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 becomputed. 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 [
4.2.1] and [
4.3.1], ensure interworking between STAMP and TWAMP Light, as described in
Section 4.6 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.
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 [
RFC 6335]. 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 [
RFC 6335]. 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.
A STAMP Session-Reflector supports the symmetrical size of test packets, as defined in
Section 3 of
RFC 6038, 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
Figure 2) and 112 octets in the authenticated mode (see
Figure 4). Generating variable length of a test packet in STAMP is defined in [
STAMP-OPTION].
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Estimate | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| |
| |
| MBZ (30 octets) |
| |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 [RFC 5905], the format used in [RFC 5357]. The STAMP node MAY support the IEEE 1588v2 Precision Time Protocol (PTP) truncated 64-bit timestamp format [IEEE.1588.2008], the format used in [RFC 8186]. 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 Figure 3:
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|S|Z| Scale | Multiplier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The S, Scale, and Multiplier fields are interpreted as they are defined in Section 4.1.2 of RFC 4656. The Z field is interpreted as it is defined in Section 2.3 of RFC 8186:
-
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.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| MBZ (12 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Estimate | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
~ ~
| MBZ (70 octets) |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| HMAC (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The field definitions are the same as the unauthenticated mode, listed in
Section 4.2.1. 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) [
RFC 2104] hash. Also, the packet includes an HMAC hash at the end of the PDU. The detailed use of the HMAC field is described in
Section 4.4.
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
Section 4.2).
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Estimate | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receive Timestamp |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session-Sender Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session-Sender Timestamp |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session-Sender Error Estimate | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Ses-Sender TTL | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 Section 4.2.1. 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 Section 4.2.1. 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.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MBZ (12 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Estimate | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| MBZ (6 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receive Timestamp |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MBZ (8 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session-Sender Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MBZ (12 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session-Sender Timestamp |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session-Sender Error Estimate | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| MBZ (6 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Ses-Sender TTL | |
+-+-+-+-+-+-+-+-+ +
| |
| MBZ (15 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HMAC (16 octets) |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The field definitions are the same as the unauthenticated mode, listed in
Section 4.3.1. 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 [
RFC 2104] hash at the end of the PDU. The detailed use of the HMAC field is in
Section 4.4.
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 [
RFC 4868]); 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 [
STAMP-YANG]. 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 [
STAMP-YANG].
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.
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 [
RFC 8545]. Thus,
Section 4 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
Section 4. 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 (
Figure 5) 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.