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plementations 6 which may ultimately threaten the original actual high speed HW implementation which we do not yet. vendor independency goal of the OpenFlow inventors have at the time of writing Rather our main contribution. As a result even if an OpenFlow device is now rich of func consists in the proposal of a viable abstraction to formally. tionalities and primitives it remains completely dumb describe a desired stateful processing of flows inside the de. with all the smartness placed at the controller side vice itself without requiring the device to be open source. Someone could argue that this is completely in line with or to expose its internal design Our abstraction relies on. the spirit of SDN s control and data plane separation And eXtended Finite State Machines XFSM which have been. to avoid misunderstandings we fully agree that network recently shown to be effective in a very different network. management and control can be logically centralized How ing field platform agnostic wireless medium access control. ever we posit that several stateful tasks just involving local programmability 8 9 More specifically we first intro. states inside single links switches are unnecessarily central duce in section 2 a simplified XFSM called Mealy Machine. ized for easy management and programmability for the only and a relevant programmatic interface which can be inter. reason that they cannot be deployed on the local Open preted as a somewhat natural generalization of the Open. Flow devices without retaining the explicit involvement of Flow match action abstraction In section 3 we discuss via. the controller for any state update for a notable example bility and implementation issues showing that XFSM sup. think to the off the shelf Layer 2 MAC learning operation1 port can largely reuse existing OpenFlow features Finally. As a result the explicit involvement of the controller for any section 4 discusses extensions towards support of full XF. stateful processing and for any update of the match action SMs 10 and the possible benefits. rules is problematic In the best case this leads to extra. signaling load and processing delay and calls for a capil Related work. lary distributed implementation of the logically central. Despite OpenFlow s data plane programmability the need. ized controller In the worst case the very slow control plane. to use advanced packet handling for key network services has. operation a priori prevents the support of network control. led to the proliferation of many types of specialized middle. algorithms which require prompt real time reconfiguration. boxes 11 The extension of programmability and flexibility. in the data plane forwarding behavior, features to these advanced network functions is a crucial as. In essence dumbness in the data forwarding plane appears. pect 12 13 and a recent trend is that of virtualizing them. to be a by product of the limited capability of the OpenFlow. in data centers on general purpose hardware platforms and. data plane API compromise rather than an actual design. to make them programmable and configurable using SDN. choice or an SDN postulate Can we then emerge with bet. approaches 14, ter data plane APIs which permit to program some level of. It is quite evident that SDN for general purpose and spe. smartness directly inside the forwarding device, cialized hardware has radically different constraints and ob. Contribution jectives on the abstraction for configuring packet handling. functionalities 13 We argue that extending the Open. As argued above our belief is that a major shortcoming of Flow switch abstraction allows to offload on high perfor. OpenFlow is its inability to permit the programmer to de mance switches a pretty large set of functions reducing the. ploy states inside the device itself Adding states to Open need to relay on controllers and middleboxes. Flow as currently under discussion in ONF is however not The need to extend the OpenFlow data plane abstraction. sufficient the programmer should be entitled to formally has been recently recognized by the research community 15. specify how states should be handled and this specification 16 6 In 15 the authors point out that the rigid table. should be executed inside the device with no further inter structure of current hardware switches limits the flexibil. action with the controller Moreover a viable solution must ity of OpenFlow packet processing to matching on a fixed. come along with two fundamental attributes First it must set of fields and to a small set of actions and introduce a. be amenable to high speed implementation Second it must logical table structure RMT Reconfigurable Match Table. not violate the vendor agnostic principle which has driven on top of the existing fixed physical tables and new action. the OpenFlow invention and which has fostered SDN in primitives Notably the proposed scheme allows not only to. essence it must emerge as a concrete and pragmatic ab consider arbitrary width and depth of the matching for the. straction rather than as a technical approach header vector but also to define actions that can take input. Our work mainly focuses on this second aspect although arguments and rewrite header fields In 16 the approach. some hints are provided in section 3 on how our proposed is more radical and similarly to the early work on active. approach can be efficiently supported by existing OpenFlow networks packets are allowed to carry a tiny code that de. hardware we do not claim to have fully addressed this as fine processing in the switch data plane A very interesting. pect as a compelling answer would require to exhibit an aspect is the proposal of targeted ASIC implementations. 