COPS Usage for Differentiated Services December 1998
Network Working Group Francis Reichmeyer
Internet Draft Kwok Chan
draft-ietf-rap-cops-ds-01.txt Bay Networks, Inc.
Expiration Date: May 1999 David Durham
Raj Yavatkar
Intel
Silvano Gai
Keith McCloghrie
Cisco Systems, Inc.
Shai Herzog
IPHighway
December 1998
COPS Usage for Differentiated Services
Status of this Memo
This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas,
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Abstract
There is a clear need for relatively simple and coarse methods of
providing differentiated classes of service for Internet traffic, to
support various types of services, and specific business
requirements. The IETF has chartered the Differentiated Service WG to
define the differentiated services architecture and a common language
for differentiated services.
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COPS Usage for Differentiated Services December 1998
In parallel, the IETF RSVP Admission Policy (RAP) WG has defined the
COPS (Common Open Policy Service) protocol [COPS].
This document describes enhancements to the Common Open Policy
Service (COPS) protocol to support policy services in a
Differentiated Services (DiffServ) environment. Further modifications
to COPS for DiffServ may be proposed in the future, but what is
presented here is thought to be the minimum necessary additions.
Table of contents
1. Terminology ......................................................3
2. Introduction .....................................................4
2.1 Basic Model...................................................6
2.2 Interaction between the PDP and the PEP.......................8
3. The definition of the Policy Tree ................................8
3.1 Description of the Policy Tree................................9
3.2 Operations Supported On a PRI................................10
3.3 PIB general information......................................10
3.4 An example of a PIB..........................................10
4. COPS DiffServ Client Data .......................................13
4.1 Policy Identifier (PRID).....................................13
4.2 BER encoded Policy instance Data (BPD).......................14
4.3 DiffServ Decision Data.......................................14
4.4 DiffServ Request Data........................................15
4.5 DiffServ Report Data.........................................15
4.5.1 Successfully Installed/Removed Data .....................15
4.5.2 Unsuccessfully Installed/Removed Data ...................15
4.5.3 Accounting Data .........................................16
5. Message Content .................................................16
5.1 Request (REQ) PEP -> PDP...................................16
5.2 Decision (DEC) PDP -> PEP..................................17
5.3 Report State (RPT) PEP -> PDP..............................18
6. Common Operation ................................................18
7. Fault Tolerance .................................................20
8. Security ........................................................21
9. References ......................................................21
10. Author Information .............................................22
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1. Terminology
o ACL: Access Control List.
o ClientSI: Client Specific Information Object.
o COPS (Common Open Policy Service): client/server model for
supporting policy control [COPS];
o Object: this term is used in the same sense as in COPS
specification. An object is identified by its C-num and C-type.
o PDP (Policy Decision Point): a network entity where policy
decisions are made.
o PEP (Policy Enforcement Point): network device where policy
decisions are enforced.
o Policy Rule: policy information specified by the PDP to be enforced
at the PEP.
o PRC (Policy Rule Class): a type of policy rule data item. In object
oriented terminology this is equivalent to a class. It inherits
from PRC. A PRC defines a vector of attributes. Each attribute has
a syntax type that is either primitive or refined. It also
overrides the READ and WRITE methods and defines new error sub-
codes.
o PRI (Policy Rule Instance): an instance of a PRC. Potentially there
are multiple instances of the same PRC. The value of a PRI consist
of a vector of values, one value for each attribute in the PRC's
vector of attributes.
o PII (Policy Instance Identifier): one or more of the PRC attributes
the values of which are used as part of the identification of a
PRI.
o PIB (Policy Information Base): policy objects are accessed via a
virtual information store, termed the Policy Information Base or
PIB. Objects in the PIB are defined using a subset of Abstract
Syntax Notation One (ASN.1) [ASN1].
o PRID (Policy Rule IDentifier): the name which identifies a
particular PRI or PRC. It has a hierarchical structure of the form
1.3.4.2.7, where the first part identifies the PRC (i.e., 1.3.4)
and the last part is the value of the PII (Policy Instance
Identifier), which identifies the instance (i.e. 2.7). The PII is
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COPS Usage for Differentiated Services December 1998
null in the case of a PRC. PRIDs are represented as a BER encoded
oids (Object Identifiers).
o BPD: BER (ASN.1 [ASN1] Basic Encoding Rule [BER]) encoded Policy
Instance Data.
