End-to-end and Split Auto-moding in MoIP gateways

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End-to-end and Split Auto-moding in MoIP gateways
Telecommunications Industry Association
(TIA)
TR-30.1/10204044
April 17-19, 2002, Albuquerque, NM
COMMITTEE CONTRIBUTION
Technical Committee TR-30 Meetings
SOURCE:
The CommWorks Corp., a 3Com company
TITLE:
End-to-end and Split Auto-moding in MoIP gateways
DISTRIBUTION:
Members of TR-30.1
CONTACT:
Jim Renkel
Office: +1.847.262.2539
E-mail: [email protected]
____________________
ABSTRACT
Previous contributions have proposed various forms of auto-moding support for MoIP gateways.
This contribution categorizes and compares them.
The company represented by this individual may have patents or published pending patent applications, the use of
which may be essential to the practice of all or part of this contribution incorporated in a TIA Publication and the
company represented by this individual is willing to grant a license to applicants for such intellectual property
contained in this contribution in a manner consistent with 2a) or 2b) of Annex H of the TIA Engineering Manual.
COPYRIGHT STATEMENT:
The contributor grants a free, irrevocable license to the Telecommunications Industry Association (TIA) to
incorporate text or other copyrightable material contained in this contribution and any modifications thereof in the
creation of a TIA Publication; to copyright and sell in TIA's name any TIA Publication even though it may include all
or portions of this contribution; and at TIA's sole discretion to permit others to reproduce in whole or in part such
contributions or the resulting TIA Publication. This contributor will also be willing to grant licenses under such
copyrights to third parties on reasonable, non-discriminatory terms 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.
Telecommunications Industry Association (TIA)
April 17-19, 2002, Albuquerque, NM
Page 2 of 14
Table of Contents
1
2
3
Introduction ............................................................................................................................................ 3
End-to-end and split automoding in xOIP networks .............................................................................. 5
Comparison of split and end-to-end auto-moding ............................................................................... 11
3.1
Split auto-moding precludes VBD mode data transfer phase ...................................................... 11
3.2
Split automoding increases the use of unmatched modulations in modem relay mode .............. 11
3.3
Only modems with modulations in the split auto-mode sequences can connect ......................... 11
3.4
More standard modulation modem pairs connect via split auto-moding ...................................... 12
3.5
Non-standard modulation modems may not connect via split auto-moding................................. 12
3.6
Modem connect times may be faster (or slower) with split auto-moding ..................................... 12
3.7
Modem relay EC / DC negotiation is more difficult with split auto-moding ................................... 12
3.8
Split auto-moding is more complex to implement ......................................................................... 13
3.9
Split auto-moding is required for integrated gateways without auto-moding................................ 13
4 Conclusions and Recommendations for V.moip .................................................................................. 14
Table of Figures
Figure 1 - Two terminals connected via the PSTN ....................................................................................... 3
Figure 2 - Simple auto-moding sequence in the PSTN ................................................................................ 3
Figure 3 - Complex auto-moding sequence in the PSTN ............................................................................. 4
Figure 4 - Two terminals connected via a packet switched xOIP network ................................................... 5
Figure 5 – A simple split auto-moding sequence .......................................................................................... 6
Figure 6 - Another simple split auto-moding sequence ................................................................................ 7
Figure 7 - A complex split auto-moding sequence ........................................................................................ 8
Figure 8 - Another complex split auto-moding sequence ............................................................................. 9
Figure 9 - Split auto-moding within the V.8 auto-mode step ....................................................................... 10
3Com / CommWorks
End-to-end and Split Auto-moding in MoIP gateways
TR-30.1/10204044
Telecommunications Industry Association (TIA)
April 17-19, 2002, Albuquerque, NM
1
Page 3 of 14
Introduction
When two non-voice terminals (modems, facsimile machines, text terminals, etc.) connect via
the (circuit switched) PSTN, they go through an auto-moding sequence to determine the
application they will use in communicating with each other (data modem, facsimile, text, etc.)
and, within that application, the modulation they will use.
