`
`very small aperture terminals
`
`Edited by
`JOHN EVERETT
`
`1
`
`Exhibit 1021
`Appl e et al. v. Uniloc
`IPR2019-00510
`
`1
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`Exhibit 1021
`Apple et al. v. Uniloc
`IPR2019-00510
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`

`

`Published by: Peter Peregrinus Lid., London, United Kingdom
`
`© 1992: Peter Peregrinus Ltd.
`
`Apartfrom any fair dealing for the purposes of research or private study,
`orcriticism or review, as permitted under the Copyright, Designs and
`Patents Act, 1988, this publication may be reproduced, stored or
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`Agency,inquiries conceming reproduction outside those terms should be
`sent to the publishers at the undermentionedaddress:
`
`Peter Peregrinus Ltd.,
`Michael Faraday House,
`Six Hills Way, Stevenage,
`Herts, SGi 2AY, United Kingdom
`
`While the editor and the publishers believe that the information and
`guidance given In this work is correct, all parties must rely upon their own
`skifl and judgment when making use ofit. Neither the editor nor the
`publishers assume anyliability to anyone for any loss or damage caused
`by any error or omission in the work, whether such error or omission is
`the result of negligence or any other cause. Any and all suchliability is
`disciaimed.
`
`The mora! right of the authors to be identified as authors of this work has
`been asserted by them in accordance with the Copyright, Designs and
`Patents Act 1988.
`
`British Library Calaloguing in Publication Data
`
`A GIP catalogue record for this book
`is available from the British Library
`
`ISBN 0 86344 2009
`
`2
`
`

`

`Satellite based messaging systems
`
`351
`
`Fig. 19.1 Network with a single central station
`RT = rural terminal
`
`HUB
`
`19.2.1 System architecture
`
`The first and most important step in the network design is the selection of a
`suitable system architecture [4]. The choice of architecture would depend upon
`the expected pattern of traffic flow in the system and expandability of a given
`architecture.
`There are a numberofpossible architectures for messaging systems but only the
`following alternatives are considered to be important.
`
`In this architecture, all terminals in the network
`19.2.1.1 Fully connected network
`can transmit to all other terminals directly via the satellite channel. The trans-
`ponder capacity can be divided into dedicated channels operating between
`different pairs of terminals or the transponder can be shared byall terminals in
`a multiaccess mode on a single channel at an adequate rate. This architecture is
`attractive from the end user point of view as messages can besent directly to all
`other terminals in the network. However,it is very difficult to implementa fully
`connected networkat the present time with low cost earth stations because of high
`transmit power requirements and large aperture of the antennas.
`
`19.2.1.2 Network with a single hub (star network) This is the most commonarch-
`itecture, depicted m Fig. 19.1, using VSATs because of minimal demandson the
`rural terminals. The central station (or hub) also acts as a post office where
`messages can beleft for users who are currently unable to communicate. It also
`acts as a central database for remote access to information and as a computing
`resource.
`This system is a two hop system;i.e. initially the message is transmitted to the
`
`3
`
`

`

`352
`
`Satellite based messaging systems
`
`a4 _
`
`HUB1
`
`a4 +
`
`mo
`
`HUB 2
`
`w
`
`Fig. 19.2 Network with multiple hubs
`
`hub and from there to the destination rural terminal. In this case the transponder
`capacity can be divided into many channels for communication to and from the
`hub to the rural terminals, or the transponder can be shared byall terminals in
`the network in a multiaccess mode. The channel(s) for communication from hub
`to rural
`terminals can follow different rules than the channel(s) from rural
`terminals to hub.
`
`19.2.1.3 Network with multiple hubs A single hub architecture fails completely if
`the hub becomes unserviceable. Accordingly, the presence of more than one hub,
`indicated in Fig. 19.2, in a network is desirable for establishing a high level of
`system reliability by virtue of in-built system redundancy. In a star network, the
`hub can rapidly become overloaded if demand outgrows the hub capacity. The
`multiple hub architecture can provide a more timely warning of impending
`congestion in the network and the system capacity can be increased by upgrading
`existing hubs or increasing the numberof hubs. This can be a valuable feature
`in large national systems.
`In this case, there are two possible alternatives depending upon the way hubs
`transmit to each other and to rural terminals. The hubs can communicate with
`each other on the same channel(s) as the one used to communicate with rural
`terminals, or the hubs can use separate channels reserved for communication
`between hubs.
`
`In this case, shown in Fig.
`19.2.1.3.1 Single/multiple hubs with asymmetric channel
`19.3,
`the satellite channel
`is asymmetric and different inbound (from rural
`terminals to hub) channels are allocated to groups of users. Each channel in a
`groupis shared by a numberofusers who contendfor it in multiaccess mode. The
`
`
`
`4
`
`

