Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1998-05-26
2002-08-27
Chin, Wellington (Department: 2664)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S256000, C370S401000
Reexamination Certificate
active
06442171
ABSTRACT:
BACKGROUND OF THE INVENTION
I. Field of the Invention
The present invention relates to digital networks. In particular the invention relates to the interconnection of digital networks.
II. Description of the Related Art
In recent years, digital network systems have been rapidly evolving and becoming increasingly prevalent. For example, the number of digital wireless telephone systems has grown tremendously in both rural areas and large cities. In addition to the standard 900 MHz cellular telephone systems, personal communication systems which operate at 1.8 GHz are also emerging in the larger markets. Personal communication systems are scheduled for continued deployment in smaller markets.
In less developed areas, wireless local loop systems are emerging as a substitute for wireline systems. Wireless local loop systems have certain advantages over wireline systems. In order to provide wireline service, actual copper wire must be installed and connected to each building in which service is provided. The process of laying wire often entails the destruction of existing roads or the installation of a great number of telephone poles. Such installation procedures are invasive to the existing infrastructure, time consuming and expensive. In contrast, in a wireless local loop system, service can be provided to a wide area with the installation of a single base station.
Wireless private branch exchange (PBX) systems are also becoming more prevalent. A wireless PBX system can provide coverage to a related group of users. For example, wireless PBX systems are used in large office buildings. A wireless PBX user may travel throughout the coverage area (i.e., the office building) with his telephone set. The users of a wireless PBX system may contact each other by dialing an extension rather than a full public branch exchange number.
In addition to the increased prevalence of cellular systems, new uses for cellular systems have also developed. For example, data services are commonly provided over existing cellular systems. Data services include data transfer between computers, wireless meter reading, paging services and mobile news service.
Each of the cellular systems discussed above has the characteristic that it is comprised of a plurality of spaced apart base stations. In the most general embodiment, base stations are physically located in the center of a corresponding coverage area. The coverage areas abut one another to form a large, contiguous service area. The base station may use one of a variety of existing or later developed communication techniques to communicate with remote units located within its coverage area. For example, the base station may communicate with the remote units using frequency modulation (FM), time division multiple access (TDMA), a combination of TDMA and frequency hopping (such as GSM) or code division multiple access (CDMA). The use of CDMA provides many advantages to the system such as un-interrupted handoff between base stations, immunity to fading and very high system capacity. Therefore, the following information is disclosed with reference to a CDMA system. However, the generic principles described herein are directly applicable to non-CDMA systems and also non-cellular systems in which digital networks are interconnected.
FIG. 1
shows a block diagram of a typical CDMA Cellular Land Network (CCLN).
FIG. 1
shows seven base stations
10
A-
10
G. Each one of the base stations
10
A-
10
G defines a corresponding hexagonal coverage area
12
A-
12
G in which it provides service. Although only seven base stations are shown in
FIG. 1
, in reality most CCLNs comprise a much greater number of base stations.
Assume a remote unit initiates a communication link with a land line telephone from within the coverage area
12
F. The remote unit sends an access message to the base station
10
F. The base station
10
F transfers the message to a base station controller (BSC)
26
. The BSC
26
verifies the authenticity of the remote unit, initiates the billing process and allocates resources within the base station
10
F and other portions of the system to be used during the call. This process requires the transfer of more than thirty (30) messages throughout the system. An understanding of the precise nature of these transactions is not fundamental to the present invention.
Instead, of greater importance to us is that, even before a communications link is established between the remote unit and the public switch telephone network, a great number of messages must be transferred between remotely located digital equipment units.
The transfer of messages is facilitated by the use of a CDMA interconnect subsystem (CIS)
20
. The CIS
20
is comprised of one or more distribution/consolidation (DISCO) units such as a DISCO
22
shown in FIG.
1
. The DISCO
22
is a router, which receives input from a plurality of input ports, consolidates the inputs onto an internal bus. A series of output ports are connected to the internal bus. Each output port has an associated address range. Each message on the internal bus is distributed to the output port which has an address range which includes the address of the message.
Returning to the example above, when the remote unit sends an access message to the base station
10
F, the base station
10
F creates a message (which may comprise a series of message packets) having an address indicating a control unit within the BSC
26
. The base station lo places the message on a corresponding wireline link
14
F. The wireline link
14
F conveys the message to an input port on the DISCO
22
. Within the DISCO
22
, a comparison of the address of the message is made with the address ranges of the output port of the DISCO
22
. The message has an address within the address filter range associated with a link
28
and, thus, the DISCO
22
routes the message to the BSC
26
.
When the BSC
26
allocates resources to be used during the communication with the remote unit, it must designate a cellular modem. The selector bank subsystem (SBS)
30
is comprised of a bank of cellular modems
32
A-
32
X. The BSC
26
sends a message through the DISCO
22
to alert the cellular modem
32
A of the connection. The BSC
26
also sends a message to the base station
10
F giving the address of the cellular modem
32
A.
During the connection, for each frame received from the remote unit over the wireless link, the base station
10
F sends a packet of data through the DISCO
22
to the cellular modem
32
A. Also, during the connection, the cellular modem
32
A sends frames of data intended for the remote unit through the DISCO
22
to the base station
10
F.
In this example, let us assume that the remote unit is a cellular portable telephone. The remote unit may change location during the course of the connection. A typical CDMA system employs soft handoff which allows uninterrupted connection during the handoff process from one base station to another. For example, if the remote unit moves from the coverage area
12
F to the coverage area
12
E, it establishes a connection with the base station
10
E before the connection with the base station
10
F is released. When the remote unit is simultaneously communicating with the base station
12
E and the base station
12
F, it is said to be in soft handoff. During soft handoff, the frames emanating from the remote unit are received by both the base station
10
E and the base station
10
F and forwarded to the DISCO
22
via the link
14
E and the link
14
F respectfully. The DISCO
22
routes both packet streams to the cellular modem
32
A which creates one stream of data to pass to a switch
40
.
A CCLN such as the one shown in
FIG. 1
has a rather large but limited capacity. The capacity is limited by a number of practical considerations. For example, the capacity is limited by the number of input ports and output ports which can be supported by a single CIS. The capacity is also limited by the maximum geographic distance over which the links
14
A-
14
G operate. Therefore, a large city is typically comprised o
Lee Kuo-Chun
Mohanty Bibhu
Sutton Todd R.
Ziv Noam A.
Brown Charles D.
Chin Wellington
Duong Frank
Greenhaus Bruce W.
Qualcomm Incorporated
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