Local

1
Local Wide Area NetworkingJohns Hopkins
University Course 635.412.71

• Module 5 Last Mile Technologies

2
Fundamental Last-Mile ConnectivityDial-up
Networking

• Introduction
• Still the most common way to connect to the
  Internet
• Will be a significant WAN technology for a long
  time to come!
• Three physical components to a dial-up (remote
  access) system
• Remote access concentrator (or modem pool)
• The PSTN
• The users modem and attached PC
• Three parts to the dial-up protocol stack
• Physical Layer
• DCE-to-DTE
• DCE-to-DCE
• Data Compression and Error Detection/Correction
• Data Link Layer
• The main standards for modems are contained in
  the ITU V series

3
Fundamental Last-Mile Connectivity Dial-up
Networking

• Dial-up Connection Diagram

4
Fundamental Last-Mile Connectivity Dial-up
Networking

• Historical View of Modem Standards (and Speeds)
• Bell 103/113 (1962) 300bps
• v.21 300bps (similar to but inoperable with the
  Bell 103/113 standard)
• Bell 212A 1200bps
• v.22 1200bps (similar to but incompatible with
  the Bell 212A standard)
• v.22bis 2400bps
• v.32 9600bps
• v.32bis 14,400bps
• v.34 28,800bps
• v.34bis 33,600bps
• v.90 56kbps
• v.92 enhanced 56kbps (2000)

5
Fundamental Last-Mile Connectivity Dial-up
Networking

• Early Modem Standards
• The v.32 standard (1984)
• Defines the operation of a point-to-point dial-up
  (or leased line) link on a two-wire PSTN circuit
• Maximum speed of 9600bps
• Uses trellis coding to provide Forward Error
  Correction
• Four data bits encoded into five baud (QAM-32)
• The v.34 standard (1997)
• Also defines operation across a dial-up link or
  leased line on a two-wire PSTN circuit
• Maximum speed of 28,800bps (later increased to
  33,600bps, sometimes called v.34bis)
• Uses trellis coding/FEC with a maximum symbol
  rate of 3429 baud/second
• Data rate per symbol varies but averages 8.4
  bits/symbol

6
Fundamental Last-Mile Connectivity Dial-up
Networking

• The latest Modem Standards
• The v.90 standard (1998)
• New standard that takes advantage of the
  increasing use of digital transmission facilities
  to feed modem pools
• Allows top speed of 56kbps in downstream
  direction (v.34 still used upstream for a maximum
  speed of 33.6kbps
• Modem outputs PCM codewords directly modem
  never really does modulation
• The v.92 standard (2000)
• Faster call setup times compared to v.90
• Increases speed upstream to a maximum of 48kbps
  (PCM training)
• Implements a new data compression standard called
  v.44
• Implements a new feature called modem on hold
  allows a data call to be put on hold while using
  the call waiting feature

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Fundamental Last-Mile Connectivity Dial-up
Networking

• Data Compression Error Correction
• The v.42 standard
• Provides a reliable link across a modem
  connection
• Uses a framing standard called LAP-M (similar to
  HDLC LAP-D)
• I frames used for data transfer contain FCS field
• Other options for data transfer can be negotiated
  at startup
• The v.42bis standard
• Can provide up to 41 error compression
• Substitutes common strings of characters with
  short patterns
• The v.44 standard
• Improved compression algorithm (61) compared to
  v.42bis
• Uses the new LZJH compression algorithm developed
  by Hughes Network Systems

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Fundamental Last-Mile Connectivity Dial-up
Networking

• The Data Link Layer
• While the dial-up physical layer provides a
  number of advanced features, it still doesnt
  provide all the features or flexibility desired
• To allow a dial-up link to function as a true
  network connection, the Point-to-Point Protocol
  (PPP) was developed
• Xmodem, Zmodem, Kermit
• SLIP and CSLIP
• PPP is not a single standard, but a family of
  related standards
• Basic framing (PPP)
• Link Configuration (LCP)
• Authentication Protocols
• Network Control Protocols
• PPP is also used in other scenarios (e.g.
  PoS/Packet over SONET)

