Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1999-01-29
2003-04-01
Olms, Douglas (Department: 2666)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S469000, C714S712000
Reexamination Certificate
active
06542490
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to link layer protocols, and more particularly to a data link protocol for third generation (3G) wireless systems for direct support of network layer protocol data services, i.e. the Internet Protocol (IP).
2. Description of the Related Art
Layered architecture is a form of hierarchical modularity used in data network design. All major emerging communication network technologies rest on the layers of the International Organization for Standardization (ISO/OSI) model, illustrated in
FIG. 1A. A
layer performs a category of functions or services. The OSI model defines a Physical Layer (Layer 1) which specifies the standards for the transmission medium, a Data Link Layer (Layer 2), a Network Layer (Layer 3), a Transport Layer (Layer 4) and Application Layers (Layers 5 to 7).
Data link layer protocols are used to mitigate the effects of impairments introduced by the physical transmission medium. A Radio Link Protocol (RLP) is designed for the wireless system to deal specifically with the types of impairments found on the radio link and comprises mechanisms to deal with errors on the communications link, delays encountered in transmitting information, lost information, bandwidth conservation, and contention resolution.
The third layer is the Network Layer which implements routing and flow control for the network.
The fourth layer, Transport Layer, provides reliable and transparent transfer of data between end points. It provides end-to-end error recovery and flow control. For the Internet based protocol model, the Transport Control Protocol (TCP) mainly corresponds to the Transport Layer of the OSI model.
FIG. 2
shows the OSI Data Link Protocol architecture layer proposed for a 3G wireless network, and more particularly for a code division multiple access, i.e. “The cdma2000 RTT Candidate Submission”, Jun. 2, 1998 (TIA TR-45.5) network. At the most basic level, the TIA TR-45.5 layer structure provides protocols and services that correspond to the bottom two layers Layer 1—the physical layer
20
and Layer 2—the Data Link Layer (DLC)
30
of the OSI architecture, according to the general structure specified by the “International Mobile Telecommunications-2000” (ITU IMT-2000).
Layer-1, i.e. the Physical Layer
20
is responsible for coding and modulation of data transmitted over the air, and is not shown in
FIG. 2
for simplification.
Layer-2, i.e. the Link Layer
30
is subdivided into the Link Access Control (LAC) sublayer
32
and the Medium Access Control (MAC) sublayer
31
. The separation in MAC and LAC sublayers is motivated by the need to support a wide range of upper layer services, and the requirement to provide for high efficiency and low latency data services over a wide performance range (from 1.2 Kbps to greater than 2 Mbps). Other motivators are the need for supporting high QoS delivery of circuit and packet data services, such as limitations on acceptable delays and/or data BER (bit error rate), and the growing demand for advanced multimedia services each service having a different QoS requirements.
LAC sublayer
32
is required to provide a reliable, in-sequence delivery transmission control function over a point-to-point radio transmission link
42
.
The MAC sublayer
31
includes procedures
35
for controlling the access of data services (packet and circuit) to the Physical Layer
20
, including the contention control between multiple services from a single user, as well as between users in the wireless system. The MAC sublayer
31
services include a best effort delivery RLP
33
, which provides for a reasonably reliable transmission over the radio link layer, using a Radio Link Protocol (RLP) that provides a “best effort” level of reliability. Multiplexing and QoS (quality of service) control
34
is responsible for enforcement of negotiated QoS levels by mediating conflicting requests from competing services and the appropriate prioritization of access requests. MAC Control States, block
35
, and QoS control side of block
34
, are again specific to the TIA TR-45.5 system.
The MAC is divided into two sections namely a physical layer independent convergence function (PLICF) section, and a physical layer dependent convergence function (PLDCF) section. A state machine running in the PLICF section regulates the delivery of the LAC PDU's to the Radio Link Protocol (RLP) which is mainly located in the PLDCF. The PLDCF also contains a multiplexing and QoS control module which multiplexes the RLP frames onto different physical channels based on their QoS requirements. Again, the wireless data link layer may be viewed as an interface between the upper layers and the wireless Physical Layer.
As illustrated in
FIG. 2
in the Transport Layer
50
are the Transport Control Protocol (TCP)
51
and the User Datagram Protocol (UDP)
52
. A Hyper Text Transport Protocol (HTTP), a Real-time Transport Protocol (RTP), or other protocols may also be present.
The upper layers
5
to
7
, denoted in this figure with
60
, include the session, presentation and application layers for packet data applications
61
, voice services
62
, simple circuit data applications (e.g. asynchronous fax)
63
, and simultaneous voice and packet data service. Voice services
62
may utilize directly the services provided by the TIA TR-45.5 LAC services. Signaling services
70
are illustrated over layers
40
,
50
and
60
, to indicate that the signaling information is exchanged between all layers
3
-
7
and the DLC layer.
Current wireless networks use layer 2-4 protocols designed specifically for the wired networks. However, there are some major differences between the wireless and wired environment, resulting in important differences in the way these networks operate.
In a wired network the bit error rates are typically on the order of 10
−9
or better, and errors and packet loss have a tendency to be random. Therefore, the wired transmission medium could be considered essentially error-free and the TCP data packets are lost mainly due to congestion in the intervening routers. Moreover, in a wired system the transmission channel has a constant bandwidth and is symmetrical, which means the characteristics of the channel in one direction can be deduced by looking at the characteristics of the channel in the other direction. Therefore, it is often easiest to use a common link control protocol and to solve congestion problems by adding bandwidth.
On the other hand, in a wireless environment, most of these assumptions are no longer valid. The wireless channel is characterized by a high bit error rate. The errors occur in bursts that can affect a number of successive packets. Due to fading, the low transmission power available to the Mobile Station (MS) and the effects of interference, the radio link is not symmetrical and the bandwidth of the channel rapidly fluctuates over time.
Furthermore, in a wireless environment, the amount of bandwidth available to the system is fixed and scarce. Adding bandwidth to the radio link may be expensive or even impossible due to regulatory constraints.
In addition, the issues in connection with increasing the transmission bandwidth are substantially different in the wireless environment. In a wired environment increasing the throughput is simply a matter of allocating as much bandwidth as possible to the connection. In a wireless environment, part of the bandwidth is used in error correction. More error correction means less payload. However, more error correction increases the probability of correct delivery without retransmissions. Thus, in the wireless environment increasing the end-to-end throughput may be obtained by reducing bandwidth assigned to payload and using the freed bandwidth for error correction.
The Data Link Control (DLC) protocols available to date do not attempt to be inclusive as complete DLC protocols. Basically, off-the-shelf protocols intended for different media have been adopted for wireless systems. Even though some of those protocol
Ahmadvand Nima
Fong Mo-Han
Wu Geng
Boakye Alexander
Nortel Networks Limited
Olms Douglas
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