Category: dsl

DSL – Interview Questions Dear readers, these DSL Interview Questions have been designed specially to get you acquainted with the nature of questions you may encounter during your interview for the subject of DSL. As per my experience good interviewers hardly plan to ask any particular question during your interview, normally questions start with some basic concept of the subject and later they continue based on further discussion and what you answer − What is DSL? DSL stands for Digital Subscriber Line. It is a copper loop transmission technology that satisfies bottleneck problem often associated with the last mile between the network and service providers. What do you understand by “attenuation” in DSL technology? The dissipation of the power of a transmitted signal as it travels over the copper wire line. In-home wiring also contributes to attenuation. What do you understand by “bridged taps” in DSL technology? These are unterminated extensions of the loop, which cause additional loop loss with loss peaks surrounding the frequency of the quarter wavelength of the extension length. What is “cross talk” in DSL technology? The interference between two wires in the same bundle, caused by the electrical energy carried by each of them. Explain DSL Home. DSL Home is an initiative taken by DSL-Forum. To define requirements related to home devices like residential gateways, VoIP devices and local & remote management of home devices. Which services can be enabled by DSL Home? Voice, video, data, including IPTV, video on demand, content on demand, et Which protocol is used for DSL remote management? DSL Home remote management protocol (TR-69) and its extensions are access agnostic. Which protocol is used for DSL local management? The TR64 protocol is used for DSL local management. What do you understand by TR111? TR111 allows TR69 remote management for the devices in the Home Network (HN). Explain TR98 and TR133. TR-98 and TR-133: Configuration and Management of Service differentiation (QoS) parameters in the CPE devices through TR-69 and TR-64 respectively. What is purpose of TR-104, TR-106, TR-122, WT-135, WT-140, and WT-142 protocols? TR-104 Data model for VoIP services is available for Video services too. TR-106 defines the common data model template. Defines the baseline object structure and set of accessible parameters for a TR-69 device. TR-122 defines Voice ATA Requirements. WT-135 is the object model for the STB device. WT-140 is the Object Model Network Storage Device. WT-142 is the framework for TR-069 enabled PON device. What are the options in DSL technology? Family ITU Name Ratified Maximum Speed capabilities ADSL G.992.1 G.dmt 1999 7 Mbps down 800 kbps up ADSL2 G.992.3 G.dmt.bis 2002 8 Mb/s down 1 Mbps up ADSL2plus G.992.5 ADSL2plus 2003 24 Mbps down 1 Mbps up ADSL2-RE G.992.3 Reach Extended 2003 8 Mbps down 1 Mbps up SHDSL (updated 2003) G.991.2 G.SHDSL 2003 5.6 Mbps up/down VDSL G.993.1 Very-high-data-rate DSL 2004 55 Mbps down 15 Mbps up VDSL2 -12 MHz long reach G.993.2 Very-high-data-rate DSL 2 2005 55 Mbps down 30 Mbps up VDSL2 – 30 MHz Short reach G.993.2 Very-high-data-rate DSL 2 2005 100 Mbps up/down What are the services offered by DSL Home- TR-69? The following services are offered by DSL Home TR-69 − Remote management of the devices in a secure manner (uses SSL/TLS based security) Real-time provisioning of services via auto-configuration Status and performance monitoring Diagnostics Access Control Notification Firmware upgrade What are the services offered by TR-064? The following services are offered by TR-064. Adopts the UPnP v1.0 architecture and extends the UPnP IGD v1 specification (with some restrictions). A management application (TR-64 control point) runs on a PC and it pushes the service provider and the customer specific configuration to a CPE. This happens when the CPE adds to the network. More useful during the initial installation of new CPE devices and when there is WAN side connectivity issues. Difference between TR69 and SNMP? SNMP stands for Simple Network Management Protocol. Use of SNMP requires opening of SNMP port through NAT as most of the home gateways use NAT and the devices being managed could be behind NAT. In SNMP, the request to get/set any parameters is always initiated by the manager hence the port has to be opened on the CPE to get the request. In TR-69, a TR-69 session is initiated by CPE and the server uses the same session to send get/set requests. That does away with opening of the port explicitly in NAT environment. TR-69 also defines a way where ACS can send the request to CPE and this part is taken care by TR-111 part2 transparently. Most of the SNMP implementations existing today do not implement SNMPv3, hence the messages exchanged over SNMP is not very secure. In TR-69, the security is taken care through the SSL/TLS or HTTP based authentication schemes. Most of the TR-69 implementations as of today implement SSL/TLS. What are the components of the DSL system? Following are the components of the DSL System Transport system Local Access Network Multi Service DSLAM DSL Modem/ Router POTS Splitters and Microfilters Explain the Transport system in a DSL 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. Explain the Local system in a DSL system. 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 nextgeneration DSLAM include ATM switching to accomplish it. Explain the Multi service DSLAM in DSL system. 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