1 where an extremely small set of instructions and memory. Ironically MAC learning is frequently invoked to motivate. OpenFlow extensions 5 For instance flow table synchro space can be used to define packet processing. nisation different views of the same data at different points OpenFlow standardization has so far significantly extended. of the OpenFlow pipeline to permit learning and forward the set of actions including also action bundles and func. ing functions to access the same data Or flow monitors tionalities 4 and there is some debate on the inclusion of. tracking of flow table changes in a multi controller deploy flow states in a next version 5 However extensions ap. ment to permit a device natively implement a legacy MAC pear to add more and more capabilities but with limited. learning function to inform the remote controller of any new. MAC address learned in essence to permit to break the attention to how to duly accommodate them in a clean API. original OpenFlow vision of general purpose forwarding de 7 or event rethink its foundational principles e g the. vice configured only through the data plane programming Google s OpenFlow 2 0 proposal 6 which was considered. interface too disruptive, ACM SIGCOMM Computer Communication Review 46 Volume 44 Number 2 April 2014. Port 5123 Port 5123 Port 6234 Port 7345 Port 8456 Port 22. Drop Drop Drop Drop Drop Forward OPEN state packets addressed to port 22 and only to this. port will be forwarded whereas all remaining packets will. be dropped but without resetting the state to DEFAULT. Drop Port 22,2 2 Extended Finite State Machines, A closer look at Figure 1 reveals that each state transition.
is caused by an event which specifically consists in a packet. Figure 1 port knocking example State Machine matching a given port number Moreover each state transi. tion caused by an event match is associated to a forwarding. action in the example drop or forward A state transition. Finally the usage of XFSMs was initially inspired by. thus reminds very closely a legacy OpenFlow match action. 8 where bytecoded XFSMs were used to convey a de, rule but placed in a more general framework characterized. sired medium access control operation into a specialized but. by the following two distinguishing aspects, closed 9 wireless interface card While the abstraction. XFSM is similar the context wireless protocols versus. flow processing technical choices state machine execution 2 2 1 XFSM Abstraction. engine versus table based structures and handled events We remark that the match which specifies an event not. signals and timers versus header matching are not nearly only depends on packet header information but also de. comparable pends on the state using the above port knocking example. a packet with port 22 is associated to a forward action when. in the OPEN state but to a drop action when in any other. 2 BASIC ABSTRACTION state Moreover the event not only causes an action but. also a transition to a next state including self transitions. 2 1 An illustrative example from a state to itself. The OpenFlow data plane abstraction is based on a single All this can be modeled in an abstract form by means of a. table of match action rules for version 1 0 and multiple ta simplified type2 of eXtended Finite State Machine XFSM. bles from version 1 1 on Unless explicitly changed by the re known as Mealy Machine Formally such a simplified XFSM. mote controller through flow mod messages rules are static is an abstract model comprising a 4 tuple S I O T plus. i e all packets in a flow experience the same forwarding an initial starting default state S0 where i S is a finite. behavior set of states ii I is a finite set of input symbols events. Many applications would however benefit from the abil iii O is a finite set of output symbols actions and iv. ity to evolve the forwarding behavior on a packet by packet T S I S O is a transition function which maps. basis i e depending on which sequence of packets we have state event pairs into state action pairs. received so far A perhaps niche but indeed very descriptive Similarly to the OpenFlow API the abstraction is made. example is that of port knocking a well known method for concrete while retaining platform independency by restrict. opening a port on a firewall A host that wants to estab ing the set O of actions to those available in current Open. lish a connection say an ssh session i e port 22 delivers Flow devices and by restricting the set I of events to Open. a sequence of packets addressed to an ordered list of pre Flow matches on header fields and metadata easily imple. specified closed ports say ports 5123 6234 7345 and 8456 mentable in hardware platforms The finite set of states S. Once