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High-Speed Networking: A Systematic Approach to High-Bandwidth Low-Latency Communication
VII.1
25 August 2006 High-Speed Networking 7-1
Sterbenz and TouchEnd-to-End Protocols
End-to-End Protocols1. Introduction
2. Fundamentals and design principles
3. Network architecture and topology
4. Network control and signalling
5. Network components5.1 links
5.2 switches and routers
6. End systems
7. End-to-end protocols8. Networked applications
9. Future directions
25 August 2006 High-Speed Networking 7-2
Sterbenz and TouchEnd-to-End Protocols
End-to-End Protocols
7.1. Functions and mechanisms
7.2. State management
7.3. Framing and multiplexing
7.4. Error control
7.5. Flow & congestion control
7.6. Security & info assurance
network
application
session
transport
network
link
end system
network
link
node
network
link
nodenetwork
link
node
application
session
transport
network
link
end system
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High-Speed Networking: A Systematic Approach to High-Bandwidth Low-Latency Communication
VII.2
25 August 2006 High-Speed Networking 7-3
Sterbenz and TouchEnd-to-End Protocols
Ideal End-to-End Network ModelBandwidth and Delay
Zero end-to-end delay
Unlimited end-to-end bandwidth
Mapp
Mapp
D = 0
R =
ES1
CPU
ES2
CPU
25 August 2006 High-Speed Networking 7-4
Sterbenz and TouchEnd-to-End Protocols
End-to-End ProtocolsFunctions and Mechanisms
7.1 Functions and mechanisms
7.1.1 End-to-end semantics
7.1.2 End-to-end mechanisms
7.1.3 Transport protocols
7.1.4 Control of state
7.2 State management
7.3 Framing and multiplexing7.4 Error control
7.5 Flow and congestion control
7.6 Security and information assurance
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High-Speed Networking: A Systematic Approach to High-Bandwidth Low-Latency Communication
VII.3
25 August 2006 High-Speed Networking 7-5
Sterbenz and TouchEnd-to-End Protocols
E2E Functions and MechanismsEnd-to-End Semantics
Hop-by-hop functions
link layer protocols
link compression and FEC
network forwarding
link / subnet error control
embedded protocols(e.g. protocol boosters)
End-to-end functions
transport protocols
source routing
end-to-end encryption
session protocols
application protocols
Hop-by-Hop
End-to-End
25 August 2006 High-Speed Networking 7-6
Sterbenz and TouchEnd-to-End Protocols
E2E Functions and MechanismsEnd-to-End Argument
Hop-by-hop function composition end-to-end
Examples
HBH encryption has data in clear inside network nodes
HBH link error control doesnt cover network layer errors
End-to-End Argument T-3Functions required by communicating applications can becorrectly and completely implemented only with the knowledgeand help of the applications themselves. Providing thesefunctions as features within the network itself is not possible.
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High-Speed Networking: A Systematic Approach to High-Bandwidth Low-Latency Communication
VII.4
25 August 2006 High-Speed Networking 7-7
Sterbenz and TouchEnd-to-End Protocols
E2E Functions and MechanismsHop-by-Hop Performance Enhancement
E2E functions replicated HBH if performance benefit
Example
per link error control in high bandwidth--delay networksreduce E2E control loop when error
Hop-by-Hop Performance Enhancement Corollary T-3A
It is beneficial to duplicate an end-to-end function hop-by-hop ifthe result is an overall (end-to-end) improvement inperformance.