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Fundamental Last-Mile Connectivity Dial-up
Networking

• The Point-to-Point Protocol (RFC 1661)
• Defines the basic framing and encapsulation
  method
• Frame Fields
• Protocol (8/16 bits) defines purpose frame
  content
• Info/Payload holds upper layer data (up to 1500
  bytes)
• Padding optional protocol-specific pad bytes up
  to max frame size
• In order to exchange PPP-encapsulated data, the
  link must be configured using another protocol
  called the Link Control Protocol
• Functions Link Control Protocol (LCP)
  negotiates/configures
• MRU (Maximum Received Unit)
• Authentication Use/Type
• Link Quality Protocol
• Compression Use/Type

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WAN TechnologiesDial-up Networking

• LCP Authentication
• Steps to establishing connection via LCP
• Each side sends LCP-Configure Request packets
• LCP-Configure Request contains option negotiation
  parameters the other side can either accept or
  reject request
• Link is established when both sides have
  successfully sent and received a LCP-Configure
  Request ACK packet
• LCP also used to terminate an active PPP session
• If authentication was successfully negotiated,
  then that phase comes next

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WAN TechnologiesDial-up Networking

• Authentication
• Takes place as soon as LCP configuration is
  complete
• Two basic authentication methods
• PAP (RFC 1661) cleartext username/password
  exchanged
• CHAP (RFC 1991) hashed password exchanged via
  challenge/response mechanism
• Newer advanced authentication method the
  Extensible Authentication Protocol (EAP -- RFC
  2284)
• Allows for more flexible sophisticated option
  negotiation
• Specific authentication method negotiation during
  authentication phase
• New options
• One-time password
• Smart card/Token/Biometrics
• Authentication failure terminates PPP session

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WAN TechnologiesDial-up Networking

• The Network Control Protocols (NCP)
• Once the PPP link is established, each network
  layer protocol must be separately configured by
  its associated Network Control Protocol
• NCPs may be opened and closed at any time over an
  established PPP link
• Each NCP can involve protocol-specific option
  negotiation (e.g. IP address for IPCP)
• Currently defined major Network Control
  Protocols
• IPCP (IP control protocol) RFC 1332
• ATCP (Appletalk control protocol) RFC 1378
• IPXCP (IPX/Netware control protocol) RFC 1552
• BCP (Bridging control protocol) RFC 1638
• NetBIOS Frame Control Protocol RFC 2097

13
Cable Modem Technology
14
Last Mile TechnologiesCable Modems

• Introduction
• CATV Systems have been around a long time!
• First systems showed up in the early 1960s
• Intended to distribute reliable television
  service in areas with poor reception and/or
  strict rules on antennas
• Broadcast television analog transmission
  standards were preserved
• Infrastructure really started to spread and
  mature in the 1980s as CATV began to offer
  professional content not found on broadcast
  networks
• Similarly the concept of running data over CATV
  systems is older than most people think!

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Last Mile TechnologiesCable Modems

• The first attempt at Data over CATV
• The first commercial attempt to run data of CATV
  was developed by DEC in the early 1980s
• This system was standardized by the IEEE and
  called 10-BROAD36
• 10-BROAD36 used three 6-MHz channels to provide a
  10-Mbps service
• Frequency agile modems and two-way amplifiers
  were necessary to interface to the broadband CATV
  system
• The 10-BROAD36 Ethernet variant found most of its
  popularity in localized private CATV systems few
  commercial CATV systems at the time had two-way
  amplifiers
• The reliability and service levels found with
  most commercial CATV systems was not stellar,
  leading to frequent disruptions of data service
• Equipment reliability issues
• Service personnel training and coordination
  issues
• Cost of outfitting CATV systems for data

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Last Mile TechnologiesCable Modems

• The first attempt at Data over CATV (2)
• Needless to say, the first attempt at data over
  CATV was not a huge success and died out
• The logistical and economic advantages of
  convergence were not realized
• No way of limiting bandwidth in a subscriber
  environment so the technology could never move
  into the commercial CATV arena
• For campus use, more reliable and popular
  baseband coax Ethernet flourished
• In addition more reliable and higher speed
  backbone technologies such as FDDI displaced
  10-BROAD36 at the center of campus networks

