Internet Engineering Task Force P. Cordell Internet Draft Tech-Know-Ware Ltd draft-cordell-lumas-00.txt April 2, 2003 Expires: October 2003 Lumas - A Language for Universal Message Abstraction and Specification STATUS OF THIS MEMO This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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. The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Abstract A number of methods and tools are available for defining the format of messages used for signalling protocols. However, many of these methods and tools have been designed for purposes other than message definition, and have been adopted on the basis that they are readily available rather than being ideally suited to the task. This often means that the methods make it difficult to get definitions correct, or result in unnecessary verbosity both in the definition and on the wire. Cordell [Page 1] Internet Draft Lumas April 2003 Lumas - Language for Universal Message Abstraction and Specification - has been custom designed for the purpose of message definition. It is thus easy to specify messages in a compact, extensible format that is readily machine manipulated to produce a compact encoding on the wire. 1. Introduction This document defines the Lumas message definition language, and the default text encoding method for messages defined in this way. 2. Requirements for Message Definition and Encoding A good message definition method will have the following properties. It is these properties that Lumas has been designed to have. Precise Definitions It is important to accurately capture type information in a message definition. Some message definition methods simply capture the name of a parameter without specifying the type of the parameter (e.g. integer, boolean etc). Additionally types like integers need to be constrained to appropriate values. Lumas provides this precision of definition. Compact Definitions The message definition should be as compact as possible, but no more compact. While helpful to the inexperienced developer, excessive keywords and other formatting can actually be detrimental to the understanding of the experienced developer as it is harder to extract the important material from the less important framework. Also, excessive verbosity requires increased scrolling to read a definition which is detrimental to the comprehension process. Lumas adopts a compact C like definition that contains minimal clutter and thus allows the true message structure to be readily seen at a glance. Readily Extensible The message definition and the resultant on the wire encoding need to support extensibility. As part of this, code should be able to pass over parameters that it does not understand without becoming confused. The Lumas message definition and encoding allows this. Extensible by Third Parties Cordell [Page 2] Internet Draft Lumas April 2003 It often occurs that a protocol is defined by one body and then adopted and modified by another body. In other cases a base protocol may be defined that is then augmented by external profiles. An effective method of allowing a third-party to accurately specify a message definition as deltas to an existing message definition is important in this respect. Lumas allows third-parties to specify protocol additions that should not clash with additions made by other third parties. Machine Parsable It is desirable that the message definition be machine readable so that as much of the slog involved in turning a message definition into running code is as automated as possible. This improves time to market and significantly reduces the potential for adding bugs into the code. A Lumas definition is in many respects a generalised form of C data structure definition. Therefore it is relatively simple to convert a machine independent Lumas definition into a machine dependent C definition and provide all the code to convert from one data representation to another. This process can remove a vast amount of slog. Additionally, the various compilers involved in the process can do a large amount of validating to ensure that the implementation is correct. Simplicity While accurate message definition is important, it is perhaps even more important that the message definition method be intelligible to people that do not have a great deal of time to become gurus in yet another language. Therefore the definition method should be quick and easy to learn. This means that the message definition language must have minimal complexity. As complexity of definition and expressiveness are often interrelated, in some cases it is necessary to restrict expressiveness in the interests of simplicity. Additionally, consideration should also be given to the complexity of the required parser, which may favour simplicity of format over absolute message compactness. Lumas is based on the 80-20 principle. It is a small language that can accommodate the majority of situations extremely well. There will be times where a Lumas representation is sub-optimal in terms of on-the-wire compactness. However, it is felt that on the whole, the gains in simplicity that this enables outweigh these sub-optimalities. Compact On-the-Wire Encoding As a general principle, it is desirable that encoded messages be as compact as possible. This minimises transmission bandwidth, Cordell [Page 3] Internet Draft Lumas April 2003 can make processing the messages more efficient, and prevents premature fragmentation of datagrams. Compact messages are also important in the area of mobile devices that have limited memory and possibly transmission bandwidth. This is particularly the case if the information is stored as persistent configuration data rather than being immediately discarded. Also, in many cases, compact messages are easier for developers experienced in the protocol to read than some more verbose types, and it is these developers that should be the primary target for any measure aimed at easing debugging. Given that there are limits to how compactly the actual data in a message can be represented, the compactness of a message is determined largely by the tagging. Existing protocols often use no tagging of data to minimise message size. They also allow for comma separated lists of parameters that have the same meaning rather than requiring each parameter to be separately tagged. Additionally descriptive parameter names are essential to a clear message definition, but tags used in messages are often shorter than is descriptively useful (e.g.