In general, an auto-moding sequence can be described as being comprised of a sequence of
steps, each step consisting of an offer by one terminal to use a particular modulation or set of
modulations and then an acceptance or not by the other terminal of (one of) the modulations
offered. The offer of a modulation or set of modulations and the acceptance or not of a
modulation are realized as tonal signals that in some cases have additional information encoded
in them. The modulations offered and accepted may implicitly identify the application to be used,
or the application may be explicitly encoded in offer and acceptance signals.
Because of the nature of the PSTN, this auto-moding sequence is necessarily end-to-end
between the two terminals, with the PSTN simply transporting the signals between the
terminals.
The following figure shows the connection of two terminals via the PSTN.
T1
PSTN
T2
Figure 1 - Two terminals connected via the PSTN
The following figure is an example of a rather simple end-to-end automoding sequence between
two terminals connected via a circuit switched network.
T1
T2
CM
ANSam
JM
CJ
Figure 2 - Simple auto-moding sequence in the PSTN
3Com / CommWorks
End-to-end and Split Auto-moding in MoIP gateways
TR-30.1/10204044
Telecommunications Industry Association (TIA)
April 17-19, 2002, Albuquerque, NM
Page 4 of 14
In this case, both terminals support V.8 and the auto-moding sequence consists of a single, V.8
step.
The following figure is an example of a somewhat more complex auto-moding sequence
between two terminals connected via a circuit switched network.
T1
T2
ANSam
USB1
1650 Hz
980 Hz
Figure 3 - Complex auto-moding sequence in the PSTN
In this case, the calling, T1, terminal only supports V.21 while the answering terminal, T2,
supports V.8, V.22(bis), and V.21. The automoding sequence consists of three steps,
corresponding the three modulation (groups) supported by the answering terminal.
3Com / CommWorks
End-to-end and Split Auto-moding in MoIP gateways
TR-30.1/10204044
Telecommunications Industry Association (TIA)
April 17-19, 2002, Albuquerque, NM
2
Page 5 of 14
End-to-end and split automoding in xOIP networks
When two non-voice terminals connect via a (packet switched) xOIP network, they will attempt
to go through the same auto-moding sequence as if they had been connected by the PSTN.
Now, however, because of the greater intelligence present in the xOIP network gateways, the
auto-moding sequence may be handled by the xOIP network in one (or, in fact, a mixture over
time) of several ways:
 All or a portion of the auto-moding sequence may be performed end-to-end between the two
terminals, as it was in the PSTN, with the xOIP network and its gateways simply transporting
the signals between the two terminals, as the PSTN did.
 Alternately, all or a portion of the auto-moding sequence may be performed separately
between each terminal and its adjacent gateway, with the xOIP network gateways each
terminating and generating auto-mode sequence signals from and to its adjacent terminal
with little or no communications occurring over the xOIP network between the gateways or
the end terminals.
The following figure shows two terminals connected via a packet switched xOIP netowrk.
T1
PSTN
G1
Packet
Sw itched
xOIP
Netw ork
G2
PSTN
T2
Figure 4 - Two terminals connected via a packet switched xOIP network
End-to-end automoding sequences in packet switched networks look just like they do in circuit
switched networks, with the addition of two xOIP gateways between the terminals, so no
examples of packet switched network end-to-end automoding sequences will be given.
3Com / CommWorks
End-to-end and Split Auto-moding in MoIP gateways
TR-30.1/10204044
Telecommunications Industry Association (TIA)
April 17-19, 2002, Albuquerque, NM
Page 6 of 14
The following figure is an example of a rather simple split automoding sequence between two
terminals connected via a packet switched network.
T1
G1
G2
ANSam
a
(ANS
2833
T2
m)
ANSam
AA
state
(MR!
)
CM
AC
JM(V.34)
CJ
Figure 5 – A simple split auto-moding sequence
In this case, the calling terminal, T1, only supports V.32 and the answering terminal, T2, only
supports V.34 (and, of course, V.8). The ANSam signal from T2 is passed through the gateways
using RFC 2833. T1, only supporting V.32, responds to the ANSam signal with an AA signal.