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Last Mile TechnologiesCable Modems

• CATV terminology
• CATV System components
• Headend centralized distribution point for all
  signaling on a cable system
• Trunk primary distribution cables made of
  high-quality coaxial or fiber optic cable
• Amplifiers used to boost the CATV signal where
  necessary
• Feeders local distribution cables that serve
  neighborhoods or groups of homes
• Drops connections to individual subscribers
  from a tap usually lower quality but more
  flexible coaxial cable (R/G-6)
• CATV Frequency Allocations
• Sub-split includes a 5-35 MHz return (upstream)
  channel
• Mid-split usually includes a return channel
  from 5 MHz to 60-80 MHz
• High-split has a return channel more than a 100
  MHz wide
• Sub-split with extended return includes a 5-45
  MHz return channel

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Last Mile TechnologiesCable Modems

• CATV terminology
• HFC Hybrid Fiber/Coax CATV systems
• Telephone return for data over CATV systems
• Cable Modem (CM)
• Cable Modem Termination System (CMTS)
• CMCI Cable Modem to CPE Interface
• CMTS-NSI Cable Modem Termination System/Network
  side Interface

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Last Mile TechnologiesCable Modems

• Generic CATV system diagram

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Last Mile TechnologiesCable Modems

• Evolution of data transmission over CATV (take
  two!)
• A decade after the first try at data over CATV,
  the concept was resurrected to solve a different
  problem the last mile issue
• What was different this time?
• More reliable and capable CATV systems
• Hybrid Fiber-Coax systems (HFC) with digital
  distribution video becoming the norm
• 750-MHz 1-GHz bandwidth CATV systems replacing
  older, lower-bandwidth systems
• Better electronics, especially the frequency
  agile modems and amplifiers
• More sophisticated CATV providers with better
  service organizations
• A huge untapped market for providing advanced
  data services
• Converged and intelligent service with enhanced
  revenue opportunities
• Lots of residential and small business customers
  with no high speed data service

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Last Mile TechnologiesCable Modems

• Evolution of data transmission over CATV (2)
• First attempts at second generation data over
  CATV systems were proprietary
• Systems available from several manufacturers
• Upstream speeds from 768-kbps to 1.5-Mbps and
  downstream speeds of 10-Mbps to 30-Mbps
• To help foster faster emergence of next
  generation data over CATV systems, the equipment
  manufacturers formed an industry consortium in
  December 1995 and began work on a set of
  standards
• An IEEE working group (802.14) also began
  standardization efforts in parallel
• While there are still differences, for the most
  part the DOCSIS and 802.14 standardization
  efforts have merged

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Last Mile TechnologiesCable Modems

• Standards
• The consortiums standardization efforts resulted
  in the 1999 release of the Data over Cable System
  Interface Standard (DOCSIS) version 1.0
• A revised standard, known as DOCSIS version 1.1
  was released in 2001 to provide enhanced QoS
  functionality (and, of course, is backwards
  compatible)
• The DOCSIS standards reference and reuse many
  existing standards, especially the IEEE 802.1 and
  802.3 standards
• There are two variants of the DOCSIS standard
  one to fit typical U.S. CATV systems and the
  other for European CATV systems
• The goal of the DOCSIS standard is to add packet
  data transfer capabilities to coaxial and HFC
  CATV systems
• DOCSIS covers primarily Layers 1 and 2 of the OSI
  model
• The transport of IP data is the primary goal,
  though the DOCSIS standards allow the optional
  transport of other network layer protocols (e.g.
  ATM)
• The DOCSIS compliant CATV system is supposed to
  act like a big pipe each end will provide a
  standard network interface (typically 802.3)

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Last Mile TechnologiesCable Modems

• Functional diagram of DOCSIS compliant CATV
  system

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Last Mile TechnologiesCable Modems

