Multiplex communications – Data flow congestion prevention or control – Flow control of data transmission through a network
Reexamination Certificate
1999-11-17
2004-02-24
Ngo, Ricky (Department: 2697)
Multiplex communications
Data flow congestion prevention or control
Flow control of data transmission through a network
C370S338000, C370S410000, C714S746000
Reexamination Certificate
active
06697331
ABSTRACT:
BACKGROUND
1. Field of the Invention
The present invention pertains to mobile telecommunications, and particularly to acknowledgment of receipt and retransmission of packet switched data for an upper layer protocol, such as the transmission control protocol/Internet protocol (TCP/IP), for example.
2. Related Art and Other Considerations
Initially commercial mobile or cellular telecommunications systems were primarily employed for voice calls, e.g., circuit switched connections. In more recent years, however, cellular telecommunications systems have also been employed for the transmission of data (packet switched data), with the user equipment taking forms other than a mobile telephone. For example, user equipment such mobile laptops can send data over wireless links and through a cellular telecommunications system to wired computer networks such as the internet.
Cellular telecommunications systems employ a wireless link (e.g., air interface) between the (mobile) user equipment unit and a base station (BS). The base station has transmitters and receivers for radio connections with numerous user equipment units. One or more base stations are connected to (e.g., by landlines or microwave) and managed by a radio network controller (RNC) [also known in some networks as a base station controller (BSC)]. The radio network controller is, in turn, connected through control nodes to a core telecommunications network.
Control nodes can take various forms, depending on the types of services or networks to which the control nodes are connected. For connecting to connection-oriented, circuit switched networks such as PSTN and/or ISDN, the control node can be a mobile switching center (MSC). For connecting to packet switched data services such as the Internet (for example), the control node can be a gateway data support node through which connection is made to the wired data networks, and perhaps one or more serving nodes. Examples of a particular packet data service called the General Packet Radio Service (GPRS) [provided in Europe in the context of the Global System for Mobile communications (GSM)] are provided by the following (all of which are incorporated by reference): U.S. patent application Ser. No. 09/069,969 filed Apr. 30, 1998 entitled “Dynamic Allocation of Packet Data Channels”; U.S. patent application Ser. No. 09/069,939 filed Apr. 30, 1998 entitled “Allocation of Channels for Packet Data Services”; and U.S. patent application Ser. No. 09/090,186 filed Jun. 4, 1998 entitled “Data Packet Radio Service With Enhanced Mobility Management”.
As indicated above, packet switched data services can include Internet service. In terms of Internet connection, the transmission control protocol/Internet protocol (TCP/IP) has gained wide acceptance. Although usually functioning together, the internet protocol (IP) and transmission control protocol (TCP) are actually separate protocols, with the TCP being on a higher level (transport level) than the IP (on the network level).
There are numerous implementations of TCP, each with differing characteristics, the RENO implementation perhaps being the most common. In general, TCP supports a wide range of upper-layer protocols (ULPs). A ULP can send continuous streams of data through TCP. The TCP breaks the streams into encapsulated segments, each segment including appropriate addressing and control information. TCP passes the segments to the network layer (e.g., the IP).
The IP layer encloses the TCP segments in IP packets or Internet datagrams. It is the Internet datagram that enables routing to source and destination TCPs in other networks. Thus, the IP serves, e.g., to assemble IP datagrams and enable routing of the IP datagrams between IP addresses (e.g., between hosts) which are included in the IP datagram header.
TCP provides reliability which the IP lacks. In particular, the TCP carries out segmentation and reassembly functions of a datagram to match frame sizes and data-link layer protocols. In addition, TCP performs additional functions, such as addressing within a host, retransmission of lost packets, and flow control. General concepts undergirding TCP/IP are understood from numerous publications, including Freeman,
Telecommunication System Engineering,
Third Edition, John Wiley & Sons, Inc., (1996), and W.R. Stevens,
TCP/IP Illustrated, Volume I: The Protocols
(Addison-Wesley, 1994).
Data losses because of bit errors occur over conventional wired links, but such losses are so small as to be essentially non-existent (e.g., on the order of 10
−6
over copper wire, and 10
−9
over optical fiber). Such losses over conventional wired links stem almost exclusively from overflowing buffers in routers. TCP is designed to cope with these conditions, and consequently, packet losses are regarded as a congested network. Upon detection of loss, different implementations of TCP invoke different congestion avoidance mechanisms, but generally all such congestion avoidance mechanisms decrease the transmission speed.
Some code-type error recovery capability (e.g., convolutional coding) is provided over the air interface, but such code-type error recovery cannot cope with large errors. Over the air interface, error recovery is performed locally with a local retransmission protocol, wherein all data in a transmission buffer is cached until it has been successfully delivered to the receiver. In essence, any lost data is quickly transmitted by the local retransmission protocol before TCP has a chance to detect the loss. By retransmitting the data locally, faster recover can be done and, most importantly, the TCP will not detect the loss and accordingly will not invoke the TCP congestion avoidance mechanism (unless data is lost somewhere other than over the air interface).
Thus, the task using the local retransmission protocol is how to realize quickly that data is lost, and how to retransmit the lost data. Traditionally, two primary types of strategies in local recovery have been utilized: (1) transport layer recovery of TCP packets, and (2) link layer recovery of smaller data units called segments or frames (e.g., Automatic Repeat reQuest [ARQ]). Of the two general strategies, the ARQ-type of strategy is generally preferred.
Two examples of link layer recovery retransmission protocols are SSCOP (see ITU-T Recommendation Q.2110, 1994) and Radio Link Control (RLC). The SSCOP and RLC protocols are similar, with RLC being an improved variant of SSCOP.
FIG. 13A
illustrates a scenario of SSCOP operation, wherein segment S
2
13A
is lost. Receipt of the next segment S
3
13A
triggers a negative acknowledgment message (USTAT(S
2
)). Unfortunately, as illustrated in
FIG. 13A
, the negative acknowledgment message (USTAT(S
2
)) is lost. Moreover, segment S
5
13A
is also lost. Transmission of segment S
6
13A
therefore triggers a negative acknowledgment message (USTAT(S
5
)) to recover segment S
5
13A
. The negative acknowledgment message (USTAT(S
5
)) is successfully delivered to the transmitter, which then retransmits segment S
5
13A
. At this juncture, segment S
2
13A
is still not recovered. When a poll timer maintained by SSCOP expires, a poll message is transmitted to the receiver by setting a poll bit in a header of segment S
9
13A
. Upon reception of poll message S
9
13A
, the receiver checks its reception buffer, and notices that segment S
2
13A
is missing. Upon detection that segment S
2
13A
missing, the transmitter transmits a STAT message, in particular STAT(S
2
). The STAT message is a selective acknowledgment message that can advise of gaps of one or more segments in the reception buffer. Upon reception of the STAT(S
2
) message, segment S
2
13A
is retransmitted.
FIG. 13B
illustrates a similar scenario of RLC operation, wherein segment S
2
13B
is lost. Receipt of the next segment S
3
13B
triggers both transmission of a negative acknowledgment message (USTAT(S
2
)) and starting of an EPC timer (Estimated PDU Counter) to protect the USTAT message from loss. But the USTAT(S
2
) message from the receiver i
Johansson Staffan
Riihinen Wesa
Ngo Ricky
Nixon & Vanderhye P.C.
Swickhamer Christopher M.
Telefonaktiebolaget LM Ericsson (publ)
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