the exact sequence of packets is received the firewall concretely state labels i e bit strings and the relevant. opens port 22 for the considered host Before this event all state transitions in essence the behavior of a stateful ap. packets including of course the knocking ones are dropped plication are left to the programmer s freedom. As any other stateful application such an operation can. not be configured inside an OpenFlow switch but must be 2 2 2 State Management. implemented in an external controller The price to pay Matches in OpenFlow are generically collected in flow ta. is that a potentially large amount of signalling information bles The discussion carried out so far recommends to clearly. in principle up to all packets addressed to all closed ports separate the matches which define events port matching in. must be conveyed to the controller Moreover a timely flow the port knocking example from those which define flows. mod command from the controller is needed for opening port meant as entities which are attributed a state host IP ad. 22 after a correct knocking sequence to avoid that the first dresses While event matches cause state transitions for. legitimate ssh packet finds port 22 still closed On the a given flow and are specified by an XFSM flow matches. other side implementing this application in the controller are in charge to identify and manage the state associated to. brings no gain it does not benefit from network wide knowl the flow the arriving packet belongs to Two distinct tables. edge or high level security policies 17 but uses just local State Table and XFSM table and three logical steps. states associated to specific flows on a single specific device thus naturally emerge for handling a packet Figure 2. Anyway let us postpone the discussion on where this oper. 1 State lookup It consists in querying a State Table. ation is implemented and let us rather focus on how we can. using as key the packet header field s which identifies the. model such a desired behavior Arguably the most natural. flow for instance the source IP address if a state is not. way is to associate to each host the finite state machine. illustrated in Figure 1 Starting from a DEFAULT state 2. While in this section for concreteness we limit to Mealy. each correctly knocked port will cause a transition to a se Machines in section 4 we discuss further possible extensions. ries of three intermediate states until a final OPEN state is towards the most general XFSM abstraction as defined in. reached Any knock on a port different from the expected 10 Unless ambiguity emerges we will loosely use the term. one will bring back to the DEFAULT state When in the XFSM also to refer to the special case of Mealy Machines. ACM SIGCOMM Computer Communication Review 47 Volume 44 Number 2 April 2014. State Table MAC learning XFSM,lookup scope macdst,2 0 update scope macsrc. 345678 State Event Actions Next state,0 1 2 9 7 DEFAULT in port 1 flood PORT 1. 1 State lookup PORT 1 in port 1 output 1 PORT 1,PORT 2 in port 1 output 2 PORT 1.
XFSM Table,H IEJK 5 L PORT N in port 1 output N PORT 1. E EFE L EM 8 E,A7B5CD4 K 345678,2 0 345678 345678 0 K 345678. 345678 1 K 345678 DEFAULT in port N flood PORT N,345678 2 0 K 9 7 PORT 1 in port N output 1 PORT N. 2 XFSM state transition 9 7 N O K 9 7 PORT 2 in port N output 2 PORT N. 9 7 G K 9 7,G G K A7B5CD4,PORT N in port N output N PORT N. State Table,Table 1 XFSM table for a MAC learning Layer.
2 0 9 7 2 switch with N ports in port switch input port. P Q ER9 7 of the packet action flood replicate and forward. 0 1 2 9 7 packet to all switch ports except in port state labels. 3 State update, A7B5CD4 port number to which the flow shall be forwarded. Figure 2 State Table XFSM table and packet han the same needs for instance the detection of a returning. dling for the port knocking example TCP SYNACK packet could trigger a state transition on. the opposite direction And in protocols such as FTP a. found for a queried flow we assume that a default state is control exchange on port 21 could be used to set a state on. returned the data transfer session on port 20, The root cause of this issue is that so far we have not. 2 XFSM transition The retrieved state label added, yet conceptually separated the identity of the flow to which. as metadata to the packet is used along with the header. a state is associated from the actual position in the header. fields involved in the event matching e g port number to. field from which such an identity is retrieved Since in our. perform a match on an XFSM table which returns i the. proposed abstraction flow identification is needed to lookup. associated action s and ii the label of the next state. and to update the state table we simply need to provide the. 3 State update It consists in rewriting or adding a new programmer with the ability to use an eventually different. entry to the state table using the provided next state label header field in these two accesses to the State Table We thus. define as lookup scope and update scope the ordered. The example in Figure 2 shows how the port knocking sequence of header fields that shall be used to produce the. example is supported in our proposed approach The pro key used to access