• Standards diagram from DOCSIS standards Figure
  3.2
• CM acts acts as a bridging device
• CMTS acts as a bridging or a routing device
• Downstream transmission Convergence sublayer
  exists to allow future convergence of digital
  data and MPEG video

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Last Mile TechnologiesCable Modems

• Physical Layer
• Upstream (CM-to-CMTS)
• Uses TDMA bursts with QPSK or 16-QAM modulation
  with an adaptive symbol rate (the CMTS advertises
  the downstream modulation symbol rate)
• Upstream channel is divided in 6.25 ?sec
  mini-slots for transmission
• Forward Error Correction (FEC) utilized for error
  control as well as scrambling and symbol shaping
  for better transmission characteristics
• PHY frame structure consists of preamble, FEC
  bits, higher layer data payload
• Downstream (CMTS-to-CM)
• Will use 64-QAM or 256-QAM in a center frequency
  of 91 to 857-MHz (typically in the 550-MHz to
  750-MHz range)
• Maximum possible downstream bandwidth of 30-Mbps
  (64-QAM) or 40-Mbps (256-QAM)
• As with upstream uses FEC for error control
• All downstream data is encapsulated in 188 byte
  MPEG-2 frames to allow easy multiplexing with
  digital video

26
Last Mile TechnologiesCable Modems

• Data Link Layer
• The Data Link Layer is divided into three
  sublayers
• Medium Access Control
• Link-Layer Security Sublayer
• Logical Link Control

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Last Mile TechnologiesCable Modems

• Medium Access Control
• The same basic frame format is used upstream and
  downstream consisting of a MAC header and a data
  payload
• MAC header format and fields
• MAC data payload is optional and actual content
  is specified in the MAC header (MAC FC_type
  field)
• This sublayer MUST support the encapsulation of
  standard IEEE 802.3 headers diagram on previous
  page other payload types are optional
• Other specific MAC frame types exist for special
  functions
• Timing information
• Management commands
• Bandwidth allocation requests
• Fragmentation indication

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Last Mile TechnologiesCable Modems

• Medium Access Control sublayer (continued)
• While the MAC frame is the same upstream and
  downstream the MAC techniques are not!
• Downstream there is a single transmitter and
  multiple receivers
• Upstream there are many transmitters to one
  receiver an access control mechanism is needed
  to reduce contention for the upstream channel
• Upstream Channel Specifics (CM-to-CMTS)
• The upstream channel is slotted TDMA
• Timing for upstream access is controlled by the
  CMTS (it periodically sends SYNC messages
  downstream to providing timing)
• CMs contend to request timeslots for
  transmission therefore collisions may occur an
  Ethernet-style backoff mechanism is typically
  used
• There are also optional mechanisms for allowing a
  CM to reserve timeslots for guaranteed
  bandwidth
• Service flows can be defined to provide different
  levels of service

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Last Mile TechnologiesCable Modems

• Cable Modem Initialization Sequence
• Hunting
• Frame Synchronization
• Low-level initialization
• Time synchronization with head-end
• Ranging (determining the delay characteristics of
  the upstream channel)
• Transmit power adjustment (so power of all CMs is
  equal at the CMTS)
• Transmission of Registration Request message (CM
  ? CMTS)
• Vendor ID of cable modem
• Modem capabilities
• (Optional) Modem IP address
• Transmission of Configuration file (CMTS ? CM)
• Service flow and QoS information
• Response to advertisement of Modem capabilities

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Last Mile TechnologiesCable Modems

• Cable Modem Advantages
• Economics
• Ease of deployment/Infrastructure advantages
• Multimedia integration
• Cable Modem Disadvantages
• Security
• Reliability
• Operations
• Maintainability

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Last Mile TechnologiesCable Modems

