Open Pluggable Edge Services A. Rousskov
Internet-Draft The Measurement Factory
Expires: February 25, 2004 August 27, 2003
OPES Callout Protocol Core
draft-ietf-opes-ocp-core-01
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Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This document specifies Open Pluggable Edge Services (OPES) Callout
Protocol (OCP). OCP is an application-agnostic protocol that
facilitates exchange of application messages between an OPES
processor and a callout server, for the purpose of adaptation of
application messages at the callout server.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1 Application proxies and OCP scope . . . . . . . . . . . . . 4
1.2 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 5
1.3 Protocol Development Status . . . . . . . . . . . . . . . . 6
2. Overall Operation . . . . . . . . . . . . . . . . . . . . . 8
2.1 Initialization . . . . . . . . . . . . . . . . . . . . . . . 8
2.2 Original Dataflow . . . . . . . . . . . . . . . . . . . . . 8
2.3 Adapted Dataflow . . . . . . . . . . . . . . . . . . . . . . 8
2.4 Termination . . . . . . . . . . . . . . . . . . . . . . . . 9
2.5 Exchange Patterns . . . . . . . . . . . . . . . . . . . . . 9
2.6 OCP Environment . . . . . . . . . . . . . . . . . . . . . . 10
3. Messages . . . . . . . . . . . . . . . . . . . . . . . . . . 11
3.1 Message Format . . . . . . . . . . . . . . . . . . . . . . . 11
3.2 Message Examples . . . . . . . . . . . . . . . . . . . . . . 13
3.3 Message Names . . . . . . . . . . . . . . . . . . . . . . . 13
4. Transactions . . . . . . . . . . . . . . . . . . . . . . . . 15
5. Negotiation . . . . . . . . . . . . . . . . . . . . . . . . 16
6. Capability and State Inquiry . . . . . . . . . . . . . . . . 17
7. Message Parameters . . . . . . . . . . . . . . . . . . . . . 18
7.1 Parameter Types . . . . . . . . . . . . . . . . . . . . . . 18
7.1.1 Uri . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
7.1.2 Uni . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
7.1.3 Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
7.1.4 Boolean . . . . . . . . . . . . . . . . . . . . . . . . . . 19
8. Parameter Definitions . . . . . . . . . . . . . . . . . . . 20
8.1 xid . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
8.2 rid . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
8.3 service . . . . . . . . . . . . . . . . . . . . . . . . . . 20
8.4 services . . . . . . . . . . . . . . . . . . . . . . . . . . 20
8.5 sg-id . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
8.6 am-id . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
8.7 size-request . . . . . . . . . . . . . . . . . . . . . . . . 21
8.8 offset . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
8.9 sizep . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
8.10 modp . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
8.11 result . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
8.12 error . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
8.13 feature . . . . . . . . . . . . . . . . . . . . . . . . . . 22
9. Message Definitions . . . . . . . . . . . . . . . . . . . . 23
9.1 Connection Start (CS) . . . . . . . . . . . . . . . . . . . 23
9.2 Connection End (CE) . . . . . . . . . . . . . . . . . . . . 24
9.3 Create Service Group (SGC) . . . . . . . . . . . . . . . . . 25
9.4 Destroy Service Group (SGD) . . . . . . . . . . . . . . . . 26
9.5 Transaction Start (TS) . . . . . . . . . . . . . . . . . . . 26
9.6 Transaction End (TE) . . . . . . . . . . . . . . . . . . . . 26
9.7 Application Message Start (AMS) . . . . . . . . . . . . . . 27
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9.8 Application Message End (AME) . . . . . . . . . . . . . . . 28
9.9 Data Use Mine (DUM) . . . . . . . . . . . . . . . . . . . . 28
9.10 Data Use Yours (DUY) . . . . . . . . . . . . . . . . . . . . 29
9.11 Data Pause (data-pause) . . . . . . . . . . . . . . . . . . 30
9.12 Data Paused (data-paused) . . . . . . . . . . . . . . . . . 31
9.13 Data Need (data-need) . . . . . . . . . . . . . . . . . . . 31
9.14 Data ACK (DACK) . . . . . . . . . . . . . . . . . . . . . . 32
9.15 I Am Here (pong) . . . . . . . . . . . . . . . . . . . . . . 33
9.16 Are You There? (ping) . . . . . . . . . . . . . . . . . . . 33
9.17 Negotiation Offer (NO) . . . . . . . . . . . . . . . . . . . 34
9.18 Negotiation Response (NR) . . . . . . . . . . . . . . . . . 35
9.19 I Support (i-can) . . . . . . . . . . . . . . . . . . . . . 36
9.20 Can You Support (can-you) . . . . . . . . . . . . . . . . . 36
9.21 I Currently Use (i-do) . . . . . . . . . . . . . . . . . . . 36
9.22 Do You Currently Use (do-you) . . . . . . . . . . . . . . . 37
10. Application Protocol Requirements . . . . . . . . . . . . . 38
11. IAB Considerations . . . . . . . . . . . . . . . . . . . . . 39
12. Security Considerations . . . . . . . . . . . . . . . . . . 40
13. Compliance . . . . . . . . . . . . . . . . . . . . . . . . . 42
14. To-do . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
A. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 45
B. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 46
Normative References . . . . . . . . . . . . . . . . . . . . 52
Informative References . . . . . . . . . . . . . . . . . . . 53
Author's Address . . . . . . . . . . . . . . . . . . . . . . 53
Intellectual Property and Copyright Statements . . . . . . . 54
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1. Introduction
The Open Pluggable Edge Services (OPES) architecture
[I-D.ietf-opes-architecture], enables cooperative application
services (OPES services) between a data provider, a data consumer,
and zero or more OPES processors. The application services under
consideration analyze and possibly transform application-level
messages exchanged between the data provider and the data consumer.
The OPES processor can delegate the responsibility of service
execution by communicating and collaborating with one or more remote
callout servers. As described in [I-D.ietf-opes-protocol-reqs], an
OPES processor communicates with and invokes services on a callout
server by using a callout protocol. This document specifies the core
of such a protocol.
OCP Core specification documents general, application-independent
protocol mechanisms. A separate series of documents describe
application-specific aspects of OCP. For example, "OPES adaptation of
HTTP" [XXX] describes, in part, how HTTP messages and HTTP
meta-information can be communicated over OCP.
1.1 Application proxies and OCP scope
(XXX: a better section title would be nice)
As an application proxy, OPES processor proxies a single application
protocol or converts from one application protocol to another. At the
same time, OPES processor may be an OCP client, using OCP to
facilitate adaptation of proxied messages at callout servers. It is
therefore natural to assume that OPES processor takes application
messages being proxied, passes them over OCP to callout servers, and
then puts the adaptation results back on the wire. However, such an
assumption implies that OCP is applied directly to application
messages that OPES processor is proxing, which may not be the case.
"OPES processor" "callout server"
+-----------------+ +-----------------+
| pre-processing | "OCP scope" | |
| +- - - - - - - - - - - - - - - - - - -+ |
| iteration | <== ( application data ) ==> | adaptation |
| +- - - - - - - - - - - - - - - - - - -+ |
| post-processing | | |
+-----------------+ +-----------------+
Figure 1
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OPES processor may preprocess (or postprocess) proxied application
messages before (or after) they are adapted at callout servers. For
example, a processor may take an HTTP response being proxied and pass
it as is, along with metadata about the corresponding HTTP
connection. Another processor may take an HTTP response, extract its
body, and pass that body, along with the content-encoding metadata.
Moreover, to perform adaptation, OPES processor may execute several
callout services, iterating over several callout servers. Such
preprocessing, postprocessing, and iterations make it impossible to
rely on any specific relationship between application messages being
proxied and application messages being sent to a callout service.
Similarly, specific adaptation actions at the callout server are
outside of OCP Core scope.
This specification does not define or require any specific
relationship among application messages being proxied by the OPES
processor and application messages being exchanged with callout
servers via OCP. OPES processor usually provides some mapping among
these application messages, but processor's specific actions are
beyond OCP scope. In other words, this specification is not concerned
with the OPES processor role as an application proxy, or as an
iterator of callout services. The scope of OCP Core is communication
between a single OPES processor and a single callout server.
