RFC 3441
Asynchronous Transfer Mode (ATM) Package for the Media Gateway Control Protocol (MGCP)
Pages: 50
Informational
Informational
Part 1 of 2 – Pages 1 to 19
Network Working Group R. Kumar Request for Comments: 3441 Cisco Systems Category: Informational January 2003 Asynchronous Transfer Mode (ATM) Package for the Media Gateway Control Protocol (MGCP) Status of this Memo This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2003). All Rights Reserved.Abstract
This document describes an Asynchronous Transfer Mode (ATM) package for the Media Gateway Control Protocol (MGCP). This package includes new Local Connection Options, ATM-specific events and signals, and ATM connection parameters. Also included is a description of codec and profile negotiation. It extends the MGCP that is currently being deployed in a number of products. Implementers should be aware of developments in the IETF Megaco Working Group and ITU SG16, which are currently working on a potential successor to this protocol.Table of Contents
1.0 Conventions Used in this Document..............................2 2.0 Introduction...................................................2 3.0 Local Connection Options.......................................3 3.1 ATM Bearer Connection.........................................4 3.2 ATM Adaptation Layer (AAL)....................................8 3.3 Service Layer................................................15 3.4 ATM Bearer Traffic Management................................19 3.5 AAL Dimensioning.............................................27 4.0 Signals and Events.............................................30 5.0 Connection Parameters..........................................35 6.0 Negotiation of Profiles and Codecs in ATM Applications.........37 6.1 Consistency of Parameters...................................37 6.2 Codec/Profile Negotiation in ATM Networks...................38 7.0 Security Considerations.......................................45 8.0 IANA Considerations...........................................45 9.0 References....................................................45 10.0 Acronyms......................................................48
11.0 Acknowledgements..............................................49 12.0 Author's Address..............................................49 13.0 Full Copyright Statement......................................501.0 Conventions Used in this Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14, RFC 2119. MGCP identifiers are case-insensitive. This includes package names, event names, local connection options and other elements of the MGCP header.2.0 Introduction
The Media Gateway Control Protocol or MGCP [36] is used to control voice media gateways from external call control elements. Even though the bearer network might be IP, ATM, TDM or a mix of these, MGCP is transported over IP. Packages such as the MGCP CAS packages [38] are modular sets of parameters such as connection options, signal, event and statistics definitions that can be used to extend it into specific contexts. A related, IP-based mechanism for the description of ATM connections [18] has been generated by the IETF MMUSIC group. Due to the IP-centric nature of all aspects of the MGCP device control protocol, and for consistency with other MGCP package definitions, it is desirable to publish the MGCP ATM package in an IETF document. MGCP [36] allows the auditing of endpoints for package versions supported. The package version for the MGCP ATM package, as specified in this document, is 0. Even if the ATM package is the default package for some endpoints, the package prefix "atm" shall not be omitted in local connection option names, event names, signal names etc. If the ATM package is the default package for an endpoint, it will be listed as the first package in the audit response list. It is not necessary for the MGCP ATM package to be the default package for ATM to be supported on an endpoint. The ATM package in this document consists of Local Connection Options (Section 3.0), Events and Signals (Section 4.0) and ATM Statistics Parameters (Section 5.0). Section 6.1 has guidelines for consistency in the use of Local Connection Options. Section 6.2 describes codec and profile negotiation. Section 7.0 addresses security considerations.
In the ATM networks addressed in this document, services are carried directly over ATM without an intervening IP layer. The Local Connection Options, Events, Signals and Statistics Parameters described in this section are not needed for VoIP calls which can be carried, in whole or in part, over an ATM network. In that case, the constructs defined elsewhere for IP are sufficient. The ATM local connection option names, event names and signal names MUST always have an "atm" package prefix. Backward compatibility with older implementations that use X-atm as the package name is desirable. MGCP grammar [36] must be followed with regard to the use of white spaces. The examples in this document attempt to follow MGCP grammar in this and all other respects.3.0 Local Connection Options
The Local Connection Options (LCOs) defined in this section are specific to ATM applications. Like other LCOs, these can be used in commands to create connections, modify connections and audit connections. However, unless noted otherwise below, they are not to be returned when an endpoint is audited for capabilities. ATM Local Connection Options are divided into the following categories: ATM bearer connection, ATM adaptation layer, service layer, ATM bearer traffic management and AAL dimensioning. When parameter values are represented in decimal format, leading zeros are omitted.
