Patent Publication Number: US-6212195-B1

Title: Telecommunication apparatus and method for forwarding packets using separate collision domains

Description:
FIELD OF THE INVENTION 
     The invention relates generally to an apparatus and method for integrating voice and data on a single telecommunication network. More specifically, the invention relates to a telecommunication apparatus and method for forwarding voice and data packets to the network on communication paths having separate collision domains. 
     BACKGROUND OF THE INVENTION 
     Many modem businesses use two separate telecommunication networks for voice and for data. The costs associated with installing and maintaining two networks have induced some businesses to seek ways to integrate voice and data on a single telecommunication network infrastructure. As a result, the telecommunications industry has produced systems that integrate telephones and computers onto the same network. In such systems, telephones and computers share the same cabling infrastructure for transmitting voice data and computer data. 
     Advances in technology, though, continually increase the data rate capability of networks. The Ethernet network, which is a prevalent type of local area network (LAN), is an example. Devices (or nodes) connected to an Ethernet network communicate with each other using packets having a structured format. The packets include a destination address, a source address, and the data. Initially, the 10 Mbps Ethernet network was the basis for the IEEE 802.3 standard, but Ethernet has since evolved to support network data rates of 100 and 1,000 Mbps. While current implementations of integrated telecommunication systems can adequately support network data rates of an order of 10 Mbps, such systems cannot adequately provide equivalent functionality at network speeds of 100 Mbps and beyond. This is due, in part, to the use of hubs by current implementations of integrated telecommunication systems to forward Ethernet packets on the LAN. A hub is a network device that deposits Ethernet packets received on one communication path onto another communication path. Many communication paths can meet at a hub. Because a hub does not provide separate collision domains, the devices using these communication paths compete against each other for use of the hub. A collision domain is a segment of the LAN where a collision occurs when any two devices attempt to transmit packets simultaneously on that segment. 
     When a packet collision occurs on a segment, the devices sending the packets become alerted to the collision and “back off,” that is, the sending devices wait a predetermined period of time before attempting to complete the transmission of the packets on that segment. The IEEE 802.3 standard specifies a back-off algorithm that each sending device must perform to be compliant with the standard when involved in a packet collision. 
     A problem, however, is that at high data rates (e.g., 100 Mbps data rates and beyond), a sending device can incorrectly deem a packet transmission to have been successful although that packet later encounters a collision after propagating through the network. Normally, at lower data rates (e.g., 10 Mbps), this collision causes the sending device to back-off on future attempts to transmit the packet. However, the high data rates enable the sending device to complete the packet transmission before the collision occurs or is detected. Further, the sending device may even have continued to transmit other packets on that network segment. At high data rates, the propagation delay incurred in the network can prevent the timely detection of collisions and render the operation of the integrated telecommunication system impracticable. 
     SUMMARY 
     In one aspect, the invention features a telecommunication apparatus for providing packets to at least one of a first network and a second network. The apparatus includes a first I/O device in electrical communication with the first network via a first communication path. A second I/O device is in electrical communication with the second network via a second communication path. An input port receives signals (e.g., audio signals) from an input device. A packet controller in communication with the first and second I/O devices and the input port: (a) forwards packets received by the first I/O device to the second I/O device for transmission to the second network; and (b) generates packets from the signals received by the input port for transmission to at least one of the first and second networks. 
     In one embodiment, the invention includes memory for storing packets, and a direct memory access (DMA) controller in electrical communication with the memory and the I/O devices. The DMA controller forwards packets from the first I/O device to the second I/O device via the memory. The invention also can include a table that stores addresses. The DMA controller compares a destination address of each received packet to the addresses stored in the table to determine whether that packet is to be used by the packet controller to perform an action as prescribed by that packet. 
     The memory can be organized into sections. Each memory section can be associated with one of the I/O devices and can include a receive region for storing packets received by the associated I/O device and a transmit region for storing packets to be forwarded to the associated I/O device. The receive region can include a specific block for storing packets addressed to the apparatus and a general block for storing packets addressed to other devices. The transmit region can include a priority block for storing prioritized packets and a general block for storing non-prioritized packets. 
