NETWORK ALLOCATION
CROSS REFERENCE
[0001] This application claims the benefit of U.S. Provisional Application Number
60/969,847, filed September 4, 2007, which is incorporated by reference in its
entirety.
BACKGROUND
[0002] As wireless communications have increased, utilization of IEEE 802.11
protocols has also increased. In IEEE 802.11 communications a network
allocation vector (NAV) may be utilized to reduce the probability of interference.
However, according to the IEE 802.11 protocol, a NAV that is updated by a request
to send (RTS) message may be undesirably reset by receivers if a valid physical
layer (PHY) header is not received within a certain timeout.
SUMMARY
[0003] Included are embodiments for network allocation. More specifically, one
embodiment of a method includes receiving, at a first communications device,
without a prior RTS signal being sent, a first clear to send (CTS) signal from a
second communications device, addressed to the first communications device,
the CTS signal indicating a data exchange duration and sending a second CTS
signal, from the first communications device, to the second communications
device.
[0004] Additionally, embodiments of a computer readable medium are included.
Some embodiments include receiving logic configured to receive, at a first

communications device, without a prior request to send (RTS) signal being sent,
a first clear to send (CTS) signal from a second communications device,
addressed to the first communications device, the CTS signal indicating a data
exchange duration and first sending logic configured to send a second CTS
signal, from the first communications device, to the second communications
device.
[0005] Additionally, embodiments of a system are included. Some embodiments
include means for receiving, at a first communications device, without a prior
request to send (RTS) signal being sent, a first clear to send (CTS) signal from a
second communications device, addressed to the first communications device,
the CTS signal indicating a data exchange duration and means for sending a
second CTS signal, from the first communications device, to the second
communications device.
[0006] Other embodiments and/or advantages of this disclosure will be or may
become apparent to one with skill in the art upon examination of the following
drawings and detailed description. It is intended that all such additional systems,
methods, features, and advantages be included within this description and be
within the scope of the present disclosure.
BRIEF DESCRIPTION
[0007] Many aspects of the disclosure can be better understood with reference to
the following drawings. The components in the drawings are not necessarily to
scale, emphasis instead being placed upon clearly illustrating the principles of
the present disclosure. Moreover, in the drawings, like reference numerals
designate corresponding parts throughout the several views. While several

embodiments are described in connection with these drawings, there is no intent
to limit the disclosure to the embodiment or embodiments disclosed herein. On
the contrary, the intent is to cover all alternatives, modifications, and equivalents.
[0008] FIG. 1 depicts a diagram illustrating an exemplary embodiment of a
network configuration that may be utilized for wireless communications.
[0009] FIG. 2 depicts a functional block diagram illustrating a communications
device, similar to the communications device 102 from FIG. 1.
[0010] FIG. 3A depicts a flow diagram illustrating an exemplary embodiment of a
data exchange between two communications devices, such as in the network
configuration of FIG. 1.
[0011] FIG. 3B depicts a flow diagram illustrating an exemplary embodiment of a
communication of a clear to send (CTS) signal followed by a request to send
(RTS) signal, similar to the diagram from FIG. 3A.
[0012] FIG. 3C depicts a flow diagram illustrating an exemplary embodiment of a
broadcast CTS being received at a communications device, similar to the
diagram from FIG. 3B.
[0013] FIG. 3D depicts a flow diagram illustrating an exemplary embodiment of a
plurality of CTS signals being sent, in response to a received CTS signal, similar
to the diagram from FIG. 3C.
[0014] FIG. 4 depicts a flowchart illustrating an exemplary embodiment of a
process for sending a clear to send (CTS) signal followed by a request to send
(RTS) signal, similar to the diagram from FIG. 3B.
[0015] FIG. 5 depicts a flowchart illustrating an exemplary embodiment of a
process for sending a broadcast CTS that is received at a communications
device, similar to the diagram from FIG. 3C.

