Note: Descriptions are shown in the official language in which they were submitted.
CA 02338297 2001-O1-19
1
METHOD FOR CONNECTING TERMINAL DEVICES TO EXTERNAL
MODEMS
The invention is directed in general to a method for connecting terminal
devices an modems and, stated more specifically, to a method for connecting
terminal
devices to external modems via local networks (LAN).
ADSL (or, generally, xDSL) modems will enable significantly faster
Internet access in future compared to current modems. Similar to current
analog
modems, there will also be two versions for xDSL modems: external modems in
their
own housing that are connected via cable to the terminal device (client) as
well as
1 o internal modems that are either permanently installed in the terminal
device or are in
the form of plugin cards that can also be subsequently installed.
External modems must be connected to the terminal device via
corresponding interfaces, whereby what is referred to as the Ethernet is
especially
well-suited because of the high bandwidth and the low costs. Ethernet thereby
has the
advantage that a plurality of terminal devices can access one or more modems
via a
local network. This constellation is especially interesting, for example, in
networks in
small companies.
However, Ethernet as interface between terminal device and modem has
the disadvantage that the conversion of the data packets (PPP packets) that
are
2 0 exchanged via the modem path onto the local network (LAN) is very
involved.
For this purpose, T. Kwok et al., "An Interoperable End-to-end Broadband
Service Architecture over ADSL Systems (Version 3.0)", ADSL Forum Contribution
97215, December 1997, proposes the employment of a future standard protocol
(layer
2 tunneling protocol) with whose assistance PPP packets can be transmitted via
the
2 5 local network upon employment of UDP/IP. This solution, however, has a
number of
disadvantages:
The protocol known from the Prior Art is very complex and makes high
demands of the modem.
2. The proposed protocol offers many functions that are not used for the
3 0 application in the sense of the present invention.
CA 02338297 2001-O1-19
3. The protocol requires the prior configuration of the IP addresses of
terminal device (client) and modem. This, however, is very involved.
What would be desirable, in contrast, is a plug-and-play configuration
without prior configuration on the part of the user.
4. A direct control of the modem parameters is not possible.
The object of the present invention is therefore to avoid the
aforementioned disadvantages of the Prior Art and to offer a technique for
connecting
terminal devices and modems via local networks that is particularly user
friendly.
According to the present invention, a method for connecting terminal
devices to external modems is provided therefor wherein a plurality of modems
can
enter into communication with the terminal devices with a local network. A
number
of steps are implemented between one of the plurality of terminal devices and
one of
the modems for the connection setup. First, a search request is sent from the
corresponding terminal device to all modems that are connected to the local
network.
Those modems that have free resources respond with a reply to the inquiring
terminal
device. The terminal device subsequently makes a selection from the modem that
sent a reply, and a connection setup ensues proceeding from the terminal
device to the
selected modem by exchanging control information.
The external modems can, in particular, be ADSL modems.
2 o The local network can, in particular, be an Ethernet network.
Information for the connection setup and for setting the external modems
can be exchanged between the terminal devices and the external modems via an
integrated control channel.
The search request can contain further particulars about the required
2 5 bandwidth and/or the required protocol, whereby only those external modems
that can
meet all requirements according to the further particulars reply to a search
request.
Proceeding from the terminal device, settings of the modem can be
implemented via an integrated control channel.
For flow control of the transmitted data, the respectively receiving
3 0 terminal device or modem can output start/stop commands with which the
data
CA 02338297 2001-O1-19
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transmission of the respectively transmitting terminal device or modem can be
started
or, respectively, stopped.
After the connection setup, echo data that make it possible for the modem
to recognize whether the terminal device is active can be exchanged at
periodic
intervals.
The connection between the modem and the terminal device can be
automatically cleared down after a predetermined time when the modem or the
terminal device has received none of the echo data during this predetermined
time.
For connection cleardown, cleardown dat can be exchanged between the
1 o terminal device and the modem, whereby the resources of the connection are
in turn
released after the cleardown of the connection.
The present invention is explained in greater detail below on the basis of
an exemplary embodiment and with reference to the accompanying Figures. SHown
are:
Figure 1 the schematic structure of a system for the employment of the
inventive
method; and
Figure 2 the executive sequence of the method for the setup of a connection
from a
terminal device to a modem via a local network.
