broadcast-and-select networks
DESCRIPTION
Broadcast-and-select networks. Broadcast-and-select networks. Each node is usually attached to two fibers: one to transmit, one to receive W WDM channels are available Tx and Rx operate on a single WDM channel at a time (to reduce electronic bandwidth) - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Broadcast-and-select networks](https://reader035.vdocuments.us/reader035/viewer/2022081507/568161b2550346895dd177a8/html5/thumbnails/1.jpg)
Broadcast-and-select networks
![Page 2: Broadcast-and-select networks](https://reader035.vdocuments.us/reader035/viewer/2022081507/568161b2550346895dd177a8/html5/thumbnails/2.jpg)
Broadcast-and-select networks• Each node is usually attached to two fibers: one to
transmit, one to receive W WDM channels are available• Tx and Rx operate on a single WDM channel at a time (to
reduce electronic bandwidth)• It is possible to observe collisions and contention
– Collision: two or more transmitters transmit on the same channel at the same time – Contention: a single receiver must tune to two or more channels at the same time
• We need a Medium Access Control (MAC) protocol
![Page 3: Broadcast-and-select networks](https://reader035.vdocuments.us/reader035/viewer/2022081507/568161b2550346895dd177a8/html5/thumbnails/3.jpg)
Broadcast-and-select networks• Nodes can be equipped with one or more tx and rx devices,
which may be tunable or fixed• Tunable txs and rxs are more expensive (and tunable usually
cost more than tunable txs)• For example: 2 fixed tx/rx per node allow to build a shuffle
topology
![Page 4: Broadcast-and-select networks](https://reader035.vdocuments.us/reader035/viewer/2022081507/568161b2550346895dd177a8/html5/thumbnails/4.jpg)
Level of performance
It is measured by Packet delay: The delay is specified from the
start of the packet being transmitted at the source to the end of the packet being received at the destination and
through put of network : data that are successfully received by their destination
![Page 5: Broadcast-and-select networks](https://reader035.vdocuments.us/reader035/viewer/2022081507/568161b2550346895dd177a8/html5/thumbnails/5.jpg)
Slot synchronization
![Page 6: Broadcast-and-select networks](https://reader035.vdocuments.us/reader035/viewer/2022081507/568161b2550346895dd177a8/html5/thumbnails/6.jpg)
Synchronization algorithm
• Predicts the time of arrival of the next sync pulse at its receiver
• Estimates the round trip delay • A node transmits the information one round
trip delay prior to the estimated time of arrival.
![Page 7: Broadcast-and-select networks](https://reader035.vdocuments.us/reader035/viewer/2022081507/568161b2550346895dd177a8/html5/thumbnails/7.jpg)
Slotted Aloha/Slotted Aloha protocol
Some basic assumption • No. of wavelength or channel, W<N • Each node must have a fixed –tuned
transmitter and receiver operating at control wavelength
![Page 8: Broadcast-and-select networks](https://reader035.vdocuments.us/reader035/viewer/2022081507/568161b2550346895dd177a8/html5/thumbnails/8.jpg)
Slotted Aloha/Slotted Aloha
• Aloha used in single channel broadcast network where any node that has a packet to send transmits it immediately.
• Whereas In slotted aloha time is divided into slots whose length is equal to the maximum sized packet
In multichannel network• The time is divided into slots for data as well as
the control channel
![Page 9: Broadcast-and-select networks](https://reader035.vdocuments.us/reader035/viewer/2022081507/568161b2550346895dd177a8/html5/thumbnails/9.jpg)
Basic Slotted Aloha/Slotted Aloha protocol
Operation:When a data to be send :Control packet is sent in control slotData packet is sent in data slot• Every node– Keeps listening to the control channel– When a transmission to its address is detected, it tunes the rx
on channel λTThis is called “tell-and-go” approach (data is assumed to be
received after large propagation delays)There can be collisions and contention.
