Simple Two-Way Active Measurement ProtocolZTE Corp.gregimirsky@gmail.comZTE Corp.68# Zijinghua RoadNanjingJiangsu210012China+86 18105183663guo.jun2@zte.com.cnAccedian Networkshnydell@accedian.comNokiafooter.foote@nokia.com
Transport
Network Working GroupIPPMPerformance Measurement
This document describes the Simple Two-way Active Measurement
Protocol (STAMP), which enables the measurement of both one-way and round-trip
performance metrics, like delay, delay variation, and packet loss.
Introduction
Development and deployment of the Two-Way Active Measurement Protocol (TWAMP)
and its extensions (e.g.,
, which defines Symmetrical Size for TWAMP)
provided invaluable experience. Several independent implementations of both
TWAMP and TWAMP Light exist, have been deployed, and provide
important operational performance measurements.
At the same time, there has been noticeable interest in using a more straightforward
mechanism for active performance monitoring that can provide deterministic
behavior and inherent separation of control
(vendor-specific configuration or orchestration) and test functions.
Recent work on "Performance Measurement from IP Edge to Customer Equipment using TWAMP Light"
by the
Broadband Forum demonstrates that interoperability among
implementations of TWAMP Light is difficult because the composition
and operation of TWAMP Light were not sufficiently specified in .
According to , TWAMP Light includes a subset of TWAMP-Test
functions. Thus, to have a comprehensive tool to measure packet loss and delay requires
support by other applications that provide, for example, control and security.
This document defines an active performance measurement test protocol, Simple
Two-way Active Measurement Protocol (STAMP),
that enables measurement of both one-way and round-trip performance metrics,
like delay, delay variation, and packet loss. Support of some
optional TWAMP extensions, e.g., , is discussed in .
Conventions Used in This DocumentTerminology
STAMP:
Simple Two-way Active Measurement Protocol
NTP:
Network Time Protocol
PTP:
Precision Time Protocol
HMAC:
Hashed Message Authentication Code
OWAMP:
One-Way Active Measurement Protocol
TWAMP:
Two-Way Active Measurement Protocol
MBZ:
Must be Zero
PDU:
Protocol Data Unit
Requirements Language
The key words "MUST", "MUST NOT",
"REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT",
"RECOMMENDED", "NOT RECOMMENDED",
"MAY", and "OPTIONAL" in this document are to be interpreted as
described in BCP 14
when, and only when, they appear in all capitals, as shown here.
Operation and Management of Performance Measurement Based on STAMP presents the Simple Two-way
Active Measurement Protocol (STAMP)
Session-Sender and Session-Reflector with a measurement session. In this
document, a measurement session,
also referred to as a "STAMP session", is the bidirectional
packet flow between one specific Session-Sender and one particular
Session-Reflector for a time duration.
The configuration and management of the STAMP Session-Sender,
Session-Reflector, and sessions are outside the scope of this
document and can be achieved through various means.
A few examples are Command Line Interface, telecommunication
services' Operational Support System (OSS) / Business Support System (BSS),
SNMP, and NETCONF/YANG-based Software-Defined Networking (SDN) controllers.
STAMP Reference Model | STAMP Session-Reflector |
+----------------------+ +-------------------------+
]]>Theory of Operation
The STAMP Session-Sender transmits test packets over UDP transport
toward the STAMP Session-Reflector. The STAMP Session-Reflector
receives the Session-Sender's packet and acts according to the configuration.
Two modes of the STAMP Session-Reflector characterize the expected
behavior and, consequently, performance metrics that can be
measured:
Stateless:
The STAMP Session-Reflector does not maintain test
state and will use the value in the Sequence Number field in
the received packet as the value for the Sequence Number field
in the reflected packet.
As a result, values in the Sequence Number and Session-Sender
Sequence Number fields
are the same, and only round-trip packet loss can be calculated
while the reflector is operating in stateless mode.
Stateful:
STAMP Session-Reflector maintains the test state, thus
allowing the Session-Sender to determine directionality of loss using
the combination of gaps recognized in the Session Sender Sequence
Number and Sequence Number fields, respectively.
