Multiprotocol Label Switching - Cisco BPX 8620 Installation And Configuration Manual

Chapter 1 The BPX Switch: Functional Overview
The MGX 8250 can act as a stand-alone edge concentrator or as a feeder node for the BPX switch.
Twenty-four service module slots are supported for the MGX 8250. The following interfaces are
supported for user traffic:
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Both the MGX 8230 and MGX 8250 support FRSM-VHS, Voice Service Module (VISM), and Route
Processor Module (RPM) cards. For information about VISM, refer to the Cisco Voice Interworking
Service Module Installation and Configuration Guide. For information about RPM, refer to the Cisco
Route Processor Module Installation and Configuration Guide.

Multiprotocol Label Switching

The BPX 8650 MPLS switch combines a BPX switch with a separate MPLS controller (Cisco Series
7200 or 6400 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 can 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:
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Release 9.3.30, Part Number 78-12907-01 Rev. E0, May 2005
Frame Relay (T1/E1 and T3/E3)
ATM UNI, FUNI, and optional inverse multiplexing for ATM (IMA)
Frame Relay to ATM network interworking and service interworking
CES (T1/E1 and T3/E3)
Destination
Precedence
Virtual Private Network membership
Quality of Service (QoS) information from RSVP
The route for the packet, as chosen by traffic engineering (TE)
Cisco BPX 8600 Series Installation and Configuration
BPX Switch Operation
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