© Michel Kadoch 1 Attributs et Classification des commutateurs ATM.
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Transcript of © Michel Kadoch 1 Attributs et Classification des commutateurs ATM.
© Michel Kadoch 2
Caractéristiques Architecturales des commutateurs ATM
Les caractéristiques architecturales des commutateurs ATM sont évaluées pour leur pertinence à rencontrer les exigences de performance des protocoles qui supporteront les services à offrir dans B-ISDN.Un commutateur ATM comprend un ensemble de N ports d’entrées, et N ports de sorties, un switch fabric, et un processeur de controle de gestion - management control processor (MCP).
Switch Fabric
MCP
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0
1
N
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0
1
N
Input Controllers Output Controllers
© Michel Kadoch 3
Contrôleurs I/O
contrôleurs de port d’entrées fournie:
buffering;
cell replication (copying) pour multicast;
traitement des cellules;
translation VPI/VCI;
multiplexage du trafic provenant de plusieurs equippements à basse vitesses;
demandes de connexion de chemin et réservations à travers le switch fabric.
© Michel Kadoch 4
Switch Fabric
Un “switch fabric” est un mécanisme qui achemine les cellules des ports d’entrée aux ports de sortie. Il doit s’occuper des problèmes suivants :
Établissement d’un chemin entre un port d’entrée et un port de sortie à l’intérieur du commutateur;
La discipline de service pour les ports d’entrées;
Mécanisme de résolution de contention pour les cellules qui compétitionnent pour les liens ou d’autres ressources internes du commutateur (avoir à faire avec le blockage interne);
Support de plusieurs ports d’entrée aux connexions de ports de sortie (parallélisme).
© Michel Kadoch 5
Management and Control Processor (MCP)
La fonction du MCP est de communiquer avec les controlleurs des ports et de faciliter l’opération de commutation, l’administration et la gestion tel que SNMP ou CMIP (OSI Management).
© Michel Kadoch 6
Buffering
La prévention de la congestion et du deadlock sont des problèmes majeurs dans la conception de système commutation paquets comme ATM.
La contention d’un lien par une cellule peut bloquer le lien. Buffering ou tamporisation est une solution pour les ports d’entrées et de sorties ou dans le switch fabric ou dans tous ces points ensemble.
Les stratégies “Cell scheduling” sont requises aux ports d’entrées. Une bonne approche est le mécanisme de fenêtre.
Les analyses ont démontré que le “buffering” dans les ports de sorties peut donner un meilleur débit que s’il était apliqué dans les ports d’entrées.
© Michel Kadoch 7
Classification de Switch Fabrics ATM
ATM Switch Fabrics
Timedivision
Sharedmemory
Sharedmedium
Bus Ring
Spacedivision
Singlepath
Matrix Banyan SortedBanyan
Delta
Multiplepath
AugmentedBanyan
Parallelplanes
Loadsharing
Recirculation
© Michel Kadoch 8
Commutation Time Division
La connexion physique entre les ports d’entrées et de sorties dans le switch fabric peut être développée en utilisant la méthodologie de « time or space division ».
Dans “time division switching” commutation temporelle, l’utilisation de ressources physiques est multiplexée entre plusieurs connexions d’entrées et de sorties en se basant sur des emplacements en temps discrets. Un bus est un exemple d’un médium physique qui peut faciliter le multiplexage temporel en utilisant de module de mémoire.
M e m o r yM o d u l ecells from input ports
cells to output ports
© Michel Kadoch 9
Space Division Switching
Dans la méthodologie “space division”, le switch fabric peut supporter plusieurs connexions au même moment. Les connexions sont basées sur la disponibilité de chemins physiques du switch fabric qui ne sont pas en conflit.
2 x 2switchingelement
a0
a1
b0
b1
© Michel Kadoch 10
Switching Elements
a0
a1
b0
b1
a0
a1
b0
b1
a0
a1
b0
b1
a0
a1
b0
b1
Straight through Lower broadcast
exchange Upper broadcast
© Michel Kadoch 11
Routing
Routage de cellules à travers un « space-division switch » peut être accomplit par:
self routing label routing
self routing compte sur les interconnexions régulières du switching elements dans le fabric.
label routing, le champ VCI dans l’entête est utilisé par chaque switching element pour prendre les décision de lien de sortie.
