Multiplex communications – Communication over free space – Repeater
Reexamination Certificate
1999-09-29
2003-09-23
Maung, Nay (Department: 2684)
Multiplex communications
Communication over free space
Repeater
C455S428000, C455S013300
Reexamination Certificate
active
06625131
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to a satellite communication system capable of multicast processing, and more particularly, relates to such a system in which the capacity of the multicast processing can be scaled to meet different requirements.
Modern communications networks carry staggering amounts of information. Increasingly, that information is transmitted through communication satellites. A single satellite may have, for example, the equivalent of 30 or more uplink transponders, each able to receive an uplink signal with a bandwidth of 250 MHz. The resultant uplink data path may have a capacity of 8 to 60 gigabits per second or more.
Where a satellite is a link in a communications network, many individual ground stations may encode, modulate, and transmit uplink signals to the satellite. Each uplink signal may consist of hundreds of individual data channels each, for example, carrying data for a telephone conversation. Similarly, the downlink signals produced by the satellite and transmitted to ground stations often include data for hundreds of users.
Additionally, crosslink signals may transmit data between satellites.
Satellite (and terrestrial) communication systems divide the data traffic on the uplink, downlink, and crosslink signals into discrete pieces of information, and each discrete piece of information may subsequently be transmitted over different selected channels in the communication network. The discrete pieces of information are referred to, for example, as “frames” or “ATM packets”, depending on the particular system. In past terrestrial systems, for example, the data packets may be Asynchronous Transfer Mode (ATM) cells.
Each ATM cell is a specifically formatted data packet that is 53 bytes long and includes 5 header bytes (called the “header”) and 48 information bytes (referred to below as the “information payload”). The header contains necessary information for a network to transfer cells between nodes over an ATM connection.
Specifically, the header contains a logical address consisting of an 8-bit Virtual Path Identifier (VPI) and a 16-bit Virtual Channel Identifier (VCI). The header also contains a 4-bit Generic Flow Control (GFC), a 3-bit Payload type (PT), and a 1-bit Cell Loss Priority (CLP) indicator. The header is error-protected by a 1-byte header error check (HEC) field.
The VPI/VCI field of an ATM header cell contains ATM address information. A virtual channel is used for the unidirectional transport of ATM cells, each channel having associated with it a VCI value. A virtual path (VP) is an aggregate bundle of virtual channels (VCs). These paths have associated VPI values, each VPI value identifying a bundle of one or more VCs. Because two different VCs belonging to two different VPs at a given interface may have the same VCI value, a VC is only fully identified at an interface if both its VPI and VCI values are indicated. Thus, the ATM address field is divided into two subfields. The first byte contains the VPI. The information in this field is used to switch virtual paths consisting of groups of virtual channels. The second byte contains the VCI, used to switch virtual channels. The information in the VCI identifies a single virtual channel on a particular virtual path.
Connection to an ATM network is a shared responsibility. The user and network provider must agree as to the support of application bandwidth demands and other traffic characteristics that will be provided. To further one aim of such an agreement, that is assurance that the integrity of the transmitted data packets is maintained, network users categorize cells according to Quality of Service (QoS) classes. QoS is defined by specific parameters for cells that conform to a particular traffic application. Traffic parameters are negotiated between a user and a network provider, and the user's input cells are monitored to ensure that the negotiated traffic parameters are not violated these parameters can be directly observed and measured by the user. QoS is defined on an end-to-end basis, an end, for example, being an end workstation, a customer-premises network, or a private or public ATM user-to-network. QoS is defined in terms of any number of measurement outcomes.
The measurement outcomes used to defined ATM performance parameters include successful cell transfer, errored cell transfer, lost cell, misinserted cell, and severely errored cell block. These performance parameters correspond to the generic QoS criteria of accuracy, dependability, and speed. Measurements of cell error ratio, severely errored cell block ratio, and cell misinsertion rate correspond to the QoS criterion of accuracy; measurements of cell loss ratio correspond to the QoS criterion of dependability; and measurements of cell transfer delay, mean cell transfer delay, and cell delay variation correspond to the QoS criterion of speed.
Cell error ratio (CER) is defined as the number of errored cells divided by the sum of successfully transferred cells and errored cells. Severely errored cell block ratio is defined by the total transmitted cell blocks. Cell misinsertion rate (CMR) is the number of misinserted cells divided by a specified time interval. Cell loss ration (CLR) is defined as lost cells divided by transmitted cells. Cell transfer delay is the elapsed time between a cell exit event at a measurement point and a corresponding cell entry event at another measurement point for a particular connection.
The cell transfer delay between two measurement points is the sum of the total inter-ATM node transmission delay and the total ATM node processing delay between the measurement points. Mean cell transfer delay is the average of a specified number of absolute cell transfer delay estimates for one or more connections. Cell delay variation is a measure of cell clumping, i.e., how much more closely cells are spaced than the nominal interval. Cell clumping is an issue because if too many cells arrive too closely together, cell buffers may overflow.
QoS classes are defined with pre-specified parameter threshold values. Each QoS class provides performance to an ATM virtual connection as dictated by a subset of ATM performance parameters. Additional details on ATM cell headers and QoS classes may be found in numerous references including
ATM Theory and Application
, (David E. McDysan & Darren L. Spohn, McGraw-Hill, Inc. 1995).
The use of QoS classes for ATM switches assures the integrity of the data packets. In addition, in most applications (where capacity generates revenue), one significant performance factor is the amount of information that is passed through the communication system (i.e., throughput). Generally, the higher the data throughput, the higher the revenue potential.
In the past, a bar to implementing a high throughput space-based switch was that an earth terminal could only receive information in a particularly configured downlink at any given moment in time. The downlink configuration depends on several parameters including, for example, frequency, coding, and the polarization of the downlink at the time the satellite transmits the information. Unlike information transmitted terrestrially, not every earth terminal may receive information in every downlink, because earth terminals are only configured to receive a particularly configured downlink at any given moment in time.
Thus, space-based systems, unlike terrestrial systems, face unique challenges in their delivery of information to ground stations. In other words, past terrestrial networks did not provide a suitable infrastructure for communications satellites.
Furthermore, revenue generated from operation of satellite communication systems is affected by considerations of weight and power consumption of the switch used in the satellite communication system. In a space-based implementation, higher weight and increased power consumption in the switch translates to higher spacecraft and launch costs and potential for reduced throughput. These, in turn, may have the effect of lowering potential revenue.
Gregoire Darren R.
Stroll Zoltan Z.
Takahashi Scott M.
Wong Roland Y.
Yee-Madera Gefferie H.
Gesesse Tilahun
Maung Nay
McAndrews Held & Malloy Ltd.
Northrop Grumman Corporation
LandOfFree
Satellite communication multicast processing techniques... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Satellite communication multicast processing techniques..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Satellite communication multicast processing techniques... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3092274