Furthermore, an OPES processor is at liberty to choose which proxied
application messages or information about them to send over OCP. All
proxied messages on all proxied connections (if connections are
defined for a given application), everything on some connections,
selected proxied messages, or nothing might be sent over OCP to
callout servers. OPES processor and callout server state related to
proxied protocols can be relayed over OCP as application message
metadata.
1.2 Terminology
The all-caps keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in [RFC2119].
OPES processor works with messages from application protocols and may
relay information about those application messages to a callout
server. OCP is also an application protocol. Thus, protocol elements
like "message", "connection", or "transaction" exist in OCP and other
application protocols. In this specification, all references to
elements from application protocols other than OCP are used with an
explicit "application" qualifier. References without the
"application" qualifier, refer to OCP elements.
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(XXX: Some OCP elements are called "callout" elements in the OCP
requirements document. We assume that OCP is equivalent to "callout"
in this context. For example, OCP connection is the same as callout
connection. Should we be more consistent?)
OCP message: OCP message is a basic unit of communication between an
OPES processor and a callout server. Message is a sequence of
octets formatted according to syntax rules (Section 3.1). Message
semantics is defined in Section 9.
application message: An entity defined by OPES processor and callout
server negotiation. Usually, the negotiated definition would match
the definition from an application protocol (e.g., [RFC2616]
definition of an HTTP message, including headers, body, and
trailers).
application message data: An opaque sequence of octets representing
complete or partial application message. OCP Core does not
distinguish application message structure (if any). Application
message data may be empty.
data: Same as application message data.
original Referring to application message flowing from the OPES
processor to a callout server. (XXX: we need a better term than
"original")
adapted Referring to application message flowing from an OPES callout
server to the OPES processor.
adaptation: Any kind of access by a callout server, including
modification and copying. For example, translating or logging an
SMTP message is adaptation of that application message.
agent: Client or server for a given communication protocol. A proxy
is both a client and a server and, hence, also an agent. For
example, OPES processor and callout server are OCP agents.
immediate: Performing the specified action before processing new
incoming messages or sending any new messages unrelated to the
specified action.
1.3 Protocol Development Status
(XXX: this section is to be removed from the final protocol specs)
This specification is not fully suitable for writing OCP
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implementations as some behavioral and formatting aspects are not yet
documented. They will be. Note that application-specific details are
documented separately, as described in the "Introduction" section.
Section 14 contains a list of to-be-implemented items.
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2. Overall Operation
OPES processor may use OPES callout protocol (OCP) to communicate
with callout servers. Adaptation using callout services is sometimes
called a "bump in the wire" architecture. (XXX: is this paragraph
needed? out of place?
2.1 Initialization
OPES processor establishes transport connections with callout servers
for the purpose of exchanging application messages with the callout
server(s) using OCP. After a transport-layer connection (usually TCP/
IP) is established, communicating OCP agents exchange Connection
Start (CS) (Section 9.1) messages. Next, OCP features can be
negotiated between the processor and the callout server (see Section
5). For example, OCP agents have to agree on transport encryption
and application message definition. When negotiation is complete,
OCP agents may start exchanging application messages.
2.2 Original Dataflow
When OPES processor wants to adapt an application message, the OPES
processor sends a Transaction Start (TS) (Section 9.5) message to
initiate an OCP transaction dedicated to that application message.
Some transaction properties may need to be renegotiated at this time
(XXX: undocumented and might not be needed). The processor then sends
a Application Message Start (AMS) (Section 9.7) message to prepare
the callout server for application data that will follow. Once
application message scope is established, application data can be
sent to the callout server, using Data Use Mine (DUM) (Section 9.9)
and related OCP message(s). All these messages correspond to
original dataflow.
2.3 Adapted Dataflow
The callout server receives data and metadata sent by the OPES
processor (original data flow). The callout server analyses metadata
and adapts data as it comes in. The server usually builds its version
of metadata and responds to OPES processor with an
'app-message-start' message. Adapted application message data can be
sent next, using Data Use Mine (DUM) (Section 9.9) OCP message(s).
The application message is then announced to be "closed" using
'app-message-close' message. The transaction may be closed using
'xaction-end' message as well. All these messages correspond to
adapted data flow.
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+---------------+ +-------+
| OPES | == (original data flow) ==> |callout|
| processor | <== (adapted data flow) === |server |
+---------------+ +-------+
Figure 2
Depending on the negotiated application message definition, it may be
possible or even required for callout server to respond with more
than one application message within the same transaction. In other
words, the callout server may adapt a single original application
message into multiple application messages. Each application message
sent by the callout server is individually identified by "am-id"
parameter and can be sent independently from other application
messages within the same transaction (this allows for logical- and
transport-level interleaving of OCP messages related to different
application messages).
The OPES processor receives the application message sent by the
callout server. Other OPES processor actions specific to the
application message received are out of this specification scope.
2.4 Termination
Either OCP agent can terminate application message delivery,
transaction, or connection by sending an appropriate OCP message.
Usually, the callout server terminates application message delivery
and the transaction. Abnormal terminations at arbitrary times are
supported. Termination OCP message include a result description.
2.5 Exchange Patterns
OCP agents may also exchange messages related to their configuration,
state, transport connections, application connections, etc. A callout
server may remove itself from the application message processing
loop. A single OPES processor can communicate with many callout
servers and vice versa. It is possible to think of an OPES processor
as an ``OCP client'' and of a callout server as an ``OCP server''.
The OPES architecture document [I-D.ietf-opes-architecture] describes
configuration possibilities.
The following informal rules illustrate relationships between
transport connections, transactions, OCP messages, and application
messages:
o An OCP agent may communicate with multiple OCP agents.
Communication with multiple OCP agents is outside of this
specification scope.
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o An OPES processor may have multiple concurrent OCP connections to
a callout server. Communication over multiple OCP connections is
outside of this specification scope.
o A connection may carry multiple concurrent transactions. A
transaction is always associated with a single connection (i.e., a
transaction cannot span multiple concurrent connections).
o A connection may carry at most one message at a time, including
control messages and transaction-related messages. A message is
always associated with a single connection (i.e., a message cannot
span multiple concurrent connections).
o A transaction is a sequence of messages related to application of
a given set of callout services to a single application message.
A sequence of transaction messages from an OPES processor to a
callout server is called original flow. A sequence of transaction
messages from a callout server to an OPES processor is called
adapted flow. The two flows may overlap in time.
o A transaction is always associated with a single (original)
application message. Adapted flow may transfer information about
multiple (adapted) application messages.
o An application message (adapted or original) is transferred using
a sequence of OCP messages.
2.6 OCP Environment
OCP communication is assumed to usually take place over TCP/IP
connections on the Internet (though no default TCP port is assigned
to OCP). This does not preclude OCP from being implemented on top of
any other transport protocol, on any other network. OCP only
presumes a reliable connection-oriented transport; any protocol that
provides such guarantees can be used; the mapping of OCP message
structures onto the transport data units of the protocol in question
is outside the scope of this specification.
OCP is application agnostic but it is not suitable for all
applications. This specification documents known application scope
limitations in Section 10. OCP messages can carry
application-specific information as payload or application-specific
extension parameters.
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3. Messages
As defined in Section 1.2, an OCP message is a basic unit of
communication between an OPES processor and a callout server. A
message is a sequence of octets formatted according to syntax rules
(Section 3.1). Message semantics is defined in Section 9. Messages
are transmitted on top of OCP transport.
OCP messages deal with transport and transaction management as well
as application data exchange between a single OPES processor and a
single callout server. Some messages can only be emitted by an OPES
processor; some only by a callout server; some can be emitted by both
OPES processor and callout server. Some messages require responses
(one could call such messages "requests"); some can only be used in
response to other messages ("responses"); some may be sent without
solicitation and/or may not require a response.
