Transcript Document

Architectures and Alternatives for
Broadband Access Networks
ADSL-based Access Network
• DSL is asymmetric technology:
• 6.144 Mbps (downstream)
• 640 Kbps (upstream)
Limited by the length of the line
• 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.
POTS
HomePNA
Ethernet
ADSL-based Access Network
ATU-C
ATU-C
ATU-C
Metro ring
ADM
M
D
F
Access
Server
F
D
F
ADSL
Modem
DSLAMs
MTA
Residential
Gateway
Central office
Cooper pair
Ethernet
HomePNA
Cooper pair
DSLAM
Fiber cable
ATU-C
ATU-C
ATU-C
Cooper pair
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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.
POTS
HomePNA
Ethernet
Cable-based Access Network
ADM
Router
CMTS
ADSL
Modem
Optical node
Tx
Rc
MTA
Residential
Gateway
Distribution Hub
Ethernet
Metro ring
HomePNA
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CMTS
Drop
To TV Set Top Box
Fiber backbone
RF
source
Tx
Rc
Tap
Drop
Distribution
(coaxial cable)
Amplifier
ADSL- vs. Cable- based access network
• HFC network provides
bandwidth than DSL.
relatively
higher
transmission
• 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.
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.
Fiber To The x in Access Systems
Service modes
Passive Optical splitter
Optical fiber
ONU
FTTH
Internet
ONU
Telephone
FTTB
OLT
ONU
FTTC
Interactive
Video
ONU
FTTCab
DSL
Optical Access
Basic Architecture of PON
EPON Downstream
EPON Upstream
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).
Principles of B-PON
ONU
OLT
1.55m
•
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 (1:16, 64)
Optical
splitter/coupler
1.31m
20-25 km
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.
ATM-PON
Downstream frame format
Tframe = 56 cells of 53 bytes
PLOAM ATM
Cell 1
1
ATM PLOAM ATM
2
Cell 28
Cell 27
ATM
Cell 54
53 upstream grants
Upstream frame format
ATM
Cell 1
ATM
Cell 2
ATM
Cell 3
Tframe = 53 cells per frame
ATM
Cell 53
3 bytes overhead per cell (guard time, preamble, delimiter)
PLOAM: Physical Layer Operation
And Maintenance.
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.
APON vs. EPON
APON
EPON
Standard Body
ITU-T/FSAN
IEEE
Speed
155/622 Mbps
1Gbps
Protocol overhead
for IP services
Large
Small
Scalability
Low
High (up to 10Gbps)
Service Integration
Good
Good
Players
ILECs
CLECs
APON vs. EPON
(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.
Typical Access Network Construction
Central Office
Customer
(Exchange)
Street Cabinet
Feeder Network
Distribution Network
Overhead
Feed
Underground
Feed
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 BPON) access systems..
• DSL supports the delivery of converged data, video, and voice traffic.
Overview of DSL Architecture
Central Office (CO)
Customer Premises
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DSLAM
ADSL Band
40 kHz – 1 MHz
Splitter
Splitter
Broadband
Network
DSL modem
Combined Signal
0 to 1 MHz
Voice Band
0 to 4 kHz
Telephone
switch
(PSTN)
Overview of DSL Architecture
Central Office (CO)
Customer Premises
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Broadband
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Both voice and data
use the high
frequency band
(40 kHz-1MHz)
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DSLAM
IAD
GW
PSTN
Telephone
switch
Data Traffic
Voice Traffic (Packetized)
ATM-based access network
Internet
ATM
BAS
ISP
PSTN
LE
ATM
switch
ISP
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user
DSLAM
ADSL
ATM
ADM
user
user
SONET
ADM
ADM
PON
xDSL NT
ONU
NT
ONU
OLT
ONU
user
ADM
ATU-R
ATM/xDSL
VoIP
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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.
B-PON + DSL Architecture
Customer Premises
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(CO)
PSTN
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PON access
D500 POTS
Card
OADM
ONU
OLT
GW
Splitter
Copper pair
DSL modem
DSLAM
Metro/backbone
Data and packetized
voice
Combined Signal
(Data and analog POTS)
DSL and ONU can be co-located or geographically separated
Internet
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.
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.
B-PON
+ DSL Architecture (additional slide)
CPE
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D500 POTS
Card
Splittr
DSL modem
ONU
DSLAM
OLT
DSL broadband access
E-PON access
DSL broadband access
DSL broadband access
Metro ring