Two-Way Active Measurement Protocol (TWAMP) Data Model

The Two-Way Active Measurement Protocol (TWAMP) is used to measure network performance parameters such as latency, bandwidth, and packet loss by sending probe packets and measuring their experience in the network. To date, TWAMP implementations do not come with a standard management framework and, as such, configuration depends on the various proprietary mechanisms developed by the corresponding TWAMP vendor. This document addresses this gap by formally specifying the TWAMP data model using YANG.

In current TWAMP deployments, the lack of a standardized data model limits the flexibility to dynamically instantiate TWAMP-based measurements across equipment from different vendors. In large, virtualized, and dynamically instantiated infrastructures where network functions are placed according to orchestration algorithms as discussed in , proprietary mechanisms for managing TWAMP measurements pose severe limitations with respect to programmability. Two major trends call for revisiting the standardization on TWAMP management aspects. First, we expect that in the coming years large-scale and multi-vendor TWAMP deployments will become the norm. From an operations perspective, dealing with several vendor-specific TWAMP configuration mechanisms is simply unsustainable in this context. Second, the increasingly software-defined and virtualized nature of network infrastructures, based on dynamic service chains and programmable control and management planes requires a well-defined data model for TWAMP implementations. This document defines such a TWAMP data model and specifies it formally using the YANG data modeling language .

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 .

The rest of this document is organized as follows. presents the scope and applicability of this document. provides a high-level overview of the TWAMP data model. details the configuration parameters of the data model and specifies in YANG the TWAMP data model. lists illustrative examples which conform to the YANG data model specified in this document. elaborates these examples further.

The purpose of this document is the specification of a vendor-independent data model for TWAMP implementations. illustrates a redrawn version of the TWAMP logical model found in Section 1.2 of . The figure is annotated with pointers to the UML diagrams provided in this document and associated with the data model of the four logical entities in a TWAMP deployment, namely the TWAMP Control-Client, Server, Session-Sender and Session-Reflector. As per , unlabeled links in are unspecified and may be proprietary protocols.

| Server | +----------------+ +--------+ ^ ^ | | V V +----------------+ +-------------------+ | Session-Sender | <-- TWAMP-Test --> | Session-Reflector | +----------------+ +-------------------+ [Fig. 5] [Fig. 6] ]]> As per , a TWAMP implementation may follow a simplified logical model, in which the same node acts both as the Control-Client and Session-Sender, while another node acts at the same time as the TWAMP Server and Session-Reflector. illustrates this simplified logical model and indicates the interaction between the TWAMP configuration client and server using, for instance, NETCONF or RESTCONF . Note, however, that the specific protocol used to communicate the TWAMP configuration parameters specified herein is outside the scope of this document. considers TWAMP operational commands, which are also outside the scope of this document.

A TWAMP data model includes four categories of configuration items. Global configuration items relate to parameters that are set on a per device level. For example, the administrative status of the device with respect to whether it allows TWAMP sessions and, if so, in what capacity (e.g. Control-Client, Server or both), are typical instances of global configuration items. A second category includes attributes that can be configured on a per control connection basis, such as the Server IP address. A third category includes attributes related to per test session attributes, for instance setting different values in the Differentiated Services Code Point (DSCP) field. Finally, the data model could include attributes that relate to the operational state of the TWAMP implementation. As we describe the TWAMP data model in the remaining sections of this document, readers should keep in mind the functional entity grouping illustrated in .

A TWAMP Control-Client has an administrative status field set at the device level that indicates whether the node is enabled to function as such. Each TWAMP Control-Client is associated with zero or more TWAMP control connections. The main configuration parameters of each control connection are: A name which can be used to uniquely identify at the Control-Client a particular control connection. This name is necessary for programmability reasons because at the time of creation of a TWAMP control connection not all IP and TCP port number information needed to uniquely identify the connection is available. The IP address of the interface the Control-Client will use for connections The IP address of the remote Server Authentication and Encryption attributes such as KeyID, Token and the Client Initialization Vector (Client-IV) . Each TWAMP control connection, in turn, is associated with zero or more test sessions. For each test session we note the following configuration items: The test session name that uniquely identifies a particular test session at the Control-Client and Session-Sender. Similarly to the control connections above, this unique test session name is needed because at the time of creation of a test session, for example, the source UDP port number is not known to uniquely identify the test session. The IP address and UDP port number of the Session-Sender of the path under test by TWAMP The IP address and UDP port number of the Session-Reflector of said path Information pertaining to the test packet stream, such as the test starting time or whether the test should be repeated.

Each TWAMP Server has an administrative status field set at the device level to indicate whether the node is enabled to function as a TWAMP Server. Each TWAMP Server is associated with zero or more control connections. Each control connection is uniquely identified by the 4-tuple {Control-Client IP address, Control-Client TCP port number, Server IP address, Server TCP port}. Control connection configuration items on a TWAMP Server are read-only.

There is one TWAMP Session-Sender instance for each test session that is initiated from the sending device. Primary configuration fields include: The test session name that MUST be identical with the corresponding test session name on the TWAMP Control-Client () The control connection name, which along with the test session name uniquely identify the TWAMP Session-Sender instance Information pertaining to the test packet stream, such as, for example, the number of test packets and the packet distribution to be employed.

Each TWAMP Session-Reflector is associated with zero or more test sessions. For each test session, the REFWAIT parameter (Section 4.2 of can be configured. Read-only access to other data model parameters, such as the Sender IP address is foreseen. Each test session can be uniquely identified by the 4-tuple mentioned in .

This section defines the TWAMP data model using UML and describes all associated parameters.

The twamp-client container (see ) holds items that are related to the configuration of the TWAMP Control-Client logical entity. These are divided up into items that are associated with the configuration of the Control-Client as a whole (e.g. client-admin-state) and items that are associated with individual control connections initiated by the Control-Client entity (twamp-client-ctrl-connection).

