Transcript COMP680E by M. Hamdi

Switching Architectures
for Optical Networks
COMP680E by M. Hamdi
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Internet Reality
Data
Center
SONET
SONET
DWD
M
DWD
M
SONET
SONET
Access
Metro
Long Haul
COMP680E by M. Hamdi
Metro
Access
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Hierarchies of Networks: IP / ATM /
SONET / WDM
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Why Optical?
• Enormous bandwidth made available
– DWDM makes ~160 channels/ possible in a fiber
– Each wavelength “potentially” carries about 40 Gbps
– Hence Tbps speeds become a reality
• Low bit error rates
– 10-9 as compared to 10-5 for copper wires
• Very large distance transmissions with very little
amplification.
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Dense Wave Division Multiplexing
(DWDM)
1
2
3
4
Long-haul fiber
Output fibers
Multiple wavelength bands on each fiber
– Transmit by combining multiple lasers @ different
frequencies
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Anatomy of a DWDM System
Terminal B
Terminal A
Transponder
Interfaces
M
U
X
PostAmp
Line Amplifiers
Direct
Connections
PreAmp
D
E
M
U
X
Transponder
Interfaces
Direct
Connections
Basic building blocks
• Optical amplifiers
• Optical multiplexers
• Stable optical sources
COMP680E by M. Hamdi
User Services & Core Transport
EDGE
Frame Relay
IP
IP
Router
CORE
Frame
Relay
ATM
ATM
Switch
Lease Lines
Sonet
ADM
Users
Services
TDM
Switch
OC-3
OC-3
OC-12
STS-1
STS-1
STS-1
Service Provider
Networks
Transport Provider
Networks
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• Provisioned
SONET circuits.
• Aggregated into
Lamdbas.
Core Transport Services
Circuit
Origin
• Carried over
Fiber optic cables.
Circuit
Destination
OC-3
OC-3
OC-12
STS-1
STS-1
STS-1
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WDM Network: Wavelength View
WDM link
Edge Router
Legacy
Interfaces
Legacy
( e.g., PoS, Gigabit
Interfaces
Ethernet, IP/ATM)
Interfaces
Legacy
Interfaces
Optical Switch
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Relationship of IP and Optical
• Optical brings
–Bandwidth multiplication
–Network simplicity (removal of
redundant layers)
• IP brings
–Scalable, mature control plane
–Universal OS and application
support
–Global Internet
• Collectively IP and Optical
(IP+Optical) introduces a set of
service-enabling technologies
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Typical Super POP
Interconnectio
n
Network
Core
IP
router
DWDM
DWDM
+
Metro
Ring ADM
Large
Multi-service
Aggregation
Switch
Voice
Switch
Core
ATM
Switch
OXC
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SONET
Coupler
&
Opt.amp
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Typical POP
Voice
Switch
D
W
D
M
OXC
D
W
D
M
SONET-XC
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What are the Challenges with Optical
Networks?
• Processing: Needs to be done with electronics
– Network configuration and management
– Packet processing and scheduling
– Resource allocation, etc.
• Traffic Buffering
– Optics still not mature for this (use Delay Fiber Lines)
– 1 pkt = 12 kbits @ 10 Gbps requires 1.2 s of delay => 360
m of fiber)
• Switch configuration
– Relatively slow
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Optical Hardware
• Optical Add-Drop Multiplexer (OADM)
– Allows transit traffic to bypass node optically
1
2
3
1
OADM
2
’3
3
’3
Add and Drop
DCS
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Wavelength Converters
• Improve utilization of available wavelengths on links
• All-optical WCs being developed
• Greatly reduce blocking probabilities
3
2
3
2
WC
No  converters
1
New request
1 3
With  converters
1
New request
1 3
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Late 90s: Backbone Nodes
ADM
ADM
ADM
ADM
Digital Crossconnect
DWDM
Multiplexer & Demultiplexer
IP
Router
ATM
Switch
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Problems
• About 80% traffic through each node is “pass-
through”
– No need to electronically process such traffic
• 80-channel DWDM requires 80 ADMs
• Speed upgrade requires replacing all the ADMs in
the node
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Today: Optical Cross Connect (OXC)
Optical
Crossconnect
DWDM
ATM
Backbone
Switch
Digital
Cross
Connect
Terabit
IP
Router
Multiplexer & Demultiplexer
IP
Router
ATM
Switch
COMP680E by M. Hamdi
Source: JPMS
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Wavelength Cross-Connects (WXCs)
• A WDM network consists of wavelength cross-connects (WXCs) (OXC)
interconnected by fiber links.
