1. DSL Services Gregory F. Wetzel Chief Network Architect February 11, 2004

2. Covad Confidential Agenda DSL Physical Layers CPE ADSL, SDSL, IDSL, T1 DSLAM ATM Switch DSL Logical Layers ATM connections IP Services Layered on top of DSL Markets: Consumer, SOHO, Small Business Subscriber Management Internet Access Voice / Video / other?

3. DSL Physical Layer

4. Covad Confidential Section Overview Terminology Network Elements CPE DSLAM ATM switch BRAS ADSL Service Architectures In a CLEC environment Wholesale Retail Service Matrix

5. Covad Confidential Terminology ADSL – Asymmetric DSL BRAS – Broadband Remote Access Server CLEC – Competitive Local Exchange Carrier, used in this presentation to generically reference a Local Exchange Carrier other than the Incumbent. For example, Covad, MCI, AT&T, etc. DSL – Digital Subscriber Line IDSL – ISDN-based DSL Line – loop plus ILEC-provided dial tone (think telephone line)

6. Covad Confidential Terminology Loop – copper pair connecting end user premise to central office facility Rate/Reach – DSL analog signals are limited by electrical properties of the loop. Rate/Reach is the tradeoff between getting a certain data rate at a certain distance between the transmitter and receiver. SDSL – Symmetric DSL (aka, Single Loop DSL) SMB – Small/Medium size Business SOHO – Small Office/Home Office

7. Covad Confidential General DSL Network Architecture

8. Covad Confidential DSL Technology Different Markets have Different Requirements Small-Medium Businesses Symmetric bandwidth requirements VoDSL Web hosting or Databases on site Service Level Agreements Many PCs Consumer Asymmetric bandwidth requirements One to a few PCs Price is a decider Wholesale versus Retail Managing aggregation by wholesale customer Many wholesale customers want direct PVC to end user

9. Covad Confidential DSL Technology Symmetric DSL (SDSL) Today SDSL/2B1Q is common, but not standardized ITU-T G.shdsl soon Addresses SMB market ISDN DSL (IDSL) Used today for customers beyond the reach of other DSL technologies Distance too great Behind Digital Loop Carrier Asymmetric DSL (ADSL) Standardized Focused on consumer offerings T1 Access to DSLAM Standarized Focused on business offerings

10. Covad Confidential Customer Premises Equipment (CPE) This equipment comes in a variety of models: Ethernet Bridge, common for consumer Ethernet Router, common for SOHO and SMB Can have a variety of DSL interfaces ADSL, SDSL, IDSL, T1 Different models of CPE support different DSL architectures Use of PPP over Ethernet or over ATM Static or Dynamic IP address assignments Functions Terminates a copper loop Terminates the DSL line coding (xTU-R) Extracts or Encodes the Layer 2 signal typically ATM, but can be Ethernet or Frame Relay

11. Covad Confidential DSL Access Multiplexer The DSLAM aggregates multiple DSL lines Functions Terminates copper loops Terminates the DSL line coding (xTU-C) Provides additional control on DSL signals than the CPE Extracts or Encodes the Layer 2 signal typically ATM, but can be Ethernet or Frame Relay Aggregates Layer 2 input/output from multiple subscribers onto a “backhaul” or “trunk” Typically ATM PVCs are the element of aggregation

12. Covad Confidential ATM Switch Grooms ATM PVCs between The DSLAM on which the subscriber is attached The handoff port to ISP customer or CLEC’s own IP infrastructure ATM Switches are arranged in a network Regional and/or National ATM connections from a subscriber can be handed off in the same or a different region Regulatory difference between CLEC and ILEC

13. Covad Confidential IP Termination of DSL Services Redback SMS-1800 (#2) ATM Switch BRAS IP Router Ether Switch RADIUS Proxy DNS 5 IP Network CLEC Collocation BRAS DS-3/ OC-3 IP Network IP Router DS-3/ OC-3 DS-3/ OC-3

14. Covad Confidential Broadband Access Server The BRAS terminates Layer 2 Typically ATM PVCs Also PPP over Ethernet or PPP over ATM Subscriber Management Uses RADIUS to Authenticate userid/password Configure subscriber parameters shaping profile filtering profile (e.g., restrict email servers or proxy web) Assigns IP addresses and DNS resolver addresses

15. Covad Confidential The Flavors of DSL There are many standard and proprietary versions of Digital Subscriber Line technology ADSL is the most common and is used mostly with consumers Asymmetric bandwidth allocation in the up- and down- stream directions. More in the down-stream. Achieved by allocation the spectrum asymmetrically. Current std has max 6Mbps down and 768Kbps up IDSL is used mainly by CLECs Regulations do not require ILECs to share Remote Terminals, therefore reach is an issue with CLECs IDSL bonds an ISDN BRI into a 128 or 144 kbps non- switched channel

16. Covad Confidential Flavors of DSL SDSL or SHDSL is used mainly by SMB Symmetric service needed by businesses that, e.g., host web sites Current SDSL and SHDSL supports up to 2Mbps In addition, T1s can be attached to DSLAMs, functionally making them a digital access line solution

