1. Architectures and Alternatives for Broadband Access Networks

3. Limited by the length of the line
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

4. ADSL-based Access Network
MTA
ADSL
Modem
Residential
Gateway
Ethernet
POTS
HomePNA
Central office
DSLAMs M D F
ATU-C
ATU-C
Cooper pair
HomePNA
ATU-C
Ethernet
Cooper pair
Access
Server
Metro ring
ADM
DSLAM F D
Fiber cable
ATU-C
Cooper pair
ATU-C
ATU-C

5. Cable-based Access Network
Asymmetric technology:
30 Mbps (downstream)
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.

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

7. 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.

8. 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.

9. Fiber To The x in Access Systems
Service modes
Passive Optical splitter
OLT
Optical fiber
ONU
FTTH
Internet
ONU
FTTB
Telephone
ONU
FTTC
Interactive
Video
ONU
FTTCab
DSL

10. Optical Access

11. Basic Architecture of PON

12. EPON Downstream

13. EPON Upstream

14. 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).

15. Optical splitter/coupler
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 (1:16, 64)
OLT
Optical splitter/coupler
1.55m
1.31m
20-25 km

16. ATM-PON APON systems are based upon ATM as the bearer protocol.
Downstream transmission is a continuous ATM stream at a bit rate of Mb/s or 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.

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

18. Ethernet-PON
Ethernet for subscriber access networks combines a minimal set of extensions to the IEEE 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.

19. APON vs. EPON 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
Players
ILECs
CLECs
APON vs. EPON

20. (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.

21. Typical Access Network Construction
Central Office
(Exchange)
Customer
Street Cabinet
Distribution Network
Feeder Network
Underground
Feed
Overhead
Feed

22. 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.

23. Overview of DSL Architecture
Splitter
DSL modem
DSLAM
Broadband Network
Telephone switch
(PSTN)
Customer Premises
Central Office (CO)
Combined Signal
0 to 1 MHz
Voice Band
0 to 4 kHz
ADSL Band
40 kHz – 1 MHz

24. 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)

25. ATM-based access network
Internet
ATM
BAS
ISP
PSTN LE
ATM
switch
ISP
ADM
ATM
xDSL
user
user NT
ONU NT
PON
user
DSLAM
ADM
SONET
ADM
ONU
ADSL
OLT
user
ONU
ADM
ATU-R
ATM/xDSL
VoIP NT NT NT
BAS: Broadband access Server
LE: Local Exchange
ATU-R: ATM Interface

26. 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.

27. B-PON + DSL Architecture
Customer Premises
Central Office
(CO)
PSTN
PON access
OADM
D500 POTS Card
ONU
OLT
Splitter GW
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

28. 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.

29. 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.

30. 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