Multiplex communications – Pathfinding or routing – Combined circuit switching and packet switching
Reexamination Certificate
2000-11-21
2003-10-07
Vanderpuye, Kenneth (Department: 2661)
Multiplex communications
Pathfinding or routing
Combined circuit switching and packet switching
C370S401000, C370S395100, C370S442000
Reexamination Certificate
active
06631130
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to telecommunications networks. More particularly, the invention relates to a method for switching ATM, TDM, and packet data through a single telecommunications network switch.
2. State of the Art
One of the earliest techniques for employing broadband telecommunications networks was called time division multiplexing (TDM). The basic operation of TDM is simple to understand. A high frequency signal is divided into multiple time slots within which multiple lower frequency signals can be carried from one point to another. The actual implementation of TDM is quite complex, however, requiring sophisticated framing techniques and buffers in order to accurately multiplex and demultiplex signals. The North American standard for TDM (known as T1 or DS1) utilizes twenty-four interleaved channels together having a rate of 1.544 Mbits/sec. The European standard for TDM is known as E-1 and utilizes thirty interleaved channels having a rate of 2.048 Mbits/sec. A hierarchy of multiplexing is based on multiples of the T1 or E-1 signal, one of the most common being T3 or DS3. A T3 signal has 672 channels, the equivalent of twenty-eight T1 signals. TDM was originally designed for voice channels. Today, however, it is used for both voice and data.
An early approach to broadband data communication was called packet switching. One of the differences between packet switching and TDM is that packet switching includes methods for error correction and retransmission of packets which become lost or damaged in transit. Another difference is that, unlike the channels in TDM, packets are not necessarily fixed in length. Further, packets are directed to their destination based on addressing information contained within the packet. In contrast, TDM channels are directed to their destination based on their location in the fixed frame. Today, a widely used packet switching protocol is known as IP (Internet Protocol).
More recently, broadband technologies known as ATM and SONET have been developed. The ATM network is based on fixed length packets (cells) of 53-bytes each (48-bytes payload with 5-bytes overhead). One of the characteristics of the ATM network is that users contract for a quality of service (QOS) level. Thus, ATM cells are assigned different priorities based on QOS. For example, constant bit rate (CBR) service is the highest priority service and is substantially equivalent to a provisioned TDM connection. Variable bit rate (VBR) service is an intermediate priority service which permits the loss of cells during periods of congestion. Unspecified bit rate (UBR) service is the lowest priority and is used for data transmission which can tolerate high latency such as e-mail transmissions.
The SONET network is based on a frame of 810-bytes within which a 783-byte synchronous payload envelope (SPE) floats. The payload envelope floats because of timing differences throughout the network. The exact location of the payload is determined through a relatively complex system of stuffs/destuffs and pointers. In North America, the basic SONET signal is referred to as STS-1 (or OC-1). The SONET network includes a hierarchy of SONET signals wherein up to 768 STS-1 signals are multiplexed together providing the capacity of 21,504 T1 signals (768 T3 signals). STS-1 signals have a frame rate of 51.84 Mbit/sec, with 8,000 frames per second, and 125 microseconds per frame. In Europe, the base (STM-1) rate is 155.520 Mbit/sec, equivalent to the North American STS-3 rate (3*51.84=155.520), and the payload portion is referred to as the virtual container (VC). To facilitate the transport of lower-rate digital signals, the SONET standard uses sub-STS payload mappings, referred to as Virtual Tributary (VT) structures. (The ITU calls these Tributary Units or TUs.) Four virtual tributary sizes are defined: VT-1.5, VT-2, VT-3 and VT-6. VT-1.5 has a data transmission rate of 1.728 Mbit/s and accommodates a T1 signal with overhead. VT-2 has a data transmission rate of 2.304 Mbit/s and accommodates an E1 signal with overhead. VT-3 has a data transmission rate of 3.456 Mbit/s and accommodates a T2 signal with overhead. VT-6 has a data transmission rate of 6.912 Mbit/s and accommodates a DS2 signal with overhead.
Each of the above described broadband technologies can be categorized as TDM, ATM, or Packet technologies, with SONET being a complex form of TDM. From the foregoing, it will be appreciated that TDM, ATM and Packet each have their own unique transmission requirements. Consequently, different kinds of switches are used to route these different kinds of signals. In particular, TDM requires careful time synchronization; ATM requires careful attention to the priority of cells and QOS; and packet (e.g. IP) requires the ability to deal with variable length packets. For these reasons, switching technologies for TDM, ATM, and variable length packet switching have evolved in different ways. Service providers and network designers have thus been forced to deal with these technologies separately, often providing overlapping networks with different sets of equipment which can only be used within a single network.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide methods and apparatus whereby different kinds of broadband signals can be switched through a single switching fabric.
It is also an object of the invention to provide a network element which can switch TDM, ATM, and variable length packet traffic all through the same switch fabric.
It is another object of the invention to provide a network switch chipset which can be combined with identical chip sets to provide a scalable network switch fabric.
It is a further object of the invention to provide a network switch which allows flexible partitioning among.TDM, ATM, and variable length packet traffic.
Another object of the invention is to provide a network switch with redundant switch planes so that the failure of switch elements or links does not immediately cause a connection failure.
A further object of the invention is to provide a network switch which handles multicast as well as unicast voice and data transmission.
An additional object of the invention to provide a network switch which supports Clos architectures as well as folded Clos architectures.
In accord with these objects which will be discussed in detail below, the network switch of the present invention includes at least one port processor (also referred to in the appendices as a “service processor”) and at least one switch element. The port processor has a SONET OC-x (SONET/SDH STS-x/STM-y) interface (for TDM traffic), a UTOPIA and UTOPIA-frame based interface (for ATM and packet traffic), and an interface to the switch element. An exemplary port processor has a total I/O bandwidth equivalent to a SONET OC-48 signal. An exemplary switch element has 12×12 ports and supports a total bandwidth of 30 Gbps.
A typical switch according to the invention includes multiple port processors and multiple switch elements. For a 48×48 “folded” switch, 48 port processors are coupled (four each) to 12 (first and third stage) switch elements and each of these twelve switch elements is coupled to 8 (second stage) switch elements. A three stage non-blocking switch according to the invention provides a total bandwidth of 240 Gbps and a five stage non-blocking switch provides a total bandwidth of 1 Tbps. An exemplary three stage folded Clos architecture switch includes forty-eight port processors and twenty switch-elements. Four port processors are coupled to each of twelve (first and third stage) switch elements. Each of the twelve (first and third stage) switch elements are coupled to eight (second stage) switch elements. According to the presently preferred embodiment, each port processor is provided with means for coupling to two ports of a switch element or one port of two switch elements thereby providing redundancy in the event of a link failure.
According to the invention, a data frame of 9 rows by 1700 slo
Benoit Steven E.
Lipp William B.
Renault Michael M.
Roy Subhash C.
Upp Daniel C.
Gordon & Jacobson P.C.
Nguyen Brian
Transwitch Corporation
Vanderpuye Kenneth
LandOfFree
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