Transaction Internet Protocol Working Group J. Lyon Internet-Draft Microsoft Obsoletes K. Evans Expires in 6 months J. Klein Tandem Computers September 8th, 1997 Transaction Internet Protocol Version 2.0 Status of this Memo This document is an Internet-Draft. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." To learn the current status of any Internet-Draft, please check the "1id-abstracts.txt" listing contained in the Internet-Drafts Shadow Directories on ftp.is.co.za (Africa), nic.nordu.net (Europe), munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or ftp.isi.edu (US West Coast). Abstract In many applications where different nodes cooperate on some work, there is a need to guarantee that the work happens atomically. That is, each node must reach the same conclusion as to whether the work is to be completed, even in the face of failures. This document proposes a simple, easily-implemented protocol for achieving this end. Lyon, J. [Page 1] INTERNET-DRAFT TIP Version 2.0 Sept 1997 Table of Contents Status of this memo 1 Abstract 1 Table of Contents 2 1. Introduction 3 2. Example Usage 3 3. Transactions 4 4. Connections 4 5. Transaction Identifiers 5 6. Pushing vs. Pulling Transactions 5 7. Endpoint Identification 6 8. TIP Uniform Resource Locators 7 9. States of a Connection 8 10. Protocol Versioning 9 11. Commands and Responses 10 12. Command Pipelining 10 13. TIP Commands 10 14. Error Handling 16 15. Connection Failure and Recovery 16 16. Security Considerations 17 17. Significant changes from previous version 18 App A. The TIP Multiplexing Protocol Version 2.0 19 References 23 Authors' Addresses 23 Comments 23 Lyon, J. [Page 2] INTERNET-DRAFT TIP Version 2.0 Sept 1997 1. Introduction The standard method for achieving atomic commitment is the two-phase commit protocol; see [1] for an introduction to atomic commitment and two-phase commit protocols. Numerous two-phase commit protocols have been implemented over the years. However, none of them has become widely used in the Internet, due mainly to their complexity. Most of that complexity comes from the fact that the two-phase commit protocol is bundled together with a specific program-to-program communication protocol, and that protocol lives on top of a very large infrastructure. This memo proposes a very simple two-phase commit protocol. It achieves its simplicity by specifying only how different nodes agree on the outcome of a transaction; it allows (even requires) that the subject matter on which the nodes are agreeing be communicated via other protocols. By doing so, we avoid all of the issues related to application communication semantics and data representation (to name just a few). Independent of the application communication protocol a transaction manager may use the Transport Layer Security protocol [3] to authenticate other transaction managers and encrypt messages. It is envisioned that this protocol will be used mainly for a transaction manager on one Internet node to communicate with a transaction manager on another node. While it is possible to use this protocol for application programs and/or resource managers to speak to transaction managers, this communication is usually intra-node, and most transaction managers already have more-than- adequate interfaces for the task. While we do not expect this protocol to replace existing ones, we do expect that it will be relatively easy for many existing heterogeneous transaction managers to implement this protocol for communication with each other. Further supplemental information regarding the TIP protocol can be found in [5]. 2. Example Usage Today the electronic shopping basket is a common metaphor at many electronic store-fronts. Customers browse through an electronic catalog, select goods and place them into an electronic shopping basket. HTTP servers [2] provide various means ranging from URL encoding to context cookies to keep track of client context (e.g. the shopping basket of a customer) and resume it on subsequent customer requests. Once a customer has finished shopping they may decide to commit their selection and place the associated orders. Most orders may have no relationship with each other except being executed as part of the same shopping transaction; others may be dependent on each other Lyon, J. [Page 3] INTERNET-DRAFT TIP Version 2.0 Sept 1997 (for example, if made as part of a special offering). Irrespective of these details a customer will expect that all orders have been successfully placed upon receipt of a positive acknowledgment. Today's electronic store-fronts must implement their own special protocols to coordinate such placement of all orders. This programming is especially complex when orders are placed through multiple electronic store-fronts. This complexity limits the potential utility of internet applications, and constrains growth. The protocol described in this document intends to provide a standard for internet servers to achieve agreement on a unit of shared work (e.g. placement of orders in an electronic shopping basket). The server (e.g. a CGI program) placing the orders may want to start a transaction calling its local transaction manager, and ask other servers participating in the work to join the transaction. The server placing the orders passes a reference to the transaction as user data on HTTP requests to the other servers. The other servers call their transaction managers to start a local transaction and ask them to join the remote transaction using the protocol defined in this document. Once all orders have been placed, execution of the two-phase-commit protocol is delegated to the involved transaction managers. If the transaction commits, all orders have been successfully placed and the customer gets a positive acknowledgment. If the transaction aborts no orders will be placed and the customer will be informed of the problem. Transaction support greatly simplifies programming of these applications as exception handling and failure recovery are delegated to a special component. End users are also not left having to deal with the consequences of only partial success. While this example shows how the protocol can be used by HTTP servers, applications may use the protocol when accessing a remote database (e.g. via ODBC), or invoking remote services using other already existing protocols (e.g. RPC). The protocol makes it easy for applications in a heterogeneous network to participate in the same transaction, even if using different communication protocols. 