`

`Satellite based messaging systems
`
`353
`
`\
`
`\
`
`‘,
`SN
`
`Sy
`
`\
`
`xMS
`NA
`Iw
`Nv
`ay
`NN —‘
`N
`\\ —\
`‘
`SY
`Vy
`\ \
`pS
`
`RT 4
`
`\ \A
`
`x a
`
`\
`
`yK
`
`RT 3
`
`
`
`HUB G G,
`
`
`
`
`F
`
`f,
`f,
`CHANNELDIVISION
`
`f,
`
`Fig. 19.3
`
`Single hub with asymmetric channel
`
`outbound (from hubto rural terminals) channel is a multiplexed channel and the
`messages transmitted reach all earth stations in the network. Messages are
`displayed only if they are intended for the specific station/user. Either, a preas-
`signed timeslot scheme or addressing information at the beginning of messages
`can be used for distinguishing the destination of a message. The inbound sub-
`channels are relatively low capacity, typically less than 64 kbit/s, whereas the
`outbound channelis high capacity, typically 512 kbit/s.
`This configuration gives full connectivity in two hops as every terminal can
`transmit to every other terminal on the network via hub(s). The advantages are
`the capability to support a very large numberof users and incremental network
`expansion by adding more subchannels with increase in demand. This architec-
`ture takes full advantage of the high transmit power of a hub to support a high
`speed outbound channel compared with the inbound channel whichis easily
`provided by rural terminals.
`
`Yn this architecture, depicted in
`19.2.1.3.2 Multiple hubs with symmetric channels
`Fig. 19.4, the rural terminals are able to transmit to a limited numberof hubs;
`either one or two. The hubs transmit among themselves on separate channel(s)
`reserved for the purpose. The messages from one rural terminal to another take
`three hops in the worst case.
`
`5
`
`

`

`354
`
`Satellite based messaging systems
`
`
`
`
`
`Fig. 19.4 Multiple hub with symmetric channels
`
`CHANNELDIVISION
`
`The transponderis divided into many channels and a groupofrural terminals
`and a hub share one channel. The membersof a group use a suitable multiaccess
`protocol to acquire the allocated channel. If the hub being used byagroupfails,
`the whole group may not be able to communicateatall: hence, an alternative
`arrangement must be provided. Either, a shared back-up hub can be provided
`for all groups or the rural terminals can be programmedto switch over to an
`adjacent groupin case offailure of the hub.
`
`19.2.2 Comparison of architectures
`It is highly desirable to have multiple hubs in the network because:
`e A multiple hub architectureis highly flexible and allowsfor further expansion
`of the network: hubs can be added to the network when demand increases
`e The architecture is fail-safe as the system does not collapse completely even
`if a few hubsfail simultaneously
`e Manypotential applications of the network indicate the need for a multiple
`hub architecture as discussed below.
`
`The choice of an architecture should be made after considering overall cost,
`reliability and applications to be satisfied by the system. For example, most
`
`6
`
`

`

`Satellite based messaging systems
`
`355
`
`messaging networks can also provide access to information (a query to a data-
`base), transmission of vital data, or remote access to computing resources.In all
`of these applications hierarchical structure is necessary as social, political and
`business systemsare usually organised for flow of information from rural locations
`to a central hub. The system would have a large numberofusers spread through-
`out the country and hence the traffic pattern is a key factor in arriving at a
`suitable system architecture. The existing telecommunication infrastructure in-
`dicates that most of the traffic flow is from small towns andcities to the met-
`ropolitan cities. Also, a large amountoftraffic flow is amongthese cities. This
`implies that multiple hubs with full connectivity provide an attractive architec-
`ture matched to user needs and system objectives.
`An important advantage of dividing a channelinto subchannelsis that groups
`of users with commoninterests can share a subchannel withoutinterfering with,
`or getting interfered by, other groups/users. They can share commoninterest
`data-bases and remotely located resources. Built-in security and protection mech-
`anisms exist so others outside the group can be prevented from accessing secret
`or sensitive information. The grouping can be implemented based upon geo-
`graphical criteria or upon any other commoninterest; e.g. a regional grouping
`(western, eastern, central etc) is a good choice as the majority of messages can be
`expected to flow within a region. Banks,
`libraries, railways, health services,
`community and educational institutions could form separate groups. Careful
`study of current
`traffic patterns and future needs is required to decide on
`groupingcriteria. The architecture suggested in Fig, 19.4 is flexible and can easily
`be modified as requirements change over a period oftime.
`In a system which uses hubstation(s), the traffic to and from these hub(s) will
`be highly asymmetrical. Messages originating from rural terminals are transmit-
`ted to a hub which retransmits them to the appropriate destination and
`sometimes responds to queries from rural terminals. Thus, there is almost con-
`tinuoustraffic from hub to rural terminals. On the other hand, incomingtraffic
`to the hubis bursty in nature. This imbalance betweentraffic in and out of hub(s)
`makes it highly desirable to employ different types of channel access protocols for
`inbound and outbound channels. A multiaccess protocol for
`the incoming
`channel, which is characterised by bursty traffic from a large numberofstations,
`and simple time division multiplexing for the outgoing channel, which has a
`continuous transmission to a large numberofstations, would appearto represent
`an optimum choice. This imbalance in traffic flow will be reflected in the
`difference in transmission rates between the inbound and outbound channels.
`
`19.3 Multiaccess techniques
`
`These are broadly divided into polling, reservation, demand assignment and
`random access schemes. Each has its own advantages and disadvantages. The
`suitability of each of these schemes, especially to messaging applications, will now
`be considered.
`the fact that messaging
`In evaluating the different multiaccess techniques,
`systems need not operate in an on-line real-time mode should be taken into
`account:
`this results in a relaxation of the maximum delay tolerable by the
`network. Even an access time of a few minutes will be considered acceptable in
`
`7
`
`