instead of , instead of ). Therefore, it is desirable to be able to define a descriptive name that can be used in code and a tag name that can be used on the wire. Lumas accommodates all of these requirements. Flexible Implementation While turnkey solutions are desirable, they are potentially complex to develop, and thus may incur some cost to use, thus making them inaccessible to some. Therefore a range of implementation routes are desirable, from minimal tools / maximum leg work, to maximal tools/minimum leg work. Lumas has a number of implementation routes in addition to the compilation route. A Lumas definition can be converted into an ABNF definition and implemented via that route, or a DOM like tree based parsing method can be used. Support Easy Application Debugging Ideally the messages on the wire should be in a form that is aid the debugging process. By default Lumas uses a text based line format, and is thus readily readable by human developers. Additionally it is also easy to manually generate test messages. With the aid of cb-like tools, it is possible to format messages so that they are more readable than the most compact line representation. Additional tools make it possible to automatically generate test messages and use them as test vectors to test a parser, or validate that manually generated test messages actually conform to the message definition. Cordell [Page 4] Internet Draft Lumas April 2003 Nesting of Protocols In some systems messages from one protocol are carried within messages from another protocol (TCP in IP is a simple example, as is HTML in HTTP). The definition and line encoding should allow this. Lumas allows this. Flexible On-the-Wire Encoding It is not always possible to anticipate the direction of development so flexibility in the actual wire representation of the messages is desirable. The principal Lumas on-the-wire representation in text based. However, a Lumas message definition can also be represented using alternate text formats such as XML, and can also be represented in binary. 2.1 That's Lumas Lumas has been specifically designed to meet all of the above requirements. 3. Lumas Messages Definition This section describes how Lumas specifies the content of messages. As the syntax is C-like it is felt that many will immediately understand the message definition. For this reason a short example of a message definition is presented before describing the format in detail. The example is also used to give a rough indication of what the formal definition describes, and will thus hopefully help with the understanding of the latter. 3.1 Basic Principles of the Message Definition Before presenting an example, and a more formal definition, it may be helpful to describe the basic principles of the message definition format. Following the C language format, the basic format of a parameter definition is: type name ; Type specifies things like integers, booleans, ASCII strings, Unicode strings and so on. The name is the name of the parameter. Thus a parameter definition might be: Cordell [Page 5] Internet Draft Lumas April 2003 ascii rfc-name ; This says that rfc-name is an ASCII string. In addition, a parameter definition can express constraints on the type, constraints on the cardinality (how many instances of the type are valid in a message), and the tag to be used for the value on the wire. For example, an integer may be limited to the values 0 to 255, and an ASCII string may be limited to a maximum size. The fuller format of a parameter has the form: type name [cardinality] tagging ; For example: int <1..30000> referenced-rfcs [0..255] as refers ; This defines an integer that can have values between 1 and 30000. The name of the parameter is refereced-rfcs, but is tagged on-the-wire by 'refers'. The parameter can consist of between 0 and 255 instances of the integer in a valid encoding. Two main types of compound parameter are also possible, these being 'struct' and 'union'. Having much the same meaning as they have in C, a struct specifies a group of parameters, all of which may be used in a particular instance of the struct. A union similarly specifies a group of parameters, but in this case only one of the parameters can be used in any one instance of the union. An example of a struct is: struct rfc-links { ascii rfc-name; int <1..30000> referenced-rfcs[0..255] as refers ; }; A third form of compound type called 'constructed' is also available. This allows a number of values to be concatenated together into what looks like a single value. Hence it can be used to define constructs like the character sequence 'HTTP/1.0', and that the '1' and the '0' are the major and minor version numbers. This is discussed further below. 3.2 An Example Message Definition The following is an example message definition: Cordell [Page 6] Internet Draft Lumas April 2003 module com.tech-know-ware.my-example; struct my-example { int <0..255> participant-id as ?; Action action as ?; struct my-addition[0..1] as new.tech-know-ware.com plugin { bool tkw-app-capable as ?; }; }; union action { Join join; Message message as msg; void leave; }; struct Join { ascii<0..63> name; }; struct Message { int <0..255> to-delegates[1..127] as to; ascii<0..255> message as msg; [ // Version 2 additions int <0..5> priority; bool acknowledge as ack; ] [ // Version 5 additions ascii<0..16> font-name[0..1] as font; void bold[0..1]; void italic[0..1]; void underlined[0..1] as ul; ] }; The above definition is intended to represent a very crude meeting controller. The first construct (my-example) is the root of all messages for the protocol. Each message identifies a participant using an integer in the range 0 to 255, called participant-id. When encoded on the wire, this parameter will be untagged due to the 'as ?' specification. Each message then has an action, which is also untagged. The type of the action parameter is not immediately specified, and instead references the 'Action' definition. The Action definition is a union in which only one of the specified Cordell [Page 7] Internet Draft Lumas April 2003 parameters may appear in an instance of the Action construct. This effectively represents a fork in the semantics of any given message. The options within Action can indicate that somebody has joined the meeting, left the meeting, or is sending a message to other delegates. There is no explicit tag for the 'join' and 'leave' options, so these will be tagged on-the-wire by the parameters' names, 'join' and 'leave' respectively. Conversely, an explicit tag for the 'message' parameter is specified, and hence the message option will be tagged by 'msg' on-the-wire. The join parameter also has a referenced definition. For the purposes of this example, when a person joins a meeting, all the other delegates are informed of their name. The name is an ASCII string that has a minimum length of 0 characters and a maximum length of 63 characters. The message option is also a referenced definition. Conceptually, to send a messages, the participant-id is used to identify the sender, and the to-delegates field contains the participant ids of all the people to whom the message is being sent. On-the-wire, the to-delegates parameter will be tagged with 'to'. Between 1 and 127 (inclusive) instances of the to-delegates parameter may appear in a message. Also, the message itself is included. The message will consist of ASCII characters and can be between 0 and 255 characters long. On-the-wire, the message field will have the tag 'msg'. The priority and acknowledge fields within the message struct have been added in a later version of the protocol. This is indicated by the square brackets in which the parameters are wrapped. Similarly, font-name, and associated parameters have been added in version 5 of the protocol (according to the comment). The reader should already understand enough of the definition language to understand the meaning of these fields. Returning to the 'my-example' root, a third-party has added an extension to the protocol in the form of the 'my-addition' parameter. It is identified as not being part of the base specification by the keyword 'plugin'. On-the-wire, the additional parameter will be identified by the tag 'new.tech-know-ware.com' to differentiate it from additions that may be made by other third parties. On-the-wire encoded examples of this message definition are shown in section 4.2. 