3.1 Message Format
An OCP message consists of a message name followed by optional
parameters and payload. The exact message syntax is defined by the
following Augmented Backus-Naur Form (ABNF) [RFC2234]:
message = name [anonym-parameters]
[named-parameters]
[payload]
";" CRLF
anonym-parameters = 1*(SP anonym-parameter) ; spaced parameters
named-parameters = 1*(CRLF named-parameter) ; CRLF-separated params
payload = CRLF data
anonym-parameter = value
named-parameter = name ":" SP value
value = atom / structure / list
atom = bare-value / quoted-value
structure = "{" [ value *(SP value) ] "}" ; spaced values
list = "(" [ value *("," value) ] ")" ; comma-separated values
name = ALPHA *safe-OCTET
bare-value = 1*safe-OCTET
quoted-value = DQUOTE data DQUOTE
data = size ":" <n>OCTET ; <n> == size
safe-OCTET = ALPHA / DIGIT / "-" / "_"
size = dec-number ; 0-2147483647
dec-number = 1*DIGIT ; no leading zeros or signs
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Figure 3
Several normative rules accompany the above ABNF:
o There is no "implied linear space" (LWS) rule. LWS rules are
common to MIME-based grammars, but are not used here. The
whitespace syntax is restricted to what is explicitly allowed by
the above ABNF.
o All protocol elements are case sensitive unless specified
otherwise. In particular, message names and parameter names are
case sensitive.
o Sizes are interpreted as decimal values and cannot have leading
zeros.
o Sizes do not exceed 2147483647.
o The size attribute in a quoted-value encoding specifies the exact
number of OCTETs following the column (':') separator. If size
OCTETs are not followed by a quote ('"') character, the encoding
is syntactically invalid.
o Empty quoted-values are encoded as a 4-OCTET sequence "0:".
o Any parameter value MAY be encoded as a quoted-value. A
quoted-value MUST be interpreted after the encoding is removed.
For example, number 1234 can be encoded as four OCTETs 1234 or as
eight OCTETs "4:1234", yielding exactly the same meaning. (XXX:
this makes digital signatures more difficult, see todo)
o By default, all values MUST be interpreted as having UTF-8
encoding. Note that ASCII is a UTF-8 subset, and that the syntax
prohibits non-ASCII characters outside of the "data" element.
(XXX: check that this is enough to satisfy i18n and whatever
internationalization requirements IETF has)
Messages violating formatting rules are, by definition, invalid (see
Section XXX for rules on processing invalid messages).
Informal note to implementors: OCP messages have three major parts:
anonymous parameters, named parameters, and payload. One or two
character lookups are sufficient to determine the next part. If the
first character is a semicolumn (";"), all optional parts have been
parsed. If the first lookup character is a space, anonymous
parameters follow. If the first lookup character is CRLF then the
second lookup is needed: if the second character is a digit, payload
follows; otherwise, named parameters follow. Other syntax and
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semantics rules must still be obeyed, of course. For example, once a
named parameter or payload has been discovered, no anonymous
parameters should be accepted. Similarly, a single character lookup
is sufficient to distinguish a bare value from a quoted one since
only quoted values start with a quote character.
3.2 Message Examples
OCP syntax provides for compact representation of short control
messages and required parameters while allowing for parameter
extensions. Below are examples of short control messages. Required
CRLF sequences at the end of messages are not shown explicitly.
TS 1;
ping 123 2;
data-pause 22 1;
i-can "28:http://iana.org/opes/ocp/TLS";
Figure 4
Optional parameters and extensions are possible using named
parameters approach as illustrated by the following example. The
'data-need' message in the example has three anonymous parameters and
two named parameters (the last one being an extension). Required CRLF
sequence at the end of each line is not shown explicitly.
data-need 1 3 12345
size-request: 16384
x-need-info: "26:twenty six octet extension";
Figure 5
Finally, any message may have a payload part. For example, the Data
Use Mine (DUM) (Section 9.9) message below carries 8865 bytes of raw
data. Required CRLF sequence at the end of each line is not shown
explicitly.
DUM 1 3 0 8865
modp: 75
sizep: 65537
8865:<... 8865 bytes of data ...>;
Figure 6
3.3 Message Names
Most OCP messages defined in this specification have short names,
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formed by abbreviating or compressing a longer but human-friendlier
message title. Short names without a central registration system
(like this specification or IANA registry) are likely to cause
conflicts. Informal protocol extensions should avoid short names. To
emphasize what is already defined by message syntax, implementations
must not assume that all message names are very short.
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4. Transactions
OCP transaction is a logical sequence of OCP messages processing a
single original application message. The result of the processing may
be zero or more application messages, adapted from the original. A
typical transaction consists of two message flows: a flow from the
OPES processor to the callout server (sending original application
message) and a flow from the callout server to the OPES processor
(sending adapted application messages). The number of application
messages produced by the callout server and whether the callout
server actually modifies original application message may depend on
the requested callout service and other factors. The OPES processor
or the callout server can terminate the transaction by sending a
corresponding message to the other side.
A OCP transaction starts with a explicit 'xaction-start' message sent
by the OPES processor. A transaction ends with the first
'xaction-end' message, explicit or implied, which can be sent by
either side. Zero or more OCP messages associated with the
transaction can be exchanged in between. The figure below illustrates
possible message sequence (prefix "P" stands for OCP Client, OPES
processor; prefix "S" stands for OCP callout server).
P: TS 10;
P: AMS 10 1;
... processor sending application data to the callout server
S: AMS 10 2;
... callout server sending application data to the processor
... processor sending application data to the callout server
P: AME 10 1 result;
S: AME 10 2 result;
P: TE 10 result;
Figure 7
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5. Negotiation
The negotiation mechanism allows OCP client and server to agree on
mutually acceptable set of features, including optional and
application-specific behavior as well as OCP extensions. For example,
transport encryption, data format, and support for a new message can
be negotiated. Negotiation implies intent for a behavioral change. A
related mechanism allowing an agent to query capabilities of its
counterpart without changing counterpart's behavior is described in
Section 6.
Most negotiations require at least one round trip time delay. In rare
cases when other side's response is not required immediately,
negotiation delay can be eliminated.
Two core negotiation primitives are supported: negotiation offer and
negotiation response. The Negotiation Offer (NO) message (Section
9.17) allows an agent to specify a set of features from which the
responder has to select exactly one feature it prefers. The selection
is sent using a Negotiation Response (NR) message (Section 9.18). If
the response is positive both sides assume that the selected feature
is in effect. If the response is negative, no behavioral changes are
assumed. In either case, further offers may follow.
Negotiation Offer (NO) messages may be sent by either agent. Feature
specifications MAY restrict initiator role to one of the agents. For
example, negotiation of transport security feature [XXX] is initiated
exclusively by OPES processors to avoid situations where both agents
wait for each other to make an offer.
Since either agent may make an offer, two "concurrent" offers may be
made at the same time, from the two communicating agents. Unmanaged
concurrent offers may lead to a negotiation deadlock. By giving OPES
processor a priority, offer handling rules (Section 9.17) ensure that
only one offer per transport connection is honored at a time, and the
other concurrent offers are ignored by both agents.
Violation of negotiation rules leads to OCP connection termination.
This design reduces the number of negotiation scenarios resulting in
a deadlock when one of the agents is not compliant.
(XXX: add examples)
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6. Capability and State Inquiry
This section describes OCP interface for querying the capability or
state of an agent. A related mechanism allowing agents to negotiate
features is described in Section 5.
OCP supports two inquiry primitives: capability inquiry and state
inquiry. Capability inquiry (see Section 9.20) is concerned about
supported, but not necessarily active, features. A response to such a
query (see Section 9.19) may contain ranges of supported feature
parameters. State inquiry (Section 9.22) focuses on the current state
of enabled and active features. A response to a state inquiry
(Section 9.21) contains feature parameters specific to agent's
current state at the time the inquiry is received.
For example, a capability inquiry may reveal that an agent supports
two transport security mechanisms while a state inquiry may show a
specific security profile being enabled now.
The primary purpose of these inquiries is debugging and
troubleshooting rather than automated fine-tuning of cooperating
agent behavior and configurations. The latter is directly supported
by OCP negotiation mechanism.
(XXX: do we need this OPTIONS-like feature at all?)
(XXX: add examples)
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7. Message Parameters
This section defines parameters that are used for message definitions
(Section 9). For ease of reference, each parameter is given a unique
name, even if it is used exclusively as an anonymous parameter.
7.1 Parameter Types
This sections defines parameter types. In OCP context, a type is a
named set of semantic rules attached to a known value syntax
construct (e.g., atom, list, or structure). This specification
documents expected types for each formal parameter. Before using a
parameter value, an implementation MUST check whether it matches the
expected type. A mismatch means that the message is invalid.
Specifications based on OCP Core MAY define their own types and MUST
declare types of every new formal parameter they introduce.
