Aloha optimization

An method of Aloha optimization involves designating a time period as an inroute frame. Such designating includes designating a first portion of the inroute frame as a Transaction Reservation portion, and designating a second portion of the inroute frame as an Aloha portion. A request is transmitted from a first remote terminal to the host terminal that the host terminal allocate one or more slots of the Transaction Reservation portion to the first remote terminal. One or more unallocated slots within the Transaction Reservation portion are then redesignated as extra Aloha slots. A target slot is then randomly selected by a second remote terminal from the slots within the Aloha portion and the extra Aloha slots.

BACKGROUND OF THE INVENTION 
The present invention relates to bandwidth optimization in an integrated 
satellite network, and more particularly to optimization of an Aloha 
component of bandwidth in such an integrated satellite network. 
The user aloha is one of the methods used in an Integrated Satellite 
Business Network (ISBN) to transfer data from a remote port to a hub over 
a spacelink. The spacelink has two data paths referred to herein 
respectively as the inroute and the outroute. The inroute refers to a data 
path from the remote port card to an earth orbit satellite, and from the 
earth orbit satellite to the hub. The outroute refers to a data path from 
the hub to the earth orbit satellite, and from the earth orbit satellite 
to the remote port. Typically, a plurality of remote port cards are used 
to service a corresponding plurality of user devices, whereas a single hub 
is used to service a single host. The entire data path, both inroute and 
the outroute are referred to herein as the spacelink. 
The term remote terminal as used herein, refers to the user device and the 
remote port card collectively. The term host terminal, as used herein, 
refers to the hub and the host device collectively. 
The inroute is temporally subdivided into units referred to herein an 
inroute frame. The inroute frame is further functionally subdivided into a 
first component referred to as the Stream component, a second component 
referred to as the Transaction Reservation component, a third component 
referred to as the User Aloha component, and a fourth component referred 
to as the Control Aloha component. All of these components, except the 
Control Aloha component, are optional and can be selected by the network 
operator. 
The smallest subdivision of the inroute frame is referred to as a slot, the 
size of which depends upon the frequency used to carry the inroute frame. 
There are eight bytes per slot in a 128K inroute (90 slots and 720 bytes 
total per inroute frame). 
The portion of each inroute frame allocated to stream is assigned by the 
host terminal to a single remote terminal and is used for communications 
from the single remote terminal to the host terminal via the earth orbit 
satellite. 
The portion of each inroute frame allocated to User Aloha Control Aloha and 
Transaction Reservation is configured by a network operator and is 
controlled by the hub. User Aloha and Control Aloha are configured as X' 
number of slots per burst and Y bursts User Aloha and Y' bursts Control 
Aloha per frame. Once configured, this allocation, in accordance with 
heretofore known integrated satellite business networks, remains the same 
in every inroute frame, and can only be changed manually by the network 
operator. 
Typically, the User Aloha component is used by the remote terminal to 
communicate information such as credit card authorizations, and other 
relatively short, infrequent and unscheduled communications. The 
Transaction Reservation component, on the other hand, is used for file 
transfers and other lengthy transactions. In order to send a message via 
user aloha, the remote terminal selects one of the bursts within the User 
Aloha at random, and sends the message. In contrast, in order to send a 
message via transaction reservation, the remote terminal first send a 
transaction request via Control Aloha (by selecting one of the bursts 
within the Control Aloha component at random, and sending the request 
during the selected burst). Once the host terminal receives the 
transaction request, it replies to the remote terminal on the outroute, 
assigning the remote terminal slots within the Transaction Reservation 
component (assuming such slots are available). Problematically however, 
both transaction requests sent over Control Aloha, and messages sent over 
User Aloha may be sent from one remote terminal in the same burst as a 
transaction request, or message, respectively, being sent by another 
remote terminal. In this event, a collision occurs, and neither of the two 
messages is received by the host terminal. After a timeout expires at each 
of the remote terminals that sent the collided transaction request or User 
Aloha message, the transaction request or User Aloha message is 
resent--and hopefully does not collide a second time. 