As a result, both near-end (forward) and far-end (backward) packet loss can be
computed.
That implies that the STAMP Session-Reflector MUST maintain a state
for each configured STAMP-Test session, thereby uniquely associating
STAMP-Test packets with one such session instance and, thus, enabling
the addition of a sequence number in the test reply that is individually
incremented by one on a per-session basis.
STAMP supports two authentication modes:
unauthenticated and authenticated. Unauthenticated STAMP-Test packets,
defined in Sections and
, ensure interworking
between STAMP and TWAMP Light, as described in regarding
packet formats.
By default, STAMP uses symmetrical packets, i.e., the size of the packet
transmitted by the Session-Reflector equals the size of
the packet received by the Session-Reflector.
UDP Port Numbers in STAMP Testing
A STAMP Session-Sender MUST use
UDP port 862 (TWAMP-Test Receiver Port) as the default destination UDP port
number. A STAMP implementation of the Session-Sender MUST
be able to be used as the destination UDP port numbers from the User Ports
(aka Registered Ports) and Dynamic Ports (aka Private or Ephemeral Ports)
ranges defined in . Before using
numbers from the User Ports range, the possible impact on the network
MUST be carefully studied and agreed on by all users of the
network domain where the test has been planned.
By default, an implementation of the STAMP Session-Reflector
MUST receive STAMP-Test packets on UDP port 862.
An
implementation of the Session-Reflector
that supports this specification MUST be able to define the
port number to receive STAMP-Test packets
from User Ports and Dynamic Ports ranges, which are defined in .
STAMP defines two different test packet formats: one for
packets transmitted by the STAMP Session-Sender and one for packets
transmitted by the STAMP Session-Reflector.
Session-Sender Behavior and Packet Format
A STAMP Session-Reflector supports the symmetrical size of test packets,
as defined in , as the default behavior.
A reflected base test packet includes information from
the Session-Reflector and, thus, is larger.
To maintain the symmetry between base STAMP packets,
the base STAMP Session-Sender packet includes the Must-Be-Zero (MBZ) field to
match to the size of a base reflected STAMP test packet.
Hence, the base STAMP Session-Sender packet has a minimum
size of 44 octets in unauthenticated mode (see )
and 112 octets in the authenticated mode (see ).
Generating variable length of a test packet in STAMP is defined in .
Session-Sender Packet Format in Unauthenticated ModeSTAMP Session-Sender Test Packet Format in Unauthenticated Mode
The fields are defined as following:
The Sequence Number field is four octets long. For each new session,
its value starts at zero and is incremented by one with each transmitted
packet.
The Timestamp field is eight octets long. The STAMP node
MUST support the Network
Time Protocol (NTP) version 4 64-bit timestamp format ,
the format used in . The STAMP
node MAY support the
IEEE 1588v2 Precision Time Protocol (PTP) truncated 64-bit timestamp
format , the format
used in .
The use of the specific format, NTP or PTP, is part of configuration
of the Session-Sender or the particular test session.
The Error Estimate field is two octets long with the format displayed in :
Error Estimate Format
The S, Scale, and Multiplier fields are interpreted as they are
defined in . The Z field is interpreted as it is defined in
:
0:
NTP 64-bit format of a timestamp
1:
PTPv2 truncated format of a timestamp
The default behavior of the STAMP Session-Sender and
Session-Reflector is to use the NTP 64-bit timestamp format
(Z field value of 0). An operator using configuration/management function
MAY configure the STAMP Session-Sender and Session-Reflector
to use the PTPv2 truncated format of a timestamp (Z field value of 1).
Note that an implementation of a Session-Sender that supports this specification
MAY be configured to use the PTPv2 format of a timestamp even
though the Session-Reflector is
configured to use NTP format.
The MBZ field in the Session-Sender unauthenticated packet is 30
octets long. It MUST be all zeroed on the transmission
and MUST be ignored on receipt.