3.1 ATM Bearer Connection
These local connection options are used to parameterize ATM bearer connections. TABLE 1: Local Connection Options for ATM Bearers +---------+---------------+---------------------------------------+ | LCO | Meaning | Values | +---------+---------------+---------------------------------------+ | ct | Connection |AAL1, AAL1_SDT, AAL1_UDT, AAL2, AAL3/4,| | | Type |AAL5, USER_DEFINED_AAL | +---------+---------------+---------------------------------------+ | vc |VC/Bearer type | PVC, SVC, CID | +---------+---------------+---------------------------------------+ | se | Enable path | on, off | | | set-up | | +---------+---------------+---------------------------------------+ | ci | Connection | See below | | | Element | | | | Identifier | | +---------+---------------+---------------------------------------+ Connection type (ct): This parameter describes the ATM adaptation layer. The values that can be assigned to it are: AAL1, AAL1_SDT, AAL1_UDT, AAL2, AAL3/4, AAL5 and USER_DEFINED_AAL. The user defined adaptation layer is per amendment 2 of ITU-T Q.2931. Type of Bearer/VC (vc): This indicates whether a PVC, CID or an SVC is to be used for an ATM connection. Possible values are: PVC, SVC or CID. Omitting this parameter will result in the use of a default, which could be embedded or provisioned. The value "PVC" covers both classical PVCs and SPVCs. The value "CID" covers subchannels within AAL1 [35] and AAL2 [10] virtual circuits. A value of "SVC" for atm/vc does not necessarily imply that the addressed media gateway should initiate signaling for bearer set-up, since this might be done by another node such as the far-end media gateway. Enable path set-up (se): This local connection option is used to explicitly enable or disable the use of bearer signaling for path set-up. Permitted values of this local connection option are "on" and "off". Examples of bearer signaling are SVC signaling, ITU Q.2630.1 signaling and combinations thereof. Examples of such combinations are the set-up of an AAL2 SVC and the assignment of a CID within it or the set-up of a concatenation of an AAL2 single-CID SVC and a CID channel within a multiplexed AAL2 VC. This parameter can be used with both the backward and forward bearer connection
set-up methods. In the former case, the call-terminating gateway
sets up the bearer connection. In the latter case, the call-
originating gateway sets up the bearer connection.
This option may or may not be used in conjunction with atm/sc event
notification. When this option and the atm/sc event notification are
omitted, creating and modifying connection commands, the call agent
is deferring any relevant decision to set up an ATM or AAL2
connection to the media gateways. In the absence of this parameter,
a media gateway's autonomous decision to set up an ATM or AAL2 path
via bearer signaling depends on default/provisioned behaviors, such
as the applicability and nature (backward/forward) of a bearer
connection set-up model, the network type ('nt'), connection type
('atm/ct') and bearer type/VC ('atm/vc') local connection options,
and the media gateway's awareness of whether it is the originating
gateway or terminating gateway in a call. This awareness may be
based on the presence or absence of an SDP remote connection
descriptor in the initial create connection command.
Connection Element Identifier (ci): This indicates the Virtual
Circuit or CID to be used for the bearer connection. It is used when
the call agent manages VC and/or CID resources in the bearer network.
