Transcript Slide 1

Evolution of Access Networks
[email protected]
7/8/2015
1
What is Wide Area Network (WAN)?
MCI Network
http://www1.worldcom.com/global/about/network/maps/northam/
7/8/2015
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What is Metropolitan Area Network (MAN)?
Metromedia Fiber
Network, Inc.
San Francisco Bay
Area MAN
(dark fiber)
http://www.mfn.com/network/
map_bayarea.shtm
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What is Access Network?
Access network in Davis (imaginary)
•
Connects Central Office to end customers (subscribers)
•
Also called subscriber network, “last mile”/”first mile”, local loop
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Access Network Technologies
• Dial-up
• ISDN
• T1/E1
• DSL
• Cable
• What is next?
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Analog Dial-up line
•
2.4 / 4.8 / 9.6 / 14.4 / 28.8 / 56 Kbps
•
Uses one voice channel (64 Kbps) to reach ISP’s modem across telephone network
•
Analog from user to Central office, then digital (DS0)
•
Actual speed depends on distance
•
Charged per minute
TALK / DATA
TALK
RS CS TR RD TD CD
Modem
Internet Cloud
Class V switch
Modem Pool
Modem Bank
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Class V switch
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Integrated Services Digital Network (ISDN)
• 2 bearer channels (B channels) – 64 Kbps
each. B channel can be used for voice or data
• 1 data channel (16 Kbps) for signaling.
• Total 144 Kbps.
• Digital all the way.
• Charged per minute
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T1/E1
• T1 – 24 D0 channels (1.544 Mbps)
• E1 used in Europe (30 D0 channels)
• Uses 4 wires and customer switching
unit (CSU)
• Must be provisioned be network
operator (very difficult and expensive)
• Permanent circuit! (always on)
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Digital Subscriber Line (DSL)
• Uses one twisted pair for voice and data
(different frequency)
• Data rates from 144 Kbps to 1.5 Mbps
(depends on distance and line quality)
Internet Cloud
• Distance limited to 18000 ft (5.5km). In
most cases is not available if distance from
CO exceeds 12000 ft.
DSL Access
Multiplexor
(DSLAM)
Modem Bank
TALK / DATA
TALK
RS CS TR RD TD CD
DSL modem
HF
Filter
PC
1 2
3
4 5
7 8
6
9
8
#
*
Class V switch
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Cable Modem
• Tree-like cable
network
• Serves many
subscribers (~2000)
• Requires cable
modem and CM
terminating system
(CMTS)
• Always on
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Fiber-to-the-Home/Business (FTTH/B)
• Fiber constantly reaching deeper into
the subscriber area
– Remote DSLAMs use fiber feeds
– CATV uses fiber from head end to remote
nodes (HFC architecture)
• Next generation of access networks will
bring fiber all the way to the customer
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Point-to-Point vs. PON
(a) Point-to-point network
N fibers
2N transceivers
CO
N subscribers
L km
(b) Curb-switched network
1 fiber
2N+2 transceivers
CO
Curb switch
Passive
optical
splitter
(c) Passive optical network
1 fiber
N transceivers
CO
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N subscribers
L km
L km
N subscribers
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Passive couplers
•
Fused fiber or waveguide technology
•
NxN coupler created by combining
multiple 2x2 couplers
•
Splitter: coupler with only one input
used
•
Combiner: coupler with only one
output used
(a) 4-stage 8x8 coupler
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(b) 3-stage 8x8 coupler
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PON topologies
ONU1
ONU2
ONU1
ONU2
ONU3
OLT
ONU3
OLT
ONU4
ONU4
ONU5
ONU5
(a) Tree topology (using 1:N splitter)
(c) Ring topology (using 2x2 tap couplers)
ONU1
ONU1
ONU2
ONU2
ONU3
OLT
OLT
ONU5
ONU3
ONU4
(b) Bus topology (using 1:2 tap couplers)
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ONU4
ONU5
(d) Tree with redundant trunk (using 2:N splitter)
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WDM vs. TDM PON