----------------------| mode-preference-chain | | | +-----------------------+ | | 1..* +------------+ | priority | | |<>-----| key-chain | | mode | +--------------------+ +------------+ +-----------------------+ ^ | key-id | V | secret-key | | +------------+ | 0..* +------------------------------+ | twamp-client-ctrl-connection | +------------------------------+ | ctrl-connection-name | | client-ip | | server-ip | | server-tcp-port | 0..* +-------------------------+ | dscp |<>-------| twamp-session-request | | key-id | +-------------------------+ | max-count | | test-session-name | | client-tcp-port {ro} | | sender-ip | | server-start-time {ro} | | sender-udp-port | | ctrl-connection-state {ro} | | reflector-ip | | selected-mode {ro} | | reflector-udp-port | | token {ro} | | timeout | | client-iv {ro} | | padding-length | +------------------------------+ | dscp | | start-time | +-------------+ 1 | repeat | | pm-reg-list |------<>| repeat-interval | +-------------+ | test-session-state {ro} | | pm-index | | sid {ro} | +-------------+ +-------------------------+ ]]> The twamp-client container includes an administrative parameter (client-admin-state) that controls whether the device is allowed to initiate TWAMP control and test sessions. The twamp-client container holds a list (mode-preference-chain) which specifies the preferred Mode values according to their preferred order of use, including the authentication and encryption Modes. Specifically, mode-preference-chain lists each priority (expressed as a 16-bit unsigned integer, where zero is the highest priority and subsequent values monotonically increasing) with their corresponding mode (expressed as a 32-bit Hexadecimal value). Depending on the Modes available in the Server Greeting, the Control-Client MUST choose the highest priority Mode from the configured mode-preference-chain list. Note that the list of preferred Modes may set bit position combinations when necessary, such as when referring to the extended TWAMP features in , , and . If the Control-Client cannot determine an acceptable Mode, it MUST respond with zero Mode bits set in the Set-up Response message, indicating it will not continue with the control connection. In addition, the twamp-client container holds a list named key-chain which relates KeyIDs with the respective secret keys. Both the Server and the Control-Client use the same mappings from KeyIDs to shared secrets (key-id and secret-key in , respectively). The Server, being prepared to conduct sessions with more than one Control-Client, uses KeyIDs to choose the appropriate secret-key; a Control-Client would typically have different secret keys for different Servers. The secret-key is the shared secret, an octet string of arbitrary length whose interpretation as a text string is unspecified. The key-id and secret-key encoding should follow Section 9.4 of . The derived key length (dkLen in ) MUST be 128-bits for the AES Session-key used for encryption and a 256-bit HMAC-SHA1 Session-key used for authentication (see Section 6.10 of ). Each twamp-client container also holds a list of twamp-client-ctrl-connection, where each item in the list describes a TWAMP control connection that will be initiated by this Control-Client. There SHALL be one instance of twamp-client-ctrl-connection per TWAMP-Control (TCP) connection that is to be initiated from this device. The configuration items for twamp-client-ctrl-connection are: A unique name used as a key to identify this individual TWAMP control connection on the Control-Client device. The IP address of the local Control-Client device, to be placed in the source IP address field of the IP header in TWAMP-Control (TCP) packets belonging to this control connection. If not configured, the device SHALL choose its own source IP address. The IP address belonging to the remote Server device, which the TWAMP-Control connection will be initiated to. This item is mandatory. This parameter defines the TCP port number that is to be used by this outgoing TWAMP-Control connection. Typically, this is the well-known TWAMP port number (862) as per . However, there are known realizations of TWAMP in the field that were implemented before this well-known port number was allocated. These early implementations allowed the port number to be configured. This parameter is therefore provided for backward compatibility reasons. The default value is 862. The DSCP value to be placed in the TCP header of TWAMP-Control packets generated by this Control-Client. The default value is 0. The key-id value that is selected for this TWAMP-Control connection. If an attacking system sets the maximum value in Count (2**32), then the system under attack would stall for a significant period of time while it attempts to generate keys. Therefore, TWAMP-compliant systems SHOULD have a configuration control to limit the maximum Count value. The default max-count value SHOULD be 32768. The following twamp-client-ctrl-connection parameters are read-only: The source TCP port number used in the TWAMP-Control packets belonging to this control connection. The Start-Time advertized by the Server in the Server-Start message (, Section 3.1). This is a timestamp representing the time when the current instantiation of the Server started operating. The TWAMP-Control connection state can be either active or idle. The TWAMP Mode that the Control-Client has chosen for this control connection as set in the Mode field of the Set-Up-Response message (, Section 3.1). This parameter holds the 64 octets containing the concatenation of a 16-octet challenge, a 16-octet AES Session-key used for encryption, and a 32-octet HMAC-SHA1 Session-key used for authentication. AES Session-key and HMAC Session-key are generated randomly by the Control-Client. AES Session-key and HMAC Session-key MUST be generated with sufficient entropy not to reduce the security of the underlying cipher . The