The ci parameter can be in one of the following formats:
* VCCI-<vcci>
* VCCI-<vcci>/CID-<cid>
* <ATMaddressType>-<ATMaddress>/VCCI-<vcci>
* <ATMaddress>/VCCI-<vcci>
* <ATMaddressType>-<ATMaddress>/VCCI-<vcci>/CID-<cid>
* <ATMaddress>/VCCI-<vcci>/CID-<cid>
* BCG-<bcg>/VCCI-<vcci>
* BCG-<bcg>/VCCI-<vcci>/CID-<cid>
* BCG-<bcg>/VPI-<vpi>/VCI-<vci>
* BCG-<bcg>/VPI-<vpi>/VCI-<vci>/CID-<cid>
* PORT-<portId>/VPI-<vpi>/VCI-<vci>
* PORT-<portId>/VPI-<vpi>/VCI-<vci>/CID-<cid>
* VPCI-<vpci>/VCI-<vci>
* VPCI-<vpci>/VCI-<vci>/CID-<cid>
* <ATMaddressType>-<ATMaddress>/VPCI-<vpci>/VCI-<vci>
* <ATMaddress>/VPCI-<vpci>/VCI-<vci>
* <ATMaddressType>-<ATMaddress>/VPCI-<vpci>/VCI-<vci>/CID-<cid>
* <ATMaddress>/VPCI-<vpci>/VCI-<vci>/CID-<cid>
The subparameters of the ci parameter are defined as follows:
|--------------|-----------------------|----------------------------|
| Subparameter | Meaning | Representation |
|--------------|-----------------------|----------------------------|
| vcci | VC connection Id | Decimal Integer |
| | | (16-bit equivalent) |
|--------------|-----------------------|----------------------------|
| cid | Channel Id | Decimal Integer |
| | | (8-bit equivalent) |
|--------------|-----------------------|----------------------------|
|ATMaddressType| ATM address type | "NSAP", "E164", "GWID", |
| | | "ALIAS" |
|--------------|-----------------------|----------------------------|
| ATMaddress | ATM address | 40 hex digits ("NSAP") |
| | | upto 15 digits ("EI64") |
| | | upto 32 chars ("GWID") |
| | | upto 32 chars ("ALIAS") |
|--------------|-----------------------|----------------------------|
| bcg |Bearer Connection Group| Decimal Integer |
| | | (8-bit equivalent) |
|--------------|-----------------------|----------------------------|
| vpi | Virtual Path Id | Decimal Integer |
| | | (8 or 12-bit equivalent) |
|--------------|-----------------------|----------------------------|
| vci | Virtual Channel Id | Decimal Integer |
| | | (16-bit equivalent) |
|--------------|-----------------------|----------------------------|
| portID | Port Id | Decimal Integer |
| | | (32-bit equivalent) |
|--------------|-----------------------|----------------------------|
| vpci | VP connection ID | Decimal Integer |
| | | (16-bit equivalent) |
|--------------|-----------------------|----------------------------|
The CID, or Channel ID, can refer to AAL1 as well as AAL2
applications. In AAL1 applications based on [35], it refers to the
octet position, starting from one, within an n x 64 SDT frame.
The VPCI is a 16 bit field defined in Section 4.5.16 of ITU Q.2931.
The VPCI is similar to the VPI, except for its width and the fact
that it retains its value across VP crossconnects.
The VCCI is a 16 bit field defined in ITU Recommendation Q.2941.2
[14]. The VCCI is similar to the VCI, except for the fact that it
retains its value across VC crossconnects.
In general, <vpci> and <vcci> values are unique between a pair of
nodes. When they are unique between a pair of nodes, but not unique
within a network, they need to be qualified at any node, by the ATM
address of the remote node. These parameters can be pre-provisioned
or signaled via SVC signaling messages. When VPCI and VCCI values
are pre-provisioned, administrations have the option of provisioning
them uniquely in a network. In this case, the ATM address of the far
end is not needed to qualify these parameters.
The <portId> parameter is used to identify the physical trunk port on
an ATM module. It can be represented as a decimal or hex number of
up to 32 digits.
In some applications, it is meaningful to bundle a set of connections
between a pair of ATM nodes into a bearer connection group. The
<bcg> subparameter is an eight bit field that allows the bundling of
up to 255 VPCs or VCCs.
In some applications, it is necessary to wildcard some elements of
the ci local connection option. The "$" wildcard character can be
substituted for some of the terms of this parameter. While
wildcarding, the constant strings that qualify the terms in the ci
parameter are retained. The concatenation <ATMaddressType>-
<ATMaddress> can be wildcarded in the following ways:
* The entire concatenation, <ATMaddressType>-<ATMaddress>, is
replaced with a "$".
* <ATMaddress> is replaced with a "$", but <ATMaddressType> is
not.
Examples of wildcarding the ci parameter in the AAL1 and AAL5
contexts are: VCCI-$, BCG-100/VPI-20/VCI-$.
Examples of wildcarding the ci parameter in the AAL2 context are:
VCCI- 40/CID-$, BCG-100/VPI-20/VCI-120/CID-$.
