Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
1998-06-30
2001-10-30
Maung, Nay (Department: 2681)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S557000, C370S466000, C370S467000
Reexamination Certificate
active
06311072
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to the translation of communications protocols and more specifically to translation of the signaling protocols used in telephone systems. In a particular embodiment, the invention relates to signaling protocols used in wireless telephone systems.
BACKGROUND OF THE INVENTION
Making a telephone call generally involves two kinds of channels for communicating information: a voice channel for carrying representations of audio signals between the telephones (or data signals represented using voice signals between computers) and a signal channel which carries the signaling messages needed to perform operations on the voice channel. Examples of such operations include setting up the voice channel at the beginning of the telephone call, taking it down at the end of the telephone call, providing special services such as call forwarding and 3-way calling, and in the case of mobile telephony, handing off a call as the mobile station moves from one cell to another. In order for the devices in the telephone network that provide and respond to the signaling information to work correctly, the signaling messages must conform to a protocol, that is, an exact description of the form and meaning of each of the signaling messages and of the ways in which the signaling messages may be combined to cause the telephone network to carry out its operations. The voice channel and the signaling channel may employ different physical channels or they may employ the same physical channel, as for example is the case in digital systems, where information is carried in packets and the information in the packet may either be a representation of the audio information or a signaling message.
FIG. 1
shows these channels in the context of a cellular telephony system
101
. Only the portion of system
101
relevant to the present discussion is shown in the figure. In
FIG. 101
, voice channels
105
are represented by solid lines and signaling channels are represented by dashed lines. In system
101
, a mobile switching center
107
, which is the interface between the wireless system and the wired system, is connected by a number of trunks
106
to other mobile switching centers
107
or standard wired telephone switches. Included in trunks
106
are voice channels and signaling channels. Mobile switching center
107
is further connected by voice channels and signaling channels to a number of base stations. Base stations provide voice and signaling channels
114
for mobile telephone stations. In the system shown in
FIG. 1
, each base station consists of two parts: a BS(CE)
109
and one or more base stations BS(CE)
111
(
0
. . . n) that are controlled by the BS(CC)
109
. In
FIG. 1
, only the BS(CE)s belonging to BS(CC)
109
(
0
) are shown. Each BS(CE)
111
is located in a geographical area termed a cell
115
. BS(CE)s
111
include radio transmitters and receivers which they use to provide voice channels and signaling channels
114
for mobile telephone stations
113
(
0
. . . o) that are currently within cell
115
. In the system of
FIG. 1
, BS(CC)s
109
(
0
. . . m), connect the BS(CE) they control via voice channels and signaling channels to mobile switching center
107
. In other configurations, the base stations that include the radio transmitters and receivers may be connected directly to mobile switching center
107
. Of course, the mobile telephone station may be any device which communicates by means of mobile telephony protocols.
When a mobile station
113
(
i
) is the source of a telephone call, it is said to originate the call. Originating mobile station
113
(
i
) uses the signaling channel of
114
to send a message which informs base station
111
(
j
) of its need to initiate a telephone call, of its own identity, and of the number of the telephone it wishes to call. Base station
111
(
j
) passes the request to make a call and the identification via base station controller
109
(
k
) to mobile switching center
107
, which uses the signaling channels between mobile switching center
107
and the switch to which the called telephone is attached to send call set up signaling messages to the latter switch. These messages obtain the voice channels between the switches that are necessary for the call, and each switch sets up the voice channels that are needed between the switch and the telephone.
When a mobile station
113
(
i
) is the destination of a telephone call, it is said to terminate the call. A data base in mobile telephone system
101
keeps track of the current location of each active mobile station
113
in telephone system
101
. The call may come either from another mobile station or from an ordinary telephone. In either case, when it reaches mobile telephone system
101
, a MSC
107
(
r
) queries the data base and determines that terminating mobile station
113
(
i
) is currently reachable via MSC
107
(
r
). MSC
107
(
r
) responds to the call set up message by sending signaling messages via BSC
109
(
k
) and BS
111
(
j
) to mobile station
113
(
i
) as required to terminate the call at mobile station
113
(
i
). Once the voice channels are set up, the call may proceed. When the call is finished, signaling messages must similarly be exchanged among the component of system
101
to take down the call, that is, to make the voice channels used by the call available for use by other calls.
In system
101
, there are protocols for the signaling messages exchanged by different kinds of components. The protocol for the signaling messages defines the interface between the two kinds of components. For example, the interface between a MSC
107
and its base stations
111
is termed the A interface, shown at
108
in FIG.
1
. Since there are BSCs
109
in the configuration of system
101
, the A interface is between MSC
107
and BSC
109
. Different MSCs
107
may have different A interfaces, as may different base stations, but a given MSC
107
will only work with a base station that has the same A interface, that is, that uses the signaling protocol that MSC
107
expects it to use. The same is true with regard to the other interfaces in system
101
. The requirement that components that signal each other employ the same signaling protocol severely limits the ability of builders of telephone networks to combine equipment as they wish, and thereby to achieve the best possible cost and performance tradeoffs.
What is needed if components that use different signaling protocols are to be combined at an interface such as interface A in system
101
is techniques for converting sequences of messages belonging to one of the protocols to equivalent sequences of messages belonging to another one of the protocols. Such conversion is well known in the computer arts, where it is used for example in bridges, devices which connect data networks that use different protocols for data packets and translate data packets that conform to the protocol required for one kind of network into data packets that conform to the protocol required for another kind of network.
Unfortunately, the protocol translation techniques developed in the computer arts cannot be applied directly to telephone signaling protocols. The reasons for this include the following:
telephone networks are generally more complex than computer networks;
telephone networks employ separate voice and signaling channels; and
voice communications are subject to stringent real-time constraints.
The greater complexity of telephone networks is due first to the fact that a telephone network communicates between telephones, which are comparatively “dumb” devices, while a data network communicates between computers, which are comparatively “smart” devices. Thus, designers of computer networks can keep their communications protocols, and accordingly, their routing and switching devices, very simple, can build complex protocols on top of the communications protocols, and can use the processing power of the computers to deal with the complex protocols. Designers of telephone networks, on the other
Barclay Deborah L.
Dolan Michael F.
Hall Joe Thomas
Salvador Laurel A.
Sellinger Robert S.
Gelin Jean A
Lucent Technologies - Inc.
Maung Nay
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