Because the inroute is preconfigured by the network operator based 
generally on statistical analysis of typical usage of the inroute, the 
number of slots allocated to Transaction Reservation and the number of 
bursts allocated to User Aloha may not be optimal for a given data load at 
a given time. During, e.g., daylight hours the available Transaction 
Reservation slots are relatively unused, while at night when large file 
transfers are more common amongst integrated satellite business network 
users Transaction Reservation slots can be at a premium. Similarly, while 
the configured User Aloha slots are relatively unused at night, they are 
highly utilized during the day when small messages, such as credit card 
authorizations, are more prevalent. As a result, each inroute frame, at 
any given time, may contain a number of unused slots within the 
Transaction Reservation or User Aloha components. At the same time as the 
Transaction Reservation component (or User Aloha component) is highly 
utilized, the User Aloha component (or Transaction Reservation component) 
may go virtually unused. The result of a highly utilized User Aloha 
component is increased collisions, and therefore increased delay in 
transmitting User Aloha messages. The result of a highly utilized 
transaction reservation component is greater delay in allocating 
Transaction Reservation slots, and increased requests for additional 
Transaction Reservation slots--due to the failure of the host terminal to 
reserve all of the slots requested during an initial request. These 
increased requests for additional Transaction Reservation slots result in 
greater traffic in the Control Aloha component, which in turn results in a 
greater occurrence of collisions in the Control Aloha component. Note that 
even when there are no Transaction Reservation slots in use there is still 
a chance that there will be a collision in the Control Aloha component. 
SUMMARY OF THE INVENTION 
The present invention advantageously provides for improved bandwidth 
optimization in an integrated satellite network, and in particular 
optimization of Aloha in such a network. 
In one embodiment, the invention can be characterized as a method of 
improved Aloha in an integrated satellite network. The method involves 
designating a time period as an inroute frame during which information can 
be communicated via an earth orbit satellite from one or more of a 
plurality of remote terminals to a host terminal. This designating 
includes designating a first portion of the inroute frame as a Transaction 
Reservation portion, and designating a second portion of the inroute frame 
as an Aloha portion. 
In the event a Transaction Reservation packet of information is to be 
communicated from a first of the plurality of remote terminals, a request 
is transmitted from the first of the plurality of remote terminals to the 
host terminal that the host terminal allocate one or more slots of the 
Transaction Reservation portion to the first of the plurality of remote 
terminals. After the request, if any, has been fulfilled, one or more 
unallocated slots within the Transaction Reservation portion are 
redesignated as extra Aloha slots. 
In the event an aloha packet of information is to be communicated from a 
second of the plurality of remote terminals, a target slot is selected 
from the slots within the Aloha portion and the extra Aloha slots. Because 
the selection is made from both the Aloha portion, and the extra Aloha 
slots, the second of the plurality of remote terminals has a greater 
number of slots from which to select than it would have had if it selected 
from only the Aloha portion. This greater number results in a decreased 
probability of collisions between the Aloha packet from the second of the 
plurality of remote terminals, and other Aloha packets that may be 
transmitted from others of the plurality of remote terminals.

DETAILED DESCRIPTION OF THE INVENTION 
Corresponding reference characters indicate corresponding components 
throughout the several views of the drawings. 
The following description of the presently contemplated best mode of 
practicing the invention is not to be taken in a limiting sense, but is 
made merely for the purpose of describing the general principles of the 
invention. The scope of the invention should be determined with reference 
to the claims. 
Referring first to FIG. 1, a schematic block diagram is shown of an 
Integrated Satellite Business Network 10 (ISBN) suitable for carrying out 
the teachings of one embodiment of the present invention. A remote 
terminal 12 is coupled via airwaves to an earth orbit satellite 14, and 
the earth orbit satellite 14 is coupled via airwaves to a host terminal 
16. The remote terminal 12 includes both a remote network interface 18 (or 
remote port) and a user device 20. The user device 20 can be one of a 
number of possible user devices, e.g., a personal computer, a mini 
computer, a dumb terminal, or the like. The host terminal 16 consists of a 
host network interface 22 and a host device 24. The host device 24 can 
consist of, e.g., a main frame computer or the like. 
The remote network interface 18 employs a satellite antenna 26 and suitable 
communications hardware (not shown), such as is commonly known in the art. 
In addition, the remote network interface 18 employs a number of 
subsystems, several of which are relevant to the present embodiment. 
First, the remote network interface 18 employs a System Executive 
subsystem 28, which is preferably implemented as part of a software 
control system that modifies a processor within the remote network 
interface 18. The System Executive subsystem 28 performs task scheduling 
and control. Second, an enhanced transaction processor 30, also preferably 
implemented using the control software, is used to extract broadcast 
messages from the hub, and to pass information extracted from the 
broadcast messages along to other subsystems within the remote terminal 
12. Third, an Aloha processor 32 is used to randomly select a burst within 
the number of bursts allocated to User Aloha, or Control Aloha, in which 
an outgoing Aloha message will be transmitted. Fourth, a Optimum Data Link 
Control 34 (ODLC) insures sequential, error free, delivery of data packets 
from the remote terminal to the host terminal. 
