IEEE Spectrum July, 2009 - 30

How Flow routiNG workS
Flow managers keep track of streams of packets and can protect
voice and video transmissions while reducing peer-to-peer traffic.
CONVENTIONAl ROUTER
Routing engine

Input

Output
Queue manager

Peer to peer

Packet
Web
Voice/video
Discarded
packets

1

The routing engine reads each
packet's destination address and
performs a table lookup to determine
where to send the packet.

2

3

The transmitted packets often
experience substantial and
nonuniform delays, and the router is
unable to control specific types of traffic.

The queue manager buffers packets
as they await transmission. If there's
congestion, it randomly discards packets
to reduce throughput.

FlOW mANAgER
Flow engine

Input

Output

Hash table
Hash

Discarded
packets

2

The flow engine keeps track
of each flow's duration and
throughput to identify its type. It
can selectively discard packets to
protect Web, voice, and video while
limiting peer-to-peer flows.

tification is in the hash, and if it is, that means the new packet
is part of a flow you've already routed. You'd then quickly dispatch-the more accurate term is "switch"-the packet straight
to an output port, thus saving time and power.
If traffic gets too heavy, you'll still have to discard packets.
The big advantage is that now you can do it intelligently. By
monitoring the packets as they're coming in, you can track in
real time the duration, throughput, bytes transferred, average
packet size, and other metrics of every flow. For example, if a
38

NA * iEEE SpEctrum * july 2009

Routing engine

3

If the hash table has no record
of the flow, the routing engine
determines where the packet should
go. The hash table is updated with the
new flow, so subsequent packets can
bypass the routing engine.

4

The output provides feedback
to the flow engine. If there's
bandwidth available, it increases the
flow rates or accepts more flows; if
bandwidth is limited, it reduces flows.

flow has a steady throughput, which is the case with voice and
video, you can avoid discarding such packets, protecting these
stream-based transmissions. For other types of traffic, such as
Web browsing, you can selectively discard just enough packets
to achieve specific rates without stalling those transmissions.
This capability is especially convenient for managing network overload due to P2P traffic. Conventionally, P2P is filtered
out using a technique called deep packet inspection, or DPI,
which looks at the data portion of all packets. With flow manwww.spectrum.ieee.org

emily cooper

1

The flow engine uses a hash
function to convert each packet's
header into a sequence of bits that
uniquely identifies a flow. If the flow
exists in the hash table, the packet
goes directly to the output.



http://www.spectrum.ieee.org

Table of Contents for the Digital Edition of IEEE Spectrum July, 2009

IEEE Spectrum July, 2009 - Cover1
IEEE Spectrum July, 2009 - Cover2
IEEE Spectrum July, 2009 - 1
IEEE Spectrum July, 2009 - 2
IEEE Spectrum July, 2009 - 3
IEEE Spectrum July, 2009 - 4
IEEE Spectrum July, 2009 - 5
IEEE Spectrum July, 2009 - 6
IEEE Spectrum July, 2009 - 7
IEEE Spectrum July, 2009 - 8
IEEE Spectrum July, 2009 - 9
IEEE Spectrum July, 2009 - 10
IEEE Spectrum July, 2009 - 11
IEEE Spectrum July, 2009 - 12
IEEE Spectrum July, 2009 - 13
IEEE Spectrum July, 2009 - 14
IEEE Spectrum July, 2009 - 15
IEEE Spectrum July, 2009 - 16
IEEE Spectrum July, 2009 - 17
IEEE Spectrum July, 2009 - 18
IEEE Spectrum July, 2009 - 19
IEEE Spectrum July, 2009 - 20
IEEE Spectrum July, 2009 - 21
IEEE Spectrum July, 2009 - 22
IEEE Spectrum July, 2009 - 23
IEEE Spectrum July, 2009 - 24
IEEE Spectrum July, 2009 - 25
IEEE Spectrum July, 2009 - 26
IEEE Spectrum July, 2009 - 27
IEEE Spectrum July, 2009 - 28
IEEE Spectrum July, 2009 - 29
IEEE Spectrum July, 2009 - 30
IEEE Spectrum July, 2009 - 31
IEEE Spectrum July, 2009 - 32
IEEE Spectrum July, 2009 - 33
IEEE Spectrum July, 2009 - 34
IEEE Spectrum July, 2009 - 35
IEEE Spectrum July, 2009 - 36
IEEE Spectrum July, 2009 - 37
IEEE Spectrum July, 2009 - 38
IEEE Spectrum July, 2009 - Cover3
IEEE Spectrum July, 2009 - Cover4
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_1217
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_1117
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_1017
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0917
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0817
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0717
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0617
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0517
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0417
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0317
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0217
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0117
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_1216
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_1116
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_1016
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0916
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0816
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0716
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0616
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0516
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0416
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0316
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0216
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0116
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_1215
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_1115
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_1015
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0915
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0815
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0715
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0615
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0515
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0415
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0315
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0215
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0115
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_1214
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_1114
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_1014
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0914
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0814
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0714
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0614
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0514
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0414
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0314
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0214
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0114
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_1213
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_1113
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_1013
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0913
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0813
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0713
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0613
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0513
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0413
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0313
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0213
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0113
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_1212
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_1112
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_1012
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0912
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0812
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0712
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0612
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0512
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0412
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0312
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0212
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0112
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_1211
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_1111
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_1011
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0911
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0811
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0711
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0611
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0511
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0411
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0311
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0211
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0111
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_1210
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_1110
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_1010
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0910
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0810
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0710
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0610
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0510
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0410
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0310
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0210
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0110
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_1209
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_1109
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_1009
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0909
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0809
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0709
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0609
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0509
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0409
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0309
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0209
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0109
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_1208
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_1108
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_1008
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0908
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0808
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0708
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0608
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0508
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0408
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0308
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0208
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0108
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_1207
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_1107
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_1007
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0907
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0807
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0707
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0607
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0507
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0407
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0307
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0207
https://www.nxtbook.com/nxtbooks/ieee/spectrum_na_0107
https://www.nxtbookmedia.com