25 August 2006 High-Speed Networking 7-8
Sterbenz and TouchEnd-to-End Protocols
E2E Functions and MechanismsE2E Argument Misinterpretations
E2E-only
do not replicate E2E services or features HBH
violated HBH performance enhancement corollary
Everything E2E
implement as many services or feature E2E as possible
misstatement of Internet design philosophy:simple stateless network for resilience and survivability
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High-Speed Networking: A Systematic Approach to High-Bandwidth Low-Latency Communication
VII.6
25 August 2006 High-Speed Networking 7-11
Sterbenz and TouchEnd-to-End Protocols
E2E Functions and MechanismsTransport Protocol Service Categories
Transfer mode connectionless datagram
connection-oriented
transaction
continuous media streaming
Reliability
loss tolerance
Delivery order
ordered unordered
Traffic characteristics
25 August 2006 High-Speed Networking 7-12
Sterbenz and TouchEnd-to-End Protocols
E2E Functions and MechanismsTypes of Transport Protocols
Spectrum of transport protocol specialisation general purpose
functionally partitioned
application-oriented
special purpose
Software engineering and implementation choice
Transport Protocol Functionality T-IV
Transport protocols must be organised to deliver the set of end-to-end high-bandwidth, low latency services needed byapplications. Options and service models should be modularlyaccessible, without unintended performance degradation andfeature interactions.
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High-Speed Networking: A Systematic Approach to High-Bandwidth Low-Latency Communication
VII.8
25 August 2006 High-Speed Networking 7-15
Sterbenz and TouchEnd-to-End Protocols
E2E Functions and MechanismsControl of State
Open loop control parameters
no feedback
Closed loop initial parameters
feedback dynamic adaptation
Closed loopwith HBH feedback
Nested control loops
Open loop
parameters
data
Nested control loops
initial parameters
data
E2E feedback
receiversender
Closed loop with HBH feedback
HBH feedback
initial parameters
data
E2E feedback
Closed loop
initial parameters
data
E2E feedback
HBH loop HBH loop
25 August 2006 High-Speed Networking 7-16
Sterbenz and TouchEnd-to-End Protocols
E2E Functions and MechanismsControl of State
Open- vs. Closed-loop Control T-6D
Use open-loop control based on knowledge of the network pathto reduce the delay in closed loop convergence. Use closed-loop control to react to dynamic network and applicationbehaviour; intermediate per hop feedback can sometimesreduce the time to converge.
Open-loop control
use when possible to eliminate control loop latency
particularly for high bandwidth--delay product networks
Closed-loop feedback control
use when necessary, e.g. reliability
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High-Speed Networking: A Systematic Approach to High-Bandwidth Low-Latency Communication
VII.9
25 August 2006 High-Speed Networking 7-17
Sterbenz and TouchEnd-to-End Protocols
E2E Functions and MechanismsControl of State
Aggressiveness of Closed-Loop Control T-6Da
The response to closed-loop feedback must be rapid enough so
the system converges quickly to a new stable state but not soaggressive that oscillations occur due to overreaction totransients.
Aggressiveness of closed-loop control
rapid enough to system converges
not too aggressive avoid instability and oscillations
25 August 2006 High-Speed Networking 7-18
Sterbenz and TouchEnd-to-End Protocols
End-to-End ProtocolsState Management
7.1 Functions and mechanisms
7.2 State management
7.2.1 Impact of high speed
7.2.2 Transfer modes
7.2.3 State establishment and maintenance
7.2.4 Assumed initial conditions
7.3 Framing and multiplexing7.4 Error control
7.5 Flow and congestion control
7.6 Security and information assurance
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High-Speed Networking: A Systematic Approach to High-Bandwidth Low-Latency Communication
VII.10
25 August 2006 High-Speed Networking 7-19
Sterbenz and TouchEnd-to-End Protocols
State ManagementTransport and Network Connections
L4 connections
required over
connectionless L3
path with anyconnectionlesssubnetwork
may exploit
connection-oriented L3
SETUPCONNECT
network layer
end system
transport layer
connection-orientednetwork
network layer
end system
transport layer
setup-req
network layer connection
connectionlessnetwork