the state table and perform respectively. gram contained in the XFSM table 7 entries implements a lookup or an update operation. the port knocking state machine Assume the arrival of a With such feature programming say a MAC learning. packet from host 1 2 3 4 the state lookup top figure per operation becomes trivial We start by defining the state. mits to retrieve the current state STAGE 3 Via the XFSM associated to a flow identity namely a MAC address the. table middle figure we determine that this state along current switch port to which packets should be forwarded. with the knocked port 8456 triggers a drop action and a or DEFAULT if no port has been yet learned During. state transition to OPEN middle figure The new state is state lookup the lookup scope is set to be the MAC destina. written bottom figure back in the state table for the host tion address During state update we define as udpate scope. entry In the XFSM table we assume an ordered matching the MAC source address Finally we fill the XFSM table. priority with the last row having the lowest priority As a with the transitions given in Table 1 Thanks to the udpate. result all the four transitions to the default state for packets scope the key value pair used in the State Table update. not matching the expected knocked port are coalesced in the is thus macsrc next state In this example table we on. last entry A notable characteristic of the proposed solution purpose assume compatibility with the current OpenFlow. is that the length of the tables is proportional to the number specification and the N 2 N size of the table being N. of flows state table and number of states XFSM table the number of switch ports thus depends on the OpenFlow. but not to their product limitations and not on our XFSM abstraction Indeed we. remark that the usage of parameters permitted by the Re. 2 3 Flow identification configurable Match Tables recently introduced in 15 would. Unfortunately the above described abstraction still misses yield an XFSM table comprising only two entries the de. a fundamental further step which permits to model a sub fault one plus the entry state port i event in port j. set of important stateful operations in which states for action output i next state in port j. a given flow are updated by events occurring on different. flows A prominent example is MAC learning packets are 2 4 Application Programming Interface. forwarded using the destination MAC address but the for As a summary our basic data plane programming abstrac. warding database is updated using the source MAC address tion to formally specify a stateful operation comprises the. Similarly the handling of bidirectional flows may encounter specification of two tables in terms of. ACM SIGCOMM Computer Communication Review 48 Volume 44 Number 2 April 2014. 1 an XFSM table comprising four columns i a state Rewrite of the state is handled by processing the packet. provided as a user defined label ii an event expressed as header trough a key extractor that will now refer to the. an OpenFlow match iii a list of OpenFlow actions and iv update scope the key thus obtained will be used to rewrite. a next state label each row is a designed state transition or add a new row in the state table State updates can be. 2 the lookup scope and update scope used to access performed also by the controller similarly to flow mod for. and update the State Table respectively this reason we name them as state mod messages. It is not yet clear at this stage whether it could be prac 3 1 2 Configuration. tically convenient to further generalize such an API by per. mitting to bind a different update scope to different entries We assume that by default all the flow tables that a switch. in the XFSM table in other words associate each next state provide for the pipeline processing are intended as stateless. entry with its update scope which may then differ depend i e standard Openflow The controller can hence enable. ing on the specific transition considered a row in the XFSM stateful processing for one or more flow table by sending a. table Indeed this extra flexibility for which we have not special control message to the switch Configuring a stateful. yet identified a clear use case would be paid in terms of stage is made by associating a state table to an existing flow. additional internal hardware complexity table and defining the lookup scope and the update scope. Obviously the two lookup scope and update scope must pro. vide same length keys which is coherent with the definition. 3 IMPLEMENTATION ISSUES of XFSM on a homogeneous set of flows. Once the stateful stage has been configured the controller. 3 1 Feasibility analysis can proceed installing entries in the flow table that will now. We first discuss how a switch architecture should be con match also on the current state of the flow It is important. ceptually extended to support our proposed stateful opera to note that a complete description of the XFSM can be find. tion Our specific focus is to gain insights on which currently just looking at the set of flow entries installed in the flow. available OpenFlow primitives can be reused and how and table as a combination of event and state matching state. which new primitives need to be added transitions and actions. 