• Almost here DOCSIS version 2.0
• Ratified late 2001, equipment is available but at
  last check v1.1 still predominates
• Higher upstream channel bandwidth (6.4-MHz max.)
  and data rate (30Mbps)
• Capability for symmetric service (important for
  business)
• Advanced-TDMA features new upstream modulation
  rates (32/64-QAM), slot sizes, and mixed mode
  operation for high efficiency flexibility
• Enhanced R-S error correction trellis coded
  modulation for robustness
• Possible use of S-CDMA (though rarely deployed as
  far as I can tell)
• Future DOCSIS version 3.0
• Ratified December 2007 Comcast has announced
  trial deployments of 3.0-based systems in 2008
• Channel bonding to allow up to 160-Mpbs
  downstream 120-Mbps upstream
• Support for IPv6
• Native support for high-quality IP-based video

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Digital Subscriber Line (DSL)
33
Last Mile TechnologiesDigital Subscriber Line
(DSL)

•  Introduction
• The prevalence of copper loops
• The copper telecommunications distribution
  infrastructure is the most common physical
  communications medium in existence
• There are more than 700 million telephone
  subscribers in the world
• As of June 2007 there were 200 million DSL lines
  worldwide (27.5 million in the U.S.)
• As the world moves into a new age of converged
  multimedia services the telephone companies are
  trying to leverage their copper plant to deliver
• Video on Demand
• High-Definition Video
• High bandwidth Internet Services
• As common as copper loops are, there are a number
  of challenges associated with using them to
  deliver these services

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Last Mile TechnologiesDigital Subscriber Line
(DSL)

• The bandwidth bottlenecks on a traditional copper
  loop
• In the past copper loops were installed with the
  sole purpose of transmitting voice communications
• Loops were conditioned to improve transmission
  characteristics in the 400 to 3400 Hertz
  frequency range the common method for
  accomplishing this destroyed the loops frequency
  response outside this range
• Besides conditioning there are a number of other
  issues associated with copper loops
• Distance of loop
• Condition and age of loop
• Bridged taps
• Interference

35
Last Mile TechnologiesDigital Subscriber Line
(DSL)

•  Varieties of DSL -- Asymmetric Digital
  Subscriber Line (ADSL)
• Most common variety of DSL designed for the
  residential environment
• Originally designed to deliver video, which
  requires asymmetric transmission channels (high
  bandwidth downstream for video, lower upstream
  for control)
• Current use is for always-on high speed
  data/Internet connections
• Standardized by ANSI in 1995 as standard T1.413
  with several subsequent updates and approval by
  the ITU-T (G.992.1)
• ADSL can provide speeds between 1.5 to 7-Mbps
  downstream and 64 to 800-kbps upstream on a
  single copper pair
• Actual speed depends on distance SNR
  (Signal-to-Noise ratio) of the line
• ADSL has a maximum distance from the providers
  central office of approximately 18,000 feet (3.4
  miles)
• Original generation of equipment was fixed at a
  certain speed when the modems initialized newer
  generation modems are rate-adaptive (R-ADSL) and
  can change speeds based on line conditions

36
Last Mile TechnologiesDigital Subscriber Line
(DSL)

•  Varieties of DSL -- G.Lite (ADSL-lite)
• While ADSL is in great demand, the roll out of
  lines has not gone as smoothly as hoped
• Equipment is not plug-and-play requires
  extensive customer service and technical support
• Installation requires a truck roll by a
  technician to install splitters and cabling for
  the ADSL modem
• ADSL modem components are still complex and
  expensive
• Beginning with the work of an industry
  consortium, G.Lite is now part of ITU G.992.1
  that defines a less complex but slower DSL
  implementation
• Provides a 1.5-Mbps downstream channel and
  384-kbps upstream channel at a maximum distance
  of 18,000 feet
• Meant to be installed by the customer over
  existing telephone jacks and cabling
• Modems can be constructed using cheap and simple
  Digital Signal Processors (DSPs), reducing cost
  and support issues

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Last Mile TechnologiesDigital Subscriber Line
(DSL)

