module 11: fiber optic networks and the internet
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Slide #1CENTER FORINTEGRATED ACCESS NETWORKS
Module 11: Fiber Optic Networks and the Internet
Dr. Joe TouchPostel Center Director, USC/ISIResearch Assoc. Prof., USC CS and EE/Systems Depts.
Slide #2CENTER FORINTEGRATED ACCESS NETWORKS
What is a network?
Nodes Sources and/or sinks of bits
Links A way to exchange bits between nodes
What’s hard, then? Many types of nodes Many types of links Many ways to interconnect them
Slide #3CENTER FORINTEGRATED ACCESS NETWORKS
Simple Nodes
1-link nodes Sources emits signals
Sinks receives signals
What about the rest? All transform input signal into output signal
Difference is how “deep” into the signal you look…
Slide #4CENTER FORINTEGRATED ACCESS NETWORKS
OSI stack
Layers look increasingly deep ata signal (from the bottom up): App = user program Pres = formatting Sess = multi-transport coord. Transp = order, reliability, flow Net = logical addr, path Link = bits to codes, real addr. Phys = codes over a medium
7 - Application
6 - Presentation
5 - Session
4 - Transport
3 - Network
2 - Link
1 - Physical
Slide #5CENTER FORINTEGRATED ACCESS NETWORKS
Multi-Link Nodes 2-link nodes Amplifier
analog; decreases SNRphysical
Repeater digital; increases SNRphysical
Multi-link nodes Add-drop-mux (ADM)
adds &/or removes part of signalphysical, link layer
Switch permutes inputsphysical, link, network layer
Slide #6CENTER FORINTEGRATED ACCESS NETWORKS
Link types
Direction Simplex – unidirectional Duplex – bidirectional Half-duplex – time-share a single simplex link Radio, e.g., “here I am, over. OK, over.”
Full-duplex – two separate simplex links Multiaccess – more than 2 possible transmitters Broadcast multiaccess Any transmission is received by all nodes
Non-broadcast multiaccess (NBMA)
Slide #7CENTER FORINTEGRATED ACCESS NETWORKS
What’s inside a node?
One or more transmitters
One or more receivers
Both = transciever
Driver
LED or laser
Electrical output
Amp
Photodiode
Electrical input
Slide #8CENTER FORINTEGRATED ACCESS NETWORKS
Transparent vs. opaque
Transparent Not specific to a physical encoding E.g., analog amplifiers, analog switches only
Opaque Specific to a physical encoding E.g., repeaters, frame/packet switches
It’s all relative… WDM is opaque to frequency WDM is transparent to encoding within a frequency
Slide #9CENTER FORINTEGRATED ACCESS NETWORKS
Why are links difficult?
Delay Transmission = bits x bits/symbol x symbols/sec
(symbols/sec = baud rate) Propagation delay
Fiber = 1/R, e.g., 0.6c Coax = 0.6c, ladder = 0.95c, air = 0.9997c
Attenuation Decrease in signal magnitude
Noise Decrease in signal relative to noise
Dispersion Components of signal separate (wavelength, time,…)
Slide #10CENTER FORINTEGRATED ACCESS NETWORKS
Delay
Propagation is SLOWER than other media Symbol rate is FASTER
distance
time
ElectricalHigher propagation (shallow slope)Lower symbol rate (long dashes)
OpticalLower propagation (steep slope)Higher symbol rate (short dashes)
Slide #11CENTER FORINTEGRATED ACCESS NETWORKS
Fixing other link issues
Amplify Mitigates attenuation Increases noise
Filter Decreases noise Can also attenuate
Compensate E.g., fix chromatic dispersion (e.g., as a doublet does)
Regenerate E.g., as a repeater does (OEO)
Slide #12CENTER FORINTEGRATED ACCESS NETWORKS
Typical optical links
Span = fiber without any ‘fixes’ Terrestrial = 80km (60-100km) If one-hop, can be up to 200km Submarine = 50km
Type of optical links Dark = ‘transparent’ AND not connected at its ends Most are asymmetric due to amplifiers, repeaters, etc.