3 1 1 Architecture and primitives 3 1 3 Support for multiple XFSMs. A crucial feature needed by our scheme is the ability to Multiple XFSM programs operating on different lookup. perform matches using state labels and use more than one scopes can be trivially configured using pipeling of multi. table These features are indeed available since Openflow ple stateful stages More interesting is the case of different. 1 1 table pipeline processing and metadata support have XFSMs that must be configured on a same scope As an. been introduced A packet entering an OpenFlow switch is example in the port knocking example we could wish to. processed through a set of linked flow tables that provide have a set of addresses say those originated from the sub. matching forwarding and packet modification Metadata net 131 175 16 for which we would like to have a different. are used to extend packet header so as to carry arbitrary knock sequence or even port 22 opened by default with. information from one table to the next The controller can out going through the knocking process This can be easily. install remove flow entries by sending flow mod messages accomplished by adding to the State Table the ability to. We indicate with the term stateless stage the processing match prefixes e g match IPsrc 131 175 and use pri. operated by a single flow table Conversely we define as ority ordering or longest match to determine the matching. stateful stage Figure 3 a logical block comprising a State to be used for retrieving an associated state. Table and an XFSM table and implementing our abstrac. tion A packet is first processed by a key extractor which 3 2 Software datapath implementation. produces a string of bits representing the key to be used Being a more compelling HW implementation a much. to match a row in the state table The key is derived by longer term goal we tried to gain further insights by devel. concatenating the header fields defined in the lookup scope oping a prototype software implementation We extended. The matched state label is appended to the packet headers the Openflow 1 3 software switch 18 with our proposed. as metadata In case of table miss the key is not matched stateful operation support Our implementation is available. then a DEFAULT state will be appended to the packet head at 19 so we limit to summarize here the main modifica. ers If the header fields specified by the lookup scope are not tions very few as a further proof of the low impact of our. found e g extracting the IP source address when the Eth proposal. ernet type is not IP a special state value NULL is returned To support advertisement and configuration of the pro. The XFSM table can be implemented in OpenFlow v1 1 posed state management feature a new switch capability bit. as a standard flow table whose entries are matched using OFPC TABLE STATEFUL has been defined as well as a new ta. the relevant header fields representing the event and the ble configuration bit OFPCT TABLE STATEFUL The basic flow. metadata state label We only need to specify along with table data structure has been extended with support for the. the action set to be executed a supplementary command state table and key extractors A new Openflow instruc. developed as an OpenFlow instruction specifically a new tion OFPIT SET STATE has been added to allow the Open. SET STATE instruction that will immediately trigger an up flow extended datapath to update the state table with a. date of the previous state table The usage of an instruction given next state parameter A new state modify messages. guarantees that the state update is performed at the end called OFP STATE MOD have been defined along with the rele. of the stage even when action bundles are configured and vant message structure to allow the controller to respectively. permits to pipeline our stateful stage with supplementary configure the state entries and key extractors lookup scope. stages including other stateful ones and update scope As already briefly anticipated the ac. ACM SIGCOMM Computer Communication Review 49 Volume 44 Number 2 April 2014. CONTROLLER,state mod ow mod,State table XFSM table. match key state pkt headers match elds pkt headers. state headers state actions,pkt headers Key extractor.
lookup scope,Key extractor,update scope,pkt headers next state SET STATE next state. Figure 3 Architecture of the stateful stage The XFSM table is represented by a standard Openflow table. while a SET STATE action is used to trigger updates on the state table. tual implementation and configuration of the XFSM table Note that efficient technical ways to pass extended header. has not required any modifications to the existing code as it parameters to actions have been recently discussed in 15. simply relies on the standard Openflow match table struc Simple arithmetic operations on labels The com. ture and flow mod message beside the already discussed bination of states and simple arithmetic operations permits. support for the new OFPIT SET STATE instruction several interesting extensions For instance we could triv. ially program a state machine which thwarts some IP frag. 4 BEYOND THE BASIC ABSTRACTION mentation attacks by forwarding IP