3.3 Formal Message Definition Syntax There are two types of parameter in Lumas, simple types and compound types. The ABNF definition of these is: Cordell [Page 8] Internet Draft Lumas April 2003 Lumas-parameter = simple-param / compound-param Simple types represent parameters such as integers, booleans etc. The ABNF definition of a simple param is: simple-param = simple-type WS name [ OWS cardinality ] [ WS "as" WS explicit-tag ] [ WS "plugin" ] ";" where WS represents white space, and OWS represents optional white space. The 'simple-type' represents the type of the parameter. It can have the following forms: simple-type = "void" / "bool" / "ipv4" / "ipv6" / "date" / "time" / "oid" / integer-type / string-type / bytes-type / embedded-type / const-type / reference where: integer-type = "int" OWS "<" int-constraint ">" string-type = ( "ascii" / "unquoted-ascii" / "unicode" ) [ OWS "<" string-constraint ">" ] const-type = "const" OWS "<" first-safe-char *( safe-char ) ">" ; See the section 'Notes on Comments' below bytes-type = "bytes" [ OWS "<" length-constraint ">" ] embedded-type = "embedded" [ OWS "<" length-constraint ">" ] reference = [ module-name "::" ] name ; Refers to a type defined ; elsewhere int-constraint = [ min-int-constraint ".." ] max-int-constraint [ OWS use-leading-zero-marker ] min-int-constraint = ["-"] pos-number max-int-constraint = ["-"] pos-number use-leading-zero-marker = "z" string-constraint = length-constraint [ OWS pattern-constraint ] Cordell [Page 9] Internet Draft Lumas April 2003 length-constraint = [ min-len-constraint ".." ] max-len-constraint min-len-constraint = pos-number max-len-constraint = ( pos-number / "*" ) pos-number = 1*DIGIT / ; Decimal number "0x" 1*HEX / ; Hex number 1*2DIGIT "b" ; Specifies number of binary bits In the case of the integer-type, the mandatory constraint specifies the minimum and maximum permissible values that the integer can take. If the 'z' character is included in the constraint, then the integer SHOULD be represented with leading zeros on the wire. (This is primarily applicable to constructed types.) The pos-number construct used to specify the integer value constraint has a form that can specify the number of binary bits. The number of bits specified does not include any sign bits. Hence an unsigned 32 bit number can be represented as 0..32b, whereas a signed 32 bit number can be represented as -31b..31b (although this will actually exclude the most negative value of a signed 32 bit number). In the case of string-type, the optional constraint specifies the minimum and maximum number of characters that are allowed to appear in a valid encoding and optionally a valid pattern of characters. The format of the pattern constraint is designed to simplify regular expression evaluation by preventing the need for the trial and error type processing of general regular expressions. Thus, in accordance with Lumas' 80/20 principle, valid patterns MUST not require the regular expression code to do backtracking. The pattern-constraint has the following form: Cordell [Page 10] Internet Draft Lumas April 2003 pattern-constraint = *( constraint-char quantifier ) [ '.' quantifier ] ; '.' matches any character constraint-char = char | character-class char = single-char | special-char single-char = %x20-%xff | escaped-char escaped-char = '\\' ; Matches \ | '\[' ; Matches [ | '\?' ; Matches ? | '\*' ; Matches * | '\+' ; Matches + | '\{' ; Matches { | '\.' ; Matches . special-char = '\r' ; Matches the return character | '\n' ; Matches the new line character | '\t' ; Matches the tab character | '\f' ; Matches the form feed character | '\s' ; Matches white space [ \t\r\n\f] | '\d' ; Matches any digit [0-9] | '\w' ; Matches any word character [a-zA-Z_0-9] | '\S' ; Matches anything not matched by \s | '\D' ; Matches anything not matched by \d | '\W' ; Matches anything not matched by \w character-class = matching-character-class | inverse-character-class matching-character-class = '[' *(class-char | class-range) ']' inverse-character-class = '[^' *(class-char | class-range) ']' class-char = class-single-char | special-char class-single-char = %x20-%xff | class-escaped-char class-escaped-char = '\-' ; Matches - | '\]' ; Matches ] class-range = class-single-char '-' class-single-char quantifier = '' | '?' | '*' | '+' | '{' 1*DIGIT [ ',' [ 1*DIGIT ] ] '}' Only a 'greedy' match is allowed. Note there are no grouping or alternation constructs. This is to remove the need for backtracking and is suitable for 80% (or more) of applications. (More complex patterns can be defined in comments and left to the application to validate.) Example patterns include /\d{4} \d{4} \d{4} \d{4}/ for a credit card number, or /\d{4}-\d{2}-\d{2}T\d+:\d+:\d+Z/ for a date & time matching the form 2003-03-03T12:45:32Z. For more information on regular expressions, see [PERL]. In the case of bytes-type, the optional constraint specifies the minimum and maximum number of bytes that are allowed to appear in a Cordell [Page 11] Internet Draft Lumas April 2003 valid encoding. In the constraint syntax, a maximum value '*' means infinite or unbounded. The various types have the following meaning: void A parameter that has no value. This is most useful in unions, and can also be used to represent boolean events wherein the absence of the parameter indicates false, and the presence of the parameter indicates true. It is more useful than you might at first think! bool Can be true or false int An integer value ipv4 Represents an IPv4 address, but not the port. ipv6 Represents an IPv6 address, but not the port. date Date according to the Gregorian calendar, with year, month and date. Other calendar types may be constructed from primitive types if required. time Represents the time in hours, minutes and seconds. By default the time is adjusted to UTC, unless the time can be guaranteed to have only local significance. oid This is an ASN.1 style Object Identifier. This is primarily included to enable identification of security protocols. ascii A string made up of ASCII characters, limited at most to values 0 to 127. Cordell [Page 12] Internet Draft Lumas April 2003 unquoted-ascii An ascii string usually has quote marks around it. This type does not have quotes around it. Consequently it can not have any white space, or include any special characters (such as "=", "{", and "}") that would confuse the parser. unicode A string made up of