Slide #13CENTER FORINTEGRATED ACCESS NETWORKS
Multihop links
Multihop is easier to ‘wire’ N2 links vs. N
Ways to go multihop Passive switches Switches with amplification OEO
Slide #14CENTER FORINTEGRATED ACCESS NETWORKS
Multihop Topologies
Star Simple core – passive coupler; complex to wire Doesn’t scale well
Ring Easy to wire; hard to maintain during faults Connectivity scales; bandwidth does not
Mesh Most robust Requires more intelligent switching
Bus Like a star, but inconsistent attenuation, timing
Slide #15CENTER FORINTEGRATED ACCESS NETWORKS
Multihop considerations
Devices don’t all work in all topologies Complexity is only one issue
Fault tolerance “self-healing
Symmetry Timing Signal strength Fairness
Active vs. passive OEO “wiring”
Slide #16CENTER FORINTEGRATED ACCESS NETWORKS
Ways to share a link
Dimension of sharing Space division – one party per wire Time division – one party per timeslot Wavelength division – one party per frequency Code division – one party per code
Granularity of sharing Static vs. dynamic Synchronous vs. asynchronous
Slide #17CENTER FORINTEGRATED ACCESS NETWORKS
SONET – sync. TDM
N frames every 125µs90 octets per row
9 ro
ws
3 bytes S,L overhead per row
LS
P
P
PP
Slide #18CENTER FORINTEGRATED ACCESS NETWORKS
SONET speeds
Voice channel = 56 Kbps data + 8 Kbps signalling 7-bit samples, 8,000/sec (resolves 0-4Khz, i.e., voice)
OC = Optical Connect OC-1 – one frame every 125µs
Raw = 9 rows x 90 bytes/row = 51.84 Mbps total Payload = 9 rows x 87 bytes/row = 50.112 Mbps data Exactly 783 voice channels
OC-N = N frames per 125µs Frames are byte-interleaved (why?)
Common rates are OC-3 (155Mbps), OC-12 (622Mbps), OC-196 (10Mbps), OC-768 (40G)
Slide #19CENTER FORINTEGRATED ACCESS NETWORKS
SONET Hops Path
Between endpoints of SONET circuit; controls path Line
Terminated at ADMs, muxes; controls multiplexing, timing offsets Section
Framing over a single hop; alarms, parity check, control channel Regenerated from scratch at a repeater
T
T
T
Mux
MuxM
ux Mux
TADM
Slide #20CENTER FORINTEGRATED ACCESS NETWORKS
SONET Extensions
VCAT – virtual concatenation Inverse muxing (a.k.a. striping) Aggregate K*STS-1 to emulate STS-K (a.k.a. STS-Kv) vs. Contiguous concat (CCAT)
LCAS – link capacity adjustment scheme Dynamic, “hitless” VCAT Adjust VCAT without tearing down/restarting a path
NB: SDH (ITU) != SONET (US) Like ethernet framing != 802.3 VCAT, LCAS are ITU
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Slide #21CENTER FORINTEGRATED ACCESS NETWORKS
What SONET Really Means
Precise timing Fixed-frequency bitstreams Fixed-latency (bit stream arrival doesn’t shift)
Point to point links with add/drop muxing Looks like a train to you Traincars interleave like cars
Fixed bandwidth boundaries (K*51Mb) Still just a bit stream Needs GFP, HDLC, etc. to frame IP packets
Slide #22CENTER FORINTEGRATED ACCESS NETWORKS
ATM – async. TDM
Originally the “killer” replacement for IP Small, fixed-sized cells, but NOT time-aligned like SONET Efficient switching (multistage switches) Efficient interleaving without per-packet delays Complete, kitchen-sink system
Self-inhibiting design 48 byte payload – bad compromise between US and EU Cell size based on 64 Kbps telephone circuit Prime cell size (53B) defeats alignment efficiencies Complexity shifted to endpoints (segmentation and reassembly)
Result Temporarily used as L2 layer; now basically gone
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Slide #23CENTER FORINTEGRATED ACCESS NETWORKS
Problems with TDM
Electronics can’t keep up with optics Can drive 10Gbps, not much faster But optics can support Thz bandwidths
Not transparent Electrical signals don’t propagate far without
repeaters Use WDM Smaller per-channel BW; easier to drive electronics Avoids dispersion problems
Slide #24CENTER FORINTEGRATED ACCESS NETWORKS
Dispersion and its compensation
Dispersion
Dispersion compensation
Time (or distance along a fiber)
Use two kinds of fiber (works like an achromatic doublet)
Slide #25CENTER FORINTEGRATED ACCESS NETWORKS
So what is WDM?
Like TV or radio channels Coarse = few channels, wide gaps Fine = many channels, narrow gaps
Basic components: Separate frequencies – gratings, filters Combine frequencies – couplers Change frequencies – wavelength converters
Slide #26CENTER FORINTEGRATED ACCESS NETWORKS
Typical WDM configuration
Demux = grating Mux = coupler (can use grating in reverse)
ROADM
MUX DEMUX
Dispersion Comp.