Figure 1 shows two ADSL modems 3, 4 by way of example that can set
2 o up a connection between an ADSL line 5 and a local network, for example an
Ethernet LAN 6. The ADSL modems 3, 4 can be connected to terminal devices
(client) 1, 2 with the Ethernet LAN 6.
The method for the setup of a connection between a terminal device 1, 2
and a modem 3, 4 via the Ethernet interface 6 thereby sequences as follows:
2 5 Phase 1: Seeking the modem (modems) (steps S 1, S2)
The searching terminal device l, 2 sends a search request (modem request)
to all ADSL modems 3, 4 attached to the Ethernet LAN network 6. A specific
address is employed for this purpose (also called "limited broadcast address"
255.255.255.255 in IP networks), this leading thereto that the packet of the
search
3 0 request is received by all modems 3, 4 at the connected Ethernet segment.
All
CA 02338297 2001-O1-19
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modems 3, 4 that support the protocol described here and have free resources
over and
above this, send a reply (modem reply). The terminal device 1, 2 receives all
replies
and is thus informed about all modems that still have free resources.
Subsequently,
the terminal device 1, 2 can select one of the available modems 3, 4.
Phase 2: Connection setup (steps S5, S6 [sic])
The terminal device now initiates a connection setup with the selected
modem. Specific control packets (connect request, connect confirm) are
exchanged
for this purpose, these ultimately leading to a communication relationship
(logical
connection) between terminal device and modem. Each side thereby assigns a
number (session ID) that, in conjunction with the IP address, unambiguously
identifies the communication relationship. Both numbers are contained in all
following packets of the connection.
Phase 3: Control of the modem (steps S5, S6)
In general, the terminal device now sends various control commands to the
modem (similar to current, analog modems). Among other things, the modem can
be
informed of the destination telephone number to which a connection is to be
set up.
Moreover, various modem parameters can be influenced such as, for example, bit
rate,
compression method, error correction, etc. These control commands are based on
the
commands for analog modems but can also contain specific expansions for xDSL.
2 o Phase 4: Data exchange (steps S7, S8)
When all settings have been made, the actual data exchange can begin, i.e.
PPP packets can be sent bidirectionally via the connection between modem and
terminal device. So that the reception buffers at both sides do not overflow,
a flow
control is provided according to the start/stop principle. Each receiver can
thus stop
2 5 the transmitter of the cooperating party by sending a stop command and can
restart it
in turn with a start command. Moreover, the connection can, if desired, be
monitored
from both sides by periodic transmission of echo packets. As a result thereof,
the
CA 02338297 2001-O1-19
modem can recognize when the terminal device no longer reacts or has been
switched
off.
Phase 5: Connection cleardown (steps S9, S 10)
In this phase, the connection between terminal device and modem is
5 cleared down in controlled fashion. To that end, further control packets
(release
request, release confirm) are exchanged that ultimately lead to the release of
the
occupied resources.
Message flow
Figure 2 shows the typical message flow between terminal device and
modem, beginning with the search phase (search request) up to an including the
end
of the connection. The individual messages exchanged between terminal device
and
modem or, respectively, vice versa are described in brief below.
Modem request (step S 1 )
This message is sent in order to find all modems connected to an Ethernet
segment. The message is sent to all stations and, in addition to containing
the layer-3
address of the searching terminal device, potentially contains further
information such
as user name, the desired bandwidth, the desired protocol, etc. These
information can
be interpreted by the modems, so that only those modems that can meet all
requested
demands reply.
2 o Modem reply (step S2)
All suitable modems reply with this message and thus inform the terminal
device of their own layer-3 address. This message is sent directly to the
terminal
device (no broadcast).
Connect request (step S3)
2 5 After the terminal device has selected one of the modems, the connection
setup is started proceeding from the terminal device. To this end, the
terminal device
CA 02338297 2001-O1-19
sends a connect request message to the selected modem. The parameters
contained in
the modem request message should be repeated in this message and further
parameters should be added, if necessary. The terminal device already assigns
a
session ID in order to enable an unambiguous allocation of the reply of the
modem.
