计算机网络工程PPT

• 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
• Statistical multiplexing
• DSL does not require the deployment of a new network: it runs on the existing PSTN infrastructure.
ADSL-based Access Network
• 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
POTS HomePNA Ethernet
Central office
DSLAMs
ATU-C ATU-C ATU-C
M D F
Cooper pair
Ethernet
Residential Gateway
ADSL Modem
MTA
HomePNA
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• 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:
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.
Cable-based Access Network
POTS HomePNA Ethernet
Distribution Hub
Optical node
ADM Metro ring
Router
CMTS
Tx Rc
Residential Gateway
ADSL Modem
MTA
Ethernet
HomePNA
Help
Moun t Network Traffic H lp 4 3 1 e 1950 / 7437 79%
Metro ring
ADM
Access Server
Cooper pair
F D F
DSLAM
Fiber cable
ATU-C ATU-C ATU-C
Cooper pair
Cable-based Access Network
Tap
Drop
Distribution (coaxial cable)
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.
• 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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Moun t Network Traffic H lp 4 3 1 e 1950 / 7437 79%
CMTS
Drop To TV Set Top Box
Fiber backbone
RF source
Tx Rc
Amplifier
Service modes Passive Optical splitter
Optical fiber
NU
FTTB
Telephone
OLT
ONU
FTTC
Interactive Video
ONU
FTTCab DSL
Optical Access
Basic Architecture of PON
• 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.
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.
• 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.
1.31m
•
• •
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 .
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:
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)
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.