© 2006 Cisco Systems, Inc. All rights reserved.ISCW v Teleworker Connectivity Describing DSL Technology

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v DSL Features

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v What Is a DSL? Utilizes high transmission frequencies (up to 1 MHz) Technology for delivering high bandwidth over regular copper lines Connection between subscriber and CO

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v What Is a DSL? (Cont.) Downstream and upstream transmission Symmetrical and asymmetrical services Multiple xDSL variations Can deliver data along with voice (voice over IP) Always-on data connection Bandwidth versus distance

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v DSL Types

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v DSL Variants DSL variants differ in: Nature Maximum data rate Line coding technology Data and voice support Maximum distance

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v DSL Variants Examples DSL TechnologyNature Max. Data Rate (Down / Up) [bps] Data and POTS ADSLAsymmetric8 M / 1 MYes VDSL Symmetric / Asymmetric 52 M / 13 MYes IDSLSymmetric144 k / 144 kNo SDSLSymmetric768 k / 768 kNo HDSLSymmetric2 M / 2 MNo G.SHDSLSymmetric2.3 M / 2.3 MNo

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v DSL Limitations

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v DSL Limitation Factors Factors that define maximum distance and speed: Signal attenuation Bridge tap Load coil Wire gauge Impedance mismatch Crosstalk AM radio interference

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v DSL Distance Limitations Maximum data rate and distance assume no impairments. Maximum data rate is achieved at shortest distance. Maximum distance is achieved at lowest data rate. DSL Technology Max. Data Rate (Down / Up) [bps] Max. Distance [feet / km] ADSL8 M / 1 M18,000 / 5.46 VDSL52 M / 13 M4,500 / 1.37 IDSL144 k / 144 k18,000 / 5.46 SDSL768 k / 768 k22,000 / 6.7 G.SHDSL2.3 M / 2.3 M28,000 / 8.52

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v ADSL

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v ADSL Coexists with POTS over the same copper wiring Asymmetric data rate: –High-speed downstream for intensive applications –Slow upstream for undemanding data requests

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v ADSL (Cont.) ADSL equipment: –ADSL terminal unit-remote (ATU-R) –ADSL terminal unit-central office (ATU-C) ADSL features three basic line-coding techniques: –Single carrierCAP modulation –Multicarrier with DMT –Multicarrier with G.lite ADSL operation and performance is influenced by different impairments.

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v ADSL and POTS Coexistence

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v ADSL and POTS Coexistence A key feature of ADSL is coexistence with POTS. Transmission of voice and data signals is performed on the same wire pair. Data circuits are offloaded from the voice switch.

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v ADSL and POTS Coexistence (Cont.) Splitter versus microfilter How are data and POTS channels separated? –POTS splitter at CO –Microfilters at customer premises

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v ADSL Channels and Encoding

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v CAP Modulation Single-carrier modulation technique

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v DMT Modulation Multiple-carrier modulation technique

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v Data over ADSL: PPPoE

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v Data over ADSL IP packets encapsulated over ATM Three major approaches: –RFC 1483/2684 Bridged –PPPoE –PPPoA

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v PPP over Ethernet Ethernet frame carrying PPP frame Service provider end: –DSLAM for DSL connection termination –Aggregation router for PPP session termination Subscriber end: –DSL modem for DSL connection termination –PPPoE client for PPP session termination The client device is the PC or the router at the CPE

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v PPP over Ethernet (Cont.) IP is assigned to PPPoE client functioning device. A CPE router can connect multiple users via a single ADSL connection using NAT/PAT and DHCP.

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v PPPoE Session Variables DSL and PPPoE deployment types: Router terminating DSL and with PPPoE client Modem terminating DSL and router with PPPoE client Modem terminating DSL and end-user PC with PPPoE client

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v PPPoE Session Establishment PPP session is from PPPoE client to the aggregation router. Subscriber IP address is assigned by the aggregation router via IPCP.

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v Data over ADSL: PPPoA

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v PPP over ATM Routed solution User packets routed over ATM Service provider end: –DSLAM for DSL connection termination –Aggregation router for PPP session termination Subscriber end: CPE for DSL connection and PPP session termination

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v PPP over ATM (Cont.) CPE receives an IP address via IPCP like in the dial model.

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v Summary DSL is a family of access technologies for delivering high bandwidth over regular copper lines at limited distances. In regards to the downstream and upstream, the DSL can be symmetrical or asymmetrical. DSL variants are ADSL, HDSL, RADSL, SDSL, IDSL, VDSL, and G.SHDSL. The trade-off among various DSL types is distance versus speed. Different impairments influence the achieved operational speed.

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v Summary (Cont.) ADSL is designed to coexist with POTS because there is a POTS splitter at the CO. Splitters and microfilters are used to separate voice from data channels. PPPoE and PPPoA are the most frequently used encapsulation methods. The PPPoE client software first encapsulates the end-user data into a PPP frame, and then the PPP frame is further encapsulated inside an Ethernet frame. PPPoA is a routed solution in which the CPE is set up as a router, and the CPE routes the packets from the PC of the end user over ATM to an aggregation router.

© 2006 Cisco Systems, Inc. All rights reserved.ISCW v