network layer
transport layerSETUP
CONNECT
network layer
transport layer
transport layer connection
network layer
transport layerSETUP
CONNECT
network layer
transport layer
connection-oriented
subnetwork
connectionlesssubnetwork
heterogeneous subnetworks
25 August 2006 High-Speed Networking 7-20
Sterbenz and TouchEnd-to-End Protocols
State ManagementImpact of High Speed
Connection shortening transmission delay decreases
signalling delay constant
E2E signalling significant fraction of time
slow high-speedfast
~1.5tRTT
~2.5tRTT ACK
RELEASEACK
RELEASE
tRTT
SETUP
RELEASE
ACK
tp
td
tp
td0
SETUP SETUP
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High-Speed Networking: A Systematic Approach to High-Bandwidth Low-Latency Communication
VII.11
25 August 2006 High-Speed Networking 7-21
Sterbenz and TouchEnd-to-End Protocols
State ManagementImpact of Long Latency
Connection lengthening transmission delay increases
signalling delay increases
E2E signalling open state longer
denial of resource to others
short links long links
SETUP
ACK
RELEASE
SETUP
ACK
RELEASE
25 August 2006 High-Speed Networking 7-22
Sterbenz and TouchEnd-to-End Protocols
Transfer ModesDatagram
Independent packets each has fully self-describing header
no network state needed to forward
tp+td
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High-Speed Networking: A Systematic Approach to High-Bandwidth Low-Latency Communication
VII.12
25 August 2006 High-Speed Networking 7-23
Sterbenz and TouchEnd-to-End Protocols
Transfer ModesConnection
Explicit connection setup 3-way handshake
SETUP / CONNECT / ACK
Data flow packets need connection or flow identifier
used by nodes to look up state
Release of resources and state explicit RELEASE
time out state
~tRTT
ACK
RELEASE
CONNECT
SETUP
~1.5tRTT
~tRTT
tr
25 August 2006 High-Speed Networking 7-24
Sterbenz and TouchEnd-to-End Protocols
Transfer ModesConnection
ConnectionStateMachine idle
establishing install state
initialising state
convergence steady state
closing release state
initialising
idle
steady-state
closing closing
establishing
CONNECTfrom net
requested
receiveSETUPfrom net
originateSETUPrequest
issueCONNECT
ACKfrom net
RELEASEfrom net
RELEASEfrom app
issueSETUP
issueRELEASE
issueRELEASE
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High-Speed Networking: A Systematic Approach to High-Bandwidth Low-Latency Communication
VII.14
25 August 2006 High-Speed Networking 7-27
Sterbenz and TouchEnd-to-End Protocols
Transfer ModesTransaction
Transaction request may or may not establish connection state
explicit release of connection state optional
Data returned
Overlap to reduce latency request/response with control
REQUEST
RELEASE
tr
RESPONSE
Minimise Transaction Latency T-6ACombine connection establishment with request and statetransfer to reduce end-to-end latency for transactions.
25 August 2006 High-Speed Networking 7-28
Sterbenz and TouchEnd-to-End Protocols
E2E State ManagementHard vs. Soft
Hard state
explicitly established and released
deterministic
delay to establish and memory to maintain
Soft state
established and removed as needed and memory allows
robust to failures
if not explicitly established, delay to accumulate
Hard vs. Soft State T-5A
Balance the determinism and stability of hard state against theadaptability and robustness to failure of soft state.
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High-Speed Networking: A Systematic Approach to High-Bandwidth Low-Latency Communication
VII.15
25 August 2006 High-Speed Networking 7-29
Sterbenz and TouchEnd-to-End Protocols
E2E State ManagementState Aggregation and Sharing
Sharing of state
reduces granularity ofindividual entities
state shared is fateshared state
max link ratelink characteristics
(sub)networkcharacteristics
path MTURTT estimate
perE2E path
rate/windowACKs/NAKs
global (perinterface)
pernetwork
perconnection/stream
appid1
appid2
perapplication
perapplication transfer
p
e
r
traffIc
class
25 August 2006 High-Speed Networking 7-30
Sterbenz and TouchEnd-to-End Protocols
E2E State ManagementState Aggregation and Sharing
Sharing of state
reduces granularity of individual entities
state shared is fate shared state
State Aggregation T-5BSpatially aggregate state to reduce complexity, but balanceagainst loss in granularity. Temporally aggregate to reduce oreliminate establishment and initialisation phase.State shared is fate shared.