• 2 Types of WXCs
– Wavelength selective cross-connect (WSXC)
• Route a message arriving at an incoming fiber on some
wavelength to an outgoing fiber on the same wavelength.
• Wavelength continuity constraint
– Wavelength interchanging cross-connect (WIXC)
• Wavelength conversion employed
• Yield better performance
• Expensive
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Wavelength Router
Wavelength Router
Control Plane:
Wavelength Routing
Intelligence
Data Plane:
Optical Cross
Connect Matrix
Unidirectional
DWDM Links to
other Wavelength
Routers
Single Channel Links to
IP Routers, SDH Muxes,
...
COMP680E by M. Hamdi
Unidirectional
DWDM Links to
other Wavelength
Routers
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Optical Network Architecture
UNI
Mesh Optical Network
UNI
IP Network
IP Network
IP Router
OXC Control unit
Optical Cross
Connect (OXC)
Control Path
Data Path
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OXC Control Unit
• Each OXC has a control unit
• Responsible for switch configuration
• Communicates with adjacent OXCs or the client
network through single-hop light paths
– These are Control light paths
– Use standard signaling protocol like GMPLS for
control functions
• Data light paths carry the data flow
– Originate and terminate at client networks/edge routers
and transparently traverse the core
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Optical Cross-connects (No wavelength
conversion)
2
4
All Optical Cross-connect (OXC)
Also known as Photonic
Cross-connect (PXC)
1
3
Optical
Switch
Fabric
3
4
1
2
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Optical Cross-Connect with Full Wavelength
Conversion
Wavelength
Converters
2
1
2
n
1,2, ... ,n
1
1
2
n
1,2, ... ,n
2
.
.
.
1,2, ... ,n
M
Wavelength
Demux
1,2, ... ,n
1
n
1
1
2
n
1
2
n
n
1
2
Optical CrossBar
Switch
1,2, ... ,n
2
.
.
.
1,2, ... ,n
M
Wavelength
Mux
• M demultiplexers at incoming side
• M multiplexers at outgoing side
• Mn x Mn optical switch has wavelength converters at switch
outputs
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Wavelength Router with O/E and E/O
Cross-Connect
Incoming Interface
Incoming Wavelength
Outgoing Interface
Outgoing Wavelength
1
3
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O-E-O Crossconnect Switch (OXC)
Incoming
fibers
Demux
1
2
N
WDM
(many λs)
Individual wavelengths
O
O
O/E
E/O
E
O/E
E/O
O/E
O/E
O/E
O/E
E/O
E/O
E/O
E/O
O/E
O/E
O/E
E/O
E/O
E/O
Outgoing
fibers
Mux
1
2
N
Switches information signal on a particular wavelength on an
incoming fiber to (another) wavelength on an outgoing fiber.
