Abstract:
A digital data packet transmission process and system provides more efficient and higher quality of service in applications such as Internet telephony. In one aspect of this approach, transmission control protocol (“TCP”) is used to send data from a first user or client over standard telephone lines to a local Internet service provider (“ISP”). At the ISP, the data packets are converted from TCP to user datagram protocol (“UDP”). The UDP packets are then transmitted, typically over a higher bandwidth link to another local ISP serving the recipient. The UDP packets are translated back to TCP packets and routed to the receiver. Because many existing systems currently employ UDP packets, the present approach is largely backwards compatible should a recipient be hooked up to an ISP that does not employ a TCP/UDP converter. A bidirectional TCP/UDP converter is preferable for two way communication such as Internet telephony.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to communication protocols in digital networks. More particularly, the invention relates to methods and apparatus for protocol conversion in order to minimize latency and to improve efficiency and quality of packet transmission in applications including Internet telephony.  
         BACKGROUND OF THE INVENTION  
         [0002]    More and more information is being shared and transmitted over computer networks, and more and more two-way communication is taking place using computer networks. With the growth and ubiquity of the Internet, more and more people are becoming familiar with computer networks and desire to conduct more and more of their daily affairs using computer networks, especially the Internet. With the increasing popularity of the Internet and other networks, there is a growing demand for increased speed and quality of service. The higher the quality of a particular product or service that can be provided over the Internet, the greater will be the demand for that product or service.  
           [0003]    Smaller and more uniform computer networks can provide high-quality services without excessive difficulty, since greater control can be maintained over the network servers and clients. In such an environment, strict standards and protocols can be dictated and maintained. The Internet, on the other hand, must serve a tremendous variety of users, all over the world, and must provide means for transferring data over paths which may be extremely circuitous, with components having differing characteristics and bandwidths. One application which is stimulating considerable interest and which is growing rapidly in popularity, but which is still subject to significant obstacles, is Internet telephony or in other words, real-time voice communication over the Internet. This application has the promise of introducing the Internet into the daily lives of large numbers of people in a substantial way. The promise is of providing a low-cost substitute for a long distance telephone service with which people are familiar, and which they use frequently, but which, because of its cost, they are constrained to use much less frequently than they might otherwise choose to if the costs were significantly lowered while still providing comparable service. Internet telephony holds forth the promise of allowing people to communicate with friends and loved ones all over the world for the cost of an making an Internet connection. In the present state of the art, there remain, however, significant obstacles to high-quality Internet telephony. These obstacles arise in part because of the protocols used by the Internet for data transmission. For real time voice traffic, latency must be kept to a minimum or the delays incurred will significantly interfere with the quality of the voice conversation. For limited-bandwidth transmission channels such as modems, transmission control protocol (“TCP”), through the use of Van Jacobsen compression, can accommodate small packets without the excessive overhead caused by a large header size. Such compression algorithms do not presently exist for user datagram protocol (“UDP”).  
           [0004]    If small packets are used for UDP transmission, the available bandwidth provided by today&#39;s modems may not be enough to accommodate them, given their large overhead. However, if large UDP packets are used for telephony, voice quality is degraded because a significant latency results. Such latency may arise because a wait is necessary to allow a large UDP packet to fill with data before it is dispatched.  
           [0005]    On the other hand, if TCP is used to provide transmission all the way from the initial sender, over the Internet, and to the remote receiver, latencies may be too great for telephony because of the delays occasioned by detecting and resending lost packets. When measured against the quality of standard telephone service, an acceptable quality of Internet telephony service is not yet available. Thus, there exists a need in the art for methods and apparatus to provide Internet telephony data packet transmission which can accommodate a low-bandwidth connection between a user and a local host, but which can provide high-quality data transmission with low latency.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention provides methods and apparatus for protocol conversion between transmission control protocol (“TCP”) and user datagram protocol (“UDP”). In one aspect of the present invention, TCP is used between the user and the local host. TCP is suitable for use in a modem link between a local user and an Internet Service Provider (“ISP”), because the modem itself provides a reliable connection, detecting and resending lost data. Thus, the latencies caused by TCP&#39;s detecting and retransmitting lost packets are unlikely to occur. This provides a reliable, connection-oriented transmission which can transmit small packets within the bandwidth provided by a typical modem and consistent with local telephone connections such as those provided by twisted wire pairs and standard telephone wires connecting most people to the phone network. The latency caused by TCP&#39;s detection and resending of lost packets is tolerable, because very few packets are lost at the connection between the user and the local host.  