3. Transactions "Transaction" is the term given to the programming model whereby computational work performed has atomic semantics. That is, either all work completes successfully and changes are made permanent (the transaction commits), or if any work is unsuccessful, changes are undone (the transaction aborts). The work comprising a transaction (unit of work), is defined by the application. 4. Connections The Transaction Internet Protocol (TIP) requires a reliable ordered stream transport with low connection setup costs. In an Internet (IP) environment, TIP operates over TCP, optionally using a protocol to multiplex light-weight connections over the same TCP connection. Lyon, J. [Page 4] INTERNET-DRAFT TIP Version 2.0 Sept 1997 Transaction managers which share transactions establish a TCP connection. The protocol uses a different connection for each simultaneous transaction shared between two transaction managers. After a transaction has ended, the connection can be reused for a different transaction. Optionally, instead of associating a TCP connection with only a single transaction, two transaction managers may agree on a protocol to multiplex light-weight connections over the same TCP connection, and associate each simultaneous transaction with a separate light- weight connection. Using light-weight connections reduces latency and resource consumption associated with executing simultaneous transactions. Similar techniques as described here are widely used by existing transaction processing systems. See Appendix A for an example of one such protocol. Note that although the TIP protocol itself is described only in terms of TCP, there is nothing to preclude the use of TIP with other transport protocols. However, it is up to the implementor to ensure the chosen transport provides equivalent semantics to TCP, and to map the TIP protocol appropriately. 5. Transaction Identifiers Unfortunately, there is no single globally-accepted standard for the format of a transaction identifier; there are various standard and proprietary formats. Allowed formats for a TIP transaction identifier are described below in the section "TIP Uniform Resource Locators". A transaction manager may map it's internal transaction identifiers into this TIP format in any manner it sees fit. Furthermore, each party in a superior/subordinate relationship gets to assign its own identifier to the transaction; these identifiers are exchanged when the relationship is first established. Thus, a transaction manager gets to use its own format of transaction identifier internally, but it must remember a foreign transaction identifier for each superior/subordinate relationship in which it is involved. 6. Pushing vs. Pulling Transactions Suppose that some program on node "A" has created a transaction, and wants some program on node "B" to do some work as part of the transaction. There are two classical ways that he does this, referred to as the "push" model and the "pull" model. In the "push" model, the program on A first asks his transaction manager to export the transaction to node B. A's transaction manager sends a message to B's TM asking it to instantiate the transaction as a subordinate of A, and return its name for the transaction. The program on A then sends a message to its counterpart on B on the order of "Do some work, and make it part of the transaction that your transaction manager already knows of by the name ...". Because A's TM knows that it sent the transaction to B's TM, A's TM knows to involve B's TM in the two-phase commit process. Lyon, J. [Page 5] INTERNET-DRAFT TIP Version 2.0 Sept 1997 In the "pull" model, the program on A merely sends a message to B on the order of "Do some work, and make it part of the transaction that my TM knows by the name ...". The program on B asks its TM to enlist in the transaction. At that time, B's TM will "pull" the transaction over from A. As a result of this pull, A's TM knows to involve B's TM in the two-phase commit process. The protocol described here supports both the "push" and "pull" models. 7. Endpoint Identification In certain cases after connection failures, one of the parties of a connection may have a responsibility to re-establish a new connection to the other party in order to complete the two-phase-commit protocol. If the party that initiated the original connection needs to re-establish it, the job is easy: he merely establishes a connection in the same way that he originally did it. However, if the other party needs to re-establish the connection, he needs to know how to contact the initiator of the original connection. He gets this information in the following way: After a TCP connection has been established the initiating party issues an IDENTIFY command and supplies an endpoint identifier which is used to re-establish the connection if needed. If the initiating party does not supply an endpoint identifier on the IDENTIFY command, he must not perform any action which would require a connection to be re-established (e.g. perform recovery actions). An as used in the IDENTIFY (and a few other) commands has one of the following formats: : : A is a standard name, acceptable to the domain name service. It must be sufficiently qualified to be useful to the receiver of the command. An is an IP address, in the usual form: four decimal numbers separated by period characters. The is a decimal number specifying the port at which the transaction manager is listening