DSL - System Components


In this chapter, we will discuss the Transport System, Local Access Network, Multiservice DSLAM, DSL Modem/Router and several other DSL System Components.

Transport System

This component provides the carrier backbone transmission interface for the DSLAM System. This device can provide service specific interfaces such as −

  • T1/E1
  • T3/E3
  • OC-1
  • OC-3
  • OC-12
  • STS-1 and
  • STS-3.

Local Access Network

The local access network uses inter-CO local carrier network as a foundation. To provide connectivity between multiple service providers and users of multiple services, additional hardware may be required. Frame Relay switches, ATM switches and / or routers may be provisioned in the access network for this purpose. Increasingly, ILECs and PTO are looking for ATM equipment to fulfill this role, and next-generation DSLAM include ATM Switching to accomplish it.

Sometimes, it is instructive to consider the concept of an Access Node (AN), which is where the switches and / or routing equipment are physically located. Depending on the scale of the desired access network and the costs associated with transportation, we can expect to find one or more AN by local access network, creating an overlay structure on top of the inter-CO network. In some cases, the AN is integrated in the DSLAM, as is the case with the new generation of DSLAM that incorporate ATM switching systems.

Multiservice DSLAM

Residing in the CO environment (or in a space of near virtual collocation), the DSLAM is the cornerstone of DSL solution. Functionally, the DSLAM concentrates the data traffic from multiple DSL loops on the base network for connection to the rest of the network. The DSLAM provides Backhaul Services for the packet, cell and / or circuit-based applications through concentration DSL ON 10Base-T lines, 100Base-T, T1 / E1, T3 / E3 ATM or outputs.

Some DSLAMs are maintaining the temperature "hardened" for installation in areas that are not controlled environment. This allows the installation of the Remote Terminals in DSLAM or sidewalk cabinets instead of just in the central or virtual collocation spaces. The ability to move the DSLAM in these remote locations (with extended range loop technologies) can significantly increase the footprint of a service provider, for the provision of services to customers that would otherwise be out of reach of DSL

In addition to concentration and functions according to the specific service being provisioned, a DSLAM provides added features. The DSLAM may, in some cases be necessary to open the data packets to take action. For example, to support the dynamic IP address assignment using the Dynamic Host Control Protocol (DHCP), each packet must be considered in order to direct packets to the right destination (that is considered as a function DHCP-relay).

DSL Modem/Router

The criterion for assessment modem / DSL Router is the customer site equipment to connect the service user to DSL loop. The end point of DSL is generally 10/100Base-T, V.35, ATM or T1 / E1, along with the new generations of consumer products, which also support methods such as USB, IEEE 1394 (Firewire) and factor internal PCI form. In addition, CPE parameters are being developed with additional ports designed to support specific applications, such as RJ11 ports for support of voice (for e.g. IADs for service VoDSL), ports Video for video services based on DSL, and new networking interfaces such as Home Phoneline Networking Alliance (HomePNA) or wireless network such as 802.11 wireless Ethernet interfaces.

The DSL CPE devices are available in a number of different configurations depending on the specific service being provisioned. In addition to providing basic DSL modem functionality, many parameters have additional features such as bridging, routing, ATM multiplexing or TDM.

The Bridged Parameters serve the market well with ease of installation and maintenance. All work bridge setting device should have a learning filter to keep unwanted traffic crossing the network. Routed IP settings provide flexibility to the customer's site. With a point of IP-termination current, subnets can be created and maintained for effective segmentation of remote LAN and multicast and unicast downstream recognition.

Multiple service areas may also be used by remote users on the LAN at the same time. Several service areas become important when you have a large group of users who need access to various service providers such as the corporate LAN and the Internet through different ISPs.

The transparent protocol parameters behave like a DSU / CSU. They provide an interface for DSL link for routers and / or existing FRAD, which are Frame Relay Access Devices. Routers and FRAD manage the overall management of network traffic is plugged in, while the final point of DSL pass all traffic to the upstream DSL link.

The Channelized TDM parameters can function as DSU / CSU for T1 traditional service / E1. They also provide router interfaces, FRAD, multiplexers, PBX or any other device used to a traditional service.

The DSL modem / router must be designed, so that it can be installed with little or no required configuration. In addition, many service providers have demanded that the end of the DSL to be installed by the service user, requiring simply plug and play. DSL endpoint must be very manageable by the service provider.

Generally, the features search for the following points −

  • Ability to provide Layer 1 and 2 management statistics such as signal-to noise ratio.

  • Ability to provide Layer 3 MIB statistics such as packet counts.

  • Devices that are fully manageable by the service provider, without the need for on-site personnel.

  • Devices that support performance monitoring and end-to-end visibility for rapid fault detection, isolation and correction.

  • Ability to be remotely downloaded with new software as required.

  • Interoperability with third-party CPE including IAD.

POTS Splitters and Microfilters

The POTS splitters option lie in both the CO and service users slots, allowing copper loop to use for media transmission, simultaneous DSL high-speed data and the single line telephone service, when the DSL variant uses these services.

POTS splitters generally come in two configurations −

  • A single separator version designed for mounting to the residence and

  • A multiple release separator designed for the ground connection to CO.

Note that, while the number of DSL line coding systems support only one channel POTS, others do not. Services Reference Schema-based DSL POTS splitters can be either passive or active. The active POTS splitter requires an external power source for voice and DSL to run on a single copper pair. The passive POTS splitter requires no power and typically have a higher MTBF (Mean Time between Failures) as its active counterpart. While passive POTS splitter supports vital services such as 911 in case of power loss DSLAM or DSL modem, the active POTS splitter should have a backup power supply to provide these essential services in the event of power loss.

The DSL as G.dmt ADSL, G.lite, RADSL ReachDSL and can be installed today without POTS CPE separate separator. Instead, passive devices known as micro-filters can be installed between each user POTS device in the customer's premises (such as telephones, analog modems and fax machines) and wall outlets. Microfilter is a filter "low pass" that allows voice-band services to be transmitted, while filtering the high frequencies used by DSL and eliminates interference.

The advantage of this approach is that while traditional POTS splitters were installed on the Network Interface Device (NID) by a service provider installer, micro-filters can be easily connected to the end user, eliminating the need for a service call for the installation. For a DSL service that runs on the POTS connection is always the first choice for the installation.

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