Telecommunications Industry Association
TR30.1/02-08-094
(TIA)
Waltham MA, August 6th – 9th, 2002
COMMITTEE CONTRIBUTION
Technical Committee TR-30 Meetings
SOURCE:
Conexant Systems
CONTACT:
Frank Chen
Phone:
+1 (949) 579-3296
Fax:
+1 (949) 579-3667
Email: [email protected]
TITLE:
Break Signals Process in MoIP
PROJECT:
PN-0012
DISTRIBUTION:
Members of TR-30.1
____________________
ABSTRACT
This contribution discuss break signals treatment in V.MoIP.
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and conditions for purpose of practicing a TIA Publication incorporates this contribution.
This document has been prepared by the Source Company(s) to assist the TIA Engineering Committee. It is proposed to the
Committee as a basis for discussion and is not to be construed as a binding proposal on the Source Company(s). The Source
Company(s) specifically reserves the right to amend or modify the material contained herein and nothing herein shall be
construed as conferring or offering licenses or rights with respect to any intellectual property of the Source Company(s) other
than provided in the copyright statement above.
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1.
Introduction
This contribution discusses break signal treatment in MoIP solution. It addresses how to handle
incoming break signal as well as the break acknowledge signal.
2.
Break Signals
Break signals exist for LAPM, MNP4 and V.14 protocol. In each of these protocols, the
characteristics of the break signals are different.
For V.42 LAPM the break signals are contained in a UI frame. In this UI frame, the break type
and break length may be defined. The break type is defined by two bits. These bits are the D bit
for discarding and S bit for sequential delivery. A field indicating the duration of the break is
defined and represents from 10ms to 2.54 seconds.
V.42 MNP4 transport a break signal in a LN frame. There are three types of break; destructive
and expedited, non destructive and expedited, and non-destructive and non expedited.
V.14 transports a break signal by transmitting 2M+3 or more “start” polarity data bits. The
duration of the break is determined by the number of “start” polarity bits transmitted.
Both of the V.42 LAPM and MNP protocols support a break acknowledge signal. This signal is
transmitted as an acknowledgment in response to a break signal. V.14 does not support a break
acknowledge signal.
3.
Break Signals Over IP
When a MoIP gateway receives a break signal from PSTN link, it shall relay break signal to
remote gateway. The remote gateway shall then relay the break signal to its PSTN link. A
gateway shall accurately carry break signal information across the IP link.
When a gateway receives a break acknowledge from its PSTN link, it shall forward this break
acknowledge signal to its peer gateway.
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3.1. Break Signal Conversion
In the situation where the two PSTN link of a MoIP connections are not connected using the
same error control protocol, some break information may be lost during the relay. A procedure
is necessary to translate the break characteristics in a best effort sense. This contribution
proposes the conversion as described in Table 1..
Table 1
To
LAPM
MNP4
V.14
Same
Break length
lost
Break type
lost, if no
break length,
go default*
Same
Same
Break type
lost, break
length go
default*
Treat as nonDestructive
and sequential
Treat as non
Destructive
and non
Expedited,
break length
lost
Same
From
LAPM
MNP4
V.14
* The default break length duration is 1.5 second.
3.2. Break and BreakAck Messages over IP Link
There are multiple ways to transport a break signal messages over the IP link. The followings
are two possible methods. This contribution does not present a preference to which method
should be used.
3.2.1. Multiple SPRT payload type for break signals
Three SPRT payload type are defined to uniquely transport the V.42 LAPM, MNP4 and V.14
break events as shown in Table 2
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Table 2
SPRT payload type
SPRT payload
LAPM_BRK
Break type and Break length
MNP4_BRK
Break type
V14_BRK
Break length in ms
3.2.2. Single SPRT payload type for break signals
Another alternative is to use a single SPRT payload type e.g. INFO_CTRL to transport the
break signals. This may be carried on data channel or expedited channel. The SPRT payload
could be defined in the following way as shown in Table 3.
