high performance switching and routingtiny-tera.stanford.edu/~nickm/talks/telecom_center... ·...
TRANSCRIPT
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Nick McKeownAssistant Professor of Electrical Engineeringand Computer Science
[email protected]://ee.stanford.edu/~nickm
High PerformanceSwitching and RoutingTelecom Center Workshop: Sept 4, 1997.
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Our Group
Shang-tse “Da” Chuang, Ken Chang,Pankaj Gupta, Youngmi Joo, Steve Lin,
Adisak Mekkittikul, Nick McKeown,Rolf Muralt, Kanta Yamamoto (visitor).
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1. The Demand for Bandwidth
2. The Shortage of
3. The Architecture of Switches
Switching/Routing Capacity
and Routers
4. Some (of our) solutions
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What’s the Problem?
Time
Mos
t thi
ngs
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High Performance Switching and Routing Page 5 of 52Source: http://www.mfsdatanet.com/MAE/west.stats.html
Feb Apr Jun Aug Nov
200
400
600
800
460
200150
123
Agg
rega
te b
andw
idth
(M
bps)
100
620
520
720
Feb Apr
The San Jose NAPThe demand
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The supplyR
oute
r P
erfo
rman
ce (
pack
ets/
seco
nd)
103
19901986 1994 1997
104105
106
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1986 1992 1997
pack
ets/
seco
nd
Demand
Supply
Why we need faster switches/routers
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•Exponential growth in the number of users.•Exponential growth in traffic per user per hour.•Linear growth in hours per user per day.
Why the growth?
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Time of day5am 8am
100%
30%
Dialup DemandModem usage at U.C. Berkeley
“America on Hold”
% o
f mod
ems
in u
se
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Traffic Inversion10 years ago
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ISP
ISP
Traffic InversionToday
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November 1st, 1996
Why is this a problem?
Pac
ket L
oss
(%)
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The race is on...
pack
ets/
seco
nd
Demand
Supply
- Gigabit Routers- IP Switching- Tag Switching- Layer-3 switches
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1. The Demand for Bandwidth
2. The Shortage of
3. The Architecture of Switches
Switching/Routing Capacity
and Routers
4. Some (of our) solutions
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The Architecture of
Forwarding
OutputScheduler
Signaling &
Generic Packet Processor:
Decision
Processor
Switches and Routers
Mgmt
Interconnect
(e.g. IP Router, ATM Switch, LAN Switch)
Data Hdr
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Performance of IP Routers
Min back-to-back packet size Packet size
ArrivalTime
CopyTime
Forwarding
Time
Time
Decision
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Performance of IP Routers
Min back-to-back packet size Packet size
Arrivalrate
Copyrate
Headerprocessingtime
Most routersdo this poorly!
Most routersdo this ~ ok
Time
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The Evolution of RoutersThe first shared memory routers
RoutingCPU
LineCard
LineCard
LineCard
BufferMemory
DMA DMA DMA
MAC MAC MAC
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The Evolution of RoutersThe first shared memory routers
RoutingCPU
LineCard
LineCard
LineCard
BufferMemory
DMA DMA DMA
MAC MAC MAC
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The Evolution of RoutersReducing the number of bus copies
RoutingCPU
LineCard
BufferMemory
DMA
MAC
BufferMemory
RouteCache
DMA
MAC
BufferMemory
RouteCache
DMA
MAC
BufferMemory
RouteCache
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The Evolution of RoutersReducing the number of bus copies
RoutingCPU
LineCard
BufferMemory
DMA
MAC
BufferMemory
RouteCache
DMA
MAC
BufferMemory
RouteCache
DMA
MAC
BufferMemory
RouteCache
updates
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The Evolution of RoutersAvoiding bus contention
MA
C
Buffer
Mem
ory
Route
Cache
MAC
BufferMemory
RouteCache
MA
C
Buf
fer
Mem
ory
Rou
teC
ache
BufferMemory
CPUROUTE
Advantage:Non-blocking backplane—
Disadvantage:Difficult to provide QoS
high throughput
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Multigigabit Routing
MA
C
Buf
fer
Mem
ory
BufferMemory
CPUROUTE
MAC
BufferMemory
MA
C
Buffer
Mem
ory
BBN’s Multigigabit Router
Buffer
Memory
CPU
ROUTE
2.4Gb/s
2.4Gb/s
2.4Gb/s
5Mpps
50Gb/sCrossbar
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1. The Demand for Bandwidth
2. The Shortage of
3. The Architecture of Switches
Switching/Routing Capacity
and Routers
4. Some (of our) solutions
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Some (of our)Solutions
1. Accelerating Lookups:• Label-Swapping
• Longest-matching prefixes
2. Switched Backplanes• Input Queueing
— Theory— Unicast— Multicast
• Fast Buffering
• Speedup
3.Our main project: The Tiny Tera
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Routing Lookups
212.17.9.4
Class A
Class B
Class C212.17.9.0 Port 4
Class A Class B Class C D
ExactMatch
(hash, cache,pipeline...)
Routing Table:
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212.0.0.0/8
212.17.0.0/16212.17.9.0/24
212.17.9.4
CIDR uses “longest matching prefix” routing:
Hashing, caching and pipelining are hard!
Routing Lookups withCIDR (“supernetting”)
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Solution 1:Label Swapping
Forwarding
OutputScheduler
Signaling &
Decision
ProcessorMgmt
Interconnect
Data Hdr Label
NewLabel Port
DirectLookup
IP Switching, Tag Switching, ARIS, Cell-switched Router,....