2. Introduction
The Common Open Policy Service (COPS) protocol is a query response
protocol used to exchange policy information between a network policy
server and a set of clients [COPS]. COPS is being developed within
the RSVP Admission Policy Working Group (RAP WG) of the IETF,
primarily for use as a mechanism for providing policy-based admission
control over requests for network resources [RAP].
The underlying assumption in the RAP framework is that applications
or end systems use the RSVP [RSVP] signaling protocol to communicate
Integrated Services (IntServ) reservation requests to the network
nodes along the path of a flow. These reservation requests carry
necessary flow specifications and requests for a flow to receive one
of the defined Integrated Services, Controlled Load or Guaranteed. In
the IntServ model, the RSVP messages themselves contain all the
necessary information needed at the networking device to classify and
service the flow [RSVP]. This information includes the session
identifier (source and destination addresses, port numbers, and
transmission protocol), flowspec token bucket parameters, and
requested service.
Edge Device Policy Server
+--------------+ +-----------+
| | | |
| | COPS | |
| +-----+ | REQ() | +-----+ |
RSVP | | |----|----------|->| | |
--------|-->| PEP | | | | PDP | |
| | |<---|----------|--| | |
| +-----+ | COPS | +-----+ |
| | DEC() | |
+--------------+ +-----------+
Figure 1: COPS with RSVP/IntServ
As shown in Figure 1, the network device contacts a Policy Decision
Point (PDP) to make the policy-based admission control decision. The
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COPS Usage for Differentiated Services December 1998
PDP is simply required to return a Decision, such as "accept" and the
network device acts as a Policy Enforcement Point (PEP) and uses the
session information and IntServ service parameters to classify and
service the packets belonging to the flow.
Providing policy services in a DiffServ environment requires some
different assumptions about the admission control mechanisms used in
the network. First, there might be no explicit dynamic signaling from
sources of traffic requesting a particular service, as in the case of
an IntServ network. Network resources are provisioned based on static
SLAs (Service Level Agreements) at network boundaries. Second, where
requests for allocation of resources to differentiated services are
used, they may arrive at the PDP from network entities other than the
PEP. Examples of such sources include attached users requesting
network services via a web interface into a central management
application, or H.323 gatekeeper requesting resources on behalf of a
user for a video conferencing application, as shown in Figure 2.
+----------+
Edge Device Policy Server | H.323 |
+--------------+ +-----------+ |Gatekeeper|
| | | | | |
| | | | +----------+
| ----- | COPS | ----- | |
| | | | DECs() | | | | |
| | PEP |<---|----------|--| PDP |<----------+
| | | | | | | | Service
| ----- | | ----- | Request
| | | |
+--------------+ +-----------+
Figure 2: COPS Example with DiffServ
Requests of this sort still require some policy decision to be made
to ensure the requesting user/application has permission to use the
requested services and that the resources are available. Once the
decision is made, the PDP must configure one or more PEPs to allocate
necessary resources for services requested. In addition, the PDP may
also pass to the PEP provisioning decisions about resources related
to flows of a more static nature, such as long-term SLAs established
across boundaries of adjacent ISP networks.
In summary, the interaction between the PDP and PEP is different in
at least two respects from that in the case of the IntServ
environment. First, the resource provisioning requests may originate
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COPS Usage for Differentiated Services December 1998
at places other than a PEP. Second, once the PDP makes a policy
decision to allocate resources for a service class or a flow
aggregate, it must pass sufficient information (such as packet
classification filters, traffic shaper parameters) in the decision
message to the PEPs so that PEPs can enforce policy decisions. This
draft describes the usage of the COPS protocol for communicating this
information between DiffServ clients (PEPs) and the policy servers
(PDPs).
2.1 Basic Model
Figure 2 shows a sample network configuration for a DiffServ
environment. Edge routers and boundary routers are located at the
boundary of DiffServ domains as described in [Nichols]. The BB/PS is
responsible for admission control functions and resource
provisioning.