           [0007]    After each packet arrives at the local host, it is converted to UDP format and transmitted over the Internet. While the UDP packets have a big header and thus a high overhead with respect to the amount of data per packet, the local host is able to transmit such packets using UDP with low latency, because the bandwidth between the local host networks is great enough to tolerate the overhead caused by the large header size of the UDP packets. When the packet arrives at the destination node of the local host network, it is reconverted to TCP, and thence transmitted to the user of the destination node. This conversion allows for the transmission of low latency small packets. By tailoring the protocols used to take advantage of the characteristics of the different connections, significant improvements in efficiency and quality of service may be achieved.  
           [0008]    A more complete understanding of the present invention, as well as further features and advantages of the invention, will be apparent from the following Detailed Description and the accompanying drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is an illustration of a packet transmission network of the prior art, showing connection protocols typically employed for packet transmission between users and hosts, between hosts within a single host network, and between networks;  
         [0010]    [0010]FIG. 2 is a packet transmission network employing a protocol conversion system according to the present invention, illustrating the protocols employed between the various nodes of the network;  
         [0011]    [0011]FIG. 3 is a more detailed illustration of a protocol conversion system according to the present invention;  
         [0012]    [0012]FIG. 4 is a detailed block diagram showing the use of a protocol conversion system according to the present invention, in which an active user registry server is employed in an Internet Service Provider which connects to clients using differing connection methods and which also transmits data to and from other Internet Service Providers which do not use a protocol conversion system according to the present invention;  
         [0013]    [0013]FIG. 5 is a diagram showing in greater detail the active user registry server shown in FIG. 4; and  
         [0014]    [0014]FIG. 6 is a flowchart illustrating a protocol conversion process in accordance with the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0015]    [0015]FIG. 1 illustrates a representative link  10  of the prior art between two data packet networks  36  and  38 . First network  36  serves users 1-3 ,  14 ,  16  and  18 , respectively, and second network  38  serves users 4-6 ,  30 ,  32  and  34 . Users 1-3  communicate with a first local server in a first host node  22  using UDP. First host node  22  communicates with a first network communication node  24  using UDP. First network communication node  24  and a second network communication node  26  also communicate with one another using UDP. The second network communication node  26  communicates with a second host node  28  using UDP. Host node  28  communicates with users 4-6 ,  30 ,  32  and  34  using UDP.  
         [0016]    UDP is defined at the transport layer and provides the application layer with a fast but unreliable, connectionless delivery system. UDP data units are datagrams. A datagram is encapsulated within an IP header. The header portions of UDP packets are long. Thus, the overhead for UDP packets is inherently quite large. This problem is typically overcome by making UDP packets large. With sufficiently large UDP packets, the header represents a relatively small portion of the total packet. If used to transmit small packets, however, as would be needed for high-quality Internet telephony, the large headers used by UDP would represent a large proportion of the packet size. For a typical modem connection operating at 28.8 kB, the use of small UDP packets for Internet telephony would typically overwhelm the bandwidth which could be provided by the modem. The use of small packets is best to keep down delays for quality critical applications such as Internet telephony.  
         [0017]    The use of UDP throughout the first and second networks  36  and  38  provides a fast, connectionless data transfer system between the networks and the users, but the use of UDP is not suitable for high-quality telephony as the use of UDP requires the use of large packets in order to avoid overwhelming the capabilities of the modems of the users and the regular phone lines which typically connect Internet users to their ISPs. If TCP were used for transmission between and throughout the networks  36  and  38 , however, that approach would also be unsuitable for high-quality digital telephony. Latency would again be significant, because a lost packet anywhere in the network would require the lost packet to be detected and resent. Resending a lost packet very quickly becomes superfluous in an application such as telephony or voice communication. The speaking transmitted by telephony occurs in real time. The global use of TCP would produce a significant latency in order to resend data which would be out of date and useless by the time it was resent and ultimately received.  
