Packet Sampling (psamp)

Last Modified: 2008-11-21

Additional information is available at tools.ietf.org/wg/psamp

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Description of Working Group:


The Packet Sampling working group is chartered to define a standard
set of capabilities for network elements to sample subsets of packets
by statistical and other methods. The capabilities should be simple
enough that they can be implemented ubiquitously at maximal line
rate. They should be rich enough to support a range of existing and
emerging measurement-based applications, and other IETF working groups
where appropriate.

The focus of the WG will be to (i) specify a set of selection
operations by which packets are sampled (ii) specify the information
that is to be made available for reporting on sampled packets; (iii)
describe protocols by which information on sampled packets is reported
to applications; (iv) describe protocols by which packet selection and
reporting configured.

Packet reports must be communicable in a timely manner, to
applications either on-board of off-board the sampling network
element. The streams of packet reports produced by a packet sampling
must (i) allow consistent interpretation, independent of the
particular network element that produced them; (ii) be self-defining,
in that their interpretation does not require additional information
to be supplied by the network element; (iii) allow robustness of
interpretation with respect to missing reports or part of reports;

Network elements shall support multiple parallel packet samplers, each
with independently configurable packet selectors, reports, report
streams, and export. Network elements must allow easy and secure
reconfiguration of these packet samplers by on-board or external
applications.

Export of a report stream across a network must be congestion avoiding
in compliance with RFC 2914. Unreliable transport is permitted because
the requirements at the exporter for reliable transport (state
maintenance, addressibilty, acknowledgment processing, buffering
unacknowledged data) would prevent ubiquitous deployment. Congestion
avoidance with unreliable export is to be accomplished by the
following measures, which shall be mandatory to implement and use. The
maximum export rate of a report stream must be configurable at the
exporter. A report stream must contain sufficient information for
transmission loss to be detected a collector. Then the collector must
run a congestion control algorithm to compute a new sending rate, and
reconfigure the exporter with this rate. In order to maintain report
collection during periods of congestion, PSAMP report streams may
claim more than a fair share of link bandwidth, provided the number of
report streams in competition with fair sharing traffic is limited.

Selection of the content of packet reports will be cognizant of
privacy and anonymity issues while being responsive to the needs of
measurement applications, and in accordance with RFC 2804.

Re-use of existing protocols will be encouraged provided the protocol
capabilities are compatible with PSAMP requirements.

Specifically, the PSAMP WG will perform the following tasks, in
accordance with the principles stated above:

1. Selectors for packet sampling. Define the set of primitive packet
selection operations for network elements, the parameters by which
they may be configured, and the ways in which they can be combined.

2. Packet Information. Specify extent of packet that is to be made
available for reporting. Target for inclusion the packet's IP
header, some subsequent bytes of the packet, and encapsulating
headers if present. Full packet capture of arbitrary packet
streams is explicitly out of scope. Specify variants for IPv4 and
IPv6, extent of IP packet available under encapsulation methods,
and under packet encryption.

3. Sampled packet reports. Define the format of the report that is
constructed by the network element for each sampled packet for
communication to applications. The format shall be sufficiently
rich as to allow inclusion in the packet report of (i) IP packet
information as specified in paragraph 2 above; (ii) encapsulating
packet headers as specified in paragraph 2 above; (iii) interface
or channel identifiers associated with transit of the packet across
the network element; (iv) quantities computable from packet content
and router state, (v) quantities computed during the selection
operation. All reported quantities must reflect the router state
and configuration encountered by the packet in the network element.

4. Report Streams. Define a format for a stream of packet reports, to
include: (i) the format of packet reports in the stream; (ii) the
packet reports themselves; (iii) configuration parameters of the
selectors of the packets reported on; (iv) configuration parameters
and state information of the network element; (v) quantities that
enable collectors and applications to infer of attained packet
sampling rates, detect loss during samping, report loss in
transmission, and correct for information missing from the packet
report stream; (vi) indication of the inherent accuracy
of the reported quantities, e.g., of timestamps.

5. Multiple Report Streams. Define requirements for multiple parallel
packet samplers in one network element, including the allowed
degradation of packet reporting when packets are selected by
multiple packet samplers.

6. Configuration and Management. Define a packet sampler MIB to reside
at the network element, including parameters for packet selection,
packet report and stream format, and export. Select or define a
communication protocol to configure/read this MIB.

7. Presentation, Export, and Transport of Packet Reports. Define
interface for presentation of reports to on-board applications.
Select unreliable transport protocol for remote export. Determine
rate control algorithms for export.

Initial Internet-Draft: A Framework for Passive Packet Measurement
[draft-duffield-framework-papame]


Goals and Milestones:


Done Submit initial Framework document
Done Submit initial Packet selector and packet information document
Done Submit initial Report format and report stream format document
Done Submit initial Export and requirements for collectors document
Done Submit initial MIB document
Done Submit final Framework document
Done Submit final Packet selector and packet information document
Done Submit final PSAMP protocol specification
Done Submit final PSAMP information model
Apr 2009 Submit final MIB document


No Current Internet-Drafts


Request For Comments:


A Framework for Packet Selection and Reporting (RFC 5474) (86080 bytes)
Sampling and Filtering Techniques for IP Packet Selection (RFC 5475) (101260 bytes)
Packet Sampling (PSAMP) Protocol Specifications (RFC 5476) (101620 bytes)
Information Model for Packet Sampling Exports (RFC 5477) (84673 bytes)