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High-Speed Networking: A Systematic Approach to High-Bandwidth Low-Latency Communication
VII.17
25 August 2006 High-Speed Networking 7-33
Sterbenz and TouchEnd-to-End Protocols
E2E Framing and MultiplexingPacket Size and Control Overhead
Small packets large overhead short interarrival
Grouped Blocked Large
increased delay
Jumbogram
Balance Packet Size T-8A
Trade between control overhead and fine enough grainedcontrol. Choose size and aggregation methods that make senseend-to-end.
tpkt
tpkt
tgrp
25 August 2006 High-Speed Networking 7-34
Sterbenz and TouchEnd-to-End Protocols
E2E Framing and MultiplexingPacket Size and Control Overhead
Large packets
impose jitter and delay on one another
interference
in1
in2
outdelayed
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High-Speed Networking: A Systematic Approach to High-Bandwidth Low-Latency Communication
VII.18
25 August 2006 High-Speed Networking 7-35
Sterbenz and TouchEnd-to-End Protocols
E2E State ManagementMTU and per Hop Fragmentation
Subnetworks have limits on packet size
MTU: maximum transfer unit
If |TPDU| > min(MTU)
fragmentation will occur in the network
significant impact on packet processing rate and delay
Avoid Hop-by-Hop Fragmentation T-5F
The transport layer should be aware of or explicitly negotiatethe maximum transfer unit of the path to avoid the overhead offragmentation and reassembly.
25 August 2006 High-Speed Networking 7-36
Sterbenz and TouchEnd-to-End Protocols
E2E Framing and MultiplexingPacket Size and Control Overhead
Application Layer Framing T-8A
To the degree possible, match ADU and TPDU structure. Incases where the application can better determine structure andreact to lost and misordered ADUs, ALF should be employed.
transport layer fragmentation
ADU
MTU
TPDU
ADUADU
TPDU TPDU TPDU
TPDU
ADUADU
TPDU TPDU TPDU
ADU
application layer framing
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High-Speed Networking: A Systematic Approach to High-Bandwidth Low-Latency Communication
VII.21
25 August 2006 High-Speed Networking 7-41
Sterbenz and TouchEnd-to-End Protocols
E2E Error ControlTypes and Causes of Errors2
Packet duplication
retransmission
Packet insertion
undetectable header error
long packet life (two packets with same sequence number)
Fragment loss
error multiplication:fragment loss requires entire frame loss or discard
25 August 2006 High-Speed Networking 7-42
Sterbenz and TouchEnd-to-End Protocols
E2E Error ControlImpact of High Speed
Bandwidth--delay product increases
fixed duration error event larger relative impact
reaction to errors decreases in terms of number of bits sent
Sequence numbers
sequence numbers wrap if sequence space too small
causes packet misinsertion
Packet Control Field Values T-8COptimise header control field values to trade efficiency againstexpected future requirements. Fields that are likely to beinsufficient for future bandwidth--delay products shouldcontain a scale factor.
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High-Speed Networking: A Systematic Approach to High-Bandwidth Low-Latency Communication
VII.22
25 August 2006 High-Speed Networking 7-43
Sterbenz and TouchEnd-to-End Protocols
E2E Error ControlClosed Loop Retransmission: Go-Back-n
Sliding window
packets are sequentiallyacknowledged
previous ACK used for
out of sequence packet
next packet after loss
sender timer fires if ACK not received
reset transmission beginning at lost packet
significant loss penalty for high bw--delay
go back and retransmit all since loss
many unneeded retransmissions
significant additional delay
tac
A0
A1
A1
0
1
2
3
4
5
6
2
3
4
5
6
A1
A2
A3
A4
A5
A1
0
1
2
3
5
4
25 August 2006 High-Speed Networking 7-44
Sterbenz and TouchEnd-to-End Protocols
E2E Error ControlClosed Loop Retransmission: Go-Back-n
Fast retransmito assume several duplicate ACKs are loss
o tell sender to go-back-n
+ recovers more quickly (dont need to wait for timer to fire)
Delayed ACKo aggregate several ACKs
+ reduces ACK traffic
+ allows some receiver resequencing (within ACK aggregation)
Decouple Error, Flow, and Congestion Control T-6E
Exploit selective acknowledgements and open-loop rate controlto decouple error, flow, and congestion control mechanisms.
