Real Time Flow Measurement Working Group S.W. Handelman
Internet-draft IBM
Expire in six months Hawthorne, NY USA
N. Brownlee
U of Auckland, NZ
Greg Ruth
GTE Laboratories, Inc
Waltham, MA USA
November, 1996
Real Time Flow Measurement Working Group - New Attributes for
Traffic Flow Measurement
<draft-ietf-rtfm-new-traffic-flow-00.txt>
1. Status of this Memo
This document is an Internet Draft. Internet Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
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This memo provides information for the Internet community. This memo
does not specify an Internet standard of any kind. Distribution of
this memo is unlimited.
2.1 Introduction
The Real-time Traffic Flow Measurement (RTFM) working group has
developed a rudimentary system for measuring and reporting
information about traffic flows in the Internet. This document
explores the definition of extensions to the concepts of flow
measurements as currently defined in RFC 1272 and [1].
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The RTFM Working Group has defined the concept of a standardized
meter which records flows from a traffic stream according to a Rule
Set that is active in the meter[1]. Implementations of this meter
have been done by Nevil Brownlee in the University of Auckland, NZ,
and Stephen Stibler and Sig Handelman at IBM in Hawthorne, NY, USA.
The meter implementations measure flows by marking them with time
stamps, recording total traffic in bytes and packets. In general one
may say that the meter finds the existence of flows, and records the
traffic in each flow. The RTFM WG has also discussed the Collector
Program whose job is to fetch the completed group of flows active in
the Meter.
2.1 RTFM's Definition of Flows
The RTFM Meter architecture views a flow as a set of packets between
two end-points (as defined by their source and destination attribute
values), and as BI-DIRECTIONAL (i.e. the meter effectively monitors
two sub-flows, one in each direction).
Reasons why RTFM flows are bi-directional:
- We are interested in understanding the behavior of sessions between
end-points.
- We want to perform as much data reduction as possible, so as to
reduce the amount of data to be retrieved from a remote meter.
- The end-point attribute values (the "Address" and "Type" ones) are
the same for both directions; storing them in bi-directional flows
reduces the meter's memory demands.
2.2 RTFM's Current Definition of Network Flows and their Attributes
Flows, as described in the "Architecture" I-D have the following
properties:
a. They occur between two end-points, specified as sets of attribute
values in the meter's current rule set. A flow is completely
identified by its set of end-point attribute values.
b. Each flow may also have values for "computed" attributes (Class
and Kind). These are directly derived from the end-point attribute
values.
c. A new flow comes into being when the a packet is seen which is not
classified by the Rule Set into an existing flow. The meter records
the time when this new flow is created.
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d. Attribute values in (a), (b) and (c) are set when the meter sees
the first packet for the flow, and are never changed.
e. Each flow has a "LastTime" attribute, which indicates the time the
meter last saw a packet for the flow.
f. Each flow has two packet and byte counters, one for each flow
direction (Forward and Backward). These are updated as packets are
observed by the meter.
g. ALL the attributes have (more or less) the same meaning for a
variety of protocols; IPX, AppleTalk, DECnet and CLNS as well as
TCP/IP.
Current flow attributes as described above, fit very well into the
SNMP data model. They are either static, or are continuously updated
counters. They are NEVER reset. In this document they will be
referred to as "old-style" attributes.
It is easy to add further "old-style" attributes, since they don't
require any new features in the architecture. For example:
- Count of the number of "lost" packets (determined by watching
sequence number fields for packets in each direction; only available
for protocols which have sequence numbers).
- In the future, RTFM could coordinate directly with the Flow number
from the IPv6 header.
At the June, 1996 meeting of the RTFM WG, in Montreal, Canada, a
proposal was put forth to extend the work of the group to produce an
Internet Draft "New Attributes for Traffic Flow Measurement". That
proposal has brought forth this document. The goal of this work is to
produce a simple set of abstractions, which can be easily implemented
and at the same time enhance the value of RTFM meters. This document
also defines a method for organizing the flow abstractions to
preserve the existing RTFM flow table.
An addition to the main architecture document of RTFM is the use of
High Watermarks, to set up Alerts when the value of a flow record
variable exceeds a watermark, e.g. the total byte count exceeds a
preset amount, such as no user should send more than 2,000,000
packets over a certain time period. This is a generalization of the
concept defined in RTFM to send Traps when a the Meter finds an
exception condition in its own processing (The Architecture Document
refers to running out of buffer space).
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2.3 RTFM Flows, Integrated Services, IPPM and Research in Flows
The concept of flows has been studied in various different contexts.
