Telecommunications Industry Association (TIA)
TR-30.1/01-03-009
St. Petersburg, Florida, 7-9 March 2001
COMMITTEE CONTRIBUTION
Technical Committee TR30 Meeting
SOURCE:
Surf Communication Solutions Ltd.
TITLE:
A Proposed Method for Combining MoIP type II
with Data Off-Loading service
DISTRIBUTION:
Meeting attendees
CONTACT:
Avi Fisher
Tel: +972 (4) 909-5705
Cell: +972 (5) 445-7609
Email: avi@surf-com.com
Oren Somekh
Tel: +972 (4) 909-5706
Cell: +972 (5) 429-0857
Email: oren@surf-com.com
________________________________
Abstract
This contribution presents an alternative, unified architecture for both MoIP and data
off-loading services. The new solution provides benefits in comparison to the
commonly used solution, such as higher channel density and reduced IP bandwidth
requirements.
Copyright Statement
The contributors grant a free, irrevocable license to the Telecommunications Industry
Association (TIA) to incorporate text contained in this contribution and any
modifications thereof in the creation of a TIA standards publication, to copyright in
TIA's name any standards publication even though it may include portions of this
contribution, and at TIA's sole discretion to permit others to reproduce in whole or in
part the resulting TIA standards publication.
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Telecommunications Industry Association (TIA)
St. Petersburg, Florida, 7-9 March 2001
1 Abbreviations
AC
ARQ
DC
DOL
DP
EC
GW
HDLC
IP
IPSEC
L2TP
LAC
LNS
MoIP
NS
PHY
PPP
PSTN
RARQ
UDP
VPN
Access Concentrator
Automatic Retransmission reQuest
Data-Compression
Data Off-Loading
Data-Pump
Error-Correction
GateWay
High Level Data Link Control
Internet Protocol
IP SECurity protocol
Layer 2 Tunneling Protocol
L2TP Access Concentrator
L2TP Network Server
Modem over IP
Network Server
PHYsical layer
Point-to-Point Protocol
Public Switched Telephone Network
Reliable ARQ
User Datagram Protocol
Virtual Private Network
2 Overview
DOL service is intended to off-load long Internet modem calls from the PSTN
backbone to IP networks. The commonly used solution (see Section 4) is to place
LAC unit near the DLC or CLAS 5 switch. The LAC captures the modem calls,
terminates them and tunnels them through the L2TP tunneling protocol to the LNS for
further handling (Internet access or VPN access).
This contribution is intended to provide an alternative solution to the DOL service.
This alternative solution is based on the MoIP type II (see [1], [2]). Having the same
unit handle both services (see Section 5) provides a compact solution due to protocol
stack reduction. This solution provides additional benefits like higher DOL channel
density and lower IP bandwidth utilization over the existing solution.
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Telecommunications Industry Association (TIA)
St. Petersburg, Florida, 7-9 March 2001
3 MoIP type II Architecture
The MoIP type II architecture is presented in Figure 1.
Terminal
Terminal
PPP
PPP
HDLC
DC
GW
GW
RARQ
RARQ
HDLC
DC
EC
EC
UDP
UDP
EC
EC
DP
DP
IP
IP
DP
DP
PHY
PHY
PSTN
IP
PSTN
Figure 1 – MoIP Type II Architecture
The term RARQ means a reliable ARQ transport protocol, running above the UDP
protocol (for example, see [2]). In addition, if security features are required, protocols
such as IPSEC can be used to ensure that payload and control information are
transferred in a secured manner over the IP network. The IPSEC may be added to the
GW protocol stack between the RARQ and UDP protocols.
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Telecommunications Industry Association (TIA)
St. Petersburg, Florida, 7-9 March 2001
4 Commonly Used DOL Architecture
The commonly used DOL architecture is presented in Figure 2.
Terminal
LNS
LAC
PPP
PPP
HDLC
HDLC
DC
DC
UDP
UDP
EC
EC
IP
IP
DP
DP
PHY
PHY
PSTN
L2TP
L2TP
IP
Figure 2 – Commonly Used DOL Architecture
In addition, if security features are required, protocols such as IPSEC can be used to
ensure that payload and control information are transferred in a secured manner over
the IP network. The IPSEC may be added to the LAC protocol stack between the
L2TP and the UDP protocols.
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Telecommunications Industry Association (TIA)
St. Petersburg, Florida, 7-9 March 2001
5 Proposed MoIP/DOL Architecture
The proposed MoIP/DOL architecture is presented in Figure 3.
Terminal
NS
PPP
PPP
HDLC
HDLC
GW / AC
DC
DC
RARQ
RARQ
EC
EC
UDP
UDP
DP
DP
IP
IP
PHY
PHY
PSTN
IP
Figure 3 - Proposed MoIP/DOL Architecture
As it is seen from the diagram, the architecture includes the same MoIP Type II GW
unit. The LNS unit (now called an NS unit) is slightly changed; the L2TP protocol is
replaced by the RARQ, DC and HDLC protocols.
In addition, if security features are required, protocols such as IPSEC can be used to
ensure that payload and control information are transferred in a secured manner over
the IP network. The IPSEC may be added to the GW protocol stack between the
RARQ and UDP protocols.
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Telecommunications Industry Association (TIA)
St. Petersburg, Florida, 7-9 March 2001
6 Comparison of the MoIP/OL and the Commonly
Used DOL Architectures
 The same protocol stack is implemented in the GW/AC to support MoIP and
DOL services. There is no need to implement two sets of protocol stacks, one
for DOL service and one for MoIP service.
 The implementation of the proposed MoIP/DOL scheme is much more
efficient than the commonly used DOL method in both CPU utilization and
memory consumption. There is no need to implement heavy compression
protocols in the GW/AC. This makes the channel density of a unit, based on
the proposed method, about 25% denser then conventional LAC units.
 In the proposed MoIP/DOL scheme, both PPP compression and modem
compression are performed in the same unit (end terminal or NS). Therefore, it
is possible to eliminate one of the compression layers without degrading
bandwidth performance over the IP network. In the conventional method, the
PPP compression has to be implemented, otherwise IP payload will not be
compressed. With the new V.44 standard, the IP bandwidth can be reduced to
20% (transferring HTML files).
7 References
[1] TR30.1/10103002, TR30.1/10103002, “Update Issue List for V.MoIP”, TIA
TR30.1, St. Petersburg, Florida, USA, Mar 2001.
[2] PCM01-02, “MoIP Involving Partial Modem Termination”, ITU-T SG 11/16, LasVegas, Nevada, USA, Jan 2001.
[3] PCM01-06, “Modem Transport over IP using SPRT”, ITU-T SG 11/16, LasVegas, Nevada, USA, Jan 2001.
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