     The invention can include a first media access control (MAC) device and a second MAC device. The first MAC device includes the first I/O device and the second MAC device includes the second I/O device. The first I/O device can receive a packet that includes an address. In response to that address, the packet controller can perform an action as prescribed by that packet. The packet controller can discard the packet with or without forwarding the packet to the second I/O device. The packet controller can prioritize the packet prior to forwarding the packet to the second I/O device. The packet controller uses the priority data to determine an order in which to forward packets. 
     The first and second I/O devices, the input port, and the packet controller can be disposed on an integrated circuit device. In one embodiment, the first network can be an Ethernet network and can operate at a data rate of 10 Mbps or higher. 
     In another aspect, the invention features an telecommunication apparatus that includes an input port, a first I/O device in electrical communication with a first network via a first communication path, a second I/O device in electrical communication with a second network via a second communication path, and a packet controller in electrical communication with the I/O devices. The packet controller forwards a first portion of the packets received by the first I/O device to the second I/O device and discards a second portion of the received packets without forwarding such packets to the second I/O device. 
     The packet controller can include an address table that stores addresses. The packet controller can discard each packet of the second portion of received packets when that packet includes a destination address that matches an address stored in the address table. The first portion of packets received by the first I/O device are non-prioritized and the packet controller can prioritize the first portion of packets prior to forwarding such packets. 
     In another aspect, the invention features a telecommunication apparatus that includes a first and a second I/O device, an input port, and a packet controller. The first I/O device is in electrical communication with the first network via a first communication path. A second I/O device is in electrical communication with the second network via a second communication path. An input port receives signals (e.g., audio signals) from an input device. A packet controller (a) forwards packets received by the first I/O device to the second I/O device for transmission to the second network; (b) generates packets from the signals received by the input port for transmission to at least one of the first and second networks; and (c) prioritizes packets prior to forwarding such packets to one of the I/O devices. 
     The second I/O device can include memory storing a packet to be forwarded to the second network. The packet controller can remove the packet from the memory and replace that packet with a packet having a higher priority. The packet controller can discard the replaced packet or restore the replaced packet to the memory after the packet having the higher priority is forwarded. 
     In another aspect, the invention features a telecommunication apparatus including a packet switching device, an input port, and a packet controller. The packet switching device communicates with the first network via a first communication path and with the second network via a second communication path, and forwards packets received from the first network to the second network. The packet controller generates packets from the signals received by the input port for transmission to at least one of the first and second networks through the packet switching device. In one embodiment, the input port is connected to a third network. 
     The packet controller can forward a first portion of the packets received from the first network to the second network and discards a second portion of the received packets without forwarding such packets to the second network. The packet controller can also prioritize packets prior to forwarding such packets to one of the networks. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is pointed out with particularity in the appended claims. The above and further advantages of the invention may be better understood by referring to the following description in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a diagram of an embodiment of two separate networks connected by a packet forwarding system in which the invention is practiced; 
     FIG. 2 is a diagram of an embodiment of the packet forwarding system of FIG. 1 coupled between a computer system and an Ethernet network; 
     FIG. 3 is a diagram of an embodiment of the packet forwarding system of FIG. 2, including a packet controller; 
     FIG. 4 is a diagram of another embodiment of the packet forwarding system of FIG. 2, including a packet switching device; 
     FIG. 5 is a diagram of an embodiment of the packet controller of FIG. 3; and 
     FIG. 6 is a flow chart representation of an embodiment of a process by which packets are generated and queued within the packet forwarding system. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows a packet forwarding system  10  of the invention connected between a first network  12  and a second network  14  by electrical communication paths  16  and  18 , respectively. Each of the networks  12 ,  14  can have any one of a variety of communication topologies, e.g., a local area network (LAN) or a wide area network (WAN). In one embodiment, the packet forwarding system  10  is the only electrical connection between the network  12  and the network  14 . 
     In FIG. 1, each electrical communication path  16 ,  18  is a network segment that is part of a distinct collision domain. More specifically, the collision domain that includes the network  12  and the communication path  16  is separate from the collision domain that includes the network  14  and the communication path  18 . According to the principles of the invention, the packet forwarding system  10  maintains the separation of the two collision domains. 