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Optical core network
Opaque (O-E-O) and transparent (O-O) sections
E/O
Client
signals
Transparent
optical island
O/E
O
O
from other nodes
O
O
O
E
O
O
E
E
O
O
to other nodes
E
Opaque opticalCOMP680E
network
by M. Hamdi
O
O
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OEO vs. All-Optical Switches
OEO
All-Optical
• Capable of status monitoring
• Optical signal regenerated –
improve signal-to-noise ratio
• Traffic grooming at various levels
• Less aggregated throughput
• More expensive
• More power consumption
• Unable to monitor the contents of
the data stream
• Only optical amplification – signalto-noise ratio degraded with distance
• No traffic grooming in subwavelength level
• Higher aggregated throughput
• ~10X cost saving
• ~10X power saving
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Large customers buy “lightpaths”
A lightpath is a series of wavelength links from end to end.
optical
fibers
One fiber
Repeater
cross-connect
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Hierarchical switching: Node with switches
of different granularities
A. Entire fibers
O
O
Fibers
O
Fibers
B. Wavelength
subsets
O
O
O
C. Individual
wavelengths
O
E
O
COMP680E by M. Hamdi
“Express
trains”
“Local
trains”
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Wide Area Network (WAN)
WAN :
Up to 200-500 wavelengths
40-160 Gbit/s/
wavebands (> 10 )
OXC: Optical Wavelength/Waveband Cross
Connect
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Packet (a) vs. Burst (b) Switching
Header recognition,
processing, and generation
Payload
C
Header
A
Setup
Synchronizer
1
2
A
New
headers
(a)
Control
wavelengths
Control
packets
D
C
2
2
O/E/O
1
Control packet processing
(setup/bandwidth reservation)
Offset time
2
B
2
FDL’s
1
Data
wavelengths
1
2
Fixed-length
(but unaligned)
B
Switch
1
Incoming
fibers
2
Switch
1
1
Data bursts
(b)
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MAN (Country / Region)
IP
packets
optical
burst
formation
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Optical Switching Technologies
•
•
•
•
•
•
•
•
MEMs – MicroElectroMechanical
Liquid Crystal
Opto-Mechanical
Bubble Technology
Thermo-optic (Silica, Polymer)
Electro-optic (LiNb03, SOA, InP)
Acousto-optic
Others…
Maturity of technology, Switching speed, Scalability, Cost,
Reliability (moving components or not), etc.
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MEMS Switches for Optical Cross-Connect
Moveable Micromirror
Proven technology, switching time (10 to 25 msec), moving mirrors is a
reliability problem.
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WDM “transparent” transmission system
(O-O nodes)
Wavelengths
disaggregator
O
Fibers
Wavelengths
aggregator
O
O
O
multiple
λs
O
O
Optical switching fabric (MEMS devices, etc.)
Incoming fiber
Tiny mirrors
COMP680E by M. Hamdi
Outgoing fibers
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Upcoming Optical Technologies
• WDM routing is circuit switched
– Resources are wasted if enough data is not sent
– Wastage more prominent in optical networks
• Techniques for eliminating resource wastage
– Burst Switching
– Packet Switching
• Optical burst switching (OBS) is a new method to transmit data
• A burst has an intermediate characteristics compared to the basic
switching units in circuit and packet switching, which are a
session and a packet, respectively
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Optical Burst Switching (OBS)
• Group of packets a grouped in to ‘bursts’, which is
the transmission unit
• Before the transmission, a control packet is sent out
– The control packet contains the information of burst
arrival time, burst duration, and destination address
• Resources are reserved for this burst along the
switches along the way
• The burst is then transmitted
• Reservations are torn down after the burst
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Optical Burst Switching (OBS)
• Has intermediate characteristics compared circuit
switching and packet switching
• If two bursts collide, the later burst will be dropped
because of zero buffering
• Bandwidth is reserved in a one-way process, without a
ACK, whereas in circuit switching is a two-way process
• A burst will cut through intermediate nodes without
being buffered
– In packet switching, a packet is stored and forwarded at each
intermediate node
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Optical Burst Switching (OBS)
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Optical Packet Switching
• Fully utilizes the advantages of statistical
multiplexing
• Optical switching and buffering
• Packet has Header + Payload
– Separated at an optical switch
• Header sent to the electronic control unit, which
configures the switch for packet forwarding
• Payload remains in optical domain, and is recombined with the header at output interface
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Optical Packet Switch
• Has
– Input interface, Switching fabric, Output interface and
control unit
• Input interface separates payload and header
• Control unit operates in electronic domain and
configures the switch fabric
• Output interface regenerates optical signals and inserts
packet headers
• Issues in optical packet switches
– Synchronization
– Contention resolution
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• Main operation in a switch:
–
–
–
–
The header and the payload are separated.
