Cisco BPX 8600 Series, Руководство по установке и настройке

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Cisco BPX 8600 Series Installation and Configuration
Release 9.3.0, Part Number 78-10674-01 Rev. D0, July 2001
Chapter 1 The BPX Switch: Functional Overview
BPX Switch Operation
The BPX Switch with MGX 8220 Shelves
Many network locations have increasing bandwidth requirements due to emerging applications and the
confluence of voice, data, and video digital communications. To meet these requirements, you can
overlay your existing narrowband networks with a backbone of BPX switches to utilize the high-speed
connectivity of the BPX switch operating at up to 19.2 Gbps with its T3/E3/OC-3/OC-12 network and
service interfaces.
The BPX switch service interfaces include BXM ports on the BPX switch and service ports on MGX
8220 shelves. The MGX 8220 shelves may be co-located in the same cabinet as the BPX switch,
providing economical port concentration for T1/E1 Frame Relay, T1/E1 ATM, CES, and FUNI
connections.
Multiprotocol Label Switching
The BPX 8650 MPLS switch combines a BPX switch with a separate MPLS controller (Cisco Series
7200 router). By integrating the switching and routing functions, MPLS combines the reachability,
scalability, and flexibility provided by the router function with the traffic engineering optimizing
capabilities of the switch.
Multiprotocol Label Switching (MPLS) is a high-performance method for forwarding packets (frames)
through a network. It enables routers at the edge of a network to apply simple labels to packets (frames).
ATM switches or existing routers in the network core can switch packets according to the labels with
minimal lookup overhead.
MPLS integrates the performance and traffic management capabilities of Data Link Layer 2 with the
scalability and flexibility of Network Layer 3 routing. It is applicable to networks using any Layer 2
switching, but has particular advantages when applied to ATM networks. It integrates IP routing with
ATM switching to offer scalable IP-over-ATM networks.
In contrast to label switching, conventional Layer 3 IP routing is based on the exchange of network
reachability information. As a packet traverses the network, each router extracts all the information
relevant to forwarding from the Layer 3 header. This information is then used as an index for a routing
table lookup to determine the packet’s next hop. This is repeated at each router across a network. At
each hop in the network, the optimal forwarding of a packet must be again determined.
The information in IP packets, such as IP Precedence information and information on Virtual Private
Network membership, is usually not considered when forwarding packets. Thus, to get maximum
forwarding performance, typically only the destination address is considered. However, because other
fields could be relevant, a complex header analysis must be done at each router that the packet meets.
The main concept of MPLS is to include a label on each packet.
Packets or cells are assigned short, fixed length labels. Switching entities perform table lookups based
on these simple labels to determine where data should be forwarded.
The label summarizes essential information about routing the packet:
• Destination
• Precedence
•
Virtual Private Network membership
• Quality of Service (QoS) information from RSVP
• The route for the packet, as chosen by traffic engineering (TE)