+-----+ +-----+
| BB/ | | BB/ |
| PS | | PS |
+-----+ +-----+
\ |
| /
| /
/ Stub \ / Transit \ / Stub \
/ Network \ / Network \ / Network \
+---+ | +---\ /---+ +---\ /---+ | +---+
|Tx |-| |ER1|---|BR1| |BR2|---|ER2| |-|Rx |
+---+ | +---/ \---+ ---/ \---+ | +---+
\ / \ / \ /
\ / \ / \ /
Figure 3: Sample DiffServ Network Configuration
In the COPS model, the PDP is part of the bandwidth broker/policy
server that manages policy information and resources within a
DiffServ domain. Both edge routers and boundary routers act as PEPs
and communicate with BB/PS using COPS for exchange of policy
information. The internal organization of the bandwidth broker
functionality and policy functionality may vary and the policy server
and BB may be separate entities. In that case, either the BB or the
PS may communicate with the edge devices. The BB, upon receiving COPS
messages from the PEP, would consult the policy server to make its
final admission control decision. Similarly, if the PS receives COPS
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COPS Usage for Differentiated Services December 1998
messages directly from PEP, the PS would consult the BB to verify
available resources before making a final admission control decision.
To allow for use of COPS for DiffServ specific communication and to
distinguish DiffServ usage from other uses of COPS, we have added a
new client type to COPS (client type = DiffServ client). It is
possible for an edge device to contain both a COPS-DS and a COPS-RSVP
client. Each COPS clients can communicate with different PDPs, or
they can connect to the same PDP which supports both client types, as
shown in Figure 4.
Edge Device
+-----------------+
| | PS/BB
| +---------+ | +-------------+
| | | | | |
RSVP | |COPS-RSVP| | COPS-RSVP | +-----+ |
<-------|-->| Client |<--|-----------|-->| | |
| | | | | | | |
| |---------| | | | PDP | |
| | | | | | | |
| |COPS-DS |<--|-----------|-->| | |
| | Client | | COPS-DS | +-----+ |
| | | | | |
| +---------+ | +-------------+
| |
+-----------------+
Figure 4: COPS DS and RSVP Clients in Same Edge Device
Allowing multiple COPS client types to co-exist in a single PEP means
that the same PDP can coordinate policy decisions in an environment
where, say, both RSVP/IntServ and DiffServ QoS mechanisms need to be
managed. For example, in a stub network that uses IntServ with RSVP
signaling internally and is connected to a DiffServ transit network
externally. In this case, the edge device that connects the stub
network to the transit network may require policy decisions from the
same PDP for both RSVP requests as well as for policy rules to
enforce on the egress (DiffServ is with respect to the ingress)
interface.
The two decisions may very well need to be coordinated to ensure
proper provisioning and allocation of network resources. For example,
the decision of whether to admit an RSVP flow, or not, would depend
on the provisioning policy in place at the egress interface where the
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COPS Usage for Differentiated Services December 1998
flow is leaving the stub network, and vice versa. The issue of
combining IntServ and DiffServ to provide an end-to-end QoS solution
is discussed in the draft [E2E]. Also, the RSVP WG is currently
planning on addressing the use of RSVP within the differentiated
services QoS model.
2.2 Interaction between the PDP and the PEP
When a device boots, it opens a COPS connection to its Primary PDP.
When the connection is established, the PEP sends information about
itself to the PDP in the form of a configuration request. This
information includes client specific information (hardware type,
software release, configuration information). During this phase the
client also specifies the maximum COPS-DS message size supported (see
Section 3.3).
In response, the PDP downloads all provisioned policies which are
currently relevant to that device. On receiving the provisioned
policies, the device maps them into its local QoS mechanisms, and
installs them. If conditions change at the PDP such that the PDP
detects that changes are required in the provisioned policies
currently in effect at the PEP, then the PDP sends the changes
(installs/deletes) in policy to the PEP, and the PEP updates its
local QoS mechanisms appropriately.
If, subsequently, the configuration of the device changes (board
removed, board added, new software installed, etc.) in ways not
covered by policies already known to the PEP, then the PEP sends this
new information to the PDP. On receiving this new information, the
PDP sends to the PEP any additional provisioned policies now needed
by the PEP.
3. The definition of the Policy Tree
This section defines data format for the DiffServ client specific
information carried in the Decision, Request ClientSI, and Report
ClientSI objects. DiffServ client specific data may be defined for
the other objects in the future. COPS-DS data is represented by a
policy tree containing Policy Rule Classes (PRCs) and Instances of
those classes (PRIs), as shown in Figure 5.
