Multiplex communications – Data flow congestion prevention or control – Flow control of data transmission through a network
Reexamination Certificate
1998-10-20
2003-03-04
Hsu, Alpus H. (Department: 2665)
Multiplex communications
Data flow congestion prevention or control
Flow control of data transmission through a network
C370S236200, C370S395520, C370S397000, C370S401000, C370S409000
Reexamination Certificate
active
06529479
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a network accessing technique based on an ATM (Asynchronous Transfer Mode) technique and a DSL (Digital Subscriber Line) technique.
2. Description of the Related Art
With the rapid popularization of the Internet, the demand for quickly interconnecting end users and the Internet has been increasing.
FIG. 1
is a block diagram showing the configuration of a typical system for accessing the Internet.
An Internet backbone
2101
is directly connected with Web sites
2102
, ftp sites
2103
, enterprise LANs (Local Area Networks)
2104
with dedicated lines, and access points
2105
operated by Internet Service Providers (hereinafter referred to as ISPs).
Each general user (home user) or each user
2107
in a small enterprise makes a connection to a desired site via the Internet backbone
2101
by accessing an access point
2105
from a PC (Personal Computer) or a LAN via an access network
2106
.
Since the Internet backbone
2101
and the access point
2105
are normally interconnected with a high-speed dedicated digital line, a fast access is ensured. In the meantime, the access network
2106
linking a user
2107
and an access point
2105
is typically a low-speed network such as a public telephone network, an ISDN (Integrated Services Digital Network), etc. in many cases, although a dedicated digital line network may be sometimes used.
However, it has become difficult for such a low-speed network to meet the rapidly increasing demand for the Internet in recent years. Especially, as a SOHO (Small Office/Home Office) becomes popular, the demand for quickly connecting a small-scale LAN to the Internet has been increasing.
Introduction of a new high-speed line infrastructure such as an optical fiber, etc. is a final solution in order to meet such demands. However, since this requires a lot of equipment investment, labor and time, it can hardly become a practical and short-term solution.
As a viable alternative, the DSL (Digital Subscriber Line) technique attracts public attention as a high-speed communications technique which uses telephone copper wire cables currently arranged in most homes and enterprises as they are and can coexist with communications using existing telephones.
The DSL technique is one type of modem technique. This technique includes methods such as an ADSL (Asymmetric DSL), an SDSL (Symmetric DSL), an HDSL (High bit rate DSL), a VDSL (Very high bit rate DSL), etc., which were developed for supporting various transmission rates, a symmetric/asymmetric communication, a modulation/demodulation method type, etc. These methods are generally referred to as an xDSL. The general term “xDSL” is hereinafter used in this specification.
With the xDSL technique, xDSL modems are arranged at both ends of an existing copper wire cable which links a subscriber home and an accommodation station of a common carrier. As a modulation/demodulation method in this case, any of three methods such as a 2B1Q (2 Binary 1 Quarternary), a CAP (Carrier-less Amplitude/Phase modulation), and a DMT (Discrete Multi-Tone) is adopted. With any of these modulation/demodulation methods, a high-speed communication of several-hundred to several-mega bits per second is made over a high-frequency band of approximately 30 KHz to 1 MHz.
As described above, the frequency bandwidth used in an xDSL communication differs from that of approximately 30 Hz to 4 KHz, which is used by a telephone speech signal. In such a case, a telephone speech signal and an xDSL signal can be multiplexed on one subscriber line by connecting circuits for different frequencies, which are referred to as splitters, to both of the xDLS modems within the subscriber home and within the common carrier. That is, in the subscriber home, the telephone and the xDSL modem are connected to the subscriber line via the splitter within the subscriber home. In the meantime, in the accommodation station, the existing telephone switch and the XDSL modem are connected to the subscriber line via a splitter within the accommodation station.
A collective modem which has a multiplexing capability and is referred to as a DSLAM (DSL Access Multiplexer) is mainly used as the xDSL modem within the accommodation station. With the DSLAM, xDSL signals from a plurality of xDSL lines are terminated by respective modem circuits, and the respectively terminated xDSL signals are multiplexed by a high-speed backbone interface. Use of such a DSLAM allows an xDSL line to be employed as a low-cost and high-speed access line leading to each type of backbone.
The above described backbone includes a dedicated line network, which is connected via a high-speed dedicated digital line interface and links headquarters and branch offices within an enterprise, the Internet connected via a LAN and a router, an ATM (Asynchronous Transfer Mode) network connected via an ATM interface such as a SONET interface, etc.
The technique for using the DSLAM as the front end of the ATM network among the above described techniques is expected to be a promising technique for implementing an ATM service on a global scale where common carriers tend to utilize a basic trunk line system in an ATM form. Furthermore, the ATM network is anticipated as a network for implementing the Internet backbone
2101
and the access network
2106
, which are shown in FIG.
1
. Considering this fact and the convenience where an existing copper wire cable can be used while maintaining a telephone service, it is significant that the xDSL line accommodated by the DSLAM is used as an access line to the ATM network or to the Internet.
In this case, an IP datagram transmitted, for example, from the PC or the LAN possessed by the user
2107
to the Web site
2102
, is converted into an ATM cell and is further converted into an XDSL signal by the XDSL modem in the user
2107
's home.
The xDSL signal is transmitted to the copper wire cable which is the subscriber line via the splitter in the user
2107
's home, and reaches the accommodation station.
After the xDSL signal is split from a telephone speech signal by the splitter in the accommodation station, it is received by the DSLAM within the accommodation station.
The ATM cell received by the DSLAM is multiplexed with an ATM cell received from another subscriber line, and then transmitted to an ATM interface (such as a SONET interface) leading to the access network
2106
configured by the ATM network.
The ATM cell which has passed through the access network
2106
is received by an access server within the access point
2105
. The access server extracts the IP datagram from the received ATM cell.
The extracted IP datagram is transferred to the Web site
2102
via the Internet backbone
2101
.
To typically implement the connection to the Internet, the user
2107
first makes a point-to-point connection to the access server within the access point
2105
which is the entry to the Internet backbone
2101
by using a protocol referred to as a PPP (Point to Point Protocol). At this time, the user
2107
is assigned a global IP address which is determined according to a protocol referred to as an IP (Internet Protocol) and can be uniquely identified on the Internet, from a DHCP (Dynamic Host Configuration Protocol) server etc. belonging to an access server depending on need. Thereafter, the user
2107
stores the IP datagram including the IP address of an opposing server in a PPP packet by using a global IP address which is originally possessed by the user
2107
or is dynamically assigned, and exchanges the IP datagram with a server at a destination side.
In the meantime, for example, if two communicating devices make a communication in an ATM network, ATM addresses must be respectively assigned to both of the devices. At the same time, an ATM connection (VC: Virtual Connection/Channel) which can be uniquely identified within the ATM network must be established between the two devices.
Accordingly, with the technique for integrating the xDSL line, the ATM network, and the Intern
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