Header is processed electronically.
Payload remains as an optical signal throughout the switch.
Payload and header are re-combined at the output interface.
hdr
payload
CPU
hdr
payload
hdr
payload
Wavelength i
input port j
Re-combined
Wavelength i
output port j
Optical
packet
Optical switch
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Output port contention
• Assuming a non-blocking switching matrix, more than one
packet may arrive at the same output port at the same time.
Input ports
Optical Switch
payloadhdr
.
.
.
payloadhdr
.
.
.
payloadhdr
COMP680E by M. Hamdi
Output ports
.
.
.
.
.
.
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OPS Architecture: Synchronization
Occurs in electronic switches – solved by input buffering
Slotted networks
•Fixed packet size
•Synchronization stages required
Sync.
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OPS Architecture: Synchronization
Slotted networks
•Fixed packet size
•Synchronization stages required
Sync.
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OPS Architecture: Synchronization
Slotted networks
•Fixed packet size
•Synchronization stages required
Sync.
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OPS Architecture: Synchronization
Slotted networks
•Fixed packet size
•Synchronization stages required
Sync.
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OPS Architecture: Synchronization
Slotted networks
•Fixed packet size
•Synchronization stages required
Sync.
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OPS Architecture: Synchronization
Sync.
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OPS: Contention Resolution
• More than one packet trying to go out of the same
output port at the same time
– Occurs in electronic switches too and is resolved by
buffering the packets at the output
– Optical buffering ?
• Solutions for contention
– Optical Buffering
– Wavelength multiplexing
– Deflection routing
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OPS Architecture
Contention Resolutions
1
2
3
1
1
2
1
4
3
4
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OPS: Contention Resolution
• Optical Buffering
– Should hold an optical signal
• How? By delaying it using Optical Delay Lines (ODL)
– ODLs are acceptable in prototypes, but not commercially
viable
– Can convert the signal to electronic domain, store, and reconvert the signal back to optical domain
• Electronic memories too slow for optical networks
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OPS Architecture
Contention Resolutions
•Optical buffering
1
1
2
3
1
2
1
3
4
4
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OPS Architecture
Contention Resolutions
•Optical buffering
1
1
2
2
3
3
4
4
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OPS Architecture
Contention Resolutions
•Optical buffering
1
1
1
2
2
3
3
4
4
1
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OPS: Contention Resolution
• Wavelength multiplexing
– Resolve contention by transmitting on different
wavelengths
– Requires wavelength converters - $$$
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OPS Architecture
Contention Resolutions
•Wavelength conversion
1
1
1
1
2
2
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OPS Architecture
Contention Resolutions
•Wavelength conversion
1
1
2
2
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OPS Architecture
Contention Resolutions
•Wavelength conversion
1
1
1
1
2
2
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OPS Architecture
Contention Resolutions
•Wavelength conversion
1
1
2
2
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OPS Architecture
Contention Resolutions
•Wavelength conversion
1
1
1
1
2
2
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Deflection routing
• When there is a conflict between two optical packets, one will
be routed to the correct output port, and the other will be
routed to any other available output port.
• A deflected optical packet may follow a longer path to its
destination. In view of this:
– The end-to-end delay for an optical packet may be
unacceptably high.
