ADSL access

These video and multimedia transmission services shall in general be supported on ADSL or ADSL2+ broadband access, on the current pair copper line that reaches the customer site.  Maximum downloading speeds of 8 Mbps in the case of ADSL and 24 Mbps in the case of ADSL2+ can theoretically be achieved, although in reality these speeds can be diminished by effects such as interferences with other data services or attenuation due to the length or condition of the cables, etc.

To provide this access, there must an ADSL or ADSL2+ modem in the customer’s home, which is connected by the pair copper line to data access equipment called ADSLM, located in ANTEL’s stations.  From the ADSLM, through the data core, whether ATM or Ethernet, one reaches the central devices of the solution, such as the video servers, middleware and encoders.

The ADSL modems that are mentioned have more than one Ethernet port, to be able to serve the STB and the PC or the internal network of the subscriber’s home; otherwise an additional device would be needed such as a hub or a switch to the outlet of the modem to which the STB and the PC shall be connected.

If there is a Firewall, etc., some mechanism must be provided to resolve problems such as NAT, etc., some STBs have an NAT and DHCP server incorporated.

The main characteristics to be taken into account for this type of element are the following:

• Length and condition of the cables of the external plant (metallic access network)

• ADSL access must provide sufficient bandwidth to the customer’s home and must be able to ensure a given service quality.

• An additional consideration when determining ADSLM scalability is the broadband amount it can receive.

• ADSLM Ethernet or ATM (Ethernet  prevails in IPTV networks)

• In the case of ADSLM Ethernet, these should include:

  • Functionality of IGMP Snooping or IGMP Proxy.
  • High speed of multicast channel switching toward users, when there are various users doing “zapping” and when “IGMP Proxying” or “IGMP Snooping” mechanisms are used.
  • Capability of equipment with one or more interfaces of Gigabit Ethernet network (uplink) so as to have sufficient bandwidth according to needs.
  • Management and mapping of VLAN (IEEE 802.1Q) to differentiate the traffic of various services (video, Internet, etc.)
  • Traffic prioritization according to 802.1p priority bits to give priority to services in real time such as video compared to data services.
  • Data rate limitation (policing and shaping) in the interfaces of the uplink by VLAN, etc.
  • Data rate limitation (policing and shaping) in the interfaces toward the users by PVC, by VLAN, etc.

• In case of ADSLM ATM, the following should be included:

• ADSLM must support multicast in IGMP.
• High speed of multicast channel switching to users, when there are various users doing “zapping” and when IGMP is used.
• Capability of being equipped with one or more interfaces, at least STM4 so as to have sufficient broadband depending on need.

• In some implementations, which are proprietary, eventually it can be the ADSLM itself that controls which multicast channels shall be sent to the DSL modem.

• The modems must correspond for example to some of the following possible alternatives:

• The modem must have various Ethernet ports to facilitate the integration of various STBs or PCs in the customer’s house.  The modem must differentiate the services of each port by different PVCs or VLANs toward the network.  The modem must prioritize the traffic to the network on the basis of the PVC or the VLAN.
• The modem must include, inside the STB and with various ports for various STBs and PCs in the customer’s house.  The modem/STB must differentiate the services of each port by different PVCs or VLANs toward the network.  The modem/STB must prioritize the traffic to the network on the basis of the PVC or VLAN.
• Using a modem with one single port, but the STB must have various ports for STBs or PCs in the customer’s house.  The STB must differentiate the services of each port by different VLANs toward the network.  The STB or the modem must prioritize the traffic toward the network on the basis of the VLAN.
• Using a modem with one single port and a switch in the customer’s house.  The switch must differentiate the services of each port by different VLANs toward the network.  The switch or the modem must prioritize the traffic to the network on the basis of corresponding VLAN.

• It is advisable that the modem be able to limit the traffic rate to the network by PVC or by VLAN to be applied as corresponds.

ADSL Access standards

The following table exemplifies the various xDSL access standards that are commercially available.  In the 1Q2005, the standardization of VDSL2 (G993.2) has been provided for, with speeds of up to 100 Mbps in the download direction.

At present, in ANTEL’s ADSL network, only the ADSL G.DMT is available.  Nevertheless, the new bidding process of ADSLM envisages the possibility of equipping the ADSLM Ethernet with ADSL2/ADSL2+.

Summary of Service Coverage according to Type of Network and Line and Video Coding

The previous table provides a summary of feasible service rollout situations.  It can be observed that, using the ADSL line coding, there are cases in which video service could not be given, regardless of the video coding that was used.  On the contrary, using the ADSL2+, there is a great possibility of being able to provide the service, even when the video coding is MPEG2, with enough bandwidth still remaining for Internet access solutions.

Fernando Fontán
National Telecommunications Administration
Uruguay