Upon detection of the AA signal, gateway G1 makes a definite transition to modem relay mode
(indicating split auto-moding) and responds to the AA signal with an AC signal, completing the
selection of V.32 as the modulation to be used between T1 and G1.
Upon receipt of the definite transition to modem relay mode, gateway G2 responds to the
ANSam signal from T2 with a CM signal (indicating all the modulations it supports, which
apparently includes V.34). T2, upon detection of the CM signal, responds with a JM signal
selecting V.34 as the modulation to be used between T2 and G2. G2, upon detection of the JM
signal, responds with a CJ signal, completing the V.8 auto-mode step.
3Com / CommWorks
End-to-end and Split Auto-moding in MoIP gateways
TR-30.1/10204044
Telecommunications Industry Association (TIA)
April 17-19, 2002, Albuquerque, NM
Page 7 of 14
The following figure is another example of a rather simple split automoding sequence between
two terminals connected via a packet switched network.
T1
G1
G2
T2
ANS
)
(ANS
2833
JM(V.34)
AC
ANSam
CJ
(MR!
)
AA
CM
state
Figure 6 - Another simple split auto-moding sequence
In this case, the calling terminal, T1, only supports V.34 (and, of course, V.8) and the answering
terminal, T2, only supports V.32. This is the same as the previous example except the calling
and answering terminals are reversed. The ANS signal from T2 is passed through the gateways
using RFC 2833, but gateway G1 turns it into an ANSam signal. Terminal T1 responds to the
ANSam signal from G1 with a CM signal (indicating all the modulations it supports, which
apparently includes V.34). G1, upon detection of the CM signal, makes a definite transition to
modem relay mode (indicating split auto-moding) and responds with a JM signal selecting V.34
as the modulation to be used between T1 and G1. T1, upon detection of the JM signal,
responds with a CJ signal, completing the V.8 auto-mode step.
Upon receipt of the definite transition to modem relay mode, G2 responds to the ANS signal
with an AA signal. Upon detection of the AA signal, terminal T2 responds to the AA signal with
an AC signal, completing the selection of V.32 as the modulation to be used between T2 and
G2.
3Com / CommWorks
End-to-end and Split Auto-moding in MoIP gateways
TR-30.1/10204044
Telecommunications Industry Association (TIA)
April 17-19, 2002, Albuquerque, NM
Page 8 of 14
The following figure is an example of a somewhat more complicated split automoding sequence
between two terminals connected via a packet switched network.
T1
G1
G2
ANS
)
(ANS
2833
JM(V.34)
)
USB1
ANSam
CJ
(MR!
AA
CM
state
T2
1650 Hz
980 Hz
Figure 7 - A complex split auto-moding sequence
In this case, the calling terminal, T1, only supports V.34 (and, of course, V.8) and the answering
terminal, T2, only supports V.22 and V.21, with V.25. The ANS signal from T2 is passed through
the gateways using RFC 2833, but gateway G1 turns it into an ANSam signal. Terminal T1
responds to the ANSam signal from G1 with a CM signal (indicating all the modulations it
supports, which apparently includes V.34). G1, upon detection of the CM signal, makes a
definite transition to modem relay mode (indicating split auto-moding) and responds with a JM
signal selecting V.34 as the modulation to be used between T1 and G1. T1, upon detection of
the JM signal, responds with a CJ signal, completing the V.8 auto-mode step.
Upon receipt of thsssse definite transition to modem relay mode, G2 responds to the ANS signal
with an AA signal. T2, not supporting V.32, ignores the AA signal, and eventually ANS times
out. T2 generates a USB1 signal, which is ignored by G2 (We’re assuming G2 does not support
V.22.). Eventually, T2 times out its USB1 signal and generates 1650 Hz. G2, supporting V.21,
detects the 1650 Hz signal and responds with a 980 Hz signal, completing the selection of V.21
as the modulations to be used between T2 and G2.