Session-Sender Packet Format in Authenticated ModeSTAMP Session-Sender Test Packet Format in Authenticated Mode
The field definitions are the same as the unauthenticated mode, listed in
. Also, MBZ fields are used to make
the packet length a multiple of 16 octets. The value of the field
MUST be zeroed on transmission and MUST be
ignored on receipt.
Note, that both MBZ fields are used to calculate a key hashed message
authentication code (HMAC) hash.
Also, the packet includes an HMAC hash at the end of the PDU. The detailed
use of the HMAC field is described in .
Session-Reflector Behavior and Packet Format
The Session-Reflector receives the STAMP-Test packet and verifies
it. If the base STAMP-Test packet is validated,
the Session-Reflector that supports this specification
prepares and transmits the reflected test packet symmetric
to the packet received from the Session-Sender copying the
content beyond the size of the base STAMP packet
(see ).
Session-Reflector Packet Format in Unauthenticated ModeSTAMP Session-Reflector Test Packet Format in
Unauthenticated Mode
Fields are defined as the following:
The Sequence Number field is four octets long. The value of the Sequence
Number field is set according to the mode of the STAMP
Session-Reflector:
In the stateless mode, the Session-Reflector copies the value from the
received STAMP-Test packet's Sequence Number field.
In the stateful mode, the Session-Reflector counts the transmitted
STAMP-Test packets.
It starts with zero and is incremented by one
for each subsequent packet for each test session.
The Session-Reflector uses that counter to set the value of the Sequence Number field.
The Timestamp and Receive Timestamp fields are each eight octets long. The
format of these fields, NTP or PTPv2, is
indicated by the Z field of the Error Estimate field, as described in
.
Receive Timestamp is the time the test packet was received by the
Session-Reflector. Timestamp is
the time taken by the Session-Reflector at the start of transmitting
the test packet.
The Error Estimate field has the same size and interpretation as
described in .
It is applicable to both Timestamp and Receive Timestamp.
The Session-Sender Sequence Number, Session-Sender Timestamp, and
Session-Sender Error Estimate fields
are copies of the corresponding fields in the STAMP-Test packet sent
by the Session-Sender.
The Session-Sender TTL field is one octet long, and its value is the copy of the
TTL field in IPv4 (or Hop Limit in IPv6) from the received STAMP-Test packet.
The MBZ fields are used to achieve alignment of fields within the packet
on a four-octet boundary.
The value of each MBZ field MUST be zeroed on transmission
and MUST be ignored on receipt.
Session-Reflector Packet Format in Authenticated ModeSTAMP Session-Reflector Test Packet Format in Authenticated Mode
The field definitions are the same as the unauthenticated mode, listed in
.
Additionally, the MBZ field is used to make the packet length a multiple of 16 octets.
The value of the field MUST be zeroed on transmission and
MUST be ignored on receipt.
Note that the MBZ field is used to calculate the HMAC hash value.
Also, the STAMP Session-Reflector test packet format in authenticated mode
includes the HMAC hash at the end of the PDU.
The detailed use of the HMAC field is in .
Integrity Protection in STAMP
Authenticated mode provides integrity protection to each STAMP
message by adding
Hashed Message Authentication Code (HMAC). STAMP
uses HMAC-SHA-256 truncated to 128 bits (similarly to the use
of it in IPsec defined in ); hence,
the length of the HMAC field is 16 octets. In the authenticated mode,
HMAC covers the first six blocks (96 octets). HMAC uses its
own key, which may be unique for each STAMP-Test session;
key management and the mechanisms to distribute the HMAC key
are outside the scope of this specification. One example is to
use an orchestrator to configure the HMAC key based on the STAMP YANG
data model .
HMAC MUST be verified as early as possible to
avoid using or propagating corrupted data.
Future specifications may define the use of other, more
advanced cryptographic algorithms,
possibly providing an update to the STAMP YANG data model
.
