problem today is that users demand higher speeds, rendering the shared 30 Mbps medium no longer viable. However, deploying new cable infrastructure (of any type) to the user's premises is very expensive. In the long term (20 years), there appears to be no alternative to a complete replacement of existing copper networks with fiber optics; however, as we will see, there are intermediate alternatives.
Physical and legal factors affect the choice of broadband access solutions. For example, in many countries, the traditional family living in a single-family home is the exception rather than the rule; many people live in large apartment blocks where the facilities and service costs can potentially be shared. However, these large apartment blocks are often located on streets where installing access cable is quite complicated. Additionally, in a number of countries, there are legal issues regarding the placement of operator equipment on customer premises. Another factor depending on the country of application is the legal definition of "Telephone Operator" and "Cable Operator" which determines the options available for deploying the network.
What technologies can support broadband in the future?
It's important to remember that any proposed solution must be usable indefinitely and scalable and upgradable as needed. Furthermore, any new solution must be implemented alongside existing services.
1. An ideal solution
The ideal solution is to connect each subscriber directly to the public node via a dedicated two-fiber optic (P2P) connection. This solution would satisfy any bandwidth requirements the subscriber might have and is potentially a long-term solution, although it involves a high initial implementation cost.
2. RF Solutions.
Radio frequency solutions offer a cost-effective alternative for small groups of subscribers in rural or semi-rural areas. The problem arises in densely populated areas where very tall buildings would significantly obstruct the signal, requiring the installation of a large number of base stations to serve the high number of users connecting simultaneously.
3. FTTC - Very high bit rate DSL (VDSL)
Current ADSL connections work reasonably well, but users are beginning to experience the need for significantly higher speeds. As already mentioned, the maximum ADSL speed is highly dependent on the link length (subscriber loop) due to the attenuation the cable introduces to the transmitted signal. So… why not reduce this distance? The idea is to have a distribution cabinet somewhere between the subscriber and the public node, linking them with fiber optic cable and performing optoelectric transduction in the distribution cabinet, leaving the connection to the subscriber on the original copper pair. This type of architecture is usually called FTTx, with the "x" representing almost any letter of the alphabet depending on the location of the distribution cabinet: street, building, etc.
4. Fiber to the Home (FTTH)
If it is necessary to provide service to a sizable apartment building (for example, 100 units), the fiber optic infrastructure can be extended to the building itself, and the VDSL node can be located in the building's technical rooms.
This approach avoids rewiring the interior of the building, which can be quite costly. Of course, prior permission from the building owners must be obtained. This solution is very similar to FTTC, with the advantage that the copper links are extremely short, resulting in a very high-quality service. The cost of this type of infrastructure may seem excessive for single-family homes, but it can be very attractive for large apartment buildings.
5. PON.
A solution that offers more than adequate capacity and can be implemented at a lower cost than the ideal solution is the Passive Optical Network (PON). The theory behind PON is to build an optical network infrastructure that uses splitters to connect a number of users to a single fiber at the public node. Electronic techniques are used to ensure that users share the common optical medium. See Figures 1 and 2.
PON has some even more attractive advantages, such as the elimination of the need for street cabinets, which simplifies network configuration and operation. The absence of active field equipment also simplifies maintenance. Furthermore, depending on the PON system, users can be located up to 20 kilometers from the optical line termination (OLT). Currently, a large city can have up to 500 public nodes, but with a PON system, far fewer are needed (a realistic number could be between 12 and 20), which represents significant savings in deployment, maintenance, and operation.
However, it requires a high initial investment in installing fiber optic cabling and terminating it at each subscriber's home. Installation costs (trenching, protection, conduit) are much higher than the cost of the cable itself.
Conclusion:
Regardless of the architecture adopted, it will involve the use of fiber optics in the access network. The challenge lies in designing the network to meet current user needs while also being open to future evolution, all at an acceptable cost. In most cases, FTTx may be the most attractive alternative, as it meets current needs while leaving the door open for future evolution to a PON architecture. Otherwise, deploying a PON could well be the most cost-effective long-term solution.
Author:
Juan Pablo Muñoz, Technical Manager R&M Spain/Portugal
