Subject: MSF Liaison - How to specify an ATM bearer

From: Brian Rosen <[email-masked]>
Date: Wed, 8 Sep 1999 21:33:29 -0400

My apologies for not putting this on the list sooner:
 
MSF Media Control Working Group Liaison to IETF MEGACO WG

Abstract:

In the MSF MCWG review of the MEGACO/H.248 protocol, it was noted that there
is no way to specify an ATM bearer. Specifically, there is no syntax in the
components of the Stream Descriptor in SDP and insufficient parameters in
the "native" format to specify ATM bearers.

This liaison proposes syntax for both SDP and tags for "native" formats to
specify an ATM AAL1, AAL2 and AAL5.

Disclaimer:

This document has been approved by the MSF Technical Committee as a liaison
to the IETF MEGACO Working Group. The attachment is the current version
which was issued August 26, 1999. It is representative of the current state
of work in the MSF Media Control Working Group. However, this liaison and
its attachment in no way binds MSF or any of the member organizations of MSF
to the ideas presented. It should also be noted that this work is being
submitted at this time in the interests of developing industry agreement.
The MSF may revisit this work in the future and reserves the right to make
additions, changes, or deletions, including complete withdrawal.

1.      BM__Toc458568597BM__Toc459903670General ATM properties

Properties of all AAL types for an ATM connection. 

Full Tag

Short Tag

Type

Values

ATM Address

AESA

String/Octet String

ATM End System Address

VPI/VCI

VPVC

2 x 32 bit Integer

VPI/VCI

Service Category

SC

Enumeration

CBR, UBR, nrt-VBR, rt-VBR, ABR

Broadband Bearer Class

BCOB

Enumeration

A, X, VP

Broadband Transfer Capability

BBTC

Enumeration

CBR, CBR/CLR, rt-VBR, rt-VBR/CLR, nrt-VBR, nrt-VBR/CLR, ABR

I.371 ATM Traffic capability

ATC

Enumeration

DBR, SBR 1, 2 or 3

Susceptibility to clipping

STC

Enumeration

Susceptible, Not-susceptible

User Plane connection configuration

UPCC

Enumeration

Pt-to-pt, Pt-to-mpt

Peak Cell Rate

PCR

24 bit integer

Sustainable Cell Rate

SCR

24 bit integer

Maximum Burst Size

MBS

24 bit integer

Best Effort Indicator

BEI

Boolean

Tagging

TI

Boolean

Frame Discard

FD

Boolean

Forward P-P CDV

FCDV

24 bit integer

Backward P-P CDV

BCDV

24 bit integer

Forward Cell Loss Ratio

FCLR

8 bit integer

Backward P-P Cell Loss Ratio

BCLR

8 bit integer

Forward Cell Delay Variation

FCDV

24 bit integer

Backward Cell Delay Variation

BCDV

24 bit integer

Forward Acceptable P-P-P CDV

FACDV

24 bit integer

Backward Acceptable P-P CDV

BACDV

24 bit integer

Forward Cumulative P-P CDV

FCCDV

24 bit integer

Backward Cumulative P-P CDV

BCCDV

24 bit integer

Acceptable Forward Cell Loss Ratio

FCLR

8 bit integer

Acceptable backward Cell Loss Ratio

FCLR

8 bit integer

End-to-end transit delay

EETD

16 bit integer

AAL Type

AAL

Enumeration

AAL1, AAL2, AAL5

[Brian notes: each of the PCR, SCR, MBS and CLR entries needs to have two
entries CLP=0, CLP=0+1. The original MSF liaison accidentally omitted them]

2. AAL1 Properties

Properties required for AAL1 connections 

Full Tag

Short Tag

Type

Values

AAL1 Subtype

AAL1ST

Enumeration

Voice, Circuit, Audio, Video

CBR Rate

CBRR

Enumeration

DS0,DS1,DS2,32064,DS3,97728,E1,E2,E3,

139264,Nx64 ,Nx8,Nx300

Multiplier

MULT

16 bit Integer

Multiplier, or n x 64k/8k/300

Source Clock Frequency Recovery Method

SCRI

Enumeration

NULL, SRTS,ACM

Error Correction Method

ECM

Enumeration

FEC-LOSS, FEC-DELAY

Structured Data Transfer Blocksize

SDTB

16 bit Integer

blocksize of SDT CBR service

End-to-end timing required

EETR

Boolean

In broadband bearer capability

Partially filled cells identifier

PFCI

8 bit Integer

1-47

3.      AAL5 properties

        Properties required for AAL5 connections 

Full Tag

        Short Tag

        Type

        Values

Forward Maximum CPCS-SDU Size 

        FMSDU

        32 bit Integer

        maximum CPCS-SDU size sent in the direction from the calling user to
the called user

Backwards Maximum CPCS-SDU Size 

        FMSDU

        32 bit Integer

        maximum CPCS-SDU size sent in the direction from the called user to
the calling user

SSCS Type

        VPVC

        2 x 32 bit Integer

        VPI/VCI

Service Category

        SC

        Enumeration

        SSCOP-Assured, SSCOP-NonAssured, FR-SSCS

4.      AAL2 properties

Properties required for AAL2 connections 

Full Tag

Short Tag

Type

Values

Timer_CU

Timer_CU

32 bit Integer

Milliseconds to hold partially filled cell before sending

Maximum minicell payload size

Max CPSSDU

8 bit Integer

45

Set CLP bit

SCLP

Boolean

True if CLP bit is to be set

End-to-end timing required

EETR

Boolean

Service Category

SC

Enumeration

SSCOP-Assured, SSCOP-NonAssured, FR-SSCS

4. SDP Syntax

The "c=" field contains connection data. 

The first sub-field is the network type, which is a text string giving the
type of network. "ATM" is defined to have the meaning "ATM network". 

The second sub-field is the address type. Three values are defined: "E.164",
"AESA" and "VC". In the first two cases, an explicit address is specified,
and a new VC is to be created. If VC is specified, an address is not
specified in the c= line, and an existing VC is used.

The third sub-field is the connection address.

m= A session description may contain a number of media descriptions. 

Each media description starts with an "m=" field, and is terminated by
either the next "m=" field or by the end of the session description. A media
field also has several sub-fields: 

The first sub-field is the media type. Currently defined media are "audio",
"video", "application", "data" and "control", though this list may be
extended as new communication modalities emerge (e.g., telepresense). The
difference between "application" and "data" is that the former is a media
flow such as whiteboard information, and the latter is bulk-data transfer
such as multicasting of program executables which will not typically be
displayed to the user. "control" is used to specify an additional conference
control channel for the session. 

The second sub-field is the VPI/VCI to be used. Either component can be
specified as "choose" (?), which is interpreted to mean the MG shall select
a value, which shall be returned to the MGC.

The third sub-field is optional, and is the Transport field. Values would be
similar to existing SDP practice. Specifically, RTP is used to create an RTP
connection over an ATM VC, as in H.323 Annex C.

For all other ATM parameters could be specified with a= parameters. The
"Short Tag" field from the prior tables forms the parameter name. For
example:

a=AALtype:2 Specifies an AAL2 connection. An example follows:

        c=ATM AESA 122cf.2234.ded01

        m=?/?

        a=AALtype:1

        a=PCR:171