Summary of Networked Systems Summary of Networked Systems BreakoutBreakout

Boon Thau Loo University of Pennsylvania

Net orked S stems Breako tNetworked Systems Breakout

Series of 15-20 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)g g p ( )

Discussion.

O tlineOutline

Summary of yesterday’s discussionSafe RoutinggCompositional network servicesWireless control systemsySynergies and Opportunities

One concrete use case (answering the 7 One concrete use case (answering the 7 questions)

Border Gateway Protocol (BGP)Border Gateway Protocol (BGP)

BGP: single de-facto Internet routing protocol Network is partitioned into Autonomous Systems (AS) operated by

Internet Service provider (ISP)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 ISP sets local routing policy to influence route decision

Local policy is expressed in terms of path-vector attributes

Apply import Apply exportSelect best SendReceive Apply import policies

Apply export policies

Select best route

Filter routes and tweak attributes

Based on attribute values

Filter routes and tweak attributes

Send updates

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BGP is unsafe: route oscillation, slow convergence …

Some Hard Q estionsSome 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?

F ll S f R ti (FSR) T lkitFormally Safe Routing (FSR) ToolkitHotNets’09, IEEE/ACM Transactions on Networking (ToN)

Contribution #1: Reduction of safety analysis to SMT solving Contribution #2: Provably correct distributed implementation

G ti f d l ti t ki Generation of declarative networking programs Correctness proof for the policy -> Network Datalog (NDlog) translation

Pinpoint BGP Misconfigurationsp g[SIGCOMM’11 demo, http://netdb.cis.upenn.edu/fvr/video.html]

Node 7

Node 27Node 27

Node 32

Declarative Networking Implementation

gpvRecv sig(@U,SNew,PNew) :- msg(@U,V,D,S,Path),PNew=f_concatPath(U,Path), V=f_head(Path),SNew=f_concatSig(L,S), label(@U,V,L),_f_import(L,S)=true.

gpvStore route(@U,D,S,P) :- sig(@U,S,P), D=f_last(P).

S l t l lO t(@U D f S P) t (@U D S P)gpvSelect localOpt(@U,D,a_pref<S>,P) :- route(@U,D,S,P).

gpvSend msg(@N,U,D,S,P) :- localOpt(@U,D,S,P),label(@U,N,L), 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

Ch t i ti f d l tiCharacteristics of a good solution

Must be obviously superior to having an assortment of Perl scripts and templates.

Expresses high level policy ideas 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 hopehope.

Accounts for partial information –neighbors’ configurations are probably not available.

Handles multiple protocols and multiple vendor implementations.

Wireless is transformative for e ess s a s o a e oindustrial control Paradigm shift towards multi-hop control architectures

PlantPlant Controller a tControllerPlant

Wired Control System Wireless Control System

Synthesis challenges for centralized control with multi-hop networks

Plant Controller

• Control-scheduling co-designC iti l h d li f lti l t l l– Compositional scheduling of multiple 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

Th Wi l C t l N t k (WCN)The Wireless Control Network (WCN)

In multi-hop control, nodes route information to controllerWCN

Plant Controller PlantController

Can we leverage computation of the network? Can we distribute the controller to nodes of the network?

C rrent ResearchCurrent Research

Monitoring Requirements

Intrusion DetectionLevel

Plant Dynamics

Plant Dynamics

Network Synthesis

NetworkTopology

Communication h d lTopology schedule

Embedding of existing controllers

OptimalControl

Proposed ResearchRobustness g

Wireless Control Network Configuration

Runtime Adaptation

PUMA: Declarative Policy-based Routing y gand Channel Selection

Wi l i t f

COMSNET’12, VLDB’12

Wireless interference: Links interfere if running on nearby channels

Ideally, all links use non-interfering channels However constraints exists: However, constraints exists:

# of channels, interfaces Primary users

Optimization under goal and constraints Constraint Optimization Optimization under goal and constraints Constraint Optimization Problem (COP)

D l ti Ch l S l tigoal minimize C in totalCost(C)var assignChannel(X,Y,C) forall link(X,Y)

Declarative Channel Selection

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).

c1 assignChannel(X,Y,C) -> link(X,Y), availChannel(X,C,F,St).

// primary user constraintc2 assignChannel(X Y C) -> !primaryUser(X C)c2 assignChannel(X,Y,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).Channel selection as COP (one-hop interference model) Colog rules in PUMA

18Natural mapping: COP declarative specifications

S nergies and Opport nitiesSynergies 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.y p p p Mobile control system?

Application-layer synthesis Resource management challenges at Google 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).(p g )

Software defined networking (e.g. OpenFlow).

O tlineOutline

Summary of discussionSafe RoutinggCompositional network servicesWireless control systemsy

One concrete use case (answering the 7 questions)questions)

Ro ter Config ration S nthesisRouter Configuration Synthesis

Reconcile diverse policy ideas into a coherent network-wide setup

(Q1 Programmer insights) Explore and decide on (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 (Q3 User studies) Engage expert operators in determining language of policy needs – then ask them and novices to carry out (re-)configuration tasks

Ro ter Config ration S nthesisRouter Configuration Synthesis

(Q5 Specifications) Partial configuration data, hard constraints (e.g. protocol convergence, robustness), and optimization goalsoptimization 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 capabilityreconfiguration and measurement capability

P d R t Sh h d T lkitProposed Route Shepherd ToolkitSIGCOMM’12 demo