Transcript Presentation Title - IEEE ComSoc-SCV

DSL Services
Gregory F. Wetzel
Chief Network Architect
February 11, 2004
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?
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DSL Physical Layer
Section Overview
• Terminology
• Network Elements
• CPE
• DSLAM
• ATM switch
• BRAS
• ADSL Service Architectures
• In a CLEC environment
• Wholesale
• Retail
• Service Matrix
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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)
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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
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General DSL Network Architecture
ISP
CO
HUB CO
DSLAM
Router
ATM
Switch
Internet
HUB CO
ISP
CO
ATM
Switch
Router
...
DSLAM
CO
ATM
Switch
HUB CO
ISP
Router
DSLAM
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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
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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
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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
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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
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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
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IP Termination of DSL Services
CLEC Collocation
DS-3/
OC-3
DS-3/
OC-3
BRAS
IP
Router
IP
Network
Redback
BRAS
SMS-1800
IP
Router
IP
Network
ATM
Switch
(#2)
DS-3/
OC-3
5
Ether Switch
RADIUS
Proxy
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DNS
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
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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 downstream 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 nonswitched channel
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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
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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)
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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
Data
Voice
Loop
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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
Data
Voice
Line
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Class 5
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
Data
Voice
Line
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Class 5
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.
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Line Sharing
• 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
ILEC is Customer of Record
Voice 2 wire connection
ILEC Class 5 Switch
Internet
Voice 2 wire connection
OSP Loop
Splitter
MDF
Combined voice and Data
Customer
CLEC
Data
DSLAM
Covad Space
Customer gets:
•ILEC voice
•CLEC data (Covad provided)
Covad Confidential
Covad
Networ
k
Line Splitting (UNE-P)
• 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
CLEC is Customer of Record
Voice 2 wire connection
ILEC Class 5 Switch
Internet
Voice 2 wire connection
OSP Loop
Splitter
MDF
Combined voice and Data
Customer
CLEC
Data
DSLAM
Covad Space
Customer gets:
•CLEC voice
•CLEC data (Covad provided)
Covad Confidential
Covad
Networ
k
Loop Splitting (UNE-L)
• 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
CLEC is Customer of Record
Voice 2 wire connection
CLEC Class 5 Switch
Internet
Voice 2 wire connection
OSP Loop
Splitter
MDF
Combined voice and Data
Customer
CLEC
Data
DSLAM
Covad Space
Customer gets:
•CLEC voice
•CLEC data (Covad provided)
Covad Confidential
Covad
Networ
k
DSL Logical Layers
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
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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
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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
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IP Service Model
ISP
CO
Router
DSLAM
ATM
Switch
Internet
ISP
CO
ATM
Switch
Router
DSLAM
...
DNS
CO
Auth
ATM
Switch
ISP
Router
DSLAM
Email
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Web
Host
IP POP Detail
OC-3/DS-3
ATM
switch
Redback
BRAS
F E/GE
Ethernet
Switch
OC-3/DS-3
BRAS
F E/GE
FE
FE
SMS-1800
(#2)
5
OC-3/DS-3
Cisco 19xx (Hub2)
RADIUS
Proxy
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Gateway
Router
DNS
Resolver
Backbone
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
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Questions?