•  Varieties of DSL ADSL2, ADSL2, and ADSL2-RE
• Like most technologies, ADSL has continued to
  advance to meet new needs
• ADSL2 (ITU G.992.3)
• Ratified in July 2002
• Max. 8-Mbps downstream/1-Mbps upstream with
  slightly increased reach (5)
• Improved modulation efficiency, framing overhead,
  initialization, power mgmt.
• Ability to bond lines
• ADSL2 (ITU G.992.5)
• Ratified in January 2003
• Max. 24-Mbps downstream primarily through
  doubling of downstream frequency band to 2.2-MHz
• Modulation improvements reduces crosstalk
• ADSL2-RE (ITU G.992.3 Annex L -- 2003)
• Further increases reach of DSL another 600-900
  meters at minimum allowable speeds (192-kbps
  Down/96-kbps Up)

38
Last Mile TechnologiesDigital Subscriber Line
(DSL)

•  Varieties of DSL -- Integrated Digital
  Subscriber Line (IDSL)
• Designed to provide a dedicated data link with
  speeds similar to ISDN-BRI
• Targeted for subscribers that could not get ADSL
  and did not want switched digital data service
  (ISDN-BRI)
• Runs at 144-kbps upstream and downstream
  (symmetric) at distances up to 6.5 miles from the
  provider central office
• Like other DSL varieties provides an always-on
  network connection no bonding or calls are
  necessary
• Standards-based network interfaces exist on both
  the customer-side IDSL modem (typically 802.3)
  and on the provider-side
• Between the IDSL modems ISDN-BRI coding (2B1Q) is
  used for transmission
• Higher speed symmetric interfaces are also known
  as SDSL (mentioned on next slide)

39
Last Mile TechnologiesDigital Subscriber Line
(DSL)

•  Varieties of DSL -- HDSL, HDSL-2, and SDSL
• HDSL (High-bit-rate DSL) was designed to low-cost
  T-1 service
• Uses two pairs of copper to provide a
  communications channel between the two HDSL
  modems each pair transmits a bi-directional
  768-kbps signal
• Channel coding is typically PAM or QAM on the
  customer and CO sides of the modem an ANSI
  standard T-1 interface is provided
• Unlike traditional T-1 circuits, doesnt require
  removal of bridged taps, binder group separation,
  repeaters, or other line conditioning
• The T-1 interface can be channelized or
  unchannelized some HDSL modems can run longer
  distances at half-T-1 speeds (768-kbps)
• HDSL-2 was an improvement to HDSL allowing full
  T-1 speed over a single copper pair through
  better modulation coding
• SDSL, or Symmetric Digital Subscriber Line
  provides a loop with equal speeds upstream or
  downstream but unlike HDSL has standard network
  interfaces on the modems instead of T-1 interfaces

40
Last Mile TechnologiesDigital Subscriber Line
(DSL)

•  Varieties of DSL Very High Data-rate DSL
  (VDSL)
• The next generation DSL service, meant to provide
  high-bandwidth multimedia services to residential
  and small business customers
• Will provide a downstream speed up to 100-Mbps,
  capable of providing compressed HDTV-quality
  video over short distances
• Upstream speeds of 16 to 100-Mbps allow bandwidth
  for hungry interactive multimedia applications
  (CAVEs, multipoint videoconferencing, etc.)
• Runs on loops 4,000 feet like ADSL speed is
  distance sensitive (note almost all subscriber
  loops installed in the past decade are 4,000
  feet)
• Three ITU standards have been developed and
  ratified
• G.993.1 (2004) 55-Mbps downstream/15-Mbps
  upstream
• G.993.2 VDSL2 long-reach (2005) 55-Mbps
  down/15-Mbps up
• G.993.3 VDSL2 short-reach (2005) 100-Mbps
  symmetric

41
Last Mile TechnologiesDigital Subscriber Line
(DSL)

• Technical discussion of ADSL
• ADSL Reference Architecture (System Diagram)