fragments only if they. While outlining in the previous sections our basic idea are received in strict order We recall that a very basic IP. we tried to remain grounded to the current OpenFlow func fragmentation attack consists in sending a first small frag. tionalities so as to hopefully convince the reader that what ment fragment offset 0 more fragment 1 and then. we do propose is not futuristic but can be readily deployed send a second IP fragment claimed to be the last small frag. In what follows we abandon prudence and we try to out ment of a large 64 KB packet This could be easy detected. line with no pretense of making any firm claim but rather by computing from the length of the first IP fragment the. with the goal to stimulate discussion how the same pro expected offset for the second fragment use it as a tempo. grammability model could be extended along complemen rary state label or a numerical value associated to a frag. tary directions so as to provide device programmers with ment state and forward packets only if they match such a. further network function programming abilities computed offset field i e if they are in sequence We stress. We point out that we do not claim our propose is able that albeit apparently compelling and possibly inspiring a. to implement all possible functionalities that are currently broad range of extensions such arithmetic computations. supported by complex middleboxes Nevertheless we expect may become critical at high speed and a much closer look. that some of their less complex functions can be shifted to at their viability is needed. switches for a more responsive reaction of the network 4 2 Enforcing conditions full XFSMs. 4 1 Improving state handling Flow statistics can be considered as memory registers. associated to a flow Similarly device level states such as. Soft states and event timers Adding timeouts as de. the current occupancy of an output queue or device level. scribed in OpenFlow to a state table entry is straightforward. statistics such as the amount of bytes delivered through a. and the API could be extended to permit the programmer to. given switch port can be as well interpreted as global reg. specify a different timeout for each state transition Man. isters And finally as implied in the previous section the. aging timeout expiration is also trivial but only if we do. association of a numerical value to a state can be interpreted. assume that all states return to the DEFAULT one upon. as a value stored in a per flow register The values stored. timeout expiration Indeed timeouts could be implicitly. in such registers could be used as further conditions to. managed by assuming that a state lookup which retrieves. trigger an action associated to an event, an expired state shall return a DEFAULT state Rather. Quite interestingly the definition of eXtensible Finite State. handling timer expirations as explicit events which trigger. Machine given in 10 provides a formal model which gen. meaningful non default transitions might open very inter. eralizes the Mealy Machines introduced in section 2 and. esting scenarios support for exponential backoff operation. which permits to explicitly accounts for conditions taken on. enforce a different TCP forwarding on the basis of whether. registry values And indeed the ability to set conditions in. an ACK returns before or after a time window etc but. an XFSM was actually proven to be vital in 8 for formally. arguably requires a significant leap in the implementation. specifying wireless MAC protocols,Using state labels as function parameters The. We recall from 10 than an XFSM is an abstract 7 tuple. MAC learning example illustrated in Table 1 requires an. S I O T D U F where the states S the input events I. entry for each possible port of the switch By permitting. and the output action O are the same as defined in section. the forwarding action to receive as input a parameter pro. 2 and where, vided in the meta data associated to the packet in our spe. cific case the state label interpreted as a switch port num D is an n dimensional linear space D1 Dn which. ber it is possible to implement the same program with only describes all possible configurations of n registers. two entries one for the default state MAC destination not F is a set of enabling functions fi D TRUE FALSE. found in the forwarding database and one which forwards which models conditions to be verified on the configu. the MAC frame to the switch port found in the state label ration registers to enable transitions. ACM SIGCOMM Computer Communication Review 50 Volume 44 Number 2 April 2014. U is a set of update functions ui D D which per http www2 technologyreview com article 412194 tr10. mits to model changes in the deployed registers and software defined networking. T S I F S U O is a transition function which 4 O N Foundation Openflow switch specification ver. takes as input the current state event and conditions 1 4 0 in Oct 14 2013. and outputs i the next state ii the associated action 5 B Mack Crane Openflow extensions in US Ignite. and iii the associated registry update ONF GENI workshop October 8 2013. 6 D Meyer Openflow Today s reality tomorrow s, We argue that under the restrictive condition of prede.