17. Covad Confidential CLEC Environment What do the ILECs sell? Unbundled Network Element – Loop (UNE-L) High Frequency Portion of the Loop (HFPL) Unbundled Network Element – Platform (UNE-P)

18. Covad Confidential UNE-L Primarily a copper product CLEC leases the loop and may use the loop to provide voice, data, or both. Covad uses UNE-L to provide SDSL and IDSL services, for example Loop Voice Data

19. Covad Confidential HFPL Primarily a data product CLEC leases high frequency portion of the loop to provide data service. (It only applies to ADSL) ILEC provides voice service to the end user Line Data Class 5 Voice

20. Covad Confidential UNE-P Primarily a voice product CLEC leases the entire loop plus local circuit switching (class 5 port) The CLEC may choose to put data services on the loop or designate an authorized agent (e.g. Covad) to provide the data Line Voice Data Class 5

21. Covad Confidential Service Elements How are the elements used to deliver ADSL services? Line Sharing (HFPL) Line Splitting (UNE-P) Loop Splitting (UNE-L) Perspective shown in the following slides is primarily wholesale. Covad is used as the provider name to distinguish access provider from CLEC wholesale customers.

22. Covad Confidential Line Sharing MDF DSLAM ILEC Class 5 Switch Voice 2 wire connection Splitter Voice 2 wire connection Combined voice and Data OSP Loop Data Customer Covad Space Covad Networ k Internet CLEC ILEC is Customer of Record Customer gets: ILEC voice CLEC data (Covad provided) ILEC provides local voice service to End User Covad gets access to High Frequency Portion of the Loop (HFPL) using Covad company codes (Covad billed for HFPL) CLEC is ISP to End User

23. Covad Confidential Line Splitting (UNE-P) MDF DSLAM ILEC Class 5 Switch Voice 2 wire connection Splitter Voice 2 wire connection Combined voice and Data OSP Loop Data Customer Covad Space Covad Networ k Internet CLEC CLEC is Customer of Record Customer gets: CLEC voice CLEC data (Covad provided) CLEC provides local voice service to End User using UNE-P Covad gets access to High Frequency Portion of Loop (HFPL) using CLEC company codes (CLEC billed for Linesplit loop charges) CLEC is ISP to End User

24. Covad Confidential Loop Splitting (UNE-L) MDF DSLAM CLEC Class 5 Switch Voice 2 wire connection Splitter Voice 2 wire connection Combined voice and Data OSP Loop Data Customer Covad Space Covad Networ k Internet CLEC CLEC is Customer of Record Customer gets: CLEC voice CLEC data (Covad provided) CLEC provides local voice service to End User using CLEC owned voice switch Covad gets access to High Frequency Portion of Loop (HFPL) using CLEC company codes (CLEC billed for loop charges) CLEC is ISP to End User

25. DSL Logical Layers

26. Covad Confidential What are the Layers? Layers DSL physical layer ATM layer PPP layer (not always present) IP layer ATM Layer rides on DSL Layer and consists of Typically a single PVC with UBR or VBR-nrt QoS using AAL5 Possible to have multiple PVCs Supporting different QoS per PVC Architectures using multiple PVCs become complex due to IP addressing and routing issues Support ATM OAM flows for troubleshooting

27. Covad Confidential PPP Layer PPP over Ethernet for Multi-protocol Encapsulation Used for consumers Terminates on PC (or home gateway) Provides a single login per subscriber PC CPE can be a bridge (until recently less expensive than a router) Bridge has very little configuration, good for self-install PPP over ATM Used for businesses, terminates on CPE CPE typically a router Interworks with RADIUS on the BRAS Assigns dynamic or “framed-route” IP address/subnet Pushes DNS resolver addresses

28. Covad Confidential IP Layer IP Layer spans from CPE to IP POP Premises LAN through CPE CPE encapsulates IP in PPP CPE encapsulates PPP in AAL5/ATM Transmission across ATM network BRAS undoes ATM and PPP encapsulations BRAS participates in SP’s IP routed network In retail or Layer 3 wholesale model BRAS is owned by access provider In Layer 2 wholesale model BRAS is owned by wholesale customer

29. Covad Confidential IP Service Model ISP... ATM Switch Router CO DSLAM CO DSLAM ATM Switch DSLAM ATM Switch Internet ISP... ATM Switch Router CO DSLAM CO DSLAM ATM Switch DSLAM ATM Switch Internet ISP Router ISP Router DNSAuth ISP Router ISP Router EmailWeb Host

30. Covad Confidential IP POP Detail Redback SMS-1800 (#2) ATM switch BRAS OC-3/DS-3 F E/GE Gateway Router FE Cisco 19xx (Hub2) RADIUS Proxy DNS Resolver 5 Backbone BRAS Ethernet Switch OC-3/DS-3

31. Covad Confidential Summary We’ve discussed overall DSL network architectures Impacts from market segment Impacts from government regulations Technical stacks/layering DSL ATM PPP IP Implementation of architecture

32. Questions?