token itself is encrypted using the AES (Advanced Encryption Standard) in Cipher Block Chaining (CBC). Encryption MUST be performed using an Initialization Vector (IV) of zero and a key derived from the shared secret associated with KeyID. Challenge is the same as transmitted by the Server () in the clear; see also the last paragraph of Section 6 in . The Control-Client Initialization Vector (Client-IV) is generated randomly by the Control-Client. Client-IV merely needs to be unique (i.e., it MUST never be repeated for different sessions using the same secret key; a simple way to achieve that without the use of cumbersome state is to generate the Client-IV values using a cryptographically secure pseudo-random number source. Each twamp-client-ctrl-connection holds a list of twamp-session-request. twamp-session-request holds information associated with the Control-Client for this test session. This includes information that is associated with the Request-TW-Session/Accept-Session message exchange (see Section 3.5 of ). The Control-Client is also responsible for scheduling and results collection for TWAMP-Test sessions, so twamp-session-request will also hold information related these actions (e.g. pm-index, repeat-interval). There SHALL be one instance of twamp-session-request for each TWAMP-Test session that is to be negotiated by this TWAMP-Control connection via a Request-TW-Session/Accept-Session exchange. The configuration items for twamp-session-request are: A unique name for this test session to be used for identification of this TWAMP-Test session on the Control-Client. The IP address of the Session-Sender device, which is to be placed in the source IP address field of the IP header in TWAMP-Test (UDP) packets belonging to this test session. This value will be used to populate the sender address field of the Request-TW-Session message. If not configured, the device SHALL choose its own source IP address. The UDP port number that is to be used by the Session-Sender for this TWAMP-Test session. A value of zero indicates that the Control-Client SHALL auto-allocate a UDP port number for this TWAMP-Test session. The configured (or auto-allocated) value is advertized in the Sender Port field of the Request-TW-session message (see also Section 3.5 of ). Note that in the scenario where a device auto-allocates a UDP port number for a session, and the repeat parameter for that session is true, the device is free to auto-allocate a different UDP port number when it negotiates the next (repeated) iteration of this session. The IP address belonging to the remote Session-Reflector device to which the TWAMP-Test session will be initiated. This value will be used to populate the receiver address field of the Request-TW-Session message. This item is mandatory. This parameter defines the UDP port number that will be used by the Session-Reflector for this TWAMP-Test session. This value will be placed in the Receiver Port field of the Request-TW-Session message. If this value is not set, the device SHALL use the same port number as defined in the server-tcp-port parameter of this twamp-session-request's parent twamp-client-ctrl-connection. The length of time (in seconds) that the Session-Reflector should continue to respond to packets belonging to this TWAMP-Test session after a Stop-Sessions TWAMP-Control message has been received (, Section 3.8). This value will be placed in the Timeout field of the Request-TW-Session message. The default value is 2 seconds. The number of bytes of padding that will be added to the TWAMP-Test (UDP) packets generated by the Session-Sender. This value will be placed in the Padding Length field of the Request-TW-Session message (, Section 3.5). The DSCP value to be placed in the UDP header of TWAMP-Test packets generated by the Session-Sender, and in the UDP header of the TWAMP-Test response packets generated by the Session-Reflector for this test session. This value will be placed in the Type-P Descriptor field of the Request-TW-Session message (). Time when the session is to be started (but not before the Start-Sessions command is issued). This value is placed in the Start Time field of the Request-TW-Session message. The default value of 0 indicates that the session will be started as soon as the Start-Sessions message is received. These two values together are used to determine if the TWAMP-Test session is to be run repeatedly. Once a test session has completed, the repeat parameter is checked. If the value indicates that this test session is to run again, then the parent TWAMP-Control connection for this test session is restarted - and negotiates a new instance of this TWAMP-Test session. This may occur immediately after the test session completes (if the repeat-interval is set to 0). Otherwise, the Control-Client will wait for the number of minutes specified in the repeat-interval parameter before negotiating the new instance of this TWAMP-Test session. The default value of repeat is False, indicating that once the session has completed, it will not be renegotiated and restarted. A list of one or more Performance Metric Registry Index values (see , which communicate packet stream characteristics and one or more metrics to be measured. All members of the pm-reg-list MUST have the same stream characteristics, such that they combine to specify all metrics that shall be measured on a single stream. One or more Numerical index values of a Registered Metric in the Performance Metric Registry comprise the pm-reg-list. Output statistics are specified in the corresponding Registry entry. The following twamp-session-request parameters are read-only: The TWAMP-Test session state can be either accepted or indicate the respective error code. The SID allocated by the Server for this TWAMP-Test session, and communicated back to the Control-Client in the SID field of the Accept-Session message; see Section 4.3 of .

