3com S7906E 설치 설명서

 

1-3 

MPLS TE mainly accomplishes two functions: 

z

 

Static Constraint-based Routed LSP (CR-LSP) processing to create and remove static CR-LSPs. 
The bandwidth of LSPs must be configured manually. 

z

 

Dynamic CR-LSP processing to handle three types of CR-LSPs: basic CR-LSPs, backup CR-LSPs 
and fast rerouted CR-LSPs. 

Static CR-LSP processing is simple, while dynamic CR-LSP processing involves four phrases: 
advertising TE attributes, calculating paths, establishing paths, and forwarding packets. 

MPLS TE must be aware of dynamic TE attributes of each link on the network. This is achieved by 
extending link state-based IGPs such as OSPF and IS-IS.  

OSPF and IS-IS extensions add to link states such TE attributes as link bandwidth, color, among which 
maximum reservable link bandwidth and non-reserved bandwidth with a particular priority are most 
important. 

Each node collects the TE attributes of all links on all routers within the local area or at the same level to 
build up a TE database (TEDB). 

Link state-based routing protocols use Shortest Path First (SPF) to calculate the shortest path to each 
network node. 

In MPLS TE, the Constraint-based Shortest Path First (CSPF) algorithm is used. It is derived from SPF 
and makes calculation based on two conditions:  

z

 

Constraints on the LSP to be set up with respect to bandwidth, color, preemption/holding priority, 
explicit path and other constraints. They are configured at the LSP ingress. 

z

 

TEDB 

What CSPF does to identify the shortest path to an LSP egress is first pruning TE attribute incompliant 
links from the TEDB and then performing SPF calculation  

When setting up LSP tunnels, you may use two types of signaling: CR-LDP and RSVP-TE. Both can 
carry constraints such as LSP bandwidth, some explicit route information, and color and deliver the 
same function. 

They are different in that CR-LDP establishes LSPs using TCP while RSVP-TE using raw IP. 

RSVP is a well-established technology in terms of its architecture, protocol procedures and support to 
services; while CR-LDP is an emerging technology with better scalability. 

Only RSVP-TE is supported on S7900E series. 

Packets are forwarded over established tunnels. 

Unlike ordinary LSPs established based on routing information, CR-LSPs are established based on 
criteria such as bandwidth, selected path, and QoS parameters in addition to routing information.