for requests to establish TCP connections. Two standard transaction service port numbers are defined: xxxx for TLS secured connections, and yyyy for unsecured connections. If the port number is omitted from the endpoint identifier, and if the current connection is TLS secured, then the standard TLS secured transaction service port number is assumed; otherwise the standard unsecured transaction service port number is assumed. Likewise, if a port number is specified, then it must represent a port with the same security capabilities as the current connection (i.e. TLS or unsecured). Lyon, J. [Page 6] INTERNET-DRAFT TIP Version 2.0 Sept 1997 8. TIP Uniform Resource Locators Transactions and transaction managers are resources associated with the TIP protocol. Transaction managers and transactions are located using TCP/IP endpoint identifiers. Once a TCP connection has been established, TIP commands may be sent to operate on transactions associated with the respective transaction managers. Applications which want to pull a transaction from a remote node must supply a reference to the remote transaction which allows the local transaction manager (i.e. the transaction manager pulling the transaction) to connect to the remote transaction manager and identify the particular transaction. Applications which want to push a transaction to a remote node must supply a reference to the remote transaction manager (i.e. the transaction manager to which the transaction is to be pushed), which allows the local transaction manager to locate the remote transaction manager. The TIP protocol defines a URL scheme [4] which allows applications and transaction managers to exchange references (i.e. TIP URLs) to transaction managers and transactions. A TIP URL takes the form: TIP://[:]/ where is an IP address or a DNS name as defined above; and is a valid TCP port number. may take one of two forms (standard or non-standard): i. "urn:" ":" A standard transaction identifier, conforming to the proposed Internet Standard for Uniform Resource Names (URNs), as specified by RFC2141; where is the Namespace Identifier, and is the Namespace Specific String. The Namespace ID determines the syntactic interpretation of the Namespace Specific String. The Namespace Specific String is a sequence of characters representing a transaction identifier (as defined by ). The rules for the contents of these fields are specified by [7] (valid characters, encoding, etc.). This format of may be used to express global transaction identifiers in terms of standard representations. Examples for might be or . e.g. TIP://123.123.123.123/urn:xopen:xid ii. A sequence of printable ASCII characters (octets with values in the range 33 through 126 inclusive (excluding ":")) Lyon, J. [Page 7] INTERNET-DRAFT TIP Version 2.0 Sept 1997 representing a transaction identifier. In this non-standard case, it is the combination of and which ensures global uniqueness. e.g. TIP://123.123.123.123/transid1 Except as otherwise described above, the TIP URL scheme follows the rules for reserved characters as defined in [4], and uses escape sequences as defined in [4] Section 5. Note that the TIP protocol itself does not use the TIP URL scheme. This URL scheme is proposed as a standard way to pass transaction identification information through other protocols. e.g. between cooperating application processes. The URL may then be used to communicate to the local transaction manager the information necessary to associate the application with a particular TIP transaction. e.g. to PULL the transaction from a remote transaction manager. It is anticipated that each TIP implementation will provide some set of APIs for this purpose. To create a non-standard TIP URL from a transaction identifier, first replace any reserved characters in the transaction identifier with their equivalent escape sequences, then insert the appropriate host endpoint identification. If the transaction identifier is one that you created, insert your own endpoint identification. If the transaction identifier is one that you received on a TIP connection that you initiated, insert the identification of the party to which you connected. If the transaction identifier is one that you received on a TIP connection that you did not initiate, use the identification that was received in the IDENTIFY command. 9. States of a Connection At any instant, only one party on a connection is allowed to send commands, while the other party is only allowed to respond to commands that he receives. Throughout this document, the party that is allowed to send commands is called "primary"; the other party is called "secondary". Initially, the party that initiated the connection is primary; however, a few commands cause the roles to switch. A connection returns to it's original polarity whenever Idle state is reached. These rules remain true for "virtual" connections when multiplexing is being used. At any instant, a connection is in one of the following states. From the point of view of the secondary party, the state changes when he sends a reply; from the point of view of the primary party, the state changes when he receives a reply. Initial: The initial connection starts out in the Initial state. Upon entry into this state, the party that initiated the connection becomes primary, and the other party becomes secondary. There is no transaction associated with the connection in this state. From this state, the primary can send the IDENTIFY command. Lyon, J. [Page 8] INTERNET-DRAFT TIP Version 2.0 Sept 1997 Idle: In this state, the primary and the secondary have agreed on a protocol version, and the primary supplied an endpoint identifier to the secondary party to reconnect after a failure. There is no transaction associated with the connection in this state. Upon entry to this state, the party that initiated the connection becomes primary, and the other party becomes secondary. From this state, the primary can send any of the following commands: BEGIN, MULTIPLEX, PUSH, PULL, QUERY and RECONNECT. Begun: In this state, a connection is associated with an active transaction, which can only be completed by a one-phase protocol. A BEGUN response to a BEGIN command places a connection into this state. Failure of a connection in Begun state implies that the transaction will be aborted. From this state, the primary can send an ABORT, or COMMIT command. Enlisted: In this state, the connection is associated with an active transaction, which can be completed by a one-phase or, two-phase protocol. A PUSHED response to a PUSH command, or a PULLED response to a PULL command, places the connection into this state. Failure of the connection in Enlisted state implies that the transaction will be aborted. From this state, the primary can send an ABORT, COMMIT, or PREPARE command. Prepared: In this state, a connection is associated with a transaction that has been prepared. A PREPARED response to a PREPARE command, or a RECONNECTED response to a RECONNECT command places a connection into this state. Unlike other states, failure of a connection in this state does not cause the transaction to automatically abort. From this state, the primary can send an ABORT, or COMMIT command. Multiplexing: In this state, the connection is being used by a multiplexing protocol, which provides its own set of connections. In this state, no TIP commands are possible on the connection. (Of course, TIP commands are possible on the connections supplied by the multiplexing protocol.) The connection can never leave this state. Error: In this state, a protocol error has occurred, and the connection is no longer useful. 10. Protocol Versioning This document describes version 2 of the protocol. In order to accommodate future versions, the primary party sends a message indicating the lowest and the highest version number it understands. The secondary responds with the highest version number it understands. After such an exchange, communication can occur using the smaller of the highest version numbers (i.e., the highest version number that both understand). This exchange is mandatory and occurs using the Lyon, J. [Page 9] INTERNET-DRAFT TIP Version 2.0 Sept 1997 IDENTIFY command (and IDENTIFIED response). If the highest version supported by one party is considered obsolete and no longer supported by the other party, no useful communication can occur. In this case, the newer party should merely drop the connection. 11. Commands and Responses All commands and responses consist of one line of ASCII text, using only octets with values in the range 32 through 127 inclusive, followed by either a CR (an octet with value 13) or an LR (an octet with value 10). Each line can be split up into one or more "words", where successive words are separated by one or more space octets (value 32). Arbitrary numbers of spaces at the beginning and/or end of each line are allowed, and ignored. Lines that are empty, or consist entirely of spaces are ignored. (One implication of this is that you can terminate lines with both a CR and an LF if desired; the LF will be treated as terminating an empty line, and ignored.) In all cases, the first word of each line indicates the type of command or response; all defined commands and responses consist of upper-case letters only. For some commands and responses, subsequent words convey parameters for the command or response; each command and response takes a fixed number of parameters. All words on a command or response line after the last defined word are totally ignored. These can be used to pass human-readable information for debugging or other purposes. 12. Command Pipelining The primary party of a connection is allowed to issue multiple commands without having to wait for responses. This reduces latency and allows the primary to react immediately to local state changes. Examples are a PREPARE command immediately followed by an ABORT command after the primary detected that a transaction must be aborted, or a COMMIT response immediately followed by a PULL command. The secondary must issue replies in the order of the commands received. If a command causes an error the connection enters the Error state and all subsequent commands on the connection are discarded. 13. TIP Commands Following is a list of all valid commands, and all possible responses to each (for each command, whether it pertains to a transaction, or a connection, is specified [thus]): Lyon, J. [Page 10] INTERNET-DRAFT TIP Version 2.0 Sept 1997 ABORT This command is valid in the Begun, Enlisted, and Prepared states. It informs the secondary that the current transaction of the connection will abort. Possible responses are: ABORTED The transaction has aborted; the connection enters Idle state, and the initiator of the connection becomes primary. ERROR The command was issued in the wrong state, or was malformed. The connection enters the Error state. BEGIN This command is valid only in the Idle state. It asks the secondary to create a new transaction and associate it with the connection. The newly created transaction will be completed with a one-phase protocol. Possible responses are: BEGUN A new transaction has been successfully begun, and that transaction is now the current transaction of the connection. The connection enters Begun state. NOTBEGUN A new transaction could not be begun; the connection remains in Idle state. ERROR The command was issued in the wrong state, or was malformed. The connection enters the Error state. COMMIT This command is valid in the Begun, Enlisted or Prepared states. In the Begun or Enlisted state, it asks the secondary to attempt to commit the transaction; in the Prepared state, it informs the secondary that the transaction has committed. Note that in the Enlisted state this command represents a one-phase protocol, and should only be done when the sender has 1) no local recoverable resources involved in the transaction, and 2) only one subordinate (the sender will not be involved