For the purpose of extending RTFM, a starting point is the work of
the Integrated Services WG. We will measure quantities that are often
set by Integrated Services and configuration programs. We will look
at the work of the Benchmarking - Internet Provider Performance
Metrics Working Group, and also look at the work of Claffy, Braun and
Polyzos.
An example of the use of capacity and performance information is
found in "The Use of RSVP with IETF Integrated Services". [2].
RSVP's use of Integrated Services revolves around Token Bucket Rate,
Token Bucket Size, Peak Data Rate, Minimum Policed Unit, Maximum
Packet Size, and the Slack term. These are set by TSpec, ADspec and
FLowspec (Integrated Services Keywords), and are used in
configuration and operation of Integrated Services. RTFM could
monitor explicitly Peak Data Rate, Minimum Policed Unit, Maximum
Packet Size, and the Slack term. RTFM could infer details of the
Token Bucket. We will develop measures to work with these service
metrics.
RTFM will work with several traffic measurements identified by IPPM
[3]. There are two broad areas in which RTFM is useful for IPPM.
1) RTFM could act as a passive device that can gather traffic and
performance statistics at appropriate places in TCP/IP networks
(servers or client locations).
2) RTFM could give detailed analyses of IPPM test flows that pass
through the Network segment that RTFM is monitoring.
RTFM will also incorporate work from Claffy, Braun and Polyzos [4].
We can measure flow time-outs, traffic aggregation and metrics on the
application layer using methods similar to theirs.
3. Flow Abstractions
Extensions to the current RTFM flow attributes may be divided into
three general classes:
o packet traces - collections of individual packets in a flow or a
segment of a flow
o 'aggregates' - statistics derived from the flow taken as a whole
(e.g. mean rate, max packet size).
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o 'series'- sequences of attributes that depend on more than one
packet (e.g. inter- arrival times)
The following sections suggest implementations for each of these
classes of extensions.
As an introduction to flow abstractions one fact must be emphasized.
Several of the measurements enumerated below can be implemented by a
Meter Reader that is tied to the meter with instantaneous response,
and very high bandwidth. If the Meter Reader and Meter can be
arranged in such a way, RTFM could collect Packet Traces with time
stamps, and provide them to the Meter Reader for processing by the
Meter Reader.
A more useful alternative is to have the meter calculate some flow
statistics locally. This allows a looser coupling between the meter
and Meter Reader. RTFM will create an 'extended attribute' depending
upon settings in the Rules table of RTFM. By default, RTFM will not
create any extensions without explicit instructions in the Rules
table.
RTFM's traditional flows can be analyzed at two levels. The first is
to analyze the Network traffic in terms of time, e.g. traffic load of
a particular flow, to be called Network Flows. These flows can be
looked at as an extension of the "old-style" flow attributes. The
second, is to derive a value from the flow, e.g. analyzing packet
sequence numbers and ACKS and estimating delay. This second type
will be called Derived Attributes.
3.1. Packet Traces
The simplest way of doing this in the meter would be to have a new
attribute called, say, "PacketTrace." This would be a table, with a
column for each property of interest. For example, one could have
- Arrival time (TimeTicks from SysUptime, or microseconds from
FirstTime for the flow).
- Direction (Forward or Backward)
- Sequence number (for protocols with sequence numbers)
- Flags (for TCP at least).
To add a row to the table, we only have to have a rule which PushPkts
the PacketTrace attribute.
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To use this, one would write a rule set which selected out a small
number of flows of interest, and PushPkted PacketTrace for each of
them. A MaxTraceRows default value of 2000 would be enough to allow
a Meter Reader to read 1-second ping traces every 10 minutes or so.
More realistically, a MaxTraceRows of 500 would be enough for one-
minute pings, read once each hour.
3.2. Aggregate Attributes
Performance aspects of flows are useful in the case of a flow between
a server and client. RTFM could find the same data in TCP/IP and UDP
flows, and can find additional data in TCP flows. The performance
data found by this method define the flow capacity used by the
individual flow, as experienced in the locale of the RTFM meter. The
data found in this method would help Operations Support determine
the performance of delivery in the network being measured.
For both TCP/IP and UDP, RTFM's "old-style" flow attributes count the
bytes/packets for packets which match the rule set for an individual
flow. In addition to these totals, RTFM could calculate Packet size
and Bit rate statistics.
Packet size - RTFM's packet flows can be examined to determine the
maximum packet size found in a flow. This will give the Network
Operator an indication of the MTU being used in a flow. It will also
give an indication of the sensitivity to loss of a flow, for losing
large packets causes more data to be repeated.
