Patent Publication Number: US-6035418-A

Title: System and method for improving resource utilization in a TCP/IP connection management system

Description:
TECHNICAL FIELD 
     The present invention is related to a system and method for improving resource utilization in a connection management system, more particularly, for reducing the number of connections in a waiting state. 
     BACKGROUND 
     Today&#39;s network servers, such as web servers, utilized for internet applications, can serve hundreds of requests every second. Each of the requests is typically associated with a Transmission Control Protocol (TCP) connection, which is active until the request is completed. A client typically establishes a connection to a server and issues a request. The server then processes the request, returns a response, and closes the connection. Unlike traditional network applications, such as telnet or ftp, the web requests are usually active only for a short period of time, e.g., for acquiring a HyperText Markup Language (HTML) home page. Therefore, a Transmission Control Protocol/Internet Protocol (TCP/IP) connection in a web server environment will be active only for a very short period of time in most cases, typically on the order of microseconds. 
     When a server closes a TCP connection, it is required to keep information about that connection for a period of time, typically four minutes, in case a delayed packet is found and sabotages a new incarnation of the connection. The server will leave some resources typically allocated for every single connection closed in the past four minutes. On a busy server, this can become a serious resource problem--hundreds of thousands of control blocks may need to be set aside until a four-minute TIME --  WAIT expires, which can cause not only resource under-utilization but also the contention for the limited resources. Accordingly, what is needed is an improved method and system for utilizing these resources. The present invention addresses such a need. 
     SUMMARY 
     The present invention is a method and system for improving resource utilization in a connection management system. The present invention alleviates the resource contention and resource under-utilization problems, and avoids the problem of contamination from the late arrival of delayed packets to a new connection which utilizes the same resources used in a previous connection. 
     A method according to the present invention is for utilizing resources for connection management for data transfers in a network environment, the network environment including a server, the server including connection resources, the method comprising transferring data by using the connection resources from the server; determining if an error occurred during the transfer of data; if an error is not detected, returning the connection resources to the server; and if an error is detected, waiting a predetermined period of time prior to returning the connection resources to the server. 
     The present invention alleviates these problems by keeping track of the state of each TCP connection. In the case where no re-transmission is needed, i.e., no packet lost during the time the connection is active, all the resources associated with the connection will be returned immediately to the system when the connection is closed. In the case when a retransmission is required, the system will still keep the information about closed connections with re-transmissions for a predetermined time such as four minutes. In this way, the system resources can be freed in time for other usages. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of a system in which the present invention resides. 
     FIG. 2 is a flow diagram of a conventional method for enabling and disabling connections for transferring data. 
     FIG. 3 is a flow diagram of a method according to the present invention. 
    
    
     DETAILED DESCRIPTION 
     The present invention relates to a system and method for improving resource utilization in a connection management system in a network environment. The following description is presented to enable one of ordinary skill in the art to make and use the illustrative embodiment and is provided in the context of a patent application and its requirements. Various modifications to the illustrative embodiment will be readily apparent to those skilled in the art and the generic principles herein may be applied to other embodiments. Thus, the present invention is not intended to be limited to the embodiment shown but is to be accorded the widest scope consistent with the principles and features described herein. 
     FIG. 1 is a block diagram of a system in which the present invention resides. The system includes a web server 100, an internet network 102, and client processors 104a-104c. When a client processor 104 requires information from the web server 100, the client processor 104 establishes a connection to the server 100, and issues a request. The web server 100 then processes the request, returns a response, and closes the connection. These connections are established via transmission control blocks (TCB) 106a-106c. 
     FIG. 2 is a flow diagram of a conventional method for enabling and disabling connections for data transfers. The web server typically receives a connection request via step 200 and enables a connection through a TCB via step 202. The data is then transferred via step 204. The server then typically maintains information regarding the connection for a standard period of time via step 206. In the case of TCP/IP, the recommended period of time for waiting (TIME --  WAIT) is four minutes. Once the TIME --  WAIT has elapsed, then the TCB is returned to the web server system via step 208. The fundamental problem with this conventional method is that the connections need to remain available for what is relatively a very long period of time. This problem is compounded by the web server typically requiring multiple connections for every request. 
     Since the TCP protocol demands that the information about a closed connection needs to be kept until the TIME --  WAIT expires, it is likely the utilization of the resources associated with a TCP connection is very low. Also, a web server will have to keep hundreds of thousands of control blocks for the closed TCP connections at almost any instant of time when the server is busy. This will not only cause the resource under-utilization but also introduce serious contention at the system level for the limited resources. 
     One of the mechanisms to solve this problem is to disable or use a smaller TIME --  WAIT value in the TCP implementation. But, this will violate the standard. Also, this can introduce a higher possibility of having a delayed packet arrive late to contaminate a new connection which utilizes the same resources used in a previous connection. 
     The present invention improves resource utilization by reducing the number of connections in the TIME --  WAIT state. The present invention alleviates the resource contention and resource under-utilization problems, and avoids the problem of contamination from the late arrival of delayed packets in a new connection which utilizes the same resources used in a previous connection. 
     According to the present invention, at connection set up time, a STATUS flag associated with the connection is set or reset. Once the connection is established, data exchange commences. Whenever a retransmission such as those due to a loss of a packet or transmission time out, is detected for the connection, the STATUS flag for the connection is preferably set to one. The STATUS flag can reside in the Transmission Control Block (TCB) or any data structure associated with the connection. 
     At the time an opened connection is closed, the system checks the STATUS flag for the connection. The resources associated with the connection, such as TCBs, will be released immediately if its STATUS flag has not been changed to one. In this case, all the resources associated with the closed connection can be reassigned immediately if needed. Alternatively, if the STATUS flag has been set to one, the TCB for the connection with packet retransmission is linked to the TIME --  WAIT queue. It is preferable that the TIME --  WAIT period lasts the recommended amount, which is currently four minutes. When TIME --  WAIT expires, the resources associated with the connection can then be released. 
     With addition of a single-bit STATUS flag and simple logics of recording re-transmission in exchanging data and checking the STATUS flag at closing connection, the resources associated with most of the connections can be released for reassignment at the time connection is closed. The connections with retransmission, which have potential to receive a delayed packet, will preferably wait until the TIME --  WAIT expires, as is done in the current TCP implementations, to avoid any possible contamination from late arrival of delayed packets. 
     FIG. 3 is a flow diagram of a method according to the present invention. A connection request is received by the web server via step 300. A connection is enabled by using a TCB via step 302. Then, data is transferred via step 304. It is then determined if any errors have occurred during the transfer of the data via step 306. If there has been an error in the transfer of the data, then a predetermined amount of time is allowed to elapse via step 308. The predetermined period of time is preferably the recommended amount of TIME --  WAIT, which is currently four minutes. Once the predetermined period of time has elapsed, then the TCB is returned to the system and the resources can be applied to other connections. If, however, no errors were detected in the transfer of the data via step 306, then the TCB is returned to the system without having to wait the established TIME --  WAIT period. The indication of whether there are any errors found in the transfer of the data via step 306 is preferably indicated by using a status bit that indicates if there have been any errors. 
     Although the system and method has been described in accordance with the embodiments shown, one of ordinary skill in the art will readily recognize that there could be variations to the embodiments and those variations would be within the spirit and scope of the above-described system and method. Accordingly, many modifications may be made by one of ordinary skill in the art without departing from the spirit and scope of the appended claims.