Slide #27CENTER FORINTEGRATED ACCESS NETWORKS
Combining WDM and TDM
Goal – avoid the need to reserve wavelengths Planning wavelengths is like booking trains Hard to plan; requires global coordination
Shared access without coordination? Collisions – detect and retry Replace collision with increased noise – coding
OCDMA Optical CDMA with non-orthogonal codes Shared access with graceful degradation under overload
Slide #28CENTER FORINTEGRATED ACCESS NETWORKS
OCDMA
Code = K chips Chip = multidimensional
value, e.g., wavelength and polarization
Codes are not orthogonal Electronic ones are; signals
can cancel Too hard to phase-align optics
to enable destructive interference
λ1
λ2
λ3
λ4
λ5
λ
2 - Dimensional User
Tc1 Tc2 Tc3 Tc4 Tc5
t
λ1
λ2
λ3λ4
λ5
λ1
λ2
λ3λ4
λ5
λ
Codeword (λ, t)Tc1 Tc2 Tc3 Tc4 Tc5
Slide #29CENTER FORINTEGRATED ACCESS NETWORKS
Media Access Control
Shared media challenge Without control, throughput is low and collapses easily
Determines: Transmission order – avoid starvation Transmission priority – for control frames, QoS Line acquisition method – sequence (token), idle channel
detection, timing (TDMA), explicit allocation (FDMA) LAN dimension – size of the ring/bus Transmission duration – coupled to line acquisition, order, and
efficiency (e.g., burst extension in 1Gbps)
Effi
cien
cy
Load
Effi
cien
cy
Load
Slide #30CENTER FORINTEGRATED ACCESS NETWORKS
Pre-Internet
Different network stacks Gateway translators between each pair
Net ANetB Net C
Slide #31CENTER FORINTEGRATED ACCESS NETWORKS
Heterogeneity leads to layering
M different interacting parties need M2 translators
or
M translators + common format… i.e., a layer
Slide #32CENTER FORINTEGRATED ACCESS NETWORKS
What is the Internet?
One protocol to bind them all… IP datagrams as the common interoperation layer
Internet
Net ANetB Net C
Slide #33CENTER FORINTEGRATED ACCESS NETWORKS
The Hourglass Principle
Common interchange format between layers
HTTP/DNS/FTP/NFS/IM
TCP/UDP/SCTP/RTP
Ethernet/FDDI/Sonet
λ PPM, λ CDMA, e- NRZ, e- PCM
HTTP DNS FTP NFS IM
λPPM λCDMA eNRZ ePCM
Slide #34CENTER FORINTEGRATED ACCESS NETWORKS
Timeline (RFC2235)
1945 – WWII ends; V. Bush “As We May Think” (WWW) 1958 – Sputnik launched; ARPA created 1969 – Woodstock; ARPA project sends first packets 1973 – Ethernet 1977 – email standardized 1983 – NCP to TCP/IPv4 switchover 1985 – DNS (vs. hosts.txt file) 1988 – TCP congestion control 1989 – BGP 1991 – WWW 1992 – IP multicast; IP overlays 1997 – 802.11/WiFi; QoS/RSVP 1998 – IPsec 1999 – P2P (Napster) 2000 – IPv6
Slide #35CENTER FORINTEGRATED ACCESS NETWORKS
OSI stack
Travel top-down to the physical App = user program Pres = formatting Sess = multi-transport coord. Transp = order, reliability, flow Net = logical addr, path Link = bits to codes, real addr. Phys = codes over a medium
7 - Application
6 - Presentation
5 - Session
4 - Transport
3 - Network
2 - Link
1 - Physical
Slide #36CENTER FORINTEGRATED ACCESS NETWORKS
Layer details – RFC1208
Physical: given bits, send them on a link Optical: 4B/5B encoding (e.g., Fiberchannel, FDDI), PPM Electrical: Manchester, NRZ, QPSK, QAM
Link: transfer IP packets between adjacent IP nodes “Frame” IP to link address, IP packet to link frame translations
Network: transfer IP packets between non-adjacent IP nodes “Packet” Endian conversion (IEN 137) for addresses (common byte order)
Transport: convert services to IP packets “Segment” TCP: convert user ordered bytestream to segments that fit in IP packets, provide
reliable copy of bytestream at receiver, with congestion control UDP: convert user messages to segments in IP packets DCCP: convert user messages to segments in IP packets, with congestion control
Slide #37CENTER FORINTEGRATED ACCESS NETWORKS
Stack Traversal
7 - HTTP
6 - XML
5 – (none)
4 - TCP
3 - IP
2 – Eth./802.3
1 – 802.11
HTTP
XML
(none)
TCP
IP
PPP
WDM
E/802.3
802.11 GbE
IP
E/802.3
GbE
SONET
WDM WDM
Slide #38CENTER FORINTEGRATED ACCESS NETWORKS
What IS the Internet?