Within the host network interface 22, a number of subsystems also perform 
various functions relevant to the present embodiment. These subsystems are 
also preferably realized as a part of a software control system that 
modifies a processor within the host network interface 22. A Line 
Interface Module 36 (LIM) serves as an interface between the host network 
interface and the host device and performs processing functions for the 
host device. Another subsystem used in the host network interface is a 
Demand Assignment Processor 38 (DAP). The Demand Assignment Processor 38 
controls the allocation of slots within each inroute frame, and, using a 
prioritization algorithm, makes Transaction Reservation assignments once 
per frame for one frame at a time. Every frame interval (45 ms) a frame 
that is ten frames in the future is processed by the Demand Assignment 
Processor 38 and Transaction Reservation slots are assigned in the form of 
bursts. The frame ten frames in the future is processed in order to allow 
time for the Transaction Reservation assignments to be sent to the remote 
terminals 12 before the frame itself must be sent. 
After making Transaction Reservation assignments, but before sending the 
broadcast message containing the assignments to the remotes, the Demand 
Assignment Processor 38, in accordance with the present embodiment, 
redesignates unassigned (i.e., unreserved or unallocated) Transaction 
Reservation slots as extra User Aloha slots in multiples of the 
preconfigured User Aloha burst size. The number of additional User Aloha 
bursts allocated is placed into the broadcast message containing the 
Transaction Reservation assignments for the upcoming frame. This broadcast 
message is then sent to all remote terminals monitoring the inroute. Based 
on this broadcast message, remote terminals 12 having requested 
Transaction Reservation slots are informed as to whether and to what 
extent their requests are fulfilled, and all of the remote terminals 12 
networked with the host terminal 16 are informed as to the number of 
Transaction Reservation slots that are redesignated as extra User Aloha 
slots. In accordance with the present embodiment, in the event there are 
no Transaction Reservation requests on queue and, thus, no Transaction 
Reservation assignments for a particular inroute frame, a broadcast 
message is sent to the remote terminals 12 containing only the number of 
Transaction Reservation slots redesignated as extra User Aloha bursts for 
the specified inroute frame. 
The broadcast message containing the Transaction Reservation assignments is 
received by the remote terminals 12 monitoring the inroute two frames 
before the packets must be processed that could be sent during the 
assigned slots within the upcoming frame. The Enhanced Transaction 
Processor 30 within the remote terminal 12 parses the broadcast message 
containing the Transaction Reservation assignments and passes the assigned 
number of extra User Aloha bursts for the upcoming frame to the Aloha 
Processor 32. When the remote terminal 12 has a packet to send via the 
User Aloha, the Aloha Processor 32 randomly selects a burst from the 
designated number of User Aloha bursts plus the number of extra User Aloha 
bursts within which to transmit the packet. Because the Aloha Processor 32 
adds the number of extra User Aloha bursts in the upcoming frame to the 
number of designated User Aloha bursts, the number of User Aloha bursts is 
increased from which it randomly selects a burst in which to transmit the 
packet. 
In the event another remote terminal on the inroute also randomly selects 
the same burst in which to transmit the packet of information, the two 
packets of information will collide and neither will be received by the 
host. 
After failing to receive acknowledgment of the transmitted User Aloha 
packet within a timeout period, the remote terminal 12 attempts to resend 
the packet a second time. On the second attempt to send the packet lost 
due to collision, the Aloha Processor 32 totals a number of bursts 
available in the next several frames and selects at random a burst within 
such number of bursts to utilize for transmission. Thus, the number of 
configured User Aloha bursts per frame is effectively multiplied by the 
number of frames over which the Aloha Processor 32 selects the random 
bursts. To this multiplied number of frames is added the number of extra 
User Aloha bursts allocated within the next two frames, in order to 
determine the total number of bursts from which the Aloha Processor 32 
will select a random burst for retransmission of the packet. This random 
selection from a larger number of User Aloha bursts following a collision 
is referred to as "backing off." 