DSL – VDSL-based Service Sets VDSL offers a variety of simultaneous services, which are not possible otherwise. This opens the possibility for service providers to offer a new base for your subscription and multimedia services. Telco providers offering telephony and data services can now expand their business by offering comprehensive services and a host of video-centric applications. This enables the telecom companies to compete with television operators by effective invasive cable. The original charter for ADSL was to provide a full range of broadband services for residential consumers, so why the need for VDSL? The reality is that ADSL is an Internet technology only. The following table illustrates that, in the end, ADSL is limited in its ability to provide a full range of broadband services. VDSL, on the other hand, is well suited to provide these services today and tomorrow Application Downstream Upstream ADSL VDSL Internet Access 400 kbps − 1.5 Mbps 128 kbps − 640 kbps yes yes Webhosting 400 kbps − 1.5 Mbps 400 kbps − 1.5 Mbps today only yes Video Confrencing 384 kbps − 1.5 Mbps 384 kbps − 1.5 Mbps today only yes Video on Demand 6.0 Mbps − 18.0 Mbps 64 kbps − 128 kbps today only yes Intractive video 1.5 Mbps − 6.0 Mbps 128 kbps − 640 kbps today only yes Telemedicine 6.0 Mbps 384 kbps − 1.5 Mbps today only yes Distance learing 384 kbps − 1.5 Mbps 384 kbps − 1.5 Mbps today only yes Multiple Digital TV 6.0 Mbps − 24.0 Mbps 64 kbps − 640 kbps today only yes Telecommuting 1.5 Mbps − 3.0 Mbps 1.5 Mbps − 3.0 Mbps no yes Multiple VoD 18 Mbps 64 kbps − 640 kbps no yes High-definnition TV 16 Mbps 64 kbps no yes Learning working make money

DSL – VDSL Access Technology VDSL is the technology with a high rate. Operating at speeds up to 52Mbps, VDSL is the next generation of DSL technology with higher throughput and requirements for implementing, which are simpler than ADSL. VDSL began its life being called VADSL, but was renamed VDSL by the ANSI working group T1E1.4. The main reason T1E1.4 decided VDSL on VADSL was that, unlike ADSL, VDSL is both symmetric and asymmetric. VDSL is nearly ten times faster than ADSL and is over thirty times faster than HDSL. In the tradeoff for increased speed loop length: VDSL has a shorter reach in the loop. In the following table, it shows a comparison of the various DSL technologies available today. We see that VDSL is highest in terms of bandwidth technology and supports applications both asymmetric and symmetric, and is ideal for broadband full service. DSL Type Symmetric/ Asymmetric Loop Range (kft) Downstream (Mbps) Upstream (Mbps) ISDL Symmetric 18 0.128 0.128 SDSL Symmetric 10 1.544 1.544 HDSL (2 pairs) Symmetric 12 1.544 1.544 ADSL G.lite Symmetric 18 1.5 0.256 ADSL Asymmetric 12 6 0.64 VDSL Asymmetric 3 26 3 Asymmetric 1 52 6 Asymmetric 3 13 13 Asymmetric 1 26 26 Like other DSL technologies, VDSL uses higher frequency spectrum of copper above standard frequencies used for lifeline service to the plain old telephone (POTS) and Integrated Services Digital Network Services (ISDN). This is commonly referred to technology as data and video-on-voice. This technology enables Telco’s existing copper infrastructure for the provision of broadband services over the same physical plant. VDSL spectrum is specified to range from 200 kHz to 30 MHz. Real spectral distribution vary with the line rate or based on asymmetric or symmetric rates that are used. Baseband for POTS and ISDN service use is preserved by the use of passive filters commonly called as dispatchers. Asymmetric VDSL VDSL is designed to offer a multitude of asymmetric broadband services, including Digital Television Broadcasting, Video on Demand (VoD), High-Speed Internet Access, Distance Learning and Telemedicine, to name a few. The delivery of these services requires the downstream channel to have a higher bandwidth that the channel upstream and is asymmetrical. For example, HDTV requires 18 Mbps for video content downstream. Upstream, however, it does not require the transmission of signaling information (e.g., change of channel or program selection), which is of the order of kbps. The following table specifies the rate VDSL standards established in the specification / ANSI S1.4 of T1. The downstream rates are derived from the sub-multiples of Synchronous Optical Network (SONET) and Synchronous Digital Hierarchy (SDH) speed of 155.52 Mbps canonical, i.e. 51.84, 25.92 Mbps and 12 Mbps, 96 Mbps. Typical Service Range Bit Rate (Mbps) Symbol Rate (Mbps) Comments Short range, 1 kft 6.48 0.81 baseline 4.86 0.81 optional 3.24 0.81 Medium range, 3 kft 3.24 0.405 baseline 2.43 0.405 optional 1.62 0.405 Long range, 4.5 kft 3.24 0.405 baseline 2.43 0.405 optional 1.62 0.405 Symmetric VDSL VDSL is also designed to provide symmetrical services for small and medium business customers, business enterprise, high-speed data applications, video conferencing and tele-applications, etc. Symmetric VDSL can be used to provide short-haul T1 replacements NXT1 rate and support a host of other business applications. The following table contains the symmetric VDSL standards for service established in the ANSI T1E1.4. A rate of 6.48 Mbps to 25.92 Mbps, it should be noted that VDSL provides symmetrical service between the standard T1 (1.536 Mbps) and T3 (44.376 Mbps) rates, fill the gap simplest copper twisted pair. Although ANSI has not specified distance and long-term rates for symmetric services 6 Mbps to 1.5 Mbps on loops from 3 kft to 10 kft may be supported. Typical Service Range Bit Rate (Mbps) Downstream Symbol Rate (Mbps) Upstream Symbol Rate (Mbps) Short range, 1 kft 25.92 6.48 7.29 19.44 6.48 7.29 Medium range, 3 kft 12.96 3.24 4.05 9.72 3.24 2.43 6.48 3.24 3.24 Learning working make money