Bit rate - The data could also be recorded as the maximum and
minimum data rate of the flow, found over specific time periods
during the lifetime of a flow. This measure could be used to compare
the bandwidth used by the flow with the total capacity of the media
and guarantees set for flows.
3.3 Series Attributes
The notion of series attributes, is to keep simple statistics that
involve more than one packet. Methods to derive simple percentiles,
means, and other statistics can be developed for each flow. The
notation to construct such an attribute would be a command in the
rule set, instructing the meter to compute the attribute. This is
similar to the definition above of creating an aggregate attribute.
TCP and UDP
Inter-arrival statistics - TCP and UDP. RTFM knows the time that it
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encounters each individual packet. Statistics can be kept to record
the inter-arrival times of the packets, which would give an
indication of the jitter found in the Flow.
TCP Only - Data Loss - This is an area for further study. TCP packets
have byte sequence numbers and SYNS, FINS, and ACK's associated with
them. RTFM could track the sequence numbers in the flows, and
calculate the packet loss occurring in a flow, and thus we can
develop a metric of lost packets and useful traffic.
Delay analysis - TCP flows also could be examined for the timing
between Transmissions and ACKS and thus we can get some measure of
delay. This assumes the forward and reverse packets are both visible
to the meter.
Subflow analysis - TCP flows, e.g. a Web server's httpd flows
actually contain many individual sub flows. Given, a well known Web
Server WW, and a client CC, RTFM would normally pick up an
aggregation of all the flows of text, graphics, Java programs, etc.
that are sent between WW and CC. By analyzing the Sequence numbers,
RTFM could estimate when each subflow occurs, and thus maintain
statistics about the subflows on a network.
3.4 Action on Exceptions
The user of RTFM will have the ability to define Network and Derived
flows, as having High Watermarks. The existence of abnormal service
conditions, such as non-ending flow, a flow that exceeds a given
limit in traffic (e.g. a flow that is exhausting the capacity of the
line that carries it) causes an ALERT to be sent to the Collector for
forwarding to the Manager. Operations Support may define service
situations in many different environments. This is an area for
further discussion on Alert and Trap handling.
4. Packet Flow Table
The architecture of RTFM has defined the structure of flows, and this
draft does not change that structure. The flow table could have
ancillary tables called "Packet Flow Tables", which would contain
rows of values and or actions as defined under packet traces,
aggregate attributes and series attributes. Each Packet Flow table
would be marked with the number of its corresponding flow in the RTFM
flow table. In order to identify the data in a Packet Flow Table,
the value of the Rules Table Extension will be pushed into a string
at the head of each row. For example, if a Packet Flow table entry
has Bit Rates for a particular flow, the "BitRate" string would be
found at the head of the row.
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A method of bundling the Packet Flow table and the packet data will
be developed such that an SNMP manager can retrieve whole flow table
entries, and whole Packet Flow Tables, with SNMP v2 Getbulk
instructions. This will be accomplished by creating a flow attribute
called FlowDataPackage. This will be an encoded sequence of all the
objects such that the Getbulk could operate on the whole structure.
4.1 Note on Interchange between Meter and Meter Reader
The above information on Getbulk could be superseded in the near
future by the work of the RMONMIB Bulk Data Transfer.
5. Extensions to the Rules Table
The Rules Table of "old-style" attributes will be extended for the
new flow types. A list of actions, and Keywords, such as "BitRate"-
for Bit Rate, "MaxPack", for Max Packet size will be developed and
used to inform RTFM to collect a set of extended values for a
particular flow (or set of flows).
6. Security Considerations
Security considerations are not discussed in this memo.
7. Author's Address:
Sig Handelman
IBM Research Division
Hawthorne, NY
Phone: 1-914-784-7626
E-mail: handel@watson.ibm.com
Nevil Brownlee
The University of Auckland
New Zealand
Phone: +64 9 373 7599 x8941
E-mail: n.brownlee@auckland.ac.nz
Greg Ruth
GTE Laboratories
Waltham, MA
Phone: 1 617 466 2448
E-mail: grr1@gte,com
8. References:
[1] Brownlee, N, Mills, C., Ruth, G.: "Traffic Flow Measurement:
Architecture", Internet Draft, April, 1996
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[2] Wroclawski, J., : "The Use of RSVP with IETF Integrated Services
Internet" Draft, October, 1996
[3] Almes, G. et al: "Framework for IP Provider Metrics" Internet
Draft. July 1996
[4] Claffy, K., Braun, H-W, Polyzos, G. "A Parameterizable
Methodology for Internet Traffic Flow Profiling," IEEE Journal on
Selected Areas in Communications, Vol. 13, No. 8, October 1995.
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