Multiplex communications – Data flow congestion prevention or control – Flow control of data transmission through a network
Reexamination Certificate
1999-01-11
2002-08-13
Hsu, Alpus H. (Department: 2662)
Multiplex communications
Data flow congestion prevention or control
Flow control of data transmission through a network
C370S236200, C370S241100, C370S249000, C370S252000, C370S397000, C370S395210, C370S409000
Reexamination Certificate
active
06434118
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to data communication networks and more particularly relates to a method for determining the Round Trip Time between a source end station and a destination end station utilizing the ATM Traffic Management mechanism.
BACKGROUND OF THE INVENTION
Currently, there is a growing trend to make Asynchronous Transfer Mode (ATM) networking technology the base of future global communications. ATM has already been adopted as a standard for broadband communications by the International Telecommunications Union (ITU) and by the ATM Forum, a networking industry consortium.
Asynchronous Transfer Mode
ATM originated as a telecommunication concept defined by the Comite Consulatif International Telegraphique et Telephonique (CCITT), now known as the ITU, and the American National Standards Institute (ANSI) for carrying user traffic on any User to Network Interface (UNI) and to facilitate multimedia networking between high speed devices at multi-megabit data rates. ATM is a method for transferring network traffic, including voice, video and data, at high speed. Using this connection oriented switched networking technology centered around a switch, a great number of virtual connections can be supported by multiple applications through the same physical connection. The switching technology enables bandwidth to be dedicated for each application, overcoming the problems that exist in a shared media networking technology, like Ethernet, Token Ring and Fiber Distributed Data Interface (FDDI). ATM allows different types of physical layer technology to share the same higher layer—the ATM layer.
ATM uses very short, fixed length packets called cells. The first five bytes, called the header, of each cell contain the information necessary to deliver the cell to its destination. The cell header also provides the network with the ability to implement congestion control and traffic management mechanisms. The fixed length cells offer smaller and more predictable switching delays as cell switching is less complex than variable length packet switching and can be accomplished in hardware for many cells in parallel. The cell format also allows for multi-protocol transmissions. Since ATM is protocol transparent, the various protocols can be transported at the same time. With ATM, phone, fax, video, data and other information can be transported simultaneously.
ATM is a connection oriented transport service. To access the ATM network, a station requests a virtual circuit between itself and other end stations, using the signaling protocol to the ATM switch. ATM provides the User Network Interface (UNI) which is typically used to interconnect an ATM user with an ATM switch that is managed as part of the same network.
The current standard solution for routing in a private ATM network is described in Private Network to Network Interface (PNNI) Phase
0
and Phase
1
specifications published by ATM Forum. The previous Phase
0
draft specification is referred to as Interim Inter-Switch Signaling Protocol (IISP). The goal of the PNNI specifications is to provide customers of ATM network equipment some level of multi-vendor interoperability.
The Interim Local Management Interface (ILMI) for the PNNI protocol specification provides an auto-port configuration capability. This capability functions to minimize manual configuration operations for PNNI ports of switches. The Phase
0
solution to auto-port configuration is based on hop by hop routing utilizing a ‘best match’ scheme. The Phase
1
PNNI based solution is based on Open Shortest Path First (OSPF) with the additions necessary for ATM. This scheme is essentially a ‘source routing’ scheme whereby each node has basic knowledge of the structure of the entire network and uses this knowledge to build a complete path from the source to the destination. When a connection is to be set up from a source to a destination, the source sends out a SETUP message that has within it the address of the destination. Each ATM network node along the way reads the next node from the SETUP message and forwards the message to an appropriate next node. This continues until the SETUP message arrives at its destination.
In the IISP Phase
0
specification standard, the ATM nodes in the network route the signaling SETUP message hop by hop (i.e., node by node) using a ‘best match’ scheme. ATM addresses are 20 bytes long but only 19 bytes can be used for routing purposes. According to the IISP Phase
0
standard, several prefixes of the ATM address for each link can be registered.
When a node (i.e., an ATM switch) needs to decide to which particular node to route the received SETUP message to, it compares the destination address with all the registered addresses for all of its ports. Only if an address prefix is found that fully matches the destination address can the destination address be considered for routing. After all the prefixes are compared, the prefix address that is the longest is used to determine the routing of the SETUP message. It is important to note that the standard does not require the transfer of any routing information between two neighboring nodes. In addition, the standard also does not permit the use of a TRANSIT NET ID parameter during the signaling phase, which can be used to route to a different routing domain.
A disadvantage of this scheme is that all the prefixes of all neighboring nodes must be registered manually on each of their respective ports. For example, if a port is disconnected from a neighbor and connected to a new neighbor, then the registered addresses must be manually changed in both nodes. This type of network can be termed an absolute static network.
The ATM Header
The components of the ATM header consist of the following fields. A generic flow control (GFC) field provides flow control; a virtual path identifier (VPI)/virtual channel identifier (VCI) field allows the network to associate a given cell with a given connection; a payload type identifier (PTI) field indicates whether the cell contains user information or management related data and is also used to indicate a network congestion state or for resource management (i.e., the EFCI state which is encoded in the PTI field); a cell loss priority (CLP) field indicates that cells with this bit set should be discarded before cells with the CLP bit clear; a header error check (HEC) field is used by the physical layer for detection and correction of bit errors in the cell header and is used for cell delineation.
The provisioning of an ATM network connection may include the specification of a particular class of service. The following list the various classes of service currently defined in ATM. Constant bit rate (CBR) defines a constant cell rate and is used for emulating circuit switching (e.g., telephone, video conferencing, television, etc.). Variable bit rate (VBR) allows cells to be sent at a variable bit rate. Real-time VBR can be used for interactive compressed video and non real-time can be used for multimedia e-mail.
Available bit rate (ABR) is designed for data traffic (e.g., file transfer traffic, etc.) and is the class service connected with resource management. The source is required to control its rate depending on the congestion state of the network. The users are allowed to declare a minimum cell rate, which is guaranteed to the virtual circuit by the network. ABR traffic responds to congestion feedback from the network.
Both switches and end stations in the network implement ABR. Binary switches monitor their queue lengths, set the PTI for congestion state (EFCI) in the cell headers, but do not deal with the computation of explicit rate feedback when congestion occurs.
Explicit rate switches compute the rate at which a source end station can transmit and place this information in the explicit rate field in the returning resource management cell. The destination sends one resource management cell for every N data cells transmitted. If the source does not receive a returning resource management cell, it decreases its allowed ce
3Com Corporation
Hsu Alpus H.
McDonnell & Boehnen Hulbert & Berghoff
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