![Page 10: Broadcast-and-select networks](https://reader035.vdocuments.us/reader035/viewer/2022081507/568161b2550346895dd177a8/html5/thumbnails/10.jpg)
Basic Slotted Aloha/Slotted Aloha protocol
![Page 11: Broadcast-and-select networks](https://reader035.vdocuments.us/reader035/viewer/2022081507/568161b2550346895dd177a8/html5/thumbnails/11.jpg)
Control wavelength protocol : Slotted AlohaData wavelength protocol: Slotted Aloha Thus the name Slotted Aloha / Slotted Aloha
![Page 12: Broadcast-and-select networks](https://reader035.vdocuments.us/reader035/viewer/2022081507/568161b2550346895dd177a8/html5/thumbnails/12.jpg)
Modified SA/SA
• To avoid useless transmissions on the data channels after collisions on control and data channels, it is possible to use a “wait-and-see” approach: do not transmit data until the control frame is received back (after a propagation delay); we get:
• higher throughput• higher access delays
![Page 13: Broadcast-and-select networks](https://reader035.vdocuments.us/reader035/viewer/2022081507/568161b2550346895dd177a8/html5/thumbnails/13.jpg)
Access delays
Defined as the delay between the time at which a packet is available for transmission
at a node and the time at which it is first transmitted
![Page 14: Broadcast-and-select networks](https://reader035.vdocuments.us/reader035/viewer/2022081507/568161b2550346895dd177a8/html5/thumbnails/14.jpg)
Through put analysis
Some assumptions are required1. Independent transmission2. Large “n”3. Uniform traffic
![Page 15: Broadcast-and-select networks](https://reader035.vdocuments.us/reader035/viewer/2022081507/568161b2550346895dd177a8/html5/thumbnails/15.jpg)
Independent transmission
In any slot and for any node the probability that the node has a packet for transmission is p, independent of all other slots and all other nodes.
![Page 16: Broadcast-and-select networks](https://reader035.vdocuments.us/reader035/viewer/2022081507/568161b2550346895dd177a8/html5/thumbnails/16.jpg)
Large “n”
• No. of nodes in the network n is very large compared to W
Assume that• W is fixed but n ∞ and p 0 then• The expected no. packets in the network is
Gnp
![Page 17: Broadcast-and-select networks](https://reader035.vdocuments.us/reader035/viewer/2022081507/568161b2550346895dd177a8/html5/thumbnails/17.jpg)
Uniform traffic
• Data packets is equally likely to be transmitted on any one of the W data channels
![Page 18: Broadcast-and-select networks](https://reader035.vdocuments.us/reader035/viewer/2022081507/568161b2550346895dd177a8/html5/thumbnails/18.jpg)
Throughput analysis
Expected no. of data packets that are successful in any data slot for basic SA/SA is
LGe-G/W.(e-G/W)2(L-1)
And for modified SA/SALGe-G/W.(1- Ge-G/W)2(L-1)
![Page 19: Broadcast-and-select networks](https://reader035.vdocuments.us/reader035/viewer/2022081507/568161b2550346895dd177a8/html5/thumbnails/19.jpg)
DT-WDMA• Dynamic Time-Wavelength Division Multiaccess• This protocol assume that the
– Number of nodes n is equal to the number of wavelengths W. – Each node has a 1 Fixed Tr, 1 Tunable Rx and 1 Fixed Rx for the
control channel– The size of the data slots is n times the control slots.– The data slots do not overlap in time.
• When ever a node, say xi, has a data packet to send, it sends a control packet in a control slot and the data packet in the data slot immediately following it.
• Each node continuously monitors the control channel. Thus when node xj , receives a control packet send by node xi it knows that the next data slot has a packet intended for it being transmitted on wavelength I so it tunes its TR to that wavelength.
• Features : Data packets never collide also control packet never collide.
![Page 20: Broadcast-and-select networks](https://reader035.vdocuments.us/reader035/viewer/2022081507/568161b2550346895dd177a8/html5/thumbnails/20.jpg)
Scheduling protocol is a self study. ..
![Page 21: Broadcast-and-select networks](https://reader035.vdocuments.us/reader035/viewer/2022081507/568161b2550346895dd177a8/html5/thumbnails/21.jpg)
Test beds Test beds Topology No.of
wavelengthWavelength Spacing
Bit Rate per wavelength
Lambdanet Star 18(18) 2nm 1.5Gb/s
NTT Star 100(100) 10GHz 622 Mb/s
Rainbow I Star 12(32) 1nm 300 Mb/s
Rainbow II Star 4(32) 1nm 1 Gb/s
Starnet I Star 2(80) 10GHz 1.25/2.5Gb/s
BBC Interconnected Star
-(16) 4nm 2.5 Gb/s