Unicode characters. const This type allows a constant value to be inserted into the encoded message. It will typically be untagged. One thing it might be used for is identifying the protocol of the message definition. For example: const protocol as ?; bytes An array of bytes. Also useful for carriage of opaque data. embedded The value is an embedded Lumas message. This allows layering of message definitions. Referring back to the simple-param definition, the name is the name of the parameter. If there is no explicitly defined tag, then this is also used as the parameter's tag on-the-wire. It has the format: name = ALPHA *( ALPHA / DIGIT / "-" / "_" ) The cardinality of a parameter specifies how many times a particular parameter can appear in a message. The format mirrors a C-like array specification, but uses UML style ranges rather than singular values as are required in C. If the cardinality field is absent, then one and only one instance of the parameter must occur in a valid message. The format of the cardinality specification is: cardinality = "[" [ min-occurrences ".." ] max-occurrences "]" / "?" ; Short hand for [0..1] "*" ; Short hand for [0..*] "+" ; Short hand for [1..*] min-occurrences = 1*DIGIT Cordell [Page 13] Internet Draft Lumas April 2003 max-occurrences = 1*DIGIT / "*" Once again, the '*' in max-occurrences represents infinite or unbound. Example cardinalities are as follows: [0..1] ; Zero or one time [0..*] ; Zero or more times [*] ; Same as above, zero or more times [1..*] ; One or more times [5] ; Exactly five times An explicit tag can be any sequence of characters that do not have special significance to the parser. If the tag definition begins with a "?", the "?" is discarded. Thus to specify that ? be used as the tag on-the-wire, specify explicit-tag to be ??. explicit-tag = tag ; tag defined in common definitions Marking an item as plugin indicates to the developer and the tools that this parameter is (probably) not part of the original message definition. For example, it might be a proprietary extension. It also indicates that the parameter may not be present in all received messages, and impacts on the way the binary encoding operates. The compound types are struct, union and constructed. For a struct, subject to the various parameters cardinality specifications, any all or none of the parameters that a struct groups together may appear in a valid encoding of the construct. In the case of a union, only one of the parameters may be encoded in a valid instance of the construct. The constructed form is effectively a compact encoding of a struct, but is subject to a number of constraints. The format of the compound types is similar to the simple types. They have the form: Cordell [Page 14] Internet Draft Lumas April 2003 compound-param = struct-param / union-param / constructed-param struct-param = "struct" WS name [ OWS cardinality ] [ WS "as" WS explicit-tag ] [ WS "pluggable" ] [ WS "plugin" ] OWS "{" struct-body "}" OWS ";" union-param = "union" name [ OWS cardinality ] [ WS "as" WS explicit-tag ] [ WS "pluggable" ] [ WS "plugin" ] OWS "{" union-body "}" OWS ";" contructed-param = "constructed" name [ OWS cardinality ] [ WS "as" WS explicit-tag ] [ WS "plugin" ] OWS "{" constructed-body "}" OWS ";" In a struct and union the pluggable keyword indicates that the construct is a location that the message designers have formally declared as extendible using the 'plug' mechanism that is described further below. Lumas compilers are encouraged to emit warnings when extra material has is plugged into locations that are not marked as pluggable, but should not consider it an error. Constructed types are not pluggable. The format of the struct body is: struct-body = *( untagged-lumas-parameter ) *( lumas-parameter ) *( struct-extension ) The struct body starts with all the untagged parameters. Untagged parameters may have a cardinality other than one. Note that, if the cardinality of an untagged parameter allows it to be absent, then when encoded on the wire, if the untagged parameter is absent, then all subsequent parameters, including tagged parameters must also be absent. Thus great care is recommended when defining a message syntax that allows for an untagged parameter to be absent. Following the untagged parameters, the tagged parameters are included. When the message definition is subsequently extended, another instance of the extension parameters construct is added for each version in which the construct is extended. (Note that all new parameters must always be added onto the end of an existing construct, and the order of parameters must never be rearranged from one version to the next.) All of these have a similar format to the types already defined, except that in some cases they may be untagged, or only allow a unary cardinality. To make the ABNF definition accurate it is therefore Cordell [Page 15] Internet Draft Lumas April 2003 necessary to repeat the above basic definitions with the appropriate tagging and cardinality specifications. As mentioned, the struct body may start with untagged-Lumas-parameters. These are untagged, and must have a cardinality of 1. There definition is: untagged-Lumas-parameter = untagged-simple-param / untagged-compound-param untagged-simple-type = simple-type WS name [ OWS cardinality ] WS "as" WS "?" OWS ";" untagged-compound-param = untagged-struct-param / untagged-union-param / untagged-constructed-param untagged-struct-param = "struct" WS name [ OWS cardinality ] WS "as" WS "?" [ WS "pluggable" ] OWS "{" struct-body "}" OWS ";" untagged-union-param = "union" WS name [ OWS cardinality ] WS "as" WS "?" [ WS "pluggable" ] OWS "{" union-body "}" OWS ";" untagged-constructed-param = "constructed" WS name [ OWS cardinality ] WS "as" WS "?" OWS "{" constructed-body "}" OWS ";" Note that the plugin keyword is not applicable to untagged items. The second part of a struct definition are the items that are tagged. These can have any desired cardinality. These have the basic parameter definition that was initially presented, i.e. Lumas-parameter. The third and final part of a struct body is the extension fields. These are parameters that are added in subsequent versions of the protocol specification. They are marked out separately because a parser must always consider absence of these parameters to be a valid encoding so that it can receive messages from entities that are working with an earlier version of the protocol. To do this would dictate that all extension parameters would have to have a cardinality specification that included zero. This is tedious, potentially error prone, and loses some expressiveness. Instead, extension parameters are wrapped inside square brackets to indicate that they are extensions. It is then clear to any tools and developers that these parameters may be absent if a message is Cordell [Page 16] Internet Draft Lumas April 2003 received from a host running an earlier version of the message definition. The format of the struct extension is: struct-extension = "[" 1*( Lumas-parameter ) "]" The definition of a union-body is as follows: union-body = [ integer-type WS name WS "as" WS "?" OWS ";" ] *( singular-Lumas-parameter ) *( union-extension ) A union-body may have a single untagged integer parameter. All other parameters must be tagged and have a cardinality of one and only one. A union is extended in much the same way as a struct. The untagged integer parameter allows integers to be defined that have wild-carding options. For example, a union might be defined as: union select { int<0..65535> numbered as ?; void any as *; }; Examples of the encoded form might be: select = 12 select = * The parameters within a union are only allowed unary cardinality to avoid ambiguity in the line encoding. If multiple instances of a parameter must be included as an option in a union, it is necessary to wrap the parameters within a struct, using something similar to: struct X { X x[1..