Architectures and Alternatives for Broadband Access Networks

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

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

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 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)

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.

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

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).

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

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 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.

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 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

(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 (Exchange) Customer Street Cabinet Distribution Network Feeder Network Underground Feed Overhead 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 B-PON) access systems.. DSL supports the delivery of converged data, video, and voice traffic.

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

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)

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

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 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

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 D500 POTS Card Splittr DSL modem ONU DSLAM OLT Metro ring DSL broadband access E-PON access DSL broadband access DSL broadband access