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NFD forwarding pipelines

Junxiao Shi, 2015-08-14

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Overview

• Forwarding consists of pipelines and strategies• Pipeline: a series of steps that operate on a packet

or a PIT entry• Strategy: a decision maker on whether, when, and

where to forward an Interest

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Pipelines

• incoming Interest• ContentStore miss• ContentStore hit• Interest loop• outgoing Interest• Interest reject• Interest unsatisfied• Interest finalize• incoming Data• Data unsolicited• outgoing Data

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Legend in diagrams

building block

pipeline

tables feature

strategy

face feature

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incoming Interest

incoming Data

outgoing Interest

outgoing Data

strategy API

ncc strategy

broadcast strategy

Interest reject

Interest unsatisfied

Interest loop

best route strategy

Data unsolicited

Interest finalize

ContentStore miss

ContentStore hit

access strategy

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Pipelines Overall Workflow

incoming Interest

incoming Data

outgoing Interest

outgoing Data

after receive Interest

Interest reject

Interest unsatisfied

Interest loop

Data unsolicited

before satisfy Interest

before expire Interest

unsatisfytimer

stragglertimer

Interest finalize

ContentStore miss

ContentStore hit

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incoming Interest pipeline

CS lookup

PIT insert

cancel unsatisfy & straggler timer

Y

receive Interest

detect duplicate

Nonce

Interest loopY

is pending?

Y

violates /localhost?

Y (drop)

ContentStore miss

ContentStore hit

N

N

N

N

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detect duplicate Nonce

• If any InRecord or OutRecord contains the same Nonce as the incoming Interest, or the Name and Nonce of the incoming Interest appear in Dead Nonce List, a duplicate Nonce is detected.• If the duplicate Nonce is found in InRecord only, this is a

multi-path arrival, and not a loop.• If the duplicate Nonce is found in OutRecord or Dead

Nonce Table, this is either a multi-path arrival or a loop, and these two reasons are indistinguishable.

• Nonce is later recorded on an InRecord.

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Interest loop pipeline

• Process an Interest that has been considered looped• This pipeline is currently empty, which means Interest

packet is dropped. NACK could be added here

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ContentStore miss pipeline

• This pipeline is entered when an incoming Interest• is pending (so ContentStore lookup is unnecessary), or• is miss from ContentStore

• This pipeline will start forwarding the Interest

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ContentStore miss pipeline

FIB lookup with Interest Name

dispatch to strategy

insert InRecordset PIT

unsatisfy timerInterest

unsatisfiedtimer event

in producer region?

has Selected

Delegation?

FIB lookup with SelectedDelegation

choose and set SelectedDelegation

Y

N N

Y

FIB lookup with first Delegation Name

in default-free zone?

YN

has Link object?

N

Y

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set PIT unsatisfy timer

• Given PIT entry, set an unsatisfy timer which fires when InterestLifetime expires for all unexpired InRecords• When the unsatisfy timer fires, Interest unsatisfied

pipeline is entered

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determine whether in producer region• Input:

• regionNames: the router's region names, from configuration• interest

• Algorithm:1. foreach delegation in Link:

1. foreach regionName in regionNames:1. if delegation Name is a prefix of regionName, return true and abort

these steps

2. return false

• Note:• We consider all delegations, not just SelectedDelegation, to

maximize flexibility. This is cheap because there's no table lookup.

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determine whether in default-free zone• Input:

• interest, with Link but without SelectedDelegation• FIB lookup result for the first delegation

• Algorithm:1. if FIB lookup result is the root entry (ndn:/), and the entry has

at least one nexthop record, return false2. return true

• Note:• FIB lookup will never return "no match", because the FIB always

has a root entry, but this entry can have no nexthop record.• We consider only the first delegation, to minimize table lookup

cost. Checking all delegations probably gives better results, but it requires too many lookups.

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choose and set SelectedDelegation• Input:

• interest, with Link but without SelectedDelegation• FIB

• Algorithm:1. foreach delegation in Link, sorted by increasing Preference

1. lookup FIB with delegation Name2. if a match (with non-zero nexthop records) is found, insert

SelectedDelegation field with the index of this delegation, return the match, and abort these steps

2. lookup FIB with Interest Name

• Note:• This is the only operation that requires multiple table lookups, but it

happens only once on an Interest's path at the first default-free router.

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outgoing Data

set PIT straggler timer

timer event

Interest finalize

ContentStore hit pipeline

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dispatch incoming Interest to strategy• Given FIB entry and incoming Interest, determine

which strategy should process this Interest, and trigger that strategy

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outgoing Interest pipeline

insert OutRecordpick Interest send Interest

violates /localhost?

Y

(drop)

violates /localhop?

(drop)

Y

N N

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pick outgoing Interest packet• Given PIT entry and nexthop, decide the guiders on

the outgoing Interest• Nonce and InterestLifetime come from an InRecord with

longest remaining lifetime, however InRecord with same Face as the nexthop cannot be used• InterestLifetime is carried from the original packet

without deducting the time elapsed• Scope is the most relaxed among all unexpired InRecords• The last incoming Interest is picked

• This is a simple choice until we understand the effect of guiders better

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Interest reject pipeline

• Process an Interest that has been decided that it has nowhere to go

set PIT straggler timer

timer event

cancel unsatisfy & straggler timer

Interest finalize

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Interest unsatisfied pipeline

invoke PIT unsatisfied callback

Interest finalize

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Interest finalize pipeline

PIT delete

Dead Nonce List insert

need Dead Nonce List

insert?

Y

N

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Dead Nonce List insert

• Dead Nonce List insertion is needed if:• Interest is unsatisified, OR• Interest has MustBeFresh=yes and Data FreshnessPeriod

is shorter than 6 seconds

• Nonces in OutRecords are inserted to Dead Nonce List.

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incoming Data pipeline

PIT match

receive Data

Y CS insert

outgoing Data

cancel unsatisfy & straggler timer

mark PIT satisfied

set PIT straggler timer

foreachPIT entry

foreachpendingdownstream

Data unsolicited

timer event

violates /localhost?

Y(drop)

invoke PIT satisfy callback

Interest finalize

Dead Nonce List insert

need Dead Nonce List

insert?

Y

N

N

N

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set PIT straggler timer

• Given PIT entry, set a straggler timer which fires after a short time• Tstraggler = 100ms

• When the straggler timer fires, PIT entry is deleted

• The purpose of retaining PIT entry for a short time is to facilitate loop detection and to collect measurement for non-fastest upstreams

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Data unsolicited pipeline

accept to cache?

Y

CS insert

N

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outgoing Data pipeline

traffic manager send Data

violates /localhost?

Y(drop)

N

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Pass-through traffic manager• Provide a traffic manager that does nothing and

merely passes Data packet to the next step