architectures and alternatives for broadband access networks
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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
ADMAccess Server
MDF
FDF
ATU-C
ATU-C
ATU-C
Cooper pair
Cooper pair
Fiber cable ATU-C
ATU-C
ATU-C
DSLAM
DSLAMs MT
AA
DSL
M
odem
Res
iden
tial
Gat
eway
Eth
erne
t
PO
TS
Hom
ePN
A
Central office
HomePNA T o p o l o g y F i l e E d i t L o c a t e V i e w H e l p
M o u n t 4 3 1 7 4 3 7 1 9 5 0 7 9 % / N e t w o r k
T r a f f i c H e l p Ethernet
Cooper pair
Metro ring
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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
ADM
MT
AA
DSL
M
odem
Res
iden
tial
Gat
eway
Eth
erne
t
PO
TS
Hom
ePN
A
Distribution Hub
HomePNA T o p o l o g y F i l e E d i t L o c a t e V i e w H e l p
M o u n t 4 3 1 7 4 3 7 1 9 5 0 7 9 % / N e t w o r k
T r a f f i c H e l p EthernetMetro ring
TxRc
TxRc
RF source
CMTS
CMTS
Drop To TV Set Top Box
Fiber backbone
Tap DropAmplifier
Optical node
Router
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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OLT
ONU
ONU
ONU
ONU
Fiber To The x in Access Systems
Internet
Telephone
Interactive Video
Optical fiber
Passive Optical splitter
FTTH
FTTB
FTTC
FTTCab
Service modes
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
20-25 km
Optical splitter/coupler
OLT
ONU
1.31m
1.55m
• 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)
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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
ATM Cell 1
ATM Cell 27
ATM Cell 28
ATM Cell 54
PLOAM1
PLOAM2
ATM Cell 1
ATM Cell 2
ATM Cell 3
ATM Cell 53
Upstream frame format
Downstream frame format
3 bytes overhead per cell (guard time, preamble, delimiter)
Tframe = 56 cells of 53 bytes
Tframe = 53 cells per frame
PLOAM: Physical Layer Operation And Maintenance.
53 upstream grants
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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 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
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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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Central Office
(Exchange)
Feeder Network
Street Cabinet
Distribution Network
Overhead Feed
Underground Feed
Customer
Typical Access Network Construction
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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
T o p o l o g y F i l e E d i t L o c a t e V i e w H e l p
M o u n t 4 3 1 7 4 3 7 1 9 5 0 7 9 % / N e t w o r k
T r a f f i c H e l p
Splitter
DSL modem
DSLAM
Broadband Network
Telephone switch
(PSTN)
Customer PremisesCentral Office (CO)
Combined Signal0 to 1 MHz
Voice Band0 to 4 kHz
ADSL Band40 kHz – 1 MHz
Splitter
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PSTN
T o p o l o g y F i l e E d i t L o c a t e V i e w H e l p
M o u n t 4 3 1 7 4 3 7 1 9 5 0 7 9 % / N e t w o r k
T r a f f i c H e l p
DSLAM
Broadband Network
Telephone switch
Customer PremisesCentral Office (CO)
IAD
GW
Data Traffic
Voice Traffic (Packetized)
Both voice and data use the high
frequency band(40 kHz-1MHz)
Overview of DSL Architecture
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ATM-based access network
T o p o l o g y F i l e E d i t L o c a t e V i e w H e l p
M o u n t 4 3 1 7 4 3 7 1 9 5 0 7 9 % / N e t w o r k
T r a f f i c H e l p
user
user user
DSLAM
T o p o l o g y F i l e E d i t L o c a t e V i e w H e l p
M o u n t 4 3 1 7 4 3 7 1 9 5 0 7 9 % / N e t w o r k
T r a f f i c H e l p
user
ADSL
ATM
PON
ONU
ONU
ONU
xDSL
NT
NT
T o p o l o g y F i l e E d i t L o c a t e V i e w H e l p
M o u n t 4 3 1 7 4 3 7 1 9 5 0 7 9 % / N e t w o r k
T r a f f i c H e l p T o p o l o g y
F i l e E d i t L o c a t e V i e w H e l p M o u n t 4 3 1 7 4 3 7 1 9 5 0 7 9 % / N e t w o r k
T r a f f i c H e l p
NT NT NT
ADM
ATM/xDSL
SONET
ADM
ADM ADM
OLT
PSTNLE
ATM switch
ATU-R
VoIP
ATMISP
ISP
Internet
BAS
BAS: Broadband access ServerLE: Local ExchangeATU-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
Combined Signal(Data and analog POTS)
T o p o l o g y F i l e E d i t L o c a t e V i e w H e l p
M o u n t 4 3 1 7 4 3 7 1 9 5 0 7 9 % / N e t w o r k
T r a f f i c H e l p
Splitter
DSL modem
DSLAM
Customer Premises Central Office(CO)
Data and packetized voice
D500 POTS Card
PON access
Metro/backbone
PSTN
Internet
OADM
GWOLT
ONU
Copper pair
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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• 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.
Evolution to IP-based Access Networks
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B-PON + DSL Architecture (additional slide) T o p o l o g y
F i l e E d i t L o c a t e V i e w H e l p M o u n t 4 3 1 7 4 3 7 1 9 5 0 7 9 % / N e t w o r k
T r a f f i c H e l p
Splittr
DSL modem
DSLAM
D500 POTS Card
E-PON access
OLT
ONU
Metro ring
CPE
DSL broadband access
DSL broadband accessDSL broadband access