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Chapter 2

MVIP Switching

2.1 Introduction
2.2 MVIP Standards: MVIP-90, H-MVIP, MVIP-95, H.100
2.3 MVIP Components
2.3.1 Network Interfaces
2.3.2 Processing Resources
2.3.3 MVIP Switch
2.4 Single-Board Switching
2.5 Telephony Bus Switching
2.5.1 Telephony Bus Components
2.5.2 Telephony Boards on the Bus
2.5.3 Telephony Bus Switch Connections
2.6 Multi-Chassis Switching
2.7 Switching Hierarchy

2.1 Introduction

Multi-Vendor Integration Protocol (MVIP) is a set of computer telephony hardware and software standards for integrating diverse technologies, telephone network interfaces, and applications from one or more vendors in a single PC. The MVIP standard defines:

· A digital telephony bus

The MVIP bus carries the data between PC boards via a cable, allowing PC cards to exchange information directly.

· Distributed circuit switching capability

MVIP switching supports telephone circuit switching under direct computer control, using digital switch elements distributed among MVIP boards.

· Digital clock architecture

A clock architecture maintains system stability and operation of MVIP functions even during failure of external timing sources.

· Software conventions to build systems

The device driver specification allows systems integrators to combine MVIP-compatible products from different vendors to provide totally integrated solutions.

Figure 16. The MVIP Standard





2.2	 MVIP Standards: MVIP-90, H-MVIP, MVIP-95, H.100





The original MVIP standard, called MVIP-90, was developed in 1989-90.
MVIP-90 supports up to 512 timeslots within a single computer chassis. The MVIP-90 standard includes the hardware and software definition of the bus.



After MVIP-90, the hardware and software standards were separated. Two hardware standards emerged: H-MVIP and H.100. The H-MVIP standard specifies the same physical bus cable as MVIP-90, using 8 previously-reserved wires. The H-MVIP bus is a superset of the MVIP-90 bus, supporting up to 3072 timeslots. 



The H.100 bus is a superset of all telephony bus standards. The H.100 bus supports up to 4096 timeslots and interoperates with the H-MVIP bus and the MVIP-90 bus.



The MVIP-95 device driver standard defines the software interface for the 
H-MVIP bus and the H.100 telephony bus.



Figure 17 details the MVIP telephony bus evolution.






Figure 17.	 MVIP Evolution






2.3	 MVIP Components





An MVIP system has three elements:







2.3.1	 Network Interfaces





Network interfaces provide the physical connection to the telephone network. Network interfaces transfer the voice and signaling information from the network onto data streams which are connected to the switch block.



Network interfaces exist for both analog and digital line interfaces. Analog network interfaces convert the incoming analog voice into a digital stream using time division multiplexing. The line conditions are converted into signaling data and put in the input signaling stream. When sending output to the telephone network, the network interface converts the digital data back to an analog signal.



Digital network interfaces receive digital information from various digital transmission lines such as T1 trunks or E1 trunks. The data on the digital line is already located in timeslots on data streams. The network interface re-organizes the data into voice data streams and signaling data streams.



The voice and signaling data for the network interface is available on internal data streams. There are four data streams associated with each voice and signaling path: network voice output, network voice input, network signaling output, and network signaling input.






Figure 18.	 Network Interface Input and Output Streams




The telephone channels on a network interface are available in consecutive timelsots in the network streams. For example, on an AG-T1 board, the 24 channels are located on the corresponding stream in timeslots 0..23.






2.3.2	 Processing Resources





Processing resources such as digital signal processors (DSP) perform functions such as monitoring the progress of a telephone call, digitally recording and playing back speech, or transmitting and receiving fax messages. DSP resources provide the core functionality in a system by processing input received from the telephone network and by providing output to be sent to the telephone network. 



The voice and signaling information for the DSP resource is available on internal data streams. There are four data streams associated with each voice and signaling path: DSP voice output, DSP voice input, DSP signaling output, and DSP signaling input.






2.3.3	 MVIP Switch





To develop a telephony system, the network interfaces and the DSP resources must connect. A network interface is like a simple telephone; it can't do anything by itself. The DSP resources need the input and output provided by the network interface.



The network interfaces and DSP resources connect only to a bus. They do not connect directly to each other.



The network interfaces and DSP resources connect over the bus through an MVIP switch.






Figure 19.	 Connecting DSP Resources to Network Interfaces






2.4	 Single-Board Switching





Telephony boards that contain DSP resources and network interfaces have a switch. The DSP resources and network interfaces are available on data streams on an internal or local bus. The local bus connects to the switch block.



Switch connections are made between timeslots on the local bus to connect the network interfaces and DSP resources. 






Figure 20.	 Single Board Switching




A typical configuration with single-board switching consists of the following connections:




These switch connections connect the DSP resources to the network interfaces. Each call would have associated DSP resources to perform voice and call processing.






2.5	 Telephony Bus Switching





Before the telephony bus was developed, telephony boards contained both network interfaces and DSP resources. Applications could perform voice and call processing only on the lines connected to the board. If more DSP resources were needed in a system, a complete board had to be added, even if sufficient telephone channels were available.



Telephony is a real-time environment where data must be processed with a guaranteed maximum response time. Since a standard PC bus cannot guarantee a maximum response time, a dedicated telephony bus was created.