         [0018]    TCP is defined at the transport layer and is responsible for reliable, connection-oriented, end-to-end error detection and correction data delivery services. TCP data units are segments and these segments are encapsulated within an IP header. TCP is a stream-oriented protocol that provides the application layer with the illusion that a continuous data pipeline is established along which application information is transmitted. The major features of TCP are reliable, connection-oriented, full duplex, urgent, stream data transfers and flow control. TCP reliability is provided through data segment sequence numbers, data receipt acknowledgments, retransmission timers, and segment checksums. Another important feature of TCP is that the header of a TCP packet can be compressed using van Jacobsen compression. The availability of van Jacobsen compression allows TCP protocol packets to have a low overhead.  
         [0019]    The problems of latency and limited bandwidth are substantially addressed by the present invention. A network  40  in accordance with the present invention is illustrated in FIG. 2. While network  40  is shown as serving a first user A    42  having a client computer and a second user B    44  having a remote computer, it will be recognized that a large plurality of users may be readily served. User A    42  communicates with a first node  46  using TCP. Typically, the client computer will include a modem  43  which will typically be connected to the first node  46  by regular telephone lines  45 . First node  46  passes each data packet received from user A  to a first TCP/UDP converter  48 , where the data packet is converted to a UDP packet. The UDP packet is then sent to a second node  50 . The connection of the first and second nodes  46  and  50 , respectively is typically by way of a high bandwidth connection  49 .  
         [0020]    Upon arrival at the second node  50 , the UDP packet received from user A  is passed to a second TCP/UDP converter  52  where it is converted to a TCP packet. The TCP packet is then transmitted to the user B    44  again typically using regular phone lines  51  and a modem  47  located in the client computer. Each of the converters  48  and converter  52  preferably operates in a two-way fashion, converting TCP to UDP or UDP to TCP as required. Thus, the network  40  illustrated in FIG. 2 is suitable for two-way transmission of data between user B    44  and users  42  making it advantageous for applications such as Internet telephony as discussed in greater detail below.  
         [0021]    [0021]FIG. 3 shows a more detailed illustration of the protocol converter  48  of FIG. 2. The two-way protocol converter  48  includes a TCP/UDP protocol converter  62  and a UDP/TCP protocol converter  64 . The TCP/UDP protocol converter  62  includes an incoming TCP network manager  66 , a TCP to UDP protocol header converter  68 , and an outgoing UDP network manager  70 . The outgoing UDP network manager  70  includes a calling database  72  which stores routing information for each client. This client routing information is preferably established at the time the client connects to the network. The generation and function of the calling destination database  72  will be described in greater detail below in conjunction with the discussion of FIGS. 4 and 5.  
         [0022]    The UDP/TCP protocol converter  64  includes an incoming UDP network manager  74 , a UDP to TCP protocol header converter  76 , and an outgoing TCP network manager  78 . The calling destination database  80  contains entries established for each client which are preferably established at the time of connection of the client with the network. The calling destination database  80  is described in greater detail below in conjunction with FIGS. 4 and 5.  
         [0023]    The UDP/TCP protocol converter  62  receives data packets in TCP format. For example, UDP/TCP protocol converter  62  is shown as part of a digital packet telephony network linking client computers A and B, C and D, and E and F, respectively. Client computers A, C, and E each transmit a stream of digital packets to the protocol converter  48  using TCP format. Each packet transmitted by the client computers A, C, and E contains header information in TCP format. Incoming TCP network manager  66  receives the stream of data packets from the client computers A, C, and E and passes them to TCP/UDP protocol header converter  68 . The TCP/UDP protocol header converter  68  removes the TCP header information from the packets, translates the TCP header information to UDP header information, and adds the UDP header information to the packets. TCP/UDP protocol header converter  68  then passes the data packets to outgoing UDP network manager  70 , which reads the packet headers, looks up the destination information in calling database  72 , and directs the packets to their destinations. Packets from client computer A are then routed to remote computer B, packets from client computer C to remote computer D, and packets from client computer E to remote computer F. Typically, packets will not be transmitted directly from converter  62  to a receiving remote computer, but instead will be preferably routed through another network, or another converter according to the present invention. For example, in FIG. 2 packets addressed from client computer A to remote computer B are sent from protocol converter  48  to remote network  50  and thence to protocol converter  52  before being routed to the remote computer B.  
