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Fowler, Ed. Standards Track [Page 6]
RFC 2496 DS3/E3 MIB January 1999
2.2.2. Usage of Channelization for DS3, DS1, DS0
An example is given here to explain the channelization objects in the
DS3, DS1, and DS0 MIBs to help the implementor use the objects
correctly. Treatment of E3 and E1 would be similar, with the number
of DS0s being different depending on the framing of the E1.
Assume that a DS3 (with ifIndex 1) is Channelized into DS1s (without
DS2s). The object dsx3Channelization is set to enabledDs1. When
this object is set to enabledDS1, 28 ifEntries of type DS1 will be
created by the agent. If dsx3Channelization is set to disabled, then
the DS1s are destroyed.
Assume the entries in the ifTable for the DS1s are created in channel
order and the ifIndex values are 2 through 29. In the DS1 MIB, there
will be an entry in the dsx1ChanMappingTable for each ds1. The
entries will be as follows:
dsx1ChanMappingTable Entries
ifIndex dsx1Ds1ChannelNumber dsx1ChanMappedIfIndex
1 1 2
1 2 3
......
1 28 29
In addition, the DS1s are channelized into DS0s. The object
dsx1Channelization is set to enabledDS0 for each DS1. There will be
24 DS0s in the ifTable for each DS1. Assume the entries in the
ifTable are created in channel order and the ifIndex values for the
DS0s in the first DS1 are 30 through 53. In the DS0 MIB, there will
be an entry in the dsx0ChanMappingTable for each DS0. The entries
will be as follows:
dsx0ChanMappingTable Entries
ifIndex dsx0Ds0ChannelNumber dsx0ChanMappedIfIndex
2 1 30
2 2 31
......
2 24 53
2.2.3. Usage of Channelization for DS3, DS2, DS1
An example is given here to explain the channelization objects in the
DS3 and DS1 MIBs to help the implementor use the objects correctly.
Fowler, Ed. Standards Track [Page 7]
RFC 2496 DS3/E3 MIB January 1999
Assume that a DS3 (with ifIndex 1) is Channelized into DS2s. The
object dsx3Channelization is set to enabledDs2. There will be 7 DS2s
(ifType of DS1) in the ifTable. Assume the entries in the ifTable
for the DS2s are created in channel order and the ifIndex values are
2 through 8. In the DS1 MIB, there will be an entry in the
dsx1ChanMappingTable for each DS2. The entries will be as follows:
dsx1ChanMappingTable Entries
ifIndex dsx1Ds1ChannelNumber dsx1ChanMappedIfIndex
1 1 2
1 2 3
......
1 7 8
In addition, the DS2s are channelized into DS1s. The object
dsx1Channelization is set to enabledDS1 for each DS2. There will be
4 DS1s in the ifTable for each DS2. Assume the entries in the
ifTable are created in channel order and the ifIndex values for the
DS1s in the first DS2 are 9 through 12, then 13 through 16 for the
second DS2, and so on. In the DS1 MIB, there will be an entry in the
dsx1ChanMappingTable for each DS1. The entries will be as follows:
dsx1ChanMappingTable Entries
ifIndex dsx1Ds1ChannelNumber dsx1ChanMappedIfIndex
2 1 9
2 2 10
2 3 11
2 4 12
3 1 13
3 2 14
...
8 4 36
2.2.4. Usage of Loopbacks
This section discusses the behaviour of objects related to loopbacks.
The object dsx3LoopbackConfig represents the desired state of
loopbacks on this interface. Using this object a Manager can
request:
LineLoopback
PayloadLoopback (if ESF framing)
InwardLoopback
DualLoopback (Line + Inward)
NoLoopback
Fowler, Ed. Standards Track [Page 8]
RFC 2496 DS3/E3 MIB January 1999
The remote end can also request lookbacks either through the FDL
channel if ESF or inband if D4. The loopbacks that can be request
this way are:
LineLoopback
PayloadLoopback (if ESF framing)
NoLoopback
To model the current state of loopbacks on a DS3 interface, the
object dsx3LoopbackStatus defines which loopback is currently applies
to an interface. This objects, which is a bitmap, will have bits
turned on which reflect the currently active loopbacks on the
interface as well as the source of those loopbacks.