42
Last Mile TechnologiesDigital Subscriber Line
(DSL)

• Technical discussion of ADSL
• ADSL Terminology
• Splitter device consists of a High Pass Filter
  (HPF) to block POTS from the ADSL modem and a Low
  Pass Filter (LPF)
• ADSL Modem (labeled as NT in diagram) --
  provides a standard interface to the customer
  (typically 802.3) and includes all the functional
  units necessary to connect that interface to the
  subscriber loop
• ATU-C and ATU-R (ADSL Termination Unit) the
  functional units that take frames or cells and
  perform the FEC, interleaving, and modulation
  functions
• DSLAM (DSL Access Multiplexor) the ADSL
  termination cabinet at the providers site,
  typically contains a number of ATU-R units and a
  single network aggregation system to interface
  the ATU-Rs to the providers network

43
Last Mile TechnologiesDigital Subscriber Line
(DSL)

• Technical discussion of ADSL Physical Layer
• The ITU-T physical layer modulation standard for
  ADSL is called Discrete Multitone (DMT)
• DMT divides the channel into 256 4-kHz
  subcarriers, subcarriers 6 to 32 are for upstream
  data and any higher subcarriers can be used for
  downstream data
• The number of subcarriers used upstream and
  downstream are configurable however the
  subcarriers cannot be mixed or matched
• Inside each subcarrier QAM is used to modulate
  and send data the number of QAM levels used is
  related to the SNR found in each subcarrier
• Forward Error Correction is used to ensure
  acceptable bit error rates
• The lowest 4 kHz of the subscriber loop is
  reserved for POTS (Plain Old Telephone Service)
• Though little used in current production ADSL
  equipment, there are still a number of
  pre-standard systems deployed using other
  modulation schemes (predominantly CAP and QAM)

44
Last Mile TechnologiesDigital Subscriber Line
(DSL)

• Technical discussion of ADSL Physical Layer
• Typical DMT Frequency Spectrum Allocation

45
Last Mile TechnologiesDigital Subscriber Line
(DSL)

• Technical discussion of ADSL Above the Physical
  Layer
• Above the physical layer channel created by ADSL,
  ATM is almost always used a data link layer
• Two choices for ATM transmission are possible
  Fast Slow Channel
• Fast channel has FEC but little or no
  interleaving for less delay but lower BER
• Slow channel has FEC with interleaving for higher
  delay and a better BER
• IP can be carried by ATM in a variety of methods
  (LANE, PPPoA, etc.)
• Ethernet functionality is coming but still
  appears to be a future

46
Last Mile TechnologiesDigital Subscriber Line
(DSL) vs. Cable Modems

• Which is Better?
• ADSL has a larger potential growth rate, though
  most industry watchers believe cable modems will
  match the growth rate of ADSL
• Some experts consider cable modems less secure
  than ADSL, though in reality it would be
  difficult to do much data snooping on either
• In my experience there is little real technical
  advantage in one over the other from a user
  perspective usually the engineering and
  operation of the systems are the real
  differentiators
• How congested are the back-end networks? ISP
  connections?
• How many subscribers are connected to a CMTS?
• How current are the systems with firmware
  upgrades?
• How well do the providers run their network
  services/servers (e.g. DNS, DHCP, web proxies,
  mail gateways)

47
Last Mile TechnologiesOther Technologies

• Wireless Local Loops WiMAX
• Can be a niche player, especially where it is
  technically or economically difficult to deploy
  ADSL or cable modems
• Many early proprietary systems, also a few
  deployed systems based on MMDS/LMDS (most outside
  U.S.)
• New initiative called WiMAX (IEEE 802.16) has
  high potential
• Standards developed by the IEEE 802.16 Task
  Force the original fixed standard (802.16-2004)
  and the newer 802.16e mobile standard
• Goal is to provide a single infrastructure that
  can provide high bandwidth to fixed (WLL),
  nomadic, and mobile users
• The WiMAX Forum (industry alliance) is working on
  implementation, test, and interoperability issues
  associated with 802.16 equipment
• Deployments are very limited but 2008 appears to
  be a pivotal year

48
Last Mile TechnologiesOther Technologies

• WiMAX Technical Features
• Max speed around 70-Mbps Max. range of 50km
  (obviously speed decreases with range)
• Based on scalable OFDMA (flexible subchannel
  user assignment)
• Subchannel widths from 1.25-MHz to 20-MHz
  subcarrier coding is QPSK, QAM-16, and QAM-64
  (downstream only)
• Licensed operation in 2 to 3-GHz bands (future
  unlicensed use in 5.8-GHz NII band)
• Designed for Non-LOS operation
• MIMO capable with advanced antenna features (e.g.
  - beam-forming)
• MAC based on adapted version of DOCSIS (aka
  DOCSIS)
• Advanced security options (EAP/auth, AES, control
  message protection, etc.)

