Error detection/correction and fault detection/recovery – Data processing system error or fault handling – Reliability and availability
Reexamination Certificate
2001-05-17
2004-07-06
Iqbal, Nadeem (Department: 2114)
Error detection/correction and fault detection/recovery
Data processing system error or fault handling
Reliability and availability
C370S474000
Reexamination Certificate
active
06760860
ABSTRACT:
BACKGROUND
1. Technical Field
The present invention relates generally to cellular wireless communication networks; and more particularly to the servicing of packetized communications within such cellular wireless communication networks.
2. Related Art
Wireless networks are well known. Cellular wireless networks support wireless communication services in many populated areas of the world. While wireless networks were initially constructed to service voice circuit-switched voice communications, they are now called upon to support packet-switched data communications as well.
The transmission of packetized data communications within a wireless network places different demands on networks than does the transmission of voice communications. Voice communications require a sustained bandwidth with minimum signal-to-noise ratio (SNR) and continuity requirements. Data communications, on the other hand, typically are latency tolerant but have higher total throughput requirements. Conventional circuit-switched wireless networks were designed to support the well-known voice communication requirements. Thus, wireless networks (as well as conventional circuit switched telephone networks) have been adapted to service data communications, with such adaptation providing mixed results. Thus, future wired and wireless networks will likely be fully packet switched.
The Internet, Intranets, and their underlying Wide Area Networks, and Local Area Networks are all packet switched networks. In such packet switched networks, all communications to be transmitted from a source to a destination are packetized prior to transmission and reassembled upon receipt. These networks are capable of servicing both data communications and multimedia services such as Voice Over IP (VOIP) communications. Because of the requirement of interoperability between the equipment of differing vendors, various interworking standards have been developed for packet switched networks. Most operating standards of this type are based upon the well-known Industry Standards Organization (ISO) seven layer Open Systems Interconnect (OSI) model. The OSI model includes, from lowest protocol layer to highest protocol layer, (1) the physical layer, (2) the data link layer, (3) the network layer, (4) the transport layer, (5) the session layer, (6) the presentation layer, and (7) the application layer. A corresponding TCP/IP reference model includes (1) the physical layer, (2) the network interface layer, (3) the Internet layer, (4) the transport layer, and (5) the application layer. Networked devices, e.g. computer terminals, wireless network mobile stations, etc., operating according to these standards support error free transfer of data communications. Thus, almost all devices supporting data communications operate according to one or more variations of these operating standards.
In order to ensure that packets lost in transmission are retransmitted, the operating standards sometimes employ Automatic Retransmission reQuest (ARQ) operations. Generally speaking, ARQ operations are employed to automatically request retransmission of data packets that have been transmitted but not successfully received, e.g., lost data packets, erroneous data packets, etc.
For example, in a data session established between a client computer and a web server across the Internet, the client computer requests the download of a file. The web server accesses the file, subdivides the requested file into a plurality of data packets, and uniquely identifies each data packet. The web server then transmits each of the data packets to the client computer. Upon receipt of all of the data packets, the client computer combines the data packets in the correct order to reconstruct the file. However, the client computer may not successfully receive all of the data packets from the web computer due to lost/erroneous transmissions. When this occurs, the client computer automatically sends a request to the web server to retransmit a lost/erroneously received packet. ARQ operations continue until the client computer correctly receives all data packets that make up the file.
ARQ operations are particularly important in wireless networks, e.g., cellular and satellite networks that networks support wireless links between a base station and a serviced mobile station. Wireless links are subject to interference, fading, and other factors that oftentimes prevent successful first time transmission of data packets. In wireless networks, more than one protocol layer may support ARQ operations, e.g., transport layer and link layer. Further, in some networks, the physical layer (layer
1
) may also support ARQ operations. During normal operations, however, the ARQ operations of the multiple protocol layers may interfere with one another. Such interference introduces additional delays in the packet data transmissions and, in some cases, may results in unnecessary higher-layer retransmission or may cause a transmission to fail by inadvertently causing a higher-layer time-out event.
Thus, there exists a need in the art for cooperative operation between ARQ operations of different protocol layers.
SUMMARY OF THE INVENTION
In order to overcome these shortcomings, among others, a base station, mobile station, and/or other terminal includes physical layer (layer
1
) protocol and link layer (layer
2
) protocol enhancements that interact with one another to prevent unnecessary link layer ARQ operations. These enhancements cause the link layer protocol to prevent ARQ operations for data blocks having missing data packets that are still pending at the physical layer.
According to one embodiment of the present invention, a physical layer protocol operating on a mobile station receives a data packet from a base station across a wireless link. The physical layer protocol then determines, a number, N, of data packets pending with its physical layer protocol Automatic Retransmission reQuest (ARQ) operations. The physical layer protocol then passes the data packet and the number, N, to a link layer protocol operating on the mobile station. The link layer protocol then modifies its ARQ operations based upon the number, N, of data packets pending with the physical layer protocol ARQ operations. In modifying its ARQ operations, the link layer avoids initiating ARQ operations for data blocks missing data packets that are still pending with the physical layer.
However, the link layer may also determine that it must initiate ARQ operations. According to one embodiment of these operations, upon the receipt of each data packet from the physical layer, the link layer determines its total number of missing data packets. Then, based upon the number, N, the link layer determines that physical layer ARQ operations have failed for at least one missing data packet of a corresponding data block. The link layer then initiates ARQ operations for the corresponding data block.
These operations also apply when the physical layer sends a packet erasure indication to the link layer. In such case, the physical layer determines that its ARQ operations have failed to recover a missing data packet and generates a packet erasure indication for the data packet. In such case, the physical layer also determines a number, M, of data packets pending with its ARQ operations. The physical layer then passes the data packet erasure indication to the link layer protocol operating on the mobile station. The link layer protocol then modifies its ARQ operations based upon the number, M, of data packets pending with the physical layer protocol ARQ operations.
In one particular embodiment, the link layer maintains a counter for each data block having missing data packets. Then, when the link layer determines that the counter value exceeds the number, N, it initiates ARQ operations for the data block having missing data packets. The link layer also modifies these counter values when a missing packet is received to account for the received data packet.
These operations may be embodied as method or steps performed by a base station, mobile station, o
Fong Mo-Han
Hang Zhang
Schmidt Alfred R.
Wu Geng
Yu Derek K.
Garlick Bruce
Iqbal Nadeem
Nortel Networks Limited
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