Electrical computers and digital processing systems: multicomput – Multiple network interconnecting
Reexamination Certificate
1998-10-16
2001-03-27
Maung, Zarni (Department: 2758)
Electrical computers and digital processing systems: multicomput
Multiple network interconnecting
C709S208000, C709S209000, C709S211000, C370S489000, C370S248000, C340S870030
Reexamination Certificate
active
06209039
ABSTRACT:
BACKGROUND
1. Field of the Invention
The present invention relates generally to digital communication networks. In particular, the present invention is directed toward a resilient interface that connects two frame relay communication networks.
2. Related Art
A data communications network serves to transport digital information between a number of locations. A typical data communications network consists of various physical machines called “nodes”, interconnected by conduits called “links.” Some of the network nodes have links to the network user's devices.
Circuit switching and frame-based switching are two fundamentally different transport technologies used to build data communication networks. Circuit switching is a technology that builds a physical data path dedicated to a set of users. An example of this is the Public Switched Telephone Network. Once a call is established, the network transmission resources associated with the path are dedicated to the call, whether they are used or not. Frame-based switching is a general term for technologies based on the concept of shared network transmission resources. User data is divided into various data units called frames, packets, datagrams, or cells, depending on the specific technology employed. The data unit contains routing or connection information, used by nodes along the path to route or switch the data unit to the link connected to the next node on the way to the eventual destination. As a result, data units destined for different termination points typically share physical links between intermediate nodes in the path. Transmission resources associated with these links are more fully utilized because the statistical distribution of periods of activity and inactivity of many users results in less overall inactivity of the shared resources.
The connections between users of the Frame Relay network are called Virtual Circuits because they are logical constructs of the network, and not dedicated physical circuits. Virtual circuits can be categorized as permanent or switched. A Permanent Virtual Circuit (PVC) is a relatively long-duration logical path between two Customer Premises Equipment (CPE) devices, configured by the network administration, and is typically not dismantled after a specific communications session. A Switched Virtual Circuit (SVC) is a relatively short-duration logical connection set up in response to a call made by the CPE, and is typically disconnected after a specific communications session.
Frame Relay (FR) is technically a data network access standard defined by Frame Relay Forum Implementation Agreements and ITU-T recommendation I.122. It defines a User-to-Network Interface (UNI), a framing protocol for the link connecting Customer Premises Equipment to the Frame Relay network. The frames typically have a 3-byte header, 3-byte trailer, and a variable payload of up to 4096 bytes in length. The header includes a 1-byte start flag, and an address field containing a Data Link Connection Identifier (DLCI) that identifies unique virtual circuits on the UNI. The frame relay trailer consists of a two-byte frame check sequence field, and a 1-byte end flag field. A Network-to-Network Interface (NNI), a minor variation of the UNI specification, is also specified for connections between separate Frame Relay networks.
The frame-based transport technology employed in the interior of the frame relay network is not visible to the user, and is typically proprietary to the providers of specific frame relay switching equipment. The links on the interior of the frame relay network are referred to as trunks to differentiate them from UNIs and NNIs. Whereas UNIs are standardized access links between CPE and a frame relay network, Network-to-Network Interfaces (NNIs) provide a standardized method of inter-connecting autonomous frame relay networks which use incompatible interior trunking protocols. This inter-network transparency is increasingly important, as de-regulation of the telecommunications industry results in merged and partnered companies with merged and partnered frame relay networks.
A key advantage of Frame Relay networks is that the data units can be dynamically routed around specific points of congestion or failure within the network. This self-healing property is compromised when an NNI link connects two Frame Relay networks, because the NNI constitutes a single point of failure. This means that while the individual networks can route virtual circuits around failures of interior trunk links, a failure of an NNI link is disruptive until the failure is detected, diagnosed, and repaired. It would be highly preferable if the virtual circuits could also be routed around the failure of an NNI link.
SUMMARY
The present invention is a resilient network-to-network interface (RNNI) between a first frame relay network and a second frame relay network. The RNNI is distinct from a conventional network-to-network interface (NNI) because the RNNI is resilient to the failure of a single physical link.
An RNNI comprises a plurality of data links that connect a master node in a first network to a slave node in a second network. The master and slave nodes initialize the RNNI by operating an independent instance of a Link Integrity Verification (LIV) routine on each of the data links. The LIV routine returns the operational status of the link as UP or DOWN. The master node designates one of the data links with an UP status as the ACTIVE link. The remaining data links are designated as INACTIVE. The master node then sends an initial Permanent Virtual Circuit (PVC) poll status message to the slave node over the ACTIVE link. The slave node recognizes the ACTIVE link by the receipt of the PVC poll status message.
After this initialization process, the master and slave nodes run conventional NNI procedures on the ACTIVE link, including an LIV routine and a PVC polling routine, and monitor the INACTIVE data links using an LIV routine. If the ACTIVE link fails, the conventional NNI procedures will report a DOWN status to both nodes, and the RNNI is re-initialized.
In one embodiment, the LIV routine comprises the Annex A Link Integrity Verification poll, part of ITU-T Recommendation Q.933. In an alternate embodiment, the LIV routine comprises the Annex D Link Integrity Verification poll, part of ANSI Standard T1.617.
An advantage of the present invention is that the RNNI uses multiple data links to connect the frame relay networks. This eliminates the single point of failure associated with conventional frame relay NNIs, and fully enables the self-healing capability inherent in frame relay networks.
A second advantage is that the ACTIVE data link and the INACTIVE data links are continuously monitored with a version of the LIV routine even though only the ACTIVE data link carries user data across the NNI. In one embodiment, if one or more of the INACTIVE data links returns a DOWN status, an alarm is issued so that network administration can dispatch personnel to diagnose and restore the link to operational UP status. Thus, the INACTIVE data links are maintained in a state of readiness in case the current ACTIVE data link goes DOWN.
A third advantage is that the LIV routine for the INACTIVE link can be implemented by modifying existing frame relay standards, namely Annex A of ITU-T Recommendation Q.933 or Annex D of ANSI Standard T1.617.
Further features and advantages of the present invention, as well as the structure and operation of the various embodiments of the present invention, are described in detail below with reference to the accompanying Figures.
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Albright Martin
Chen William C.
Fontenot Michael D.
Frost Todd W.
Williams James F.
Maung Zarni
MCI Worldcom, Inc.
Nguyen Thu Ha
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