Connect reply (step S4)
The modem replies with a connect reply message that also contains its
own session ID in addition to the session ID assigned by the terminal device.
This
message tells the terminal device whether the requested connection was
accepted or
refused. In case of an acceptance, the connection is in place and each side
knows the
session ID assigned by the other side, this being contained in all further
messages.
Given a refusal, the connection is cleared down from both sides.
Control (step SS)
Control commands can now be sent to the modem via the existing
connection, similar to the case given analog modems. For example, the terminal
device can interrogate various modem parameters such as type, the maximum bit
rate,
the dial capability, the ATM traffic classes that are supported, etc. The
terminal
device can also potentially influence some modem parameters and can initiate
the
setup of a dialed connection. In addition to the telephone number, other
parameters
that are required for the connection setup can also be indicated (for example,
the ATM
2 0 traffic class and the appertaining parameters such as peak bit rate and
the like).
ControlAck (step S6)
Each control command is acknowledged by a separate message that can
also contain the reply of the modem.
PayloadPacket (steps S7, S8)
2 5 This message contains the actual payload data, It can be sent in both
directions between terminal device and modem. Payload data are transmitted
CA 02338297 2001-O1-19
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unprotected; the loss of payload data can therefore not be recognized within
the
protocol described here.
Stop
This message can be sent in order to avoid the overflow of the proper
reception buffer. When a stop message is received, payload data are no longer
sent in
the opposite direction until a start message is received.
Start
See above.
Echo request
This message is employed in order to check the availability and
functionability of the respective cooperating party during an active
connection. When
an echo request is not answered with an echo reply message within a specific
time
span, the connection can be cleared down. For example, this mechanism allows
the
modem to clear down all active network connections when the terminal device
was
switched off without clearing the connection down in controlled fashion.
Echo reply
The reception of an echo request message is immediately acknowledged
with an echo reply message. As a result thereof, the cooperating party is
assured that
the connection is still active.
2 o Release request (step S9)
This message can be sent from both sides and serves the purpose of
clearing down an existing connection. The reception of a release request
message is
acknowledged with a release confirm message by the cooperating party.
Release confirm
2 5 See release request.
CA 02338297 2001-O1-19
Advantages of the disclosed method
The invention has the following advantages over known methods:
~ No modem-specific data need be configured in the terminal device. The
layer-3 address of the modem is determined by the method, and further
modem parameters can also be automatically determined by the terminal
device without a need for the user to intervene. A simple installation
without specific technical expertise is thus enabled (plug-and-play).
The method enables the direct control of the modem via an integrated
control channel. As a result thereof, modem commands can be
communicated like via a serial interface.
The proposed method is significantly simpler to realize.
Possible expansions
The described method assumes that the terminal device already has a
functioning Ethernet interface and an appertaining layer-3 address (for
example, IP)
address available to it. In order to likewise avoid this configuration event
and enable
a completely independent auto-configuration, the disclosed method can be
combined
with further protocols such as BOOTP or DHCP. To this end, the modem functions
as a simple BOOTP (DHCP) server from which the terminal device can receive its
configuration data. The configuration data (essentially the layer-3 address
and a few
2 0 other parameters such as sub-network mask) must be offered on the modem
for this
purpose. This can be Garner out by the manufacturer or by the network
operator. The
driver SW of the terminal device should be pre-set such that an automatic
configuration ensues via BOOTP (DHCP) as well as with the method described
here.
Any and all user-side configuration is avoided in this way.
2 5 The disclosed method can also be expanded in that the search message
(modem request) is transported across routers (similar to a BOOTP/DHCP proxy).
As
a result thereof, modems that are not directly connected to the local Ethernet
segment
but can only be reached via routers can also be found in larger networks. To
this end,
the router must contain a proxy function that forwards the sub-message to all
3 0 connected Ethernet segments (or, respectively, to all segments that
support broadcast).
CA 02338297 2001-O1-19
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The following advantages can, in particular, be realized by the present
invention:
In the introduction of the automatic search event with whose assistance all
connected modems can be automatically recognized.
2. In the introduction of a separate control channel via which the modem can
be configured and controlled.
In the employment of a simple method for flow control between terminal
device and modem.
4. In the combination with BOOTP or DHCP, as a result whereof a complete
auto-configuration is enabled.
