RFC 3896
Definitions of Managed Objects for the DS3/E3 Interface Type
Network Working Group O. Nicklass, Ed. Request for Comments: 3896 RAD Data Communications, Ltd. Obsoletes: 2496 September 2004 Category: Standards Track Definitions of Managed Objects for the DS3/E3 Interface Type Status of this Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2004).Abstract
This memo defines a portion of the Management Information Base (MIB) for use with network management protocols in the Internet community. In particular, it describes objects used for managing DS3 and E3 interfaces. This document is a companion to the documents that define Managed Objects for the DS0, DS1/E1/DS2/E2 and Synchronous Optical Network/Synchronous Digital Hierarchy (SONET/SDH) Interface Types. This document obsoletes RFC 2496.Table of Contents
1. The Internet Standard Management Framework. . . . . . . . . . 2 1.1. Changes from RFC 2496 . . . . . . . . . . . . . . . . . 2 1.2. Changes from RFC 1407 . . . . . . . . . . . . . . . . . 3 1.3. Companion Documents . . . . . . . . . . . . . . . . . . 4 2. Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1. Use of ifTable for DS3 Layer . . . . . . . . . . . . . 4 2.2. Usage Guidelines. . . . . . . . . . . . . . . . . . . . 5 2.2.1. Usage of ifStackTable . . . . . . . . . . . . . 5 2.2.2. Usage of Channelization for DS3, DS1, DS0 . . . 7 2.2.3. Usage of Channelization for DS3, DS2, DS1 . . . 8 2.2.4. Usage of Loopbacks . . . . . . . . . . . . . . 9 2.3. Objectives of this MIB Module . . . . . . . . . . . . . 10 2.4. DS3/E3 Terminology . . . . . . . . . . . . . . . . . . 10 2.4.1. Error Events. . . . . . . . . . . . . . . . . . 10 2.4.2. Performance Parameters. . . . . . . . . . . . . 11 2.4.3. Performance Defects . . . . . . . . . . . . . . 14
2.4.4. Other Terms . . . . . . . . . . . . . . . . . . 16
3. Object Definitions . . . . . . . . . . . . . . . . . . . . . . 16
4. Appendix A - Use of the dsx3IfIndex and dsx3LineIndex. . . . . 54
5. Appendix B - The delay approach to Unavailable Seconds . . . . 56
6. Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . 58
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 58
7.1. Normative References . . . . . . . . . . . . . . . . . . 58
7.2. Informative References . . . . . . . . . . . . . . . . . 59
8. Security Considerations. . . . . . . . . . . . . . . . . . . . 60
9. Author's Address . . . . . . . . . . . . . . . . . . . . . . . 62
10. Full Copyright Statement . . . . . . . . . . . . . . . . . . . 63
1. The Internet Standard Management Framework
For a detailed overview of the documents that describe the current
Internet-Standard Management Framework, please refer to section 7 of
RFC 3410 [RFC3410].
Managed objects are accessed via a virtual information store, termed
the Management Information Base or MIB. MIB objects are generally
accessed through the Simple Network Management Protocol (SNMP).
Objects in the MIB are defined using the mechanisms defined in the
Structure of Management Information (SMI). This memo specifies a MIB
module that is compliant to the SMIv2, which is described in STD 58,
RFC 2578 [RFC2578], STD 58, RFC 2579 [RFC2579] and STD 58, RFC 2580
[RFC2580].
1.1. Changes from RFC 2496
The changes from [RFC2496] are the following:
(1) The dsx3FracIfIndex SYNTAX matches the description range.
(2) Reference was added to Circuit Identifier object.
(3) Usage of ifStackTable section was updated.
(4) Align the DESCRIPTION clauses of few statistic objects with
the near end definition, the far end definition and with
[RFC3593].
(5) Add new value, dsx3M13, to dsx3LineType.
