Architectures and Alternatives for

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Architectures and Alternatives for Broadband
Access Networks
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ADSL-based Access Network

• DSL is asymmetric technology
• 6.144 Mbps (downstream)
• 640 Kbps (upstream)
• Always-On broadband access
• PSTN is completely replaced by an IP network to
  offer integrated voice and data services.
• DSLAMs, installed in CO, could efficiently
  aggregate several hundreds of DSL connections
• Statistical multiplexing
• DSL does not require the deployment of a new
  network it runs on the existing PSTN
  infrastructure.

Limited by the length of the line
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ADSL-based Access Network
Central office
DSLAMs
M D F
ATU-C
ATU-C
Cooper pair
HomePNA
Ethernet
ATU-C
Cooper pair
Access Server
ADM
Metro ring
DSLAM
F D F
Fiber cable
ATU-C
Cooper pair
ATU-C
ATU-C
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Cable-based Access Network

• Asymmetric technology
• 30 Mbps (downstream)
• 1.3-5.1 Mbps (upstream)
• Always-On broadband access
• Cable TV network is upgraded to allow new
  services such as data over cable.
• Cable modems are installed at the customer
  premise cable modem termination systems (CMTS)
  at the head-end.
• Data over cable relies on data channels shared by
  multiple users using statistical multiplexing.
• Requires power supplies to run deployed active
  elements, such as amplifiers and nodes.

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Cable-based Access Network
Distribution Hub
Optical node
ADM
Tx Rc
Router
CMTS
HomePNA
Metro ring
Ethernet
CMTS
To TV Set Top Box
Drop
Fiber backbone
Tx Rc
RF source
Amplifier
Drop
Tap
Distribution (coaxial cable)
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ADSL- vs. Cable- based access network

• HFC network provides relatively higher
  transmission bandwidth than DSL.
• Recent studies showed that HFC solution is
  relatively cheaper than DSL due to the increased
  cost of DSLAMs.
• However, DSLAM port costs are subject to
  significant cost reductions.
• DSL coverage area is limited.

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ADSL- vs. Cable- based access network

• HFC architecture has a great degree of equipment
  sharing
• Pros
• Statistical multiplexing.
• Possibility to accommodate more users.
• Cons
• Security issues.
• Cost of providing service will increase with
  traffic growth and new bandwidth intensive
  applications.
• Efficiency drops substantially during peak hours.
• HFC architecture deploys active elements in the
  distribution network (DN) i.e., requires power
  supplies throughout the DN.

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Fiber To The x in Access Systems
Service modes
Passive Optical splitter
OLT
Optical fiber
FTTH
ONU
Internet
ONU
FTTB
Telephone
ONU
FTTC
Interactive Video
ONU
FTTCab
DSL
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Optical Access
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Basic Architecture of PON
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EPON Downstream
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EPON Upstream
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B-PON architectures

• Deploying FTTH is expensive and its deployment is
  very limited.
• FFTB is a cost effective solution, its deployment
  is vital.
• FFTC and FTTCab are architectures that provide
  broadband services to customers where fiber
  optics is not feasible to be deployed
• Service is carried over a DSL access network that
  connects customers to CO (where the ONU resides)
  through DSL connections.
• Thus, B-PON either alone or in conjunction with
  DSL provides a basis for the implementation of a
  full service access network (FSAN).

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Principles of B-PON
ONU

• One downstream/upstream channel.
• MAC arbitration mechanism is required to avoid
  collision between simultaneous transmissions in
  the upstream direction.
• Fixed-TDM is one possible solution.
• Dynamic Bandwidth Allocation is more suited for
  bursty traffic.
• Channel speed is 1Gbps.
• Data rate per ONU depends on the splitting ratio
  of the splitter (116, 64)

Optical splitter/coupler
OLT
1.55?m
1.31?m
20-25 km
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ATM-PON

• APON systems are based upon ATM as the bearer
  protocol.
• Downstream transmission is a continuous ATM
  stream at a bit rate of 155.52 Mb/s or 622.08
  Mb/s with dedicated Physical Layer OAM (PLOAM)
  cells inserted into the data stream .
• Upstream transmission is in the form of bursts of
  ATM cells, with a 3 byte physical overhead
  appended to each 53 byte cell in order to allow
  for burst transmission and reception.
• APON provides a very rich and exhaustive set of
  OAM features, including BER monitoring, alarms
  and defects, auto-discovery and automatic
  ranging, churning as a security mechanism for
  downstream traffic encryption etc.

