Information Technology Reference
In-Depth Information
3 COPS and COPS-PR Protocols Supporting XML-Encoded Data
The proposed representation of low-level policy needs that the COPS and COPS-PR
protocols support XML-encoded data. These protocols are independent of the type of
policy carried, but they assume a data model based on the concept of PIB.
3.1 XML Encoded Data in the COPS and COPS-PR Messages
The COPS object descriptions use BER as the encoding type. But this encoding type
is not unique, as additional encodings can be used. This is the case of XML.
COPS encapsulates data in request messages, decision messages and report mes-
sages. Request messages include the Named ClientSI (Named Client Specific Infor-
mation) object for relaying specific information about the PEP. Decision messages
made by the PDP send the Named Decision Data object in response to configuration
requests. And report messages encapsulate Named ClientSI for reporting information
from the PEP to PDP. The Named ClientSI and Named Decision Data objects are
composed of one or more bindings. Each binding associates a PRID (Provisioning In-
stance Identifier) object and an EPD (Encoded Provisioning Instance Data) object.
The PPRID (Prefix PRID) is used in the Remove Decisions and can also compose a
Named Decision Data.
Furthermore, the PRID, PPRID and EPD objects encapsulate S-Num and S-Type
identifier. The S-Num identifies the general purpose of the object, and the S-Type de-
scribes the specific encoding used for the object. The IETF documents usually use the
BER as the encoding type (S-Type = 1).
In this context, we have defined an additional encoding to carry XML string-based
XPath and XER as encoding type; the new value that we have assigned is S-Type = 2.
We have also take the convention that the PRID and PPRID objects make use of
XPath, and the EPD objects make use of XER encoding.
Provisioning Instance Identifier (PRID)
This object carries the identifier of a Provisioning Class (PRC) Instance. This identi-
fier is encoded following the BER rules as a SNMP Object Identifier (OID). PRID is
the OID of the Provisioning Class plus the Instance Identifier (InstanceId).
We propose to use XPath for XML encoding. This path has two parts: the first one
identifies the PRC and the second one identifies the particular instance of this PRC.
Prefix PRID (PPRID)
PPRIDs are only used in the Remove Decisions command to identify a group of in-
stances with the same PRID prefix and to avoid a sequence of individual Remove De-
cisions. PPRID is encoded following the BER rules as a SNMP Object Identifier
(OID) like the PRID object commented before.
We also propose to use XPath for encoding PPRID in XML. For example, a PRID
equal to the following path:
//iso/org/dod/internet/pib/frameworkPib/
frwkBasePibClasses/frwkPibIncarnationTable/FrwkPibIncarnationEntry/*
identifies
all instances of the PRC called PIB Incarnation Table of the PIB Framework.
