Electrical computers and digital processing systems: multicomput – Network-to-computer interfacing
Reexamination Certificate
1999-11-12
2004-04-13
Maung, Zarni (Department: 2154)
Electrical computers and digital processing systems: multicomput
Network-to-computer interfacing
C709S230000, C709S237000, C370S465000, C370S466000, C370S467000
Reexamination Certificate
active
06721805
ABSTRACT:
BACKGROUND
The number of devices that can be categorized as personal computing and communication assistants (PCCAs) increases daily. The PCCA class of devices comprises laptop and palmtop computers, personal digital assistants (PDAs), pocket organizers, cellular phones, pagers, etc. The general objective of all these devices is to allow their owner to organize himself or herself and contact his or her business in an orderly manner. This is accomplished by allowing a person to be accessible (almost) anywhere (using pagers and cellular phones), and by using personal information management (PIM) utilities like calendars, things-to-do, telephone books (using PDAs and organizers).
Many PCCAs are capable of being connected to a desktop computer for backing-up or updating data stored in them. Some PCCAs can also connect to data networks, like the Internet, via a modem and enable networked data services like e-mail and web-surfing. In general, PCCAs are capable of connecting to and interacting with other computer devices either directly or indirectly via intermediate communication devices, e.g., modems. In these cases, the PCCAs communicate to these other devices via point-to-point dedicated communication channels.
Dedicating a communications channel for the exclusive use of only two devices is not always desirable since it usually results in poor utilization of communication resources. For example, when a modem is used to connect a PCCA with a remote application server, only a single PCCA can use the modem to connect to the server. It is known that data transmissions are bursty in nature, in that data sources are mostly inactive, with occasional periods of data activity. During periods that the PCCA idles the modem could have been used by another PCCA to connect to the same or other application servers. Dedicating though the channel between a single PCCA and the modem does not allow sharing of the communication resources, e.g., the modem, among various communicating devices (the PCCAs and the application servers). Using separate modems and telephone lines to connect multiple PCCAs to application servers is not a very attractive solution as it prohibitively increases the cost of communication. In this case, sharing the communication resources is highly desirable because it reduces the cost of interconnecting several devices simultaneously.
Sharing communication resources is a common practice in local area networks (LANs), where a number of computer nodes connect with each other via a shared communication medium, e.g., twisted pair, cable, and air. Devices, also referred to as stations or nodes, attached to the LAN coordinate their transmissions using a commonly agreed medium access (MAC) protocol. The most popular MAC protocols are the IEEE 802.3 protocol, commonly referred to as Ethernet, and the IEEE 802.5 protocol, commonly referred to as Token Ring. Both of these protocols use a cable, such as a twisted pair or coaxial cable, as the transmission medium. A more recent protocol for sharing an over-the-air radio frequency (RF) band in LAN environments is the IEEE 802.11 protocol.
Network interface cards (NICs), or adapter cards, are added internally to a device in an expansion slot within the device and are used for interfacing the device to the transmission medium of the LAN. NICs are also attached externally via a device's PCMCIA slots (if available), usually referred to as PC card. PCMCIA cards provide functionalities similar to adapter cards that are usually added internally to a computer, e.g., memory cards, hard-disk drivers, modems, NICs, etc., but due to convenience and space are simply added externally to the computer. PC cards are not used for connecting PCCAs directly to each other.
However, not all PCCAs can be opened up to add a NIC and not all of them are equipped with PCMCIA, or other similar, ports to which NICs can be attached. Thus, some devices cannot be part of a LAN and share in the cost benefits that a shared medium LAN solution provides. Therefore, there is a need in enabling LAN-oriented communications for the plethora of PCCAs that are otherwise only capable of communicating with other devices one-at-a-time using dedicated communication resources.
FIG. 1
shows a typical scenario where a mobile host device
101
, e.g., a personal digital assistant (PDA), connects to a desktop host computer
102
. One reason for connecting the two devices is to back up data in the mobile host
101
to the desktop host
102
. Another reason is to update data in the mobile host
101
with data in the desktop host
102
. This process is usually achieved by using two complementary pieces of software, an interactive application client
103
residing on the mobile host
101
and an interactive application server
104
residing in the desktop host
102
. The two complementary pieces of software check the latest data versions stored on the two devices and perform any necessary backups and updates.
The interactive application software modules use the services of a communication protocol stack
106
and
107
for transporting the data between the two hosts. A communication protocol stack is a collection of rules that governs how data is formatted and organized for transport between devices on a computer communication network. In the typical scenario shown in
FIG. 1
, the two communicating devices are connected using their serial ports
108
and
109
. A typical communication protocol used is the RS-232 protocol. The RS-232 protocol requires, among other things, that data that is to be transported between two devices are sent serially one byte at a time and that each byte is prepending by 1 start-bit and 1, 1.5, or 2 stop bits. The number of stop bits is configurable and both communicating devices need to agree on the same number of such bits. The communication between the two devices is done using an RS-232 cable
110
wired in a null-modem configuration. Since, the two devices are directly connected to each other, no data addressing for routing to the correct destination is needed. Hence, the communication protocol stack in this case is quite shallow and no additional information is appended on the data to be transmitted except from the start and stop bits required by the RS-232 protocol.
Since, the only elements that are physically connected are the serial ports on the two devices, only the link
110
is a real one. Any other communication between the complementary software modules, like
105
and
111
, is virtual in that it is performed using the services of a lower communication layer.
FIG. 2
shows another typical scenario, which expands the connectivity scenario in
FIG. 1
over the public switched telephone network (PSTN)
204
. In this case, the two host devices are first connected to a data communications equipment (DCE)
202
and
203
, commonly referred to as a modem, via a regular RS-232 cable
201
. When one modem transmits to another one, it modulates the information signal received from the serial ports
108
and
109
of the device it is directly attached too into an audible signal appropriate for transmission over the public switched telephone network (PSTN)
204
. The receiving modem demodulates the waveform into an information signal appropriate for receipt by the receiving device. In the sequel, as well as in
FIGS. 1 and 2
, the terms mobile and desktop host could be interpreted rather generically as two computing end-devices able to exchange data over a proper communications means, e.g., point-to-point links, networks, etc.
FIG. 3
shows yet another realization of the connection scenario in FIG.
2
. The mobile host
101
is connected again to PSTN
204
as in FIG.
2
. In this case the communication protocol stack
302
in the mobile host includes not only the serial protocol
309
, but also an industry standard transport control protocol/internet protocol (TCP/IP)
303
and point-to-point protocol (PPP)
306
, as well. These protocols enable an interactive application on the mobile host
101
, like a web-browser
312
, to use the services of a corporate i
Bhagwat Pravin
Bisdikian Chatschik
Janniello Frank James
Korpeoglu Ibrahim
Naghshineh Mahmoud
Beck Thomas A.
Herzberg Louis P.
Hu Jinsong
Maung Zarni
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