📄 rfc1695.txt
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types including one for the best effort traffic [9].
4.3.2. Cell Loss Priority
To prioritize traffic during resource congestion, ATM cells are
assigned one of the two types of Cell Loss Priority (CLP), CLP=0 and
CLP=1. ATM cells with CLP=0 have a higher priority in regard to cell
loss than ATM cells with CLP=1. Therefore, during resource
congestions, CLP=1 cells are dropped before any CLP=0 cell is
dropped.
4.3.3. QoS Class
A VCC or VPC is associated with one of a number of Quality of Service
(QoS) classes. The following service classes have been specified:
Service Class A: Constant bit rate video and Circuit
emulation
Service Class B: Variable bit rate video/audio
Service Class C: Connection-oriented data
Service Class D: Connectionless data
Four QoS classes numbered 1, 2, 3, and 4 have been specified with the
aim of supporting service classes A, B, C, and D respectively. The
VCLs (or VPLs) concatenated to form a VCC (or VPC) will all have the
same QoS class as that of the VCC (or VPC). The Cell Loss Ratio
(CLR), Cell Delay Variation (CDV), and end-to-end Cell Delay (CD)
parameters are defined as part of QoS Class definition. In addition,
Ahmed & Tesink [Page 6]
RFC 1695 ATM Management Objects August 1994
an unspecified QoS Class numbered 0 is specified for best effort
traffic.
5. Overview
ATM management objects are used to manage ATM interfaces, ATM virtual
links, ATM cross-connects, AAL5 entities and AAL5 connections
supported by ATM hosts, ATM switches and ATM networks. This section
provides an overview and background of how to use this MIB and other
potential MIBs for this purpose.
The purpose of this memo is primarily to manage ATM PVCs. ATM SVCs
are also represented by the management information in this MIB.
However, full management of SVCs may require additional capabilities
which are beyond the scope of this memo.
5.1. Background
In addition to the MIB module defined in this memo, other MIB modules
are necessary to manage ATM interfaces, links and cross-connects.
Examples include MIB II for general system and interface management
(RFC 1213 and RFC 1573), the DS3 or SONET MIBs for management of
physical interfaces, and, as appropriate, MIB modules for
applications that make use of ATM, such as SMDS. These MIB modules
are outside the scope of this specification.
The current specification of this ATM MIB is based on SNMPv2.
5.2. Structure of the MIB
The managed ATM objects are arranged into the following groups:
(1) ATM interface configuration group
(2) ATM interface DS3 PLCP group
(3) ATM interface TC Sublayer group
(4) ATM interface virtual link (VPL/VCL) configuration
groups
(5) ATM VP/VC cross-connect groups
(6) AAL5 connection performance statistics group
Note that, managed objects for activation/deactivation of OAM cell
flows and ATM traps notifying virtual connection or virtual link
failures are outside the scope of this memo.
5.3. ATM Interface Configuration Group
This group contains information on ATM cell layer configuration of
local ATM interfaces on an ATM device in addition to the information
Ahmed & Tesink [Page 7]
RFC 1695 ATM Management Objects August 1994
on such interfaces contained in the ifTable.
5.4. ATM Interface DS3 PLCP and TC Layer Groups
These groups provide performance statistics of the DS3 PLCP and TC
sublayer of local ATM interfaces on a managed ATM device. DS3 PLCP
and TC sublayer are currently used to carry ATM cells respectively
over DS3 and SONET transmission paths.
5.5. ATM Virtual Link and Cross-Connect Groups
ATM virtual link and cross-connect groups model bi-directional ATM
virtual links and ATM cross-connects. The ATM VP/VC link groups are
implemented in an ATM host, ATM switch and ATM network. The ATM
switch and ATM network also implement the ATM VP/VC cross-connect
groups. Both link and cross-connect groups are implemented in a
carrier's network for Customer Network Management (CNM) purposes.
The ATM virtual link groups are used to create, delete or modify ATM
virtual links in an ATM host, ATM switch and ATM network. ATM
virtual link groups along with the cross-connect groups are used to
create, delete or modify ATM cross-connects in an ATM switch or ATM
network (e.g., for CNM purposes).
6. Application of MIB II to ATM
6.1. The System Group
For the purposes of the sysServices object in the System Group of MIB
II [2], ATM is a data link layer protocol. Thus, for ATM switches
and ATM networks, sysServices will have the value "2".
6.2. The Interface Group
The Interfaces Group of MIB II defines generic managed objects for
managing interfaces. This memo contains the media-specific
extensions to the Interfaces Group for managing ATM interfaces.