[0016] FIG. 6 depicts a flowchart illustrating an exemplary embodiment of a
process for sending a plurality of CTS signals, in response to a received CTS
signal, similar to the diagram from FIG. 3D.
DETAILED DESCRIPTION
[0017] Embodiments disclosed herein may be configured to transmit a frame
addressed to a recipient, followed by the RTS message addressed to the same
recipient, wherein the endpoint of the duration field of a request to send (RTS) does
not exceed that of a clear to send (CTS). Similarly, some embodiments may be
configured to transmit a clear to send (CTS) message addressed to a recipient,
which is not a response to an RTS from that recipient. In response, the recipient
may transmit a CTS back to the sender of the first CTS.
[0018] Similarly, some embodiments may be configured to transmit a CTS
addressed to the node and transmit a following RTS to the same recipient (referred
to as a CTS-to-AP if the addressee is an access point). The CTS-to-AP
configuration may be configured to set a non-resetting NAV (because updated
from a CTS) at the other devices but not at the addressed node (e.g., the access
point), so that the addressed device can still respond to a following RTS. The RTS
does not update the NAV at stations other than the addressed recipient when the
endpoint of the duration field does not exceed that of the preceding CTS. This
means that surrounding devices can not reset their NAV if those devices do not
receive a valid physical layer (PHY) header within a certain time after hearing the
RTS. So after the CTS-to-AP/RTS/CTS exchange, there may be no need to
transmit a frame that can be decoded by the surrounding stations, which is what

happens, for instance, when Dual CTS is used (as described in 802.11 n draft 2.0
section 9.2.5.5a).
[0019] Referring now to the drawings, FIG. 1 depicts a diagram illustrating an
exemplary embodiment of a network configuration that may be utilized for
wireless communications. As illustrated in the nonlimiting example from FIG. 1,
network 100 may be coupled to access points 110a and 110b. The access
points 110a and 110b can be configured to provide wireless communications to
communications devices 102a, 102b, 102c and/or 102d. More specifically,
depending on the particular configuration, access points 110a and/or 110b may
be configured for providing voice over internet protocol (VoIP) services, wireless
fidelity (WIFI) services, WiMAX services, wireless session initiation protocol (SIP)
services, bluetooth services and/or other wireless communication services.
Additionally coupled to the network 100 is a server 106. The server 106 may be
configured as a web server, SIP server, and/or other type of server.
[0020] The network 100 may include a public switched telephone Network
(PSTN), an integrated services digital Network (ISDN), the Internet, a cellular
network, and/or other mediums for communicating data between communication
devices. More specifically, as a nonlimiting example, while the communications
devices 102a and 102d may be configured for WIFI communications,
communications devices 102c, 102d, and/or 106 may be coupled to the network
100 and may be configured for VoIP communications, bluetooth
communications, WIFI communications, and/or other wireline and/or wireless
communications.
[0021] FIG. 2 depicts a functional block diagram illustrating a communications
device, similar to the communications device 102 from FIG. 1. As illustrated in

FIG. 2, in terms of hardware architecture, the communications device 102 may
include a processor 282, a memory component 284, a display interface 294, a data
storage component 295, and one or more input and/or output (I/O) device
interface(s) 296 that are communicatively coupled via a local interface 292. The
local interface 292 can include, for example but not limited to, one or more buses
and/or other wired or wireless connections. The local interface 292 may have
additional elements, which are omitted for simplicity, such as controllers, buffers
(caches), drivers, repeaters, and receivers to enable communications. Further, the
local interface 292 may include address, control, and/or data connections to enable
appropriate communications among the aforementioned components. The
processor 282 may be a hardware device for executing software, particularly
software stored in the memory component 284.
[0022] The processor 282 can be any custom made or commercially available
processor, a central processing unit (CPU), an auxiliary processor among several
processors associated with the communications device 102, a semiconductor
based microprocessor (in the form of a microchip or chip set), a macroprocessor,
or generally any device for executing instructions.
[0023] The memory component 284 can include any one or combination of volatile
memory elements (e.g., random access memory (RAM, such as DRAM, SRAM,
SDRAM, VRAM, etc.)) and nonvolatile memory elements (e.g., ROM, hard drive,
tape, CD-ROM, etc.). Moreover, the memory component 284 may incorporate
electronic, magnetic, optical, and/or other types of storage media. Note that the
memory component 284 can also have a distributed architecture, where various
components are situated remotely from one another, but can be accessed by the
processor 282.