If the addressType is NSAP, the address is expressed in the standard
dotted hex form. This is a string of 40 hex digits, with dots after
the 2nd, 6th, 10th, 14th, 18th, 22nd, 26th, 30th, 34th and 38th
digits. The "0x" prefix is not used, since this is always
represented in hex. The last octet of the NSAP address is the
'selector' field that is available for non-standard use. For
example:
L: atm/ci:NSAP-47.0091.8100.0000.0060.3e64.fd01.0060.3e64.fd01.00/
VCCI-65
If the ATMaddressType is E164, the ATMaddress is expressed as a
decimal number with up to 15 digits. For example:
L: atm/ci:E164-9738294382/VCCI-100
The E.164 numbers used can be in the International Format E.164 or
conform to a private numbering plan.
If the ATMaddressType is GWID, it means that the address is a Gateway
Identifier or Node Alias. This may or may not be globally unique.
In this format, the ATMaddress is expressed as an alphanumeric string
("A"-"Z", "a"-"z", "0" - "9",".","-","_"). For example:
L: atm/ci:GWID-officeABCmgx101vism12
The keyword "ALIAS" can be substituted for "GWID". For example:
L: atm/ci:ALIAS-officeABCmgx101vism12
An example of a GWID (ALIAS) is the CLLI code used for telecom
equipment. For all practical purposes, it should be adequate for the
GWID (ALIAS) to be a variable length string with a maximum size of 32
characters.
When an endpoint supporting the ATM package is audited for
capabilities, the following local connection options from Section 3.1
shall be returned: connection type (atm/ct) and VC/bearer type
(atm/vc). If more than one value is supported, these shall be
expressed as a list of semicolon-separated values. Although this is
not very useful, it is permissible for these values to have
overlapping semantics (e.g., AAL1 and AAL1_SDT). An example of
returning, in audit response, the local connection options defined in
Section 3.1 is:
A: atm/ct:AAL1_SDT;AAL2, atm/vc:PVC;CID
3.2 ATM Adaptation Layer (AAL)
These local connection options are used to parameterize the ATM
adaptation layer (AAL). These are further classified as: generic AAL
connection options, AAL1-related connection options and AAL2-related
connection options. Currently, there are no local connection options
defined in this category that pertain to AAL5.
TABLE 2: Generic Local Connection Options for the AAL
+---------+---------------+---------------------------------------+
| LCO | Meaning | Values |
+---------+---------------+---------------------------------------+
| aalApp | Application |itu_h323c,af83,AAL5_SSCOP, |
| | |itu_i3661_unassured, itu_i3661_assured |
| | |itu_i3662, itu_i3651, itu_i3652, |
| | |itu_i3653, itu_i3654, |
| | |FRF5, FRF8, FRF11,itu_h2221 |
+---------+---------------+---------------------------------------+
| sbc | Subchannel | 1...24 for T1-based applications |
| | Count | 1...31 for E1-based applications |
+---------+---------------+---------------------------------------+
AAL application (aalApp): This connection option specifies the
controlling standard for an application layer above the ATM
adaptation layer. Other strings can be defined. If used, these need
to be prefixed with an "X-".
"itu_h323c" Annex C of H.323 which specifies direct
RTP on AAL5 [12].
"af83" af-vtoa-0083.001, which specifies
variable size AAL5 PDUs with PCM voice
and a null SSCS [13].
"AAL5_SSCOP" SSCOP as defined in ITU Q.2110 [14]
running over an AAL5 CPS [27].
No information is provided regarding
any layers above SSCOP such as Service
Specific Coordination Function (SSCF)
layers.
"itu_i3661_unassured" SSCS with unassured transmission,
per ITU I.366.1 [11].
"itu_i3661_assured" SSCS with assured transmission,
per ITU I.366.1 [11]. This uses SSCOP
[14].
"itu_i3662" SSCS per ITU I.366.2 [2].
"itu_i3651" Frame relay SSCS per ITU I.365.1 [15].
"itu_i3652" Service-specific coordination function,
as defined in ITU I.365.2, for Connection
Oriented Network Service (SSCF-CONS)
[16]. This uses SSCOP [14].
"itu_i3653" Service-specific coordination function,
as defined in ITU I.365.3, for Connection
Oriented Transport Service (SSCF-COTS)
[17]. This uses SSCOP [14].
"itu_i3654" Service-specific coordination function,
as defined in ITU I.365.4 [28].
"FRF5" Use of the FRF.5 frame relay standard
[23], which references ITU I.365.1 [15].
"FRF8" Use of the FRF.8 frame relay standard
[24]. This implies a null SSCS and the
mapping of the frame relay header
into the ATM header.
"FRF11" Use of the FRF.11 frame relay standard
[25].
