SPECIAL REPORT: Understanding IP ROUTERS
Aug 1, 2006 12:00 PM, BY CIPRIAN POPOVICIU
Router architecture
With the rapid adoption of IP, more is required of IP networks and IP routers. Large amounts of traffic must be switched with minimal packet loss, and time-sensitive applications require packet delivery with minimal delay and jitter. These requirements demand high-performance router architectures that leverage powerful processors or the implementation of forwarding functions into hardware. Figure 4 on compares software and hardware router architectures.
Figure 3. A representation of IP packet forwarding operation Click image to enlarge.
A router's position within the network dictates its required capabilities. Core routers must forward large amounts of traffic, a capability that can be implemented in hardware, while edge routers must support a rich set of features and functions that might not be suited for full hardware implementations. Their price and flexibility ultimately dictates the router selection for specific roles within a network.
Advanced router features
IP has outgrown its original scope of simply transporting data between two end points. It is now used to deliver a wide variety of services, each service requiring advanced functionalities and feature support by the IP routers. For example:
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Voice, audio and video services require a certain QoS to be enforced. Thus, routers support a set of congestion avoidance, congestion management and resource management mechanisms that enable them to treat IP packets based on the service requirements.
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Content delivery and collaborative services are supported in a scalable manner by enabling the IP networks and their routers to optimally multicast packets from a source to a set of listeners.
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Figure 4. A representation of router designs Click image to enlarge.
Traffic control and security concerns require routers to be capable of filtering traffic based on certain parameters and to make more complex forwarding decisions than simply looking up the packet destination address in the forwarding table.
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The operation of today's networks requires routers to support various additional control and management protocols.
These functions — some integrated in hardware while others handled exclusively by the CPU — stand witness to the extraordinary evolution of the IP router from its original, basic IP switching role to its current critical role in supporting complex services.
Ciprian Popoviciu, PhD, CCIE, is a technical leader within the Networked Solutions Integration Test Engineering (NSITE) group at Cisco Systems.
Ciprian is an author of “Deploying IPv6 Networks,” a comprehensive guide to IPv6 concepts, service implementation and existing interoperability in IPv4 environments. It's available from Cisco Press at www.ciscopress.com/title/1587052105.
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