[0024] The software in the memory component 284 may include one or more
separate programs, each of which includes an ordered listing of executable
instructions for implementing logical functions. In the example of FIG. 2, the
software in the memory component 284 may include communications logic 288, as
well as an operating system 286. As illustrated, the communications logic 288 may
include receiving logic 290 configured to receive, at a first communications device,
without a prior request to send (RTS) signal being sent, a first clear to send (CTS)
signal from a second communications device, addressed to the first
communications device, the CTS signal indicating a data exchange duration. Also
included is sending logic 293 configured to send a second CTS signal, from the
first communications device, to the second communications device. Other
components may also be included.
[0025] Additionally, while the logic components 290,291, and 293 are each
illustrated in this nonlimiting example as a single piece of logic, these components
can include one or more separate software, hardware, and/or firmware modules.
Similarly, one or more of these logical components can be combined to provide the
desired functionality. Additionally, the operating system 286 may be configured to
control the execution of other computer programs and may be configured to
provide scheduling, input-output control, file and data management, memory
management, and communication control and related services.
[0026] A system component embodied as software may also be construed as a
source program, executable program (object code), script, and/or any other entity
that includes a set of instructions to be performed. When constructed as a source
program, the program is translated via a compiler, assembler, interpreter, or the

like, which may or may not be included within the volatile and nonvolatile memory
284, so as to operate property in connection with the operating system 286.
[0027] The input/output devices that may be coupled to system I/O Interface(s) 296
may include input devices, for example but not limited to, a keyboard, mouse,
scanner, microphone, camera, proximity device, receiver, efc. Further, the
input/output devices may also include output devices, for example but not limited
to, a printer, display, transmitter, efc. The input/output devices may further include
devices that communicate both as inputs and outputs, for instance but not limited
to, a modulator/demodulator (modem for accessing another device, system, or
network), a radio frequency (RF) or other transceiver, a telephonic interface, a
bridge, a router, WIFI communications device, WiMAX communications device,
bluetooth communications device, efc. Similarly, a network interface 298, which is
coupled to local interface 292, can be configured to communicate with a
communications network, such as the network from FIG. 1. While this
communication may be facilitated via the communications device 102, this is not a
requirement.
[0028] More specifically, the network interfaces 298 may be configured for
facilitating communication with one or more other devices. The network interface
298 may include any component configured to facilitate a connection with another
device. While in some embodiments, among others, the client device 102 can
include the network interface 298 that includes a Personal Computer Memory Card
International Association (PCMCIA) card (also abbreviated as "PC card") for
receiving a wireless network card, this is a nonlimiting example. Other
configurations can include the communications hardware within the client device
102, such that a wireless network card is unnecessary for communicating

wirelessly. Similarly, other embodiments include the network interfaces 298 for
communicating via a wired connection. Such interfaces may be configured with
Universal Serial Bus (USB) interfaces, serial ports, and/or other interfaces. In
operation, the wireless network interfaces 298 may be configured to communicate
with other client devices 102, access points 110, and other wireless devices via a
wireless local area network (WLAN) or other wireless network.
[0029] If the communications device 102 is a personal computer, workstation, or
the like, the software in the memory component 284 may further include a basic
input output system (BIOS) (omitted for simplicity). The BIOS is a set of software
routines that initialize and test hardware at startup, start the Operating System 286,
and support the transfer of data among the hardware devices. The BIOS is stored
in ROM so that the BIOS can be executed when the communications device 102 is
activated.
[0030] When the communications device 102 is in operation, the processor 282
can be configured to execute software stored within the memory component 284,
to communicate data to with the memory component 284, and to generally control
operations of the communications device 102 pursuant to the software. Software
in memory 284, in whole or in part, may be read by the processor 282, perhaps
buffered within the processor 282, and then executed. Additionally, one should
note that while the above description is directed to a communications device 102,
other devices can also include the components described in FIG. 2.
[0031] One should note that the access point 110 (which may also be seen as a
communications device) can be configured with one or more of the components
and/or logic described above with respect to the communications device 102.
Additionally, the access point 110, the communications device 102, and/or