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High-Speed Networking: A Systematic Approach to High-Bandwidth Low-Latency Communication
VII.28
25 August 2006 High-Speed Networking 7-55
Sterbenz and TouchEnd-to-End Protocols
E2E Flow and Congestion ControlOpen-Loop Rate Control
network
conforming traffic
admissioncontrol
ratescheduling
ratepolicing excess traffic
receivernegotiation
Initial negotiation
admission control limits traffic to available resources
receiver negotiates what it can accept (flow control)
Steady state policingenforces traffic contract from transmitter
excess traffic may be marked and passed if capacity available
25 August 2006 High-Speed Networking 7-56
Sterbenz and TouchEnd-to-End Protocols
E2E Flow and Congestion ControlOpen-Loop Rate Control
Use Knowledge of Network Paths for Open-Loop T-6Do
Control Exploit open-loop rate and congestion control basedon a priori knowledge to the degree possible to reduce the needfor feedback control.
Requires connection establishment
overhead and delay for connection setup
optimistic establishment or fast reservations ameliorate
+ QOS guarantees possible in steady state
+ feedback control loops not needed during transmission
+ network stability less dependent on congestion control
unless resources significantly overbooked
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High-Speed Networking: A Systematic Approach to High-Bandwidth Low-Latency Communication
VII.29
25 August 2006 High-Speed Networking 7-57
Sterbenz and TouchEnd-to-End Protocols
E2E Flow and Congestion ControlOpen-Loop Rate Control: Parameters
Main parameters
peak rate rp average rate ra burstiness (peak to average ratio or max burst size)
Derived parameters jitter
rp
rabursty
uniform
time
25 August 2006 High-Speed Networking 7-58
Sterbenz and TouchEnd-to-End Protocols
Open Loop Rate ControlExample:7.7ATM Traffic Classes
peak rate*best effortnoneunspecified bit rateUBR
minimum rate
peak rate*dataopen loopguaranteed frame rateGFR
minimum rate
peak rate*datahybridavailable bit rateABR
peak and average rateburst
datafast reservation
open loopATM block transferABT
peak and average rateburst
dataopen loopnon-real-time
variable bit ratenrt-
VBR
peak and average rateburst, jitter, latency
dataopen loopreal-time
variable bit ratert-VBR
peak ratereal timeopen loopconstant bit rateCBR
ParametersTrafficControlNameClass
* specified in SETUP but not guaranteed
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High-Speed Networking: A Systematic Approach to High-Bandwidth Low-Latency Communication
VII.30
25 August 2006 High-Speed Networking 7-59
Sterbenz and TouchEnd-to-End Protocols
E2E Flow and Congestion ControlClosed-Loop Flow and Congestion Control
Use Closed-Loop Congestion Control to Adjust to T-6Dc
Network Conditions Closed-loop feedback is needed toadjust to network conditions when there are no hardreservations.
networkcongestion
control
packetscheduling
flow
control
25 August 2006 High-Speed Networking 7-60
Sterbenz and TouchEnd-to-End Protocols
E2E Flow and Congestion ControlClosed-Loop Flow Control
Feedback from receiver to limit rate
Window to limit amount of unacknowledged data
static window
dynamic window
combined with congestion control
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High-Speed Networking: A Systematic Approach to High-Bandwidth Low-Latency Communication
VII.31
25 August 2006 High-Speed Networking 7-61
Sterbenz and TouchEnd-to-End Protocols
E2E Flow and Congestion ControlCongestion Avoidance and Control
knee cliff
offered load
ideal1.0
1.0
carried
load
offered load
ideal
1.0
delay
knee
cliff
CA CC
throughput
dmin
delay
CA
CC
Congestion Avoidance T-II.4c
Congestion should be avoided before it happens. Keep queuesfrom building and operate just to the left of the knee tomaximise throughput and minimise latency.
