architectures and alternatives for broadband access networks

Architectures and Alternatives for Broadband Access Networks

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

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

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Eth

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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

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.

Cable-based Access Network

ADM

MT

AA

DSL

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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)

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.

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.

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

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

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)

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

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

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.

Central Office

(Exchange)

Feeder Network

Street Cabinet

Distribution Network

Overhead Feed

Underground Feed

Customer

Typical Access Network Construction

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.

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

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

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

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

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

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.

• 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

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