3Com / CommWorks
End-to-end and Split Auto-moding in MoIP gateways
TR-30.1/10204044
Telecommunications Industry Association (TIA)
April 17-19, 2002, Albuquerque, NM
Page 9 of 14
The following figure is an example of another somewhat more complicated split automoding
sequence between two terminals connected via a packet switched network.
T1
G1
G2
T2
CT
2833
(CT)
CT
CJ
USB1
JM(V.34)
ANSam
CM
ANSam
am)
!)
(ANS
2833 state(MR
1650 Hz
980 Hz
Figure 8 - Another complex split auto-moding sequence
In this case, the calling terminal, T1, only supports V.21, with V.25, and the answering terminal,
T2, only supports V.34 (and, of course, V.8). Immediately upon connection, T1 transmit a calling
tone (CT) which is passed through the gateways to T2. The ANSam signal from T2 is passed
through the gateways using RFC 2833. G2, having seen CT, makes a definite transition to
modem relay mode, and responds to the ANSam signal from T2 with a CM signal (indicating all
the modulations it supports, which apparently includes V.34). T2, upon detection of the CM
signal, responds with a JM signal selecting V.34 as the modulation to be used between T2 and
G2. T1, upon detection of the JM signal, responds with a CJ signal, completing the V.8 automode step.
T1, not supporting V.8 or V.32, ignores the ANSam signal, and eventually ANSam times out. G1
generates a USB1 signal, which is ignored by T1 since it does not support V.22. Eventually, G1
times out its USB1 signal and generates 1650 Hz. T1, supporting V.21, detects the 1650 Hz
3Com / CommWorks
End-to-end and Split Auto-moding in MoIP gateways
TR-30.1/10204044
Telecommunications Industry Association (TIA)
April 17-19, 2002, Albuquerque, NM
Page 10 of 14
signal and responds with a 980 Hz signal, completing the selection of V.21 as the modulation to
be used between T1 and G1.
The following figure is another example of a simple split automoding sequence, in fact inside the
V.8 auto-mode step, between two terminals connected via a packet switched network.
T1
G1
G2
T2
ANSam
am)
(ANS
2833
ANSam
(MR!
)
CJ
JM(V.34)
CM(V.34)
CJ
JM(V.34)
CM(V.34)
state
Figure 9 - Split auto-moding within the V.8 auto-mode step
In this case, the both terminals only support V.34 (and, of course, V.8). The ANSam signal from
T2 is passed through the gateways using RFC 2833 to T1. Terminal T1 responds to the ANSam
signal from G1 with a CM signal (indicating it supports V.34). G1, upon detection of the CM
signal, makes a definite transition to modem relay mode (indicating split auto-moding) and
responds with a JM signal selecting V.34 as the modulation to be used between T1 and G1. T1,
upon detection of the JM signal, responds with a CJ signal, completing the V.8 auto-mode step.
Upon receipt of the definite transition to modem relay mode, G2 responds to the ANSam from
T2 signal with a CM signal (indicating it supports V.34, perhaps among other modulations). T2,
upon detection of the CM signal responds with a JM signal selecting V.34 as the modulation to
be used between T2 and G2. G2, upon detection of the JM signal, responds with a CJ signal,
completing the V.8 auto-mode step.
3Com / CommWorks
End-to-end and Split Auto-moding in MoIP gateways
TR-30.1/10204044
Telecommunications Industry Association (TIA)
April 17-19, 2002, Albuquerque, NM
3
Comparison of split and end-to-end auto-moding
3.1
Split auto-moding precludes VBD mode data transfer phase
Page 11 of 14
Split auto-moding requires the gateways to operate in modem relay mode. To have all or part of
the auto-moding or modulation training or both phases performed with the gateways in modem
relay mode, then have the gateways come back to VBD mode, and have the modems
successfully communicate seems difficult, if not impossible.
Thus, where split auto-moding is employed, the modems’ data transfer phases will be
performed with the gateways in modem relay mode.
End-to-end auto-moding, however, allows the modems’ data transfer phase to be performed
with the gateways in either modem relay or VBD mode.