1.2. Changes from RFC 1407
The changes from RFC 1407 are the following: (1) The Fractional Table has been deprecated. (2) This document uses SMIv2. (3) Values are given for ifTable and ifXTable. (4) Example usage of ifStackTable is included. (5) dsx3IfIndex has been deprecated. (6) The definition of valid intervals has been clarified for the case where the agent proxied for other devices. In particular, the treatment of missing intervals has been clarified. (7) An inward loopback has been added. (8) Additional lineStatus bits have been added for Near End in Unavailable Signal State, Carrier Equipment Out of Service. (9) A read-write line Length object has been added. (10) Added a lineStatus last change, trap and enabler. (11) Textual Conventions for statistics objects have been used. (12) A new object, dsx3LoopbackStatus, has been introduced to reflect the loopbacks established on a DS3/E3 interface and the source to the requests. dsx3LoopbackConfig continues to be the desired loopback state while dsx3LoopbackStatus reflects the actual state. (13) A dual loopback has been added to allow the setting of an inward loopback and a line loopback at the same time. (14) An object has been added to indicated whether or not this is a channelized DS3/E3. (15) A new object has been added to indicate which DS1 is to set for remote loopback.
1.3. Companion Documents
This document is a companion to the documents that define Managed Objects for the DS0 [RFC2494], DS1/E1/DS2/E2 [RFC3895], and Synchronous Optical Network/Synchronous Digital Hierarchy (SONET/SDH) [RFC3592] Interface Types.2. Overview
These objects are used when the particular media being used to realize an interface is a DS3/E3 interface. At present, this applies to these values of the ifType variable in the Internet-standard MIB: ds3 (30) The DS3 definitions contained herein are based on the DS3 specifications in ANSI T1.102-1987 [ANSI-T1.102], ANSI T1.107-1988 [ANSI-T1.107], ANSI T1.107a-1990 [ANSI-T1.107a], and ANSI T1.404-1989 [ANSI-T1.404]. The E3 definitions contained herein are based on the E3 specifications in CCITT G.751 [CCITT-G.751] and ETSI T/NA(91)18 [ETSI-T/NA(91)18].2.1. Use of ifTable for DS3 Layer
Only the ifGeneralInformationGroup needs to be supported. ifTable Object Use for DS3 Layer =================================================================== ifIndex Interface index. ifDescr See interfaces MIB [RFC2863] ifType ds3(30) ifSpeed Speed of line rate DS3 - 44736000 E3 - 34368000 ifPhysAddress The value of the Circuit Identifier. If no Circuit Identifier has been assigned this object should have an octet string with zero length. ifAdminStatus See interfaces MIB [RFC2863] ifOperStatus See interfaces MIB [RFC2863] ifLastChange See interfaces MIB [RFC2863]
ifName See interfaces MIB [RFC2863]
ifLinkUpDownTrapEnable Set to enabled(1).
ifHighSpeed Speed of line in Mega-bits per second
(either 45 or 34)
ifConnectorPresent Set to true(1) normally, except for
cases such as DS3/E3 over AAL1/ATM where
false(2) is appropriate
2.2. Usage Guidelines
2.2.1. Usage of ifStackTable
The object dsx3IfIndex has been deprecated. This object previously
allowed a very special proxy situation to exist for Routers and CSUs.
This section now describes how to use ifStackTable to represent this
relationship.
The paragraphs discussing dsx3IfIndex and dsx3LineIndex have been
preserved in Appendix A for informational purposes.
The ifStackTable is used in the proxy case to represent the
association between pairs of interfaces, e.g., this DS3 is attached
to that DS3. This use is consistent with the use of the ifStackTable
to show the association between various sub-layers of an interface.
In both cases entire PDUs are exchanged between the interface pairs -
in the case of a DS3, entire DS3 frames are exchanged; in the case of
PPP and HDLC, entire HDLC frames are exchanged. This usage is not
meant to suggest the use of the ifStackTable to represent Time
Division Multiplexing (TDM) connections in general.
External&Internal interface scenario: the SNMP Agent resides on a
host external from the device supporting DS3/E3 interfaces (e.g., a
router). The Agent represents both the host and the DS3/E3 device.