7.1.1 Uri
Uri (universal resource identifier) is an atom formatted according to
URI rules in [RFC2396].
Often, a uri parameter is used as a unique (within a given scope)
identifier. Many uri parameters are URLs. Unless noted otherwise, URL
identifiers do not imply existence of a serviceable resource at the
location they specify. For example, an HTTP request for "http://
ietf.org/opes/ocp/raw/tcp" URL (XXX: identifying an OCP transport
profile) may result in a 404 (Not Found) response.
7.1.2 Uni
Uni (universal numeric identifier) is an atom formatted as dec-number
and with a value in the [0, 2147483647] inclusive range.
Often, a uni parameter is used as a unique (within a given scope)
identifier.
7.1.3 Size
Size is an atom formatted as dec-number and with a value in the [0,
2147483647] inclusive range.
OCP cannot handle application messages that exceed 2147483647 OCTETs
in size or require larger sizes as a part of OCP marshaling process.
However, since the definition of an application message is up to OCP
agents, it is possible to work around this limitation at a processing
level above OCP.
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7.1.4 Boolean
Boolean type is an atom formatted as dec-number and with a value in
the [0, 1] inclusive range. A value of zero ("0") is interpreted as
"false". A value of one ("1") is interpreted as "true".
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8. Parameter Definitions
8.1 xid
"Xid", an OCP transaction identifier, has "uni" type. "Xid" uniquely
identifies an OCP transaction originated by a given OPES processor.
8.2 rid
"Rid", an OCP request identifier, has "uni" type. "Rid" uniquely
identifies an OCP request message on a connection. Request
identifiers are used to match certain requests and responses.
8.3 service
"Service" is an "{id}" structure, where the id member is an OPES
service identifier of type "Uri". Services may have service-dependent
parameters. A document defining the service identifier for use with
OCP MUST also define service-dependent parameters as additional
"service" structure members, if any. For example, a "service" value
may look like this:
{"28:http://ietf.org/opes/ocp/tls" "8:blowfish"}
8.4 services
"Services" is a list of "service" values. Unless noted otherwise, the
order of the values is the requested or actual service application
order.
This parameter MAY appear in any message from the callout server that
has an "am-id" parameter. If this parameter appears in a message from
the callout server that carries or refers to application data, its
value indicates the services actually applied to that data. If this
parameter appears in a message from the callout server that neither
carries nor refers to application data, its value indicates the
services that MAY be applied to that application message in the
future. (XXX: say where it cannot appear?)(XXX: make it symmetric
with processor)
8.5 sg-id
"Sg-id", a service group identifier, is of type "uni". "Sg-id"
uniquely identifies a group of services on an OCP connection.
8.6 am-id
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"Am-id", an application message identifier, is of type "uni". "Am-id"
uniquely identifies an application message within an OCP transaction.
8.7 size-request
"Size-request" is of type "Size". The sender uses "size-request" to
specify the number of data or metadata OCTETs it desires to receive.
8.8 offset
"Offset" is of type "Size". "Offset" describes payload start position
relative to the application message data or metadata. The offset of
the first application byte has a value of zero.
8.9 sizep
Remaining application data size prediction in octets. The value
excludes data in the current OCP message, if any. The prediction
applies to a single application message. This parameter can be used
with any OCP message that has am-id parameter.
8.10 modp
Future data modification prediction in percents. A modp value of 0
(zero) means the sender predicts that there will be no data
modifications. A value of 100 means the sender is predicts that there
will be data modifications. The value excludes data in the current
OCP message, if any. The prediction applies to a single application
message. This parameter can be used with any OCP message that has
am-id parameter.
8.11 result
OCP processing result. Result is a structure with two documented
members: a required Uni status code and an optional string containing
informative textual information, not intended for automated
processing. For example,
{ 200 "2:OK" }
This specification defines two result codes: 200 (success) and 400
(failure). This specification does not document any result-specific
actions for 200 (success) result recipients. A recipient of a 400
(failure) result of a AME, TE, or CE message MUST destroy any state
or data associated with the corresponding data flow, transaction, or
connection. For example, adapted version of the application message
data must be purged from the proxy cache if the OPES processor
receives an Application Message End (AME) message with result code of
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400 (failure).
Extending result semantics is possible by adding new structure
members or explicitly negotiating additional result codes (e.g., as a
part of a negotiated profile). A recipient of an unknown result code
MUST treat it as if code 400 (failure) was received.
The result parameter is optional. By definition, an absent result
parameter is semantically equivalent to a {200} result. (XXX: how to
make this statement more normative?).
(XXX: Since we only support success/failure indication, and since
there is probably no reason to supply textual information with
successful messages, we should probably just replace "result" with an
optional named parameter "Error: text"! That parameter would have the
same semantics as code 400 (failure) documented above).
8.12 error
A flag indicating abnormal conditions at the sender that cannot be
expressed via result parameter. It is RECOMMENDED that the recipient
deletes all state associated with the corresponding OCP message.
8.13 feature
A OCP feature identifier with optional feature parameters (sometimes
called attributes). Used to declare support and negotiate use of OCP
optional or extension features.
This specification defines three features:
TLS transport encryption (Section XXX),
Raw Application Binding (Section XXX), and
Processor Data Copying (Section XXX).
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9. Message Definitions
This section describes specific OCP messages. Each message is given a
unique name and usually has a set of anonymous and/or named
parameters. The order of anonymous parameters is specified in the
message definitions below. No particular order for named parameters
is implied by this specification. No more than one named-parameter
with a given name can appear in the message; messages with multiple
equally-named parameters are semantically invalid.
A recipient MUST be able to parse any syntactically valid message
(see Section 3.1), subject to recipient resources limitations. If
resources are exhausted or if a syntactically malformed message is
received, the recipient MUST terminate processing of the
corresponding connection using a Connection End (CE) message (Section
9.2) with an error flag. (XXX: the error information should identify
the problem and distinguish resource limitation from syntax errors?)
Unknown or unexpected message names, parameters, and payloads may be
valid extensions. For example, an "extra" anonymous parameter may be
used for a given message, in addition to what is documented in the
message definition below. A recipient MUST ignore any unknown or
unexpected name, parameter, or payload. Recipients MAY report (e.g.,
log) unknown or unexpected elements, of course.
Except for messages that introduce new identifiers, all sent
identifiers MUST be known (i.e., introduced and not ended by previous
messages). Except for messages that introduce new identifiers, the
recipient MUST ignore any message with an unknown identifier. For
example, recipient must ignore a Data Use Mine (DUM) (Section 9.9)
message if the xid parameter refers to an unknown transaction.
Message definitions below clearly state rare exceptions to the above
rules.
(XXX can we define "ignore"?) (XXX move these rules elsewhere?)
(XXX Message parameters in [square brackets] are OPTIONAL. Other
parameters are REQUIRED.)
9.1 Connection Start (CS)
name: CS
anonymous parameters: none
named parameters: none
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payload: no
senders: OPES processor only
A Connection Start (CS) message indicates the start of an OCP
communication from the OPES processor. An OPES processor MUST send
this message immediately after establishing a transport connection to
the callout server. If the first message a callout server receives is
not Connection Start (CS), the callout server MUST terminate the
connection with a Connection End (CE) message (Section 9.2).
Upon receiving of this message, the callout server MUST either start
maintaining connection state or refuse further processing by
responding with a Connection End (CE) message (Section 9.2). A
callout server MUST maintain the state until it detects the end of
the connection or until it terminates the connection itself.
A callout server MUST NOT send this message (XXX: why?). If the first
message received by an OPES processor is a Connection Start (CS)
message, the processor MUST terminate the connection with a
Connection End (CE) message (Section 9.2).
An OPES processor MUST NOT resend this message. If a callout server
receives this message and it is not the first message on a
connection, then, the callout server MUST terminate the connection
with a Connection End (CE) message (Section 9.2).
With TCP/IP as transport, raw TCP connections (local and remote peer
addresses) identify an OCP connection. Other transports may provide
OCP connection identifiers to distinguish connections that share the
same transport. For example, a single BEEP [RFC3080] channel may be
designated as a single OCP connection.