     The packet forwarding system  10  includes input/output (I/O) devices  15  for transmitting signals to and receiving signals from a local device  17 . In one embodiment, the I/O devices  15  include a microphone, a keypad, and a telephone handset. Other I/O devices are possible, (e.g., a headset). The I/O devices  15  also include a liquid crystal display (LCD), light-emitting diodes (LEDs), speakers, and the telephone handset. Other types of I/O devices can be used to practice the invention. The local device  17  can be any device capable of using the I/O devices  15  to receive signals from or transmit signals to the packet forwarding system  10  (e.g., a computer or a human operator). The packet forwarding system  10  can also include a first codec (not shown) coupled to the microphone and the speakers and a second codec (not shown) coupled to the telephone handset for performing analog-to-digital and digital-to-analog conversions of audio signals. 
     According to the principles of the invention, the packet forwarding system  10  uses and/or forwards packets received from one of the networks to the other of the networks. More specifically, the packet forwarding system  10  uses and/or forwards packets received from the network  12  to the network  14  and uses and/or forwards packets received from the network  14  to the network  12 . For example, some received packets may specifically target the packet forwarding system  10  (e.g., the destination address in such packets is the address for the system  10 ). In this event, the packet forwarding system  10  uses but does not forward these packets to one of the networks  12 ,  14 . In another embodiment, the packet forwarding system  10  uses and forwards the packets. Other types of received packets, (e.g., broadcast packets), can be of interest to and used by the packet forwarding system  10 . 
     Packets can also originate at the packet forwarding system  10 , such as when a user places a telephone call. To place the telephone call, the user presses several keys on the keypad and speaks into the handset. The packet forwarding system  10  generates packets from the signals produced by the keypad and the handset and forwards the generated packets to either or both of the networks  12 ,  14 . The contents of such packets depend upon the source of the signals. For the audio (i.e., voice) signals, the generated packets include voice data. For the digital signals produced by the keypad, the generated packets include control data. The packet forwarding system  10  can also initiate the generation of packets (e.g., to issue an alarm or other types of status packets). 
     As described further below, the packet forwarding system  10  may add a priority level to the packets, with the level of priority depending upon the type of data included in such packets. In general, there are at least two levels of priority. In one detailed embodiment, a packet has one of three levels of priority: high, medium, and nonprioritized (i.e., no priority given to the packet). In one embodiment, the level of priority effects the order in which the packet forwarding system  10  queues in memory the associated packets for transmission to one of the networks  12 ,  14 . In another embodiment, the priority determines the order in which the packets are removed from memory when forwarding to one of the networks  12 ,  14 . 
     The packet forwarding system  10  can detect when the networks  12 ,  14  are inadvertently connected to each other by a path other than through the packet forwarding system  10 . In one embodiment, the packet forwarding system  10  periodically transmits a packet via one of the communication paths  16 ,  18  and determines whether that packet returns to the packet forwarding system  10  via the other communication path. In another embodiment, the packet forwarding system can determine that identical packets have arrived from both communication paths  16 ,  18  at almost the same time. The packet forwarding system  10  can display a warning on the LCD and disable communication via one of the two communication paths  16 ,  18  until the inadvertent connection is disconnected. Notwithstanding, it is to be understood that the principles of the invention can be practiced even though the networks  12 ,  14  are inadvertently connected. 
     FIG. 2 depicts an exemplary embodiment of the packet forwarding system  10  as a telecommunication device  10  bridging two Ethernet networks  12  and  14 . Examples of telecommunication devices include a telephone set and a telephone line interface module (TLIM) device. For exemplary purposes, the telecommunication device throughout the following description is a telephone set (hereafter, telephone set  10 ). The first network  12  is an Ethernet network including a file server  20 , and the second network  14  is a computer system  14 . The computer system  14  plugs into a receptacle of the telephone set  10 . Thus, a single network infrastructure supports both computers and telephones. Although only one telephone set is shown, it should be understood that multiple telephone sets, each of which can be coupled to computer systems, can be similarly connected to the Ethernet network  12 . 