promise an architectural perspective in SDN, fined hard coded in the device and exposed via the program. Summit 2013 Paris France March 2013 2013, ming interface rather than freely programmed set of avail. able registers enabling functions and update func 7 P Peresini M Kuzniar and D Kostic OpenFlow. tions this abstraction appears at reach with current tech Needs You A Call for a Discussion About a Cleaner. nology and hence promising to be explored further Indeed OpenFlow API in 2nd EU Workshop on Software. conditions could be exploited in many scenarios such as Defined Network EWSDN 2013. QoS differentiated packet treatment when above a given 8 I Tinnirello G Bianchi P Gallo D Garlisi. count threshold currently addressed in OpenFlow with a F Giuliano and F Gringoli Wireless MAC. dedicated new extension the meters load balancing set Processors Programming MAC Protocols on. forwarding port for a new flow based on queue status or Commodity Hardware in IEEE INFOCOM 2012. link load statistics monitoring and so on pp 1269 1277. 9 G Bianchi P Gallo D Garlisi F Giuliano,F Gringoli and I Tinnirello MAClets active MAC. 5 CONCLUSIONS protocols over hard coded devices in 8th ACM. This paper aims to propose a first step in the direction CoNext 12 2012 pp 229 240. of supporting stateful per flow processing over closed plat 10 K T Cheng and A S Krishnakumar Automatic. forms In our proposal and in full adherence with the Open Functional Test Generation Using The Extended. Flow strategy we took a very pragmatic approach we com Finite State Machine Model in ACM Int Design. promised on generality and we restricted to the stateful Automation Conference DAC 1993 pp 86 91. handling of standard OpenFlow match action rules This 11 Z Qazi C C Tu R Miao L Chiang V Sekar and. permitted us to emerge with an apparently immediately de M Yu Practical and incremental convergence. ployable programmatic abstraction relying on core primi between sdn and middleboxes in Open Network. tives and data structures mostly present in OpenFlow im Summit Santa Clara CA April 2013 2013. plementation Our abstraction generalizes the OpenFlow 12 G Gibb H Zeng and N McKeown Initial thoughts. match action rules in terms of an extensible finite state ma on custom network processing via waypoint services. chines which are directy executed inside the switching device in WISH 3rd Workshop on Infrastructures for. thus offloading controllers and perhaps more interestingly Software Hardware co design CGO 2011 April 2011. entailing control functions which require wire speed packet Chamonix France 2011. by packet operation i e which cannot be delegated to the. 13 B Anwer T Benson N Feamster D Levin and, slow logically centralized control plane operation. J Rexford A slick control plane for network, As a compromise we obviously have no pretense to claim.
middleboxes in HotSDN 2013 Hot Topics in, that our abstraction can support all the possible flow. Software Defined Networking 2013, processing needs Nevertheless we believe that stateful han. dling of OpenFlow rules can be beneficial in many scenar 14 M e a Ciosi Network functions virtualization. ios some of those illustrated via use case examples and ETSI White Paper in SDN and OpenFlow World. we hope to stimulate a broader discussion on the many Congress Darmstadt Oct 22 24 2012. questions that our paper opens high speed implementation 15 P Bosshart G Gibb H S Kim G Varghese. should restrict to Mealy Machines or could support more N McKeown M Izzard F Mujica and M Horowitz. general XFSMs Which network processing function today Forwarding metamorphosis Fast programmable. implemented in the controller or in dedicated middleboxes match action processing in hardware for sdn in ACM. can be described using XFSMs And how the ability to SIGCOMM 2013 ACM 2013 pp 99 110. dynamically control flow states directly in the device may 16 V Jeyakumar M Alizadeh C Kim and D Mazieres. influence broader SDN frameworks Tiny packet programs for low latency network. control and monitoring in ACM Workshop on Hot,Topics in Networks HOTNETS 2013 2013. 6 REFERENCES 17 A K Nayak A Reimers N Feamster and R Clark. 1 N McKeown T Anderson H Balakrishnan Resonance Dynamic access control for enterprise. G Parulkar L Peterson J Rexford S Shenker and networks in 1st ACM Workshop on Research on. J Turner OpenFlow enabling innovation in campus Enterprise Networking WREN09 2009. networks ACM SIGCOMM Comput Commun Rev 18 OpenFlow 1 3 Software Switch. vol 38 no 2 pp 69 74 Mar 2008 http cpqd github io ofsoftswitch13. 2 N Feamster J Rexford and E Zegura The Road to 19 Prototype implementation of an OpenFlow 1 3. SDN An Intellectual History of Programmable software switch with XFSM support. Networks ACM Queue To appear 2014 http bit ly Mte0zb. 3 K Greene TR10 Software defined network, ing 2009 MIT Technology Review available online at. ACM SIGCOMM Computer Communication Review 51 Volume 44 Number 2 April 2014.

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1 THREE ESSAYS ON EQUALIZATION TRANSFERS IN A FISCAL FEDERALISM JIN WOONG KIM Thesis submitted to the Faculty of Graduate and Postdoctoral Studies

Non-cognitive Skills and Factors in Educational Attainment

Non cognitive Skills and Factors in Educational Attainment

to research in learning innovations from the learning sciences view. Learning sciences is an interdisciplinary field that draws on multiple theoretical perspectives and research with the goal of advancing knowledge about how people learn. The field includes cognitive science, educational psychology, anthropology, computer