This memo assumes the interpretation of the Interfaces Group to be in
accordance with [5] which states that the interfaces table (ifTable)
contains information on the managed resource's interfaces and that
each sub-layer below the internetwork layer of a network interface is
considered an interface. Thus, the ATM cell layer interface is
represented as an entry in the ifTable. This entry is concerned with
the ATM cell layer as a whole, and not with individual virtual
connections which are managed via the ATM-specific managed objects
specified in this memo. The inter-relation of entries in the ifTable
is defined by Interfaces Stack Group defined in [5].
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RFC 1695 ATM Management Objects August 1994
6.2.1. Support of the ATM Cell Layer by ifTable
Some specific interpretations of ifTable for the ATM cell layer
follow.
Object Use for the generic ATM layer
====== =============================
ifIndex Each ATM port is represented by an ifEntry.
ifDescr Description of the ATM interface.
ifType The value that is allocated for ATM is 37.
ifSpeed The total bandwidth in bits per second
for use by the ATM layer.
ifPhysAddress The interface's address at the ATM protocol
sublayer; the ATM address which would be used
as the value of the Called Party Address
Information Element (IE) of a signalling
message for a connection which either:
- would terminate at this interface, or
- for which the Called Party Address IE
would need to be replaced by the Called
Party SubAddress IE before the message
was forwarded to any other interface.
For an interface on which signalling is
not supported, then the interface does not
necessarily have an address, but if it
does, then ifPhysAddress is the address which
would be used as above in the event that
signalling were supported. If the interface
has multiple such addresses, then ifPhysAddress
is its primary address. If the interface has
no addresses, then ifPhysAddress is an octet
string of zero length. Address encoding is as
per [9]. Note that addresses assigned for
purposes other than those listed above (e.g.,
an address associated with the service provider
side of a public network UNI) may be represented
through atmInterfaceAdminAddress.
ifAdminStatus See [5].
ifOperStatus Assumes the value down(2) if the ATM cell
layer or any layer below that layer is down.
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RFC 1695 ATM Management Objects August 1994
ifLastChange See [5].
ifInOctets The number of received octets over the
interface, i.e., the number of received,
assigned cells multiplied by 53.
ifOutOctets The number of transmitted octets over the
interface, i.e., the number of transmitted,
assigned cells multiplied by 53.
ifInErrors The number of cells dropped due to
uncorrectable HEC errors.
ifInUnknownProtos The number of received cells discarded
during cell header validation, including
cells with unrecognized VPI/VCI values,
and cells with invalid cell header patterns.
If cells with undefined PTI values are discarded,
they are also counted here.
ifOutErrors See [5].
ifName Textual name (unique on this system) of the
interface or an octet string of zero length.
ifLinkUpDownTrapEnable Default is disabled (2).
ifConnectorPresent Set to false (2).
ifPromiscuousMode Set to false(2).
ifHighSpeed See [5].
ifHCInOctets The 64-bit version of ifInOctets; supported
if required by the compliance statements in [5].
ifHCOutOctets The 64-bit version of ifOutOctets; supported
if required by the compliance statements in [5].
7. Support of the AAL3/4 Based Interfaces
For the management of AAL3/4 CPCS layer, see [6].
8. Support of the AAL5 Managed Objects
Support of AAL5 managed objects in an ATM switch and ATM host are
described below.
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RFC 1695 ATM Management Objects August 1994
8.1. Managing AAL5 in a Switch
Managing AAL5 in a switch involves:
(1) performance management of an AAL5 entity as
an internal resource in a switch
(2) performance management of AAL5 per virtual connection
AAL5 in a switch is modeled as shown in Figures 4 and 5. AAL5 will
be managed in a switch for only those virtual connections that carry
AAL5 and are terminated at the AAL5 entity in the switch. Note that,
the virtual channels within the ATM UNIs carrying AAL5 will be
switched by the ATM switching fabric (termed as ATM Entity in the
figure) to the virtual channels on a proprietary internal interface
associated with the AAL5 process (termed as AAL5 Entity in the
figure). Therefore, performance management of the AAL5 resource in
the switch will be modeled using the ifTable through an internal
(pseudo-ATM) virtual interface and the AAL5 performance management
per virtual connection will be supported using an additional AAL5
connection table in the ATM MIB. The association between the AAL5
virtual link at the proprietary virtual, internal interface and the
ATM virtual link at the ATM interface will be derived from the
virtual channel cross-connect table and the virtual channel link
table in the ATM MIB.
___________________________
| |
| ============= |
| | AAL5 | |
| | Entity | |
| ============= |
| | |
| -----Prop. Virtual Interface
| | |
| ============= |
| | ATM | |
| | Entity | |
| ============= |
|_____|__|__|__|__|_______|
| | | | |
---------------- ATM UNIs
| | | | |
| | | | |
v v v v v
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