Patent Publication Number: US-2003227907-A1

Title: Apparatus for providing QoS of VoIP traffic on IP router and forwarding method therefor

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to providing Quality of Service (QoS) of voice traffic transmitted by a router when voice traffic converges on an Internet Protocol (IP) network, and more particularly, to an apparatus in which a router provides enough QoS to satisfy VoIP&#39;s demand, by receiving and managing information on VoIP flow from a softswitch and referring to the information in packet forwarding, and a packet forwarding method.  
       [0003] 2. Description of the Related Art  
       [0004] Voice over IP (VoIP) service technologies have been developed and introduced as private network technologies for providing voice virtual private network (VPN) of major business subscribers. Accordingly, in order to provide VoIP services to a large number of ordinary subscribers, a lot of functions should be improved, and on top of this, there is Quality of Service(QoS). To provide QoS of VoIP, delay and delay variation should be minimized. However, in most of conventional routers forming IP networks, it is difficult to support QoS of VoIP at present. As a network apparatus for establishing a converged network supporting VoIP on IP networks, a softswitch has been developed to provide interoperability among VoIP signaling protocols. To provide QoS of VoIP as a whole, QoS should be first provided in the network level though improvement in terminal apparatuses is also needed. In the conventional routers forming a network, QoS as high as possible that can be provided by the routers should be allocated so that VoIP packets can be identified and recognized and QoS requested by VoIP can be provided. However, since in the router it is not easy to recognize VoIP packets due to IP protocol structures, it is difficult to provide QoS of VoIP in the network level.  
       SUMMARY OF THE INVENTION  
       [0005] To solve the above problems, it is an object of the present invention to provide an apparatus for providing QoS of VoIP traffic on IP routers and a forwarding method in a router.  
       [0006] To solve the above problems, it is another object of the present invention to provide a computer readable medium having embodied thereon a computer program for the forwarding method.  
       [0007] According to an aspect of the present invention, there is provided a voice over IP (VoIP) quality of service (QoS) providing apparatus in an Internet protocol (IP) network containing data traffic and providing VoIP service, the VoIP QoS providing apparatus comprising: a softswitch which performs a VoIP call coordination function in the IP network and transmits VoIP call connection information in a multicast transmission method; and a router which provides QoS in forwarding a VoIP packet, by using the information received from the softswitch.  
       [0008] According to another aspect of the present invention, there is provided a packet forwarding method which provides QoS of VoIP traffic in an IP router, comprising: determining whether or not a received packet is included in information of the forwarding table of the router; checking whether or not the packet is a VoIP packet; setting a field value of an IP precedence in the format of an IP service type, to a predetermined value; and outputting a packet queued according to the precedence value. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0009] The above objects and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which:  
     [0010]FIG. 1 is a schematic diagram showing an entire network structure to which the present invention is applied;  
     [0011]FIG. 2 is a block diagram of functional elements of a softswitch according to the present invention;  
     [0012]FIG. 3 is a block diagram of functional elements of a router according to the present invention;  
     [0013]FIG. 4 is a diagram of a structure in which connection establishment and/or termination information of VoIP call according to the present invention is transferred;  
     [0014]FIG. 5 is a diagram of a structure of message information communicated between a softswitch and a router according to the present invention;  
     [0015] FIGS.  6 ( a ) and  6 ( b ) show a preferred embodiment of an octet format of an IP service type according to the present invention; and  
     [0016]FIG. 7 is a flowchart showing a method for forwarding a packet in a router according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0017]FIG. 1 is a schematic diagram showing the structure of an IP network to which the present invention is applied. The IP network  110  for providing VoIP services as well as conventional data traffic comprises routers  120  for routing among different sub networks and forwarding packets, a softswitch  130  which is connected to the IP network  110  and performs a connection function for VoIP signal protocols, and terminal apparatuses  140 . According to the size of the network, one or more softswitches  130  may be placed.  
     [0018]FIG. 2 is a block diagram of functional elements of a softswitch according to the present invention.  
     [0019] A call control unit  250  unifies the functions of a call agent, a call server, a media gateway controller. A service application unit  240  introduces a connection function for different signal methods, and an open architecture so as to easily accommodate new services and to provide compatibility and interoperability. A signal protocol unit  260  provides an SS7 signal interface for VoIP signal protocols such as an H.323 or a Session Initiation Protocol (SIP), and for PSDN connection, and provides connection functions for IP networks. The softswitch also comprises a system management unit  210  which manages the entire system, a network management unit  220  which manages an IP network, and a QoS control unit  230  which performs a QoS control function.  
     [0020] Since the VoIP signaling protocol is an end-to-end type, in connection establishment and termination of a call which the router  120  in the softswitch  130  needs in providing flow classification of VoIP packets and QoS, VoIP flow information is transferred to the router  120 . The QoS control module  203  performs this role as a whole. Call connection establishment and termination information includes the source IP address and destination IP address of an end-to-end VoIP call, UDP port numbers, etc.  
     [0021]FIG. 3 is a block diagram of functional elements of a router according to the present invention, in which routing and forwarding are separated so that the router can operate at a speed of tens of gigabits per second.  
     [0022] A processor module  310  comprises a routing protocol unit  311  which performs routing protocols  304  such as RIP, OSPF, and BGP; a routing database (DB)  314  which maintains and manages routing table information; a QoS control unit  312  which performs a QoS control function; a network management agent unit  313  which performs a network management agent function  313 ; a traffic control database  315  which manages a traffic flow control table for providing QoS; and a QoS mapping unit  316  which relates to system resource management for providing QoS received from upper layers.  