in any transaction recovery process). Possible responses are: ABORTED This response is possible only from the Begun and Enlisted states. It indicates that some party has vetoed the commitment of the transaction, so it has been aborted instead of committing. The connection enters the Idle state. COMMITTED This response indicates that the transaction has been Lyon, J. [Page 11] INTERNET-DRAFT TIP Version 2.0 Sept 1997 committed, and that the primary no longer has any responsibilities to the secondary with respect to the transaction. The connection enters the Idle state. ERROR The command was issued in the wrong state, or was malformed. The connection enters the Error state. ERROR This command is valid in any state; it informs the secondary that a previous response was not recognized or was badly formed. A secondary should not respond to this command. The connection enters Error state. IDENTIFY | "-" This command is valid only in the Initial state. The primary party informs the secondary party of the lowest and highest protocol version supported (all versions between the lowest and highest must be supported), and optionally of an IP address and a port number at which the other party can re-establish a connection if ever needed. If the primary party does not supply an endpoint identifier the secondary party will respond with ABORTED or READONLY to any PREPARE commands. Possible responses are: IDENTIFIED The accepting party has saved the identification. The response contains the highest protocol version supported by the secondary party. All future communication is assumed to take place using the smaller of the protocol versions in the IDENTIFY command and the IDENTIFIED response. The connection enters the Idle state. ERROR The command was issued in the wrong state, or was malformed. This response also occurs if the accepting party does not support any version of the protocol in the range supported by the initiator. The connection enters the Error state. The initiator should close the connection. MULTIPLEX This command is only valid in the Idle state. The command seeks agreement to use the connection for a multiplexing protocol that will supply a large number of connections on the existing connection. The primary suggests a particular multiplexing protocol. The secondary party can either accept or reject use of this protocol. At the present, the only defined protocol identifier is "TMP2.0", Lyon, J. [Page 12] INTERNET-DRAFT TIP Version 2.0 Sept 1997 which refers to the TIP Multiplexing Protocol, version 2.0. See Appendix A for details of this protocol. Other protocol identifiers may be defined in the future. Note that when using TMP V2.0, a single TIP command (TMP application message) must be wholly contained within a single TMP packet. If the MULTIPLEX command is accepted, the specified multiplexing protocol will totally control the underlying connection. This protocol will begin with the first byte after the line terminator of the MULTIPLEX command (for data sent by the initiator), and the first byte after the line terminator of the MULTIPLEXING response (for data received by the initiator). This implies that an implementation must not send both a CR and a LF octet after either the MULTIPLEX command or the MULTIPLEXING response, lest the LF octet be mistaken for the first byte of the multiplexing protocol. Possible responses to the MULTIPLEX command are: MULTIPLEXING The secondary party agrees to use the specified multiplexing protocol. The connection enters the Multiplexing state, and all subsequent communication is as defined by that protocol. All connections created by the multiplexing protocol start out in the Idle state. CANTMULTIPLEX The secondary party cannot support (or refuses to use) the specified multiplexing protocol. The connection remains in the Idle state. ERROR The command was issued in the wrong state, or was malformed. The connection enters the Error state. PREPARE This command is valid only in the Enlisted state; it requests the secondary to prepare the transaction for commitment (phase one of two-phase commit). Possible responses are: PREPARED The subordinate has prepared the transaction; the connection enters PREPARED state. ABORTED The subordinate has vetoed committing the transaction. The connection enters the Idle state, and the connection initiator becomes primary. After this response, the superior has no responsibilities to the subordinate with respect to the transaction. READONLY The subordinate no longer cares whether the transaction Lyon, J. [Page 13] INTERNET-DRAFT TIP Version 2.0 Sept 1997 commits or aborts. The connection enters the Idle state, and the connection initiator becomes primary. After this response, the superior has no responsibilities to the subordinate with respect to the transaction. ERROR The command was issued in the wrong state, or was malformed. The connection enters the Error state. PULL This command is only valid in Idle state. This command seeks to establish a superior/subordinate relationship in a transaction, with the primary party of the connection as the subordinate (i.e., he is pulling a transaction from the secondary party). Note that the entire value of (as defined in the section "TIP Uniform Resource Locators") must be specified as the transaction identifier. Possible responses are: PULLED The relationship has been established. Upon receipt of this response, the specified transaction becomes the current transaction of the connection, and the connection enters Enlisted state. Additionally, the roles of primary and secondary become reversed. (That is, the superior becomes the primary for the connection.) NOTPULLED The relationship has not been established (possibly, because the secondary party no longer has the requested transaction). The connection remains in Idle state. ERROR The command was issued in the wrong state, or was malformed. The connection enters the Error state. PUSH This command is valid only in the Idle state. It seeks to establish