*] as ?; }; As mentioned, most of the parameters within a union are tagged and have a cardinality of one. Their defininition is: Cordell [Page 17] Internet Draft Lumas April 2003 singular-Lumas-parameter = singular-simple-param / singular-compound-param singular-simple-param = simple-type WS name [ WS "as" WS explicit-tag ] [ WS "plugin" ] OWS ";" singular-compound-param = singular-struct-param / singular-union-param / singular-constructed-param singular-struct-param = "struct" WS name [ WS "as" WS explicit-tag ] [ WS "pluggable" ] [ WS "plugin" ] OWS "{" struct-body "}" OWS ";" singular-union-param = "union" WS name [ WS "as" WS explicit-tag ] [ WS "pluggable" ] [ WS "plugin" ] OWS "{" union-body "}" OWS ";" singular-constructed-param = "constructed" WS name [ WS "as" WS explicit-tag ] [ WS "plugin" ] OWS "{" constructed-body "}" OWS ";" The union extension operates in a similar fashion to that of the struct, but references singular-Lumas-parameters. Its definition is: union-extension = "[" 1*( singular-Lumas-parameter ) "]" The constructed compound type provides a simple mechanism for defining new constructed types similar to that used for date and time. All the members of a constructed type are encoded on the wire using their untagged form and concatenated together with no intervening white space. The result of the encoding MUST meet all the constraints of an unquoted-ascii value. Additionally, each unquoted-ascii parameter MUST have a fixed number of characters, and the first character of the unquoted-ascii and const parameter MUST NOT be a digit. The form of the constructed body is: constructed-body = *( constructed-simple-type WS name ";" ) constructed-simple-type = integer-type / const-type / "unquoted-ascii" OWS "<" 1*DIGIT ">" In many respects the constructed type simply makes the encoded form look prettier, and anything that can be encoded with the constructed Cordell [Page 18] Internet Draft Lumas April 2003 type can also be represented with the struct type. The constructed type should also not be used for defining patterns of ascii or Unicode characters. Note also that a constructed type is not pluggable and hence can not be extended. It is therefore recommended that the constructed type be used sparingly. An example of a constructed type is: constructed protocol as ? { const const1; int<0..99> major-version; const <.> const2; int<0..99> minor-version; }; Which might be encoded as: HTTP/1.1 Constructed types also allow you to define numbers that contain decimal points. An example of such is: union currency as ? { void dollars as $; void pounds as ú; void francs as FFr; } constructed amount as ? { int<-31b..31b> main-denomination; const <.> const2; int<0..99z> sub-denomination; }; Which might be encoded as: $ 100.05 It was mentioned previously that unions and structs could reference types that are defined elsewhere. The format of a referenced type can now be defined. Referenced types have a cardinality of one, and are untagged. This is because the cardinality and tagging of the type are defined in the item that does the referencing, rather than where the referenced type is defined. (If a referenced type needs a cardinality other than one, it is recommended that the technique for giving a parameter within a union a non-unary cardinality be used.) The definition of the referenced types are: Cordell [Page 19] Internet Draft Lumas April 2003 referenced-Lumas-parameter = referenced-simple-param / referenced-compound-param referenced-simple-param = simple-type WS name ";" referenced-compound-param = referenced-struct-param / referenced-union-param / referenced-constructed-param referenced-struct-param = "struct" WS name [ WS "pluggable" ] OWS "{" struct-body "}" OWS ";" referenced-union-param = "union" WS name [ WS "pluggable" ] OWS "{" union-body "}" OWS ";" referenced-constructed-param = "constructed" WS name OWS "{" constructed-body "}" OWS ";" A protocol may be extended by a third party without modifying the original definition. This may be due to a proprietary extension, or an externally defined profile of the base protocol. The specification for this type of extension is: third-party-extension = "plug" WS tp-struct-extension / tp-union-extension "into" WS name *( "::" name ) *( COMMA name *( "::" name ) ) OWS ";" tp-struct-extension = Lumas-parameter tp-union-extension = singular-Lumas-parameter This specifies a parameter that is to be plugged into an existing construct. For example, if the following were defined: plug ascii cookie as cookie.tkwlumas.com into my-example.my-addition; The resulant definition would be treated as if it were: Cordell [Page 20] Internet Draft Lumas April 2003 struct my-example { int <0..255> participant-id as ?; Action action as ?; struct my-addition[0..1] as tech-know-ware.com plugin; { bool tkw-app-capable as ?; ascii cookie as cookie.tkwlumas.com plugin; }; }; The name field indicates that name of the construct that the item is to be plugged into. A single protocol may be defined in a number of message definition files. This might be for the purpose of accessing predefined libraries, or specifying a definition that the current definition extends. A message definition therefore begins with a set of optional directives expressing this information. They have the form: Lumas-directive = OWS [ "module" WS module-name OWS ";" OWS ] [ "extends" WS module-name [ WS "as" WS name ] OWS ";" OWS ] *( "import" WS module-name [ WS "as" WS name ] OWS ";" OWS ) module-name = name *( "." name ) The 'module' directive specifies the name of the module. The 'extends' directive is used in a definition that contains a third party extension. The module-name in the extends specification indicates the message definition that is being extended. The 'import' statement indicates a library message definition that contains referenced types that are referenced within the message definition. The module-name follows the hierarchical format used in Java. It is based on a domain name that is created from the name of the protocol, combined with the domain name of the entity that defined it. For example, if a protocol called the Simple Conference Protocol (SCP) were defined by Tech-Know-Ware Ltd with a domain name of tech-know-ware.com, the module name might be: com.tech-know-ware.scp