• Non-traditional connectivity
– Downstream: broadcast
– Upstream: Point-to-point,
but collisions possible
ONU 1
OLT
• Upstream channels must be
separated
ONU N
– WDM
• each ONU must have
different 
• OLT must have a receiver
array
– TDM
• Receiver and electronics
run at higher speed
• time synchronization
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ONU 1
OLT
ONU N
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Single-Fiber PON
• Use 2 wavelength, but save fiber (repair and maintenance)
• Use TDM in the upstream to avoid collisions
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ATM Passive Optical Network (APON)
• Uses ATM cells to carry data traffic
– Full Service Access Networks (FSAN)
Initiative - 1995
– Too expensive
– Too complicated
– Less efficient (than Ethernet)
• Example: For 44-byte IP datagram,
Ethernet will use 64-byte frame + 8-byte
preamble + 12-byte IFG = 84 bytes
ATM will add 12-byte AAL5 and will use 2 cells =
106 bytes
• For tri-modal packet distribution (CAIDA.org) cell
tax is 13%
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Ethernet Passive Optical Network (EPON)
1
• Use Ethernet frames
to carry the data
• Dynamic bandwidth
allocation (DBA) –
slot size depends on
queue length
(request/grant
scheme)
USER 1
2
1
3
1
1
• Static bandwidth
allocation (SBA) –
each user gets fixed
slot size
1
ONU 1
3
1
1
2
3
1
2
2
OLT
ONU 2
USER 2
1
3
1
2
802.3 frame
header
Payload
3
FCS
ONU 3
USER 3
Downstream traffic
ONU 1
USER 1
1
1
1
OLT
ONU 2
1 1
USER 2
2
2
3 3 3
2
time slot
3
802.3 frame
3
3
ONU 3
USER 3
3
header
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Payload
3
3
FCS
Upstream traffic
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IPACT – Dynamic Bandwidth Allocation Scheme
ONU
1
2
3
OLT
ONU1
ONU2
ONU3
Bytes
6000
3200
1800
Polling Table
RTT
200
170
120
Tx 6000
OLT
Rx
Tx
6000 bytes
550
6000
Rx
ONU
1
2
3
Tx
ONU1
ONU2
Rx
Tx
ONU3
Rx
Bytes
6000
3200
1800
RTT
200
170
120
Tx 6000
3200
Rx
Tx
6000 bytes
OLT
ONU1
ONU2
ONU3
Bytes
6000
3200
1800
Tx 6000
Tx
Tx
Rx
OLT
6000 bytes
550
6000
Tx
Tx
ONU3
Rx
(b)
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ONU1
ONU2
Rx
550
550
3200 bytes 5700
3200
Rx
Tx
Rx
ONU
1
2
3
3200
1800
6000 bytes
RTT
200
170
120
(c)
RTT
200
170
120
Rx
Bytes
550
3200
1800
6000
Rx
(a)
ONU
1
2
3
ONU
1
2
3
Bytes
6000
3200
1800
Tx 6000
RTT
200
170
120
3200
Rx
Tx
Rx
Tx
Rx
6000 bytes
ONU
1
2
3
Bytes
550
3200
1800
1800
6000 bytes
550
RTT
200
170
120
ONU
1
2
3
Bytes
550
5700
1800
RTT
200
170
120
3200 bytes 5700
550
6000
3200 bytes 5700
3200
Tx
1800 bytes 4400
1800
Rx
(d)
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SBA vs. DBA
Averag e P acket D elay
Averag e Qu eu e S iz e
1.0E + 01
1.0E + 08
1.0E + 07
1.0E + 00
1.0E -01
B yte s
De lay ( s)
1.0E + 06
1.0E + 05
1.0E -02
1.0E + 04
TDM A
1.0E -03
TDM A
1.0E + 03
IP A CT
IP A CT
1.0E + 02
1.0E -04
0.0
0.2
0.4
0.6
O ffered Load
0.8
1.0
0.0
0.2
0.4
0.6
0.8
1.0
Offered Load
IPACT: Interleaved Polling with Adaptive Cycle Time
(Photonic Network Communications, vol. 4, no. 1, January 2002)
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Upgrade scenarios
• Wavelength upgrade
–
–
–
–
Move premium ONUs to separate wavelengths
Less ONUs per  = more bandwidth per ONU
Inventory problem (ONUs are different)
Receiver array in OLT
• Rate upgrade
– Increase rate of EPON (1 Gbps -> 10 Gbps)
– OLT should receive new rate (from premium ONUs) and old
rates (from non-premium ONUs)
– Dispersion penalties affect maximum distance
• Spatial upgrade
– Split 32-user EPON into two 16-user EPONs
– Deploy multiple trunks or splitter in the CO
– Eventually becomes point-to-point topology
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Conclusion
• Advantages of PON
– Allows longer distances between CO and
customer premises.
– Minimizes fiber deployment
– Provides higher bandwidth
– Allows downstream video broadcasting.
– Eliminates multiplexers and demultiplexers
in the field
– Transparent. Easy upgrades to higher bit
rates or additional wavelengths
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