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-------+-------+----------+---PRC--+--PRI
| | | +--PRI
| | +---PRC-----PRI
| +---PRC--+--PRI
| | +--PRI
| | +--PRI
| | +--PRI
| | +--PRI
| +---PRC-----PRI
+---PRC---PRI
Figure 5: Example of a Policy Tree
The policy tree is based on SMI and MIBs. COPS for RSVP does not need
a policy tree, since the information exchanged has a simple format
and is defined by existing RSVP objects. COPS for DiffServ needs much
more structure, since it needs to represent policies, mappings, ACLs,
interfaces etc.
PRIs (Policy Rule Instances) and PRCs (Policy Rule Classes) have
names called PRIDs (Policy Rule IDentifiers). PRIDs have a
hierarchical structure of the form 1.3.4.2.7, where the first part
identifies the PRC (e.g., 1.3.4) and the last part identifies the
instance (e.g. 2.7).
The policy tree names all the policy rule classes and instances and
this creates a common view of the policy organization between the
client (PEP) and the server (PDP). Therefore, when the PEP receives
data from the PDP, the data itself specifies what a PEP is supposed
to do with the data. The current granularity of access, i.e., the
atomicity of replacement, is proposed as a vector of values.
Note that the PRCs/PRIs in the above diagram are each a vector of
values. This proposal is that the hierarchy of PRCs/PRIs is for
benefit of human understanding, not for programmatic understanding,
or inheritance.
3.1 Description of the Policy Tree
The Policy Tree is described using SMI and PIBs. SMI and PIBs are
defined based on the ASN.1 data definition language [ASN1]. To
simplify the implementation and re-use the SNMP encoding/decoding
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COPS Usage for Differentiated Services December 1998
code, the representation of the policy information on the wire must
follow BER both for the PRID and for the BPD [BER].
3.2 Operations Supported On a PRI
The following operations are supported on a PRI:
o Install - creates a new instance of a PRC, i.e. a new PRI, or
modifies an existing instance. The instance is automatically
enabled. Parameters to this operation are a PRID (see Section 4.1)
and an "BPD (BER encoded Policy instance Data)" containing the
value to assign to the new PRI see (Section 4.2). The BPD specifies
all the attributes of the new PRI.
o Delete - This operation is used to delete an instance of a PRC. The
parameter is a PRID (see Section 4.1).
3.3 PIB general information
The PIB has a branch that contains general information. Examples of
information stored in this branch are:
o TTL (Time To Live): a period of time in seconds. In the event the
PEP looses the COPS-DS connection with the PDP, it tries to re-
establish the connection with the primary and secondary PDPs. If
this fails for a period of time greater than the TTL, the DS
policies are discarded. The TTL specified in this branch is the
default TTL and may be overridden by TTLs present in specific
branches. A TTL = 0 means infinite.
o MCMS (Maximum COPS-DS Message Size): a message size in bytes. The
COPS-DS Client-Open ClientSI MUST specify the MCMS supported by the
client. This value must be in the range 4KB - 64KB.
o Interface to be provisioned.
o Capability information: This may include what filters the PEP
supports, what kind of profiles or dispositions it can perform.
3.4 An example of a PIB
This section contains a simple example of a PIB describing a simple
set of filters for IP packets. Each filter is able to match either
the source IP address, the destination IP address or both. This
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example is provided only for the benefit of understanding how a PIB
is structured. It is not necessarily supposed to describe any actual
policy data.
policyFilterPIB OBJECT IDENTIFIER ::= { policyPIB 1 }
ipHeaderFilterTable OBJECT-TYPE
SYNTAX SEQUENCE OF IpHeaderFilterEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION "This table contains a simple ACL, i.e. one or
more IP filters."
::= {policyFilterPIB 1}
ipHeaderFilterEntry OBJECT-TYPE
SYNTAX IpHeaderFilterEntry
MAX-ACCESS write-only
STATUS current
DESCRIPTION "Each row of the table has four columns. The
ipHeaderFilterIndex uniquely identifies a particular IP
filter. The ipHeaderFilterMatchType specifies the type of
match (source only, destination only, source and destination).
The ipHeaderFilterSourceAddress and
ipHeaderFilterDestinationAddress contain the source and
destination IP addresses."
INDEX {ipHeaderFilterIndex}
::= {ipHeaderFilterTable 1}
IpHeaderFilterEntry ::= SEQUENCE {
ipHeaderFilterIndex INTEGER,
ipHeaderFilterMatchType BITS,
ipHeaderFilterSourceAddress IpAddress,
ipHeaderFilterDestinationAddress IpAddress
}
ipHeaderFilterIndex OBJECT-TYPE
SYNTAX INTEGER
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION "The index of the table, used to identify each
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individual IP filter"
::= {ipHeaderFilterEntry 1}
ipHeaderFilterMatchType OBJECT-TYPE
SYNTAX BITS {
matchSource (0),
matchDestination (1)
}
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION "This field indicates which one or more of the
addresses are required to match the corresponding addresses
of the IP packet."