a superior/subordinate relationship in a transaction with the primary as the superior. Note that the entire value of (as defined in the section "TIP Uniform Resource Locators") must be specified as the transaction identifier. Possible responses are: PUSHED The relationship has been established, and the identifier by which the subordinate knows the transaction is returned. The transaction becomes the current transaction for the connection, and the connection enters Enlisted state. ALREADYPUSHED The relationship has been established, and the identifier by Lyon, J. [Page 14] INTERNET-DRAFT TIP Version 2.0 Sept 1997 which the subordinate knows the transaction is returned. However, the subordinate already knows about the transaction, and is expecting the two-phase commit protocol to arrive via a different connection. In this case, the connection remains in the Idle state. NOTPUSHED The relationship could not be established. The connection remains in the Idle state. ERROR The command was issued in the wrong state, or was malformed. The connection enters Error state. QUERY This command is valid only in the Idle state. A subordinate uses this command to determine whether a specific transaction still exists at the superior. Possible responses are: QUERIEDEXISTS The transaction still exists. The connection remains in the the Idle state. QUERIEDNOTFOUND The transaction no longer exists. The connection remains the Idle state. ERROR The command was issued in the wrong state, or was malformed. The connection enters Error state. RECONNECT This command is valid only in the Idle state. A superior uses the command to re-establish a connection for a transaction, when the previous connection was lost during Prepared state. Possible responses are: RECONNECTED The subordinate accepts the reconnection. The connection enters Prepared state. NOTRECONNECTED The subordinate no longer knows about the transaction. The connection remains in Idle state. ERROR The command was issued in the wrong state, or was malformed. The connection enters Error state. [Note: Commands which pertain to connections are: IDENTIFY, MULTIPLEX. Commands which pertain to transactions are: ABORT, BEGIN, COMMIT, PREPARE, PULL, PUSH, QUERY, RECONNECT.] Lyon, J. [Page 15] INTERNET-DRAFT TIP Version 2.0 Sept 1997 14. Error Handling If either party receives a line that it cannot understand it closes the connection. If either party (either a command or a response), receives an ERROR indication or an ERROR response on a connection the connection enters the Error state and no further communication is possible on that connection. An implementation may decide to close the connection. Closing of the connection is treated by the other party as a communication failure. Receipt of an ERROR indication or an ERROR response indicates that the other party believes that you have not properly implemented the protocol. 15. Connection Failure and Recovery A connection failure may be caused by a communication failure, or by any party closing the connection. Depending on the state of a connection, transaction managers will need to take various actions when a connection fails. If the connection fails in Initial or Idle state, the connection does not refer to a transaction. No action is necessary. If the connection fails in the Multiplexing state, all connections provided by the multiplexing protocol are assumed to have failed. Each of them will be treated independently. If the connection fails in Begun or Enlisted state, each party will abort the transaction. If the connection fails in Prepared state, then the appropriate action is different for the superior and subordinate in the transaction. If the superior determines that the transaction commits, then it must eventually establish a new connection to the subordinate, and send a RECONNECT command for the transaction. If it receives a NOTRECONNECTED response, it need do nothing else. However, if it receives a RECONNECTED response, it must send a COMMIT request and receive a COMMITTED response. If the superior determines that the transaction aborts, it is allowed to (but not required to) establish a new connection and send a RECONNECT command for the transaction. If it receives a RECONNECTED response, it should send an ABORT command. The above definition allows the superior to reestablish the connection before it knows the outcome of the transaction, if it finds that convenient. Having succeeded in a RECONNECT command, the connection is back in Prepared state, and the superior can send a COMMIT or ABORT command as appropriate when it knows the transaction outcome. Lyon, J. [Page 16] INTERNET-DRAFT TIP Version 2.0 Sept 1997 If a subordinate notices a connection failure in Prepared state, then it should periodically attempt to create a new connection to the superior and send a QUERY command for the transaction. It should continue doing this until one of the following two events occurs: 1. It receives a QUERIEDNOTFOUND response from the superior. In this case, the subordinate should abort the transaction. 2. The superior, on some connection that it initiated, sends a RECONNECT command for the transaction to the subordinate. In this case, the subordinate can expect to learn the outcome of the transaction on this new connection. If this new connection should fail before the subordinate learns the outcome of the transaction, it should again start sending QUERY commands. Note that if a TIP system receives either a QUERY or a RECONNECT command, and for some reason is unable to satisfy the request (e.g. the necessary recovery information is not currently available), then the connection should be dropped. 