Multiplex communications – Data flow congestion prevention or control – Flow control of data transmission through a network
Reexamination Certificate
2001-11-29
2004-12-28
Lee, Andy (Department: 2663)
Multiplex communications
Data flow congestion prevention or control
Flow control of data transmission through a network
C370S400000, C709S241000
Reexamination Certificate
active
06836465
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a method and system for acquiring information from a packet communications network. More particularly, the present invention relates to a method and system for determining the set of links and routers that are traversed by traffic to and/or from an individual user of a packet communications network.
BACKGROUND OF THE INVENTION
An Internet protocol (IP) network is a large distributed system in which individual routers automatically adjust their decisions on how to forward packets based on information they learn from their neighbors about the state of the network. This design permits rapid recovery in case of link or router failures by allowing affected routers to re-route packets around the failure as soon as they discover it.
However, this distributed mode of operation and the associated robustness it affords come at a price. For example, accuracy in characterizing the behavior of the network at any given time is a complex task. Because of this, many of the network management functions that are available for networks based on more traditional technologies, e.g., connection-oriented such as frame relay or asynchronous transfer mode (ATM), are difficult if not impossible to replicate in IP networks. For example, in a connection-oriented network, the state associated with each connection/user provides the network administrator with a ready handle for tracing its path and monitoring the resources it relies on. In contrast, in IP networks because routing decisions are made in a distributed fashion by many routers that are only concerned with local packet forwarding decisions, there is no single entity with complete knowledge of the entire path that a packet will follow at any given time. Again, this makes it more difficult for a network administrator to precisely identify the path that the traffic between, for example, two customer sites, is following when traversing the network.
As a consequence, upon identifying a highly congested link, a network administrator has no or only limited visibility into which customers may be experiencing poor performance as a result of this congestion. Similarly, in the presence of a link failure, identifying which customers are immediately affected as well as predicting which ones may also experience a change in service performance shortly after the failure is again a very complex task in IP networks.
Management tools do exist for IP networks, but they are typically reactive or operate at a coarse granularity, i.e., not at the level of the end-to-end performance of an individual customer or site. For example, routers typically support standard Management Information Bases (MIBs) that can be queried using protocols such as the Simple Network Management Protocol (SNMP). MIBs provide detailed state information about individual routers, e.g., interface status, number of packets or bytes transmitted and received on each interface, etc. However, this information is local to each device, and does not offer a network wide perspective. Furthermore, piecing together MIB information from multiple routers to derive end-to-end performance measures of relevance to a given customer is not an easy task. A similar limitation exists when relying on traffic monitoring information that is routinely gathered at routers using mechanisms such as Cisco's NetFlow™ or Juniper cflowd™. These monitoring devices capture detailed information about the traffic crossing a given interface, but again do not have the ability to identify end-to-end paths. Converting such traffic monitoring data into end-to-end intelligence is a laborious task.
A few tools exist that are capable of end-to-end sampling of paths traversing an IP network. Most of them are based on two core utilities built into the Internet Protocol, ping and traceroute, which allow a network administrator to probe the network in order to generate estimates of end-to-end performance measures such as packet loss and delay, and record full path information. However, solutions based on utilities such as ping and traceroute often are not desirable because they are neither scalable nor capable of providing real-time information about the network behavior as a user experiences it.
Accordingly, it is desirable to provide an improved method and system for monitoring, tracking, and/or predicting the distributed routing state of an IP network.
The following is provided as additional background information about the Internet and Internet routing protocols to help the reader understand the context of the present invention:
The Internet is a global network that consists of multiple interconnected smaller networks or Autonomous Systems (AS). The delivery of packets across this Interconnection of Networks is carried out under the responsibility of the IP suite. In particular, routing protocols disseminate information that allows distributed decisions to be made on how best to forward packets towards their destination.
Internet routing protocols can be divided into intra-domain and inter-domain protocols, with inter-domain protocols communicating information between ASs, while intra-domain protocols are responsible for determining the forwarding of packets within each AS. This general architecture and the associated suite of protocols are rapidly becoming the de facto technology on which modem communication networks are built. This dominance extends from simple local area networks to large-scale, international carrier networks, and is largely due to the robustness and efficiency of networks built using it. In particular, IP networks are often referred to as “connectionless”, and the delivery of data packets to their intended destination is performed through a number of “independent” decisions made by the routers to which a packet is being forwarded.
SUMMARY OF THE INVENTION
It is therefore a feature and advantage of the present invention to provide an improved method and system for monitoring, tracking, and/or predicting the routing path of one or more packets under an IP protocol.
In accordance with one embodiment of the present invention, a method of identifying a path of travel for a packet in a multi-area domain operated according to a link state routing protocol includes the step of receiving topology information from a plurality of individual areas in a domain. It also includes the steps of identifying a plurality of intra-area least cost paths from the topology information, and assembling a subset of the plurality of intra-area least cost paths into an end-to-end path between a starting address and a destination address. Each least cost path preferably comprises a series of routers, with links or networks between routers.
Optionally and preferably, in the identifying step, at least one exit point from the first area through which the destination address is reachable is identified, at least one least cost path segment within the first area between the starting address and at least one of the exit points is constructed, and at least one of the least cost path segments is selected to result in at least one selected first area least cost segment. As an additional option, the exit point from first area may be the destination address. The identifying step may also include identifying all exit points from the first area through which the destination address is reachable.
The identifying step may also include the step of, for at least one of the exit points associated with at least one of the selected least cost path segments, identifying a second area within the domain to which said at least one exit point is connected. The identifying step may also include the steps of identifying at least one exit point from the second area through which the destination address is reachable, constructing at least one least cost path segment within the second area between the at least one exit point of the first area and at least one exit point of the second area, and selecting at least one of the least cost segments within the second area to result in at least one selected second ar
Guerin Roch
Rajan Rajendran
Ipsum Networks, Inc.
Lee Andy
Pepper Hamilton LLP
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