Table 3
SPRT payload
content
1 byte
1 – LAPM, 2-MNP4, 3 – V.14
2nd byte
Break type (if not applicable, fill with 0)
3rd byte
Break length (if not applicable, fill with 0)
st
3.2.3. Break Ack message
The Break acknowledgement signal shall be sent over the IP link whenever a gateway receives
a break acknowledge from the PSTN link. This message may be defined as a simple SPRT
payload type with no content.
Table 4
SPRT payload type
SPRT payload
BRK_ACK
Break Acknowledge
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4.
Break Signal Process in MoIP
4.1. Non Destructive Break Signal
Whenever a gateway receives a non-destructive break signal from the PSTN link, it shall
respond with a break acknowledge to PSTN link and pass the break signal to the remote
gateway. No further action is needed by the gateway. It shall not take any further action or
response if it receives a break acknowledgement from IP link.
4.2. Destructive Break Signal
Whenever a gateway receives a destructive break signal from the PSTN link, proper action
needs to be taken to maintain the error control and compression integrity.
A gateway when it sends a destructive break signal to IP link, knows if it is likely to receive a
break acknowledge message back or not from the remote gateway. If the remote gateway has an
error correcting PSTN link, it will respond with a break acknowledge to the IP link, otherwise,
it will not send break ack to IP link.
4.2.1. Remote Gateway Has Non Error Correcting Connection
For this case, a gateway that receives a break signal from the PSTN link shall immediately reinitialise its link layer and reset its compression engine (if used). The gateway shall respond
with a break acknowledge to the PSTN link and forward a break message to the IP link.
The remote gateway shall relay the break signal from IP network to PSTN network.
4.2.2. Remote Gateway Has Error Correcting Connections
In this scenario, the gateway that receives a break signal from the PSTN link shall relay the
break signal to the remote gateway and also cease sending data to the remote gateway until a
break acknowledge is received from the remote gateway. Once it receives break acknowledge
from the remote gateway, it shall reset the trans-compression engine and resume sending data to
remote gateway.
Upon receiving a break signal from the IP network, the remote gateway shall relay the break
signal to PSTN and wait for break acknowledge from the PSTN. Upon receiving the break
acknowledge, it shall reset the trans-compression engine and relay a break acknowledge to the
IP network. The break acknowledgement message over IP network shall be sent using the same
channel as used for data. This will guarantee synchronization of the trans-compression engines
of the two gateways. Data sent before a break acknowledge shall be discarded before transcompression and data sent after a break acknowledge shall be trans-compressed and relayed to
the PSTN link.
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Upon receiving a break signal from the PSTN link, a gateway may respond with break
acknowledge immediately or it may wait until it receives a break acknowledge from the remote
gateway.
In the case where a gateway responds to a break from PSTN link immediately with a break
acknowledge, the gateway shall reinitialise the link layer and flow off further data from the
PSTN link into trans-compression engine. Once it receives the break acknowledge from the
remote gateway and has reset its trans-compression engine, it shall resume receiving data from
the PSTN link and input data to trans-compression engine.
In the situation where a gateway does not send a break acknowledge to the PSTN link
immediately, there will be no data coming from the PSTN link and the gateway does not need
to take any action on PSTN link. Once it receives a break acknowledge from the remote
gateway, the gateway shall relay the break acknowledge to the PSTN link and resume receiving
data from the PSTN link.
5.
Summary
It is proposed that the committee agrees to the following:
A
Agreed
V.MoIP gateway shall relay break signal from PSTN to
remote gateway.
B
Agreed
V.Moip gateway shall relay break signal from IP network
to PSTN
C
Agreed
V.Moip gateway shall relay break ACK from PSTN to IP
network
D
Agreed
V.Moip gateway shall use table 1 to convert break signal
when both PSTN links have different connections
E
Agreed
F
Agreed
V.Moip gateway shall stop sending data after sending
destructive break to IP network. When it receives break
ACK from IP link it shall flush trans-compression and
resume sending data over IP.
V.Moip gateway shall stop sending data to PSTN after it
sends destructive break to PSTN. It shall flush transcompression and resume sending data to PSTN when it
receives break ACK from PSTN.
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