         [0024]    The UDP/TCP protocol converter  64  operates in a similar manner, receiving, as an illustrative example, packets from the remote computers B, D, and F to be transmitted to the client computers A, C, and E. Each packet received by protocol converter  64  from the remote computers B, D, and F contains header information in UDP format, a portion of the header information identifying the packet destination. This is because remote computers B, D and F originally transmitted the packets in UDP format, or because the packets were converted to UDP format enroute to protocol converter  64 . The packets arrive at the incoming UDP network manager  74 , where they are passed along to UDP/TCP protocol header converter  76 . The UDP/TCP protocol header converter  76  removes the UDP headers from the packets, translates the headers into TCP format, and reconstructs the packets as TCP packets. The TCP packets are then routed to the outgoing TCP network manager  78 . Outgoing TCP network manager  78  determines the destination by looking it up in the calling destination database  80 . Each packet is then sent to its appropriate destination.  
         [0025]    The remote computers B, D, and F can be either end users or further networks or converters. Thus, the protocol converter of the present invention has great flexibility. One network employing a protocol converter according to the present invention can be used to transmit data to arrive at another similar network, thus providing all the advantages described above, or, if the destination does not belong to such a network, the data packets can nevertheless be transmitted to any standard TCP/IP network. This feature provides the significant advantage of allowing the ability to communicate with users who do not subscribe to networks employing a protocol converter according to the present invention. This feature is illustrated in greater detail in FIG. 4 below.  
         [0026]    [0026]FIG. 4 illustrates communication with a large Internet Service Provider A (“ISP A ”)  82  using a protocol converter according to the present invention. The illustrated communication occurs both between its own clients and between its own clients and those of an Internet Service Provider B (“ISP B ”)  108  which does not use a protocol converter according to the present invention.  
         [0027]    ISP A    82  has multiple Points of Presence (“POP”) of which POP 1    84  and POP 2    86  are shown as representative examples. A POP is a server system or network which typically provides access to ISP A  to users within a local telephone service area. Each of POP 1    84  and POP 2    86  typically serves clients within a local calling area. POP 1    84  and POP 2    86  typically communicate with one another through ISP A  packet network  88 . Each of POP 1    84  and POP 2    86  communicates with networks and computers outside of ISP A    82  through a connection to Internet  90 .  
         [0028]    Each POP serves a large number of clients, of which client 1    92  and client 2    94  are shown as representative examples. Client 1    92  connects to POP 1    84  through a modem  96 . Modem  96  provides access via the Plain Old Telephone System (POTS)  98 . Client 2    94  connects to POP 1    84  through one of a number of alternative connections  100 . Such connections may include cable, LAN/WAN connections,  800  numbers, ISDN, wireless, or any other suitable presently known connections or connections which may be developed in the future.  
         [0029]    POP 1    84  includes a modem pool  102  to accommodate clients such as the client 1    92 , who connect to POP 1    84  through modems such as the modem  96 . POP 1    84  also includes a variety of other edge terminators  104 , which accommodate clients such as the client 2    94 , who connect through alternative means. Each of the clients, client 1    92  and client 2    94 , connects to the POP 1    84  using the TCP protocol. POP 1    84  also includes a router  103 . Router  103  includes a converter  105 , one suitable example of which is the converter  62  described above. POP,  84  also includes an active user registry server  106 , which is described in further detail below in connection with the discussion of FIG. 5. The active user registry server  106  provides dynamic addressing. In other words, it establishes and stores a virtual address for each user at the time the user first establishes a session with POP,  84 . Active user registry server  106  associates with each user a converter address. These converter addresses associated with each client such as the clients  92  and  94  are stored, and are used to provide necessary addressing information.  