© Michel Kadoch 12
Representative Architecture
Matrix and Fully-Connected Switches Also referred to as crossbar switches. Provide N2 paths between N input and N output ports. A single contact pair for each input-ouput combination.
inputs outputs
Complexity grows with the number of links, i.e., O(N2)
© Michel Kadoch 13
Knockout Switch
A knockout switch is a matrix architecture. Any input can transmit to any output. The switch is self routing.
input
0
1
N-1
output
Knockoutconcentrator
filter
R R
0 N-1
Filtering is based on the packet destination address
The concentrator with R buffers (R<N)implements a selection algorithm for selecting R cells outof the maximum N possible cells arriving at that port. Worse case:N-R cells lost
R out of N selection algorithm is used by the concentrator
bus
bus drivers
Separate outputbuffers can be maintained and a shifter can beused to allocatecells to thebuffers in order to ensure propersequencing of transmitted cells on each virtual connection in anATM Network.
© Michel Kadoch 14
Multistage Switches
Two of the basic switching fabrics used for multistage switching are the Banyan and the Delta networks.
Delta Networks
N input port switch composed of b x b simpler switching elements. There are K stages, where N = bK (K=logbN) and N/b switches in each stage (column).
© Michel Kadoch 15
Example of Delta network
8 x 8 Delta 2 network, where b = 2, N = 8, K = log28 = 3 columns (switches in a column)
K
01
01
01
01
01
01
01
01
01
01
01
01
000001
010011
100101
110111
N
01
234
56
7
one half of
the deck
theother half of
the deck
a perfect shuffle a perfect shuffle
© Michel Kadoch 16
Multiple connectionsThe bits of the destination address provide the required routing tags. The digits in the destination address are used to set the state of the stages.
01
01
01
01
01
01
01
01
01
01
01
01
001010011
100101
110111
0123
4567
000
Perfect shuffle Perfect shuffleStage 1 Stage 2 Stage 3
011
101
011
101
011
101
011
101
0
10
1 1
1
destination port
address
white bitcontrolsswitchsetting
in each stage
© Michel Kadoch 17
Internal blocking Internal link blocking as well as output blocking can happen in a Delta
network. The following example illustrates an internal blocking for connections of input 0 to output 3 and input 4 to output 2.
01
01
01
01
01
01
01
01
01
01
01
01
001010011
100101
110111
01
23456
7
000
Perfect shuffle Perfect shuffleStage 1 Stage 2 Stage 3
blocking link011
010
011
010
??? ???
???
© Michel Kadoch 18
Output Blocking The following example illustrates output blocking for the connections between input 1 and output 6, and input 3 and output 6.
01
01
01
01
01
01
01
01
01
01
01
01
001010011
100101
110111
01
23456
7
000
Perfect shuffle Perfect shuffleStage 1 Stage 2 Stage 3
110
110
110
110
110
110
output blocking
© Michel Kadoch 19
Blocking Reduction
Means to reduce the probability of blocking or increase throughput: installation of a distribution (randomizing) network in front of the
switch to reduce or eliminate the possibility of internal blocking. Recirculate packets that cause blocking to the input ports,
including them in the next cycle. Provide a contention resolution phase among the input ports. Subject the traffic between the stages of the network to a
handshake protocol that synchronizes transmission and reception across the stages.
Add extra stages to the multistage network and produce extra paths.
Provide a number of buffers on each link or in the switching elements.
Increase the bandwidth of the internal links relative to the input links.
Increase network throughput by using several networks in parallel.
© Michel Kadoch 20
The Banyan Network
The banyan network is another self-routing switching fabric, similar in topology to the delta network.