     [0023] A line card  330  performs a packet forwarding function, in which a forwarding table unit  331  maintains a forwarding table restructured based on routing table information of the routing DB  314  in order to provide high speed forwarding, and a packet classifying unit  333  performs data packet classification and forwarding of received packets. A scheduler unit  337  performs precedence queueing for providing appropriate QoS to the classified packets and performs output scheduling according to the precedence queue. When an input packet is output through other line card  330 , the packet is transferred to the softswitch  130  through a switch interface unit  335 , and is forwarded to the network through the line card  330  of an output port.  
     [0024]FIG. 4 is a diagram of a structure in which connection establishment and/or termination information of VoIP call according to the present invention is transferred.  
     [0025] A structure of transmitting VoIP call connection establishment and termination information between the softswitch  410  and routers  420  through  450  is based on multicast transmission and targets to minimize load to the system when the softswitch  410  transmits information. Here, by using a reliable multicast transmission method, all receivers should receive accurate data. For this, a transmitting side should be able to manage the state of a receiving side. All routers on a router path providing VoIP QoS should provide a multicast function and form a reliable multicast tree among routers. The softswitch  410  selects a representative receiving side for multicast transmission so that the representative receiving side can transmit data to all routers  420  through  450  that have to receive the data, through the multicast path. The routers  440  and  450  become able to recognize voice data packets transmitted and received by VoIP terminal apparatuses  460  and  470 , and in order to provide QoS, precedence queueing and forwarding are provided.  
     [0026] The softswitch  410  and the routers  420  through  450  operate in a master-slave relation. First, in order to start functions, a process for establishing a connection for control is needed. If a multicast environment is supported, management for initial joining, including joining in a multicast group, is needed in routers that are clients. Based on thus established control information transmitting environment, information on VoIP sessions performed by the softswitch  410  or end-to-end call connections, including information on establishing a connection and terminating the connection, are transmitted to the routers  420  through  450  included in an object group performing a VoIP QoS management function. The routers  420  through  450 , which receive this information, recognize the VoIP data packet by adding the packet to or deleting the packet in the flow table managed by each router, and processes the packet according to the precedence.  
     [0027]FIG. 5 is a diagram of a structure of message information communicated between a softswitch and a router according to the present invention.  
     [0028] Basically, the message comprises a common header  510  field and a VoIP call connection control/state information  520  field. The common header  510  field includes an operation code, the message length, etc. The VoIP call connection control/state information  520  field includes a call type (H.323, SIP, etc.), a source IP address, a destination IP address, a TCP/UDP port number, state information, or QoS information.  
     [0029] FIGS.  6 ( a ) and  6 ( b ) show a preferred embodiment of an octet format of an IP service type according to the present invention. In FIG. 6( a ), the highest 3 bits in an octet format of a service type defined in the IP indicates IP precedence  610 , in which, the greater the number is, the higher the precedence is. The next 4 bits indicates an additional service type, representing requirements such as delay, throughput, reliability, cost, etc. FIG. 6( b ) shows a format defined to use the octet of the conventional IP service type, in order to provide differentiated services from the IP. Here, the conventional IP service octet is used without change. The highest 6 bits indicate a differentiated service code point (DSCP)  630 , and overlaps the precedence field of the conventional IP. To solve this problem, some routers use a method in which in VoIP packet forwarding, DSCP value 40 (101000B) of FIG. 6( b ) corresponding to the same value as the IP precedence value 5 (101 B) of FIG. 6( a ) is used. A CU field  640  after the DSCP field  630  is 2-bits long and not used at present.  
     [0030]FIG. 7 is a flowchart showing a method for forwarding a packet in a router according to the present invention.  
     [0031] If the line card of a router receives a packet in step  710 , by accessing the destination IP address of the IP header of the received packet in the forwarding table of the line card, it is first determined whether or not there is a next hop to be transmitted in step  720 . If it is a flow which does not exist, the packet is discarded or forwarded to a default router in step  780 . If it is a flow in the table, it is determined whether or not it is a VoIP packet in step  730 . If it is a VoIP packet, it is determined whether or not the IP precedence field value of the ToS octet is 5 in step  740 , and if it is not 5, set the field value to 5 or change the DSCP value to 40 in step  750 . Precedence value corresponding to the flow is accessed in the forwarding table in step  760  and according to the obtained precedence, the packet is queued in step  770 . The packets queued according to the precedence is output according to the precedence by the scheduler. That is, the first ingress router to which the VoIP packet is transmitted makes the routers in the middle nodes check the service type field to recognize a VoIP packet flow. In a method, by recognizing a VoIP flow only with the precedence of the service type, a high precedence transmission is performed. In another method, by confirming VoIP call connection information obtained from additional communications with the softswitch, a stable precedence transmission performed. The routes in the middle nodes are made to use one of two selective methods.  
     [0032] The present invention may be embodied in a code, which can be read by a computer, on a computer readable recording medium. The computer readable recording medium includes all kinds of recording apparatuses on which computer readable data are stored.  
     [0033] The computer readable recording media includes storage media such as magnetic storage media (e.g., ROM&#39;s, floppy disks, hard disks, etc.), optically readable media (e.g., CD-ROMs, DVDs, etc.) and carrier waves (e.g., transmissions over the Internet). Also, the computer readable recording media can be scattered on computer systems connected through a network and can store and execute a computer readable code in a distributed mode.  
     [0034] As described above, according to the present invention, the softswitch provides VoIP call connection information to routers, and by using this, the routers can recognize a VoIP packet and provide QoS. In providing VoIP connection information to each router, reliable multicast transmission method is used such that load to the system is reduced when the softswitch additionally processes related function. Since in the router, VoIP QoS flow and QoS information are added to a flow table for performing packet forwarding, VoIP packet recognition and QoS providing are enabled. In addition, flow management for providing QoS in a variety of shapes in the similar manner can be provided.