Electrical computers and digital processing systems: multicomput – Computer network managing
Reexamination Certificate
2000-09-15
2004-11-16
Alam, Hosain (Department: 2155)
Electrical computers and digital processing systems: multicomput
Computer network managing
C709S238000, C709S236000, C709S248000
Reexamination Certificate
active
06820120
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to routing data packets in heterogeneous networks and, in one aspect, to a method for routing Open Systems Interconnect (OSI) data packets over Internet Protocol (IP) networks.
BACKGROUND TO THE INVENTION
As persons skilled in the art will appreciate, many conventional data networks, such as, for example, Synchronous Optical Network (SONET) or Synchronous Digital Hierarchy (SDH) networks, use the OSI protocol to enable communication between network elements.
In an OSI network there are four significant architectural entities: hosts (also known as End Systems), areas, backbones, and domains. A domain is any portion of an OSI network that is under common administrative authority and is similar in concept to an IP Autonomous System (AS). Within any OSI domain, one or more areas can be defined. An area is a logical entity; it is formed by a set of contiguous routers and the data links that connect them. All routers in the same area exchange information about all of the hosts that they can reach.
Areas are connected by level 2 routers (described below) which together form a backbone of the domain. All routers on the backbone know how to reach all areas. The term end system (ES) refers to any non-routing host or node; intermediate system (IS) refers to a router. These terms are the basis for the OSI End System-to-Intermediate System (ES-IS) (described in ISO 9543, available from the International Organization for Standardization (ISO) at www.iso.ch, the contents of which are hereby incorporated herein by reference) and Intermediate System-to-Intermediate System (IS-IS) (described in ISO 10589, “Intermediate system to Intermediate system intra-domain routing information exchange protocol for use in conjunction with the protocol for providing the connectionless-mode Network Service (ISO 8473)” also available from the ISO, the contents of which are hereby incorporated herein by reference) protocols.
Routing can be divided into two categories or levels: level 1 routing refers to intra-area routing; while level 2 routing refers to inter-area routing. An IS (i.e., a router) that can only perform intra-area routing is referred to as a level 1 IS. Similarly, an IS capable of inter-area (or intra-domain) routing is considered to be a level 2 IS.
As a result of their functionality, a level 1 IS need only be aware about the level 1 ISs and ESs within its area and the nearest level 2 IS should a packet received by a level 1 IS require inter-area routing. In contrast, a level 2 IS must be aware of the topology of the area it serves (i.e., the level 1 ISs and ESs in the area); the other level 2 ISs within its domain; and how to reach all other areas within its domain.
IS-IS routing is the standard intra-domain (i.e., inter-area) routing protocol in the OSI protocol suite. The IS-IS routing protocol, being a link state protocol, requires each IS running the IS-IS protocol to determine (e.g., “meet”) each of its neighbors and assess the state of each link between itself and its neighbors. This information is stored in a link state circuit table which is used to generate Link State Advertisements or Packets (LSPs) which are transmitted or flooded across the network to each IS. A circuit identifies a logical connection or channel over which communication can occur. LSPs are transmitted whenever an IS determines that there has been change in a link between itself and a neighboring IS. For example, an IS transmits LSPs when it is determined that a link has failed or changed with respect to the link's cost metric (hereinafter “costs”), or when a new neighbor is discovered. Only those routers which are directly connected to each other can form an adjacency and become “nearest neighbours” (i.e. neighboring routers must be directly adjacent to each other and share a common data link).
On receipt of these LSPs, an IS is able to determine a complete picture of the domain topology and compute optimal routes to each ES in the domain. The routing algorithm used by IS-IS is the Shortest Path First (SPF) algorithm.
Other information is also included in the LSPs transmitted and received by the ISs. For example, LSPs also include costs associated with the use of each link. As a result, costs associated with the optimal routes can also be calculated. Further, LSPs include sequence number and remaining lifetime fields which are used to determine if a duplicate LSP has been received, whether the link information is too old, etc.
While OSI compliant networks are popular and quite common, the use of IP networks has proliferated and continues to gain in popularity. As a result, there is a need to enable the co-existence of these two networking protocols. Accordingly, a protocol (often referred to in the art as “Integrated IS-IS”) has been developed to enable routers to support both the IS-IS and IP routing protocols. Integrated IS-IS (described in Request For Comment (RFC) 1195, available from the Internet Engineering Task Force (IETF) and available at www.ietf.org, the contents of which are hereby incorporated herein by reference) provides for the routing of IP packets by simply using existing IS-IS packets with the addition of IP-specific fields. Accordingly, each IS router need only run the OSI Integrated IS-IS routing protocol to provide for the routing of IP packets. Use of Integrated IS-IS routing protocol has been reasonably successful in the past in addressing the needs of heterogeneous networks which have been comprised of predominately OSI network elements (i.e., elements transmitting OSI-compliant packets) with small numbers of IP network elements.
However, the relatively recent widespread adoption of IP networking technology has resulted in heterogeneous networks which have, to a larger extent than previous, relatively large numbers of IP network elements. This increase in IP network elements combined with an increase in the number of IP packets being transmitted (and, thus, requiring routing) has demonstrated that the use of Integrated IS-IS in these heterogeneous networks is somewhat inefficient. For example, Integrated IS-IS, while providing the routing protocol, does not provide the forwarding functionality. This results in each protocol stack still being responsible for the forwarding of packets. IP routing using Integrated IS-IS routers is also limited to those IP sub-networks which are contained within a single OSI area. If multicasting capability is desired, Integrated IS-IS requires a router to run a separate multicasting protocol which results in further overhead and degradation of performance. Moreover, many data transmissions require exterior routing (i.e., routing between domains) which, in the Integrated IS-IS protocol, is simply not as well developed as IP exterior routing. Further, it has been noted that Integrated IS-IS does not scale well due to L2 router connectivity requirements.
Other attempted solutions to provide OSI and IP routing run software implementing the complete OSI and IP routing protocols completely independently from one another (often referred to as the Ships In the Night (SIN) method). However, this method has not been satisfactory due to the increased computational overhead required to run two separate and independent protocols.
Accordingly, providing a manner for the routing of data packets in heterogeneous networks which addresses these shortcomings is desirable.
SUMMARY OF THE INVENTION
Advantageously, embodiments of the present provide improved routing of data packets in heterogeneous networks especially in networks that comprise network elements transmitting predominately IP messages. Specifically, routers embodying aspects of the present invention may, in some instances, run software implementing portions of the OSI routing protocol and software implementing the IP routing protocol simultaneously. Moreover, these embodiments provide for the exchange of routing information between software implementing these two protocols.
In one embodiment, routers initially run only the IP routing protocol and a router will
Barry Peter J.
Keats Bruce D.
Stanke Brian E.
Alam Hosain
Bruckart Ben
Nortel Networks Limited
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