Lumas defines a number of pseudo top level domains for its own purposes. These are currently as follows: +ietf A pseudo top level domain for the Internet Engineering Task Cordell [Page 21] Internet Draft Lumas April 2003 Force. +iso A pseudo top level domain for the International Standards Organisation. The sub-domains of this domain follow the structure of ISO defined Object Identifiers. (All spaces must be removed and numbers in brackets should be ignored when parsing this domain. E.g. iso(1) member-body(2) us(840) rsadsi(113549) digestAlgorithm(2) 5 is represented as +iso(1).member-body(2).us(840).rsadsi(113549).digestAlgorithm(2).5 and looked up as +iso.member-body.us.rsadsi.digestAlgorithm.5) +itu A pseudo top level domain for the International Telecommunications Union. The sub-domains of this domain follow the structure of ITU defined Object Identifiers. Processing of such identifiers follows that defined for processing ISO Object Identifiers. +lumasA pseudo top level domain for defining Lumas extensions and libraries. +uuid A pseudo top level domain that uses Universally Unique Identifiers for identification. An example is: +uuid.4d36e96c-e325-11ce-bfc1-08002be10318 National standards bodies such as ANSI and BSI are defined under their national top-level domain. The 'name' part of the import statement is used as an alias of the 'module-name', so that items within 'module-name' can be referenced in the abbreviated form of: name::item For example, if a parameter definition called 'id' is contained in the module 'com.tech-know-ware.scp', and the following import statement is specified: import com.tech-know-ware.scp as scp; Then 'id' can be referenced using: scp::id Finally, we are in a position to describe a complete Lumas message definition. This is: Lumas-definition = Lumas-directives 1* ( referenced-Lumas-parameter / third-party-extension ) Cordell [Page 22] Internet Draft Lumas April 2003 The first parameter defined within the message definition is the root of the message definition tree, and is thus the outer-most construct of an encoded message. 3.4 Complete ABNF This section presents the complete ABNF of a message definition without narrative. Some definitions are common with the on-the-wire ABNF and a presented in a separate section. Lumas-definition = Lumas-directives 1* ( referenced-Lumas-parameter / third-party-extension ) Lumas-directive = OWS [ "module" WS module-name OWS ";" OWS ] [ "extends" WS module-name [ WS "as" WS name ] OWS ";" OWS ] *( "import" WS module-name [ WS "as" WS name ] OWS ";" OWS ) module-name = name *( "." name ) referenced-Lumas-parameter = referenced-simple-param / referenced-compound-param referenced-simple-param = simple-type WS name ";" simple-type = "void" / "bool" / "ipv4" / "ipv6" / "date" / "time" / "oid" / integer-type / string-type / bytes-type / embedded-type / const-type / reference integer-type = "int" OWS "<" int-constraint ">" string-type = ( "ascii" / "unquoted-ascii" / "unicode" ) [ OWS "<" string-constraint ">" ] bytes-type = "bytes" [ OWS "<" length-constraint ">" ] const-type = "const" OWS "<" first-safe-char *( safe-char ) ">" ; See the section 'Notes on Comments' below embedded-type = "embedded" [ OWS "<" length-constraint ">" ] reference = [ module-name "::" ] name ; Refers to a type ; defined elsewhere int-constraint = [ min-int-constraint ".." ] max-int-constraint [ OWS use-leading-zero-marker ] min-int-constraint = ["-"] pos-number max-int-constraint = ["-"] pos-number use-leading-zero-marker = "z" string-constraint = length-constraint [ OWS pattern-constraint ] Cordell [Page 23] Internet Draft Lumas April 2003 length-constraint = [ min-len-constraint ".." ] max-len-constraint min-len-constraint = pos-number max-len-constraint = ( pos-number / "*" ) pos-number = 1*DIGIT / ; Decimal number "0x" 1*HEX / ; Hex number 1*2DIGIT "b" ; Specifies number of binary bits pattern-constraint = *( constraint-char quantifier ) [ '.' quantifier ] ; '.' matches any character constraint-char = char | character-class char = single-char | special-char single-char = %x20-%xff | escaped-char escaped-char = '\\' ; Matches \ | '\[' ; Matches [ | '\?' ; Matches ? | '\*' ; Matches * | '\+' ; Matches + | '\{' ; Matches { | '\.' ; Matches . special-char = '\r' ; Matches the return character | '\n' ; Matches the new line character | '\t' ; Matches the tab character | '\f' ; Matches the form feed character | '\s' ; Matches white space [ \t\r\n\f] | '\d' ; Matches any digit [0-9] | '\w' ; Matches any word character [a-zA-Z_0-9] | '\S' ; Matches anything not matched by \s | '\D' ; Matches anything not matched by \d | '\W' ; Matches anything not matched by \w character-class = matching-character-class | inverse-character-class matching-character-class = '[' *(class-char | class-range) ']' inverse-character-class = '[^' *(class-char | class-range) ']' class-char = class-single-char | special-char class-single-char = %x20-%xff | class-escaped-char class-escaped-char = '\-' ; Matches - | '\]' ; Matches ] class-range = class-single-char '-' class-single-char quantifier = '' | '?' | '*' | '+' | '{' 1*DIGIT [ ',' [ 1*DIGIT ] ] '}' name = ALPHA *( ALPHANUM / "-" / "_" ) referenced-compound-param = referenced-struct-param / referenced-union-param / referenced-constructed-param Cordell [Page 24] Internet Draft Lumas April 2003 referenced-struct-param = "struct" WS name [ WS "pluggable" ] OWS "{" struct-body "}" OWS ";" struct-body = *( untagged-Lumas-parameter ) *( Lumas-parameter ) *( struct-extension ) referenced-union-param = "union" WS name [ WS "pluggable" ] OWS "{" union-body "}" OWS ";" union-body = [ integer-type WS name WS "as" WS "?" OWS ";" ] *( singular-Lumas-parameter ) *( union-extension ) referenced-constructed-param = "constructed" WS name OWS "{" constructed-body "}" OWS ";" constructed-body = *( constructed-simple-type WS name ";" ) constructed-simple-type = integer-type / const-type / "unquoted-ascii" OWS "<" 1*DIGIT ">" untagged-Lumas-parameter = untagged-simple-param / untagged-compound-param untagged-simple-type = simple-type WS name [ OWS cardinality ] WS "as" WS "?" ";" untagged-compound-param = untagged-struct-param / untagged-union-param / untagged-constructed-param untagged-struct-param = "struct" WS name [ OWS cardinality ] WS "as" WS "?" [ WS "pluggable" ] OWS "{" struct-body "}" OWS ";" untagged-union-param = "union" WS name [ OWS cardinality ] WS "as" WS "?" [ WS "pluggable" ] OWS "{" union-body "}" OWS ";" untagged-constructed-param = "constructed" WS name [ OWS cardinality ] WS "as" WS "?" [ WS "pluggable" ] OWS "{" constructed-body "}" OWS ";" Lumas-parameter = simple-param / compound-param Cordell [Page 25] Internet Draft Lumas April 2003 simple-param = simple-type WS name [ OWS cardinality ] [ WS "as" WS explicit-tag ] [ WS "plugin" ] ";" cardinality = "[" [ min-occurrences ".." ] max-occurrences "]" / "?" ; Short hand for [0..1] "*" ; Short hand for [0..*] "+" ; Short hand for [1..