Multiplex communications – Communication over free space – Combining or distributing information via time channels
Reexamination Certificate
2001-11-16
2004-08-31
Chin, Wellington (Department: 2664)
Multiplex communications
Communication over free space
Combining or distributing information via time channels
C370S352000
Reexamination Certificate
active
06785259
ABSTRACT:
TECHNICAL FIELD
The present invention relates to packet networks and, more particularly, improved transport layer performance over wireless links.
DISCUSSION OF RELATED ART
As pointed out by A. V. Bakre et al in “Implementation and Performance Evaluation of Indirect TCP”
IEEE Transactions on Computers
, Vol. 46, No. 3, March 1997 at pp. 260-278, wireless links are slower and less reliable compared to wired links and consequently the use of existing network protocols, which were developed mainly for the high bandwidth and faster wired links, will create unique performance problems arising from host mobility and due to the characteristics of the wireless medium. An indirect protocol model was proposed by Bakre et al so that whenever an interaction between two IP hosts on an internetwork, such as between a mobile host and a stationary host, involves communication over two drastically different kinds of media (e.g., wireless and wired), the interaction is split into two separate interactions—one for each kind of communication medium. A fixed network protocol such as TCP is used for communication between the fixed host and a mobility support router (base station) and a wireless protocol (e.g., wireless TCP) for communication between the mobile host and the mobility support router (see Section 3 “Indirect Protocols” at pp. 261-2). The protocol stack is split at the mobility support router in order to enable the taking of corrective measures to address the change in the environment from wired to wireless.
A criticism of this approach is some resulting performance issues. Every packet incurs the overhead of going through TCP protocol processing twice at the base station, although extra copies are avoided by an efficient implementation. Another disadvantage of this approach is that the end-to-end semantics of TCP acknowledgements is violated, since acknowledgements to packets can now reach the source even before the packets actually reach the mobile host. Also, since this protocol maintains a significant amount of state at the base station per TCP connection, handoff procedures tend to be complicated and slow. These problems are described in detail in the article “A Comparison of Mechanisms for Improving TCP Performance Over Wireless Links” by H. Balakrishnan et al appearing in
Proc. ACM SIGCOMM
'96, August 1996 and also in the more recent article “TCP Performance Issues over Wireless Links” by G. Xylomenos et al,
IEEE Communications
, April 2001.
DISCLOSURE OF INVENTION
An object of the present invention is to optimize throughput of applications transmitted over a wireless link interfacing with other, non-wireless links.
According to a first aspect of the invention, a method for use in a packet-based communication between two end points in a communication network during which a plurality of packets are communicated at least in part over a wireless link is characterized by identifying or recognizing a packet as a special packet at an end point of the wireless link, and by applying special treatment to the special packet at the end point of the wireless link to ensure reliable transmission over the wireless link.
Further according to the first aspect of the invention, the special treatment is applied at a link layer of the end point of the wireless link.
Further still according to the first aspect of the invention, the end point of the wireless link comprises a sending endpoint for sending the plurality of packets over the wireless link. The special treatment may be applied at a link layer of the sending end point of the wireless link.
Still in accord with the first aspect of the present invention, the identifying or recognizing comprises identifying the special packet at an application layer of the endpoint and by notifying a link layer of the endpoint for applying the special treatment to the identified special packet at the link layer.
Still further in accord with the first aspect of the invention, the identifying or recognizing comprises recognizing the special packet at a link layer of the endpoint and by controlling the link layer of the endpoint for applying the special treatment to the special packet at the link layer. Further yet in accord with the first aspect of the invention, the recognizing comprises recognizing the special packet by timing arrivals of packets having a same characteristic code associated therewith and identifying a packet having the code arriving a selected period after arrival of a last packet having the code as the special packet.
According to a second aspect of the invention, a device for use in a packet-based communication between two end points in a communication network during which a plurality of packets are communicated at least in part over a wireless link is characterized by means for identifying or recognizing a packet as a special packet at an end point of the wireless link, and by means for applying special treatment to the special packet at the end point of the wireless link to ensure reliable transmission over the wireless link.
Further according to the second aspect of the invention, the special treatment is applied at a link layer of the end point of the wireless link.
Further still according to the second aspect of the invention, the end point of the wireless link comprises a sending endpoint for sending the plurality of packets over the wireless link. As mentioned above, the special treatment may be applied at a link layer of the sending end point of the wireless link.
Still in accord with the second aspect of the present invention, the identifying or recognizing comprises identifying the special packet at an application layer of the endpoint and by notifying a link layer of the endpoint for applying the special treatment to the identified special packet at the link layer.
Still further in accord with the second aspect of the invention, the identifying or recognizing comprises recognizing the special packet at a link layer of the endpoint and by controlling the link layer of the endpoint for applying the special treatment to the special packet at the link layer.
Further yet in accord with the second aspect of the invention, the recognizing comprises recognizing the special packet by timing arrivals of packets having a same characteristic code associated therewith and identifying a packet having the code arriving a selected period after arrival of a last packet having the code as the special packet.
According to a third aspect of the invention, a system having a pair of hosts communicating packets in an end-to-end application over communication links including wireless links, each wireless link having a mobile host at one end and an access network at another end, is characterized by an enhancement in a link layer at an end of the wireless link for providing special link layer treatment to a packet identified as a special packet for ensuring reliable transmission of the special packet over the wireless link.
Further according to the third aspect of the invention, the application identifies the special packet as special to the link layer when providing the special treatment at an end of the wireless link co-located with the application.
According still further to the third aspect of the invention, the link layer inspects the packets for identifying the special packet when the link layer is providing the special treatment at an end of the wireless link not co-located with the application.
Further still according to the third aspect of the invention, the enhancement is characterized by means for identifying or recognizing the special packet at an endpoint of the wireless link, and by means for applying the special link layer treatment to the special packet at the end. The end of the wireless link may comprise a sending end for sending the packets over the wireless link.
As compared to the snoop TCP mechanism discussed in the above-mentioned articles, the present invention does not require any caching of TCP data, and does not manipulate the original TCP messages (i.e., there is no hiding of duplicate acknowledgements and no TCP-level
Kakani Naveen K.
Le Khiem
Swami Yogesh
Chin Wellington
Pham Brenda
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