PMC Exhibit 2029
`Apple v. PMC
`IPR2016-01520
`Page 1
`
`

`

`

`

`

`

`153
`
`COMPUTER NETWORKS AND THEIR PROTOCOLS
`
`
`
`terminals are intended to be located very close to broadcast systems user devices
`thus obviating the need for long and expensive land-based connections.
`c0mparatively limited capacity. Such packet terminals can even be mobile:
`mounted on vehicles. an important consideration in military and other contain-1;.1
`The greatest portability is possible in packet radio systems. where hand-held' "
`pocket terminals are quite feasible.
`'
`The technology of all broadcast systems. whatever their nature, has a. grew;
`deal in common. though the problems of cantention resolution are somewhau
`different and require different techniques for their resolution. Much of todaygr'g.’
`technology has sprung from developments of the ALOHA system, which i553
`ground radio system. We shall therefore cansider this system first, then panama}:
`to a discussion of the more complicated ground radio systems; this will.
`followed by an account of satellite broadcast systems and cable broadcaszg;
`systems.
`
`PMC Exhibit 2
`
`5.2 PACKET RADIO SYSTEMS
`
`The ALOHA system is essentially a UHF packet broadcast system cream-(fl.
`for very pragmatic reasons (including the poor quality of local telephone lines):
`by a team at the University of Hawaii: it first became operational in 19m. The:
`system covers the Hawaiian islands, Figure 5.2. and is centred on the island of-
`Oahu. lnexpensive access is afforded to central time-sharing computer systems:
`for several hundred terminal users. In the first instance communication 'was
`limited to a large group of terminals in the Honolulu district within direct radio
`range of the central station. User-to-user communication is also catered for.
`
`Kauai 3
`
`M Menehune central station
`
`it Repeater station
`- User node
`
`60 miles
`I—l
`
`Figure 5.2 The ALOHA network coverage
`
`PMC Exhibit 2029
`Apple v. PMC
`IPR2016-01520
`Page 4
`
`

`

`PACKET BROADCAST SYSTEMS
`
`The Basic ALOHA System
`
`The aim of the ALOHANET is to previde cheap and easy access for a large
`number of terminal users to central computing facilities. A summary of the
`ALOHA project may be found in Binder er al.‘ User-to-computer communi—
`cation is via a 100 kHz random-access channel at 407.350 MHz; the broadcast
`return channel. computer-to—user,
`is also of 100 kHz bandwidth at 413.475
`MHz. Direct user-to-user communication is not catered for (user—‘to-user com-
`munication is possible by transferring data to the central switch and then
`forwarding it to the destination user) and. until the addition of packet repeaters,
`the system was logically equivalent to a star-connected network. The central
`communications processor. the Menshune (or packet station). locatedat Hon-
`olulu on Oahu. which receives packets from users and is responsible for sending
`packets to them. is an HP 2100 minicomputer. Menehune is a Hawaiian name
`for an imp—a reference to the ARPA node. The packet transmission data rate
`is 9600 baud. packets consisting of a header (32 bits), a header parity check
`field (16 bits), and up to 80 bytes of data. followed by a data parity check field
`(16 bits). Maximum size packets are therefore 704 bits in length and take about
`73 milliseconds to transmit; propagation time is negligible in comparison.
`Control of the broadcast channel from the central computer to the users
`presents no problem. because only one transmitter is using the channel. Packet
`headers contain user addresses which enable individual receivers to identify the
`traffic intended for them. The user-to-computer channel. referred to above as
`random-access, could have been apportioned to individual users by a fixed
`allocation scheme, such as frequency division multiplexing or time division
`multiplexing. However. the nature of terminal traffic is almost always bursty
`and a fixed allocation would hardly make the best use of the communication
`medium. hence the choice of a random-access scheme.
`This scheme, known as pure ALOHA. allows a packet terminal to transmit
`packets at times which are completely independent of packet transmissions from
`other terminals. A natural consequence of this independence of action is that
`packets from different sources may be transmitted at the same time and therefore
`collide or overlap as they arrive at the Menehune central station; an overlap
`that affects only the smallest fraction of transmission time has the same effect
`as an overlap of complete packets: both packets are irretrievably corrupted.
`Figure 5.3 indicates the way in which overlaps may occur. Packets subject to
`such overlap are rejected by the Menehune and the fact of overlap is made
`known to the respective transmitting terminals by absonce of the acknowledge-
`ment signal which would otherwise be sent by the Menehune to the packet
`terminals. Packets refused by the Menehune on account of an overlap are
`retransmitted by the packet terminals after a time-out period. It is plainly
`obvious that an immediate retransmission of packets by these terminals, or.
`indeed. retransmission after a fixed, uniform time interval, would just result in
`
`PMC Exhibit 2
`
`
`PMC Exhibit 2029
`Apple v. PMC
`IPR2016-01520
`Page 5
`
`

`

`160
`
`commas NETWORKS AND THEIR psorocors
`
`'
`
`Collision
`
`a secoad overlap: therefore retransmission takes place at each terminal aftew
`random delay. Clearly the number of overlaps is a function of traffic intensity
`the greater the traflic, the greater the probability of overlaps. It is also essential:
`that acknowledgement packets should be sent with highest non-'preempfifi}
`priority from the Menehune to the packet terminals; otherwise unwante'fi‘t
`retransmission may occur.
`I
`"
`Error control on the broadcast channel (Menehune to packet terminals):
`presents difficulties. Ideally this should be on the same positive acknowledgemenfi
`basis as the error control in the other direction on the random-access Channel,-
`HoweVer. acknowledgement packets destined to the Menehune would have as.
`contend for the random-access channel in just the same way as data packet§__
`Binder er of.“ state that. because of this contention, at full channel loading eaczhg
`random-access packet must be retransmitted an average of 1.? times: thus each-
`data packet or acknowledgement packet must be sent 2.? times on average
`before it is successfully received. In an error-free situation. to ensure that the;
`acknowledgement
`is successfully transmitted by the packet
`terminal,
`the;
`Menehune must send the data packet 2.? times on average. even though the:
`packet may have arrived correctly the first time. Where errors occur, the.
`multiple transmissions from the Menehune will be essential if an acknmalrleclg'e.a
`ment system is to operate correctly. This is evidently very wasteful of bandwidth
`and can be avoided by not using acknowledgements in this channel. relying on-
`low error rates and a system of reporting errors to the uSer, who may decide to
`repeat a transaction. Where, for particular users, this is not acceptable, a system
`of positive acknowledgement may be introduced on a selective basis.
`
`PMC Exhibit 2
`
`
`
`
`
`Terminul_1_ _
`
`Terminol_2___
`
`Terminal 3
`
`Terminul_ [1 __
`
`Collision I
`:crossiseclion:
`l.
`
`Figure 5.3 Packet timing in pure ALOHA
`
`PMC Exhibit 2029
`Apple v. PMC
`IPR2016-01520
`Page 6
`
`

`

`

`

`

`

`

`

`

`

`

`

`

`

`