::= {ipHeaderFilterEntry 2}
ipHeaderFilterSourceAddress OBJECT-TYPE
SYNTAX IpAddress
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION "IP source address to be matched against the
packet in the event the ipHeaderFilterMatchType has the
corresponding bit set.
::= {ipHeaderFilterEntry 3}
ipHeaderFilterDestinationAddress OBJECT-TYPE
SYNTAX IpAddress
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION "IP destination address to be matched against the
packet in the event the ipHeaderFilterMatchType has the
corresponding bit set.
::= {ipHeaderFilterEntry 4}
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4. COPS DiffServ Client Data
The COPS-DS extensions define a new client type:
Client Type = 2; DiffServ Client
DiffServ specific information is sent in a COPS message containing a
Common Header with the DiffServ Client type specified:
0 1 2
3
+----------------+----------------+----------------+----------------+
| Version| //// | Op Code | Client Type = 0x02 |
+----------------+----------------+----------------+----------------+
| Message Length |
+----------------+----------------+----------------+----------------+
The COPS protocol specification defines several objects which may
carry client specific information between PDP and PEP:
o Context Object (Context)
o Reason code Object (Reason code)
o Decision Object (Decision)
o Error Object (Error)
o Client Specific Info Object (ClientSI) which includes:
o Request ClientSI
o Report ClientSI
o Client-Open ClientSI
4.1 Policy Identifier (PRID)
This object is used to carry the PRID of the Policy Rule Instance to
be installed or deleted.
0 1 2 3
+----------------+----------------+----------------+----------------+
| Length | Type = PRID |
+----------------+----------------+----------------+----------------+
| Policy Rule Identifier |
+----------------+----------------+----------------+----------------+
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4.2 BER encoded Policy instance Data (BPD)
This object is used to carry the value of a Policy Data Instance to
be installed, It contains an BER coding of the Policy Data Instance
[BER].
0 1 2 3
+----------------+----------------+----------------+----------------+
| Length | Type = "BER type" |
+----------------+----------------+----------------+----------------+
| BER Encoded PRI Value |
+----------------+----------------+----------------+----------------+
4.3 DiffServ Decision Data
The DiffServ Named Decision Data (<Decision: Named Data>, see Section
5.2) is composed of one or more bindings. Each binding associates a
PRID object and an BPD object. The PRID object is always present, the
BPD object MUST be present in the case of an install decision and
MUST NOT be present in the case of a delete decision.
The BPD object contains the value to be assigned to the PRI that is
created or updated.
The DiffServ specific decision data uses the following format:
C-Num = 7
C-Type = 5
<Decision: Named Data> ::= <Install Decision> |
<Remove Decision>
This depends from the <Decision: Flag>, see Section 5.2.
<Install Decision> :: = <Binding(s)>
<Binding(s)> ::= <Binding> <Binding(s)> |
<Binding>
<Binding> ::= <PRID> <BPD>
<Remove Decision> ::= <PRID(s)>
<PRID(s)> ::= <PRID> <PRID(s)> |
<PRID>
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Please note that the delete has the capability of deleting an entire
table with a single operation.
4.4 DiffServ Request Data
The diffServ Configuration request will utilize the COPS Named
ClientSI (C-Num=10 C-Type=2) object to carry the same bindings as
described above. The DiffServ request Named ClientSI data has the
following format:
<ClientSI: Named> ::= <DiffServ Request Data>
<DiffServ Request Data (Named ClientSI)> ::= <Binding(s)>
4.5 DiffServ Report Data
DiffServ specific report data is used in the RPT message. The format
of the report data is dependant on the value of the accompanying COPS
Report Type object. Report types can be Installed/Removed or
NotInstalled/NotRemoved indicating to the PDP that a particular set
of policies has been either successfully or unsuccessfully
installed/deleted on the PEP.
4.5.1 Successfully Installed/Removed Data
When used with the "Installed" or "Removed" report type, the DiffServ
Named ClientSI object in the Report Message has the following
format:
<ClientSI: Named> ::= <DiffServ Report Data>
<DiffServ report data> ::= [<PRID(s)>]
where <PRID(s)> is the set of PRID successfully installed/deleted.
