Multiplex communications – Fault recovery
Reexamination Certificate
1998-09-18
2003-09-23
Ton, Dang (Department: 2666)
Multiplex communications
Fault recovery
C370S242000, C370S395630, C370S465000
Reexamination Certificate
active
06625114
ABSTRACT:
SEQUENCE LISTING
Not applicable.
STATEMENT AS TO ANY INVENTION RIGHTS UNDER FEDERALLY SPONSORED RESEARCH
Not applicable.
BACKGROUND OF THE INVENTION
The present invention generally relates to telecommunication networks, and more particularly to a system and method for providing carriers the ability to offer switched virtual circuit services to customers for frame relay communications.
Frame relay is a high performance, cost-effective means of connecting an organization's multiple LANs and systems network architecture (SNA) services through the use of various techniques. Like the old X.25 packet-switching services, frame relay uses the transmission links only when they are needed. Frame relay was created using the benefits of the switched network and the packet arrangements of previous networks.
Asynchronous Transfer Mode (ATM) is similar in concept to frame relay. Both take advantage of the reliability and fidelity of modem digital facilities to provide faster packet switching than X.25. ATM, at its higher data rate, is even more streamlined in its functionality than frame relay. ATM is a network technology capable of transmitting data, voice, video, and frame relay traffic in real time. Data, including frame relay data is broker into packets containing 53 bytes each, which are switched between two nodes in the system at rates ranging from 1.5 Mbps to 622 Mbps. ATM is defined in the broadband ISDN protocol at the levels corresponding to levels
1
and
2
of the ISO/OSI model, which are the physical layer and data-link layer. In computer networks, the physical layer is responsible for handling both the mechanical and electrical details of the physical transmission of a bit stream. At the physical layer, the communicating systems must agree on the electrical representation of a binary 0 and 1, so that when data are sent as a stream of electrical signals, the receiver is able to interpret the data properly as binary data. This layer is implemented in the hardware of the networking device. The data-link layer is responsible for handling the frames, or fixed-length parts of packets, including any error detection and recovery that occurs in the physical layer. Although this technology has traditionally been used in local area networks involving workstations and personal computers, it has now been adopted by telephone companies.
As is known, time-division multiplexed (TDM) circuit switching creates a full-time connection or a dedicated circuit for the duration of the connection, between any two attached devices. TDM divides the bandwidth into fixed time slots, that allow multi-channel communication. Specifically, multiple devices may communicate across a single physical line, by being assigned one of the TDM time slots. Unfortunately, when an attached device is not sending data the time slots remain empty, thereby wasting the use of the bandwidth. Hence, a higher speed device on the network can be slowed down or bottled up waiting to transmit data, but the capacity that sits idle cannot be allocated to this higher device for the duration of the transmission. Thus TDM is not well suited for burst data transmissions which are common.
As is further known, X.25 packet-switching was created to solve the limitations of the fixed bandwidth allocation of TDM circuit switching. X.25 packet switching allowed the bandwidth to be allocated on the fly. Instead of putting the data into a fixed time slot, the user data is broken down into smaller pieces called packets, each containing both the source and the destination addressing information, as well as other control functional information. When a-user sends data in a burst, multiple packets will be generated and routed across the network based on the address information contained in the packets. The network creates a virtual circuit between each source and destination to keep track of the packets on each connection. Multiple virtual circuits can be active on the same line. This form of multiplexing is called statistical time-division multiplexing (STDM). STDM uses the analyses of the past users to allocate more interleaved packet slots to the heavier users and less interleaved packet slots to the lighter users. Although guaranteed delivery and integrity was a prerequisite for the development of the X.25 networks, the major drawback to this scheme is the penalty paid in speed of delivery. Taking the features of the switched network and the packet arrangements, the network arrived at a frame relay service.
The increased need for speed across the network platforms within the end user and the carrier networks was one reason why frame relay was developed. The need for higher speeds has been driven in part by the move away from the original textbased services to the current graphics-oriented services and the bursty time-sensitive data needs of the user through new applications. The proliferation of LANs and client/server architectures that are being deployed have shifted the paradigm of computing platforms. To accommodate this new paradigm of availability, speed and reliability of communications between systems and services, reduced overhead associated with the network by eliminating some of the processing, mainly in the error detection and correction schemes were introduced. Frame relay was designed to take advantage of the network's ability to transport data on a low-error, high-performance digital network, and serve the needs of the intelligent synchronous applications of the newer and more sophisticated user applications. Analog transmission systems were extremely noisy and produced a significant amount of network errors and data corruption. Digital networks are much more dependable with respect to integrity of data transmissions.
Frame relay makes the design of the network much simpler than using a mesh of private leased lines. In frame relay, instead of having a costly private leased line between each site requiring communications requiring a large number of leased lines, frame relay access from each site is provided into a network cloud, requiring only a single connection point. Data transported across the network is interleaved on a frame-by-frame basis. Multiple sessions can be running on the same link concurrently. Communications from a single site to any of the other sites can be easily accommodated using the pre-defined network connections of virtual circuits. In frame relay, these connections use permanent logical links (PLL), more commonly referred to as permanent virtual circuits (PVC). In contrast, switched virtual circuits (SVC) are logical connections which are not permanent, but only established when data is to be transmitted. Each of the PVCs and SVCs connects two sites just as a private line would, but in this case the bandwidth is shared among multiple users, rather than being dedicated to one site for access to a single site. Using this multiple-site connectivity on a single link reduces the costs associated with customer premises equipment, such as CPU ports, router ports, or other connectivity arrangements.
When designing a frame relay service, the speed of access is important to manage, both prior to and after installation. First, customers ask a service provider to provision a PVC, if they plan to communicate through frame relay often. The PVC is used to communicate between two sites exclusively. The customer must select and be aware of the need for a specified delivery rate. There are various ways of assigning the speed, from both an access and from a pricing perspective. The flat rate service offers the speed of service at a fixed rate of speed. The pay-as-you-go service is usage-based and might include no flat rate service. The combined service is a mix of both offerings. The customer selects a committed information rate (CIR) at a certain speed. The committed information rate is a guaranteed rate of throughput when using frame relay. The CIR is assigned to each of the PVCs selected by the user. Each PVC should be assigned a CIR that is consistent with the average expected volume of traffic to the destination p
Mehra Inder Pal
Paradyne Corporation
Thomas Kayden Horstemeyer & Risley
Ton Dang
LandOfFree
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