16. Security Considerations If a system implements this protocol, it is in essence allowing any other system to attempt to reach an atomic agreement about some piece of work. However, since this protocol itself does not cause the work to occur, the security implications are minimal. If a system does not protect itself through usage of another protocol such as the Transport Layer Security protocol, then security implications fall into the following categories: 1. Someone PUSHED a new transaction to us that we don't want. Depending on his correctness or intentions, he may or may not ever complete it. Thus, an arbitrary computer may cause us to save a little bit of state. An implementation concerned about this will probably drop the TCP connection if the other system does not complete transactions in a timely manner. The Transport Layer Security protocol [3] may be used by a transaction manager to restrict access to trusted clients only. 2. Someone PULLED a transaction from us when we didn't want him to. In this case, he will become involved in the atomic commitment protocol. At worst, he may cause a transaction to abort that otherwise would have committed. Since transaction managers traditionally reserve the right to abort any transaction for any reason they see fit, this does not represent a disaster to the applications. However, if done frequently, it may represent a denial-of-service attack. Implementations concerned about this kind of attack can use the Transport Layer Security protocol [3] to restrict access to trusted partners (i.e. to control from which remote endpoints TIP transactions will be accepted, and to verify that an end-point is genuine), and encrypt TIP commands thus preventing unauthorized Lyon, J. [Page 17] INTERNET-DRAFT TIP Version 2.0 Sept 1997 disclosure of transaction identifiers. 3. Someone violates the TIP commitment protocol. (e.g. a COMMIT command is injected on a TIP connection in place of an ABORT command). This yields the possibility of data inconsistency. Implementations concerned about this kind of attack can also use the Transport Layer Security protocol [3] to restrict access to only trusted partners and to encrypt TIP commands. It is assumed that implementation-specific configuration information will define whether a partner should be connected to using either a mandatory TLS secured connection, or an unsecured connection (in which case any security risk is accepted). "Optionally TLS secured" is in effect unsecured (since there is no guarantee of a TLS secured connection). 17. Significant changes from previous version of this Internet-Draft (): The Session Control Protocol I-D has been incorporated as an addendum to this I-D, and renamed the TIP Multiplexing Protocol. Use of the URN scheme for standard transaction identifiers has been added. Numerous editorial changes to aid understanding and fix errors have been made. Lyon, J. [Page 18] INTERNET-DRAFT TIP Version 2.0 Sept 1997 Appendix A. The TIP Multiplexing Protocol Version 2.0. This appendix describes version 2.0 of the TIP Multiplexing Protocol (TMP). TMP V2.0 is the same as the Session Control Protocol (SCP) version 2.0, as described by [6]. TMP is intended solely for use with the TIP protocol, and forms part of the TIP protocol specification (although it's implementation is optional), hence it's inclusion in this document. TMP V2.0 is the only multiplexing protocol supported by TIP V2.0. The following text is a copy of [6] with no substantive changes, it is edited only as necessary to reflect the name change and for inclusion in this document. The only protocol change is the removal of the PUSH flag (which is no longer required given the rule that a single TIP command must be wholly contained within a single TMP packet). Abstract TMP provides a simple mechanism for creating multiple lightweight connections over a single TCP connection. Several such lightweight connections can be active simultaneously. TMP provides a byte oriented service, but allows message boundaries to be marked. A.1. Introduction There are several protocols in widespread use on the Internet which create a single TCP connection for each transaction. Unfortunately, because these transactions are short lived, the cost of setting up and tearing down these TCP connections becomes significant, both in terms of resources used and in the delays associated with TCP's congestion control mechanisms. The TIP Multiplexing Protocol (TMP) is a simple protocol running on top of TCP that can be used to create multiple lightweight connections over a single transport connection. TMP therefore provides for more efficient use of TCP connections. Data from several different TMP connections can be interleaved, and both message boundaries and end of stream markers can be provided. Because TMP runs on top of a reliable byte ordered transport service it can avoid most of the extra work TCP must go through in order to ensure reliability. For example, TMP connections do not need to be confirmed, so there is no need to wait for handshaking to complete before data can be sent. A.2. Protocol Model The basic protocol model is that of multiple lightweight connections operating over a reliable stream of bytes. The party which initiated the connection is referred to as the primary, and the party which accepted the connection is referred to as the secondary. Connections may be unidirectional or bi-directional; each end of a bi-directional connection may be closed separately. Connections may Lyon, J. [Page 19] INTERNET-DRAFT TIP Version 2.0 Sept 1997 be closed normally, or reset to indicate an abortive release. Aborting a connection closes both data streams. Once a connection has been opened, applications can send messages over it, and signal the end of application level messages. Application messages are encapsulated in TMP packets and transferred over the byte stream. A single TIP command (TMP application message) must be wholly contained within a single TMP packet. A.3. TMP Packet Format A TMP packet consists of a 64 bit header followed by zero or more octets of data. The header contains three fields; a flag byte, the connection identifier, and the packet length. Both integers, the connection identifier and the packet length must be sent in network byte order. FLAGS +--------+--------+--------+--------+ |SFPR0000| Connection ID | +--------+--------+--------+--------+ | | Length | +--------+--------+--------+--------+ A.3.1. Flag Details +-------+-----------+-----------------------------------------+ | Name | Mask | Description | +-------+-----------+ ----------------------------------------+ | SYN | 1xxx|0000 | Open a new connection | | FIN | x1xx|0000 | Close an existing connection | | RESET | xxx1|0000 | Abort the connection | +-------+-----------+-----------------------------------------+ A.4. Connection Identifiers Each TMP connection is identified by a 24 bit integer. TMP connections created by the party which initiated the underlying TCP connection must have even identifiers; those created by the other party must have odd identifiers. A.5. TMP Connection States TMP connections can exist in several different states; Closed, OpenWrite, OpenSynRead, OpenSynReset, OpenReadWrite, CloseWrite, and CloseRead. A connection can change its state in response to receiving a packet with the SYN, FIN, or RESET bits set, or in response to an API call by the application. The available API calls are open, close, and abort. The meaning of most states is obvious (e.g. OpenWrite means that a connection has been opened for writing). The meaning of the states OpenSynRead and OpenResetRead need more explanation. Lyon, J. [Page 20] INTERNET-DRAFT TIP Version 2.0 Sept 1997 In the OpenSynRead state a primary opened and immediately closed the output data stream of a connection, and is now waiting for a SYN response from the secondary to open the input data stream for reading. In the OpenResetRead state a primary opened and immediately aborted a connection, and is now waiting for a SYN response from the secondary to finally close the connection. A.6. Event Priorities and State Transitions The state table shown below describes the actions and state transitions that occur in response to a given event. The events accepted by each state are listed in priority order with highest priority first. If multiple events are present in a message, those events matching the list are processed. If multiple events match, the event with the highest priority is accepted and processed first. Any remaining events are processed in the resultant successor state. For example, if a TMP connection at the secondary is in the Closed state, and the secondary receives a packet containing a SYN event, a FIN event and an input data event (i.e. DATA-IN), the secondary first accepts the SYN event (because it is the only match in Closed state). The secondary accepts the connection, sends a SYN event and enters the ReadWrite state. The SYN event is removed from the list of pending events. The remaining events are FIN and DATA-IN. In the ReadWrite state the secondary reads the input data (i.e. the DATA-IN event is processed first because it has higher priority than the FIN event). Once the data has been read and the DATA-IN event has been removed from the list of pending events, the FIN event is processed and the secondary enters the CloseWrite state. If either party receives a TMP packet that it does not understand, or an event in an incorrect state, it closes the TCP connection. Lyon, J. [Page 21] INTERNET-DRAFT TIP Version 2.0 Sept 1997 +==============+=========+==========+==============+ | Entry State | Event | Action | Exit State | +==============+=========+==========+==============+ | Closed | SYN | SYN | ReadWrite | | | OPEN | SYN | OpenWrite | +--------------+---------+----------+--------------+ | OpenWrite | SYN | Accept | ReadWrite | | | WRITE | DATA-OUT | OpenWrite | | | CLOSE | FIN | OpenSynRead | | | ABORT | RESET | OpenSynReset | +--------------+---------+----------+--------------+ | OpenSynRead | SYN | Accept | CloseRead | +--------------+---------+----------+--------------+ | OpenSynReset | SYN | Accept | Closed | +--------------+---------+----------+--------------+ | ReadWrite | DATA-IN | Accept | ReadWrite | | | FIN | Accept | CloseWrite | | | RESET | Accept | Closed | | | WRITE | DATA-OUT | ReadWrite | | | CLOSE | FIN | CloseRead | | | ABORT | RESET | Closed | +--------------+---------+----------+--------------+ | CloseWrite | RESET | Accept | Closed | | | WRITE | DATA-OUT | CloseWrite | | | CLOSE | FIN | Closed | | | ABORT | RESET | Closed | +--------------+---------+----------+--------------+ | CloseRead | DATA-IN | Accept | CloseRead | | | FIN | Accept | Closed | | | RESET | Accept | Closed | | | ABORT | RESET | Closed | +--------------+---------+----------+--------------+ TMP Event Priorities and State Transitions Lyon, J. [Page 22] INTERNET-DRAFT TIP Version 2.0 Sept 1997 References [1] Gray, J. and A. Reuter (1993), Transaction Processing: Concepts and Techniques. San Francisco, CA: Morgan Kaufmann Publishers. (ISBN 1-55860-190-2). [2] RFC2068 Standards Track "Hypertext Transfer Protocol -- HTTP/1.1". R. Fielding et al. [3] Internet-Draft "The TLS Protocol Version 1.0". T. Dierks et al. [4] RFC1738 Standards Track "Uniform Resource Locators (URL)". T. Berners-Lee et al. [5] Internet-Draft "Transaction Internet Protocol - Requirements and Supplemental Information". K. Evans et al. [6] Internet-Draft "Session Control Protocol V 2.0". K. Evans et al. [7] RFC2141, "URN Syntax". R. Moats. Authors' Addresses Jim Lyon Keith Evans Microsoft Corporation Tandem Computers, Inc. One Microsoft Way 5425 Stevens Creek Blvd Redmond, WA 98052-6399, USA Santa Clara, CA 95051-7200, USA Phone: +1 (206) 936 0867 Phone: +1 (408) 285 5314 Fax: +1 (206) 936 7329 Fax: +1 (408) 285 5245 Email: JimLyon@Microsoft.Com Email: Keith@Loc252.Tandem.Com Johannes Klein Tandem Computers Inc. 10555 Ridgeview Court Cupertino, CA 95014-0789, USA Phone: +1 (408) 285 0453 Fax: +1 (408) 285 9818 Email: Klein_Johannes@Tandem.Com Comments Please send comments on this document to the authors at , , , or to the TIP mailing list at . You can subscribe to the TIP mailing list by sending mail to with the line "subscribe tip" somewhere in the body of the message. Lyon, J. [Page 23]