4.5.2 Unsuccessfully Installed/Removed Data
When used with the "Not Installed" or "Not Removed" report type, the
DiffServ specific report data has the following format:
<ClientSI: Named> ::= <DiffServ Report Data>
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<DiffServ report data> ::= <no-comit(s)>
<no-commit(s)> ::= <no-commit> | <no-commit(s)> <no-commit>
<no-commit> ::= <PRID> <Error> [<Binding(s)>]
where:
<PRID> is the PRID of the unsuccessful install/delete, <Error> is the
error code and <Binding(s)> are conflicting bindings that caused the
error.
The COPS-DS adds also the following two error codes:
- 12 COPS Client Specific Error Code;
- 13 Vendor Specific Error Code.
In the case of "no commit" the PEP MUST report at least the first
error and should report as many errors as possible.
4.5.3 Accounting Data
TBD
5. Message Content
This section describes the COPS messages exchanged between a PEP and
PDP for use with DiffServ policy services.
5.1 Request (REQ) PEP -> PDP
The REQ message is used by COPS DiffServ clients for issuing a config
request to the PDP, as described in the COPS protocol. The Client
Handle is associated with request state originated by the PEP and the
PEP is responsible for notifying the PDP when the Handle is no longer
in use and can be deleted.
The DiffServ request data, defined above, may be included in the
config request form PEP to PDP. Currently, the request data is
defined for carrying configuration/feature negotiation information
from the PEP. This provides the server with information on the types
of policy that the interface can enforce and the types of policy data
the PEP can install.
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The config request message serves as a request from the PEP to the
PDP for any DiffServ configuration data which the PDP may have pre-
defined for the PEP device, such as access control lists, etc., and
any future access data or updates. The pre-configured and any
asynchronous DiffServ configuration data can then be sent to the PEP
over time via decisions, as decided by the PDP. The configuration
information supplied by the PDP is of the consistent client specific
format defined above. The PDP responds to the config request with a
DEC message containing any available configuration information.
<Request> ::= <Common Header>
<Client Handle>
<Context = config request>
[ <interface> ]
<DiffServ request data>
5.2 Decision (DEC) PDP -> PEP
The DEC message (<Decision Message>) is sent from the PDP to a
DiffServ client in response to a config REQ received from the PEP.
The Client Handle must be the same Handle that was received in the
REQ message. The Client Specific Decision Data for DiffServ clients
(<Decision: ClientSI Data>), to be used in the DEC message, is
defined in Section 4.3.
The DEC message is sent as an immediate response to a config request
with the solicited decision flag set, used to carry pre-defined
configuration information set in the PDP, to the PEP. Subsequent DEC
messages may also be sent at any time after the original DEC message
to continue supplying the PEP with additional/updated policy
information. The state carried in the DEC message is correlated with
an initial request state by the Client Handle and provides the
appropriate PRID information.
Each DEC message may contain multiple decisions. This allows with a
single message to install some policies and delete some others. In
general a COPS-DS decision message should contain at most one delete
decision followed by at most one install decision. This is used to
solve a precedence issue, not a timing issue: the delete decision
deletes what it specifies, except those items that are installed in
the same message.
A COPS-DS decision message is also a "transaction", i.e. all the
bindings in a message either succeed or fail. This allow to delete
some policies only if other policies can be installed in their place.
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COPS Usage for Differentiated Services December 1998
For each decision (<Decision>), the PEP performs the operation
specified in the Decision Flags object (<Decision: Flags>) on the
decision data (<Decision: ClientSI Data>]).
<Decision Message> ::= <Common Header>
<Client Handle>
<Decision(s)> | <Error>
<Decision(s)> ::= <Decision> | <Decision(s)> <Decision>
<Decision> ::= <Context>
<Decision: Flags>
[<Decision: Named Data>]
If no configuration state is available when the config REQ is
processed by the PDP, a DEC is sent with the "No Configuration Data"
decision flag set.
In response to a DEC message, the DiffServ client sends a RPT back to
the PDP to inform the PDP of the actual action taken. For example, in
response to a DEC with the "Install" flag (only) set, the PEP informs
the PDP if the decision data can be installed, based on the other
policy data on the device (are there conflicts, etc.).
