Electrical computers and digital processing systems: multicomput – Computer-to-computer protocol implementing – Computer-to-computer data framing
Reexamination Certificate
1998-09-15
2001-12-04
Harrell, Robert B. (Department: 2152)
Electrical computers and digital processing systems: multicomput
Computer-to-computer protocol implementing
Computer-to-computer data framing
C709S227000, C709S230000, C709S237000, C709S238000
Reexamination Certificate
active
06327626
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The invention relates to computer networks. More particularly, the invention relates to a computer network protocol.
2. Description of the Prior Art
TCP/IP is a well known information exchange protocol. See, for example, J. Postel,
Internet Protocol
, RFC791 (September 1981); J. Postel,
Internet Control Message Protocol
, RFC792 (September 1981); J. Postel,
Transmission Control Protocol
, RFC793 (September 1981); R. Braden,
Requirements for Internet Hosts—Communications Layers
, RFC1122 (October 1989); V. Jacobsen, R. Braden,
TCP Extensions for Long-Delayed Paths
, RFC1072 (October 1988); J. Postel,
The TCP Maximum Segment Size and Related Topics
, RFC879 (November 1983); and J. Mogul, S. Deering,
Path MTU Discovery
, RFC1191 (November 1990).
When a TCP connection sends a segment, the size of that segment is limited by the Maximum Segment Size (MSS) and the path Maximum Transmission Unit (MTU). The MSS used by the local TCP protocol stack is set during the establishment of each TCP connection. The MSS used by each station is determined independently using the following algorithm:
Each end station sends a desired MSS to the remote endpoint in the SYN packet. This desired MSS is the MTU of the interface being used, minus the IP and TCP frame overhead (typically 40 bytes).
Each end station then derives an MSS value to be used, which is the minimum of the MSS received in the SYN packet and the MTU of the local interface, minus the IP and TCP frame overhead.
When two networks having different MTUs are connected, each resulting MSS used by each end station is the smaller of the two MSSs. In addition, if the MSS is larger than the empirically determined path MTU, only segments conforming to the path MTU are sent. This allows communications to occur without the need for IP fragmentation, but removes the efficiency and performance advantages provided by interfaces having larger MTUs.
It would be desirable to allow a host using the TCP transport protocol to choose the larger of two unequal MSS values received during the MSS negotiation when establishing a connection between two stations.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to increase the data transfer rate in network by removing the limitation provided by current systems. A mechanism referred to as MSS spoofing intercepts and modifies the MSS value specified in a TCP SYN packet containing a TCP MSS option. The local TCP protocol stack is spoofed such that it appears to the local stack that the remote station has an MSS value that is different from its actual MSS value. Thus, MSS spoofing allows the local TCP protocol stack to use an MSS value that is derived solely from its own MTU.
The MSS spoofing interface changes the received MSS value to a value at least as large as the local MTU before passing the packet up the protocol stack. This forces the TCP protocol stack to use a larger MSS that it would otherwise use. This way, the TCP protocol stack always uses a TCP segment size that is based on the MTU of the local interface.
In another embodiment, MSS spoofing may be implemented on any intermediate point between two TCP protocol entities, for example, in the device driver or network interface card (NIC). MSS spoofing may also be implemented in an intermediate routing or switching entity.
The mechanism described allows a host using the TCP transport protocol to choose the larger of two unequal MSS values received during MSS negotiation when establishing a connection between two stations. As a result, the determination mechanism of the local MSS value used by the TCP/IP protocol stack is changed to be the larger of the two unequal offered MSS values, instead of being the smaller of the two. The host TCP/IP protocol stack is not modified. Thus, a transmitting host can send TCP segments that are sized to the sending station MTU without modifying the TCP protocol stack on every station.
REFERENCES:
patent: 5425023 (1995-06-01), Haraguchi et al.
patent: 5751970 (1998-05-01), Bournas
patent: 6076114 (2000-06-01), Wesley
patent: 6091733 (2000-07-01), Takagi et al.
Hastings et al., “TCP/IP spoofing fundamentals”, IEEE Fifteenth Annual International Phoenix Conference, pp. 218-224, Mar. 1996.*
RFC 0791 Internet Protocol—Darpa Internet Program Protocol Specification, Information Sciences Institute, University of Southern California, pp. 1-45, Sep. 1981.*
RFC 0793 Transmission Control Protocol—Darpa Internet Program Protocol Specification, Information Sciences Institute, University of Southern California, pp. 1-85, Sep. 1981.
Hathaway Wayne
Hayes John
Schroeder Theodore
Alteon Networks, Inc.
Glenn Michael A.
Harrell Robert B.
Romero Almari
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