The twamp-server container (see ) holds items that are related to the configuration of the TWAMP Server logical entity (recall ).

------| key-chain | | servwait | +------------+ | dscp | | key-id | | count | | secret-key | | max-count | +------------+ | modes | | | 0..* +-----------------------------------+ | |<>------| twamp-server-ctrl-connection | +--------------------+ +-----------------------------------+ | client-ip {ro} | | client-tcp-port {ro} | | server-ip {ro} | | server-tcp-port {ro} | | server-ctrl-connection-state {ro} | | dscp {ro} | | selected-mode {ro} | | key-id {ro} | | count {ro} | | max-count {ro} | | salt {ro} | | server-iv {ro} | | challenge {ro} | +-----------------------------------+ ]]> A device operating in the Server role cannot configure attributes on a per TWAMP-Control connection basis, as it has no foreknowledge of what incoming TWAMP-Control connections it will receive. As such, any parameter that the Server might want to apply to an incoming control connection must be configured at the overall Server level, and will then be applied to all incoming TWAMP-Control connections. Each twamp-server container holds a list named key-chain which relates KeyIDs with the respective secret keys. As mentioned in , both the Server and the Control-Client use the same mappings from KeyIDs to shared secrets. The Server, being prepared to conduct sessions with more than one Control-Client, uses KeyIDs to choose the appropriate secret-key; a Control-Client would typically have different secret keys for different Servers. key-id tells the Server which shared-secret the Control-Client wishes to use for authentication or encryption. Each incoming control connection that is active on the Server will be represented by an instance of a twamp-server-ctrl-connection object. All items in the twamp-server-ctrl-connection object are read-only, as we explain later in this section. The twamp-server container items are as follows: This administrative parameter controls whether the device is allowed to operate as a TWAMP Server. As defined in the roles of Server and Session-Reflector can be played by the same host; recall . For a host operating in this manner, this parameter controls whether the device is allowed to respond to TWAMP control and test sessions. This parameter defines the well known TCP port number that is used by TWAMP-Control. The Server will listen on this port number for incoming TWAMP-Control connections. Although this is defined as a fixed value (862) in , there are several realizations of TWAMP in the field that were implemented before this well-known port number was allocated. These early implementations allowed the port number to be configured. This parameter is therefore provided for backward compatibility reasons. The default value is 862. TWAMP-Control (TCP) session timeout, in seconds ((, Section 3.1)). The DSCP value to be placed in the IP header of TWAMP-Control (TCP) packets generated by the Server. Section 3.1 of specifies that the server SHOULD use the DSCP value from the Control-Client's TCP SYN. However, for practical purposes TWAMP will typically be implemented using a general purpose TCP stack provided by the underlying operating system, and such a stack may not provide this information to the user. Consequently, it is not always possible to implement the behavior described in in an OS-portable version of TWAMP. The default behavior if this item is not set is to use the DSCP value from the Control-Client's TCP SYN, as per Section 3.1 of . Parameter used in deriving a key from a shared secret as described in Section 3.1 of , and are communicated to the Control-Client as part of the Server Greeting message. count MUST be a power of 2. count MUST be at least 1024. count SHOULD be increased as more computing power becomes common. If an attacking system sets the maximum value in count (2**32), then the system under attack would stall for a significant period of time while it attempts to generate keys. Therefore, TWAMP-compliant systems SHOULD have a configuration control to limit the maximum count value. The default max-count value SHOULD be 32768. The bit mask of TWAMP Modes this Server instance is willing to support; see IANA TWAMP Modes Registry. Each bit position set represents a mode; see TWAMP-Modes at http://www.iana.org/assignments/twamp-parameters/twamp-parameters.xhtml. Note: Modes requiring Authentication or Encryption MUST include the related attributes. There SHALL be one instance of twamp-server-ctrl-connection per incoming TWAMP-Control (TCP) connection that is received and active on the Server device. All items in the twamp-server-ctrl-connection are read-only. Each instance of twamp-server-ctrl-connection uses the following 4-tuple as its unique key: client-ip, client-tcp-port, server-ip, server-tcp-port. The twamp-server-ctrl-connection container items are all read-only: The IP address on the remote Control-Client device, which is the source IP address used in the TWAMP-Control (TCP) packets belonging to this control connection. The source TCP port number used in the TWAMP-Control (TCP) packets belonging to this control connection. The IP address of the local Server device, which is the destination IP address used in the TWAMP-Control (TCP) packets belonging to this control connection. The destination TCP port number used in the TWAMP-Control (TCP) packets belonging to this control connection. This will usually be the same value as the server-tcp-port configured under twamp-server. However, in the event that the user re-configured twamp-server:server-tcp-port after this control connection was initiated, this value will indicate the server-tcp-port that is actually in use for this control connection. The Server TWAMP-Control connection state can be active or SERVWAIT. The DSCP value used in the IP header of the TWAMP-Control (TCP) packets sent by the Server for this control connection. This will usually be the same value as is configured in the dscp parameter under the twamp-server container. However, in the event that the user re-configures twamp-server:dscp after this control connection is already in progress, this read-only value will show the actual dscp value in use by this TWAMP-Control connection. The Mode that was chosen for this TWAMP-Control connection as set in the Mode field of the Set-Up-Response message. The KeyID value that is in use by this TWAMP-Control connection. The Control-Client selects the key-id for the control connection. The count value that is in use by this TWAMP-Control connection. This will usually be the same value as is configured under twamp-server. However, in the event that the user re-configured twamp-server:count after this control connection is already in progress, this read-only value will show the actual count that is in use for this TWAMP-Control connection. The max-count value that is in use by this TWAMP-Control connection. This will usually be the same value as is configured under twamp-server. However, in the event that the user re-configured twamp-server:max-count after this control connection is already in progress, this read-only value will show the actual max-count that is in use for this control connection. A parameter used in deriving a key from a shared secret as described in Section 3.1 of . Salt MUST be generated pseudo-randomly (independently of anything else in the RFC) and is communicated to the Control-Client as part of the Server Greeting message. The Server Initialization Vector (IV) is generated randomly by the Server. A random sequence of octets generated by the Server. As described in challenge is used by the Control-Client to prove possession of a shared secret.

The twamp-session-sender container, illustrated in , holds items that are related to the configuration of the TWAMP Session-Sender logical entity. There are no global configuration items that apply to the Session-Sender entity as a whole. There is one instance of twamp-sender-test-session for each TWAMP-Test session for which packets are being sent.

-----| twamp-sender-test-session | +----------------------+ +---------------------------+ | test-session-name | | ctrl-connection-name {ro} | | fill-mode | | number-of-packets | | sender-session-state {ro} | | sent-packets {ro} | | rcv-packets {ro} | | last-sent-seq {ro} | | last-rcv-seq {ro} | +---------------------------+ ^ V | 1 +---------------------+ | packet-distribution | +---------------------+ | periodic / poisson | +---------------------+ | | +-------------------------+ | | periodic-interval | | | periodic-interval-units | | +-------------------------+ | +------------------------+ | lambda | | lambda-units | | max-interval | | truncation-point-units | +------------------------+ ]]> The twamp-sender-test-session container items are: A unique name for this TWAMP-Test session to be used for identifying this test session by the Session-Sender logical entity. The name of the parent TWAMP-Control connection that is responsible for negotiating this TWAMP-Test session. Indicates whether the padding added to the TWAMP-Test (UDP) packets will contain pseudo-random numbers, or whether it should consist of all zeroes, as per Section 4.2.1 of . The overall number of TWAMP-Test (UDP) packets to be transmitted by the Session-Sender for this test session. Defines whether TWAMP-Test (UDP) packets are to be transmitted with a fixed interval between them, or whether a Poisson distribution is to be used. If packet-distribution is set to periodic, these two values are used together to determine the period to wait between the first bits of TWAMP-Test (UDP) packet transmissions for this test session. periodic-interval-units is one of seconds, milliseconds, microseconds, nanoseconds; see . If packet-distribution is Poisson, the lambda parameter determines the corresponding average rate of packet transmission. lambda-units defines the units of lambda in reciprocal seconds; see . If packet-distribution is Poisson, then this parameter keeps a stream active by setting a maximum time between packet transmissions. One of seconds, milliseconds, microseconds, nanoseconds. The following twamp-sender-test-session parameters are read-only: This read-only item can be either Active or Idle. The number of TWAMP-Test (UDP) packets belonging to this session that have been transmitted by the Session-Sender. The number of TWAMP-Test (UDP) packets belonging to this session that have been received from the Session-Reflector. The round trip loss for a test session can be calculated as sent-packets - rcv-packets. The value in the sequence number field of the last TWAMP-Test (UDP) packet transmitted for this test session. Sequence numbers start from zero, so this should always be one less than the sent-packets value. The value in the sequence number field of the last TWAMP-Test (UDP) packet received for this test session. In the case of packet loss in the Session-Sender to Session-Reflector direction, this value minus the last-sent-seq will quantify the number of packets that were lost in the Session-Sender to Session-Reflector direction.