5.3 Report State (RPT) PEP -> PDP
The RPT message is sent from the DiffServ client to the PDP to report
accounting information from PEP to PDP on request state installed at
the PEP. It is also used as a mechanism to inform the PDP about the
action taken at the PEP, in response to a DEC message. The DiffServ
report data format, as defined above, depends on the Report Type
included in the RPT message.
<Report State> ::= <Common Header>
<Client Handle>
<Report Type>
[<DiffServ report data>]
6. Common Operation
This section describes, in general, typical exchanges between a PDP
and DiffServ COPS client.
First, a connection is established between the PEP and PDP and the
PEP sends a Client-Open message with the Client-Type = 2, DiffServ
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COPS Usage for Differentiated Services December 1998
client. If the PDP supports the DiffServ client, the PDP responds
with a Client-Accept (CAT) message. If the client type is not
supported, a Client-Close (CC) message is returned by the PDP to the
PEP, possibly identifying an alternate server that is known
(believed?) to support the policy for the DiffServ client.
Once the CAT message is received, the client can send requests to the
server. The request a COPS DiffServ client sends to the server is for
configuration information, that is a REQ with "Configuration Request"
set in the context object that identifies a specific interface/module
and any relevant client specific information (see also Section 3.3).
The config request message serves two purposes in COPS-DS. First, it
is a request from the PEP to the PDP for any DiffServ configuration
data which the PDP may have pre-defined for the PEP device, such as
acces control lists, etc. Also, the config request is a request to
the PDP to send asynchronous DiffServ configuration data to the PEP,
as it is received by the PDP. This asynchronous data may be new
policy data or an update to policy data sent previously.
If the PDP has DiffServ QoS policy configuration information for the
client, that information is returned to the client in a DEC message
containing the DiffServ client policy data within the COPS Decision
object. If no filters are defined, the DEC message will simply
specify that there are no filters using the "No Configuration"
Decision Flags object. The PEP MUST specify a client handle (which
can be zero) in the request message. The PDP MUST process the client
handle and copy it in the decision message. This is to prevent the
PEP from timing out the REQ and deleting the Client Handle.
The PDP can then add new policy data or update existing state by
sending subsequent DEC message(s) to the PEP, with the same Client
Handle. The PEP is responsible for removing the Client handle when it
is no longer needed, for example when the interface goes down, and
informing the PDP that the handle is to be deleted.
For DiffServ purposes, access state, and access requests to the
policy server can be initiated by other sources besides the PEP.
Examples of other sources include attached users requesting network
services via a web interface into a central management application,
or H.323 servers requesting resources on behalf of a user for a video
conferencing application. When such a request is accepted, the edge
device affected by the decision (the point where the flow is to enter
the network) must be informed of the decision. Since the PEP in the
edge device did not initiate the request, the specifics of the
request, e.g. flowspec, packet filter, and PHB to apply, must be
communicated to the PEP by the PDP. This information is sent to the
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COPS Usage for Differentiated Services December 1998
PEP using the Decision message containing DiffServ client specific
data objects in the COPS Decision object as specified. Any updates to
the state information, for example in the case of a policy change or
call tear down, is communicated to the PEP by subsequent DEC messages
containing the same Client Handle and the updated DiffServ request
state. Updates can specify that policy data is to be deleted or
installed.
The PEP acknowledges the DEC message and action taken by sending a
RPT message with a "Installed" or "Removed" Report-Type object. This
serves as an indication to the PDP that the requestor (e.g. H.323
server) can be notified that the request has been accepted by the
network. If the PEP needs to reject the DEC operation for any reason,
a RPT message is sent with a Report-Type of value "Not Installed" or
"Not Removed" and optionally a Client Specific Information object
specifying the policy data that was rejected. The PDP can then
respond to the requestor accordingly.
The PEP can report to the PDP the local status of any installed
request state when appropriate. This information is sent in a Report-
State (RPT) message with the "Accounting" flag set. The state being
reported on is referenced by the Client Handle associated with the
request state and the client specific data identifier.
Finally, Client-Close (CC) messages are used to cancel the
corresponding Client-Open message. The CC message informs the other
side that the client type specified is no longer supported.
7. Fault Tolerance
When communication is lost between PEP and PDP, the PEP attempts to
re-establish the TCP connection with the PDP it was last connected
to. If that server cannot be reached, then the PEP attempts to
connect to a secondary PDP, assumed at this time to be manually
configured at the PEP.