9.2 Connection End (CE)
name: CE
anonymous parameters: [result]
named parameters: [error]
payload: no
senders: both OPES processor and callout server
Indicates an end of a transport connection. The agent initiating
closing or termination of a connection MUST send this message
immediately prior to closing or termination. The recipient MUST free
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associated state, including transport state. The destruction of the
state ensures that messages outside of the old connection are
ignored.
Connection termination without a Connection End (CE) message
indicates that the connection was prematurely closed without the
closing-side agent prior knowledge or intent. When an agent detects a
prematurely closed connection, the agent MUST behave as if an
Connection End (CE) message indicating a fatal error was received.
A Connection End (CE) message implies the end of all transactions,
negotiations, and service groups opened or active on the connection
being ended.
9.3 Create Service Group (SGC)
name: SGC
anonymous parameters: sg-id services
named parameters: none
payload: no
senders: both OPES processor and callout server
Create Service Group (SGC) message instructs the recipient to
associate a list of services with a given service group identifier
("sg-id"). The group can then be referred by the sender using the
identifier. The recipient MUST maintain the association until a
corresponding Destroy Service Group (SGD) message is received or
implied.
Service groups have a connection scope. Transaction management
messages do not affect existing service groups.
Maintaining service group associations requires resources (e.g.,
storage to keep the group identifier and a list of service IDs).
Thus, there is a finite number of associations an implementation can
maintain. Callout servers MUST be able to maintain at least one
association for each OCP connection they accept. If a recipient of
the Create Service Group (SGC) message does not create the requested
association, it MUST immediately terminate the connection with a
Connection End (CE) message.
(XXX: document that wrong sq-id lead to semantically invalid
messages)
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9.4 Destroy Service Group (SGD)
name: SGD
anonymous parameters: sg-id
named parameters: none
payload: no
senders: both OPES processor and callout server
Destroy Service Group (SGC) message instructs the recipient to forget
about the service group associated with the specified "sg-id"
identifier. If "sg-id" refers to an existing group, the recipient
MUST destroy the association. Otherwise, the recipient MUST treat the
message as invalid.
9.5 Transaction Start (TS)
name: TS
anonymous parameters: xid sg-id
named parameters: none
payload: no
senders: OPES processor only
Indicates the start of an OCP transaction. A callout server MUST NOT
send this message. Upon receiving of this message, the callout server
MUST either start maintaining transaction state or refuse further
processing by responding with a 'xaction-end' message. A callout
server MUST maintain the state until it receives a message indicating
the end of the transaction or until it terminates the transaction
itself.
The "sg-id" parameter refers to a service group created with a Create
Service Group (SGC) message. If no group is associated with "sg-id",
the callout server MUST treat the message as invalid. Otherwise, the
callout server MUST use the list of services associated with "sg-id".
This message introduces transaction identifier (xid).
9.6 Transaction End (TE)
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name: TE
anonymous parameters: xid, result
named parameters: [error]
payload: no
senders: both OPES processor and callout server
Indicates the end of the OCP transaction. The recipient MUST free
associated state. The destruction of the state ensures that future
messages referring to the same transaction, if any, will be ignored.
This message terminates the life of the transaction identifier (xid).
An OCP agent MUST send a Transaction End (TE) message immediately
after it makes a decision to send no more messages related to the
corresponding transaction. Violating this requirement may cause, for
example, unnecessary delays and even timeouts for OPES processors
that rely on this end-of-file condition to proceed.
9.7 Application Message Start (AMS)
name: AMS
anonymous parameters: xid, am-id
named parameters: none
payload: no
senders: both OPES processor and callout server
Indicates the start of processing of an application message. The
recipient MUST either start processing the application message (and
maintain its state) or refuse further processing with an
'app-message-end' message. The recipient MUST maintain the state
until it receives a message indicating the end of application message
processing or until it terminates the processing itself.
When 'app-message-start' message is sent to the callout server, the
callout server usually sends an app-message-start message back,
announcing the creation of an adapted version of the original
application message. Such response may be delayed. For example, the
callout server may wait for more information to come from the OPES
processor.
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When 'app-message-start' message is sent to the OPES processor, an
OPTIONAL "services" parameter describes callout services that the
server MAY apply to the application message. Usually, the "services"
value matches what was asked by the OPES processor.
This message introduces application message identifier (am-id).
9.8 Application Message End (AME)
name: AME
anonymous parameters: xid, am-id, result
named parameters: [error]
payload: no
senders: both OPES processor and callout server
Informs the recipient that there will be no more data for the
corresponding application message and indicates the end of
application message processing. The recipient MUST free associated
application message state. The destruction of the state ensures that
future messages referring to the same application message, if any,
will be ignored.
An AME (Application Message End) message ends any data preservation
commitments associated with the corresponding application message.
This message terminates the life of the application message
identifier (am-id).
An OCP agent MUST send an Application Message End (AME) message
immediately after it makes a decision to send no more data for the
corresponding application message. Violating this requirement may
cause, for example, unnecessary delays and even timeouts for callout
servers that rely on this end-of-file condition to proceed.
9.9 Data Use Mine (DUM)
name: DUM
anonymous parameters: xid, am-id, offset
named parameters: [As-is: am-id offset], [Kept: offset], [Wont-Use:
used-size], [sizep], [modp], [ack]
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payload: yes
senders: both OPES processor and callout server
This is the only OCP message that may carry application data. There
MUST NOT be any gaps in data supplied by Data Use Mine (DUM) and Data
Use Yours (DUY) messages (i.e., the offset of the next data message
must be equal to the offset plus the payload size of the previous
data message) (XXX: we do not need offset then; should we keep it as
a validation mechanism?) (XXX: document what to do when this MUST is
violated). Zero payload size is permitted and is useful for
communicating predictions without sending data.
When an OPES processor sends a "Kept" parameter, the processor MUST
keep a copy of the attached data (the preservation commitment
starts). The offset parameter specifies the offset of the first OCTET
in the payload (XXX: relative to what? DUM messages may transmit
metadata that is not kept). The first "Kept" offset sent is zero. The
next "Kept" offset sent is the previous "Kept" offset sent plus the
size of the previous "Kept" payload, modulo 2^32. Recipients of
invalid "Kept" parameters, MUST either terminate the corresponding
transaction or MUST not use any "Kept" parameter during the
transaction, including those received before the invalid one. This
requirement helps preserve data integrity when "Kept" optimization is
used by the processor.
If a Wont-Use named parameter is present, is semantics is determined
exactly as for Data Use Yours (DUY) messages.
An "as-is" parameter, sent only by the callout server, MUST specify a
data fragment in the original data flow. The callout server informs
the processor that the attached data is identical to an original data
fragment the processor sent earlier. Identical means that all adapted
OCTETs have the same numeric value as the corresponding original
OCTETs. The "am-id" field MUST correspond to the original application
message identifier for the same transaction. If the parameter does
not specify any original data fragment, the parameter is invalid.
Invalid "as-is" parameters MUST be ignored.
The recipient of an "ack" parameter MUST respond with a 'data-ack'
message. Note that OCP Core does not require these acknowledgments to
successfully exchange data; they are supported for debugging and
similar important applications outside of the Core scope.
9.10 Data Use Yours (DUY)
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name: DUY
anonymous parameters: xid, am-id, kept-offset, kept-size
named parameters: [Wont-Use: used-size]
payload: no
senders: callout server only
Tells the OPES processor to use "kept-size" bytes of preserved data
starting at "kept-offset" offset, as if that data came from the
callout server in a Data Use Mine (DUM) message with payload size
equal to the "kept-size" parameter. The identified data fragment
MUST be under the preservation commitment. If the OPES processor
receives a Data Use Yours (DUY) message for data not under
preservation commitment, the message is invalid.
If a Data Use Yours (DUY) message is invalid, the OPES processor MUST
abort am-id message processing (XXX: document how processing should
be aborted).
If no Wont-Use named parameter is present, the Data Use Yours (DUY)
message terminates preservation commitment (if any) for data below
(kept-offset + kept-size) offset. If a valid Wont-Use named parameter
is present, the DUY message terminates preservation commitment (if
any) for data below (0 + used-size). OPES processor MUST ignore a
Wont-Use parameter with a used-size value below previously received
used-size values.
Note that (0 + used-size) may be less than (kept-offset + kept-size),
indicating that some of the kept data referred to in the DUY message
needs to be preserved. Similarly, (0 + used-size) may exceed
(kept-offset + kept-size), indicating that callout server is not
going to use preserved data that has not been referred to yet. For
example, "Wont-Use: 2147483647" message parameter indicates that the
server is not going to send any more DUY messages.