Example:
A shelf full of CSUs connected to a Router. An SNMP Agent residing
on the router proxies for itself and the CSU. The router has also an
Ethernet interface:
+-----+
| | |
| | | +---------------------+
|E | | 44.736 MBPS | ds3 M13 Line#A | ds3 C-bit Parity
|t | R |---------------+ - - - - - - - - - +------>
|h | | | |
|e | O | 44.736 MBPS | ds3 M13 Line#B | ds3 C-bit Parity
|r | |---------------+ - - - - - - - - - - +------>
|n | U | | |
|e | | 44.736 MBPS | ds3 M13 Line#C | ds3 C-bit Parity
|t | T |---------------+ - - - -- -- - - - - +------>
| | | | |
|-----| E | 44.736 MBPS | ds3 M13 Line#D | ds3 C-bit Parity
| | |---------------+ - - - - -- - - - - +------>
| | R | |_____________________|
| | |
| +-----+
The assignment of the index values could for example be:
ifIndex Description
1 Ethernet
2 Line#A Router
3 Line#B Router
4 Line#C Router
5 Line#D Router
6 Line#A CSU Router
7 Line#B CSU Router
8 Line#C CSU Router
9 Line#D CSU Router
10 Line#A CSU Network
11 Line#B CSU Network
12 Line#C CSU Network
13 Line#D CSU Network
The ifStackTable is then used to show the relationships between the
various DS3 interfaces.
ifStackTable Entries
HigherLayer LowerLayer
2 6
3 7
4 8
5 9
6 10
7 11
8 12
9 13
If the CSU shelf is managed by itself by a local SNMP Agent, the
situation would be identical, except the Ethernet and the 4 router
interfaces are deleted. Interfaces would also be numbered from 1 to
8.
ifIndex Description
1 Line#A CSU Router
2 Line#B CSU Router
3 Line#C CSU Router
4 Line#D CSU Router
5 Line#A CSU Network
6 Line#B CSU Network
7 Line#C CSU Network
8 Line#D CSU Network
ifStackTable Entries
HigherLayer LowerLayer
1 5
2 6
3 7
4 8
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 [RFC2494],
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.
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 [RFC3895], 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
The remote end can also request lookbacks either through the FDL
channel if ESF or inband if D4. The loopbacks that can be requested
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 applied to an interface. This object, 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 [ANSI- T1.231]. 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.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.
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.)
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. Similarly, it must be 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 foregoing description implies that
the PCV, CCV, PES, CES, PSES, CSEC, SEFS, and UAS counts for
the PREVIOUS interval must be adjusted. In this case
successive GETs of the affected dsx3IntervalPSESs and
dsx3IntervalUASs objects will return differing values if the
first GET occurs during the first few seconds of the window.
The agent may instead choose to delay updates to the various
statistics by 10 seconds in order to avoid retroactive
adjustments to the counters. A way to do this is sketched in
Appendix B.
In any case, a linkDown trap shall be sent only after the agent has
determined for certain that the unavailable state has been entered,
but the time on the trap will be that of the first UAS (i.e., 10
seconds earlier). A linkUp trap shall be handled similarly.
According to [ANSI-T1.231] unavailable time begins at the _onset_ of
10 contiguous severely errored seconds -- that is, unavailable time
starts with the _first_ of the 10 contiguous SESs. Also, while an
interface is deemed unavailable all counters for that interface are
frozen except for the UAS count. It follows that an implementation
which strictly complies with this standard must _not_ increment any
counters other than the UAS count -- even temporarily -- as a result
of anything that happens during those 10 seconds. Since changes in
the signal state lag the data to which they apply by 10 seconds, an
ANSI-compliant implementation must pass the one-second statistics
through a 10-second delay line prior to updating any counters. That
can be done by performing the following steps at the end of each one
second interval.
i) Read near/far end CV counter and alarm status flags from the
hardware.
ii) Accumulate the CV counts for the preceding second and compare
them to the ES and SES threshold for the layer in question.
Update the signal state and shift the one-second CV counts
and ES/SES flags into the 10-element delay line. Note that
far-end one-second statistics are to be flagged as "absent"
during any second in which there is an incoming defect at the
layer in question or at any lower layer.
iii) Update the current interval statistics using the signal state
from the _previous_ update cycle and the one-second CV counts
and ES/SES flags shifted out of the 10-element delay line.
This approach is further described in Appendix B.
