ADSL

ADSL is an acronym for Asymmetric Digital Subscriber Line. It is one of several of the xDSL family (HDSL, VDSL,...). ADSL supports high bit rates over existing metallic twisted pair access networks. When using ATM/ADSL, in the downstream channel (towards the ATM end system e.g. home) data rates up to 6Mbits/sec. In the upstream direction data rates are up to 640Kbits/sec. (Some sites will have reverse traffic demands, i.e. web servers.)

ADSL uses an adaptive bit rate, so the data rates depend on line quality typically depending on the loop length.

ADSL is deployed with POTS typically. ADSL uses frequencies higher than POTS, so the POTS (analogue) signals are transmitted along with the ADSL signals on the same pair. (ADSL would start at 20-40KHz). It would also seem possible to run ISDN in parallel with ADSL by starting the ADSL starting frequency above the ISDN spectrum. (ADSL would start at 170KHz). High end of the used frequency range is 2.2MHz.

When used as delivery mechanism for ISPs, IP address allocation is handled with DHCP.

ADSL Technologies

CAP is a single-carrier modulation technique. ADSL has three frequency ranges -- 900 kHz for downstream data transmission, 75 kHz for upstream data transmission, and 4 kHz for plain old telephone service. CAP treats the data frequency ranges as one big pipe through which to pump as many bits as possible.

DMT, on the other hand, is a multicarrier modulation technique that breaks the data transmission channels into 256 subchannels and divides up the data among them. The advantage is that data is directed away from channels with too much interference, a not uncommon problem with decades-old copper wire, and sent down clear transmission paths.

CAP speeds currently are 1.5Mbps downstream and 64Kbps upstream. (Westell Technologies plans to deliver a 2Mbps upstream, 900Kbps downstream modem in the first quarter of next year.) DMT transmits at 6Mbps downstream and 640Kbps upstream.

IP with ATM and ADSL

Classical ethernet ARP

ARP
Node wishes to contact an IP address in same subnet, broadcasts an ARP request on subnet/segment and that station respondes.
RARP
Reverse ARP. A (diskless) station broadcasts a reverse ARP request on a segment (the driver can find the hardware MAC address) and a RARP server responds with an IP address corresponding. (Can it get multiple replies for multiple subnets? (DHCP comes in here somewhere too, since the IP address allocation is its business)

Classical IP/ATM

ATMARP
Node wishes to contact an IP address in same subnet, sends an ATMARP request to the ATMARP server which respondes.
InvATMARP
Given a PVC/SVC in existence node sends InvARP to find IP address of station at other end of VC.

Functions Required

Where functionality required for IP/ATM/ADSL

Where

IP over ATM

LANE

MPOA

ATU-R

Ethernet PHY
Ethernet MAC
IP ARP
Routing
LIS Client
ATM NIC with UNI

Ethernet PHY
Ethernet MAC
LEC
ATM NIC with UNI

Ethernet PHY
Ethernet MAC
LEC
MPC
ATM NIC with UNI

In Network

ATMARP Server
IP router

LES, LECS, BUS
ATM Routers

LES, LECS, BUS
MPS, MARS, MCS

At Service Provider

IP-based service
LIS client
ATM NI

etherent service
LEC
ATM NI

IP/???-based service
MPC
ATM NI

See ATML Forum-TR4 pg 27.

Management

ADSL-F [TR5, TR6] define a MIB. This is very much a physical and fault and performance management view. This MIB contains many TRAP/NOTIFICATIONS, and while these can be turned on and off and while there is a very high degree of control on the thresholds, it seems very likely that the fault management system supporting this will have to be able to handle a high event processing rate. (Since there will be many lines all capable of having identified traps). Also the performance MIBs have a lot of history, and potentially a huge number of lines on which performance data is captured, so the processing of this could consume a large amount of network traffic, CPU power in the agents, CPU power and disk space in the NMS.