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Solution 2:Perform Lookups Faster!
Size ofRouting Tables
Cost of Memory(per byte)
Observation #1:
Time
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Performing Lookups Faster
Prefix length
Numberin routingtable
24
212.17.9.0/24
212.17.9.40 232-1
256
Observation #2:
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212.17.9.1 101
0
1
1
Port 4
Port 4Port 3
look further
look furtherPort 3
256Port 4Port 5
Port 4Port 5
16Mbytes of 50ns DRAM
<1Mbyte of 50ns DRAM
Solution 2 (cont):20 million lookups per second
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1. Accelerating Lookups:• Label-Swapping
• Longest-matching prefixes
2. Switched Backplanes• Input Queueing
— Theory— Unicast— Multicast
• Fast Buffering
• Speedup
3.Our main project: The Tiny Tera
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Shared Memory:
Input Queueing:
Should we use shared memory
Advantages:SimplicityHigh Bandwidth
Disadvantages:HOL BlockingLess efficient
Advantages:Highest Throughput.
Disadvantages:N-fold internal speed-up
N p
orts
Difficult to control packet delay.
or input-queueing?
Possible to control packet delay.
Shared Memory
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TimeM
emor
y S
ize
Time
Mem
ory
Spe
ed
SRAM
DRAM
Memory Bandwidth
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An aside: How fast can sharedmemory operate?
Route Lookup
SharedMemory
200byte packet
5ns SRAM
How fast can a 16 port switch run with this architecture?
5ns per packet 2 memory operations per cell time×aggregate bandwidth is 160Gb/s⇒
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Because of ashortage of memory bandwidth, mostmultigigabit and terabit switches and routers useeither:
1. Input Queueing, or2. Combined Input and Output Queueing.
Should we use shared memoryor input-queueing?
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1 24 21 2
Inputs Outputs
ρmax 2 2– 58%= =
Input Cell Buffer
Cells CellsN
The Problem A Solution....
Head of Line Blocking
“Virtual Output Queueing”
ρmax 100%=
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Input 1
Q(1,1)
Q(1,n)
A1(t)
Input m
Q(m,1)
Q(m,n)
Am(t)
D1(t)
Dn(t)
Output 1
Output n
Matching, MA1,1(t)
?
....but requires scheduling...
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RequestGraph
BipartiteMatching
1234
1234
1234
1234
(Weight = 18)
25
242
7
....which is equivalent to graph matching
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Practical Algorithms
1. iSLIP — Weight = 1
2. iLQF — Weight = Occupancy
— Simple to implement
— Iterative round-robin
3. iOCF — Weight = Cell Age
4. MCFF — Weight = Backlog
Simple, fast,efficient
Good fornon-uniformtraffic.Complex!Good fornon-uniformtraffic.Simple!
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Multicast TrafficQueue Architecture
2. Why treat multicast differently?1. Making use of the crossbar
3. Why maintain a single FIFO queue?4. Fanout-splitting
134
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0.1
1
10
100
1000
10000
0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 0.22 0.24
Ave
rage
Cel
l Lat
ency
Offered Load
Fanout-splittingNo Fanout-splitting
Fanout-Splitting
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Multicast Traffic
1. Residue Concentration
2. Tetris-based schedulers
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Gigabit and TerabitRouting
1. Accelerating Lookups:• Label-Swapping
• Longest-matching prefixes
2. Switched Backplanes• Input Queueing
— Theory— Unicast— Multicast
• Fast Buffering
• Speedup
3.Our main project: The Tiny Tera
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High Performance Switching and Routing Page 45 of 52
Fast BufferingPing-pong Memory
BufferMemory
BufferMemory
BufferMemory
M
M/2
M/2
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High Performance Switching and Routing Page 46 of 52
Fast BufferingPing-pong Memory
M
t
Occupancy
M/2
M/2
Maximum “cost” = M/2
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High Performance Switching and Routing Page 47 of 52
In practise, cost <5%
Fast BufferingPing-pong Memory
Buffer size, M
Loss rate with
Loss rate with
single memory: M
ping-pong: (M/2,M/2)LossRate
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High Performance Switching and Routing Page 48 of 52
Gigabit and TerabitRouting
1. Accelerating Lookups:• Label-Swapping
• Longest-matching prefixes
2. Switched Backplanes• Input Queueing
— Theory— Unicast— Multicast
• Fast Buffering
• Speedup
3.Our main project: The Tiny Tera
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Combined Input- and Output-Queueing:
Matching Output Queueingwith Input- and Output- Queueing
How much speedup is enough?
k readsand writes
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Conventional wisdom suggests:
Matching Output Queueingwith Input- and Output- Queueing
How much speedup is enough?
A speedupk 2 4–= leads to high throughput
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Fact To match output queueing, with FIFO input queues:k = N
Matching Output Queueingwith Input- and Output- Queueing
=?Traffic
Output QueuedSwitch
Combined Input
Switchand Output Queued
Fact To match output queueing, with virtual output queues:k = 4 is sufficient
Conjecture: To match output queueing, with VOQs:k = 2 is sufficient
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High Performance Switching and Routing Page 52 of 52
1. Accelerating Lookups:• Label-Swapping
• Longest-matching prefixes
2. Switched Backplanes• Input Queueing
— Theory— Unicast— Multicast
• Fast Buffering
• Speedup
3.Our main project: The Tiny Tera