Overview of Existing Routing Protocols for Low Power and Lossy

Networksdraft-levis-roll-overview-protocols-00

Phil Levis, Stanford Univ.JP. Vasseur, Cisco SystemsDavid Culler, UC Berkeley

IETF 70 ROLL WG Meeting

Goal (1)

• Provide a discussion platform for building a rough consensus around the suitability, ill-suitability, and technical trade-offs in utilizing existing IETF protocols for Routing Over Low-power and Lossy networks.

In pictures

Existing Protocols

3. Link State Protocols 3.1. OSPF 3.2. OLSR 3.3. TBRPF ……4. Distance Vector protocols 4.1. RIP 4.2. DSDV 4.3. AODV 4.4. DYMO 4.5. DSR . . . . …

Overview ID

Common understanding of basis for analyzing alternatives and rough consensus on assessment

Future

“roll proto”

Goal (2)

• Provide a discussion platform for building a rough consensus around the suitability, ill-suitability, and technical trade-offs in utilizing existing IETF protocols for Routing Over Low-power and Lossy networks.

• Not to design a final protocol, but a baseline and framework for the process of defining one.

Outcome

Crit 0 Crit 1 Crit 2 Crit 3 …

3. Link State 3.1. OSPF 3.2. OLSR 3.3. TBRPF …4. Distance Vector 4.1. RIP 4.2. DSDV 4.3. AODV 4.4. DYMO 4.5. DSR …

Rough Consensus on the Criteria

Rough Consensus on the Analysis

Quantitative and qualitative

The Technical Task

Application DomainRequirements Simplifications

TechnologicalConstraints Challenges

Routingover

Low-Power & Lossy

… scalability… … low rate …

Preliminary Analysis

• N – nodes

• C – communicating nodes

• P – pairs (active routes)

• D – destinations

• d – degree (denisty, nbrs)

• c – link churn

• h – hops (diameter, route length)

Use Ctrl Routing ovhd state

3. Link State 3.1. OSPF wired O(NNdc) O(Nd) 3.2. OLSR wireless O(NN) O(Nd) 3.3. TBRPF wireless O(NN) O(Ndd)…4. Distance Vector 4.1. RIP wired O(ND) O(D) 4.2. DSDV wireless O(NCc) O(Cd) 4.3. AODV wireless O(ND) O(D) 4.4. DYMO wireless O(NCch) O(Ch+d) 4.5. DSR wireless O(NNdh) O(Dh)…

… just to get discussion ROLLing

What’s different in ROLL?

Routing

• … exchange of information to establish and maintain local tables such that each node can compute– next hop, IF := R(destination)

• in a manner consistent with the underlying connectivity graph

IF := R(d)

Wireless (nLP, nL) Routing• No a priori underlying connectivity graph

– a link exists if it works when you try it– “self-organization”, discovery

• Next hop is a neighbor node selection–nbr set may vary in time due environmental effects, movement, interference, obstacles, other communication, …

Topology is determined by physical placement

e.g, impact on d? …of d?

Parameters (first pass)

• N (Nodes): # points of interest

• d (degree): density of deployment / range– max degree may be huge

• h (hops): physical extent / range

• c (churn): environmental factors

• C (Communicators): active portion

• D (Destinations): concentration of flows

Constraints• Low Power

– lifetime, physical size, rate of activity, cost, applicability, … all dictated by power consumption

– Short range, high loss rate, small MTU, low rate links

– Low (ave) data rates typical• Routing protocol rate must be << application rate

Routing protocol comm. costs matter• Discovery, maintenance, repair, …• Computed wrt deployment characteristics

– N, d, h, c, C, D, …

Constraints

• Low Power• Footprint

– microcontrollers (outnumber microprocessors 25:1) typically have kilobytes of memory, not megabytes or gigabytes.

– $s• ram $0.40/kb, 100x sram, 10,000x dram

– Standby power (which dominates in low duty cycle) determined by leakage

• MB ram => discarded in sleep, restored on wake All routing state matters

route tables, neighbor tables, caches, DBs, buffers• N, d, h, c, C, D

– Summarization, partial information, …

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Approx $

Flash

RAM

MSP430x1xx Price per Flash x RAM

Challenges• Lossy

– Low Transmit Power • Low SNR, short range [d?, h?]

– Low sensitivity– Physical attenuation, occlusion, interference, motion

• generally cannot move the node to make the network happy

– Receiver diversity, in addition to temporal, frequency, spatial

• loss is typical, not exceptional– often transient, not necc. excess data rate [c?]– typically, should not trigger costly repair– Loss No Link

– Reception Link present– Multiple paths permit local rerouting

• Scale is often very large

Rock and ROLL• Requires rigorous routing protocol design

– Can’t just throw resources at it.– Can’t just throw bandwidth at it.– Must use prolonged observation, not

instantaneous.– Faces same concerns as embedded

applications

• ROLL operates “between a rock and a hard spot”

Can we tackle such a hard problem?

• Lots of existence proofs in the industry today• Application domains introduce important

simplifications– The “not required” or “infrequent” is as important as

the “is required”– Routing Requirement drafts are defining these– This draft represents them parametrically

• Example– Vast majority of flows are in to and out of a single (or

few) points [ D?, C?, P?]– Minority of mobile nodes within static extent– …

Start of a Process• Important to have a analysis template to gain

consensus on the relevant parameters, the criteria and the analysis across protocols

• Each entry in the table will have considerable supporting evidence

• Goal is common understanding of facts, not “winning the match”.– There may be no “winner” but important lessons

learned from each entrant.– No “sacred cows” assumed.

• Expect an active, interactive exchange between Phili and Dublin