07-11-2012, 01:23 PM
Optical burst switching
[attachment=38398]
Optical burst switching (OBS)
Combines merits of optical circuit switching (OCS) & optical packet switching (OPS) while avoiding respective shortcomings
Switching granularity at burst level allows for statistical multiplexing at lower control overhead than OPS
Only control packets carried on one or more control wavelength channels undergo OEO conversion at each intermediate node
Data bursts are transmitted on separate set of data wavelength channels that are all-optically switched at intermediate nodes
OBS combines transparency of OCS with statistical multiplexing gain of OPS
OBS framework
OBS network edge
One or more users (typically electronic IP routers with OBS interface) attached to an OBS node
OBS network core
OBS nodes interconnected by WDM fiber links
Burst assembly
OBS users
collect traffic originating from upper layers (e.g., IP),
sort it based on destination addresses, and
aggregate it into variable-size bursts by using burst assembly algorithms
Burst assembly algorithms have significant impact on performance of OBS networks & have to take the following parameters into account
Timer
Used by OBS user to determine when to assemble new burst
Minimum & maximum burst size
Determine length of assembled burst
Burst assembly
Timer & burst size parameters must be set carefully
Long bursts hold network resources for long time periods => higher burst loss
Short bursts cause increased number of control packets => higher control overhead
Padding may be used to assemble minimum-size burst when timer expires
Burst assembly helps reduce degree of self-similarity of higher-layer traffic & make it less bursty => decreased queueing delay & smaller packet loss
Signaling
Used to set up connection for assembled burst between given pair of source & destination edge OBS users
OBS networks may deploy one of two types of signaling
Distributed signaling with one-way reservation or
Centralized signaling with end-to-end reservation
Most of proposed OBS network architectures use distributed signaling with one-way reservation
Source OBS user sends control packet on separate out-of-band control channel to ingress OBS node prior to transmitting corresponding burst after certain offset
Out-of-band control channel may be dedicated signaling wavelength channel or separate control network
Control packet contains information about burst (e.g., size)
Control packet is OEO converted & processed in electronic domain at each intermediate OBS node
End-to-end reservation
Second less frequently used OBS signaling approach uses centralized signaling with end-to-end reservation
OBS users send connection set-up requests to ingress OBS nodes
Ingress OBS nodes inform central request server about set-up requests
Based on global knowledge about current OBS network status, central server processes set-up requests & sends ACKs to requesting OBS users
Upon receipt of ACKs, OBS users transmit bursts
[attachment=38398]
Optical burst switching (OBS)
Combines merits of optical circuit switching (OCS) & optical packet switching (OPS) while avoiding respective shortcomings
Switching granularity at burst level allows for statistical multiplexing at lower control overhead than OPS
Only control packets carried on one or more control wavelength channels undergo OEO conversion at each intermediate node
Data bursts are transmitted on separate set of data wavelength channels that are all-optically switched at intermediate nodes
OBS combines transparency of OCS with statistical multiplexing gain of OPS
OBS framework
OBS network edge
One or more users (typically electronic IP routers with OBS interface) attached to an OBS node
OBS network core
OBS nodes interconnected by WDM fiber links
Burst assembly
OBS users
collect traffic originating from upper layers (e.g., IP),
sort it based on destination addresses, and
aggregate it into variable-size bursts by using burst assembly algorithms
Burst assembly algorithms have significant impact on performance of OBS networks & have to take the following parameters into account
Timer
Used by OBS user to determine when to assemble new burst
Minimum & maximum burst size
Determine length of assembled burst
Burst assembly
Timer & burst size parameters must be set carefully
Long bursts hold network resources for long time periods => higher burst loss
Short bursts cause increased number of control packets => higher control overhead
Padding may be used to assemble minimum-size burst when timer expires
Burst assembly helps reduce degree of self-similarity of higher-layer traffic & make it less bursty => decreased queueing delay & smaller packet loss
Signaling
Used to set up connection for assembled burst between given pair of source & destination edge OBS users
OBS networks may deploy one of two types of signaling
Distributed signaling with one-way reservation or
Centralized signaling with end-to-end reservation
Most of proposed OBS network architectures use distributed signaling with one-way reservation
Source OBS user sends control packet on separate out-of-band control channel to ingress OBS node prior to transmitting corresponding burst after certain offset
Out-of-band control channel may be dedicated signaling wavelength channel or separate control network
Control packet contains information about burst (e.g., size)
Control packet is OEO converted & processed in electronic domain at each intermediate OBS node
End-to-end reservation
Second less frequently used OBS signaling approach uses centralized signaling with end-to-end reservation
OBS users send connection set-up requests to ingress OBS nodes
Ingress OBS nodes inform central request server about set-up requests
Based on global knowledge about current OBS network status, central server processes set-up requests & sends ACKs to requesting OBS users
Upon receipt of ACKs, OBS users transmit bursts