The following restrictions/rules apply to loopbacks:
The far end cannot undo loopbacks set by a manager.
A manager can undo loopbacks set by the far end.
Both a line loopback and an inward loopback can be set at the same
time. Only these two loopbacks can co-exist and either one may be
set by the manager or the far end. A LineLoopback request from the
far end is incremental to an existing Inward loopback established by
a manager. When a NoLoopback is received from the far end in this
case, the InwardLoopback remains in place.
2.3. Objectives of this MIB Module
There are numerous things that could be included in a MIB for DS3/E3
signals: the management of multiplexors, CSUs, DSUs, and the like.
The intent of this document is to facilitate the common management of
all devices with DS3/E3 interfaces. As such, a design decision was
made up front to very closely align the MIB with the set of objects
that can generally be read from DS3/E3 devices that are currently
deployed.
2.4. DS3/E3 Terminology
The terminology used in this document to describe error conditions on
a DS3 interface as monitored by a DS3 device are based on the late
but not final draft of what became the ANSI T1.231 standard [11]. If
the definition in this document does not match the definition in the
ANSI T1.231 document, the implementer should follow the definition
described in this document.
Fowler, Ed. Standards Track [Page 9]
RFC 2496 DS3/E3 MIB January 1999
2.4.1. Error Events
Bipolar Violation (BPV) Error Event
A bipolar violation error event, for B3ZS(HDB3)-coded signals,
is the occurrence of a pulse of the same polarity as the
previous pulse without being part of the zero substitution
code, B3ZS(HDB3). For B3ZS(HDB3)-coded signals, a bipolar
violation error event may also include other error patterns
such as: three(four) or more consecutive zeros and incorrect
polarity. (See T1.231 section 7.1.1.1.1)
Excessive Zeros (EXZ) Error Event
An EXZ is the occurrence of any zero string length equal to or
greater than 3 for B3ZS, or greater than 4 for HDB3. (See
T1.231 section 7.1.1.1.2)
Line Coding Violation (LCV) Error Event
This parameter is a count of both BPVs and EXZs occurring over
the accumulation period. An EXZ increments the LCV by one
regardless of the length of the zero string. (Also known as
CV-L. See T1.231 section 7.4.1.1)
P-bit Coding Violation (PCV) Error Event
For all DS3 applications, a coding violation error event is a
P-bit Parity Error event. A P-bit Parity Error event is the
occurrence of a received P-bit code on the DS3 M-frame that is
not identical to the corresponding locally- calculated code.
(See T1.231 section 7.1.1.2.1)
C-bit Coding Violation (CCV) Error Event
For C-bit Parity and SYNTRAN DS3 applications, this is the
count of coding violations reported via the C-bits. For C-bit
Parity, it is a count of CP-bit parity errors occurring in the
accumulation interval. For SYNTRAN, it is a count of CRC-9
errors occurring in the accumulation interval. (See T1.231
section 7.1.1.2.2)
2.4.2. Performance Parameters
All performance parameters are accumulated in fifteen minute
intervals and up to 96 intervals (24 hours worth) are kept by an
agent. Fewer than 96 intervals of data will be available if the
agent has been restarted within the last 24 hours. In addition,
there is a rolling 24-hour total of each performance parameter.
Fowler, Ed. Standards Track [Page 10]
RFC 2496 DS3/E3 MIB January 1999
There is no requirement for an agent to ensure fixed relationship
between the start of a fifteen minute interval and any wall clock;
however some agents may align the fifteen minute intervals with
quarter hours.