"itu_h2221" Use of the ITU standard H.222.1 for
audiovisual communication over AAL5
[22].
Subchannel count (sbc): This parameter indicates the number of DS0s
in an n x 64 connection. Such connections use an ATM adaptation
layer 1 (ATM forum af-vtoa-78) or 2 (ITU I.366.2). For T1-based
applications, it can take on integral values in the inclusive range
[1...24]. For E1-based applications, it can take on integral values
in the inclusive range [1...31]. When this parameter is omitted, the
subchannel count must be known by other means.
TABLE 3: Local Connection Options for AAL Type 1
+---------+---------------+---------------------------------------+
| LCO | Meaning | Values |
+---------+---------------+---------------------------------------+
| pf | Partial fill | 1...48 |
| | | |
+---------+---------------+---------------------------------------+
| crt | Clock Recovery| NULL, SRTS, ADAPTIVE |
| | Type | |
+---------+---------------+---------------------------------------+
| fe | FEC enable | NULL, DELAY_SENSITIVE,LOSS_SENSITIVE |
+---------+---------------+---------------------------------------+
Partial Fill Count (pf): When present, the 'pf' parameter is used to
indicate the fill level of cells. When this local connection option
is absent, then other means (such as provisionable defaults) are used
to determine the presence and level of partial fill.
This parameter indicates the number of non-pad payload octets, not
including any AAL SAR or convergence sublayer octets. For example,
in some AAL1 applications that use partially filled cells with
padding at the end, this attribute indicates the number of leading
payload octets not including any AAL overhead.
In general, permitted values of the pf parameter are integers in the
range 1 - 48 inclusive. However, this upper bound is different for
different adaptations since the AAL overhead, if any, is different.
If a specified partial fill (e.g. 47) is greater than or equal to the
maximum fill (in this example, 46 for AAL1 P-cells), then complete
fill (46 in this example) is used. Using a 'partial' fill of 48
effectively disables partial fill. Values below or above the
permissible range of 1-48 MUST be rejected with an error code of 532
{Unsupported value(s) in LocalConnectionOptions}.
In the AAL1 context, this parameter applies uniformly to both P and
non-P cells. In AAL1 applications that do not distinguish between P
and non-P cells, a value of 47 indicates complete fill (i.e., the
absence of partial fill). In AAL1 applications that distinguish
between P and non-P cells, a value of 46 indicates no padding in
P-cells and a padding of one in non-P cells.
If partial fill is enabled (i.e., there is padding in at least some
cells), then AAL1 structures must not be split across cell
boundaries. These shall fit in any cell. Hence, their size shall be
less than or equal to the partial fill size. Further, the partial
fill size is preferably an integer multiple of the structure size.
If it is not, then the partial fill size stated in the local
connection options shall be truncated to an integer multiple of the
structure size (e.g., a partial fill size of 40 is truncated to 36 to
support six 6 x 64 channels).
Clock recovery type (crt): This is used in AAL1 UDT (unstructured
data transfer) applications only. It can be assigned the values:
"NULL", "SRTS", or "ADAPTIVE". A value of "NULL" is equivalent to
omitting this parameter and implies that the stream (T1 or E1)
encapsulated in ATM is either synchronous to the ATM network or is
re-timed, before AAL1 encapsulation, via slip buffers. The default
value used in the absence of this LCO can be hardcoded or
provisioned.
Forward Error Correction Enable (fe): This indicates whether FEC, as defined in ITU I.363.1 [1], is enabled or not. Possible values are: "NULL", "DELAY_SENSITIVE" and "LOSS_SENSITIVE". FEC can be enabled differently for delay-sensitive and loss-sensitive connections. A "NULL" value implies disabling FEC for an AAL1 connection. TABLE 4: Local Connection Options for AAL Type 2 +---------+---------------+---------------------------------------+ | LCO | Meaning | Values | +---------+---------------+---------------------------------------+ | pfl | Profile List | See below | | | | | +---------+---------------+---------------------------------------+ | smplCPS | Simplified CPS| on, off | | | [21] | | +---------+---------------+---------------------------------------+ | tmcu | Combined use | Integer microseconds | | | timer | (32-bit equivalent) | +---------+---------------+---------------------------------------+ | aalsap |Service access | AUDIO, MULTIRATE | | |point | | +---------+---------------+---------------------------------------+ | cktmd | Circuit mode | on, off | | | | | +---------+---------------+---------------------------------------+ | frmd | Frame mode | on,off | | | enable | | +---------+---------------+---------------------------------------+ | genpcm | Generic PCM | PCMA, PCMU | | | setting | | +---------+---------------+---------------------------------------+ | ted | Transmission | on,off | | |error detection| | +---------+---------------+---------------------------------------+ |rastimer | SSSAR | | | | reassembly | Integer microseconds | | | timer | (32-bit equivalent) | +---------+---------------+---------------------------------------+ Profile List (pfl): This is a list of profiles. Profile types are followed by profile numbers for each type. The ordering of profiles can imply preference, with the most preferred profile first. There can be multiple instances of the same profile type in this list. Spaces are used as delimiters within this list. Therefore, to comply with MGCP syntax [36], it is necessary to enclose this list in double quotes.