other components of FIG. 1 can include other components and/or logic for
facilitating the operations described herein. Additionally, depending on the
particular configuration, the access point 110 may include both a wireless
interface for communicating to the client devices and a second interface for
communicating with the network. The access point 110 may be combined with
other network services, (e.g., network address translation (NAT), dynamic host
control protocol (DHCP), routing, firewall).
[0032] FIG. 3A depicts a flow diagram illustrating an exemplary embodiment of a
data exchange between two communications devices, such as in the network
configuration of FIG. 1. As illustrated in the nonlimiting example of FIG. 3A, the
communications device 102c may be configured to send a CTS-to-Self signal
302 to an access point 110. The CTS-to-Self message 302 may be a CTS that is
sent by a communications device 102 and addressed to the communications
device 102 that send the CTS. The CTS signal 302 may be broadcast to and
received by a plurality of communications devices, including the access point
110. Upon receiving the CTS-to-Self signal 302, the access point 110 can set a
network allocation vector (NAV) 304 that indicates a time for data exchange. The
NAV 304 may be set for a plurality of devices, however this is not a requirement.
[0033] Additionally, the communications device 102c can send a request to send
(RTS) signal 306 to the access point 110. However, because of the rules of the
IEEE 802.11 protocol, the access point 110 may be unable to respond.
[0034] One should note that, while the above listed exchange occurs between a
communications device 102c and an access point 110, this is a nonlimiting
example. More specifically, the data exchanges disclosed herein may involve

any of communications device (e.g., communications devices 102, server 106,
and/or access point 110).
[0035] FIG. 3B depicts a flow diagram illustrating an exemplary embodiment of a
communication of a clear to send (CTS) signal followed by a request to send
(RTS) signal, similar to the diagram from FIG. 3A. As illustrated in the
nonlimiting example of FIG. 3B, the communications device 102c can transmit a
CTS signal 308 (or other short frame that does not require a response),
addressed to the communications device 102a. Additionally, followed by the
CTS signal 308, the communications device 102c can transmit an RTS signal
310 addressed to communications device 102a ("A"). The CTS signal 308 may
be configured to set a non-resetting NAV with other communications devices (not
shown) who may receive the CTS. The communications device 102a may send
a CTS signal 314 addressed to communications device 102c, indicating that a
transmission channel is clear to send data. The communications device 102c
can then send the data 316. The data 316 can use a PHY header, which may
not be backward compatible with nearby legacy devices, because the nearby
legacy devices set a NAV based on the receipt of the CTS 308 and/or CTS 314,
which (in at least one exemplary embodiment) cannot be reset.
[0036] FIG. 3C depicts a flow diagram illustrating an exemplary embodiment of a
broadcast CTS being received at a communications device, similar to the
diagram from FIG. 3B. As illustrated in the nonlimiting example of FIG. 3C, the
access point 110 may send an unsolicited CTS signal 318, addressed to
communications device 102a. As discussed above, according to IEEE 802.11
protocol, a communications device that receives an unsolicited CTS cannot
respond to the received signal. However, if a change in IEEE 802.11 protocol

occurs (and/or if operating in an non-IEEE 802.11 environment), the
communications device 102a can send a CTS 233 addressed to the access point
110 in response to receipt of an unsolicited CTS addressed at the device 102a.
The access point 110 can then transmit data 324 to the communications device
102a. In this exemplary frame exchange, the unsolicited CTS 318 replaces the
RTS in an RTS/CTS exchange, so that a NAV can be set in the network, which
does not reset according to the NAV reset rules of the IEEE 802.11 protocol.
[0037] FIG. 3D depicts a flow diagram illustrating an exemplary embodiment of a
plurality of CTS signals being sent, in response to a received CTS signal, similar
to the diagram from FIG. 3C. As illustrated in the nonlimiting example of FIG.
3D, the communications device 102c can send an unsolicited CTS 326 to the
access point 110. The access point 110 can then send two CTS messages 330,
332 to the communications device 102c. The first CTS message 330 may be
transmitted at a first modulation (e.g., for short range transmission). Similarly,
the second CTS message 332 may be transmitted at a second modulation (e.g.,
for longer range transmission). The communications device 102c can then send
data 334 to the access point 110. The PHY header of the second CTS response
message 332 may use a PHY header that (in at least one embodiment) cannot
be decoded by legacy stations, which will not reset a NAV at the legacy stations,
because the NAV was set by a CTS.
[0038] FIG. 4 depicts a flowchart illustrating an exemplary embodiment of a
process for sending a clear to send (CTS) signal followed by a request to send
(RTS) signal, similar to the diagram from FIG. 3B. As illustrated in the
nonlimiting example of FIG. 4, the communications device 102a can send a CTS
and an RTS to the communications device 102b (block 432). The

