Internet DRAFT - draft-shi-dclc-latency-test
draft-shi-dclc-latency-test
DCLC Research Group Y. Shi
INTERNET-DRAFT UCI
Intended Status: Informational S. Duan
Expires: January 22, 2015 CATR
L. Deng
China Mobile
July 21, 2014
Test and Analysis on Forwarding Latency in Terms of Queuing Length
draft-shi-dclc-latency-test-00
Abstract
We test the influence of the queue length, packet size and so on to
the forwarding latency of the typical access switch, which is meant
to set off our efforts in studying the relationship between the
queuing length and the transport performance of some latency-
sensitive applications in a DC network.
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Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3 Objective of the Tests . . . . . . . . . . . . . . . . . . . . 3
4 Preparation of the Test Environment . . . . . . . . . . . . . . 3
5 Test Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5.1 Test of Buffer Configuration in Switch . . . . . . . . . . . 4
5.2 Test of Forwarding Delay in Switch . . . . . . . . . . . . . 4
6 Result Analysis . . . . . . . . . . . . . . . . . . . . . . . . 5
7 Future Works . . . . . . . . . . . . . . . . . . . . . . . . . . 6
8 Security Considerations . . . . . . . . . . . . . . . . . . . . 6
9 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
10 References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
10.1 Normative References . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7
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1 Introduction
To investigate the effective optimization mechanism of the congestion
control in the internal network of the data center, we test the
influence of the queuing length and packet size to the forwarding
latency of an access switch. From the analysis, we try to find the
relationship between the queuing length and the transport performance
of some latency-sensitive application.
2 Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
3 Objective of the Tests
As a typical interconnection network with super high bandwidth,
simultaneous multipath and low end-to-end delay, data center network
has been widely used in uploading from traditional applications and
desktop virtualization to highly interconnected distributed
applications. The uploading method can be made by providing physical
resources to the application system, or it can be made by providing
virtual sources(virtual machine, virtual network and virtual
equipment, etc.) through the abstract of the physical resources which
is done by virtualized infrastructure.
It is suggested that the interior network of the data center still
has problems with the delivery performance of the latency-sensitive
application for the mismatch between end-to-end congestion control
and the variation of delay in IP level.
To investigate the effective optimization mechanism of the congestion
control in the internal network of the data center, we test the
influence of the queuing length, packet size and so on to the
forwarding latency of the representative COTS switch, which is
assumed to be served as a basis for finding the control mechanism for
the latency-sensitive applications when they are doing end-to-end
local transportation.
4 Preparation of the Test Environment
We use an access switch as the test instrument. The measurement
instrument is Spirent's TestCenter C1(SPT C1).
To simulate the condition of the congestion, we use 3 switch ports in
real test. 2 ports(port1 and port2)sent to the third one(port3)
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simultaneously. The total two input flow is larger than the output
port bandwidth.
5 Test Cases
We tried two test cases to investigate:
1)buffer configuration of the switch and how the buffer space is
shared; and
2)no-packet-loss forwarding time delay of the switch when enabling a
tail drop feature on a queue with configured consumption ratio (i.e.
the buffer(%)).
5.1 Test of Buffer Configuration in Switch
The buffer configuration test aims to evaluate the size of the
queue's length in the switch, and how different packets share the
buffer allocated to a given port. Since there are commonly multiple
queues for different QoS packets passing a single port, and we are
focusing on queuing length rather than service differentiation, we
ignore the class of QoS and the priority queue schemes in the switch.
When setting the length of the buffer, we ask the switch to drop the
packet when the buffer allocated to the queue meets a threshold in
percentage (i.e. the buffer(%)).
We set each of the input flow be 51% of the wire bandwidth to make
sure that there will be a queue building (congestion) at the
corresponding output port.
Back-to-back test of the 3 ports is done by using RFC 2544 of SPT C1.
The packet sizes are 512 and 1024. The test step is 0.1% of the
bandwidth. The maximum number of received frame when the queue just
meets the threshold is the real value of the length of the buffer.
To verify the effectiveness of the value, we choose 50% queue and
100% queue to test separately to see the change of the maximum number
of received frame.
5.2 Test of Forwarding Delay in Switch
Forwarding delay test mainly inspects the relationship between the
queuing at the switch and the delay. Therefore, we verified the
maximum buffer queue length to drop the packet when the buffer(%)
reached the threshold.
We use RFC 2544 to go through the latency test of the three ports.
Each input sets the flow percentage from 49.8% to 50.2% with an
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increase of 0.2% each time. The tested frame sizes are 64, 128, 256,
512, 768, 1024, 1280 and 1518, as recommended in [RFC2544]. The
buffer(%) is set to 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%,
90%, 100% of the maximum queue length to analyze the delay time of
different frame under different queue length.
6 Result Analysis
We did a group of tests and got a bunch of data. The data were
analyzed by univariate statistics first, and then by using linear
regression model, we did the multivariate statistics. In this way, we
found out that minimum delay time shown different relations with the
variants under observation, while the maximum delay time and the
average delay time share very similar features when we considered the
packet size and the buffer(%) as the independent variable.
6.1 The Minimum Delay
Observation 1: when buffer(%) is fixed, the delay increases linearly
with the packet size.
Observation 2: When packet size is fixed, the buffer(%) seems has no
influence on the minimum delay time.
This was also been proved when we did the multivariate analysis. The
coefficient of the buffer(%) was 0 in the fitting line.
6.2 The Maximum/Average Delay
Observation 1: Both the maximum and average delay have almost the
same tendency and values.
Observation 2: When buffer(%)is fixed, with increasing packet size,
delay time will also increase. Seen from the data, the maximum and
average delay time have a nonlinear relationship with the packet
size. Besides, we noticed that when the packet size is too big or
small, the maximum delay time and the average delay time are more
influenced by the packet size compared with the one with moderate
packet size.
Observation 3: When packet size is fixed, maximum and average delay
increase linearly with the buffer(%). Also, with bigger packet size,
the delays are more influenced by the buffer(%) since the slot of the
fitting line is higher.
Compared with the minimum delay time, we come to the conclusion that
average delay time is more influenced by maximum delay time, rather
than the minimum delay time.
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In the multivariate statistics, since the relationship between the
delay time and the packet size is nonlinear, we tried a lot of
nonlinear models, such as polynomial equations. The best fitting
result so far is the combination of packet number(buffer(%)/packet
size) and first order of buffer(%) and a constant number.
Since the minimum delay time is only related to the packet size, we
replaced the packet size with the minimum delay time in the maximum
and average delay time's fitting equations, in this way both the
maximum and average delay can be represented by the minimum delay
time and buffer(%).
7 Future Works
Later we will have more tests and try to have a clear understanding
of the influence of the congestion and the reason for the congestion.
The preliminary considerations are:
1) Test and analyze on other access switches and aggregate switches.
2) Test and analyze on a more complicated internetworking topology
(e.g. sequence of or parallel union of multiple switches).
3) Measure the RTT for TCP data flow, and analyze the relationship
between the forwarding delay and TCP RTT.
8 Security Considerations
N/A.
9 IANA Considerations
N/A.
10 References
10.1 Normative References
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Authors' Addresses
Yang Shi
University of California, Irvine
Email: shiy4@uci.edu
Shihui Duan
China Academy of Telecommunication Research of MIIT
Email: duanshihui@catr.cn
Lingli Deng
China Mobile
Email: denglingli@chinamobile.com
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