The format of the pfl parameter is as follows:
"<profileType#1><format list#1><profileType#2><format list#2> ...
<profileType #M><format list#M>"
where <format list#i> has the form <profile#i_1>...<profile#i_N>
The <profileType> parameter indicates the type of profile. It is
expressed in the format AAL2/<profileClass> where <profileClass>
identifies the source of the definition of the profile.
The <profileClass> can be assigned a string value indicating the
source of the subsequent profile numbers until the next <profileType>
field. The following rules apply to the contents of the
<profileClass> field:
- <profileClass> = "ITU" indicates profiles defined by ITU.
Examples: profiles defined in the I.366.2 specification [2].
- <profileClass> = "ATMF" indicates profiles defined by ATM
forum. Examples: profiles defined in af-vtoa-0113 [3] or af-
vmoa-0145.000 [21].
- <profileClass> = "custom" indicates profiles defined by a
corporation or a multi-vendor agreement. Since there is no
standard administration of this convention, care should be
taken to preclude inconsistencies within the scope of a
deployment.
- <profileClass> = <corporateName>
An equipment vendor or service provider can use its registered,
globally unique corporate name (e.g., Cisco, Telcordia etc.) as
a string value of the <profileClass>. It is suggested that
organizations maintain consistent definitions of the advertised
AAL2 profiles that bear their corporate name.
- The <profileClass> can be based on IEEE Standard 802-1990,
Section 5.1, which defines the globally unique, IEEE-
administered, three-octet OUIs used in MAC addresses and
protocol identifiers. In this case, the <profileClass> field
shall be assigned a string value of "IEEE:" concatenated with
<oui> where <oui> is the hex representation of a three-octet
field identical to the IEEE OUI. Since this is always
represented in hex, the "0x" prefix is not used. Leading zeros
may be omitted. For example, "IEEE:00000C" and "IEEE:C" both
refer to Cisco Systems, Inc.
The <profile#> parameter is expressed as a decimal number in the
range 1-255.
An example of the use of the pfl parameter is: L: atm/pfl:"AAL2/ITU 8 AAL2/ATMF 7 8 AAL2/custom 100 AAL2/cisco 200" The syntax for pfl can be represented compactly in the following ABNF (RFC2234) form: pfl = "%x22" 1*(profileType (1*profile#))"%x22" profileType = "AAL2/" profileClass space profile# = 1-255 space ; decimal integer followed by space profileClass = "ATMF"/"ITU"/"custom"/corporateName/("IEEE:" oui) corporateName = 1*ALPHA ;one or more alphanumeric characters oui = 1*6 HEXDIG; 1-6 hex digits per IEEE Standard 802-1990 space = %d32 Simplified CPS (smplCPS): This enables the AAL2 CPS simplification described in [21]. It can be assigned the following values: on, off. Under this simplification, each ATM cell contains exactly one AAL2 packet. If necessary, octets at the end of the cell are padded with zeros. AAL2 combined use timer (tmcu): This is defined in ITU I.363.2 [10]. It is an integer number of microseconds, represented as the decimal equivalent of 32 bits. AAL service access point (aalsap): The service access point for AAL2 is defined in ITU I.366.2 [2]. The aalsap local connection option can take on the following string values: AUDIO, MULTIRATE. Circuit mode (cktmd): This is used to enable circuit mode data [2]. It can be assigned a value of "on" or "off". Frame mode (frmd): This is used to enable frame mode data [2]. It can be assigned a value of "on" or "off". Generic PCM setting (genpcm): This indicates whether generic PCM encoding in AAL2 profiles is A-law or Mu-law. It can be assigned the string values of "PCMA" and "PCMU". Transmission error detection (ted): Transmission error detection is defined in ITU I.366.1 [11]. The ted local connection option can take on the following values: on, off. This local connection option is useful in qualifying the aalApp local connection option, when the value of the latter is "itu_i3661_unassured".
