Boon Thau Loo University of Pennsylvania

Transcription

1 Summary of Networked Systems Breakout Boon Thau Loo University of Pennsylvania

2 Networked Systems Breakout Series of minute talks: Challenges in safe routing (Alex Gurney) Compositional network services (Pamela Zave) Synthesis in wireless control networks (George Pappas) Existing solutions as starting points (Boon Thau Loo) Discussion.

3 Outline Summary of yesterday s discussion Safe Routing Compositional network services Wireless control systems Synergies and Opportunities One concrete use case (answering the 7 One concrete use case (answering the 7 questions)

4 Border Gateway Protocol (BGP) BGP: single de-facto Internet routing protocol Network is partitioned into Autonomous Systems (AS) operated by Internet Service provider (ISP) ebgp across autonomous systems (ASes) + ibgp within one AS ASes exchange routing information using path-vector protocol ISP sets local routing policy to influence route decision Local policy is expressed in terms of path-vector attributes Receive advertisement Apply import policies Select best route Apply export policies Send updates Filter routes and tweak attributes Based on attribute values Filter routes and tweak attributes BGP is unsafe: route oscillation, slow convergence

5 Some Hard Questions Can we formalize policy intentions? Can we tell whether a given implementation (set of configurations) matches the intent? How can intentions (plus constraints) be used to synthesize network configurations?

6 Formally Safe Routing (FSR) Toolkit HotNets 09, IEEE/ACM Transactions on Networking (ToN) Contribution #1: Reduction of safety analysis to SMT solving Contribution #2: Provably correct distributed implementation Generation of declarative networking programs Correctness proof for the policy -> Network Datalog (NDlog) translation

7 Pinpoint BGP Misconfigurations [SIGCOMM 11 demo, Node 7 Node 27 Node 32

8 Declarative Networking Implementation gpvrecv :- PNew=f_concatPath(U,Path), V=f_head(Path), SNew=f_concatSig(L,S), f_import(l,s)=true. gpvstore :- D=f_last(P). gpvselect lo :- gpvsend :- f_export(l,s)=true. Receiving routes: gpvrec computes new route signature according to P, I Storing routes: gvpstore builds routing table and stores all candidate routes Selecting routes: gpvselect selects best route according to route preference < Sending routes: gpvsend propagates routes according to export filter E

9 Characteristics ti of a good solution Must be obviously superior to having an assortment of Perl scripts and templates. Expresses high level policy ideas Bogons and martians must never appear Stay close to a 3:2 traffic ratio on this link Never cause BGP convergence failure Must have a debugging story not just synthesize and hope. Accounts for partial information neighbors configurations are probably not available. Handles multiple protocols and multiple vendor implementations.

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13 Wireless eessis transformative so a for industrial control Paradigm shift towards multi-hop control architectures Plant Controller Plant Controller Wired Control System Wireless Control System

14 Synthesis challenges for centralized control with multi-hop networks Plant Controller Control-scheduling co-design Compositional scheduling of multiple l control loops Controller design incorporating TDMA-based properties Network topology design based on physical plant properties Robustness Robustness analysis with respect to packet loses, node failures Robustness with respect to faulty or malicious nodes

15 The Wireless Control Network (WCN) In multi-hop control, nodes route information to controller WCN Plant Controller Plant Can we leverage computation of the network? Can we distribute the controller to nodes of the network?

16 Current Research Intrusion Detection Level Monitoring Requirements Plant Dynamics Network Topology Network Synthesis Communication schedule Optimal Control Robustness Embedding of existing controllers Proposed Research Wireless Control Network Configuration Runtime Adaptation

17 PUMA: Declarative Policy-based Routing and Channel Selection COMSNET 12, VLDB 12 Wireless interference: Links interfere if running on nearby channels Ideally, all links use non-interfering channels However, constraints exists: # of channels, interfaces Primary users Optimization under goal and constraints Constraint Optimization Optimization under goal and constraints Constraint Optimization Problem (COP)

18 Declarative Channel Selection goal minimize C in totalcost(c) var assignchannel(x,y,c) forall link(x,y) s1 cost(x,y,z,c) :- assignchannel(x,y,c1), assignchannel(x,z,c2), Y!=Z, C=1, C1-C2 <F_mindiff. s2 totalcost(count<c>) :- cost(x,y,z,c). Channel selection as COP (one-hop interference model) c1 assignchannel(x,y,c) -> link(x,y), availchannel(x,c,f,st). // primary user constraint c2 assignchannel(x,y,c) C) ->!primaryuser(x,c). c3 assignchannel(x,y,c) -> assignchannel(y,x,c). c4 uniquechannel(x,count) -> numinterface(x,k), Count<=K. s3 uniquechannel(x,unique<c>) :- assignchannel(x,y,c). Colog rules in PUMA Natural mapping: COP declarative specifications 18

19 Synergies and Opportunities Wireless control networks + declarative networking Distributed constraint solving Probabilistic notions, exploiting performance and robustness tradeoffs High level objectives, realized in network layer functionalities. Compositional network synthesis Mobility options as an optimization problem. Mobile control system? Application-layer synthesis Resource management challenges at Google Determining number/placement of replicas, caching, number of servers allocated, etc. to provide consistency, robustness, and fault tolerance. Initial work in declarative cloud resource orchestration (poster last night). Software defined networking (e.g. OpenFlow).

20 Outline Summary of discussion Safe Routing Compositional network services Wireless control systems One concrete use case (answering the 7 questions)

21 Router Configuration Synthesis Reconcile diverse policy ideas into a coherent networkwide setup (Q1 Programmer insights) Explore and decide on tradeoffs when goals conflict (Q2 Feedback) Use simulation or live network link to gather data and demonstrate traffic-flow consequences; present examples of problematic feature interactions (Q3 User studies) Engage expert operators in determining language of policy needs then ask them and novices to carry out (re-)configuration tasks

22 Router Configuration Synthesis (Q5 Specifications) Partial configuration data, hard constraints (e.g. protocol convergence, robustness), and optimization goals (Q6/7 Strategies and tools) Combinatorial theory, mechanized with SMT, constraint solving, etc.; single representation usable by multiple related tools (Q4 Artifacts) Router configurations, with a deployment, reconfiguration and measurement capability

23 P d R t Sh h d T lkit Proposed Route Shepherd Toolkit SIGCOMM 12 demo