*] min-occurrences = 1*DIGIT max-occurrences = 1*DIGIT / "*" explicit-tag = tag ; tag defined in common definitions compound-param = struct-param / union-param / constructed-param struct-param = "struct" WS name [ OWS cardinality ] [ WS "as" WS explicit-tag ] [ WS "pluggable" ] [ WS "plugin" ] OWS "{" struct-body "}" OWS ";" union-param = "union" WS name [ OWS cardinality ] [ WS "as" WS explicit-tag ] [ WS "pluggable" ] [ WS "plugin" ] OWS "{" union-body "}" OWS ";" contructed-param = "constructed" name [ OWS cardinality ] [ WS "as" WS explicit-tag ] [ WS "plugin" ] OWS "{" constructed-body "}" OWS ";" struct-extension = "[" 1*( Lumas-parameter ) "]" singular-Lumas-parameter = singular-simple-param / singular-compound-param singular-simple-param = type WS name [ WS "as" WS explicit-tag ] [ WS "plugin" ] ";" singular-compound-param = singular-struct-param / singular-union-param / singular-constructed-param singular-struct-param = "struct" WS name [ WS "as" WS explicit-tag ] [ WS "pluggable" ] [ WS "plugin" ] "{" struct-body "}" ";" singular-union-param = "union" WS name [ WS "as" explicit-tag ] [ WS "pluggable" ] [ WS "plugin" ] Cordell [Page 26] Internet Draft Lumas April 2003 "{" union-body "}" ";" singular-constructed-param = "constructed" WS name [ WS "as" WS explicit-tag ] [ WS "plugin" ] OWS "{" constructed-body "}" OWS ";" third-party-extension = "plug" WS tp-struct-extension / tp-union-extension "into" WS name *( "::" name ) *( "," name *( "::" name ) ) ";" tp-struct-extension = Lumas-parameter tp-union-extension = singular-Lumas-parameter 3.5 Locating Lumas within a Specification It is not sufficient to use Lumas allow to define a protocol. Additional narrative is required to define the semantics of a protocol in addition to the syntax defined be Lumas. Thus Lumas and narrative typically need to be combined in a separate document. The main issue here is that at some point the Lumas must be extracted from the specification to be useful. If the Lumas is intermingled with the narrative, it can be manually removed using cut and paste, however this is tedious and error-prone. An alternative is to put all the Lumas in a separate section so that it can be easily extracted. However, this distances the Lumas from the narrative that explains it which is undesirable. A third option is to do both - interleave one copy of the Lumas with the narrative and a separate copy that can be used for compiling. This approach makes it difficult to keep the two versions in step, and errors can easily sneak in. Lumas compilers MUST implement a fourth option. Before parsing a file, a compiler should first look for a line of text on which the first non-white space text is lumas*/ and only has white space after it. If such a line is found, compilation starts at the following line. Subsequent narrative is then include in /* */ comment marks. If no such line is found, then compilation begins at the beginning of the file. For example, if any */ character sequences that follow this example are removed, a Lumas compiler must be able to find and process the following Lumas syntax: Cordell [Page 27] Internet Draft Lumas April 2003 lumas*/ // The first 'official' line of Lumas struct top { not-much not-much; }; */ This is narrative. */ int <0..1> not-much; /* 4. On-the-Wire Representation 4.1 Principles of On-the-Wire Encoding The basic format of the text based on-the-wire encoding is to use the format: tag = value If there are multiple instances of a parameter, then they may either be conveyed as multiple instances of the above construct, and as a comma separated list, as in: tag = value, value, value If a tag is explicitly specified in the message definition, then this is used on the wire. If no tag is explicitly specified, then the name of the parameter is used as the tag. It is also possible to explicitly specify that no tag should be used on the wire by setting the tag field to '?'. All untagged items must appear in a struct in the same order that they are defined in the message definition, and must appear before any tagged items within a struct definition. Untagged parameters that have greater than one instance must be constructed as a comma separated list. In these cases, the format on the wire becomes: value or: value, value, value If an untagged parameter has a cardinality that allows it to be absent from an encoded message, then all subsequent parameters in the enclosing struct, including tagged parameters, must also be absent. Consequently, great care should be taken when defining a message definition that allows untagged parameters to be absent. Thus, for the examples quoted earlier, that is: Cordell [Page 28] Internet Draft Lumas April 2003 ascii rfc-name ; int <1..30000> referenced-rfcs [0..255] as refers; The format on the wire would be something like (depending on the actual values in question): rfc-name = 'Lumas' refers = 822, 791, 2543 4.2 Example On-the-Wire Representation The following are example on-the-wire representations of the example message. 1 join = { 'Alice' } tech-know-ware.com = { True } 1 msg = { to = 2, 5, 8, 58 msg = 'Where are we going for dinner' } 1 leave 4.3 Formal On-the-Wire Representation The principle representation of a Lumas defined message on the wire is text based. Parameters may be untagged as long as they appear before any other tagged parameters. Untagged parameters that have non-singular cardinality must be comma separated. The top-level construct of a Lumas definition is a referenced type, which essentially has no tag associated with it. (Indeed, the presence of such a tag would not convey any information.) The top-level construct is therefore either a struct body, a union body, or a simple value, as in: Lumas-text-message = ( struct-body / union-body ) A struct body can contain untagged and tagged parameters. All untagged parameters must appear before any tagged parameters. The definition of a struct-body is therefore: Cordell [Page 29] Internet Draft Lumas April 2003 struct-body = OWS *( value *( COMMA value ) WS ) *( ( tag WS ) / ; For a void parameter ( tag EQUAL value *( COMMA value ) WS ) ) ; WS not required if it's the last item All items of a union body must be tagged, except for a single integer parameter that may be untagged. Also, parameters must only have a cardinality of one in the encoding to avoid ambiguities in the encoded message. Therefore a union body has the form: union-body = OWS (integer-value WS / tag WS / ; For a void parameter ( tag EQUAL value WS ) ) where: value = simple-value / compound-value simple-value = bool-value / integer-value / oid-value / ipv4-value / ipv6-value / ascii-value / unquoted-ascii-value / unicode-value / const-value / embedded-value / bytes-value / date-value / time-value bool-value = "True" / "False" / "T" / "F" int-value = [ "-" ] 1*DIGIT oid-value = 1*DIGIT *( "~" 1*DIGIT ) ; Only the oid's numerical parts are represented ipv4-value = 1*3DIGIT "." 1*3DIGIT "." 1*3DIGIT "." 