– Optical packets may have to be re-ordered at the destination
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Electronic Switches Using
Optical Crossbars
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Scalable Multi-Rack Switch Architecture
Optical links
Line card
rack
Switch Core
• Number of linecards is limited in a single rack
– Limited power supplement, i.e. 10KW
– Physical consideration, i.e. temperature, humidity
• Scaling to multiple racks
– Fiber links and central fabrics
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Logical Architecture of Multi-rack Switches
Scheduler
Line Card
Local
Fiber I/O
Framer
Buffers
Laser
Laser
Line Card
Laser
Laser
Local
Buffers
Framer
Fiber I/O
Crossbar
Line Card
Local
Fiber I/O
Framer
Buffers
Line Card
Laser
Laser
Laser
Laser
Local
Buffers
Framer
Fiber I/O
Switch Fabric System
• Optical I/O interfaces connected to WDM fibers
• Electronic packet processing and buffering
– Optical buffering, i.e. fiber delay lines, is costly and not mature
• Optical interconnect
– Higher bandwidth, lower latency and extended link length than copper
twisted lines
• Switch fabric: electronic? Optical?
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Optical Switch Fabric
Scheduler
Line Card
Local
Fiber I/O
Framer
Buffers
Laser
Laser
Line Card
Laser
Local
Laser
Buffers
Framer
Fiber I/O
Crossbar
Line Card
Local
Fiber I/O
Framer
Buffers
Line Card
Laser
Laser
Laser
Laser
Local
Buffers
Framer
Fiber I/O
Switch Fabric System
•
Less optical-to-electrical conversion inside switch
– Cheaper, physically smaller
•
Compare to electronic fabric, optical fabric brings advantages in
–
–
–
–
•
Low power requirement
Scalability
Port density
High capacity
Technologies that can be used
– 2D/3D MEMS, liquid crystal, bubbles, thermo-optic, etc.
•
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Hybrid architecture takes advantage of the strengths of both electronics and optics
Electronic Vs. Optical Fabric
Electronic
Trans. Buffer InterLine
connection
Inter- Buffer Trans.
connection
Line
Switching
Fabric
Optical
Electronic
E/O or O/E
Conversion
Optical
Trans. Buffer InterLine
connection
Inter- Buffer Trans.
connection
Line
Switching
Fabric
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Multi-rack Hybrid Packet Switch
Rack
Buf f er
E/O
O/E
Buf f er
Buf f er
E/O
O/E
Buf f er
Optical Optical
Fiber Crossbar
Buf f er
E/O
Optical
Fiber
O/E
Buf f er
O/E
Buf f er
Linecard
Buf f er
E/O
Switch Core
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Features of Optical Fabric
• Less E/O or O/E conversion
• High capacity
• Low power consumption
• Less cost
However,
• Reconfiguration overhead (50-100ns)
– Tuning of lasers (20-30ns)
– System clock synchronization (10-20ns or higher)
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Scheduling Under Reconfiguration Overhead
• Traditional slot-by-slot approach
Scheduler
Schedule Reconfigure Transfer
Time Line
• Low bandwidth usage
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Reduced Rate Scheduling
Fabric setup (reconfigure)
Traffic transfer
Time slot
Slot-by-slot Scheduling, zero fabric setup time
Slot-by-slot Scheduling with reconfigure delay
Reduced rate Scheduling, each schedule is held for some time
•
Challenge: fabric reconfiguration delay
–
•
Traditional slot-by-slot scheduling brings lots of overhead
Solution: slow down the scheduling frequency to compensate
–
•
Each schedule will be held for some time
Scheduling task
1.
2.
Find out the matching
Determine the holding time
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Scheduling Under Reconfiguration
Overhead
• Reduce the scheduling rate
– Bandwidth Usage = Transfer/(Reconfigure+Transfer)
Constant
• Approaches
– Batch scheduling: TSA-based
– Single scheduling: Schedule + Hold
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Single Scheduling
• Schedule + Hold
– One schedule is generated each time
– Each schedule is held for some time (holding time)
– Holding time can be fixed or variable
– Example: LQF+Hold
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Routing and
Wavelength
Assignment
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Optical Circuit Switching
• An optical path established between two nodes
• Created by allocation of a wavelength throughout the path.
• Provides a ‘circuit switched’ interconnection between two nodes.
– Path setup takes at least one RTT
– No optical buffers since path is pre-set
Desirable to establish light paths between every pair of nodes.
• Limitations in WDM routing networks,
– Number of wavelengths is limited.
