Abstract:
A system and method are disclosed for managing an assignment of IP addresses in a cable modem system. According to the disclosed system and method, an IP address of a specific kind is assigned to a client according to the classification of the client. A private IP address is issued in case of the client being a cable modem and a global IP address is issued in other cases so that the number of global addresses needed in the cable modem system can be reduced.

Description:
BACKGROUND OF THE INVENTION 
     I. Field of the Invention 
     The present invention generally relates to a cable modem system comprising a mechanism which dynamically assigns an Internet protocol (IP) address in response to a client request. More particularly, the present invention relates to a cable modem system in which an IP address-assigning mechanism assigns a private address and a global address according to a classification of a requesting client. 
     II. Background and Material Information 
     Cable modem systems, which enable digital communication over a coaxial cable network for cable television (CATV), have recently become widespread. The cable modem system realizes high-speed computer communication using the same signal that a regular television system uses, i.e., a radio frequency (RF) signal. In the cable modem system, both television service and digital communication service can be provided to a member via the same cable. 
     FIG. 3 is an exemplary block diagram showing the configuration of a cable modem system. FIG. 4 is an exemplary block diagram showing the configuration of a cable modem (CM). FIG. 5 is showing exemplary communication between two CMs connected to the same cable. 
     As shown in FIG. 3, a cable modem system mainly comprises a cable modem terminate system (CMTS)  302 , a CM  304 , and a CATV cable  306  via which CMTS  302  and CM  304  are connected to each other. CMTS  302  receives data from a provider&#39;s network  308 , which conforms to a standard for local area networks (LAN) such as 100BASE-T or asynchronous transfer mode (ATM), and transforms the data into an RF signal and vice versa. CM  304  is generally located at a home, for instance, to realize a small office/home office (SOHO). CM  304  is connected to a user computer such as personal computer or workstation (PC/WS)  310  via a user&#39;s network  312  conforming to a standard such as 10BASE-T or 100BASE-T. 
     CMTS  302  and CM  304  enable unsymmetrical high-speed communication in the cable modem system, i.e., communication from CMTS  302  to CM  304  (hereinafter referred to as “downstream communication”) at a predetermined rate, e.g., 10 Mbps-40 Mbps and communication from CM  304  to CMTS  302  (hereinafter referred to as “upstream communication”) at a predetermined rate, e.g., 1 Mbps-10 Mbps. A plurality of CMs  304   a - 304   b  connected to single CATV cable  306  share both the downstream frequency (F 1 ) and the upstream frequency (F 2 ) on CATV cable  306 . 
     As shown in FIG. 4, CM  304   a  comprises an RF receiver  402  and an RF transmitter  404 . CM  304   a  assists PC/WS  310   a  in communicating with another user computer  310   c  connected to another CM  304   b , however, CM  304   a  can not receive an RF signal directly from CM  304   b  because of the difference in frequencies between the downstream communication and the upstream communication. 
     Therefore, as shown in FIG.5, CMTS  302  comprises a relay unit  502  which receives a data frame sent from CM  304   a  and sends it to another CM  304   c . Relay unit  502  enables the CATV cable  306  to be treated in the same way as an ethernet LAN and allows the application of techniques used for a regular LAN. 
     Originally, CM  304  just needed a media access control (MAC) address and did not need an IP address. However, recently, even a hub or a modem has become a mechanism conforming to a network management protocol such as simple network management protocol (SNMP), which requires an IP address, so that a provider&#39;s SNMP server can grasp conditions of the hub or the modem and alter their definition information. 
     Single CM  304  is usually supposed to be assigned to single user. For an operator to manually assign those IP addresses would be a hard task. Therefore, a mechanism conforming to a dynamic host configuration protocol (DHCP) is usually used. A server which comprises the mechanism is called DHCP servers and it dynamically assigns an IP address to a client, such as CM  304  or PC/WS  310 , in response to a request from the client. 
     In the case of a huge cable modem system, the number of CMs  304  is very large, e.g., thousands through ten thousands. Moreover, because CM  304  is usually kept working without being shut off the power, many IP addresses are capable of being held by most CM  304 s. Therefore, more IP addresses are required so that the system can efficiently work in this situation. 
     However, the number of IP addresses is limited and an exhaustion of IP addresses has turned into a grave issue. Therefore, it is difficult to own many IP addresses and costly for a company. 
     An IP address for accessing to the Internet is also called a “global address”. Originally, an “IP address” meant an address used in an IP network, one of which is the Internet. However, “IP address” is now often used to mean just an address used for the Internet. To avoid confusion, an IP address for accessing to Internet will be referred as to “global address” and an IP address other than a “global address” will be referred to as a “private address” in the following. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, the present invention is directed to a system and method for managing an assignment of IP addresses in a cable modem system that substantially obviates one or more of the problems due to limitations and disadvantages of the past approaches. 
     In accordance with an aspect of the present invention, as embodied and broadly described, the present invention is directed to a cable modem system. The system comprises at least one cable modem, at least one user computer connected to the cable modem, a CMTS, a cable via which the cable modem and the CMTS are connected, and means connected to the CMTS for assigning an IP address of a specific kind according to the classification of a client in response to a request for an IP address from the client. 
     In accordance with another aspect of the present invention, there is provided a method for managing an assignment of IP addresses in a cable modem system. The method comprises issuing a request for an IP address by a client and issuing an IP address of a specific kind according to the classification of the client by a server. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed. Further features and/or variations may be provided in addition to those set forth herein. For example, the present invention may be directed to various combinations and subcombinations of the disclosed features and/or combinations and subcombinations of several further features disclosed below in the detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate various embodiments and/or features of the invention and together with the description, serve to explain the principles of the invention. In the drawings: 
     FIG. 1 is an exemplary block diagram showing the configuration of a cable modem system  100 , according to the principles of the present invention; 
     FIG. 2 is an exemplary flowchart showing an action of Cable modem system  100 ; 
     FIG. 3 (prior art) is an exemplary block diagram showing the configuration of a cable modem system; 
     FIG. 4 (prior art) is an exemplary block diagram showing the configuration of a CM; and 
     FIG. 5 (prior art) is showing communication between two CMs connected to the same cable. 