Packets Variable-sized, self-addressed data units
Common message format One universal interchange for data unit: IP packet
Best effort delivery NO guarantees
Globally unique IDs Name = location = forwarding indicator
Local forwarding decisions Based on longest-prefix matching
internet->Internet A deliberately contagious disease (transitive closure)
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Slide #39CENTER FORINTEGRATED ACCESS NETWORKS
Circuits – a sure thing
Trains on a train track Scheduled in advance Allocated whether in use or not Resources locked along entire path Path is fixed
Guarantees no competing traffic Fixed delay, fixed jitter, fixed capacity, lossless Can’t share resources concurrently
Slide #40CENTER FORINTEGRATED ACCESS NETWORKS
Internet Best Effort – NO guarantees
Cars on a highway No need to schedule Resource used only during transit Path can vary, even given identical header
Focuses on sharing Aggregate, concurrent resource use Results in variable delay, variable jitter, variable capacity, and
loss
Slide #41CENTER FORINTEGRATED ACCESS NETWORKS
Bellheads vs. Packetheads
Bellhead Smart core, simple edge
Cheaper for a monopoly Scarce resources motivate
Provider controls services
Packethead Simple core, smart edge Users control services
Slide #42CENTER FORINTEGRATED ACCESS NETWORKSInternet-2 July
20 200442
Path to Optical Routers
Evolution of electronics
Evolution of optics
VCswitches
Tag-switchedpaths
Line-raterouters
WDM Burstswitching
Opticalrouters
Slide #43CENTER FORINTEGRATED ACCESS NETWORKSInternet-2 July
20 200443
Current Optical Focus
WDM as a bonus Needed to overcome dispersion Can be used to partition? or route?
Connection-based/-like traffic ATM/MPLS flow-based setups (MPλS, SWAP) BUT: Setup doubles connection latency
Packet-train setup on-the-fly (OBS, TBS) BUT: Setup requires large gap after first packet
BUT: Both expect long flows or aggregation
Slide #44CENTER FORINTEGRATED ACCESS NETWORKSInternet-2 July
20 200444
Goal – Optical Internet
IP over light No setup Single terabit channels
(no WDM ) Works for short flows,
or for single packets
Implications One channel for routers Use wavelengths for link coding
Slide #45CENTER FORINTEGRATED ACCESS NETWORKSInternet-2 July
20 200445
Challenges
Router Design Forwarding via partial filters TTL decrement IP checksum Queue-free switch design
LAN Issues (second part of this talk) OCDMA MAC design NIC design LAN architecture issues
Slide #46CENTER FORINTEGRATED ACCESS NETWORKS
IPv4 Header
Ver IHL TOS Total Length
ID Flags Fragment Offset
TTL Protocol Header Checksum
Source Address
Destination Address
Red = changes per hopOrange = indexed per hopYellow = changes on generation
Key IPv6 changes:longer addressesno ID or checksum
Slide #47CENTER FORINTEGRATED ACCESS NETWORKSInternet-2 July
20 200447
xElectronicswitch fabric
Inside Current Routers
Forwarder + switch fabric Queues everywhere
Forwarding tableForwarderO/Econverter
Slide #48CENTER FORINTEGRATED ACCESS NETWORKS
Forwarder Functions
Filter Mark, drop as needed
Lookup next hop Longest prefix match
Decrement the TTL To prevent loops
Recompute the IP checksum IPv4 only, but seems persistent
Queue Random access storage for reordering, delay
Checksum
Decr. TTL
Addr match
Filter
Queue
Slide #49CENTER FORINTEGRATED ACCESS NETWORKS
Optical correlator
Sequence of Bragg filters Tuned to match 0,1,X 0,1 requires pairs, X is pass-through
0
1
1 1 1 0
0 0 0 1
Slide #50CENTER FORINTEGRATED ACCESS NETWORKS
Forward via Filters
Bit-subset groups share next-hops Remainder to helper router
R = 0%
1 1 0 1‘MATCH’SignalAND
Input
Threshold = 3
“1” “1” “0” “1”
R = 0%R = 0%R = 0%
Threshold = 0
“1” bits correlator
Match = ‘high’
Match = ‘low’NOT
“0” bits correlator
“1” “1” “0” “1”