     The computer system  14  can access the file server  20  through the packet forwarding operation provided by the telephone set  10 . To request access to the server  20 , the computer system  14  transmits Ethernet packets including the destination address of the server  20  to the telephone set  10  via the communication path  18 . Upon receiving the packets, the telephone set  10  determines that the packets are not directed to the telephone set  10 , and queues the packets for transmission to the network  12  via communication path  16 . 
     Concurrent with this request by the computer system  14 , a user of the telephone set  10  may be holding a telephone conversation with the user of another telephone set (not shown) connected to the network  12 . The audio signals enter the telephone set  10  through one of the I/O devices  15 , (e.g., the handset). From these audio signals, the telephone set  10  produces packets including voice data. Because voice data are time-sensitive, (i.e., as time elapses the usefulness of the voice data decreases significantly), the telephone set  10  can give higher priority to packets including voice data than packets including control data, such as the server request made by the computer system  14 . Consequently, the telephone set  10  may preempt the transmission of the packets representing the server request and first queue the voice data packets for transmission. 
     While the telephone set  10  prepares to transmit the voice data packets to the network  12 , voice data packets generated by the other telephone set engaged in the conversation may be received by the telephone set  10  via the communication path  16 . The destination addresses in these voice data packets can indicate that the telephone set  10  is the targeted recipient. In this event, the telephone set  10  produces audio signals from the voice data in the packets and outputs the audio signals to one of the I/O devices  15 , (e.g., the handset). As a result, the user of the telephone set  10  hears the audio signals generated by the other user. The telephone set  10  can then discard the received voice data packets or forward the packets to the computer system  14 . 
     The user of the telephone set  10  can engage in a “conference call” (i.e., a conversation with users of two or more other telephone sets connected to the network  12 ). From audio signals produced by the user, the telephone set  10  generates packets including voice data. The telephone set  10  then transmits the generated packets to the network  12 . 
     In one embodiment, each telephone set involved in the conference call receives a list of all participants at the start of the conference call. This list of participants can be generated prior to the start of the conference call and can change as participants are added or dropped. The telephone set  10  generates a unicast packet for each other telephone set on the list of participants. For example, when the telephone set  10  is engaged in a conference call with two other participants, the telephone set  10  generates two unicast packets having the same voice data and the telephone set  10  as the source address. The destination address in one of the two unicast packets is the address of one of the two other telephone sets, and the destination address in the second unicast packet is the other of the two other telephone sets. 
     In another embodiment, at the start of the conference call, each telephone set receives an identifier associated with the conference call. This identifier can be generated prior to the start of the conference call and can change during the conference call. The telephone set  10  generates multi-cast packets that include the identifier associated with the conference call. In each multi-cast packet, the telephone set  10  is the source address and the identifier can be the destination address. 
     The telephone set  10  uses only those packets from telephone sets known to be engaged in the conference call. For unicast packets, the source address of the received packets can be compared against the list of participants. For multi-cast packets, the identifier can indicate whether the packet came from a participant of the conference call. 
     When the telephone set  10  receives a packet, the telephone set  10  determines that the packet came from a participant in the conference call, produces audio signals corresponding to the voice data in the packet, and outputs the audio signals to the handset (or speaker). When multiple packets arrive at a telephone set from different sources, that telephone set combines the received packets and outputs audio signals corresponding to the voice data of the combination. The telephone set  10  can combine packets received from other telephone sets with packets generated by the telephone set  10  from locally received audio signals. 
     To produce the combination, the telephone set  10  can combine the voice data of the received packets or select for processing (i.e., producing audio signals from the voice data packets) one or more of the packets according to a predetermined criteria. One criteria can be to process the packet with the voice data having the highest volume (i.e., loudest). The telephone set  10  can discard or forward unused voice data packets. 
     FIG. 3 shows, in more detail, an exemplary embodiment of the telephone set  10 . The telephone set  10  includes a packet controller  24  coupled to an input/output (I/O) port  26 , two media access control (MAC) devices  28  and  32 , memory  36 , and I/O control circuitry  50 . An outline  62  encloses those components  24 ,  26 ,  28 ,  32 , and  50  that, in one embodiment of the invention, are disposed on an integrated circuit device (ASIC). It will be appreciated that other ASIC designs are possible, such as, for example, one in which the memory  36  is included on the ASIC. 