SSSAR reassembly timer (rastimer): This is defined in ITU I.366.1 [11]. It is an integer number of microseconds, represented as the decimal equivalent of 32 bits. When an endpoint supporting the ATM package is audited for capabilities, the following local connection options from Section 3.2 shall be returned: application (atm/aalApp). Further, if one of the values atm/ct is "AAL2", the following additional local connection options shall be returned: profile list (atm/pfl), simplified CPS (atm/smplCPS), service access point (atm/aalsap), circuit mode enable(atm/cktmd), frame mode enable (atm/frmd) and generic PCM setting (atm/genpcm). If more than one value is supported, these shall be expressed as a list of semicolon-separated values. For atm/smplCPS, atm/cktmd and atm/frmd, an audit can return "on", "off" or "on;off" depending on whether the mode is mandatory, unsupported or optional for the endpoint. An example of returning, in audit response, the local connection options defined in Section 3.2 is: A: atm/aalApp:itu_i3662, atm/pfl:"AAL2/ATMF 7 8", smplCPS:on;off, aalsap:MULTIRATE, cktmd:off, frmd:off, genpcm:PCMU;PCMA3.3 Service Layer
TABLE 5: Local Connection Options for the Service Layer +--------------+---------------+----------------------------------+ | LCO | Meaning | Values | +--------------+---------------+----------------------------------+ | vsel | Voice codec | See below | | | Selection | | +--------------+---------------+----------------------------------+ | dsel | Data codec | See below | | | Selection | | +--------------+---------------+----------------------------------+ | fsel | Fax codec | See below | | | Selection | | +--------------+---------------+----------------------------------+ | ccnf | Codec | Even number (4 - 32) hex digits | | | Configuration | | +--------------+---------------+----------------------------------+ | usi | ISUP User | Two hex digits | | | Information | | +--------------+---------------+----------------------------------+
Voice codec selection (vsel): This is a prioritized list of one or
more 3-tuples describing voice service. Each vsel 3-tuple indicates
a codec, an optional packet length and an optional packetization
period.
The vsel local connection option is structured as follows:
"<encodingName #1> <packetLength #1><packetTime #1>
<encodingName #2> <packetLength #2><packetTime #2>
...
<encodingName #N> <packetLength #N><packetTime #N>"
where the <encodingName> refers to a codec name such as PCMU, G726-
32, G729 etc. See [18] and [34] for a list of codecs with static
payload types. The <packetLength> is a decimal integer
representation of the packet length in octets. The <packetTime> is a
decimal integer representation of the packetization interval in
microseconds.
Voiceband data codec selection (dsel): This is a prioritized list of
one or more 3-tuples describing voiceband data passthrough service.
Each dsel 3-tuple indicates a codec, an optional packet length and an
optional packetization period. Depending on the application, the
dsel local connection option may or may not cover facsimile service.
This is indicated via an <fxIncl> flag preceding the list of 3-
tuples. This flag indicates whether the dsel list explicitly
addresses facsimile ("on" value) or not ("off" value). This flag can
also be set to "-", which is equivalent to setting it to "off".
If <fxIncl> is "on", then it is rarely useful to also include an fsel
option. However, it is syntactically correct to do so as long as the
dsel and fsel options include an identical set of 3-tuples, perhaps
in a different order.
If <fxIncl> is "off", then any fsel list may still be ignored if the
media gateway does not provide separate treatment of voiceband data
passthrough and fax. Since, in this case, there is no distinct
facsimile service from the media gateway's perspective, any fsel list
does not apply.
The dsel local connection option is structured as follows:
"<fxIncl> <encodingName #1> <packetLength #1><packetTime #1>
<encodingName #2> <packetLength #2><packetTime #2>
...
<encodingName #N> <packetLength #N><packetTime #N>"
where the <encodingName> refers to a codec name such as PCMU, G726-
32, G729 etc. The <packetLength> is a decimal integer representation
of the packet length in octets. The <packetTime> is a decimal
integer representation of the packetization interval in microseconds.