The Aloha Processor 32, in this embodiment, does not attempt to predict the 
allocation of additional User Aloha bursts beyond those received from the 
demand assignment processor for the next two frames. However, once a burst 
has been randomly selected in a frame, the Aloha processor 32 waits for 
that randomly selected burst before transmitting the packet. Any extra 
bursts that are allocated beyond those allocated in the next two frames, 
are "counted" for purposes of "waiting" for the selected random burst. 
Thus, if additional bursts continue to be allocated in future frames, 
beyond the next two frames, the packet may be transmitted in an earlier 
frame than would otherwise be anticipated. 
For example, if there are eight bursts designated as User Aloha bursts, and 
in the next frame the broadcast message indicated that there are four 
extra User Aloha bursts and in the frame two frames after the current 
frame there are two extra User Aloha frames indicated, and the remote 
terminal has randomly selected the forty-fifth User Aloha burst out of the 
next fifty-four User Aloha bursts in which to retransmit a previously 
collided User Aloha message, the User Aloha message will be transmitted in 
the fifth frame following the current frame, assuming no other extra User 
Aloha bursts are allocated. However, in the event four extra User Aloha 
bursts are designated in the third frame following the current frame, and 
six extra User Aloha frames are designated in the fourth frame following 
the current frame, the forty-fifth User Aloha burst will occur during the 
fourth frame following the current frame, thus causing the transmission of 
the User Aloha message one frame earlier than it would have been 
transmitted absent the designation of the other extra User Aloha bursts. 
In accordance with another embodiment of the invention, no User Aloha 
bursts are designated by the network operator. Thus in this embodiment, 
only Stream, Transaction Reservation and Control Aloha make up the inroute 
frame. In a manner similar to that described above, unallocated 
Transaction Reservation slots are allocated as Control Aloha bursts. Thus, 
in the event there is little or no traffic in the Transaction Reservation 
component, most or all of the slots in the Transaction Reservation 
component are redesignated as Control Aloha slots. Similarly, when the 
Transaction Reservation slots are all or almost all allocated, no or few 
extra Control Aloha bursts are allocated. 
Advantageously, the present embodiment causes the probability of a 
collision to decrease whenever there is less Transaction Reservation 
traffic, which is when requests sent over Control Aloha are most likely to 
be honored anyway. Similarly, when Transaction Reservation is highly 
utilized, i.e., when transaction requests are likely to be dishonored, the 
probability of a collision increases. Thus, the number of "wasted" 
transaction requests, i.e., transaction requests that collide, but 
otherwise would have been honored, is reduced by the present embodiment by 
the redesignating of unused Transaction Reservation slots as Control Aloha 
bursts (in multiples of the Control Aloha burst size) whenever there are 
unused Transaction Reservation slots. 
Referring next to FIG. 2, a schematic diagram is shown of a typical inroute 
frame format used in an Integrated Satellite Business Network (ISBN) to 
transfer data from the remote terminal to the host terminal over the space 
link via the inroute. As can be seen, a first group of slots within the 
frame is allocated as the Stream 50. As mentioned above, the Stream 50 is 
used in a conventional manner in the embodiments described herein. 
The next group of slots is designated by the host terminal as the 
Transaction Reservation component 52. Generally, the Transaction 
Reservation component 52 is a group of slots that are assigned on demand 
by the hub for use in transmitting information from a remote to the hub. 
The Transaction Reservation component 50 is commonly used, for example, 
for performing file transfers, where a large amount of data must be 
prescheduled for transmission over the inroute. 
In contrast, the next component of the inroute frame is the User Aloha 
component 54, which consists of a group of bursts (each made of Y slots) 
that are randomly utilized by remote terminals to transmit short messages 
from the remote terminals to the host terminal. 
In the event two or more remote terminals randomly select the same User 
Aloha burst within which to transmit information during a particular 
frame, a collision occurs and neither of the packets of information reach 
the host. In this case, the transmitting remote terminals will time out 
after a preconfigured period of time during which the remote terminals 
fail to receive an acknowledgment from the host terminal. In this event, 
the remote terminals retransmit the failed User Aloha transmission (after 
"backing off", as described above) in hopes that a subsequent transmission 
does not result in a collision. As will be understood by one skilled in 
the art, as User Aloha traffic increases, the probability of collisions 
also increases. 
The last group of allocated slots in FIG. 2 is the Control Aloha component 
56. Control Aloha 56 is used by the remote terminals to transmit control 
messages to the host terminal and is allocated by the remote terminals 
based on a random selection similar to that used to allocate User Aloha 
54. As with transmissions made over the User Aloha component 54, 
transmissions made over the Control Aloha component 56 may from time to 
time result in collisions. Thus, as utilization of the Control Aloha 
component 56 increases, the probability of a collision occurring also 
increases. 