The twamp-session-reflector container, illustrated in , holds items that are related to the configuration of the TWAMP Session-Reflector logical entity. A device operating in the Session-Reflector role cannot configure attributes on a per-session basis, as it has no foreknowledge of what incoming sessions it will receive. As such, any parameter that the Session-Reflector might want to apply to an incoming TWAMP-Test session must be configured at the overall Session-Reflector level, and will then be applied to all incoming sessions. Each incoming TWAMP-Test session that is active on the Session-Reflector will be represented by an instance of a twamp-reflector-test-session object. All items in the twamp-reflector-test-session object are read-only.

The twamp-session-reflector configuration items are: The Session-Reflector MAY discontinue any session that has been started when no packet associated with that session has been received for REFWAIT seconds. The default value of REFWAIT SHALL be 900 seconds, and this waiting time MAY be configurable. This timeout allows a Session-Reflector to free up resources in case of failure. Instances of twamp-reflector-test-session are indexed by a session identifier (sid). This value is auto-allocated by the Server as test session requests are received, and communicated back to the Control-Client in the SID field of the Accept-Session message; see Section 4.3 of . When attempting to retrieve operational data for active test sessions from a Session-Reflector device, the user will not know what sessions are currently active on that device, or what SIDs have been auto-allocated for these test sessions. If the user has network access to the Control-Client device, then it is possible to read the data for this session under twamp-client:twamp-client-ctrl-connection:twamp-session-request:sid and obtain the SID (see ). The user may then use this SID value as an index to retrieve an individual twamp-session-reflector:twamp-reflector-test-session instance on the Session-Reflector device. If the user has no network access to the Control-Client device, then the only option is to retrieve all twamp-reflector-test-session instances from the Session-Reflector device. This could be problematic if a large number of test sessions are currently active on that device. Each Session-Reflector TWAMP-Test session contains the following 4-tuple: {parent-connection-client-ip, parent-connection-client-tcp-port, parent-connection-server-ip, parent-connection-server-tcp-port}. This 4-tuple corresponds to the equivalent 4-tuple {client-ip, client-tcp-port, server-ip, server-tcp-port} in the twamp-server-ctrl-connection object. This 4-tuple allows the user to trace back from the TWAMP-Test session to the (parent) TWAMP-Control connection that negotiated this test session. All data under twamp-reflector-test-session is read-only: An auto-allocated identifier for this TWAMP-Test session, that is unique within the context of this Server/Session-Reflector device only. This value will be communicated to the Control-Client that requested the test session in the SID field of the Accept-Session message. The IP address on the remote device, which is the source IP address used in the TWAMP-Test (UDP) packets belonging to this test session. The source UDP port used in the TWAMP-Test packets belonging to this test session. The IP address of the local Session-Reflector device, which is the destination IP address used in the TWAMP-Test (UDP) packets belonging to this test session. The destination UDP port number used in the TWAMP-Test (UDP) test packets belonging to this test session. The IP address on the Control-Client device, which is the source IP address used in the TWAMP-Control (TCP) packets belonging to the parent control connection that negotiated this test session. The source TCP port number used in the TWAMP TCP control packets belonging to the parent control connection that negotiated this test session. The IP address of the Server device, which is the destination IP address used in the TWAMP-Control (TCP) packets belonging to the parent control connection that negotiated this test session. The destination TCP port number used in the TWAMP-Control (TCP) packets belonging to the parent control connection that negotiated this test session. The DSCP value present in the IP header of TWAMP-Test (UDP) packets belonging to this test session. The number of TWAMP-Test (UDP) response packets that have been sent by the Session-Reflector for this test session. The number of TWAMP-Test (UDP) packets that have been received by the Session-Reflector for this test session. Since the Session-Reflector should respond to every test packet it receives, the sent-packets and rcv-packets values should always be identical. The value in the sequence number field of the last TWAMP-Test (UDP) response packet transmitted for this test session. The value in the sequence number field of the last TWAMP-Test (UDP) packet received for this test session.

This section formally specifies the TWAMP data model using YANG.

This section presents a simplified graphical representation of the TWAMP data model using a YANG tree diagram. Readers should keep in mind that the limit of 72 characters per line forces us to introduce artificial line breaks in some tree diagram nodes.

This section presents the YANG module for the TWAMP data model defined in this document.

