Appendix A: Examples from Commercial Systems

This appendix will use commercial systems to help illustrate some of the hardware and software architectural points discussed in the earlier chapters. This is intended only to outline the key features based on public information (feature sheets available on the manufacturer Web sites and books) and not provide a detailed description.

In keeping with the common thread in this book, we will look at IP Routers and consider two manufacturers: Cisco Systems and Juniper Networks. The two products considered are core routers, i.e., multi-board systems. Readers are encouraged to look up the Web sites of these vendors (www.cisco.com and www.juniper.net) for up-to-date information about their products. In addition, readers should also check out the information provided by other router manufacturers like Avici Systems, Extreme Networks, Foundry Networks, Netgear, Nortel Networks, and Riverstone Networks.

Juniper Networks M-Series Routers

Juniper Networks first started out making routers for the core of the Internet, where high data rates and large traffic volumes are the most important considerations. The company has subsequently branched out into edge routers, further strengthened by its acquisition of Unisphere Networks in 2002. The specific focus in our discussion will be on the M-series routers running the Junos™ software.

The M-series routers range from the M5, with 5 Gbps throughput, to the M160, with 160 Gbps throughput. For illustration, we will consider the M160, which has 2 chassis per rack and 32 PICs (Physical Interface Cards) per chassis and also provides switch fabric and routing engine redundancy. This type of router is an example of a multi-board system using the Single Control Card + Multiple Line Card Architecture. The Routing Engine is the control card running the Junos™ software, and it uses an Intel-based PCI platform. It uses a dedicated connection to the Packet Forwarding Engine (similar to the switch fabric) for changing the forwarding tables used by the PFE for switching traffic.

The Junos™ software is based on a protected memory design in which one process cannot corrupt another. This facility is also useful for in-service upgrades of specific software modules, a feature provided by the fact that Junos is not a 'monolithic code base.'

The key processes in the system include:

  1. Routing Protocol Processes

  2. Interface Process-to configure and control the various interfaces

  3. SNMP and MIB-II Process-for management from an external SNMP manager

  4. Management Process-for managing the other processes in the system, including the CLI and restarting processes that have failed

  5. Routing Kernel Process-used for communication with the Packet Forwarding Engine regarding the forwarding table changes

The architecture is similar to IPS except for the presence of additional processes like the Interface Process and the Management Process. A multi-board implementation of IPS would need to have processes similar to the ones in Junos.

For management, Junos offers both a CLI- and an XML-based API called JunosScript.

Apart from these, the router can also be configured via SNMP.



Designing Embedded Communications Software
Designing Embedded Communications Software
ISBN: 157820125X
EAN: 2147483647
Year: 2003
Pages: 126
Authors: T. Sridhar

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