9.11 Data Pause (data-pause)
name: data-pause
anonymous parameters: xid am-id
named parameters: none
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payload: no
senders: callout server only
Sent by a callout server, the data-pause message informs the OPES
processor that it must stop sending data to the callout server until
the callout server explicitly asks for more data using a 'data-need'
message. Upon receiving a 'data-pause' message, the OPES processor
SHOULD stop sending application message data to the callout server.
If the OPES processor stops sending, it SHOULD send a corresponding
'data-paused' message to the callout server. Until the OPES
processor receives the message, it may continue sending data to the
callout server, of course. Thus, when the callout server sends this
message, it MUST NOT mark the application message as "paused". (XXX:
should we use MUST or MAY instead of SHOULDs above?)
An OPES processor MUST NOT send this message. A callout server MUST
ignore this message.
9.12 Data Paused (data-paused)
name: data-paused
anonymous parameters: xid, am-id
named parameters: none
payload: no
senders: OPES processor only
Sent by an OPES processor, the 'data-paused' message informs the
callout server that there will be no more data for the specified
application message until the callout server explicitly asks for data
using a 'data-need' message. After sending a 'data-paused' message,
the OPES processor MUST stop sending application message data to the
callout server. At that time, there may be still unprocessed data in
the callout server queue, of course. When the callout server receives
the message, it MAY mark the application message as "paused". If the
callout server receives data for a paused message (a violation of the
above MUST), the callout server MAY abort application message
processing.
A callout server MUST NOT send this message. An OPES processor MUST
ignore this message.
9.13 Data Need (data-need)
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name: data-need
anonymous parameters: xid am-id offset
named parameters: [Size-request: size]
payload: no
senders: callout server only
Informs the OPES processor that the callout server needs more
application message data. The "offset" parameter indicates the amount
of data already received.
If a "Size-request" parameter is present, its value is the suggested
data size, and it MAY be ignored by the OPES processor. An absent
"Size-request" parameter implies "any size". The callout server MUST
clear the "paused" state of the application message processing just
before sending this message.
The OPES processor MUST ignore a data-need message if the OPES
processor already sent request data.
An OPES processor MUST NOT send data-need messages (XXX: should we
give an OPES processor the same abilities to pause/resume message
processing that a callout server has?)
9.14 Data ACK (DACK)
name: DACK
anonymous parameters: xid, am-id, offset, size
named parameters: [wont-forward]
payload: no
senders: callout server only
Informs the OPES processor that the corresponding data chunk has been
received by the callout server.
An optional "wont-forward" flag terminates preservation commitment
for the corresponding data, if any. The flag is defined for callout
server 'data-ack' messages only.
Responding with Data ACK (DACK) messages to Data Use Mine (DUM)
(Section 9.9) messages with an "ack" flag is REQUIRED. Responding
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with DACK messages to DUM messages without an "ack" flag is OPTIONAL.
Implementations SHOULD be able to support debugging mode where every
DUM message is acked. (XXX: should we require responses for Data Use
Yours messages as well?)
A 'data-ack' response SHOULD be sent as soon as possible. If the
callout server does not know immediately whether it will forward the
data, it MUST respond without a "wont-forward" flag. If, at any time,
the callout server decides that it will not forward the data, it
SHOULD send a 'data-ack' message with a "wont-forward" flag. Thus,
multiple 'data-ack' messages and unsolicited 'data-ack' messages are
allowed.
Sending of a DACK message means that a complete DUM message has been
received, but does not imply that the data has been processed in any
other way.
The data acknowledgment mechanism has several purposes: to allow OPES
processor to gauge the speed at which the callout server is receiving
data (for optimization purposes); to send back "wont-forward"
notifications; and to assist in debugging OCP communications.
9.15 I Am Here (pong)
name: pong
anonymous parameters: [xid [am-id]]
named parameters: none
payload: no
senders: both OPES processor and callout server
Parameterless form informs the recipient that the sender is still
maintaining the OCP connection. If "xid" or "am-id" identifier(s) are
used, the message informs the recipient that the sender is still
processing the corresponding transaction or an application message.
An 'i-am-here' message MAY be sent without solicitation.
An 'i-am-here' message MUST be sent in response to an 'are-you-there'
request. The response MUST have the same set of "xid" and "am-id"
parameters if those identifiers are still valid. The response MUST
NOT use invalid identifiers.
9.16 Are You There? (ping)
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name: ping
anonymous parameters: [xid [am-id]]
named parameters: none
payload: no
senders: both OPES processor and callout server
Solicits an immediate 'i-am-here' response. If the response does not
use the same set of "xid" and "am-id" parameters, the recipient MAY
assume that missing identifier(s) correspond to OCP transaction or
application message that was not maintained at the time the response
was generated.
The recipient MUST handle an 'are-you-there' request even if
transaction or application message identifiers are invalid from the
recipient point of view. Normally, messages with invalid identifiers
are ignored.
9.17 Negotiation Offer (NO)
name: NO
anonymous parameters: (list of features)
named parameters: [SG: sg-id]
payload: no
senders: both OPES processor and callout server
A Negotiation Offer (NO) message solicits a selection of a single
"best" feature out of a supplied list, using a Negotiation Response
(NR) message. The sender is expected to list preferred features first
when possible. The recipient MAY ignore sender preferences. If the
list of features is empty, the negotiation is bound to fail but
remains valid.
Both OPES processor and callout server are allowed to send
Negotiation Offer (NO) messages. The rules in this section ensure
that only one offer is honored if two offers are submitted
concurrently. An agent MUST NOT send a Negotiation Offer (NO) message
if it still expects a response to its previous offer on the same
connection.
If an OPES processor receives a Negotiation Offer (NO) message while
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its own offer is pending, the processor MUST disregard the server
offer. Otherwise, it MUST respond immediately.
If a callout server receives a Negotiation Offer (NO) message when
its own offer is pending, the server MUST disregard its own offer. In
either case, it MUST respond immediately.
If an agent receives a message sequence that violates any of the
above rules in this section, the agent MUST terminate the connection
with an error.
An optional "SG" parameter assigns the result of negotiation to the
specified service group. If SG is present, the negotiated features
are enabled only for transactions that use the specified service
group ID. An invalid service group identifier makes the entire
Negotiation Offer message invalid.
9.18 Negotiation Response (NR)
name: NR
anonymous parameters: [feature]
named parameters: [SG: sg-id], [Rejects], [Unknowns]
payload: no
senders: both OPES processor and callout server
A Negotiation Response (NR) message conveys recipient reaction to a
Negotiation Offer (NO) request. An accepted offer is indicated by
the presence of a "feature" parameter, containing the selected
feature. If the selected feature does not match any of the offered
features, the offering agent MUST consider negotiation failed and MAY
terminate the connection.
A rejected offer is indicated by omitting the "feature" parameter.
If negotiation offer contains an SG parameter, the responder MUST
include that parameter in the Negotiation Response (NR) message. The
recipient of a Negotiation Response (NR) message without the expected
SG parameter MUST treat negotiation response as invalid.
If negotiation offer lack an SG parameter, the responder MUST NOT
include that parameter in the Negotiation Response (NR) message. The
recipient of a Negotiation Response (NR) message with an unexpected
SG parameter MUST treat negotiation response as invalid.
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When accepting or rejecting an offer, the sender of the NR message
MAY supply additional details via Rejects and Unknowns parameters.
The Rejects parameter can be used to list features that were known to
the NO recipient but could not be supported given negotiated state
that existed when NO message was received. The Unknowns parameter can
be used to list features that were unknown to the NO recipient.
9.19 I Support (i-can)
name: i-can
anonymous parameters: [feature]
named parameters: none
payload: no
senders: both OPES processor and callout server
An I Support (i-can) message is sent in response to a Can You Support
(can-you) question. If the sender supports feature identifier, the
sender MUST respond with a "feature" parameter, set to match actually
supported feature and its attributes, if any. Otherwise, the sender
MUST respond without a "feature" parameter. Note that supported
features attributes of the sender may differ from those in the Can
You Support (can-you) question, indicating a partial match or a
mismatch.