communications device 102b can then send a CTS to the communications
device 102a (block 436). The communications device 102a can then send data
to the communications device 102b (block 438).
[0039] FIG. 5 depicts a flowchart illustrating an exemplary embodiment of a
process for sending a broadcast CTS that is received at a communications
device 102, similar to the diagram from FIG. 3C. As illustrated in the nonlimiting
example of FIG. 5, the communications device 102a can send a CTS to the
communications device 102b (block 532). The communications device 102b can
additionally send a CTS to the communications device 102a (block 536). The
communications device 102a can then send data to the communications device
102b (block 538).
[0040] FIG. 6 depicts a flowchart illustrating an exemplary embodiment of a
process for sending a plurality of CTS signals, in response to a received CTS
unsolicited signal, similar to the diagram from FIG. 3D. As illustrated in the
nonlimiting example of FIG. 6, the communications device 102a can send a CTS
to the communications device 102b (block 632). The communications device
102b can send a first CTS and a second CTS to the communications device
102a (block 636). The communications device 102a can then send data to the
communications device 102b (block 638).
[0041] The embodiments disclosed herein can be implemented in hardware,
software, firmware, or a combination thereof. At least one embodiment disclosed
herein may be implemented in software and/or firmware that is stored in a
memory and that is executed by a suitable instruction execution system. If
implemented in hardware, one or more of the embodiments disclosed herein can
be implemented with any or a combination of the following technologies: a

discrete logic circuit(s) having logic gates for implementing logic functions upon
data signals, an application specific integrated circuit (ASIC) having appropriate
combinational logic gates, a programmable gate array(s) (PGA), a field
programmable gate array (FPGA), etc.
[0042] One should note that the flowcharts included herein show the architecture,
functionality, and operation of a possible implementation of software. In this
regard, each block can be interpreted to represent a module, segment, or portion
of code, which comprises one or more executable instructions for implementing
the specified logical function(s). It should also be noted that in some alternative
implementations, the functions noted in the blocks may occur out of the order
and/or not at all. For example, two blocks shown in succession may in fact be
executed substantially concurrently or the blocks may sometimes be executed in
the reverse order, depending upon the functionality involved.
[0043] One should note that any of the programs listed herein, which can include
an ordered listing of executable instructions for implementing logical functions,
can be embodied in any computer-readable medium for use by or in connection
with an instruction execution system, apparatus, or device, such as a computer-
based system, processor-containing system, or other system that can fetch the
instructions from the instruction execution system, apparatus, or device and
execute the instructions. In the context of this document, a "computer-readable
medium" can be any means that can contain, store, communicate, or transport
the program for use by or in connection with the instruction execution system,
apparatus, or device. The computer readable medium can be, for example but
not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or
semiconductor system, apparatus, or device. More specific examples (a

nonexhaustive list) of the computer-readable medium could include an electrical
connection (electronic) having one or more wires, a portable computer diskette
(magnetic), a random access memory (RAM) (electronic), a read-only memory
(ROM) (electronic), an erasable programmable read-only memory (EPROM or
Flash memory) (electronic), an optical fiber (optical), and a portable compact disc
read-only memory (CDROM) (optical). In addition, the scope of the certain
embodiments of this disclosure can include embodying the functionality
described in logic embodied in hardware or software-configured mediums.
[0044] One should also note that conditional language, such as, among others,
"can," "could," "might," or "may," unless specifically stated otherwise, or otherwise
understood within the context as used, is generally intended to convey that
certain embodiments include, while other embodiments do not include, certain
features, elements and/or steps. Thus, such conditional language is not
generally intended to imply that features, elements and/or steps are in any way
required for one or more particular embodiments or that one or more particular
embodiments necessarily include logic for deciding, with or without user input or
prompting, whether these features, elements and/or steps are included or are to
be performed in any particular embodiment.
[0045] It should be emphasized that the above-described embodiments are
merely possible examples of implementations, merely set forth for a clear
understanding of the principles of this disclosure. Many variations and
modifications may be made to the above-described embodiment(s) without
departing substantially from the spirit and principles of the disclosure. All such
modifications and variations are intended to be included herein within the scope
of this disclosure.