     The I/O port  26  is in electrical communication with the I/O devices  15 , (i.e., the microphone, headset, or the handset), to receive audio signals from a user of the telephone set  10  and to transmit audio signals to the I/O devices  15 , (e.g., the speaker or the handset), so that such signals are audible to the user. The I/O control circuitry  50  is coupled to I/O devices  15 , (e.g., the keypad, the LCD, and the LED), to receive input signals from the keypad and to transmit control signals to the LCD and the LED. 
     The packet controller  24  is in electrical communication with the I/O port  26  by signal line  52  and with the I/O control circuitry  50  by signal line  53 . The packet controller  24  is in electrical communication with the memory  36  via signal lines  35 , with the MAC device  28  via signal lines  54 , and with the MAC device  32  via signal line  56  to control the transfer of packets between the memory  36  and the MAC devices  28  and  32 . The packet controller  24  includes a timer  63 . 
     In the embodiment, the MAC devices  28 ,  32  are 10/100 Ethernet ports capable of operating at a 100 Mbps network data rate. The MAC devices  28 ,  32  are the physical interfaces for receiving and transmitting packets to the Ethernet networks  12 ,  14 . Each MAC device  28 ,  32  provides a separate collision domain for packets being transmitted on the respective communication paths  16 ,  18 . The first collision domain is the network segment that includes the MAC device  28  in electrical communication with the network  12  via communication path  16 . The second collision domain includes the MAC device  32  in electrical communication with the computer system  14  via communication path  18 . 
     As a result of the separate collision domains, the MAC devices  28 ,  32  operate such that both can concurrently transmit packets and/or concurrently receive packets, or one of the MAC devices can receive packets while the other transmits packets, without collisions occurring between networks. 
     Each MAC device  28 ,  32  includes buffer memory  30 ,  34  for storing packets prepared for transmission to the network  12  or packets received from network  12  via the communication paths  16 ,  18 . The buffer memory  30 ,  34  includes a receive buffer  29 ,  34  and a transmit buffer  31 ,  35 . In one embodiment, the buffer memory  30 ,  34  is sized to store 8 or 16 bytes of data. The buffer memory  30 ,  34  can be internal or external to the MAC devices  28 ,  32 . In one embodiment, each MAC device  28 ,  32  includes a buffer controller for handling packet transfers to and from the buffer memory. Other embodiments combine the controllers in a single component or incorporate the buffer controller within the packet controller  24 . 
     The memory  36  can be implemented using synchronous dynamic random access memory (SDRAM). Other types of memory devices can be used (e.g., SRAM). The organization of the memory  36  provides separate, dedicated memory sections  38 ,  44  for each of the MAC devices  28 ,  30 . The separate sections  38 ,  44  operate to maintain the separate collision domains provided by the MAC devices  28 ,  30 . Memory section  38  supports the MAC device  28  via signal lines  58  and the memory section  44  supports the MAC device  32  via signal lines  60 . 
     The memory sections  38 ,  44  are each partitioned into a receive region  40 ,  46  and a transmit region  42 ,  48 . Each receive region  40 ,  46  is partitioned into a specific block  41 ,  49  for storing packets addressed to the telephone set  10  and a general block  43 ,  51  for storing packets addressed to a device other than the telephone set  10 . Each transmit region  42 ,  48  is partitioned into a priority block  45 ,  55  for packets having priority and a general block  47 ,  57  for non-prioritized packets. 
     Other ways of using the memory  36  to implement priority are contemplated. For example, the memory  36  can be organized as a buffer to store packets as the packets arrive at the telephone set. Rather than evaluate each packet as that packet arrives to determine the block of memory in which to store that packet, each packet can be directly stored in the memory  36  upon arrival and subsequently examined for prioritizing when selecting a packet to forward to one of the I/O devices. 