9.20 Can You Support (can-you)
name: can-you
anonymous parameters: feature
named parameters: none
payload: no
senders: both OPES processor and callout server
A Can You Support (can-you) message solicits a declaration of support
for the supplied feature, using an I Support (i-can) message. The
recipient MUST respond immediately.
9.21 I Currently Use (i-do)
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name: i-do
anonymous parameters: feature
named parameters: none
payload: no
senders: both OPES processor and callout server
9.22 Do You Currently Use (do-you)
name: do-you
anonymous parameters: feature
named parameters: none
payload: no
senders: both OPES processor and callout server
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10. Application Protocol Requirements
Not all application protocols can be adapted with OCP. Compiling a
complete list of known limitations is impossible since "application
protocol" is not a well defined term. However, listing known
limitations can help it determining OCP applicability. This section
is not a normative part of the OCP specification.
Application protocol messages must have byte boundaries. OCP can
only handle application messages with the number of bits divisible
by 8.
XXX
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11. IAB Considerations
OPES treatment of IETF Internet Architecture Board (IAB)
considerations [RFC3238] are documented in [XXX].
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12. Security Considerations
This section examines security considerations for OCP. OPES threats
are documented in [XXX-Threat-Doc].
OCP relays application messages that may contain sensitive
information. Appropriate transport encryption can be negotiated to
prevent information leakage or modification (see section XXX on
transport security profile negotiation), but OCP agents may support
unencrypted transport by default. Such default OCP agent
configurations will expose application messages to third party
recording and modification, even if OPES agents themselves are
secure.
OCP implementation bugs may lead to security vulnerabilities in OCP
agents, even if OCP traffic itself remains secure. For example, a
buffer overflow in a callout server caused by a malicious OPES
processor may grant that processor access to information from other
(100% secure) OCP connections, including connections with other OPES
processors.
Careless OCP implementations may rely on various OCP identifiers to
be unique across all OCP agents. A malicious agent can inject an OCP
message that matches identifiers used by other agents, in an attempt
to get access to sensitive data. OCP implementations must always
check an identifier for being "local" to the corresponding connection
before using that identifier.
OCP is a stateful protocol. Several OCP commands increase the amount
of state that the recipient has to maintain. For example, a Create
Service Group (SGC) message instructs the recipient to maintain an
association between a service group identifier and a list of
services.
Implementations that cannot handle resource exhaustion correctly
increase security risks. The following are known OCP-related
resources that may be exhausted during a compliant OCP message
exchange:
OCP message structures: OCP message syntax does not limit the nesting
depth of OCP message structures and does not place an upper limit
on the length (number of OCTETs) of most syntax elements.
concurrent connections: OCP does not place an upper limit on the
number of concurrent connections that a callout server may be
instructed to create via Connection Start (CS) messages.
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service groups: OCP does not place an upper limit on the number of
service group associations that a callout server may be instructed
to create via Create Service Group (SGC) messages.
concurrent transactions: OCP does not place an upper limit on the
number of concurrent transactions that a callout server may be
instructed to maintain via Transaction Start (TS) messages.
concurrent flows: OCP Core does not place an upper limit on the
number of concurrent adapted data flows that an OPES processor may
be instructed to maintain via Application Message Start (AMS)
messages.
Denial of service attacks using OCP may slow a callout server down,
affecting performance of many independent OPES processors and, hence,
user-perceived performance. (XXX: this has nothing to do with OCP and
should be deleted from these specs, right?)
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13. Compliance
This specification defines compliance for the following subjects:
OCP client implementations (OPES processors), OCP server
implementations (callout servers), OCP application profiles, and OCP
extensions. A subject is compliant if it satisfies all applicable
"MUST" and "SHOULD" level requirements. By definition, to satisfy a
"MUST" level requirement means to act as prescribed by the
requirement; to satisfy a "SHOULD" level requirement means to either
act as prescribed by the requirement or have a reason to act
differently. A requirement is applicable to the subject if it
instructs (addresses) the subject.
Informally, OCP compliance means that there are no known "MUST"
violations, and all "SHOULD" violations are conscious. In other
words, a "SHOULD" means "MUST satisfy or MUST have a reason to
violate". It is expected that compliance claims are accompanied by a
list of unsupported SHOULDs (if any), in an appropriate format,
explaining why preferred behavior was not chosen.
Only normative parts of this specification affect compliance.
Normative parts are: parts explicitly marked using the word
"normative", definitions, and phrases containing unquoted capitalized
keywords from [RFC2119]. Consequently, examples and illustrations are
not normative.
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14. To-do
L4+ binding: Mention that transport might be L4 or above
timeouts: document what messages cause what timers to be [re]set.
parameter scope: Document that parameter names have message scope. A
known parameter name in an unknown message does not identify a
known parameter.
name named-paramters: Document names for all named parameters.
header signatures: Current syntax allows for quoting of values that
do not need to be quoted. Named parameter order is also not fixed.
These make digital signatures of headers impossible without
interpretation. Is this a problem?
modified: replace with as-is approach
meta-data format: How/when do OPES processor and callout server agree
on meta-data format and contents? Note that meta-data should
usually describe actual data encoding. Data-encoding may, however,
be also negotiated. How? When?
explain preservation: Add a section explaining data preservation
mechanism.
asis: Can a callout server refer to parts of [copied] data messages
from the OPES processor? If yes, do we need to worry about
fragmentation if yes? If no, will this restriction kill the
optimization for mid-size application messages (the common case?)
that are likely to be passed to the callout server in just one or
two chunks?
dack: Make data acknowledgment mechanism symmetric. Both agents
should be able to request DACK messages. Should we make the
acknowledgment mechanism to work with any OCP message? Merge with
ping/pong mechanism?
flags: Document flag parameter syntax ("0/1" or present/absent).
str vs token: Document somewhere that strings such as "OK" in {200
"2:OK"} result must be encoded as strings, not tokens.
partial: Should we support partial application message exchange
(exchange only a part of the application message)? Who decides
what parts to exchange? Should the callout server be able to ask
which part it wants? How will it describe the part if it has not
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seen the entire message?
loss: Should OPES processor be able to signal loss of data to the
callout server. The current wording assumes that offset is
incremented using sizes of actually received data fragments; if
the processor detects loss it cannot pass that information and can
only hope that the callout server will notice (by interpreting the
data) or will not care (the server may be application- and/or
loss-agnostic; e.g., a logging or billing server)
break: allow a callout server to get out of the processing loop
without losing the data. Add a i-want-out server message.
xact boundary: Document that transactions cannot cross connections,
but see "fast track" todo item.
fast track: Document messages that may be sent on alternative
connections. Require other-connections messages to be duplicated
on the primary connection.
modp: Min and max values (0 and 100) should be "commitments" rather
than "probabilities".
transactions-end: Decide whether we need a 'transactions-end' message
to terminate multiple transactions efficiently. Is terminating a
connection good enough?
error: Do we need this flag or should we use result codes to relay
the same meaning?
abort negotiation: Should we let the other side affect the abort
decision on OPES level? Perhaps the callout server is doing some
logging or accounting and MUST see every byte received by the OPES
processor, even if the application message is aborted by the
processor. Should we add some kind of 'xaction-need-all' message?
Or should we assume that the dispatcher always knows callout
server needs and vice versa?
proxying Can OCP be proxied above transport layer? Perhaps to
implement parts of a given service, transparently to the OPES
processor?
normative IDs: To be normative, OPES Internet-Drafts must be replaced
with corresponding RFCs when the latter are published.
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Appendix A. Acknowledgements
The author gratefully acknowledges the contributions of: Abbie Barbir
(Nortel Networks), Oskar Batuner (Independent Consultant), Karel
Mittig (France Telecom R&D), Markus Hofmann (Bell Labs), Hilarie
Orman (The Purple Streak), Reinaldo Penno (Nortel Networks), Martin
Stecher (Webwasher) as well as an anonymous OPES working group
participant.
Special thanks to Marshall Rose for his xml2rfc tool.
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Appendix B. Change Log
Internal WG revision control ID: $Id: ocp-core.xml,v 1.13 2003/08/28
03:58:28 rousskov Exp $
head-sid15
* Removed leftovers of data-have message name. Use Data Use Mine
instead (Karel Mittig).
* Anonymized named parameters and removed currently unused "rid"
parameter in ping and pong messages (Karel Mittig).