    
    
     DETAILED DESCRIPTION 
     The various aspects and features of the present invention will be hereinafter described with reference to the accompanying drawings. 
     FIG. 1 is an exemplary block diagram showing the configuration of a cable modem system  100  according to the present invention. Explanations regarding the same elements that are already explained referring to FIG.  3 -FIG. 5 will be omitted in the following. 
     Cable modem system  100  is the system explained in the Background and Material Information section additionally provided with an IP address assigning mechanism. A DHCP server  102  is provided, connecting to both Provider&#39;s network  308  and an unshown gateway to the Internet as an apparatus for dynamically assigning IP addresses. CMTS  302  comprises a responding unit  104  and a CM information file  106 . CM information file  106  stores a list of MAC address of every operating CM  304 . 
     DHCP server  102  is a server computer which works according to the DHCP and dynamically assigns an IP address to a client such as CM  304  or PC/WS  310  when each of them starts up. DHCP server  102  comprises a dividing unit  108 , a temporary address assigning unit  110 , an inquiring unit  112 , and a permanent address assigning unit  114 . 
     Dividing unit  108  judges if a request from a client is a first request using a list of issued temporary addresses stored in Temporary address assigning unit  110 . 
     Temporary address assigning unit  110  assigns a temporary address to both CM  304  and PC/WS  310 . Term of validity of the temporary address is set by DHCP server  102  to a comparatively short time, for instance, 1-10 minutes. 
     Inquiring unit  112  requests CMTS  302  for property information on the client which is assigned with a temporary address. 
     A client assigned with a temporary address requests DHCP server  102  for another IP address when the term of validity expires. Permanent address assigning unit  114  issues a permanent address in response to this request. Term of validity of the permanent address is set by DHCP server  102  to a comparatively long time, for instance, 1 hour-1 day. 
     When a requesting client is PC/WS  310 , permanent address assigning unit  114  assigns the client a global address. When a requesting client is CM  304 , permanent address assigning unit  114  assigns the client a private address. A private address may be decided in a self-serving manner as far as form, because it is not used for access to the Internet. 
     CMTS  302  working as a bridge controls CM  304  and retains information regarding CM  304  including a media access control (MAC) address. 
     Responding unit  104  refers to CM information file  106  and sends information if a client is a CM to DHCP server  102  on receiving an inquiry. 
     FIG. 2 is an exemplary flowchart showing an operation of cable modem system  100 . 
     At first, a client, e.g., CM  304  or PC/WS  310 , issues a request (hereinafter referred to as a “DHCP request”) to DHCP server  102  for an IP address when the client starts up (step S 1 ). At that time, DHCP server  102  obtains a MAC address of the client in a conventional manner, as is known in the art. For example, see “Dynamic Host Configuration Protocol by R. Droms ( 1993 )” 
     Dividing unit  108  judges if a request from a client is a first request using a list of issued temporary addresses stored in temporary address assigning unit  110  (step S 2 ). The threshold for assigning a permanent address may be shifted to a larger number of requests. 
     When the request is a first request from the client, temporary address assigning unit  110  assigns a private address as a temporary address and sends the address to the client (step S 3 ). The term of validity of the temporary address must be longer than a term required by inquiring unit  112  to get the information regarding a classification of the client from CMTS  302 . 
     Inquiring unit  112  inquires if the client is a CM  304  or another apparatus, for instance, PC/WS  310  (step S 4 ), by sending the MAC address obtained at the step S 1  to CMTS  302 . 
     Responding unit  104  checks with CM information file  106 , judges if the client is CM  304  or not, and replies with the result to DHCP server  102  (step S 5 ). Returning to the start, DHCP server  102  waits fr a next request. 
     The term of the temporary address given to the client in the step S 3  expires, e.g., 1-10 minutes later. And the client issues another DHCP request (step S 1 ). 
     When the request is a second request (step S 2 ), permanent address assigning unit  114  checks with the reply from responding unit  104  whether the client is a CM (step S 6 ). 
     When permanent address assigning unit  114  judges the client is a CM  304 , permanent address assigning unit  114  assigns the client a private address as a permanent address. Because CM  304  itself does not access the Internet, a private address is enough for CM  304  to work in a local IP network (step S 7 ). 
     When permanent address assigning unit  114  judges the client is a PC/WS  310 , permanent address assigning unit  114  assigns the client a global address as a permanent address because the client tends to require access to the Internet (step S 8 ). 
     Thus, permanent address assigning unit  114  assigns one of a global address or a private address as a permanent address according to the classification of the requesting client. 
     As described above, consistent with the principles of the present invention, a client is classified as one of two types, namely, a CM  304  or something others such as PC/WS  310 . PC/WS  310  is assigned a global address and CM  304  is assigned a private address. This has the effect in a cable modem system of reducing the number of global addresses to a number equal to the member of PC/WS. Therefore the cable modem system can efficiently work despite using fewer IP addresses. 
     Further, consistent with the principles of the present invention, a temporary address is assigned in response to a first request for an IP address and a permanent address is assigned in response to a second request for an IP address. As a result, the system can secure enough time for checking if the requesting client is a CM  304 . 
     Other embodiments of the present invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the present invention being indicated by the following claims.