Facsimile codec selection (fsel): This is a prioritized list of one
or more 3-tuples describing fax service. Each fsel 3-tuple indicates
a codec, an optional packet length and an optional packetization
period. If the dsel option includes facsimile, the fsel connection
option should be consistent with it. Each fsel 3-tuple indicates a
codec, an optional packet length and an optional packetization
period. The fsel local connection option is structured as follows:
"<encodingName #1> <packetLength #1><packetTime #1>
<encodingName #2> <packetLength #2><packetTime #2>
...
<encodingName #N> <packetLength #N><packetTime #N>"
where the <encodingName> refers to a codec name such as PCMU, G726-
32, G729 etc. The <packetLength> is a decimal integer representation
of the packet length in octets. The <packetTime> is a decimal
integer representation of the packetization interval in microseconds.
Since spaces are used as delimiters within the vsel, dsel and fsel
lists, it is necessary to enclose these lists in double quotes [36].
The vsel, fsel and dsel parameters complement the rest of the local
connection options and should be consistent with them.
Examples of the use of these parameters are:
L: atm/vsel:"G729 10 10000 G726-32 40 10000"
L: atm/dsel:"off PCMA 10 10000 G726-32 40 10000"
L: atm/fsel:"PCMU 40 5000 G726-32 20 5000"
L: atm/vsel:"G729 10 10000 G726-32 40 10000"
L: atm/dsel:"on PCMA 10 10000 G726-32 40 10000"
The <packetLength>and <packetTime> can be set to "-" when not needed.
A <fxIncl> value of "-" is equivalent to setting it to "off". For
example:
L: atm/vsel:"G729 - - G726-32 - -"
L: atm/dsel:"- G729 - - G726-32 - -"
L: atm/fsel:"G729-24 - -"
The vsel, dsel and fsel local connection options can be used in the AAL1, AAL2 and AAL5 contexts. The <packetLength> and <packetTime> are not meaningful in the AAL1 case and should be set to "-". In the AAL2 case, these local connection options indicate the preferred use of some or all of the rows in a given profile table. If multiple 3- tuples are present, they can indicate a preferentially ordered assignment of some rows in that profile to voice, voiceband data passthrough or facsimile service (e.g., row A preferred to row B etc). If multiple profiles are specified in the pfl parameter (described in section 3.2), the profile qualified by these local connection options is the first profile in the list. Codec configuration (ccnf): This is used to convey the contents of the single codec information element (IE) defined in [30]. The contents of this IE are: a single-octet Organizational Identifier (OID) field, followed by a single-octet Codec Type field, followed by zero or more octets of a codec configuration bit-map. The semantics of the codec configuration bit-map are specific to the organization[30, 31]. Since this bit-map is always represented in hex format, the "0x" prefix is omitted. Leading zeros are not omitted. For example: L: atm/ccnf:01080C indicates an Organizational Identifier of 0x01(the ITU-T). Using [57], the second octet (0x08) indicates a codec type of G.726 (ADPCM). The last octet, 0x0C indicates that 16 kbps and 24 kbps rates are NOT supported, while the 32 kbps and 40 kbps rates ARE supported. ISUP User Information (usi): This is used to convey the contents of the 'User Information Layer 1 protocol' field within the bearer capability information element defined in Section 4.5.5 of [32], and reiterated as the user service information element (IE) in Section 3.57 of [33]. The 'User Information Layer 1 protocol' field consists of the five least significant bits of Octet 5 of this information element. The usi LCO represented as a string of two hex digits. The "0x" prefix is omitted since this value is always hexadecimal. These hex digits are constructed from an octet with three leading '0' bits and the last five bits equal to the 'User Information Layer 1 protocol' field described above. Digits to the left are more significant than digits to the right. The resulting values of the usi local connection option are as follows:
VALUE MEANING
0x01 CCITT standardized rate adaption V.110 and X.30
0x02 Recommendation G.711 Mu-law
0x03 Recommendation G.711 A-law
0x04 Recommendation G.721 32 kbps ADPCM
and Recommendation I.460
0x05 Recommendations H.221 and H.242
0x06 Recommendation H.223 and H.245
0x07 Non-ITU-T standardized rate adaption
0x08 ITU-T standardized rate adaption V.120
0x09 CCITT standardized rate adaption X.31 HDLC flag stuffing
(page 19 continued on part 2)