3.2
Split automoding increases the use of unmatched modulations in modem
relay mode
End-to-end auto-moding essentially observes the auto-moding sequence between the two
modems and “jumps in” to the sequence if the auto-moding sequence picks modulation(s) for
the modems to use that are supported by their adjacent gateways. At that time, the gateways
switch to modem relay mode, complete the modulation training and error correction and data
compression negotiation if appropriate, and then perform the data transfer phase.
Since, at any given time, end-to-end auto-moding is performing the same auto-mode step at
both modems. and the modulations to be used by the modems during data transfer phase are
chosen within the same auto-moding step, the only opportunity within end-to-end automoding
for different modulations to be chosen for the modems to use in data transfer phase in during a
V.8 auto-moding step. This is because only the V.8 step allows significantly different
modulations to be chosen during it. Ignoring trivial variants such as V.22bis versus V.22, no
other auto-moding step allows more than one modulation to be chosen during it.
Split auto-moding, on the other hand, does not necessarily perform the same auto-mode step at
both modems at the same time. That may occur in practice, but if it does it’s a co-incidence. Nor
need the modulation(s) to be used by the modems in data transfer phase be chosen within the
same auto-moding step. Again, that may occur in practice, but if it does it’s a co-incidence.
Thus split auto-moding increases the use of unmatched modulations in modem relay mode data
transfer phase.
3.3
Only modems with modulations in the split auto-mode sequences can
connect
In split auto-moding, each modem must have a modulation in common with its adjacent
gateway. This is more probable with standard modulations and gateways that implement a large
number of, if not all, standard modulations.
However, modems, at least one of which does not have a modulation in common with its
adjacent gateway will connect, in VBD mode, when end-to-end auto-moding is used, so long as
the two modems have a modulation in common.
3Com / CommWorks
End-to-end and Split Auto-moding in MoIP gateways
TR-30.1/10204044
Telecommunications Industry Association (TIA)
April 17-19, 2002, Albuquerque, NM
3.4
Page 12 of 14
More standard modulation modem pairs connect via split auto-moding
This follows directly from the previous observation. Two modems that do not have a modulation
in common may none-the-less connect using split auto-moding so long as they each have a
modulation in common with their adjacent gateway. While this connection may be made with
end-to-end auto-moding if the modems implement V.8 and the (unmatched) modulations can be
reached from V.8, the connection will be made when split auto-moding is used and the
modulations can not be reached from V.8.
As it is more likely that a gateway will implement a standard modulation than a proprietary one,
more standard modulation modem pairs connect via split auto-moding.
3.5
Non-standard modulation modems may not connect via split auto-moding
Conversely, modems that would connect through a circuit switched network only via a
proprietary modulation will only connect through a packet switched network using split automoding if both gateways have implemented that modulation.
As it is less likely that a gateway will implement a proprietary modulation than a standard one,
less non-standard modulation modem pairs will connect via split auto-moding.
3.6
Modem connect times may be faster (or slower) with split auto-moding
Modem connect time is defined as the time from the completion of the “physical” connection
between the modems through a circuit switched or packet switched network until the start of
data transfer between them. In end-to-end automoding, it is the sum of the automoding time (to
select the modulation(s) to be used between the modems), plus the modulation(s) training time,
plus the error correction / data compression negotiation time. With end-to-end auto-moding
through a packet switch network, the connect time will be close to that in a circuit switched
network.
In split auto-moding through a packet switched network, the end-to-end modem connect time is
the maximum of the two modem / gateway connect times. Depending on the order of the steps
in the two auto-moding sequences, and at which step in each sequence the modulation to be
used by a modem / gateway is chosen, one or the other or both of these connect times, and
hence the maximum, can vary greatly from the connect time in a circuit switched network or in a
packet switched network with end-to-end auto-moding.
3.7
Modem relay EC / DC negotiation is more difficult with split auto-moding
The negotiation of the error correction and data compression protocols to be used over a
modem connection begins as soon as the modulation training is complete. In connections over
a circuit switched network or over a packet switched network using VBD mode, there is only one
modulation and it is used end-to-end between the two modems. Hence, the error correction and
data compression negotiation is relatively straight forward.