2.4.3. Performance Defects
Failure States:
The Remote Alarm Indication (RAI) failure, in SYNTRAN
applications, is declared after detecting the Yellow Alarm
Signal on the alarm channel. See ANSI T1.107a-1990 [ANSI-
T1.107a]. The Remote Alarm Indication failure, in C-bit
Parity DS3 applications, is declared as soon as the presence
of either one or two alarm signals are detected on the Far
End Alarm Channel. See [ANSI-T1.107]. The Remote Alarm
Indication failure may also be declared after detecting the
far-end SEF/AIS defect (aka yellow). The Remote Alarm
Indication failure is cleared as soon as the presence of the
any of the above alarms are removed.
Also, the incoming failure state is declared when a defect
persists for at least 2-10 seconds. The defects are the
following: Loss of Signal (LOS), an Out of Frame (OOF) or an
incoming Alarm Indication Signal (AIS). The Failure State is
cleared when the defect is absent for less than or equal to
20 seconds.
Far End SEF/AIS defect (aka yellow)
A Far End SEF/AIS defect is the occurrence of the two X-bits
in a M-frame set to zero. The Far End SEF/AIS defect is
terminated when the two X-bits in a M-frame are set to one.
(Also known as SASCP-PFE. See T1.231 section 7.4.4.2.6)
Out of Frame (OOF) defect
A DS3 OOF defect is detected when any three or more errors in
sixteen or fewer consecutive F-bits occur within a DS3 M-
frame. An OOF defect may also be called a Severely Errored
Frame (SEF) defect. An OOF defect is cleared when reframe
occurs. A DS3 Loss of Frame (LOF) failure is declared when
the DS3 OOF defect is consistent for 2 to 10 seconds. The
DS3 OOF defect ends when reframe occurs. The DS3 LOF failure
is cleared when the DS3 OOF defect is absent for 10 to 20
seconds. (See T1.231 section 7.1.2.2.1)
An E3 OOF defect is detected when four consecutive frame
alignment signals have been incorrectly received in there
predicted positions in an E3 signal. E3 frame alignment
occurs when the presence of three consecutive frame alignment
signals have been detected.
Loss of Signal (LOS) defect
The DS3 LOS defect is declared upon observing 175 +/- 75
contiguous pulse positions with no pulses of either positive
or negative polarity. The DS3 LOS defect is terminated upon
observing an average pulse density of at least 33% over a
period of 175 +/- 75 contiguous pulse positions starting with
the receipt of a pulse. (See T1.231 section 7.1.2.1.1)
Alarm Indication Signal (AIS) defect
The DS3 AIS is framed with "stuck stuffing." This implies
that it has a valid M-subframe alignments bits, M-frame
alignment bits, and P bits. The information bits are set to
a 1010... sequence, starting with a one (1) after each M-
subframe alignment bit, M-frame alignment bit, X bit, P bit,
and C bit. The C bits are all set to zero giving what is
called "stuck stuffing." The X bits are set to one. The DS3
AIS defect is declared after DS3 AIS is present in contiguous
M-frames for a time equal to or greater than T, where 0.2 ms
<= T <= 100 ms. The DS3 AIS defect is terminated after AIS
is absent in contiguous M-frames for a time equal to or
greater than T. (See T1.231 section 7.1.2.2.3)
The E3 binary content of the AIS is nominally a continuous
stream of ones. AIS detection and the application of
consequent actions, should be completed within a time limit
of 1 ms.
2.4.4. Other Terms
Circuit Identifier
This is a character string specified by the circuit vendor,
and is useful when communicating with the vendor during the
troubleshooting process (see M.1400 [ITU-T-M.1400] for
additional information).
Proxy
In this document, the word proxy is meant to indicate an
application which receives SNMP messages and replies to them
on behalf of the devices which implement the actual DS3/E3
interfaces. The proxy may have already collected the
information about the DS3/E3 interfaces into its local
database and may not necessarily forward the requests to the
actual DS3/E3 interface. It is expected in such an
application that there are periods of time where the proxy is
not communicating with the DS3/E3 interfaces. In these
instances the proxy will not necessarily have up-to-date
configuration information and will most likely have missed
the collection of some statistics data. Missed statistics
data collection will result in invalid data in the interval
table.
(page 16 continued on part 2)