49
Last Mile TechnologiesOther Technologies

• Satellite
• Some interesting systems exist (Starband,
  Tachyon, DirectPC)
• Speeds for home/SMB comparable to DSL higher
  speed options (10-40Mbps) available to larger
  customers
• Most systems use Geosynchronous satellites
  LEO/MEO implementations are possible but have
  engineering challenges
• Early implementations were one-way with dialup
  return most now 2-way
• Typically Ku or Ka band
• Technical challenges (and costs) with satellite
• Satellite launch/maintenance costs Customer
  Equipment Costs
• Latency on Connections
• Use/tuning of proxies
• Line of Sight issues

50
Last Mile TechnologiesOther Technologies

• FTTH/FTTP (Fiber to the Home)
• Can you say FiOS? If you are lucky, you are a
  Verizon customer who can actually get direct
  fiber connectivity/services
• Usually based on Passive Optical Networking
  (PONs)
• Original standard was ITU G.983 (APON/BPON),
  moving to G.984 (GPON)
• An optical line terminal (ONT) generates outbound
  signal over SM fiber, usually split to serve 32
  premises
• Multiple wavelengths allow provisioning of voice,
  data, video each on a separate lambda
• FiOS now provides customer maximum 30-Mbps
  down/5-Mbps upstream
• Very expensive (4000 per home passed)
• FTTH is still the exception so infrastructure
  build-out is costly time consuming
• Upside is once in place the service opportunities
  are wide open

51
Last Mile TechnologiesOther Technologies

• Powerline-based systems (BPL)
• Interesting concept, with some systems in
  deployment (Manassas, VA) domestically and
  worldwide
• Use existing commercial power infrastructure to
  provide Internet Access
• Possible DSL/Cable Modem Speeds (2-3Mbps
  downstream/256kbps upstream)
• Issues/Concerns
• Interference is a concern (possible FCC
  intervention) OFDM used to mitigate
  interference with other users of spectrum
  (amateur radios)
• Lack of Standards (the IEEE has a Study Group,
  but no final standards have been issued)
• Transformers in the power grid

52
Last Mile TechnologiesOther Technologies

• Digital Cellular
• 3G Cellular Data Networks do provide speeds that
  approach the broadband capabilities of current
  DSL/Cable Modems
• EV-DO 1x Rev.A -gt 3-Mbps downstream/1-Mbps
  upstream
• HSDPA -gt 2-Mbps downstream/384-500kbps upstream
• As speeds increase, why not use your Verizon
  Broadband card for your home access too?
• A real wildcard, depending on speeds, prices, and
  coverage
• The Future may see 4G cellular networks and
  merge WiMAX and/or WiFi technologies

53
Homework Assignment

• Homework 3 (due March 31)
• Question 1 (50) as you can see there are a
  number of new technologies poised to compete with
  DSL and Cable Modems. Research one of the
  following explaining what it is, how it works,
  its advantages disadvantages, and prospects for
  wide deployment (around 2-3 pages)
• Choices Satellite, FTTH/PON, DOCSIS v3.0, VDSL,
  BPL, WiMAX
• Note that the more detail I gave in the slides
  the more new information I expect in your
  submission (and cite your references!)
• Question 2 (25) Using a packet sniffer
  download analyze the packet capture file from
  the class website. Explain what is happening in
  the capture and detail the protocols/commands/func
  tions you see.
• Question 3 (25) Strange as it sounds,
  protocols have been developed for IP over Fibre
  Channel as well as FC over IP. Research one of
  these and in a page describe what technical
  challenges are involved. Also briefly describe
  what practical use you can see for the standard
  you chose.