     Each packet received by a MAC device from the network  12  includes the necessary information for determining the location in memory  36  to store the packet. Categories of packets include “telephone-specific,” “telephone-general,” or “general other.” The telephone set  10  uses (i.e., performs an action as prescribed by the information in the packet) telephone-specific and telephone-general packets. Examples of actions include converting packets with voice data into audio signals and outputting the audio signals to a local I/O device  17 , displaying a message on the LCD, resetting error flags, setting the current time on a internal clock of the telephone set  10 , and other housekeeping functions. 
     The telephone set  10  forwards telephone-general packets, but not telephone-specific packets, to the computer system  14 . An example of telephone-general packets are those packets produced during a conference call. Both categories of packets, telephone-specific and telephone-general, are stored within the specific block  41 ,  49  of the receive region  40 ,  46 . Packets that are general-other are stored in the general block  43 ,  51  and subsequently forwarded to the computer system  14 . The telephone set  10  does not use such packets. 
     FIG. 4 shows another embodiment  10 ′ of the telephone set  10  in FIG.  3 . The telephone set  10 ′ includes a packet controller  24 ′ coupled to an input/output (I/O) port  26 ′, a MAC interface  23 , memory  36 ′, and I/O control circuitry  50 ′. The MAC interface  23  is in electrical communication with a packet switching device  21  for forwarding packets between the network  12  and the computer system  14 . In another embodiment, the MAC interface  23  can be removed to allow direct connection from the packet controller  24 ′ to the switching device  21 . The above descriptions for the packet controller  24 , I/O port  26 , memory  36 , I/O control circuitry  50  in FIG. 3 are the same as the corresponding components in FIG.  4 . The MAC interface  23  provides an interface that controls the communication between the network  12  and the computer system  14  with the telephone set  10 ′. 
     The switching device  21  provides a function accomplished by the two MAC devices  28 ,  32  of FIG. 3, which is to maintain separate collision domains for the network  12  and the computer system  14 . The switching device  21  can be implemented using an NP313, a 3-port Fast Ethernet Integrated Circuit developed by NeoParadigm Labs, Inc. (NPL). The manner in which the switching device  21  can handle packets includes the following: the switching device  21  can forward a packet from the network  12  to the computer  14  (or in the opposite direction), the switching device  21  can ignore a packet received from either the network  12  or the computer  14 ; and the switching device  21  can use a packet to perform an action as prescribed by that packet, without forwarding the packet to either the network  12  or the computer  14 . 
     A current impediment to the use of the switching device  21  is the costs associated with the hardware and software needed to implement the operation of the device  21  according to IEEE standards. This impediment can be eliminated over time if the costs of the switching device  21  decrease. 
     FIG. 5 shows an exemplary embodiment of the packet controller  24 . The packet controller  24  includes a timer  63 , a digital signal processor (DSP)  64 , a processor  66  (e.g., an ARM processor), a direct memory access (DMA) controller  68 , control circuitry  70 , an address table  72 , and a memory controller  74  coupled to each other by a signal bus  76 . Although shown separately, the timer  63  and the table  72  can be included within one of the other functional components  66 ,  68 ,  70 , and  74 . 
     The DSP  64  is in electrical communication with the I/O port  26  by signal lines  52 . The memory controller  74  is in electrical communication with the memory  36  by signal lines  78 . The DMA controller  68  is in electrical communication with the MAC devices  28 ,  32  by signal lines  54 ,  56 . In one embodiment, the memory controller  74  can be included in the DMA controller  68 . Either the processor  66  or the DMA controller  68  can control the transfer of memory between the MAC devices  28 ,  32  and the memory  36 . 
     The address table  72  stores addresses that are of importance to the telephone set  10 . Examples of such addresses include the address of the telephone set  10 , the identifier for a conference call, and a general broadcast address. 
     The DMA controller  68  accesses the table  72  whenever the telephone set  10  receives a packet to determine whether the telephone set  10  uses the packet as described above. When the packet has a destination address matching one of the addresses stored in the table  72 , the telephone set  10  performs an action as prescribed by the packet. The telephone set  10  may or may not subsequently forward the packet to the network  12  or the computer system  14 , as explained above. 