When a connection is finally re-established, either with the primary
PDP or a secondary PDP, the PEP should provide the last PDP address
of the PDP for which it is still caching decisions. Based on this
information, the PDP may request the PEP to re-synch its current
state information (SSQ message). If no decisions are being cached on
the PEP (due to reboot or TTL timeout of state) the PEP must not
included the last PDP address information. If after re-connecting,
the PDP does not request the synchronization, the client can assume
the server recognizes it and the current state at the PEP is correct.
Any changes state changes which occurred at the PEP while connection
was lost must be reported to the PDP in a RPT message. If re-
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COPS Usage for Differentiated Services December 1998
synchronization is requested, the PEP should reissue its
configuration requests and the PDP should delete the appropriate PRCs
on the PEP (thus, removing all previous decisions below the PRC,
effectively resetting all state).
While the PEP is disconnected from the PDP, the request state at the
PEP is to be used for policy decisions. If the PEP cannot re-connect
in some pre-specified period of time (some multiple of the keep-alive
time? - TBD), the request state is to be deleted and the associated
Handles removed. The same holds true for the PDP; upon detecting a
failed TCP connection, the time-out timer is started for the request
state associated with the PEP and the state is removed after the
specified period without a connection.
8. Security
The use of COPS for DiffServ introduce no new security issues over
the base COPS protocol. The use of IPSEC between PDP and PEP, as
described in [COPS] is sufficient.
9. References
[COPS] Boyle, J., Cohen, R., Durham, D., Herzog, S., Raja, R.,
Sastry, A., "The COPS (Common Open Policy Service)
Protocol", IETF <draft-ietf-rap-cops-03.txt>, December
1998.
[RAP] Yavatkar, R., et al., "A Framework for Policy Based
Admission Control",IETF <draft-ietf-rap-framework-00.txt>,
November, 1997.
[E2E] Bernet, Y., Yavatka,r R., Ford, P., Baker, F., Nichols, K.,
Speer, M., "A Framework for End-to-End QoS Combining
RSVP/Intserv and Differentiated Services", IETF <draft-
ietf-DiffServ-rsvp-00.txt>, March 1998.
[RSVP] Braden, R., Zhang, L., Berson, S., Herzog, S., and Jamin,
S., "Resource Reservation Protocol (RSVP) Version 1
Functional Specification", IETF RFC 2205, Proposed
Standard, September 1997.
[ASN1] Information processing systems - Open Systems
Interconnection, "Specification of Abstract Syntax Notation
One (ASN.1)", International Organization for
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COPS Usage for Differentiated Services December 1998
Standardization, International Standard 8824, December
1987.
[BER] Information processing systems - Open Systems
Interconnection - Specification of Basic Encoding Rules for
Abstract Syntax Notation One (ASN.1), International
Organization for Standardization. International Standard
8825, (December, 1987).
[Nichols] K. Nichols, V. Jacobson, L. Zhang, " A Two-bit
Differentiated Services Architecture for the Internet,"
draft-nichols-diff-svc-arch-00.txt
10. Author Information
Francis Reichmeyer
Bay Networks, Inc.
3 Federal Street
Billerica, MA 01821
Phone: (978) 916-3352
Email: freichmeyer@baynetworks.com
Kwok Ho Chan
Bay Networks, Inc.
600 Technology Park
Billerica, MA 01821
Phone: (978) 916-8175
Email: khchan@baynetworks.com
David Durham
Intel
2111 NE 25th Avenue
Hillsboro, OR 97124
Phone: (503) 264-6232
Email: david.durham@intel.com
Raj Yavatkar
Intel
2111 NE 25th Avenue
Hillsboro OR 97124
Phone: (503) 264-9077
Email: yavatkar@ibeam.intel.com
Silvano Gai
Cisco Systems, Inc.
Reichmeyer, Chan, Durham, Gai, McCloghrie [Page 22]
COPS Usage for Differentiated Services December 1998
170 Tasman Dr.
San Jose, CA 95134-1706
Phone: (408) 527-2690
email: sgai@cisco.com
Keith McCloghrie
Cisco Systems, Inc.
170 Tasman Dr.
San Jose, CA 95134-1706
Phone: (408) 526-5260
email: kzm@cisco.com
Shai Herzog
IPHighway
400 Kelby St., Suite 1500
Parker Plaza
Fort Lee, NJ 07024
Phone: (201) 585-0800
Email: herzog@iphighway.com
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