Slide #51CENTER FORINTEGRATED ACCESS NETWORKS
TTL Decrement
Unsigned, 8-bit field Decrement by 1 each IP hop Drop if zero before decrement
Current design: 8-bit parallel Arithmetic subtract-by-1
+
0 1 1 0 1 0 0 0
1 1 1 1 1 1 1 1
0 1 1 0 0 1 1 1
Slide #52CENTER FORINTEGRATED ACCESS NETWORKS
Optical Decrementer
Serial LSB-first: Invert until 1 Stop @ 1st “1 (delete if no “1”)
D
Slide #53CENTER FORINTEGRATED ACCESS NETWORKS
All-Optical Decrementer
Implemented using optical latch
Replace latch with fast latching laser
Electronic controlElectronic control
λ MOD
SOA λ1(CW)
Signal inversion10 Gbit/s NRZ
“ databar”
PD
“data”
D-flip flop
MODλpPPLN
D Q
Q
MODλpPPLN
λ packet out w/updated TTL
1 MOD
SOA λ1(CW)
Signal inversion10 Gbit/s NRZ
“ ”
PD
“data”
TTL start
D-flip flop
MODλpPPLN
D Q
Q
MODλpPPLN
2
Slide #54CENTER FORINTEGRATED ACCESS NETWORKS
Internet Checksum
16-bit, 1’s complement sum In 2’s complement sum Add carry back in Can be done in words, doubles, etc. with a folded
result…
Current electronic hardware: 2’s complement accumulators Groups of full-adds; carries wired in a loop
Slide #55CENTER FORINTEGRATED ACCESS NETWORKS
Fast Parallelized Checksum
Recognizes symmetry in 1s complement adds Carries loop around
Xi
CoYi
Ci
SiXj
CoYj
Cj
Sj
Xk
Cok
Yk
Cik
Sk
Xl
Col
Yl
Cl
S
Ii Ii IiIi
Slide #56CENTER FORINTEGRATED ACCESS NETWORKS
Optical Checksum
Serial 1-bit full-adder
Xi
Co
Yi
Ci
S
16 bit delay
16 bit delay
Slide #57CENTER FORINTEGRATED ACCESS NETWORKS
Avoiding Queuing
Electronic routers queue via RAM VOQ requires random-access storage Store for delay Store for reordering
Optical routers can queue But cannot store for arbitrary periods Consider other kinds of queues, e.g., “conveyor
queues”
Slide #58CENTER FORINTEGRATED ACCESS NETWORKS
Packet Aggregator
Supports access networks
With a multiplexer (like horizontal Tetris)
Slide #59CENTER FORINTEGRATED ACCESS NETWORKS
PC Switch Architecture
Slide #60CENTER FORINTEGRATED ACCESS NETWORKS
Various PC-OQ Tests
Slide #61CENTER FORINTEGRATED ACCESS NETWORKS
Number of Packets in Contention
CDF of the number of packets in a contention graph for Poisson arrival with multiple distributions of packet length (mean = 165). The distribution with lower variance is listed first.
Slide #62CENTER FORINTEGRATED ACCESS NETWORKS
Results – no impact
Throughput of a 32x32 switch for quasipoisson-expo(165) for unbuffered switch and precognition optical switch running exhaustive search algorithm.
Slide #63CENTER FORINTEGRATED ACCESS NETWORKS
Lookahead-Shift Mux
Slide #64CENTER FORINTEGRATED ACCESS NETWORKS
Key Properties
Packet-oriented No seg/reassy Native support for variable length
Shifts only No reordering No recirculation
Simple processing One-pass Encourages batch processing Small holding area
Slide #65CENTER FORINTEGRATED ACCESS NETWORKS
Results are Promising…
Slide #66CENTER FORINTEGRATED ACCESS NETWORKS
Optical Interfaces
Back to wavelengths Here they help
MAC protocols Manage shared-access media Avoid congestion collapse, starvation
NIC design Push functions into optics (performance) Coordinate coding, power, timing issues
Overall arch. Issues “Impedence matching” LAN/Access Net/WAN
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Slide #67CENTER FORINTEGRATED ACCESS NETWORKS
Optical MAC Issues
Electronic collision detection (CD) 2 outcomes: 1 or none on channel
“If I can’t hear, nobody can”
Detected by matching sent to received (trivial)
Optical interference detection (ID) 4 outcomes:
I’m OK, they’re OK (no interference) I’m OK, they’re not (destructive) I’m not, they’re OK (self-destructive) I’m not, they’re not (mutually destructive)
Infeasible to detect state of others Amplified by additive nature of noncoherent light
Slide #68CENTER FORINTEGRATED ACCESS NETWORKS
Does a MAC matter?