As shown in FIG. 2, the Stream component 50, the Transaction Reservation 
component 52, the User Aloha component 54 and the Control Aloha component 
56, are all preconfigured fixed portions of the inroute frame. Such 
preconfiguration is performed by the network administrator at the host 
terminal. Unfortunately, as is frequently the case, from time to time the 
Transaction Reservation component 52 may be under utilized, or not 
utilized at all. Similarly, as is also frequently the case, the User Aloha 
component 54 may be from time to time under utilized or not utilized at 
all. Unfortunately, in heretofore available Integrated Satellite Business 
Systems, fine tuning of the size of the Transaction Reservation component 
and the User Aloha component had to be performed based on statistical 
analysis of the utilization of inroute frames over a long period of time. 
This statistical analysis, while representing an optimum allocation of 
slots within the inroute frame over a large period of time, often is not 
reflective of the optimum allocation of slots between the Transaction 
Reservation component and the User Aloha component for any given short 
period of time. For example, as described above, many users of Integrated 
Satellite Business Networks perform credit card verification transactions 
at random times during the business day. These credit card verification 
transactions are relatively short and occur at unpredictable times. Thus, 
they are suited for transmission over the User Aloha component 54 of the 
inroute frame. The same users, however, frequently transfer large files to 
the host terminal, such as daily reports, during the night. These large 
file transmissions, in contrast to the relatively short credit card 
verification transmissions, lend themselves to transmission over the 
Transaction Reservation component 52 of the inroute frame. While the 
remote terminals are able to dynamically allocate these transmissions to 
either the User Aloha component 54 or the Transaction Reservation 
component 52, because many remote terminals have similar transmissions to 
transmit during particular times of the day, the Transaction Reservation 
component 52, for example, may go virtually unused during certain hours, 
e.g., during the daytime, while the User Aloha component 54 may go 
virtually unused during others, e.g., during the nighttime. 
Referring next to FIGS. 3, 4 and 5, frame diagrams are shown of an inroute 
frame wherein the User Aloha component 54 is dynamically allocated by the 
hub as a function of the traffic present on the Transaction Reservation 
component 52 of the inroute frame. The present embodiment allows the 
network operator to define several parameters that permit the 
implementation of what is referred to herein as User Aloha optimization. 
First, the network administrator may disable User Aloha optimization and 
thereby opt to have a particular Integrated Satellite Business Network 
function in a conventional manner. As shown in FIG. 3, the entire 
Transaction Reservation component is allocable to User Aloha. In practice, 
this configuration will permit the entire Transaction Reservation 
component 52 to be redesignated for 54 in the event there are no 
Transaction Reservation slots assigned. When there are Transaction 
Reservation requests, however, these requests will be serviced by 
allocating the Transaction Reservation component 52. Any remaining slots 
within the Transaction Reservation component 52, after all outstanding 
Transaction Reservation requests have been serviced, will be redesignated 
as User Aloha 54. Thus, all, some or none of the Transaction Reservation 
component 52 may, in any given frame, be dynamically redesignated as User 
Aloha 54. In FIG. 4, a frame diagram is shown wherein a portion, i.e., one 
or more slots, of Transaction Reservation component 52 is reserved. The 
remaining, unreserved, slots within the Transaction Reservation component 
52 are redesignated by the host terminal as User Aloha 54. Such 
redesignation is broadcast to all of the remote terminals in the 
Integrated Satellite Business Network using the same message that is used 
to broadcast transaction reservations. This broadcast is sent two frames 
before the frame for which the broadcast makes Transaction Reservation 
assignments and/or redesignation of Transaction Reservation slots 52 to 
User Aloha bursts 54. 