25 August 2006 High-Speed Networking 7-62
Sterbenz and TouchEnd-to-End Protocols
E2E Flow and Congestion ControlClosed-Loop Congestion Control
Feedback from network to limit rate
Window to limit amount of unacknowledged data
dynamic window
conservation of packets in the network
self clocking
Required unless open loop with hard reservations
Use Closed-Loop Congestion Control to Adjust to T-6Dc
Network Conditions Closed-loop feedback is needed toadjust to network conditions when there are no hardreservations.
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High-Speed Networking: A Systematic Approach to High-Bandwidth Low-Latency Communication
VII.35
25 August 2006 High-Speed Networking 7-69
Sterbenz and TouchEnd-to-End Protocols
E2E Flow and Congestion ControlExample7.8 TCP Congestion Control
Fast recovery
1/2 congestion window after 3dupACK rather than slow start
Partial acknowledgement response [Hoe 1996]
1/2 window reduction only once with partial retransmit ACK
rather than per packet
RED: random early detection (discard) [Floyd 1993]
discard packets when router queue threshold exceeded
throttle TCP source earlier before congestion occurs
ECN: explicit congestion notification [Floyd 1994] use IP ECN to trigger multiplicative decrease
25 August 2006 High-Speed Networking 7-70
Sterbenz and TouchEnd-to-End Protocols
E2E Flow and Congestion ControlExample7.8 TCP Congestion Control
Research optimisations [jury still out]
Pacing [Visweswaraiah 1997]
spread segment transmissions
rather than burst
Rate control [Padhye 1998]
rate based on equations that describe TCP behaviour
can also make UDP transmission TCP friendly
ETEN: explicit transport error notification [Samaraweera 1997] signal loss due to channel bit errors
loss of ACK is not misconstrued as congestion
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High-Speed Networking: A Systematic Approach to High-Bandwidth Low-Latency Communication
VII.37
25 August 2006 High-Speed Networking 7-73
Sterbenz and TouchEnd-to-End Protocols
E2E ProtocolsExample7.9 TCP High-Speed Optimisations
TCP/IP headers
bw--delay fields that limit
sequence space
timer related
window size
Field predictability use template for
constant
predictable must compute
highly variable
payload
TCP header40B
IP header40B
payload
source port #
rcv window size
destination port
sequence number
acknowledgement number
checksum urgent pointer
total length
destination address
frag offset
source address
identifier
ver TOShl
flags
TTL header checksum
source port #
rcv window
destination port #
sequence number
acknowledgement number
checksum urgent pointer
hdr len
total length
destination address
frag offset
source address
identifier
ver TOShl
flags
TTL header checksum
UAPRSF hdr len UAPRSF
protocolprotocol
constantpredictablebw--delay sensitive
25 August 2006 High-Speed Networking 7-74
Sterbenz and TouchEnd-to-End Protocols
E2E ProtocolsExample7.9 TCP High-Speed Optimisations
Common optimisations [RFC 1323]
Window scale option [RFC 1323]
SYN option power-of-2 multiplier to initial window
RTTM (round-trip time measurement) [RFC 1323]
timestamp to allow RTT measurement
PAWS (protection against wrapped seq. nos.) [RFC 1323]
32-bit timestamp augments 32-bit sequence number
SACK (selective acknowledgement) [RFC 2018] byte range header options for 3 4 selective ACK ranges
Fast retransmit [RFC 2581]
retransmit on triple duplicate ACKs without waiting for timer
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