SERVICE INTERWORKING METHOD

Abstract: In a method of providing communication between data terminal units connected to respective packet-based networks running different protocols, packets of a first protocol are mapped into packets of a second protocol in an interworking unit between the networks. The interworking unit also provides call establishment interworking.

Description: SERVICE INTERWORKINO METHOD This invention relates to a method of providing communication between data transmission network devices running different protocols, such as X.25 and frame relay. Frame relay is a technology optimized for running over high quality transmission facilities. Although this is the case for most of North America, the same cannot be said of transmission facilities in other parts of the globe. In such instances, communication using the older X.25 protocol is required. International business networks spanning the globe need a mix of the above communications technologies to meet their requirements. Currently, it is not possible for customers with X.25 DTEs (Data Terminal Equipment) to communicate directly with Frame Relay Users. ITU recommendation Q.922 provides for the encapsulation of X.25 packets in Frame Relay frames. This allows an X.25 DTEs to have access to an X.25 Host through a frame relay network, but does not allow the X.25 DTE to communicate with a frame relay user. Thus, for example, an office in North America with connected to a frame relay network would need X.25 equipment in order to access an X.25 terminal. The customer could not communicate with the X.25 terminal using its existing frame relay equipment. An object of the present invention is to permit users of networks running different protocols to communicate with each other directly. Accordingly the present invention provides a method of providing communication between data terminal units connected to respective packet-based networks running different protocols, characterized in that packets of a first said first protocol are mapped into packets of said second protocol in an interworking unit located between said networks and providing a termination point for a call in each of said networks, said interworking unit also providing call establishment interworking. The first protocol is conveniently X.25 and the second protocol frame relay, in which case the X.25 packets are mapped into frame relay frames and vice versa. The service interworking unit preferably operates in two modes: normal reliability and superior reliability mode. In the normal reliability mode, delivery of frames across the frame relay portion of the X.25/Frame relay virtual circuit is not guaranteed. This mode is suitable when the application layer performs recovery and the transmission fabric carrying the frame relay traffic has as a low bit error probability rate. In superior reliability mode, delivery and sequencing of frames is provided between the interworking unit and the Frame Relay terminal equipment. In addition, the service interworking unit can provide dynamic mapping of X.25 SVCs to FR PVC on a per X.25 call basis, mapping of X.25 PVCs (permanent virtual connections) to FR PVC, and FR SVC to X.25 SVC/PVC mappings as FR SVCs standards develop. The unit may also handle congestion on the FR path and flow controls the X.25 transmit window. The advantages of such a unit are that it allows service interworking between X.25 and Frame relay users, provides graceful migration from X.25 to frame relay services, protects customer investment in X.25 equipment, allows use of X.25 for communication in areas of poor transmission quality and use of frame relay in areas of superior transmission quality on a given Virtual Circuit, and allows use of many X.25 features such as call accounting and security otherwise not available for frame relay connections. The invention is applicable to any network user or organization using both X.25 and frame relay where ubiquitous service interworking is a requirement . This includes customers with a large installed base of X.25 equipment who are migrating to frame relay but require a smooth transition or desire to retain their existing X.25 base while adding new applications/services with frame relay, and service bureau companies who want to attract both X.25 and frame relay users to use their service. The invention can be implemented, for example, in a Newbridge Networks Corporation MainStreet™ 36xx series bandwidth manager. The invention will now be described in more detail by way of example only with reference to the accompanying drawings, in which: - Figure 1 shows one embodiment of an X.25 to Frame Relay service interworking network; Figure 2 is another embodiment of an X.25 to Frame Relay service interworking network connected to a public switched data network; and Figure 3 shows the frame relay interworking protocol stacks. Referring to figure 1, the service interworking network comprises a plurality of X.25 data terminal equipment units (DTE) 1, connected to respective X.25 packet engines 2, which provide a switching function for the X.25 packets. The packet engines 2 are connected to packet engine/interworking network unit 5 over X.25 switched virtual circuits 6. Frame relay device 3 is connected to frame relay engine 4, which in turn is connected to packet engine/interworking network unit 5 over frame relay permanent virtual connection (PVC) 7. Packet engine/interworking unit 5 is connected via frame relay PVCs (Permanent Virtual Connections) to frame relay host 13. In Figure 1, frame relay host 13 can communicate directly with frame relay device 3 over PVCs 12 and 7 of with X.25 DTEs over PVC 12 and SVCs 6. Figure 2 is similar to Figure 1 except that Packet engine/interworking unit 5 is also connected to public switched data network 9, connected over an X.25 link to an X.25 host 11. Frame relay host 13 can communicate with X.25 host through interworking unit 5. The X.25 FR Service Interworking Unit (IWU) is a network element responsible for mapping X.25 packets into frame relay frames and providing call establishment interworking. The unit provides reliability (sequenced, ordered, and non-lossy transfer) when operating in superior reliability mode over the FR PVC: sequenced, ordered and non-lossy transfer of frames between IWU and host; X.25 to FR Call Cross Connection for X.25 SVCs and PVCs; FR to X.25 Call Cross Connection once FR SVCs are developed; and handles congestion on the FR path and eventually flow controls the X.25 transmit window. The (Interworking unit) IWU is built into each X.25 Packet engine 2, 4, 5. As shown in Figure 3, the IWU is implemented using Trillium Q.2110 software running as a subsystem 20 in the Transport Layer. The Q.2110 protocol layer between IWU 5 and the frame relay host is optional and distinguishes "superior reliability" mode. The IWU is the termination point for both the X.25 call and the FR PVC. The X.25 DTE 1 communicates over switched or permanent virtual circuits 6 with the packet engine 2 at the LAP-B layer over which is the X.25 protocol layer. Virtual trunks are established between the packet engine 2 and IWU 5. Terminal 13 communicates with frame relay switch 21 and IWU over frame relay PVCs. The X.25 call packets are routed to the IWU 5 from DTE 1 using the called address field (X.121 or E.164) of the destination FR host 13. When the call arrives at the IWU/PE 5, the X.25 DCE routes the call to the transport layer. The IWU 5 uses a list of configured addresses to determine whether to connect the incoming call to a frame relay PVC. If a frame relay PVC to the requested host is operational, the IWU sends a Call ACCEPT packet to the X.25 DTE . If no FR PVC is available, the IWU 5 sends a call clear packet back to the X.25 DTE. Since the IWU 5 provides reliable delivery of frames over the frame relay PVC, the X.25 accounting data provides accurate billing data. The IWU 5 implements Q.2110 congestion control mechanisms when operating in superior reliability mode for reacting to congestion occurring along the frame relay path. Prolonged frame relay congestion results in temporary closure of the X.25 transmit window. The invention thus allows X.25 terminals to communicate directly with frame relay terminals, resulting in substantial economies for the customer who must contend with diverse networks .