– Physical constraints:
• limited number of optical transceivers limit the number of channels.
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Routing and Wavelength Assignment (RWA)
• Light path establishment involves
– Selecting a physical path between source and destination
edge nodes
– Assigning a wavelength for the light path
• RWA is more complex than normal routing because
– Wavelength continuity constraint
• A light path must have same wavelength along all the links in
the path
– Distinct Wavelength Constraint
• Light paths using the same link must have different wavelengths
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No Wavelength Converters
WSXC
Access Fiber
Wavelength 1
POP
POP
Wavelength 2
Wavelength 3
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Wavelength Conversion
• Process of converting the wavelength of an incoming channel
to another wavelength at the outgoing channel.
• Assume that two packets are destined to go out of the same
output port at the same time. Both packets can be still be
transmitted, but on two different wavelengths.
• Different categories of wavelength conversion are:
– Full conversion:
• Convert an incoming wavelength to any outgoing wavelength.
– Limited conversion:
• Convert an incoming wavelength to a subset of the outgoing wavelengths.
– Fixed conversion:
• Convert an incoming wavelength to a fixed outgoing wavelength (e.g., from
λ1 to λ3 and λ7).
– Sparse wavelength conversion:
• Networks are comprised of a mix of wavelength converters.
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Wavelength Converters
Input
Output
Full Wavelength conversion
Limited Wavelength
conversion
Fixed Wavelength conversion
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With Wavelength Converters
WIXC
Wavelength 1
Access Fiber
POP
POP
Wavelength 2
Wavelength 3
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Routing and Wavelength
Assignment (RWA)
• RWA algorithms based on traffic assumptions:
• Static Traffic
– Set of connections for source and destination pairs are given
• Dynamic Traffic
– Connection requests arrive to and depart from network one by
one in a random manner.
– Performance metrics used fall under one of the following
three categories:
• Number of wavelengths required
• Connection blocking probability: Ratio between number of blocked
connections and total number of connections arrived
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Static and Dynamic RWA
• Static RWA
– Light path assignment when traffic is known well in
advance
– Arises in capacity planning and design of optical networks
• Dynamic RWA
– Light path assignment to be done when requests arrive in
random fashion
– Encountered during real-time network operation
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Static RWA – Virtual Topology Design
• Problem
– Given physical topology, and traffic demands, set up
long-lived light paths among the edge nodes such that
the RWA constraints are satisfied
– Light paths create a logical or virtual topology and hence
the name
• A simple solution
– Given N edge nodes, create a completely connected
N(N-1) virtual topology
– Will work great, provided
• So many wavelengths can be supported in a fiber
• Each node (OXC) can be built with so many Rcv and Xmt
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Static RWA – Virtual Topology Design
• RWA is usually solved as an optimization problem
with Integer Programming (IP) formulations
• Objective functions
– Minimize average weighted number of hops
– Minimize average packet delay
– Minimize the maximum congestion level
– Minimize number of Wavelenghts
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Static RWA – Virtual Topology Design
• Methodologies for solving Static RWA
– Heuristics for solving the overall ILP sub-optimally
– Algorithms that decompose the static RWA problem into
a set of individual sub-problems, and solve a sub-set
– http://www.tct.hut.fi/~esa/java/wdm/
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Virtual Topology
• An example
B
A
Lightpath
C
B
A
D
C
D
Physical Topology
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Virtual Topology
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Solving Dynamic RWA
• During network operation, requests for new lightpaths come randomly
• These requests will have to be serviced based on the
network state at that instant
• As the problem is in real-time, dynamic RWA
algorithms should be simple
• The problem is broken down into two sub-problems
– Routing problem
– Wavelength assignment problem
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Optical Circuit Switching
all the Way: End-to-End
!!!
Why might this be possible:
• Huge CS bandwidth (large # of wavelength) – BW
efficiency is not very crucial
• Circuit switches have a much higher capacity than
Packet switches, and QoS is trivial
• Optical Technology is suited for CS
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How the Internet Looks Like Today
The core of the Internet is already “predominantly” CS.