Things missing include

ADSL Modem functionsare categorised

Random notes

Acronyms

USB
UNiversal Serial BUS Interface
AAL
ATM Adaptation Layer
ABR
Available Bit Rate
ADM
SDH/Sonet Add Drop Multiplexor
ADSL
Asymmetric Digital Subscriber Line
ADT
ATM Digital Terminal
AINI
ATM Inter-Network Interface
AIU
ATM Interworking Unit
AMI
Alternate Mark Inversion
AN
Access node. Concentration point for broadband and narrowband data.
ANI
Access Network Interface
ANSI
American National Standards Institute
ANT
ADSL Network Termination
ARP
Address Resolution Protocol
ATE
ATM Terminating Equipment
ATM
Asynchronous Transfer Mode
ATPARP
ATM Address Resolution Protocol
ATU-C
ADSL Transmission Unit at the network end (central office)
ATU-R
ADSL Transmission Unit at customer premises (remote)
ATU
ADSL Transceiver Unit
AWG
American wire Gauge
B
Auxiliary data input to Service Module (set top box)
B-ISUP
Broadband Integrated Services User Part
BCCP
Bearer Connection Control protocol
BER
Bit Error Ratio
Broadcast
broadcast data input in simplex mode (typically broadcast video).
CAP
carrierless amplitude and phase modulation (c.f. DMT)
CATV
Cable Television
CBR
Constant Bit Rate
CDV
Cell Delay Variation
CEBus
Consumer Electronics Bus
CLEC
Competitive Local Exchange Carrier
ILEC
Incumbent Local Exchange Carrier
CPE
Customer Premises Equipment
CSMA/CD
Carrier Sense Multiple Access Collision Detect
CTD
Cell Transfer Delay
DAML
Digital Added Main Line
DAVIC
Digital Audio Visual Council
DCS
Digital Cross-connect System (SDH/Sonet)
DMT
Discreet multitone (c.f. CAP)
DSLAM
DSL Access multiplexer
ES
Errored Second.
ETSI
European Telecommunications Standards Institute
FEC
Forward Error Correction
FTTC
Fiber-to-the-curb
FTTH
Fiber-to-the-home
G.703
ITU Physical/electrical characteristics of Hierarchical Digital Interfaces
G.704
ITU Synchronous frame structures used at Primary and Secondary Hierarchy Levels
G.992.1
ADSL Transceivers (previously G.dmt)
G.992.2
Splitterless ADSL Transceivers (previously G.lite)
G.994.1
Handshake Procedures for DSL Transceivers, (previously G.hs or G.handshake)
G.995.1
Overview of DSL Recommendations, (previously G.ref)
G.996.1
Test Procedures for DSL Transceivers, (previously G.test)
G.997.1
Physical Layer Management for DSL Transceivers, (previously G.ploam)
HAN
Home ATM Network
HDN
Home Distribution Network
HDSL2
High-bit-rate DSL (version 2)
HDT
Host Digital Terminal
HFC
Hybrid Fiber Coax
HPF
High Pass Filter
ILMI
Integrated Local Management Interface
ISA
Industry Standard Architecture (A PC bus standard)
ISDL
ISDN-like DSL
ISDN
Integrated Services Digital Network (called DSL in ANSI T1.413)
ISP
Internet Service Provider
InARP
Inverse Address Resolution Protocol
L2TP
Layer Two Tunnelling Protocol (draft-ietf-pppext-l2tp-*)
LCS
Line Code Specific
LOF
Loss of Frame
LOL
Loss of Link
LOS
Loss of Signal
LPR
Loss of Power
Loop
twisted pair copper telephone line.
MAC
Media Access Controller
MCR
Minimum Cell Rate
MGN
Margin
MSDSL
Moderate speed Digital Subscriber line
MSDSL
Multi-rate Symmetric DSL
NEXT
Near end crosstalk
NGDLC
Next Generation Digital Loop Carrier
NHRP
Next Hop Resolution Protocol
NID
Network Interface Device
NNI
Network Node Interface
NT
Network Termination
