Unbundled & Shared DSL Access Technologies for the Local Loop
1. Alternative ISPs in Areas Without Coverage
In areas where alternative ISP networks lack access to Telefónica’s ADSL infrastructure, two main options exist. The speed of these options reflects the market conditions at the time of Telefónica’s recruitment.
ADSL Resold (Almost Obsolete)
This service, based on GigADSL, was used by alternative operators in the early days of ADSL. The alternative ISP rents all connection layers from Telefónica, including ATM, IP address, and transport network to a Point of Access Interface (PAI). A whois lookup on the client’s IP address would show Telefónica as the subscriber. This service typically uses the RIMA IP network and offers only a slight price reduction compared to Telefónica’s ADSL, along with basic value-added services like email and web space.
Indirect ADSL
This is the most common method for alternative ISPs to reach areas without direct coverage due to its lower cost. Based on the GigaIP service, the alternative ISP rents the ATM transport layer and transport network to the PAI from Telefónica, while providing its own IP layer. The ADSL connection is identified as belonging to the alternative ISP. User authentication is handled by the alternative ISP’s RADIUS server.
2. Areas with Direct Coverage from Alternative ISPs
In these areas, the alternative ISP has its own infrastructure to provide ADSL services. The speed is limited only by the operator’s offerings and the technology itself, currently reaching up to 20 Mbps and including various TV services over ADSL.
2.1. Direct ADSL (Shared Loop) – Shared OBA
This is the most common service used by ISPs like Orange, Jazztel, and Ya.com in areas with their own coverage. More attractive offerings are becoming available with fully unbundled loop access, providing greater benefits to operators. The alternative ISP’s network reaches the customer’s telephone line and connects to the ISP’s DSLAM. From there, the connection is shared with Telefónica, which provides the voice circuit. 
Technically, this requires disconnecting the subscriber loop from Telefónica’s switching equipment at the Urban Delivery (RPCA) and connecting it to the alternative ISP’s distribution frame. This process, called OBA (Opening the Loop), involves connecting the line to a splitter, which separates voice and data signals. The voice signal is routed back to Telefónica’s equipment, while the data signal goes to the operator’s distribution point (RDO) and then to the DSLAM. This results in a brief interruption of voice and data services. The alternative ISP manages all connection layers, including ATM, IP, and transport network, as well as user authentication. Voice calls are typically pre-allocated at the circuit level to the alternative ISP, but the physical line remains with Telefónica. Customers can still contract calls with other operators using a 4-digit prefix or pre-allocate with one operator, eliminating the need for the prefix. Calls can also be made using the 1077 prefix. This process is managed by software, and calls from other operators are routed to the nearest border exchange.
2.2. Direct ADSL (Unbundled) – Disaggregated OBA
Offered by Orange, Jazztel, Ya.com, and Tele2, this option provides the best prices for customers due to higher profit margins for operators. It involves a complete unbundling of the line from Telefónica, including both voice and data, eliminating the monthly fee paid to Telefónica. Technically, this is based on number portability, transferring the customer’s number to the alternative ISP. The physical line is also transferred, and Telefónica may require a new line application with high portability. Unbundled service is not compatible with voice pre-allocation with other companies or internet service from other providers.
Digital Voice (VoIP)
This innovative service, offered by Tele2, Orange, and Ya.com, eliminates the traditional voice circuit. The connection runs directly from the RPCA to the operator’s RDO and then to the DSLAM, creating a pure data circuit. 
Voice is transmitted over ADSL, and the router at the customer’s premises converts the analog voice signal to digital. Some providers may re-inject the voice signal onto the line, while others require connecting the phone directly to the router. This simplifies the ADSL circuit, reducing the risk of breakdowns. However, it can introduce lag in calls and requires the router to be always on.
Analog Voice (POTS)
This option uses traditional voice service and is the most common type of unbundling. Jazztel currently uses it for their 20 Mbps service. The alternative ISP installs equipment for voice service in the collocation room (OBA) or a nearby room. Jazztel uses a Huawei DSLAM with analog voice capability. The line splitter is integrated into the DSLAM. If a separate room is used at the RPCA, distribution frames connect to the alternative ISP’s external location, which houses the RDO and other necessary equipment.