CLAIMS
Therefore, at least the following is claimed:
1. A method, comprising:
receiving, at a first communications device, without a prior request to send
(RTS) signal being sent, a first clear to send (CTS) signal from a second
communications device, addressed to the first communications device, the CTS
signal indicating a data exchange duration; and
sending a second CTS signal, from the first communications device, to the
second communications device,
wherein a network allocation vector (NAV) is set by at least one other
communications device.
2. The method of claim 1, further comprising receiving, at the first
communications device, a request to send (RTS) signal that directly follows the
first CTS signal.
3. The method of claim 2, wherein the RTS signal is addressed at the first
communications device, the RTS signal indicating a data exchange duration that
does not exceed the data exchange duration of the CTS signal.
4. The method of claim 1, further comprising sending, by the first
communications device payload data to the second communications device.

5. The method of claim 1, further comprising sending a third CTS signal
from the first communications device to the second communications device, the
third CTS signal being sent directly after the second CTS signal.
6. The method of claim 5, wherein the second CTS is configured at a first
modulation and the third CTS is configured at a second modulation.
7. The method of claim 1, wherein the NAV is configured to be non-
resetting at the at least one other communications device.
8. A computer readable medium, comprising:
first receiving logic configured to receive, at a first communications device,
without a prior request to send (RTS) signal being sent, a first clear to send
(CTS) signal from a second communications device, addressed to the first
communications device, the CTS signal indicating a data exchange duration; and
first sending logic configured to send a second CTS signal, from the first
communications device, to the second communications device.
9. The computer readable medium of claim 8, further comprising second
receiving logic configured to receive, at the first communications device, a
request to send (RTS) signal that directly follows the first CTS signal.
10. The computer readable medium of claim 9, wherein the RTS is
addressed at the first communications device, the RTS indicating a data
exchange duration that does not exceed the data exchange duration of the CTS.

11. The computer readable medium of claim 8, further comprising second
sending logic configured to send, by the first communications device payload
data to the second communications device.
12. The computer readable medium of claim 8, further comprising third
sending logic configured to send a third CTS signal from the first communications
device to the second communications device, the third CTS signal being sent
directly after the second CTS signal.
13. The computer readable medium of claim 12, wherein the second CTS
is configured at a first modulation and the third CTS is configured at a second
modulation.
14. The computer readable medium of claim 8, wherein the NAV is
configured to be non-resetting at the at least one other communications device.

15. A system, comprising:
means for receiving, at a first communications device, without a prior
request to send (RTS) signal being sent, a first clear to send (CTS) signal from a
second communications device, addressed to the first communications device,
the CTS signal indicating a data exchange duration; and
means for sending a second CTS signal, from the first communications
device, to the second communications device,
wherein a network allocation vector (NAV) is set by at least one other
communications device.
16. The system of claim 15, further comprising means for receiving, at the
first communications device, a request to send (RTS) signal that directly follows
the first CTS signal.
17. The system of claim 16, wherein the RTS is addressed at the first
communications device, the RTS indicating a data exchange duration that does
not exceed the data exchange duration of the CTS.
18. The system of claim 15, further comprising means for sending, by the
first communications device payload data to the second communications device.
19. The system of claim 15, further comprising means for sending a third
CTS signal from the first communications device to the second communications
device, the third CTS signal being sent directly after the second CTS signal.

20. The system of claim 19, wherein the second CTS is configured at a
first modulation and the third CTS is configured at a second modulation.
21. A device, comprising:
a first receiving component configured to, at a first communications
device, without a prior request to send (RTS) signal being sent, receive a first
clear to send (CTS) signal from a second communications device, addressed to
the first communications device, the CTS signal indicating a data exchange
duration; and
a first sending component configured to send a second CTS signal, from
the first communications device, to the second communications device,
wherein a network allocation vector (NAV) is set by at least one other
communications device.
22. The device of claim 21, further comprising:
a second receiving component configured to, at the first communications
device, receive a request to send (RTS) signal that directly follows the first CTS
signal;
a second sending component configured to send, by the first
communications device, payload data to the second communications device; and
a third sending component configured to send a third CTS signal from the
first communications device to the second communications device, the third CTS
signal being sent directly after the second CTS signal.

Included are embodiments for network allocation. More specifically, one embodiment of a method includes receiving,
at a first communications device, without a prior RTS signal being sent, a first clear to send (CTS) signal from a second
communications device, addressed to the first communications device, the CTS signal indicating a data exchange duration and sending
a second CTS signal, from the first communications device, to the second communications device.