Patent Application
20080089230
Each TCP data packet received by the switch 16 is monitored, where the processor 20 in the switch 16 looks at each packet to determine transmission characteristics of the packet, particularly where the packet is to be transmitted. Each TCP window includes a header having a 16-bit field that identifies how big the TCP window can be. A TCP window target size identifies the size of the TCP window that can be handled by the connection speed of the station 14 and the size of the buffer 18. If the size of the TCP window is greater than the target size, then the processor 20 replaces the TCP window size identified in the header with a TCP window size equal to the target size identified by the connection speed of the station 14 and the size of the buffer 18.
When a work station 14 requests a TCP file from the server 12, the 16-bit field in the header of the request message identifies the size of the TCP window that is pre-programmed into the station 14, such as by Windows™. The server 12 responds to the file request from the station 14 in a negotiation to transmit the file through the TCP. During this negotiation between the server 12 and the station 14, the number of data packets transmitted between the server 12 and the station 14 is generally small, and does not present a problem for the size of the buffer 18 and the connection speed of the station 14. As the processor 20 is monitoring the TCP packets being transmitted between the server 12 and the station 14, it will determine whether the requested TCP window size for the station 14 can be supported by the connection speed of the station 14 and the size of the buffer 18. If the processor 20 determines that the requested TCP window size can not be supported by the connection speed of the station 14 and the size of the buffer 18, then it will change the 16-bit field in the header to change the TCP window to a size that will be supported by the connection speed of the station 14 and the size of the buffer 18.
Once the server 20 receives the new TCP window size, it will send data packets for that window size, and the likelihood of dropped packets will be reduced, preferably to zero. The processor 20 will continue to monitor the 16-bit field in the header of the TCP data packets as they are transmitted from the server 20 to the station 14 to ensure that the TCP window size is maintained as previously set.
As discussed above, the processor 20 in the switch 16 adjusts the size of the TCP window based on connection speed of the station 14 and the size of the buffer 18. In an alternate embodiment, the processor 20 can set the TCP window size based solely on the size of the buffer 18 and other switch limitations. Particularly, the processor 20 would change every TCP window size to a predetermined window size for every TCP data packet transmission between the server 20 and the station 14. In one non-limiting embodiment, the TCP window size is 8 k bytes.
Each TCP data packet also includes a check-sum that is used to determine whether the data packet is valid. As is well understood to those skilled in the art, an extra digit or digits, called the check-sum digit(s), are sometimes added to the header of a data packet to check for errors after the data packet has been transmitted. In one embodiment, the check-sum exclusive-ORs a group of bits in the header with the next same size group of bits in the header all the way through the header to provide an accumulated value that must match a predetermined value to establish that the data packet is valid. If the switch 16 changes the TCP window size, it should also change the TCP check-sum to validate the new TCP window size. In other words, any time the data packet is modified, the TCP check-sum is also modified.
In one example, the station 14 is running Windows™ that typically requires a 64 k byte TCP window size. Further, the connection speed to the station 14 may be 100 mega-bits/per second. The processor 20 in the switch 16 may reduce the window size to an 8 k byte window size, which would accommodate about five TCP data packets.
Based on the discussion above, the technique of changing the size of the TCP windows may offer a number of advantages in a local area network (LAN) environment. This is because the distance that the TCP data packets have to travel is relatively short. Fewer advantages may be realized in a wide area network (WAN) environment where large TCP window sizes can provide performance advantages because of the transmission distances. The advantages in a LAN environment include reducing the size of the buffer 18, possibly providing the buffer 18 and the processor 20 on the same chip, and providing an improved packet throughput in speed mismatched situations with essentially no additional cost.
The foregoing discussion discloses and describes merely exemplary embodiments. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims, that various changes, modifications or variations can be made therein without departing from the spirit and scope of the embodiments as defined in the following claims.