* Renamed DUM.please-ack to "DUM.ack" (Karel Mittig). More work
is needed to polish and simplify acknowledgment mechanism.
head-sid14
* Documented known resource-exhaustion security risks.
* Polished compliance definition. Avoid two levels of compliance.
head-sid13
* Added SG parameter to Negotiation Offer (NO) and Negotiation
Response (NR) messages to limit the result of negotiations to
the specified service group. Still need to document SG-related
logic in the Negotiation section.
* Removed "services" parameter from Transaction Start (TS)
message because we have to rely on service groups exclusively,
because only service groups can have negotiated application
profiles associated with them.
* Replaced data-id parameter with "Kept: kept-offset" and
"Wont-Use: used-size" parameter. We probably need octet-based
granularity, and old data-id only offered fragment-based
granularity.
* Made AME and TE messages required.
* Documented result parameter syntax and two result codes: 200
(success) and 400 (failure).
* Added optional "result" parameter to CE.
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head-sid12
* Fixed BNF to remove extra SP and "," in front of structure and
list values.
* Fixed the type of "id" field in a "service" structure.
* Documented "sg-id" parameter.
* Renamed "copied" to "data-id" so that it can be used by both
agents. An OPES processor uses named "Copied: data-id"
parameter and a callout server uses anonymous "data-id"
parameter (instead of previously documented "copy-am-offset").
* Removed "rid" parameter from Negotiation Offer (NO) message as
unused.
* Removed "size" parameter from messages with payload since
payload syntax includes an explicit size value.
* Renamed Data Have (DH) message to Data Use Mine (DUM) message
to preserve the symmetry with Data Use Yours (DUY) message and
to prepare for possible addition of Data Check Mine (DCM)
message.
* Finished phasing out the "modified" message parameter.
* Added an "As-is" named-parameter to mark adapted pieces of data
identical to the original.
* Replaced a huge "message nesting" figure with a set of short
specific rules illustrating the same concept. Added a new
"Exchange Patterns" subsection to accommodate the rules and
related matters. The figure was not clear enough. Hopefully,
the rules are.
head-sid10
* Removed the concept of OCP connection as a group of messages
sharing the same group of callout services. Now there is no
difference between OCP connection and transport connection.
* Added a concept of a Service Group, which is a list of services
with an identifier, for now. A given Service Group is
referenced by the creating/destroying side only, to prevent
destruction synchronization.
* Removed Connection Services (CSvc) message.
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* Removed connection priority until proven generally useful. Can
be implemented as an extension.
head-sid9
* Added Negotiation and Capability Inquiry sections.
* Deleted data-end message because AME (Application Message End)
already does the same thing and because there is no data-start
message.
* Deleted meta-* messages. Data-* messages are now used for both
metadata and data since OCP does not know the difference, but
must provide the same exchange mechanism for both.
* Use a single message name (short or long, depending on the
message) instead of using full and abbreviated versions and
trying to enforce abbreviations on the wire. Be more consistent
in creating short message names.
* Resurrected OCP scope figure based on popular demand.
* Applied Martin Stecher comments dated 2003/05/30.
head-sid8
* Added structure and list values to ABNF syntax.
* Messages with multiple equally-named parameters are
semantically invalid.
* Added types for message parameters.
* Started replacing complicated, error-prone, and probably mostly
useless "modified" parameter with a clear and simple "as-is"
parameter.
* Converted parameter descriptions from list items to
subsections.
* OCP syntax requires one or two character lookups to determine
the next message part. Fixed a comment for implementors saying
that one lookup is always sufficient.
head-sid7
* Mentioned TCP/IP/Internet as assumed transport/network, with
any other reliable connection-oriented transport/network usable
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as well. We do not document how OCP messages are mapped to TCP
but it should be obvious. See Overall Operation section.
* Applied Martin Stecher's corrections to OCP message syntax and
definitions of messages.
* Restricted full message name use to documentation, debuggers,
and such. The differences in abbreviated and full name usage
still need more consideration and polishing.
* IAB Considerations section now refers to the future opes-iab
draft.
head-sid6
* Added OCP message syntax. Reformatted message descriptions to
match new syntax concepts.
* Started adding meta-have message to exchange metadata details.
Removed negotiation messages for now (posted new messages to
the list for a discussion).
* Added Security Considerations section (based on Abbie Barbir's
original text).
head-sid4
* Changed document labels to reflect future "WG draft" status.
* Added Acknowledgments section.
* Added "Core" to the title since we expect application specific
drafts to follow and because this document, even when complete,
cannot specify a "working" protocol without
application-specific parts. This change is still debatable.
* Added reference to required future application-specific specs
in the Introduction.
* Moved all rant about irrelevance of application protocols
proxied by an OPES processor to the "Application proxies and
OCP scope" section. Removed "processor input" and "processor
output" terms. No reason to define a new term when its only
purpose is to document irrelevance?
* Moved "OCP message" definition to the terminology section.
* Clarified "application message" definition based on recent WG
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discussions and suggestions. There seems to be consensus that
"application message" is whatever OPES processor and callout
server define or agree on, but OCP needs some minimal structure
(content + metadata)
* Synced data and metadata definitions with the new "application
message" definition.
* Simplified "Overall Operation" section since it no longer need
to talk about irrelevance of application protocols proxied by
an OPES processor.
* Illustrated nesting/relationship of key OCP concepts
(application message, OCP message, transaction, connection,
transport connection, etc.). The figure needs more work.
* Listed all from-processor and from-server OCP messages in one
place, with references to message definitions.
* Added "services" message parameter, assuming that more than one
service may be requested/executed with one transaction.
* Gave callout server ability to report what services were
actually applied (see "services" parameter definition).
head-sid3
* clarified application message definition and OCP boundaries by
introducing three kinds of "applications": processor input,
processor output, and OCP application
* made "Overall Operation" a top-level section since it got long
and has its own subsections now; lots of editorial changes in
this sections, new figures
* added illustrations of OCP messages, transactions, and
connections
head-sid2
* introduced a notion of meta-data to both simplify OCP and make
OCP agnostic to application meta-data; previous approach
essentially assumed existence of a few common properties like
protocol name or application message source/destination while
not allowing any other properties to be exchanged between OCP
agents); specific meta-data format/contents is not important to
OCP but OCP will help agents to negotiate that format/contents
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* removed wording implying that OCP adapts application messages;
OCP only used to exchange data and meta-data (which facilitates
adaptation)
* changed most of the definitions; added definitions for
meta-data, original/adapted flows, and others
* split 'data-pause' message into 'data-pause' request by the
callout server and 'data-paused' notification by the OPES
processor; fixed "paused" state management
* added motivation for data acking mechanism
* replaced "am-proto", "am-kind", "am-source", and
"am-destination" parameters with "meta-data"
* replaced SERVER and CLIENT placeholders with "callout server"
and "OPES processor"
* added editing marks
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Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[RFC2396] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396,
August 1998.
[I-D.ietf-opes-architecture]
Barbir, A., "An Architecture for Open Pluggable Edge
Services (OPES)", draft-ietf-opes-architecture-04 (work in
progress), December 2002.
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Informative References
[I-D.ietf-opes-protocol-reqs]
Beck, A., "Requirements for OPES Callout Protocols",
draft-ietf-opes-protocol-reqs-03 (work in progress),
December 2002.
[I-D.ietf-opes-scenarios]
Barbir, A., "OPES Use Cases and Deployment Scenarios",
draft-ietf-opes-scenarios-01 (work in progress), August
2002.
[I-D.ietf-fax-esmtp-conneg]
Toyoda, K. and D. Crocker, "SMTP Service Extension for Fax
Content Negotiation", draft-ietf-fax-esmtp-conneg-06 (work
in progress), February 2003.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Nielsen, H.,
Masinter, L., Leach, P. and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC3080] Rose, M., "The Blocks Extensible Exchange Protocol Core",
RFC 3080, March 2001.
[RFC3238] Floyd, S. and L. Daigle, "IAB Architectural and Policy
Considerations for Open Pluggable Edge Services", RFC
3238, January 2002.
Author's Address
Alex Rousskov
The Measurement Factory
EMail: rousskov@measurement-factory.com
URI: http://www.measurement-factory.com/
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Rousskov Expires February 25, 2004 [Page 55]