1*3DIGIT ; N.B. The IPv4 address format within an IPv6 address is not ; supported ipv6-value = hexseq / hexseq "::" [ hexseq ] / "::" [ hexseq ] hexseq = hex4 *( ":" hex4) hex4 = 1*4HEXDIG Date and time parameters have fixed width to aid parsing. As such the various fields have leading zeros if required. (They adopt one of the formats of ISO-8601.) Dates are according to the Gregorian calendar. Other calendar types may be constructed from primitive types if required. Typically the time should be converted to UTC prior to including in a message, unless the time can be guaranteed to have only local significance. Cordell [Page 30] Internet Draft Lumas April 2003 date-value = date-year "-" date-month "-" date-day date-year = 4DIGIT ; e.g. 2002 date-month = 2DIGIT ; With leading zeros, e.g. 02 date-day = 2DIGIT ; With leading zeros, e.g. 05 time-value = time-hours ":" time-minutes ":" time-seconds time-hours = 2DIGIT ; With leading zeros, e.g. 02 time-minutes = 2DIGIT ; With leading zeros, e.g. 02 time-seconds = 2DIGIT ; With leading zeros, e.g. 02 ; Uses 24 hour clock notation ; All times presented in UTC ascii-value = "'" *( %x00-26 / %x28-5B / %x2D-x7F / "\\" / "\'" ) "'" unquoted-ascii-value = first-safe-char *( safe-char ) ; See the section 'Notes on Comments' below unicode-value = DQUOTE *( %x00-21 / %x23-5B / %x5D-xFF / "\\" / "\" DQUOTE ) DQUOTE ; DQUOTE defined in RFC 2234 bytes-value = "^" BASE64 BASE64 = *( 4BASE64-CHAR ) ( ( 4BASE64-CHAR ) / ( 3BASE64-CHAR "=" ) / ( 2BASE64-CHAR "=" "=" ) ) BASE64-CHAR = ALPHA / DIGIT / "+" / "/" const-value = first-safe-char *( safe-char ) ; See the section 'Notes on Comments' below embedded-value = "(" *(%x00-FF) ")" ; any occurrence of '(' within embedded message must be ; matched by a corresponding ')'. Illustrating the recursiveness of the message format, we have: compound-value = struct-value / union-value / constructed-value struct-value = "{" struct-body "}" union-value = union-body constructed-value = unquoted-ascii-value ; On the wire these ; types are equivalent Cordell [Page 31] Internet Draft Lumas April 2003 EQUAL = OWS "=" OWS COMMA = OWS "," OWS 4.4 Marking Message Boundaries Before a message is parsed it is necessary to know the boundaries of the message. There are many ways in which this can be done, and the method adopted should be specified in the protocol specification. However, in the absence of any other way, Lumas parsers should take the presence of an unmatched closing brace to be the end of message marker. Hence, the definition of a message delimited in this way becomes: delimited-Lumas-text-message = Lumas-text-message ( "}" / ")" ) 4.5 Illustration of Encoded Types This section illustrates how the types look once they have been encoded according to the syntax above. The tag of each item has the format 'my-XXXX'. Except in the case of the 'void' example, the XXXX part indicates the type that is encoded to the right of the equals sign. my-void // Tag only for a void parameter my-bool = True my-int = 5643 my-ipv4 = 10.0.0.1 my-ipv6 = 201:123::0 my-date = 2002-02-28 my-time = 12:00:00 my-oid = 1~2~840~113549~2~5 my-ascii = 'Lumas' my-unquoted-ascii = Lumas my-unicode = "Lumas" my-const = Lumas my-bytes = ^01AF3C== my-embedded = ( my-other-int=5 single-closing-bracket-text=')' ) Cordell [Page 32] Internet Draft Lumas April 2003 my-struct = { 5434 All time=98787654654 } my-union = 5434 my-union1 = Switch my-union2 = Volume = 11 5. Common ABNF Definitions The following definitions are common to both the definition syntax and the on the wire representation. tag = [ "?" ] first-tag-safe-char *( safe-char ) first-tag-safe-char = %x21 / ; Not " %x23-26 / ; Not ' ( ) %28-2B ; Not , - %x2E-2F / ; Not 0 1 2 3 4 5 6 7 8 9 %x3A-3C / ; Not = %x3E-5D ; Not ^ %x5F-7A / ; Not { %7C / ; Not } %7E-7F ; Visible characters except = , " ' { } ( ) ^ - ; and digits (tag must not get confused with number) first-safe-char = first-tag-safe-char / DIGIT / "-" safe-char = first-safe-char / DQUOTE / "'" / "{" / "(" / "^" ; Not = } ) , OWS = [ WS ] ; Optional white space WS = comment / " " / HTAB / CR / LF ; HTAB, CR, LF defined in RFC-2234 Cordell [Page 33] Internet Draft Lumas April 2003 ; See section 'Notes on Comments' below comment = c-comment / cpp-comment c-comment = "/*" (nested-end / hard-end ) nested-end = "*/" hard-end = "**/" cpp-comment = "//" *( HTAB / %x20-%7f ) ( CR / LF ) ; A comment is treated as a single space for the ; purposes of parsing 6. Notes on Comments To aid development Lumas allows comments to appear in both a message definition and a message. On the wire, const and unquoted-ascii values MUST NOT begin with comment start markers ('//' and '/*'). However, if the values contain comment start marker characters, the characters are interpreted as part of the value, and do not indicate the start of a comment. For example, in the first of the examples below, the text "This-is-a-comment" MUST be treated as a comment, whereas in the second example the text "this-is-part-of-the-value" MUST be treated as part of the value. ascii-value = /*This-is-a-comment*/This-is-the-value ascii-value = and-//this-is-part-of-the-value In a message definition (but not in a message) the c-comment style of commenting allows nesting of comments. In a nested comment, each '/*' character sequence MUST be matched by a corresponding '*/' character sequence before the comment ends. Additionally, if a comment starts with the '/*' character sequence, the end of the comment can be forced by the hard end of comment marker defined as '**/', which overrides the nesting. (This provision allows the commenting out of headers and footers in text only message definition documents.) 7. Mandatory to Understand Many protocols require the capability to signal that certain extension parameters be mandatory to understand, or the message should be rejected in some way. Lumas provides no in-built mechanism for this feature. Instead implementers are recommended to use a feature similar to SIP's 'Require' header [SIP]. 8. Security Considerations Lumas itself does not have any security issues related to it, but the security requirements of a protocol must be borne in mind when writing a Lumas message definition. Common advice is that it is Cordell [Page 34] Internet Draft Lumas April 2003 difficult to add security to a protocol once it has been released, and hence security issues must be considered from the outset. This is of issue to a Lumas message definition as it may affect the format of messages. This is particularly the case for integrity check values that are effectively appended to the message once the message is encoded. 9. References [ABNF]D. Crocker, & P. Overell, "Augmented BNF for Syntax Specifications: ABNF, " Internet Engineering Task Force, RFC 2234, November 1997. [XML] "Extensible Markup Language (XML) 1.0 (Second Edition)", W3C REC-xml, October 2000. [PERL]L. Wall, T.Christiansen, & J. Orwant, "Programming Perl", O'Reilly, ISDN-0-596-00027-8. [SIP] J. Rosenberg et al., "SIP: Session Initiation Protocol," Internet Engineering Task Force, RFC 3261, June 2002. 10. Author's Address Pete Cordell Tech-Know-Ware Ltd P.O. Box 30 Ipswich, IP5 2WY UK pete@tech-know-ware.com Full Copyright Statement Copyright (C) The Internet Society (2002). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be Cordell [Page 35] Internet Draft Lumas April 2003 revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society. Cordell [Page 36]