         [0030]    The converter  105  receives TCP packets from each of the clients  92  and  94  and converts these packets to UDP packets. POP 1    84  then transmits these UDP packets to their destinations. For example, POP 1    84  transmits some of the packets to other points of presence within ISP A    82  over ISP A  packet network  88 . When POP 2    86 , to take a representative example, receives a packet whose destination is one of its users, for example client 1a    92   a,  it sends the packet to a router  103   a  where the packet is converted by converter  105   a  from UDP to TCP, finds the user to which the packet is addressed in its calling destination database, and transmits the packet to the client 1a    92   a,  who is connected to POP 2    86  via modem  96   a.    
         [0031]    To take another example, a packet&#39;s destination may be to client 1b  via ISP B    108 . In this case, POP 1    84  would transmit the packet over the Internet  90 , where it would be routed to ISP B    108 . The packet would remain in UDP protocol while ISP B    108  routed it to client 1b    110  via modem  111 .  
         [0032]    Protocol converters in accordance with the teachings of the present invention maintain compatibility with users who are clients of systems that do not employ a protocol converter according to the present invention. A packet routed to client 1b    110  remains in UDP protocol. While communication between client 1    92  and client 1b    110  does not have all of the advantages of a protocol converter according to the present invention, the use of a protocol converter according to the present invention does not interfere in any way with communication between client 1    92  and client 1b    110 . This feature provides backwards compatibility with existing systems, and thus promotes the universal applicability of the present invention.  
         [0033]    [0033]FIG. 5 is a more detailed illustration of the active user registry server  106  shown in FIG. 4. The active user registry server  106  preferably consists of a network connection manager  112 , a client lookup system  114 , a register client circuit  116 , and an active user database  118 . When a client, such as client 1    92 , first connects to a POP such as POP 1    84 , client,  92  or POP 1    84  sends register message to the network connection manager  112  which passes the register message to the register message input  112   a  of the register client circuit  116 . The register message preferably contains a converter IP address, a client IP address, and a unique identifier for client 1    92 . This information is associated with client 1    92  and stored in the active user database  118 . When a client, such as client 1a    92   a,  wants to determine how to route a communication to client,  92 , it sends a message to the active user registry server  106 . The network communications manager  112  determines that the message is a client look up request message, and sends it to the client lookup system  114 . The system  114  does the look up for client,  92  in the active user database  118  and sends the necessary routing information to the requesting client. The requesting client now has all the routing information required to send packets to the client 1    92 .  
         [0034]    [0034]FIG. 6 is a flowchart illustrating process steps which may be suitably carried out by a protocol converter according to the teachings of the present invention. In step  600 , an incoming message is detected and the operating system sends a network interrupt for the incoming message. In step  601 , it is determined whether a first packet of the incoming message is in TCP format. If the packet is a TCP packet, the control process follows the branch including the steps  602 ,  604 ,  606  and  607 . The packet is received, step  602 , the address of the client addressee is looked up, step  604 , the TCP packet is converted to UDP, step  606 , and routed to the remote addressee, step  607 . It will be recognized that the order of converting and lookup are not critical, and that these steps may be performed in reverse order or in parallel. If additional TCP packets are received as part of the same incoming message, the process continues to repeat itself. If no additional packets are being received by the system, the process will idle until the next network interrupt indicative of an incoming message occurs.  
         [0035]    If in step  601 , it had been determined that a TCP packet was not incoming, it would next be determined in step  608  if a UDP packet was incoming. If a UDP packet was identified, process control would follow the control process branch including steps  610 - 616 . In step  610 , the UDP packet is received, and in step  612 , the client address of the addressee is looked up. In step  614 , the packet is converted to TCP. In step  616 , the packet is routed to the addressee. Control is then transferred back to block  600 . It will be recognized that the process may be suitably extended to other packet formats by determining whether such packet formats are being received and following similar process steps.  
         [0036]    While the present invention is disclosed in the context of a presently preferred embodiment, it will be recognized that a wide variety of implementations may be employed by persons of ordinary skill in the art consistent with the above discussion and the claims which follow below.