Confidentiality Protection in STAMP
If confidentiality protection for STAMP is required, a
STAMP-Test session MUST use a secured
transport. For example,
STAMP packets could be transmitted in the dedicated IPsec
tunnel or share the IPsec tunnel with the
monitored flow. Also, the Datagram Transport Layer Security protocol
would provide the desired confidentiality protection.
Interoperability with TWAMP Light
One of the essential requirements to STAMP is the ability to interwork with a
TWAMP Light device. Because STAMP and TWAMP use different algorithms in
authenticated mode (HMAC-SHA-256 versus HMAC-SHA-1), interoperability is only
considered for unauthenticated mode. There are two possible combinations for
such a use case:
STAMP Session-Sender with TWAMP Light Session-Reflector
TWAMP Light Session-Sender with STAMP Session-Reflector
In the former case, the Session-Sender might not be aware that its Session-Reflector
does not support STAMP. For example, a TWAMP Light Session-Reflector may not
support the use of UDP port 862, as specified in .
Thus, permits a STAMP
Session-Sender to use alternative ports. If any of STAMP extensions are
used, the TWAMP Light Session-Reflector will view them as the Packet
Padding field.
In the latter scenario, if a TWAMP Light Session-Sender does not support
the use of UDP port 862, the test management system MUST set
the STAMP Session-Reflector to use UDP port number, as permitted by . The Session-Reflector
MUST be set to use the default format for its timestamps,
NTP.
A STAMP Session-Reflector that supports this specification will transmit the base packet
()
if it receives a packet smaller than
the STAMP base packet. If the packet received from the TWAMP Session-Sender is
larger than the STAMP base packet,
the STAMP Session-Reflector that supports this specification will copy the
content of the remainder of the received packet to transmit a reflected packet
of symmetrical size.
Operational Considerations
STAMP is intended to be used on production networks to enable
the operator to assess service level agreements based on packet delay,
delay variation, and loss. When using STAMP over the Internet, especially
when STAMP-Test packets are transmitted with the destination UDP port number from
the User Ports range, the possible impact of the STAMP-Test packets
MUST be thoroughly analyzed.
The use of STAMP for each case MUST be agreed by users of
nodes hosting the Session-Sender and Session-Reflector before starting
the STAMP-Test session.
Also, the use of the well-known port number as
the destination UDP port number in STAMP-Test packets transmitted
by a Session-Sender would not impede
the ability to measure performance in an Equal-Cost Multipath environment,
and analysis in
fully applies to STAMP.
IANA Considerations
This document has no IANA actions.
Security Considerations does not identify security
considerations specific to TWAMP-Test but refers to
security considerations identified for OWAMP in . Since both OWAMP and TWAMP include control-plane and
data-plane components,
only security considerations related to OWAMP-Test discussed in Sections
and
of apply to STAMP.
STAMP uses the well-known UDP port number allocated for the
OWAMP-Test/TWAMP-Test Receiver Port. Thus, the security considerations and
measures to mitigate the risk of the attack using the registered port
number documented in equally apply to STAMP. Because of the control and
management of a STAMP-Test being outside the scope of this specification,
only the more general requirement is set:
To mitigate the possible attack vector, the control and management of a
STAMP-Test session MUST use the secured transport.
The load of the STAMP-Test packets offered to a network
MUST be carefully estimated,
and the possible impact on the existing services MUST be
thoroughly analyzed before launching the test session.
provides
guidance on handling network load for UDP-based protocol. While the
characteristic of test traffic depends on the test objective, it is
highly recommended to stay in the limits, as provided in .
Use of HMAC-SHA-256 in the authenticated mode protects the data integrity
of the STAMP-Test packets.
ReferencesNormative ReferencesIEEE Standard for a Precision Clock Synchronization Protocol for
Networked Measurement and Control SystemsIEEEInformative ReferencesPerformance Measurement from IP Edge to Customer Equipment
using TWAMP LightBroadband ForumAcknowledgmentsThe authors express their appreciation to and
for their great insights into the
security and identity protection as well as the most helpful and practical suggestions. Also, our sincere thanks to
, , and for
their thorough reviews and helpful comments.