Another parameter that affects the allocation of the component 54 is the 
User Aloha component size. In accordance with the present embodiment, the 
User Aloha size is, in effect, a minimum size in that the User Aloha may 
in fact be larger than the configured User Aloha size for any given 
inroute frame. (Such is the case when Transaction Reservation slots 52 are 
redesignated as User Aloha bursts 54.) The User Aloha component 54, 
however, will never be smaller than the configured User Aloha size. As 
shown in the frame diagram of FIG. 5, all of the designated Transaction 
Reservation slots 52 have been reserved by the host terminal. Thus, none 
of the Transaction Reservation slots 52 are redesignated as User Aloha 54, 
and only those slots designated by the network administrator function as 
User Aloha bursts 54. Note that in a particular case, it may be desirable 
to configure the minimum User Aloha component size to zero, thus relying 
entirely on dynamically redesignated Transaction Reservation slots 52 for 
use as User Aloha bursts 54. One consequence of this configuration, 
however, is that there will be no User Aloha bursts 54 available when all 
Transaction Reservation slots 52 are assigned by the host terminal. During 
times of extremely heavy Transaction Reservation traffic, User Aloha 
messages, therefore, will be unable to be transmitted. 
Referring next to FIG. 6, a frame diagram is shown wherein the network 
administrator has designated that no User Aloha bursts will be allocated. 
Thus, as can be seen, three components make up the integrated satellite 
business network frame: the Stream component 50, the Transaction 
Reservation component 52 and the Control Aloha component 56. As these 
three components are described herein above, further description is not 
provided here. As with heretofore known allocation schemes for User Aloha, 
the fixed allocation for Control Aloha by the network administrator at the 
host terminal also suffers from potentially inefficient bandwidth 
utilization. For example, when neither the Transaction Reservation 
component 52 nor the Control Aloha component 56 are highly utilized, or 
when the Control Aloha component 56 is highly utilized and the Transaction 
Reservation component 52 is not highly utilized, collisions still result 
among messages being transmitted on Control Aloha 56 when two or more 
remote terminals randomly select the same burst in which to transmit 
Control Aloha messages. 
Referring next to FIGS. 7, 8 and 9, a frame diagram is shown of an 
Integrated Satellite Business Network frame wherein unused Transaction 
Reservation bursts are dynamically redesignated as Control Aloha bursts. 
As with the redesignation of Transaction Reservation slots as User Aloha 
bursts described above, the network administration is able to configure 
several parameters. One of these parameters allows the network 
administrator to disable Control Aloha optimization, causing the host 
terminal to perform in a conventional manner. Another parameter allows the 
network administrator to specify the number of Control Aloha bursts 56 
(which is effectively a minimum number of Control Aloha bursts). In FIG. 
7, an exemplary frame is shown wherein no Transaction Reservation requests 
have been queued. As a result, no slots within the Transaction Reservation 
component 52 are reserved. In accordance with the present embodiment, the 
host terminal dynamically redesignates these Transaction Reservation slots 
52 as Control Aloha bursts 56 (to the extent Transaction Reservation slots 
are available in multiples of the configured Control Aloha burst size). By 
increasing the number of designated Control Aloha bursts 56, the host 
terminal is able to significantly reduce the likelihood of collisions 
between Control Aloha transmissions from the remote terminals. When some 
Transaction Reservation transmissions have been requested and allocated by 
the hub, as shown in FIG. 8, the number of redesignated Transaction 
Reservation slots 52 is reduced so as to recapture these slots for 
Transaction Reservation purposes. When a limited number of Transaction 
Reservation requests have been made, some Transaction Reservation bursts 
52 are still dynamically redesignated as Control Aloha bursts 56. As 
Transaction Reservation activity increases, the dynamically allocated 
Transaction Reservation bursts 52 may become completely allocated as 
Transaction Reservation bursts 52, as shown in FIG. 9, leaving only the 
preallocated Control Aloha bursts 56 available for Control Aloha messages. 
Note that in some cases the network administrator may wish to allocate 
very few bursts as Control Aloha bursts 56, relying on the dynamic 
redesignation of Transaction Reservation slots 52 to provide bandwidth for 
Control Aloha transmissions. The consequence of this allocation of Control 
Aloha is that when transaction reservation traffic is high, Control Aloha 
will be small. The result of this small Control Aloha is that requests for 
additional Transaction Reservation slots will not get through to the host 
terminal, because of collisions. As fewer Transaction Reservation slots 52 
within each frame are reserved, the number of Control Aloha bursts 56 
increases, thereby increasing the probability that requests for additional 
Transaction Reservations will be successfully received by the host 
terminal. Thus, a sort of self-tuning Control Aloha component 56 is 
created wherein Control Aloha permits more requests for Transaction 
Reservation slots 52 when there are more Transaction Reservation slots 52 
available. 
While the invention herein disclosed has been described by means of 
specific embodiments and applications thereof, numerous modifications and 
variations could be made thereto by those skilled in the art without 
departing from the scope of the invention set forth in the claims.