     In one embodiment, the table  72  also functions to filter out packets from subsequent forwarding by including addresses of the computer system  14 . In this embodiment, the DMA controller  68  uses the addresses stored in the table  72  to discard, rather than forward, packets that are neither addressed to the telephone set  10  nor the computer system  14 . 
     Destination addresses can be added to or removed from the table  72 . For example, when a conference call starts, the processor  66  (or the DMA controller  68 ) stores the conference call identifier in the table  72  and removes the identifier when the conference call ends. Implementation of this table  72  can be in hardware or software, but the lookup of addresses in the table  72  occurs faster when implemented in hardware in the described embodiment. 
     Packet Forwarding Operation 
     The following description describes the packet forwarding process along a path from the network  12  and the MAC device  28  to the MAC device  32  and the computer system  14 . However, it is to be understood that the process functions similarly in the reverse direction. When the MAC device  28  receives a packet, the MAC device  28  stores that packet in the receive buffer  29 . The DMA controller  68  moves the received packet from the receive buffer  29  to the receive region  40  of the memory  36  and compares the destination address of the packet against the addresses stored in the address table  72 . If the addresses match, then the telephone set  10  uses the packet, as explained previously. 
     When there is no address match or when the packet is a telephone-general packet, then the packet moves from the receive region  40  to the transmit region  42  for subsequent forwarding to the computer system  14 . The processor  66  evaluates the packet to determine in which block,  45  or  47 , of the transmit region  42  to place the packet. If the packet has priority, then the processor  66  places the packet in the priority block  45 . If the packet has no priority status, then the processor  66  places the packet in the general block  47  or gives the packet a priority status and then places the packet in the priority block  45 . 
     From the transmit region  40 , the DMA controller  68  moves the packet to the transmit buffer  35  of the MAC device  32 , which shifts the packet onto the communication path  18  to the computer system  14 . When processing a series of packets, the DMA controller  68  continually supplies the memory  36  with packets and keeps the transmit buffer  35  of the MAC device  32  full. 
     Packet Generating Operation 
     FIG. 6 provides a flow chart describing a process by which the packet controller  24  constructs voice data packets from audio signals received by the I/O port  26 . The generated packets can be unicast or multi-cast packets for use in an end-to-end telephonic communication or in a conference call. In step  78 , the DSP  64  digitizes consecutive samples of audio signals and concatenates the digitized signals into a data structure including voice data corresponding to the audio signals. When the data structure includes voice data generated from audio signal samples that span a predetermined duration, (e.g., 24 ms), the DSP  64  signals the processor  66  (Step  80 ). The processor  66  builds a frame around the data structure and produces, in one embodiment, an Ethernet packet. Because of the time-sensitive nature of voice data, the processor  66  may add data to the data structure that indicate that the packet has priority. In step  82 , the packet is queued in the priority block  45 ,  55 , of the transmit section  42 ,  48 . The DMA controller  68  subsequently passes the packet in the priority block  45 ,  55  to the MAC device  28 ,  32  for transmission as an Ethernet packet. 
     On-Time Delivery 
     When moving packets from the memory  36  to the MAC devices  28 ,  32 , the DMA controller  68  gives priority to packets stored in the priority block  45 ,  55 . Priority operates to increase the importance of certain packets so that such packets receive special treatment for getting onto one or both of the networks  12 ,  14 . The ability of the telephone set  10  to concurrently forward non-prioritized packets and generate prioritized packets can produce occasions where a packet of low importance is queued in a MAC device, waiting to be forwarded, when a time-sensitive voice packet is generated. For voice data to be useful, typically, such data must get to the destination within a certain time period (i.e., up to about 50 ms), whereas the critical period of time for delivery of control data is generally longer. Other types of data may not be time-sensitive. 
     Rather than wait until the queued packet leaves the transmit buffer of the MAC device, and risk reducing the usefulness of the voice data packet, the processor  66  can preempt the transmission of that packet and replace that packet with the higher priority voice data packet. The processor  66  can discard the replaced packet, or store the packet until the voice transmission finishes, at which time the transmission of the replaced packet resumes. Giving high priority to voice data packets facilitates on-time delivery of real-time data. 
     While the invention has been shown and described with reference to specific preferred embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the following claims.