Performance parameters are of types PerfCurrentCount,
PerfIntervalCount and PerfTotalCount. These textual conventions are
all Gauge32, and they are used because it is possible for these
objects to decrease. Objects may decrease when Unavailable Seconds
occurs across a fifteen minutes interval boundary. See Unavailable
Seconds discussion later in this section.
Line Errored Seconds (LES)
A Line Errored Second is a second in which one or more CV
occurred OR one or more LOS defects. (Also known as ES-L. See
T1.231 section 7.4.1.2)
P-bit Errored Seconds (PES)
An PES is a second with one or more PCVs OR one or more Out of
Frame defects OR a detected incoming AIS. This gauge is not
incremented when UASs are counted. (Also known as ESP-P. See
T1.231 section 7.4.2.2)
P-bit Severely Errored Seconds (PSES)
A PSES is a second with 44 or more PCVs OR one or more Out of
Frame defects OR a detected incoming AIS. This gauge is not
incremented when UASs are counted. (Also known as SESP-P. See
T1.231 section 7.4.2.5)
C-bit Errored Seconds (CES)
An CES is a second with one or more CCVs OR one or more Out of
Frame defects OR a detected incoming AIS. This count is only
for the SYNTRAN and C-bit Parity DS3 applications. This gauge
is not incremented when UASs are counted. (Also known as
ESCP-P. See T1.231 section 7.4.2.2)
C-bit Severely Errored Seconds (CSES)
A CSES is a second with 44 or more CCVs OR one or more Out of
Frame defects OR a detected incoming AIS. This count is only
for the SYNTRAN and C-bit Parity DS3 applications. This gauge
is not incremented when UASs are counted. (Also known as
SESCP-P. See T1.231 section 7.4.2.5)
Severely Errored Framing Seconds (SEFS)
A SEFS is a second with one or more Out of Frame defects OR a
detected incoming AIS. This item is not incremented during
unavailable seconds. (Also known as SAS-P. See T1.231 section
7.4.2.6)
Fowler, Ed. Standards Track [Page 11]
RFC 2496 DS3/E3 MIB January 1999
Unavailable Seconds (UAS)
UAS are calculated by counting the number of seconds that the
interface is unavailable. The DS3 interface is said to be
unavailable from the onset of 10 contiguous PSESs, or the
onset of the condition leading to a failure (see Failure
States). If the condition leading to the failure was
immediately preceded by one or more contiguous PSESs, then the
DS3 interface unavailability starts from the onset of these
PSESs. Once unavailable, and if no failure is present, the
DS3 interface becomes available at the onset of 10 contiguous
seconds with no PSESs. Once unavailable, and if a failure is
present, the DS3 interface becomes available at the onset of
10 contiguous seconds with no PSESs, if the failure clearing
time is less than or equal to 10 seconds. If the failure
clearing time is more than 10 seconds, the DS3 interface
becomes available at the onset of 10 contiguous seconds with
no PSESs, or the onset period leading to the successful
clearing condition, whichever occurs later. With respect to
the DS3 error counts, all counters are incremented while the
DS3 interface is deemed available. While the interface is
deemed unavailable, the only count that is incremented is
UASs.
Note that this definition implies that the agent cannot
determine until after a ten second interval has passed whether
a given one-second interval belongs to available or
unavailable time. If the agent chooses to update the various
performance statistics in real time then it must be prepared
to retroactively reduce the PES, PSES, CES, and CSES counts by
10 and increase the UAS count by 10 when it determines that
available time has been entered. It must also be prepared to
adjust the PCV, CCV, and SEFS count as necessary since these
parameters are not accumulated during unavailable time. It
must be similarly prepared to retroactively decrease the UAS
count by 10 and increase the PES, CES, PCV, and CCV counts as
necessary upon entering available time. A special case exists
when the 10 second period leading to available or unavailable
time crosses a 900 second statistics window boundary, as the
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