Even a “large” portion of the access networks use CS (Modem, DSLs)
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How the Internet Really Looks Like Today
SONET/SDH
DWDM
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How the Internet Really Looks Like Today
Modems, DSL
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Why Is the Internet Packet Switched in the First
Place?
• PS is bandwidth
efficient
“Statistical
Multiplexing”
• PS networks are
robust
Gallager:
“Circuit switching is rarely used
for data networks, ... because of
very inefficient use of the links”
Tanenbaum:
”For high reliability, ... [the
Internet] was to be a datagram
subnet, so if some lines and
[routers] were destroyed,
messages could be ... rerouted”
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Are These Assumptions Valid Today?
•
• PS is bandwidth
efficient
• PS networks are
robust
•


10-15% average link
utilization in the
backbone today.
Similar story for
access networks
Routers/Switches are
designed for <5s down-time
per year.
They take >1min to recover
when they do (circuit
switches must recover in
<50ms).
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How Can Circuit Switching Help the Internet?
•
Simple switches/routers:
•
•
•
•
No buffering
No per-packet processing (just
per connection processing)
Possible all-optical data path
Peak allocation of BW
•
No delay jitter
COMP680E by M. Hamdi
Higher
capacity
switches
Simple but
strict QoS
95
Myth: Packet switching is simpler
• A typical Internet router contains over 500M
gates, 32 CPUs and 10Gbytes of memory.
• A circuit switch of the same generation could run
ten times faster with 1/10th the gates and no
memory.
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Instructions per arriving byte
Packet Switch Capacity
What we’d like: (more features)
QoS, Multicast, Security, …
What will happen: (fewer features)
Or perhaps we’re doing something wrong?
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time
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What Is the Performance of Circuit Switching?
End-to-End
File = 10Mbit
100 clients
1 Gb/s
1 server
x 100
Circuit sw Packet sw
Flow BW 1 Gb/s
10 Mb/s
Avg latency 0.505 s
1s
Worst latency 1 s
1s
COMP680E by M. Hamdi
99% of
Circuits
Finish
Earlier
98
What Is the Performance of Circuit Switching?
File = 10Gbit/10Mbit
100 clients
1 Gb/s
1 server
x 99
Circuit sw Packet sw
Flow BW 1 Gb/s
10Mb/s+1Gb/s
Avg latency 10.495 s
1.099 sec
Worst latency 10.990 s 10.990 sec
COMP680E by M. Hamdi
A big file
can kill CS
if it blocks
the link
99
What Is the Performance of Circuit Switching?
File = 10Gbit/10Mbit
100 clients
1 Gb/s
1 server
x 99
1 Mb/s
Circuit sw Packet sw
Flow BW 1 Mb/s
1 Mb/s
Avg latency
109.9s
109.9sec
Worst latency 10,000 s 10,000 sec
COMP680E by M. Hamdi
No
difference
between
CS and PS
in core
100
Possible Implementation
TCP
Switching
• Create a separate circuit for each
flow
• IP controls circuits
• Optimize for the most common
case
– TCP (85-95% of traffic)
– Data (8-9 out of 10 pkts)
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TCP Switching Exposes Circuits to IP
IP routers
TCP Switches
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TCP “Creates” a Connection
Source
Router
Router
Router
SYN
Destination
SYN+ACK
DATA
Packets
Packets
Packets
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Packets
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State Management Feasibility
• Amount of state
– Minimum circuit = 64 kb/s.
– 156,000 circuits for OC-192.
• Update rate
– About 50,000 new entries per sec for OC-192.
• Readily implemented in hardware or software.
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Software Implementation Results
TCP Switching boundary router:
• Kernel module in Linux 2.4 1GHz PC
• Forwarding latency
– Forward one packet: 21s.
– Compare to: 17s for IP.
– Compare to: 95s for IP + QoS.
• Time to create new circuit: 57s.
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