NFD forwarding
pipelines
Junxiao Shi, 2015-08-14
1
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
2
Pipelines
•
•
•
•
•
•
•
•
•
•
•
incoming Interest
ContentStore miss
ContentStore hit
Interest loop
outgoing Interest
Interest reject
Interest unsatisfied
Interest finalize
incoming Data
Data unsolicited
outgoing Data
3
Legend in diagrams
pipeline
building block
strategy
tables feature
face feature
4
incoming
Interest
Interest
loop
ContentStore
miss
ContentStore
hit
outgoing
Interest
Interest
reject
Interest
unsatisfied
Interest
finalize
strategy API
broadcast
strategy
incoming
Data
Data
unsolicited
ncc strategy
best route
strategy
outgoing
Data
access strategy
5
Pipelines Overall Workflow
Interest
loop
incoming
Interest
after receive
Interest
Interest
reject
before expire
Interest
outgoing
Interest
ContentStore
miss
unsatisfy
timer
Interest
unsatisfied
ContentStore
hit
incoming
Data
before satisfy
Interest
straggler
timer
Interest
finalize
outgoing
Data
Data
unsolicited
6
incoming Interest pipeline
receive Interest
violates
/localhost?
Y
(drop)
Y
N
Interest
loop
detect
duplicate
Nonce
PIT insert
N
cancel unsatisfy
& straggler timer
Y
is
pending?
N
CS
lookup
Y
N
ContentStore
miss
ContentStore
hit
7
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.
8
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
9
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
10
ContentStore miss pipeline
insert InRecord
Y
has Link
object?
N
set PIT
unsatisfy timer
in
producer
region?
N
timer event
has
Selected
Delegation
?
Y
Y
FIB lookup with
Interest Name
FIB lookup with
SelectedDelegation
dispatch to
strategy
Interest
unsatisfied
N
FIB lookup with first
Delegation Name
N
Y
in defaultfree zone?
choose and set
SelectedDelegation
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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
12
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.
13
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 false
2. 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.
2.
lookup FIB with delegation Name
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.
15
ContentStore hit pipeline
Interest
finalize
timer event
set PIT
straggler timer
outgoing
Data
16
dispatch incoming Interest to
strategy
• Given FIB entry and incoming Interest, determine
which strategy should process this Interest, and
trigger that strategy
17
outgoing Interest pipeline
(drop)
(drop)
Y
Y
violates
/localhost?
N
violates
/localhop?
pick Interest
N
insert
OutRecord
send Interest
18
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
19
Interest reject pipeline
• Process an Interest that has been decided that it
has nowhere to go
cancel unsatisfy
& straggler timer
set PIT
straggler timer
timer event
Interest
finalize
20
Interest unsatisfied pipeline
invoke PIT unsatisfied
callback
Interest
finalize
21
Interest finalize pipeline
need Dead
Nonce List
insert?
Y
Dead Nonce
List insert
N
PIT delete
22
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.
23
incoming Data pipeline
receive Data
violates
/localhost?
N
PIT
match
N
Data
unsolicited
Y
Y
(drop)
CS insert
invoke PIT satisfy
callback
foreach
cancel unsatisfy
PIT entry & straggler timer
need Dead
Nonce List
insert?
Y
Dead Nonce
List insert
N
mark PIT
satisfied
set PIT
straggler timer
outgoing
foreach
Data
pending
downstream
timer event
Interest
finalize
24
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
25
Data unsolicited pipeline
accept to
cache?
N
Y
CS insert
26
outgoing Data pipeline
violates
/localhost?
Y
(drop)
N
traffic manager
send Data
27
Pass-through traffic manager
• Provide a traffic manager that does nothing and
merely passes Data packet to the next step
28