01
01
01
01
01
01
01
01
01
01
01
01
001010011
100101110111
0123
4567
000
Stage 1 Stage 2 Stage 3
011
101
011
101
011
101 0
10
1
1
1011
101
011
101
© Michel Kadoch 21
Adding Load Distribution Because of internal blocking, input traffic is sorted on the
destination ports. The network is known as Batcher sorter
01
01
01
01
01
01
01
01
01
01
01
01
001
010011
100101
110111
000
Perfect shuffle Perfect shuffleStage 1 Stage 2 Stage 3
B
A
01
01
01
01
A
B
A = Connection to output port 3 (011)B = Connection to output port 2 (010)
© Michel Kadoch 22
Output blocking
To eliminate output contention if there are multiple packets with the same destination:
Remove the duplicate-destination packets from the group and include them in the next batch for sorting and routing;
submit only requests (into the group to be sorted) that have no destination in common.
© Michel Kadoch 23
Adding Recirculation
Recirculating networks can redistribute, to the input ports, packets that were not successfully delivered in a given cycle.
Switchfabric
recirculation buffer
This technique deals with output or internal blocking.
© Michel Kadoch 24
Starlight Switch Structure
The Trap network examines the output of the sort network and removes all packets with the same destination address. The duplicates are routed back to the sort network for the next cycle with a higher priority.
Concentrator
Sortnetwork
Trapbuffer Routing
Banyan Network
Input Output
© Michel Kadoch 25
Adding a contention resolution phase
Three Phase AlgorithmPhase 1
The input ports that have traffic, submit a transmission request to the sorting network. The sorter sorts the requests based on the destination. One of the requests that contests the access to the destination is selected; the others with the same destination address are purged.
Phase 2The sorter sends an acknowledgement to the input ports from which requests have been received and selected.
Phase 3The ports selected transmit their packets.
This method can have some blocking problems, and phase 1 and 2 are overhead.
© Michel Kadoch 26
Adding Extra Stages
One way to augment a Banyan network is to add extra stages to increase the number of paths from input ports to output ports.
Each additional stage doubles the number of paths between any input-output pair.
A better load distribution can increase throughput, alleviate blocking, and make the fabric less sensitive to the load on input ports.
© Michel Kadoch 27
Adding Internal Buffers
Adding buffers also augments a Banyan network. The resulting configurations are known as buffered Banyans.
The Integrated Service Packet Network (ISPN) described by Turner1.
The switch is constructed from 2 x 2 switches in which each link buffers one packet. The fabric connects 1024 ports using 5120 switching elements arranged in 10 stages. The internal links operate at eight times the speed of the external ports. So, for 100% load, an input port results in only 12.5% load on the internal links. A back pressure flow mechanism prevents contention at the internal links. When a packet arrives at a free link, the packet is not buffered.
1. J. Turner, « Design of an Integrated Service Packet Network », Proceedings Ninth ACM Data Comm. Symposium, ACM, New York, 1985,pp. 125-133.
© Michel Kadoch 28
Adding Parallel Switching Planes
One way to increase throughput is to connect the input and output ports to multiple planes of the switch fabric.
Each input port can distribute its traffic to the multiple homogeneous fabric planes. Similarly, each output port can be fed from multiple fabric planes.
© Michel Kadoch 29
Putting it all together The Sunshine switch is an example that incorporates: Batcher Banyan; Internal and output buffering; parallel fabrics; recirculation with dedicated input ports; self routing; level of service priority; trunk groups between internal nodes.
Batchersort
1
N
TrapNetwork
Concentrator
Banyan 1
Banyan K
1
N
Delay T T
Select at mostK cells per destination.
Separate selectedcells from the rest.
Selector
Input port Output port
© Michel Kadoch 30
Commercial Systems
ATM strategy for major vendor classes and some commercially available ATM switches.
Hub and Router VendorsUses two stage strategy for introducing ATM.Phase 1
Add interface board to connect hubs or routers to an ATM switch over SONET (OC-3) or T3.Phase 2
The next step will be to incorporate an ATM switching module (switch fabric) into
the hub or router. Several vendors are considering attaching to an ATM adaptor box.
© Michel Kadoch 31
Multiplexer and WAN Vendors
They are working on or have already released ATM switches or adapters for the LAN. Examples: ATMX from Adaptive, Newbridge’s 361X ATM switch, the Synchrony product from Ascom Timplex, Stratacom’s BPX, GTE Government System’s ATM switch.