1

NFD forwarding pipelines

Junxiao Shi, 2015-07-02

2

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

3

Pipelines

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

4

Legend in diagrams

building block

pipeline

tables feature

strategy

face feature

5

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

6

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

7

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

8

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.

9

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

10

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

11

ContentStore miss pipeline

FIB lookup

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

12

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

13

determine whether in producer region• Input:

• routerName: the router's Name, from configuration• interest

• Algorithm:1. if the Interest does not have a Link object, return true and

abort these steps2. let delegationName be the first delegation Name in the Link

object3. if delegationName is a prefix of routerName, return true and

abort these steps4. let delegationName be the next delegation Name in the Link

object, goto step 35. return false

14

FIB lookup with SelectedDelegation• Given an Interest with Link object and

SelectedDelegation, perform a FIB lookup using the delegation Name indexed by SelectedDelegation.

15

choose and set SelectedDelegation• Input:

• interest, with Link but without SelectedDelegation

• Algorithm:1. sort delegations by increasing Preference2. let delegationName be the first delegation Name3. lookup FIB with delegationName4. if a match is found, insert SelectedDelegation field onto

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

5. let delegationName be the next delegation Name, goto step 3

6. lookup FIB with Interest Name

16

outgoing Data

set PIT straggler timer

timer event

Interest finalize

ContentStore hit pipeline

17

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

which strategy should process this Interest, and trigger that strategy

18

outgoing Interest pipeline

insert OutRecordpick Interest send Interest

violates /localhost?

Y

(drop)

violates /localhop?

(drop)

Y

N N

19

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

20

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

21

Interest unsatisfied pipeline

invoke PIT unsatisfied callback

Interest finalize

22

Interest finalize pipeline

PIT delete

Dead Nonce List insert

need Dead Nonce List

insert?

Y

N

23

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.

24

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

25

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

26

Data unsolicited pipeline

accept to cache?

Y

CS insert

N

27

outgoing Data pipeline

traffic manager send Data

violates /localhost?

Y(drop)

N

28

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

merely passes Data packet to the next step