Throughput improves with good scheduling
• Simulation results• Results are
averaged over 100 trials
• Random phases are chosen uniformly over N
• Results are similar for smaller codesets
• The “good” phasing algorithm is not the optimal algorithm
Slide #69CENTER FORINTEGRATED ACCESS NETWORKS
Interference Avoidance
Electronic: State detection (feedback + matching) Output scheduling (backoff algorithms primarily)
Optical: State Estimation Line state cannot be completely known
State is the set of codes in active use Can measure sum of codes Cannot decompose sum into component codes
No way to factor a sum! Transmission Scheduling
Chip shifting to avoid interference
Slide #70CENTER FORINTEGRATED ACCESS NETWORKS
Interference Avoidance MAC
More complex than CDMA State Estimation Transmission Scheduling
Three variants All avoid collapse in simulation
Vs. Aloha (“no MAC”) One has lowest loss in simulation
Threshold Scheduling (TS) All compatible with CCM
Loss proven by real testbed 4 user testbed 6dBM benefit for TS
Implemented Hardware demonstrated Aloha
(no MAC)
IA-MAC(TS)
Slide #71CENTER FORINTEGRATED ACCESS NETWORKS
Overload analysis N=100
• Simulation results– N=100– Same parameters
otherwise
100 users transmitting
at load of 0.01 each
10000 users transmitting
at load of 0.01 each
Slide #72CENTER FORINTEGRATED ACCESS NETWORKS
Hardware design
Bus
Optical CDMAReceiver
Transmitbuffer
State estimation
module
Transmission scheduling
module
Sampling module
Codewordbuffer
Optical CDMATransmitter
Synchronization module
Receivebuffer
Ranging module
Bus
Transmitfiber
Receivefiber
Controller Feasibillity based on:
10 Gc/s N=100, w =3, = 1, K=3 Diameter of network =
2000m 100 nodes Transmission scheduling
Threshold, th = 0.3 State estimation
Continuous, window ne= 16
Expected utility @load=1.0 Hardware MAC
= 0.25 through No MAC = 0.05 through
Network interface card
Slide #73CENTER FORINTEGRATED ACCESS NETWORKS
MAC Implementation
Slide #74CENTER FORINTEGRATED ACCESS NETWORKS
OCDMA NIC design
Asynchronous OCDMA Avoids need for endpoint sync Code-cycle modulation (CCM) is pair-wise equivalent
of sync; increases throughput of n-chip code by a factor of log2(n)
CCM matches on all n-chip shifts Splitting the signal n-ways defeats the benefit We developed a novel receiver that matches on any
n-chip shift with out splitters
Slide #75CENTER FORINTEGRATED ACCESS NETWORKS
Circular Correllator
Matches any chip-shift without splitter
Slide #76CENTER FORINTEGRATED ACCESS NETWORKS
Receiver Module
Circular correlator on all wavelengths to generate match signal w/shift indicated
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Slide #77CENTER FORINTEGRATED ACCESS NETWORKS
Continuous Reception
Single buffer needs 1-codeword gap Use “double-buffering” tactic:
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Slide #78CENTER FORINTEGRATED ACCESS NETWORKS
Network Arch. Issues
Location of tuners Fixed receiver, variable transmitter fits IP Converse requires a coordination channel
Avoid sequences and hierarchies of contention channels Tokens avoid contention sequences Full routers needed to avoid hierarchies
“Impedence matching” Changes in broadcast, MAC creates boundary
interactions that decrease efficiency, need buffering
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Slide #79CENTER FORINTEGRATED ACCESS NETWORKS
Grand challenges
Ps switching Random-access buffering LSI integration Low signal loss switching Designing to “think optical”
Slide #80CENTER FORINTEGRATED ACCESS NETWORKS
More info…
Many collaborators: Alan Willner, USC Joe Bannister, Aerospace Corp. PhD students: P. Kamanth, S. Suryaputra
Many papers And a few patents…
Many project URLs: www.isi.edu/odcma - NIC/MAC issues www.isi.edu/pow - TTL, header match www.cian-erc.org – precog, Tetris switch, checksum
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