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ATM-PON
Downstream frame format
Tframe 56 cells of 53 bytes
ATM Cell 1
ATM Cell 28
ATM Cell 54
ATM Cell 27
PLOAM 2
PLOAM 1
53 upstream grants
Upstream frame format
Tframe 53 cells per frame
ATM Cell 2
ATM Cell 3
ATM Cell 53
ATM Cell 1
3 bytes overhead per cell (guard time, preamble,
delimiter)
PLOAM Physical Layer Operation And Maintenance.
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Ethernet-PON

• Ethernet for subscriber access networks combines
  a minimal set of extensions to the IEEE 802.3
  Media Access Control (MAC) and MAC Control
  sub-layers with a family of Physical (PHY)
  Layers.
• MPCP (Multi-Point Control Protocol) is defined as
  a function within the MAC control sub-layer.
  MPCP uses messages, state machines, and timers,
  to control access to a P2MP topology. Each ONU
  in the P2MP topology contains an instance of the
  MPCP protocol, which communicates with an
  instance of MPCP in the OLT.
• A P2P Emulation Sub-layer makes an underlying
  P2MP network appear as a collection of point to
  point links to the higher protocol layers (at and
  above the MAC Client). It achieves this by
  pre-pending a Logical Link Identification (LLID)
  to the beginning of each packet, replacing two
  octets of the preamble.
• EPON uses variable Ethernet variable frames for
  transmission.

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APON vs. EPON
APON vs. EPON
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(B-PON DSL) architecture

• A new network architecture that allows more
  bandwidth, quick provisioning, guaranteed QoS in
  a cost effective manner is required.
• PON technology offers mechanism to enable
  sufficient network bandwidth for the delivery of
  new services and applications.
• PON is a distribution architecture that provides
  a unified broadband transport system of converged
  services from homes and buildings, through
  FTT-H,-B, or through FTT-C, -Cab by using xDSL
  transmission technology for residential areas.

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Typical Access Network Construction
Central Office (Exchange)
Customer
Street Cabinet
Distribution Network
Feeder Network
Underground Feed
Overhead Feed
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Overview of DSL Architecture

• DSL is a subscriber access network.
• CPE (Customer Premise Equipment) is connected by
  ADSL to a DSL Access Multiplexer (DSLAM) located
  in the CO of the network service provider.
• DSLAM aggregates traffic from different customers
  and sends it over high speed links towards the
  core of the network (possibly over B-PON) access
  systems..
• DSL supports the delivery of converged data,
  video, and voice traffic.

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Overview of DSL Architecture
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Overview of DSL Architecture
Central Office (CO)
Customer Premises
Broadband Network
Both voice and data use the high frequency
band (40 kHz-1MHz)
DSLAM
IAD
GW
PSTN
Telephone switch
Data Traffic
Voice Traffic (Packetized)
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ATM-based access network
Internet
ATM
BAS
ISP
PSTN
LE
ATM switch
ISP
ATM
xDSL
NT
ADM
user
user
ONU
NT
PON
SONET
ADM
user
ONU
ADM
DSLAM
ADSL
OLT
ONU
user
ADM
ATU-R
ATM/xDSL
VoIP
NT
NT
NT
BAS Broadband access Server LE Local
Exchange ATU-R ATM Interface
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ATM-based access network

• ATM in the access complicated the management of
  the access network, especially when on resource
  reservation is required.
• VCs creation/termination requires a VB5.2
  signaling protocol that is extremely complex.
• IP traffic is expected to be the dominant
  traffic, thus IP/ATM solution will add more
  overhead.

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B-PON DSL Architecture
Customer Premises
Central Office (CO)
PSTN
PON access
OADM
ONU
D500 POTS Card
OLT
GW
Splitter
Copper pair
DSL modem
DSLAM
Metro/backbone
Internet
Data and packetized voice
Combined Signal (Data and analog POTS)
DSL and ONU can be co-located or geographically
separated
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Hybrid xDSL-PON Architecture

• A hybrid xDSL-PON architecture is an effective
  migration to a FSAN delivering converged data,
  video and voice.
• This architecture will provide high bandwidth
  access to customers without requiring to install
  a network that runs in parallel with the PSTN.
• DSLAMs are installed in COs to aggregate traffic
  from multiple high speed connections. Increased
  service coverage area.
• DSLAMs in turn could be co-located with ONUs or
  connected to ONUs.

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Evolution to IP-based Access Networks

• Develop QoS functional model that includes
  functions and features required to support
  stringent SLA.
• Define how QoS mechanisms can be applied at
  various points in the network to achieve
  appropriate performance characteristics.
• Leverage IP QoS mechanisms (e.g. IP Diffserv) to
  deliver QoS.
• Integration of DSL signaling with MPCP signaling
  to achieve a cost effective signaling transparent
  to the protocol framing structure.

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B-PON DSL Architecture (additional slide)
CPE
D500 POTS Card
Splittr
DSL modem
ONU
DSLAM
OLT
Metro ring
DSL broadband access
E-PON access
DSL broadband access
DSL broadband access