Physically scoped multicast in multi-access networks

Details Physically scoped multicast in multi-access networks Physically scoped multicast in multi-access networks

2001-11-13

2004-09-28

Rao, Seema S. (Department: 2666)

Multiplex communications

Pathfinding or routing

Switching a message which includes an address header

C370S432000, C370S474000

Reexamination Certificate

active

06798773

ABSTRACT:

FIELD OF THE INVENTION
The invention relates generally to telecommunication networks. More particularly, the invention concerns a mechanism for physically limiting the scope of multicast messages in such networks.
BACKGROUND OF THE INVENTION
Telecommunication networks for mobile devices generally allow mobile devices to move geographically by “handing off” localized communication links among transmission towers and associated base stations. For example, such networks allow Internet Protocol-enabled devices such as wireless Personal Digital Assistants (PDAs) and mobile computers to move about geographically dispersed areas while maintaining a connection to the Internet.
As is well known, mobile terminals can be served by one or more access routers that service terminals within a particular area. Such access routers allow the mobile terminals to access one or more computer networks, such as the Internet, using mobile IP protocols or other protocols. Mobile terminals may communicate using one of various access technologies, such as GPRS, Bluetooth, or others.
As mobile services have become more widespread, the need has increased for users of mobile terminals to have access to devices that are located within a reasonably close geographic proximity to the user at a particular point in time. For example, the user of a wireless PDA may move into an office building and have a need to print out a document at a printer located in the office building. Aside from determining the precise geographic location of the user and all printers in the building (e.g., using GPS technology), there is no easy way to determine which printer or printers might be available for printing the document, particularly if devices within the building are connected through a different administrative domain from the access router that is serving the mobile terminal. Although multicast messages can be used to send service inquiries to destinations of indeterminate specificity, using such messages to locate a “nearby” printer would not be feasible.
FIG. 1
illustrates the nature of the problem referred to above. Suppose that the user of a wireless PDA
100
moves into an area served by access router
101
, which is coupled to a network
105
and ultimately to the Internet
106
. Suppose further that a Bluetooth-enabled printer
102
is located within a close geographic proximity to PDA
100
, illustrated by dashed line
104
, but is serviced by a different access router
103
, using a different access technology (e.g., Bluetooth). If the user of PDA
100
wants to print a document to the nearest printer, there is no easy way for the system to determine that the user should print to printer
102
. The problem may be compounded by the fact that the addresses used to communicate with access router
101
and
103
lie in different administrative domains; i.e., they are “administratively scoped” rather than geographically or physically scoped.
The Internet Engineering Task Force has defined the Service Location Protocol (RFC 2165) as a standard way of discovering services in a network. Suppose that PDA
100
or access router
101
were to send a message to a multicast address requesting information on printers or other devices that are available to print a document. Conventional multicast routing protocols rely on administrative scoping rules to determine where such a message should be sent. For example, RFC 2365 (“Administratively Scoped IP Multicast,” July 1998), published by the Internet Engineering Task Force, defines a local administratively scoped multicast space. The protocol is unable to determine that printer
102
is geographically close to PDA
100
because they are in different administrative domains (and possibly served by different access technologies, such as wireless LAN technology for PDA
100
and Bluetooth for printer
102
). Devices such as access routers that are physically close to the mobile terminal may be many “hops” away in the IP network topology, and therefore do not appear to be visible to the mobile terminal.
Consequently, a need exists for a mechanism to permit mobile devices to identify other devices that are in the same geographic vicinity even though they may reside within different administrative domains. A further need exists to permit mobile devices to send multicast messages to devices within a particular geographic area irrespective of administrative domains that are associated with the devices.
SUMMARY OF THE INVENTION
The invention provides a system and method for multicast packet delivery that is based on physical neighborhood information. Each of a plurality of access routers maintains information concerning neighboring devices (e.g., access routers).
Multicast packets arriving at an access router are classified as either physically scoped or administratively scoped. Physically scoped packets are “tunneled” by encapsulating them in a unicast packet, based on locally available physical neighborhood information, and sent via unicast to physically adjacent access routers.
Administratively scoped packets are handled using conventional administrative scoping protocols.
Devices that transmit packets to an access router indicate whether each packet should be administratively or physically scoped. In one variation, physical scoping is determined by the sender specifying a maximum number of hops between access routers. A device can transmit packets to a nearby device by transmitting a physically scoped multicast packet.
Other features and advantages of the invention will become apparent through the following detailed description, the figures, and the claims.


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Meyer, D., Administratively Scoped IP Multicast, printed from http://www.ietf.org/rfc/rfc2365.txt?number=2365 . . . Administratively Scoped IP Multicast dated Jul., 1998 (8 pages).
Handley, et al., M., Multicast-Scope Zone Announcement Protocol (MZAP), printed from http://www.ietf.org/rfc/rfc2776.txt?number=2776 . . . Multicast-Scope Zone Announcement Protocol (MZAP) dated Feb. 2000 (26 pages).
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