file "ietf-twamp@2015-06-30.yang" module ietf-twamp { namespace "urn:ietf:params:xml:ns:yang:ietf-twamp"; //namespace need to be assigned by IANA prefix "ietf-twamp"; import ietf-inet-types { prefix inet; } organization "IETF IPPM (IP Performance Metrics) Working Group"; contact "draft-cmzrjp-ippm-twamp-yang@tools.ietf.org"; description "TWAMP Data Model"; revision "2015-06-30" { description "01 version. RFC5357, RFC5618, RFC5938 and RFC6038 is covered. draft-ietf-ippm-metric-registry is also considered"; reference "draft-cmzrjp-ippm-twamp-yang"; } feature control-client { description "This feature relates to the device functions as the TWAMP Control-Client."; } feature server { description "This feature relates to the device functions as the TWAMP Server."; } feature session-sender { description "This feature relates to the device functions as the TWAMP Session-Sender."; } feature session-reflector { description "This feature relates to the device functions as the TWAMP Session-Reflector."; } typedef ctrl-connection-state { type enumeration { enum active { description "Control session is active."; } enum idle { description "Control session is idle."; } } description "Control connection state"; } typedef mode { type bits { bit unauthenticated { position "0"; description "Unauthenticated"; } bit authenticated { position "1"; description "Authenticated"; } bit encrypted { position "2"; description "Encrypted"; } bit unauth-test-encrpyt-control { position "3"; description "Mixed Security Mode per RFC 5618. Test protocol security mode in Unauthenticated mode, Control protocol in Encrypted mode."; } bit individual-session-control { position "4"; description "Individual session control per RFC5938."; } bit reflect-octets { position "5"; description "Reflect octets capability per RFC6038."; } bit symmetrical-size { position "6"; description "Symmetrical size per RFC6038."; } } description "Authentication mode bit mask"; } typedef test-session-state { type enumeration { enum ok { value 0; description "Test session is accepted."; } enum failed { value 1; description "Failure, reason unspecified (catch-all)."; } enum internal-error { value 2; description "Internal error."; } enum not-supported { value 3; description "Some aspect of request is not supported."; } enum permanent-resource-limit { value 4; description "Cannot perform request due to permanent resource limitations."; } enum temp-resource-limit { value 5; description "Cannot perform request due to temporary resource limitations."; } } description "Test session state"; } typedef server-ctrl-connection-state { type enumeration { enum "active" { description "Active"; } enum "servwait" { description "Servwait"; } } description "Server control connection state"; } typedef fill-mode { type enumeration { enum zero { description "Zero"; } enum random { description "Random"; } } description "Indicates whether the padding added to the UDP test packets will contain pseudo-random numbers, or whether it should consist of all zeroes."; } typedef units { type enumeration { enum seconds { description "Seconds"; } enum milliseconds { description "Milliseconds"; } enum microseconds { description "Microseconds"; } enum nanoseconds { description "Nanoseconds"; } } description "Time units"; } typedef sender-session-state { type enumeration { enum setup { description "Test session is active."; } enum failure { description "Test session is idle."; } } description "Sender session state."; } grouping maintenance-statistics { description "Maintenance statistics grouping"; leaf sent-packets { type uint32; config "false"; description "Packets sent"; } leaf rcv-packets { type uint32; config "false"; description "Packets received"; } leaf last-sent-seq { type uint32; config "false"; description "Last sent sequence number"; } leaf last-rcv-seq { type uint32; config "false"; description "Last received sequence number"; } } container twamp { description "Top level container"; container twamp-client { if-feature control-client; presence "twamp-client"; description "Twamp client container"; leaf client-admin-state { type boolean; mandatory "true"; description "Indicates whether this device is allowed to run TWAMP to initiate control/test sessions"; } list mode-preference-chain { key "priority"; unique "mode"; leaf priority { type uint16; description "priority"; } leaf mode { type mode; description "Authentication mode bit mask"; } description "Authentication mode preference"; } list key-chain { key "key-id"; leaf key-id { type string { length "1..80"; } description "Key ID"; } leaf secret-key { type string; description "Secret key"; } description "Key chain"; } list twamp-client-ctrl-connection { key "ctrl-connection-name"; description "Twamp client control connections"; leaf ctrl-connection-name { type string; description "A unique name used as a key to identify this individual TWAMP control connection on the Control-Client device."; } leaf client-ip { type inet:ip-address; description "Client IP address"; } leaf server-ip { type inet:ip-address; mandatory "true"; description "Server IP address"; } leaf server-tcp-port { type inet:port-number; default "862"; description "Server tcp port"; } leaf dscp{ type inet:dscp; default "0"; description "The DSCP value to be placed in the IP header of the TWAMP TCP Control packets generated by the Control-Client"; } leaf key-id { type string { length "1..80"; } description "Key ID"; } leaf max-count { type uint32 { range 1024..4294967295; } default 32768; description "Max count value."; } leaf client-tcp-port { type inet:port-number; config "false"; description "Client TCP port"; } leaf server-start-time { type uint64; config "false"; description "The Start-Time advertized by the Server in the Server-Start message"; } leaf ctrl-connection-state { type ctrl-connection-state; config "false"; description "Control connection state"; } leaf selected-mode { type mode; config "false"; description "The TWAMP mode that the Control-Client has chosen for this control connection as set in the Mode field of the Set-Up-Response message"; } leaf token { type binary { length "64"; } config "false"; description "64 octets, containing the concatenation of a 16-octet challenge, a 16-octet AES Session-key used for encryption, and a 32-octet HMAC-SHA1 Session-key used for authentication"; } leaf client-iv{ type binary { length "16"; } config "false"; description "16 octets, Client-IV is generated randomly by the Control-Client."; } list twamp-session-request { key "test-session-name"; description "Twamp session requests"; leaf test-session-name { type string; description "A unique name for this test session to be used as a key for this test session on the Control-Client."; } leaf sender-ip { type inet:ip-address; description "Sender IP address"; } leaf sender-udp-port { type inet:port-number; description "Sender UDP port"; } leaf reflector-ip { type inet:ip-address; mandatory "true"; description "Reflector IP address."; } leaf reflector-udp-port { type inet:port-number; description "Reflector UDP port. If this value is not set, the device shall use the same port number as defined in the server-tcp-port parameter of this twamp-session-request's parent client-control-connection."; } leaf timeout { type uint64; default "2"; description "The time (in seconds)Session-Reflector MUST wait after receiving a Stop-Session message."; } leaf padding-length { type uint32{ range "64..4096"; } description "The number of bytes of padding that should be added to the UDP test packets generated by the sender. Jumbo sized packets supported."; } leaf dscp { type inet:dscp; description "The DSCP value to be placed in the UDP header of TWAMP-Test packets generated by the Session-Sender, and in the UDP header of the TWAMP-Test response packets generated by the Session-Reflector for this test session."; } leaf start-time { type uint64; default "0"; description "Time when the session is to be started (but not before the Start-Sessions command is issued). This value is placed in the Start Time field of the