In a modem connection using modem relay over a packet switched network, there are two
modulations used, one between each gateway and its adjacent modem. Those modulations
may be the same or may be different. It is unlikely that both modulations will complete their
training at exactly the same time, and this complicates the error correction and data
compression negotiation.
3Com / CommWorks
End-to-end and Split Auto-moding in MoIP gateways
TR-30.1/10204044
Telecommunications Industry Association (TIA)
April 17-19, 2002, Albuquerque, NM
Page 13 of 14
With end-to-end auto-moding, the selection of the two modulations and the start of their training
is nearly simultaneous. The major factor then in any difference in the completion of their training
is the relative lengths of the two modulations’ training.
With split auto-moding, the two modulations are not necessarily selected at the same time, and
hence the difference in the start of their training also become a factor in the difference in the
completion of their training. The differences in the times of the start of training may offset the
differences in the lengths of the training, making the difference in the end of the training and the
start of the error correction and data compression negotiation smaller. This would simplify the
negotiation.
But the differences in the start of training and the differences in the length of training also may
NOT offset. This will complicate the error correction and data compression negotiation.
3.8
Split auto-moding is more complex to implement
In end-to-end auto-moding, the auto-moding is driven by the modem that is operating in answer
mode. The gateways simply react to the signals that are exchanged between the end modems.
In split auto-moding, one gateway, the originate mode gateway (That is, the gateway that is
adjacent to the modem that is operating in answer mode.) must drive an auto-mode sequence
as if it were an end modem operating in answer mode (The other gateway, the answer mode
gateway, simply reacts to the auto-mode sequence as if it were a modem operating in originate
mode.).
While, for any given connection, only one gateway in a split auto-moding connection will be
driving an auto-moding sequence, all gateways that support split auto-moding must have the
ability to drive an auto-mode sequence. This is because we cannot guarantee in advance that a
gateway will always be operating in originate mode.
As the implementation and testing of an answer mode auto-mode sequence can be as difficult
and complex as the implementation and testing of another modulation, this will be a significant
increase over the difficulty and complexity of implementing and testing a gateway that only
supports end-to-end auto-moding.
3.9
Split auto-moding is required for integrated gateways without auto-moding
An integrated gateway is a gateway in which the modems that are adjacent to it and normally
external to the gateway are integrated with and internal to the gateway. This can be a significant
complexity reduction in the construction of a gateway and modem concentrator combination. A
further significant complexity reduction can be achieved if the gateway does not have to support
VBD mode, i.e., it operated only in relay mode.
This type of gateway can be easily constructed on a standard COTS server platform, eliminating
the need for hardware that is customized to gateway or modem concentrator application. This
would reduce the implementation of such a gateway to a strictly software effort, with no
modulation software being necessary.
To further reduce the software development and testing complexities, it is desirable that this
gateway not have to drive an auto-moding sequence. As driving an auto-mode sequence would
only be necessary in an end-to-end auto-moding connection when the gateway’s modem was
3Com / CommWorks
End-to-end and Split Auto-moding in MoIP gateways
TR-30.1/10204044
Telecommunications Industry Association (TIA)
April 17-19, 2002, Albuquerque, NM
Page 14 of 14
operating in answer mode, the implementation of an answer mode auto-mode sequence can
only be avoided if the other gateway supports split auto-moding.
4
Conclusions and Recommendations for V.moip
From the above, it is not possible to conclude that one form of auto-moding, either split or endto-end, is inferior to the other in all situations and, therefore, need not be considered in the
V.moip specification.
Therefore we recommend that V.moip support both split and end-to-end auto-moding.
Specifically, we recommend that the following agreements be adopted:
7.x0
7.x1
Agreed
(04/02)
Agreed
(04/02)
that V.moip shall include support for end-to-end auto-moding.
that V.moip shall include support for split auto-moding.
3Com / CommWorks
End-to-end and Split Auto-moding in MoIP gateways
TR-30.1/10204044
TR-30.1 /
10204044
TR-30.1 /
10204044

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