Electrical computers and digital data processing systems: input/ – Input/output data processing – Peripheral configuration
Reexamination Certificate
2001-03-23
2003-12-02
Park, Ilwoo (Department: 2182)
Electrical computers and digital data processing systems: input/
Input/output data processing
Peripheral configuration
C710S010000, C710S014000, C710S015000, C710S016000, C710S017000
Reexamination Certificate
active
06658499
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to customer premises equipment (“CPE”) asymmetric digital subscriber line (“ADSL”) modems. More specifically, the invention relates to CPE ADSL universal serial bus (“USB”) modems.
BACKGROUND OF THE INVENTION
ADSL USB modems utilize some of the latest advances in computer interface and telecommunications technology. ADSL is a form of DSL (digital subscriber line) technology that is typically utilized for Internet access because of its fast downstream data transmission characteristic. One significant benefit of certain types of DSL technology, such as ADSL, is that it can be conducted over existing telephone lines by using higher frequency signals than common voice-band signals. Thus, in an ADSL application, a telephone line can be utilized as the common, simultaneous transmission medium for Internet data and voice-band data.
USB is a hardware interface technology that offers the capability to connect multiple devices (“USB devices”) to a computer, such as a personal computer (“PC”) or network server, via a common bus (a “USB bus”). Many computers are now produced with USB capability, and many computer peripherals are now produced to operate as USB devices, for example, printers, modems, and digital cameras. One significant benefit obtained by the use of USB technology is “hot-swap” capability, that is, the capability to connect or disconnect USB devices from a computer while its operating system is active. Further, USB devices can be installed without physically making internal access to the computer (e.g., to access a card slot), since the USB bus provides a means for external connections to the computer. Thus, the combination of ADSL and USB technology in a modem implementation can offer significant benefits for the transfer of data between a computer and a telecommunications network.
An ADSL USB modem is a CPE (customer premises equipment) ADSL modem that connects to a computer that has a USB bus. In an ADSL USB network, the ADSL line and the USB bus are the two links that have variable bandwidth (i.e., data transmission capacity).
FIG. 1
shows a block diagram of a typical ADSL USB network
100
, as is known in the prior art. The network
100
includes several elements. A DSL access multiplexer (DSLAM)
102
, typically located at a telephone company central office (CO), intermixes voice signals and data signals (e.g., Internet data) that are transmitted to a customer premises (CP) via the local loop of an ADSL line
108
. An ADSL USB modem
104
interfaces the ADSL line
108
to a USB bus
110
. A computer
106
connects to the ADSL USB modem
104
via the USB bus
110
and typically transceives data signals with the DSLAM
102
. Although not shown, other CPE devices capable of transceiving voice or data signals may also be connected to the ADSL line
108
in the network
100
. Furthermore other CPE USB devices (not shown) may be connected to the computer
106
via the USB bus
110
.
In a typical communications network, such as the ADSL USB network
100
, there may be several other components that are intermediate between the DSLAM
102
and the local loop of an ADSL line
108
, for example, a main distribution frame (MDF). In
FIG. 1
as well as in subsequent figures that are applicable, the existence of such components is acknowledged by a break in the ADSL line
108
between the DSLAM
102
and the ADSL USB modem
104
. Such additional components will not be shown in the figures or be described since the discussion of them is not needed to facilitate the description of the present invention.
As previously mentioned, the ADSL line and the USB bus are the two links in an ADSL USB network, such as the network
100
of
FIG. 1
, that have variable bandwidth. For example, in a typical ADSL USB network, the data rate (i.e., the data transmission speed) of the ADSL line can be described by the following relational equation: 32 Kbps≦Data Rate≦8.192 Mbps, where Kbps is kilo-bits per second and Mbps is mega-bits per second. It is noted that the actual data rate of a given: ADSL line is dependent on several factors, including line quality and level of service, and a data rate above the typical 8.192 Mbps may be available in some networks. Furthermore, the available bandwidth on a given isochronous (i.e., time dependent) channel of the USB bus in a typical ADSL USB network can be described by the following relational equation: 0 bps≦Available Bandwith≦8.184 Mbps. It is noted that the actual isocohronous bandwidth available on a given channel is dependent on several factors, including the number of USB devices connected to the USB bus. From the two relational equations above, it can be seen that it is possible for the ADSL line data rate to exceed the available USB bus bandwidth.
In order for the end-to-end system of an ADSL line and a USB bus to operate efficiently, a certain relationship must be maintained between them. Specifically, the USB bus bandwidth that is allocated to the interfacing ADSL USB modem must be somewhat greater than the ADSL line data rate If this relationship is not maintained, data being transmitted to the computer via the ADSL USB network (e.g., network
100
of
FIG. 1
) will eventually overflow the ADSL USB modem buffer and be lost, an event commonly referred to in the art as “bottle-necking”. When such an event occurs, the upper layer protocols, such as TCP/IP (Transmission Control Protocol/Internet Protocol), will detect an error and request re-transmission, resulting in degraded system throughput.
An important aspect of a USB bus, as previously mentioned, is that it can be shared to connect multiple USB devices to a computer. There are several data transfer modes that can be implemented to transfer data over a USB bus. Three of these modes, bulk, interrupt, and isochronous, are typically very applicable for high bandwidth USB devices (i.e., devices that consume a large portion of the total USB bandwidth). In practice, such devices include those that operate in the 0.5 Mbps to 8 Mbps range. In this regard,
FIGS. 2A-2C
show illustrations of typical signal formats for bulk, interrupt, and isochronous transfer modes, as are known in the prior art.
FIG. 2A
shows an illustration of a typical bulk transfer mode signal format
200
, as is known in the prior art. The bulk mode format
200
includes token packets
202
,
206
, data packets
203
,
207
, and hand-shake packets
204
,
208
. Each packet is identified by a packet ID (PID). For example, token packet
202
has an “IN” PID which identifies the packet as input token packet (i.e., from a USB device to the computer) and token packet
206
has an “OUT” PID which identifies the packet as output token packet (i.e., from the computer to a USB device). As shown in
FIG. 2A
, other PID's exist to identify packets in the bulk mode format
200
, but further discussion of such PID's is not necessary for the description of the present invention.
FIG. 2B
shows an illustration of a typical interrupt transfer mode signal format
210
, as is known in the prior art. Similar to the bulk mode format
200
(FIG.
2
A), the interrupt mode format
210
includes a token packet
211
, a data packet
212
, and a hand-shake packet
213
. In an early version of the interrupt mode format
210
, only input token packets are available (as shown), but later versions may also have output token packets as well. Finally,
FIG. 2C
shows an illustration of a typical isochronous transfer mode format
220
, as is known in the prior art. As is shown, the isochronous mode format is different from the bulk mode
200
or interrupt mode
210
formats. This is because isochronous transfer mode is time-dependent. Thus, the isochronous mode format
220
has only a token packet
221
and a data packet
222
to give it less signal overhead.
Isochronous transfer mode differs from bulk or interrupt transfer modes (which, as stated above, are quite similar) in the way that transfers are scheduled by the computer and in the amount of protocol overhead that transf
Day Robert A.
Khederzadeh Kamran
Patel Kamal
Globespanvirata, Inc.
Park Ilwoo
Thomas Kayden Horstemeyer & Risley
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