Request-TW-Session message. The default value of 0 indicates that the session will be started as soon as the Start-Sessions message is received."; } leaf repeat { type boolean; default "false"; description "If the test session is to be run repeatedly. The default value of repeat is False, indicating that once the session has completed, it will not be renegotiated and restarted"; } leaf repeat-interval { when "../repeat='true'" { description "When repeat is true"; } type uint32; description "Repeat interval (in minutes)"; } list pm-reg-list { key "pm-index"; leaf pm-index { type uint16; description "One or more Numerical index values of a Registered Metric in the Performance Metric Registry"; } description "A list of one or more pm-index values, which communicate packet stream characteristics and one or more metrics to be measured."; } leaf test-session-state { type test-session-state; config "false"; description "Test session state"; } leaf sid{ type string; config "false"; description "The SID allocated by the Server for this test session"; } } } } container twamp-server{ if-feature server; presence "twamp-server"; description "Twamp sever container"; leaf server-admin-state{ type boolean; mandatory "true"; description "Indicates whether this device is allowed to run TWAMP to respond to control/test sessions"; } leaf server-tcp-port { type inet:port-number; default "862"; description "This parameter defines the well known TCP port number that is used by TWAMP."; } leaf servwait { type uint32 { range 1..604800; } default 900; description "SERVWAIT (TWAMP Control (TCP) session timeout), default value is 900"; } leaf dscp { type inet:dscp; description "The DSCP value to be placed in the IP header of TCP TWAMP-Control packets generated by the Server"; } leaf count { type uint32 { range 1024..4294967295; } description "Parameter used in deriving a key from a shared secret "; } leaf max-count { type uint32 { range 1024..4294967295; } default 32768; description "Max count value."; } leaf modes { type mode; description "The bit mask of TWAMP Modes this Server instance is willing to support."; } list key-chain { key "key-id"; leaf key-id { type string { length "1..80"; } description "Key IDs."; } leaf secret-key { type string; description "Secret keys."; } description "KeyIDs with the respective secret keys."; } list twamp-server-ctrl-connection { key "client-ip client-tcp-port server-ip server-tcp-port"; config "false"; description "Twamp server control connections"; leaf client-ip { type inet:ip-address; description "Client IP address"; } leaf client-tcp-port { type inet:port-number; description "Client TCP port"; } leaf server-ip { type inet:ip-address; description "Server IP address"; } leaf server-tcp-port { type inet:port-number; description "Server TCP port"; } leaf server-ctrl-connection-state { type server-ctrl-connection-state; description "Server control connection state"; } leaf dscp { type inet:dscp; description "The DSCP value used in the IP header of the TCP control packets sent by the Server for this control connection. This will usually be the same value as is configured for twamp-server:dscp under the twamp-server. However, in the event that the user re-configures twamp-server:dscp after this control connection is already in progress, this read-only value will show the actual dscp value in use by this control connection."; } leaf selected-mode { type mode; description "The mode that was chosen for this control connection as set in the Mode field of the Set-Up-Response message."; } leaf key-id { type string { length "1..80"; } description "The key-id value that is in use by this control connection."; } leaf count { type uint32 { range 1024..4294967295; } description "The count value that is in use by this control connection. This will usually be the same value as is configured under twamp-server. However, in the event that the user re-configured twamp-server:count after this control connection is already in progress, this read-only value will show the different count that is in use for this control connection."; } leaf max-count { type uint32 { range 1024..4294967295; } description "The max-count value that is in use by this control connection. This will usually be the same value as is configured under twamp-server. However, in the event that the user re-configured twamp-server:max-count after this control connection is already in progress, this read-only value will show the different max-count that is in use for this control connection."; } leaf salt{ type binary { length "16"; } description "Salt MUST be generated pseudo-randomly"; } leaf server-iv { type binary { length "16"; } description "16 octets, Server-IV is generated randomly by the Control-Client."; } leaf challenge { type binary { length "16"; } description "Challenge is a random sequence of octets generated by the Server"; } } } container twamp-session-sender{ if-feature session-sender; description "Twamp session sender container"; list twamp-sender-test-session{ key "test-session-name"; description "Twamp sender test sessions"; leaf test-session-name { type string; description "A unique name for this test session to be used as a key for this test session by the Session-Sender logical entity."; } leaf ctrl-connection-name { type string; config "false"; description "The name of the parent control connection that is responsible for negotiating this test session."; } leaf fill-mode { type fill-mode; default zero; description "Indicates whether the padding added to the UDP test packets will contain pseudo-random numbers, or whether it should consist of all zeroes."; } leaf number-of-packets { type uint32; description "The overall number of UDP test packets to be transmitted by the sender for this test session."; } choice packet-distribution { description "Packet distributions, poisson or periodic"; case periodic { leaf periodic-interval { type uint32; description "Periodic interval"; } leaf periodic-interval-units { type units; description "Periodic interval units"; } } case poisson { leaf lambda{ type uint32; description "The average rate of packet transmission."; } leaf lambda-units{ type uint32; description "Lambda units."; } leaf max-interval{ type uint32; description "maximum time between packet transmissions."; } leaf truncation-point-units{ type units; description "Truncation point units"; } } } leaf sender-session-state { type sender-session-state; config "false"; description "Sender session state."; } uses maintenance-statistics; } } container twamp-session-reflector { if-feature session-reflector; description "Twamp session reflector container"; leaf refwait { type uint32 { range 1..604800; } default 900; description "REFWAIT (TWAMP test session timeout), the default value is 900"; } list twamp-reflector-test-session { key "sender-ip sender-udp-port reflector-ip reflector-udp-port"; config "false"; description "Twamp reflector test sessions"; leaf sid{ type string; description "An auto-allocated identifier for this test session, that is unique within the context of this Server/Session-Reflector device only. "; } leaf sender-ip { type inet:ip-address; description "Sender IP address."; } leaf sender-udp-port { type inet:port-number; description "Sender UDP port."; } leaf reflector-ip { type inet:ip-address; description "Reflector IP address."; } leaf reflector-udp-port { type inet:port-number; description "Reflector UDP port."; } leaf parent-connection-client-ip { type inet:ip-address; description "Parent connction client IP address."; } leaf parent-connection-client-tcp-port { type inet:port-number; description "Parent connection client TCP port."; } leaf parent-connection-server-ip { type inet:ip-address; description "Parent connection server IP address."; } leaf parent-connection-server-tcp-port { type inet:port-number; description "Parent connection server TCP port"; } leaf dscp { type inet:dscp; description "The DSCP value present in the IP header of TWAMP UDP test packets belonging to this test session."; } uses maintenance-statistics; } } } }

