Network Working Group J. Lyon Internet-Draft Microsoft Obsoletes <draft-lyon-itp-nodes-00.txt> K. Evans Expires in 6 month J. Klein Tandem Computers February 7th, 1997 Transaction Internet Protocol <draft-lyon-itp-nodes.01.txt> 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). Distribution of this document is unlimited. Please send comments to the authors at <JimLyon@Microsoft.Com>, <Evans_Keith@Tandem.Com>, <Klein_Johannes@Tandem.Com>, or to the TIP mailing list at <tip@Tandem.Com>. You can subscribe to the TIP mailing list by sending mail to <listserv@Tandem.Com> with the line "subscribe tip" somewhere in the body of the message. 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. 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, Lyon [Page 1]
Internet-Draft Transaction Internet Protocol February 7th, 1997 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 Secure Socket Layer 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. 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 (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. Lyon [Page 2]
Internet-Draft Transaction Internet Protocol February 7th, 1997 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 acknowledgement. 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. 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. 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. While the TIP protocol is described in the context of TCP/IP, other reliable ordered stream transports may be used to replace TCP/IP. 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. Lyon [Page 3]
Internet-Draft Transaction Internet Protocol February 7th, 1997 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 [3] for an example of one such protocol. Transaction Identifiers Unfortunately, there is no globally-accepted standard for the format of a transaction identifier; various transaction managers have their own proprietary formats. Therefore, for the purposes of this protocol, a transaction identifier is any sequence of printable ASCII characters (octets with values in the range 33 through 126, inclusive). A transaction manager may map its internal transaction identifiers into this printable sequence 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. 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. 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. Lyon [Page 4]
Internet-Draft Transaction Internet Protocol February 7th, 1997 The protocol described here supports both the "push" and "pull" models. 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 <endpoint identifier> as used in the IDENTIFY (and a few other) commands has one of the following formats: <dns name> <ip address> <dns name>:<port number> <ip address>:<port number> A <dns name> 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 <ip address> is an IPv4 or IPv6 address, in the usual form: four | (or six??) decimal numbers separated by period characters. The <port number> is a decimal number specifying the port at which the transaction manager is listening for requests to establish TCP connections. If the port number is omitted from the endpoint identifier, the standard transaction service port number is assumed. 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 Lyon [Page 5]
Internet-Draft Transaction Internet Protocol February 7th, 1997 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. An TIP URL takes the form: TIP://<host>[:<port>]/<transaction identifier> where <host> is an IP address or a DNS name as defined above, <port> is a valid TCP port number, and <transaction identifier> is a sequence of printable characters representing a transaction identifier as defined above. The TIP 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 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. 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. Lyon [Page 6]
Internet-Draft Transaction Internet Protocol February 7th, 1997 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. 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. 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. Lyon [Page 7]
Internet-Draft Transaction Internet Protocol February 7th, 1997 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 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. 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 each word is 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. Command Pipelining The primary party of a connection is allowed to issue multiple Lyon [Page 9]
Internet-Draft Transaction Internet Protocol February 7th, 1997 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 an IDENTIFY command immediately followed by a BEGIN, PUSH, or 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. Commands Following is a list of all valid commands, and all possible responses to each: 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 <transaction identifier> 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 Lyon [Page 10]
Internet-Draft Transaction Internet Protocol February 7th, 1997 to commit the transaction; in the Prepared state, it informs the secondary that the transaction has committed. 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 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 <lowest protocol version> <highest protocol version> <initiating party's endpoint identifier> | "-" This command is valid only in the Initial state. The primary party informs the secondary party of the lowest and highest protocol version 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 <protocol version> 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. Lyon [Page 11]
Internet-Draft Transaction Internet Protocol February 7th, 1997 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 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. MULTIPLEX <protocol> 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 "SCP1.1", which refers to the Session Control Protocol, version 1.1, without header compression. See [5] for details on this protocol. Other protocol identifiers may be defined in the future. 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. Lyon [Page 12]
Internet-Draft Transaction Internet Protocol February 7th, 1997 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. PULL <superior's transaction identifier> <subordinate's transaction identifier> 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). 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 <superior's transaction identifier> 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. Possible responses are: PUSHED <subordinate's transaction identifier> The relationship has been established, and identifier by which Lyon [Page 13]
Internet-Draft Transaction Internet Protocol February 7th, 1997 the subordinate knows the transaction is returned. The transaction becomes current for the connection, and the connection enters Enlisted state. ALREADYPUSHED <subordinate's transaction identifier> The relationship has been established, and the identifier by 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 <superior's transaction identifier> 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 <subordinate's transaction identifier> 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 Lyon [Page 14]
Internet-Draft Transaction Internet Protocol February 7th, 1997 The command was issued in the wrong state, or was malformed. The connection enters Error state. 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. Connection Failure A connection fails when being closed. This 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 Lyon [Page 15]
Internet-Draft Transaction Internet Protocol February 7th, 1997 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. 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. 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] RFC1945 Informational "Hypertext Transfer Protocol -- HTTP/1.0" T. Berners-Lee, R. Fielding, and H. Frystyk, May 1997. [3] Internet Draft "The SSL Protocol Version 3.0" A. Freier, P. Karlton, P. Kocher. [4] RFC1738 Standards Track "Uniform Resource Locaters (URL)" T. Berners-Lee, L. Masinter, M. McCahill [5] "SCP - Session Control Protocol V 1.1" http://sunsite.unc.edu/ses/scp.html S. Spiro 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 Secure Socket Layer protocol security implications fall into the following two 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 Lyon [Page 16]
Internet-Draft Transaction Internet Protocol February 7th, 1997 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 Secure Socket Layer 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 Secure Socket Layer protocol [3] to restrict access to trusted clients and encrypt messages thus preventing unauthorized disclosure of transaction identifiers. Changes from version 0 of this Internet-Draft: The IDENTIFY command is now mandatory, and its format has slightly changed. The PUSHTO and PULLFROM commands have been deleted. The MULTIPLEX command has been added. The TIP URL scheme has been added. Pipelining of commands is now permitted. The version of the protocol is now 2. 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: Evans_Keith@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 Lyon [Page 17]