NAP
Network Access Provider
NSP
Network Service Provider
NTP
Network Transport Provider
OAM
Operations and Management
OAN
Optical Access Network
OLT
Optical Line Termination
ONU
Optical Network Unit
OSS
Operation Support System
PC
Personal Computer
PCI
Peripheral Component Interconnect
PCMCIA
Personal Computer Memory Card International Association
PCR
Peak Cell Rate
PDN
Premises distribution network (ATU-R <-> SM) active/passive
PHY
Physical (layer)
PMD
Physical Media Dependent (sub-layer)
PNNI
Private Network Node Interface
POF
Plastic Optical Fiber
PON
Passive Optical Network
POP
Point of Presence
POTS
Plain Old Telephone Service
POTS-C
I/F between PSTN and POTS splitter at network end
POTS-R
I/F between PSTN and POTS splitter at premises end
PSD
Power Spectral Density
PSTN
Public Switched Telephone Network
PVC
Permanent Virtual Circuit
PVC
Permanent Virtual Connection
QAM
Quadrate Amplitude Modulation (c.f. DMT, CAP)
QoS
Quality of Service
RADIUS
Remote Authentication Dial In User Service (RFC2138)
RADSL
Rate Adaptive DSL
RAM
Remote Access multiplexer
RARP
Reverse Address Resolution Protocol
RBB
Residential Broadband
RJ45
10BASE-T Connector standard for UTP cabling
RSVP
(IETF) Resource Reservation Protocol
RT
Remote terminal
RTP
Real Time Protocol
SDH
Synchronous Digital Hierarchy
SDSL
Symmetric DSL
SM
Service Module (e.g. set top box)
SNR
Signal to Noise Ratio
SONET
Synchronous Optical Network
STB
Set Top Box
STM
Synchronous transfer Mode
SVC
Switched Virtual Circuit
Splitter
Filter to separate low frequency POTS from high (ADSL)
T-SM
I/F ATU-R <-> PDN
T1.403
Carrier to customer installation DS1 Metallic
T1.413-1995
ANSI Standard for ADSL Modems
T1
A Telecommunications Standard Committee
T1E1.4
ANSI Committee for interfaces, network power & Protection digital subscriber loop access
T
I/F PDN <-> SM
TC
Transmission Convergence (sub-layer)
TDR
Time domain reflectometry
TIA422
Medium range (300m)serial data data transmission standard
TL1
Transaction Language 1
TX
Transmit
U-C
I/F loop <-> POTS splitter on network side
U-C2
I/F ATU-C <-> POTS splitter on network side
U-R
I/F loop <-> POTS splitter on premises side
U-R2
I/F ATU-R <-> POTS splitter on network side
UBR
Unspecified Bit Rate
UNI
User Network Interface
UPI
User Premises Interface
VA
(logical) I/F ATU-C <-> Access Node
VC
(logical) I/F Network <-> Access Node
VBR
Variable Bit Rate
VDSL
Very High Speed Digital Subscriber Line
nrt-VBR
Non-Real-Time Variable bit Rate
rt-VBR
Real-Time Variable bit Rate

References

ADSL Forum http://www.adsl.com. The tech reports contain hundreds of pages of specs, in pre-formatted HTML which makes printing a hassle, but also available in MS word. The diagrams don't print properly.

ATM Forum's residential broadband working group. The base document is the RBB architectural framework ftp://af6948:ion,wala@ftp.atmforum.com/atm/approved-specs/af-rbb-0099.000.pdf. DAVIC is 'competing' with ATMF?

DAVIC tries to specify a specific tool for each application. Docs include

Other Overviews

 

David Horton
This document can be found on the Intranet at http://mango/home/horton/doc/ADSL.html, or from unix at /home/horton/doc/ADSL.html.

Last modified: Tue Nov 3 16:54:59 EST 1998