Claims: Claims : 1. A method of providing communication between data terminal units connected to respective packet-based networks running different protocols, characterized in that packets of a first said first protocol are mapped into packets of said second protocol in an interworking unit located between said networks and providing a termination point for a call in each of said networks, said interworking unit also providing call establishment interworking. 2. A method as claimed in claim 1, characterized in that call packets are routed to said interworking unit using a called address field of the destination terminal. 3. A method as claimed in claim 2, characterized in that said first protocol is X.25 and said second protocol is frame relay. 4. A method as claimed in claim 3, characterized in that said called address field is the X.121 or E.164 address field. 5. A method as claimed in claim 3, characterized in that the terminal connected to the X.25 network routes call packets to a transport layer in said interworking unit, which uses a list of configured addresses to determine whether to connect the incoming call to a frame relay permanent virtual connection. 6. A method as claimed in claim 5, characterized in that said interworking unit returns a call accept packet to the X.25 terminal if a permanent virtual connection to the requested host is available. 7. A method as claimed in claim 5, characterized in that said interworking unit returns a call clear packet to the X.25 terminal if no permanent virtual connection to the requested host is available. 8. A method as claimed in claim 3, characterized in that the interworking unit implements congestion control to react to congestion along the frame relay path. 9. A method as claimed in claim 8, characterized in that sequencing and delivery of frames is provided between the interworking unit and frame relay terminal by software located in the interworking unit and the frame relay terminal . 10. A method as claimed in claim 8, characterized in that prolonged congestion causes temporary closure of the X.25 transmit window.

Inventors: BENNING REX, HURD JIM, BENNING, REX, HURD, JIM
Applicants: BENNING REX, HURD JIM, NEWBRIDGE NETWORKS CORP, BENNING, REX, HURD, JIM, NEWBRIDGE NETWORKS CORPORATION
Application year: 1996
Main classification: H04L29
IPC codes: H04L12, H04L29