]]>



    
      This section presents a simple but complete example of configuring
      all four entities in , based on the YANG
      module specified in . The example is illustrative
      in nature, but aims to be self-contained, i.e. were it to be executed in
      a real TWAMP implementation it would lead to a correctly configured test
      session. A more elaborated example, which also includes authentication
      parameters, is provided in .

      
        The following configuration example shows a Control-Client with
        client-admin-state enabled. In a real implementation following  this would permit the initiation of TWAMP-Control connections and TWAMP-Test sessions.

        
          
   
      True
   

]]>
        

        The following configuration example shows a Control-Client with two
        instances of twamp-client-ctrl-connection, one called "RouterA" and
        another called "RouterB". Each TWAMP-Control connection is to a different
        Server. The control connection named "RouterA" has two test session
        requests. The TWAMP-Control connection named "RouterB" has no TWAMP-Test
        session requests.

        
          
   

      
         RouterA
         203.0.113.1
         203.0.113.2
         
            Test1
            10.1.1.1
            4000
            10.1.1.2
            5000
            0
         
         
            Test2
            203.0.113.1
            4001
            203.0.113.2
            5001
            0
         
      

      
         RouterB
         203.0.113.1
         203.0.113.3
      

   

]]>
        
      

      
        This configuration example shows a Server with server-admin-state
        enabled, which permits a device following  to respond to TWAMP-Control
        connections and TWAMP-Test sessions.

        
          

          
   
      True
   

]]>
        

        The following example presents a Server with the TWAMP-Control connection
        corresponding to the control connection name (ctrl-connection-name)
        "RouterA" presented in .

        
          
   
   
      
         203.0.113.1
         16341
         203.0.113.2
         862
         
            active
         
      
   
   

]]>
        
      

      
        The following configuration example shows a Session-Sender with the
        two TWAMP-Test sessions presented in .

        
          
   
   
      
         Test1// read-only
         RouterA
         900
         
            1
            seconds
         
      

      
         Test2
         
           RouterA
          // read-only
         900
         
            1
            1
            2
            seconds
      	
      

   

]]>
        
      

      
        The following example shows the two Session-Reflector TWAMP-Test sessions
        corresponding to the test sessions presented in .

        
          
   
   
       
         1232
         10.1.1.1
         10.1.1.2
         4000
         5000
         
            203.0.113.1
          
         
            16341
          
         
            203.0.113.2
          
         
            862
          
         2
         2
         1
         1
      

      
         178943
         203.0.113.1
         192.68.0.2
         4001
         
            203.0.113.1
          
         
            16341
          
         
            203.0.113.2
          
         
           862
         
         5001
         21
         21
         20
         20
      
 
   

]]>
        
      
    

    
      TBD
    

    
      This document registers a URI in the IETF XML registry . Following the format in ,
      the following registration is requested to be made.

      URI: urn:ietf:params:xml:ns:yang:ietf-twamp

      Registrant Contact: The IPPM WG of the IETF.

      XML: N/A, the requested URI is an XML namespace.

      This document registers a YANG module in the YANG Module Names
      registry .

      name: ietf-twamp

      namespace: urn:ietf:params:xml:ns:yang:ietf-twamp

      prefix: twamp

      reference: RFC XXXX
    

    
      We thank Gregory Mirsky, Kevin D'Souza, and Robert Sherman for their thorough and
      constructive reviews, comments and text suggestions.

      Haoxing Shen contributed to the definition of the YANG module in
      .

      Kostas Pentikousis is partially supported by FP7 UNIFY
      (http://fp7-unify.eu), a research project partially funded by the
      European Community under the Seventh Framework Program (grant agreement
      no. 619609). The views expressed here are those of the authors only. The
      European Commission is not liable for any use that may be made of the
      information in this document.



  
    
      

	  

      

      

      

      

      
    

    
      

      

      

      

      

      

      

      

      

      

      
	  
	  

      
        
          Research directions in network service chaining

          
            John, W., Pentikousis, K., et al.
          

          
        

        
      
    

    
      This appendix extends the example presented in  by configuring more fields such as authentication
      parameters, dscp values and so on.

      
        
          
   

      True

      
         0
         0x00000002
      
      
         1
         0x00000001
      

      
         KeyClient1ToRouterA
         secret1
      
      
         KeyForRouterB
         secret2
      

      
         RouterA
         203.0.113.1
         203.0.113.2
         32
         KeyClient1ToRouterA
         
            Test1
            10.1.1.1
            4000
            10.1.1.2
            5000
            0
            0
            ok
            1232
         
         
            Test2
            203.0.113.1
            4001
            203.0.113.2
            5001
            32
            0
            ok
            178943
         
      
 
   

]]>
        
      

      
        
          
   

      True
      1800
      32
      0x00000003
      256

      
         KeyClient1ToRouterA
         secret1
      
      
         KeyClient10ToRouterA
         secret10
      

      
         203.0.113.1
         16341
         203.0.113.2
         862
         
            active
          
         32
         0x00000002
         KeyClient1ToRouterA
         1024
      

   

]]>
        
      

      
        
          
   
   
      
         Test1 // read-only
         RouterA
         32
         zero
         900
         
            1
            seconds
         
         Active
         2
         2
         1
         1
      

      
         Test2
         
           RouterA
          // read-only
         32
         random
         900
         
           1
           1
           2
           seconds
         
         Active
         21
         21
         20
         20
      

   

]]>
        
      

      
        
          
   
   
      
         1232
         10.1.1.1
         10.1.1.2
         4000
         5000
         
            203.0.113.1
         
         
            16341
         
         
            203.0.113.2
         
         
            862
         
         32
         2
         2
         1
         1
      

      
         178943
         203.0.113.1
         192.68.0.2
         4001
         
            203.0.113.1
         
         
            16341
         
         
            203.0.113.2
         
         
            862
         
         5001
         32
         21
         21
         20
         20
      

   

]]>
        
      
    

    
      This document is targeted at configuration details for TWAMP.
      Operational actions such as how TWAMP sessions are started/stopped, how
      results are retrieved, or stored results are cleared, and so on, are not
      addressed by this configuration model and are out of scope of this
      document.

      TWAMP operational commands could be performed programmatically or
      manually, e.g. using a command-line interface (CLI). With respect to
      programmability, YANG can be used to define NETCONF Remote Procedure
      Calls (RPC), therefore it would be possible to define RPC operations for
      actions such as starting or stopping control or test sessions or groups
      of sessions; retrieving results; clearing stored results, and so on.

      However,  does not attempt to describe such
      operational actions, and it is likely that different TWAMP
      implementations could support different sets of operational commands,
      with different restrictions. Therefore, this document considers it the
      responsibility of the individual implementation to define its
      corresponding TWAMP operational commands data model.