CISCO GSR与Juniper骨干路由器比较( 二 )

Finally, the PFE delivers maximum stability during exceptional conditions, while also providing a significantly lower part count. This stability reduces power consumption and increases mean time between failure.
Flexible PIC Concentrators
The FPCs house PICs and connect them to the rest of the PFE. There is a dedicated, full-duplex 3.2-Gbps channel between each FPC and the core of the PFE.
You can insert up to eight FPCs in an M40 chassis. The OC-48c/STM-16 PIC occupies an entire FPC. Otherwise, each FPC supports up to four PICs in any combination, providing unparalleled interface density and configuration flexibility. Each FPC contains shared memory for storing data packets received; the Distributed Buffer Manager ASICs on the SCB manage this memory. In addition, the FPC houses the I/O Manager ASIC, which performs a variety of queue management and class-of-service functions.
Physical Interface Cards
PICs provide a complete range of fiber optic and electrical transmission interfaces to the network. The M40 router offers flexibility and conserves rack space by supporting a wide variety of PICs and port densities. All PICs occupy one of four PIC spaces per FPC except for the OC-48c/STM-16 PIC, which occupies an entire FPC slot. An additional Tunnel Services PIC enables the M40 router to function as the ingress or egress point of an IP-IP unicast tunnel, a Cisco generic routing encapsulation (GRE) tunnel, or a Protocol Independent Multicast - Sparse Mode (PIM-SM) tunnel.
For a list of available PICs, see the M-series Internet Backbone Routers Physical Interface Cards datasheet.
System Control Board
Hosting the Internet Processor II ASIC, the SCB performs sampling, filtering, and packet forwarding decisions. The SCB also houses a processor that processes exception and control packets, monitors system components, and controls FPC resets.
Routing Engine
The Routing Engine maintains the routing tables and controls the routing protocols, as well as the JUNOS software processes that control the router’s interfaces, the chassis components, system management, and user access to the router. These routing and software processes run on top of a kernel that interacts with the PFE. _ The Routing Engine processes all routing protocol updates from the network, so PFE performance is not affected.
_ The Routing Engine constructs and maintains routing tables with a complete set of Internet features and provides full flexibility for advertising, filtering, and modifying routes. Routing policies are set according to route parameters, such as prefixes, prefix lengths, and BGP attributes.
JUNOS Internet Software
JUNOS software is optimized to scale to large numbers of network interfaces and routes. The software consists of a series of system processes running in protected memory on top of an independent operating system. The modular design improves reliability by protecting against system-wide failure and by preventing the failure of one process from affecting the other software processes. JUNOS software offers unmatched configuration flexibility by providing an XML-based JUNOScript? API in addition to the CLI interface.
总结和观点
CISCO从1984年开发出他的第一台路由器到今天网络技术发展经历的是一个多元化到IP统一的发展过程,其实至今网络应用中也还存在大量的SNA、AppleTalk、TokenRing、FDDI等。CISCO长期占据市场绝对优势也在于他的产品可以提供完全的解决方案。到今天，这成了CISCO的优势，也在一定程度上成为了CISCO的包袱。
我们再看看Juniper推出第一台路由器的时候，IP统一的趋势已经浮出水面，骨干网络上IP与ATM的争论也几乎证实骨干网络上跑IP数据包将成为技术发展趋势。这时候Juniper推出第一台骨干路由器，他就看准了IP技术这一个潮流。他没有这个包袱，而且不准确的说可能至今Juniper还没有推出支持SNA、AppleTalk、TokenRing、FDDI的路由器。