The telephony bus allows boards to exchange information with minimal impact on the host computer. With the development of the telephony bus, it is possible for some boards to contain only network interfaces and other boards to contain only DSP resources. When the application makes switch connections across the telephony bus, line interfaces on one board use the DSP resources on another board. The telephony bus transports data between different boards.






Figure 21.	 Telephony Bus Switching






2.5.1	 Telephony Bus Components





The telephony bus consists of serial data streams and related clock signals.






Figure 22.	 Telephony Bus




The clock signals on the bus are generated from high quality timing references within the public telephone network (typically T1 or E1 digital trunks). This provides long-term timing for a system which matches the public network.



Information is exchanged on the telephony bus using the data streams. The data streams on the bus provide information such as voice from a telephone line or signaling from a telephone line.






The number of data streams depends on the hardware implementation. The duration of each frame in the data stream must be 125 microseconds. Each frame can contain multiple timeslots. The number of timeslots increases with the speed of the bus. 





 Hardware Standard



 Bus Capacity




 MVIP-90



 16 streams, 32 timeslots (2 MHz streams)




 H-MVIP



 24 streams, up to 128 timeslots (2 MHz and 8 MHz streams)




 H.100



 32 streams, up to 128 timeslots (2 MHz, 4 MHz, and 8 MHz streams)
















Each timeslot on a data stream can represent information transmitted from a single DSP or network device.






2.5.2	 Telephony Boards on the Bus





Some boards do not have a switch block. (These boards are referred to as resource boards in the MVIP-90 standard.) The DSP resources on boards without switches are configured to a particular stream and timeslot on the telephony bus. The resources may always be assigned to specific streams or may be configurable via a configuration file or on-board jumpers. Resources appearing at fixed bus locations are referred to as nailed up.



Telephony boards typically contain multiple elements. For example, an AG-24 resource board has DSP processing power to support 24 lines. Each independent functional unit is called a port. An AG-24 board contains 24 ports of DSP resources. Applications make switch connections between timeslots on the telephony bus to connect ports to other ports.



The ports on an AG resource board occupy consecutive timeslots in a stream with parallel streams supporting full duplex connections. As shown in Figure 23, the AG-24 board has 24 ports of voice and call processing nailed up to the telephony bus. Each port of DSP resources is available on a different timeslot. When the application calls a function running on the resource board, the input is received from the input stream:timeslot and the output is sent to the corresponding output stream:timeslot.






Figure 23.	 AG-24 Board Connected to the Telephony Bus




Boards containing network interfaces have a switch block. These boards have access to voice and signaling data from the telephone network and may also contain local DSP resources. For example, an AG-T1 board connects to a T1 trunk and has 24 ports of DSP resources.



Boards which contain a switch do not have nailed up bus connections. The network interfaces and DSP resources are available on a local bus which is connected to the switch block. Network interfaces and local resources are connected to other boards in the system by making switch connections across the telephony bus.






Figure 24.	 Network Board Connected to the Telephony Bus






2.5.3	 Telephony Bus Switch Connections





The switch block determines how data is routed on the telephony bus. Data is routed on a timeslot-by-timeslot basis, as follows:




The switch block is controlled by the application. The application makes and breaks switch connections.



For example, to connect a telephone channel from an AG-T1 board to the DSP resources on an AG-24 board, a switch connection is made to connect the T1 channel on the local bus to the stream:timeslot of the DSP resources on telephony bus. This is shown in Figure 25.






Figure 25.	 A Switch Connection Across the Bus




The most common switch connection is connecting a DSP resource to a network interface. The DSP resource provides the processing resources to play a voice recording. The network port provides the input and output channel. Network port to network port connections are made to connect a call to an operator station or to connect a call to another phone line.






2.6	 Multi-Chassis Switching





Multi-chassis switching allows developers to build distributed systems for applications which no longer fit in a single PC chassis.



MC1 (MVIP Multi Chassis) technology is similar to single-chassis MVIP but operates over SCSI-3 cable of up to 15 meters. An MC1 system can contain up to 15 nodes with each node having an MC1 interface. 



There are additional multi-chassis standards (MC2, MC3, and MC4), where each standard uses a different physical medium.



Each chassis in a multi-chassis system contains telephony boards (including one MC1 board) connected to each other by a single-chassis telephony bus. Boards in a single chassis exchange information by making switch connections on this bus.



The MC1 board in each PC connects to the MC1 boards in the other PCs over the MC1 bus as shown in Figure 26. The MC1 bus has 24 data streams, each with 64 timeslots. Connections between boards in different PCs are made by making switch connections to the MC1 bus.






Figure 26.	 MC1 Bus Connection




Figure 27 shows the exchange of data between two boards located in different PC chassis. 




The AG-24 board and AG-T1 board do not know the information is exchanged over the MC1 bus.






Figure 27.	 MC1 Bus Switching






2.7	 Switching Hierarchy





Figure 28 shows the switching hierarchy. Intra-board switching involves switching DSP resources and network interfaces on a single board. Inter-board switching is switching across multiple boards in a single PC chassis. Inter-chassis switching is switching across boards in multiple PC chassis.






Figure 28.	 Switching Hierarchy Levels















 
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