Recent literature on traffic control in datacenter intra- and interconnect has moved from optical burst switching and FCoE to the cut-through mode enforced e2e on commodity ethernet lines. E2e cut-through sessions -- aka, effectively, circuits -- are implemented as optimized schedules in which bulk transfer sessions are mixed with a large number of small flows. This paper presents a new optimizational viewpoint, formulated as the Switchboard Traffic Engineering Problem (STEP). First, the mixed schedule of input flows is mapped to a finite number of (physical) output lines some of which are implemented as (physical) e2e cut-through paths. The second part of the problem is to physically shuffle input ports (hence the switchboard) on switches with output lines in such a way that overall contention is minimized. This paper deals with the formulation of the optimization problem and leaves the otherwise obvious (robotics) implementation of the shuffling part of the technology to future publications.

1. for Mixed Contention/Cut-Through
Marat Zhanikeev
maratishe@gmail.com
maratishe.github.io
2016/11/18@PN研@KDDI研
The Switchboard
PDF: bit.do/161118
Traffic Engineering Problem
#STEP
#TE #TrafficEngineering
#OSPF
#cut-through
#contention
#SDNOutput Channels

2. .
Commutators are Back (as robots)
• all the technology is already there, we just need to start using it
• basically, switching robotics
◦ this paper proposed the Switchboard Traffic Engineering Problem
(STEP)
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3. .
Cut-Through Mode as Basis for STEP
C: Cut Through
Check,
etc. Q: Queue
D: Drop
QoS
classes
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4. .
STEP (1)
• each outgoing port gets multiple slots, i.e. the n-by-m switchboard
• can be implemented as multiple ethernet ports, fiber wavelengths, etc.
A switch
4-port
switchPhysical Logical Switchboard
n×m
switching
matrix
xth port,
y slots n ports
m slots
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5. .
STEP (2) The Weight Setting Problem
• 1st element: weights per slot, the same way as in the OSPF problem
• 2nd element: migrations of some slots to other outgoing ports
Switchboard
n×m
switching
matrix
n ports
m slots
Occupied/used slot
Empty slot
Migration
(1:3 to 3:2)
w11 w21
wnm
wn1…
…
…
Weight setting
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6. .
Formulations (1) OSPF Cases
• unit demand as source s, destination d, volume v, time t, and sometimes optical
wavelength λ, can be written as Ti = ⟨s, d, v, t⟩
• traditional/OSPF : Ti = ⟨s, d, v⟩ → ⟨s, a, b, ..., d⟩
• optimal w/out switching : Ti = ⟨s, d, v⟩ → ⟨s, λ⟩
• optical with switching : Ti = ⟨s, d, v⟩ → ⟨s, λs, λa, λb, ...⟩
• e2e circuits : Ti = ⟨s, d, v, t1, t2⟩ → ⟨s, λ, t⟩
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7. .
Formulations (2) The STEP Problem
• M load spread across n outgoing ports, each with m slots (n-by-m switchboard)
◦ unit of load is flowsize vi
• load aggregated per slot xy : Lxy = max
{
vi
}
xy
, i ∈ xy
• fitness of the slot xy : Fxy = wxyLxy
• aggregate slots into ports as potential : Px =
∑ {Fj
Vj
}
y
, j ∈ x
• optimize (w/out migrations) : minimize max
{
P
}
x
subject of x ≤ n
• optimize (with migrations) : minimize a · max
{
P
}
x
+ (1 − a) ·
∑
i∈m Ci
◦ .... subject of x ≤ n, a ≤ 1, m ≤ Q.
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8. .
Experiment (1) Setup
0 20 40 60 80 100
Decreasing order
0
0.35
0.7
1.05
1.4
1.75
2.1
2.45
2.8
log(value)
Class A
Class B
Class C
Class D
Class E • hotspot distributions for
picking weights -- same as
in OSPF, (i.e. large flows repel other flows)
• use WIDE packet traces for
real packets/flows
• otherwise, the same as in
OSPF -- just optimize the
weights
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9. .
Experiment (2) Results
0 1 2 3 4 5 6
X (port) + Y (slot) coordinate
9560
9600
9640
9680
9720
9760
9800
Loadindex(logofhotspot)
1
1
1
2
2
2
3
3
3
4
4
4
5
5
5
1
1
1
2 2
2
3
3
3
4
4
4
5
5
5
Method : real
0 1 2 3 4 5 6
X (port) + Y (slot) coordinate
9560
9600
9640
9680
9720
9760
9800
Loadindex(logofhotspot)
1
1
1
1
1
2
2
2
3
3
3
4
4
4
51
1
1
2
2
2
3
3
3
3
34
4
4
5
Method : optimal
Hotspot class : D
• real = based on real traces and not
optimized
• optimal is the optimized version of
the switchboard
• visual effect: STEP spreads the
traffic across ports
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10. .
Experiment (3) Layouts (good)
0 2 4 6 8 10 12 14
Decreasing order
0
2
4
6
8
10
log(1+fitness)
before
before#10.6
hotclass#E
migrations#5
10.4
0
2.5
10
10.5
3.1
0
0
10.6
10.4
0
3.1
9.9
10.1
7.8
before
0 5 10 15 20 25
Decreasing order
0
2
4
6
8
10
log(1+fitness)
after
after#10.6 (diff#-0.1)
hotclass#E
migrations#5
10.4
0
2.5
0
10
0
0
3.1
0
10.4
0
0
10.6
0
0
0
0
0
0
10.5
9.9
10.1
7.8
0
3.1
after
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11. .
Experiment (4) Layouts (bad)
0 2 4 6 8 10 12 14
Decreasing order
0
2
4
6
8
10
log(1+fitness)
before
before#10.7
6.2
10
6.7
8.6
9.3
9.3
9.8
0
5.7
0
0
10.7
0
0
9.8
before
0 5 10 15 20 25
Decreasing order
0
2
4
6
8
10
log(1+fitness)
after
after#10.7 (diff#0)
6.2
10
6.7
0
0
8.6
9.3
9.3
0
0
0
0
5.7
0
0
0
0
10.7
0
0
0
0
9.8
9.8
0
after
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12. .
Summary
• cut-through circuits are possible even under a large number of flows
• will work with 2+ independent outgoing ports
• future steps: actually build a switching robot
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13. .
That’s all, thank you ...
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14. .
STEP is NOT a scheduling problem
Line=
outgoing
port
Overhead =
contention
No. of flows
Line=
outgoing
port
Overhead
Scheduling
Traditional
Circuits
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15. .
Future NOC...
• ... will manage a pool of packet and circuit ports
NOC
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16. .
STEP in the Hotspot Context
• version 1: map all heavy hitter flows as circuits
• version 2: offer a paid service that some of the bulk transfer services can
use
eziswolF
Decreasing flow size
TopN
parameter
In Out
Switch
Circuits
Packets
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