Download (direct link):
request message containing an ER-hop TLV which it does not support, the LSR will not progress the label message to the next hop downstream LSR and it will send back a no route notification message. The L bit is used to indicate whether the ER-hop is loose or strict (see Section 6.2.3). The contents field contains a node or an abstract node representing a group of nodes.
THE CONSTRAINED-BASED ROUTING LABEL DISTRIBUTION PROTOCOL
Route pinning is applicable to segments of a CR-LSP that are loosely routed. It is signaled using the route pinning TLV. The resource classes that can be used to set up an CR-LSP are indicated in the resource class TLV.
The preemption TLV is used to assign a setup priority and a holding priority of the CR-LSP. These priorities are used to determine if the new CR-LSP can preempt an existing one. Assigning a higher holding priority means that the CR-LSP, once it has been set up, has a low chance of being preempted. Assigning a high setup priority means that, in the case that resources are unavailable, the CR-LSP has a high chance of preempting existing CR-LSPs.
The traffic parameters TLV is used to signal the values of the traffic parameters that characterize the CR-LSP that is being established. This TLV will be discussed in detail in Section 7.2.4.
7.2.3 The Label Mapping Message
The label mapping message is shown in Figure 7.14. The U bit is set to 0, and the message type set to label mapping (0x0400). The FEC and LSPID TLVs are the same as in the CR-LDP label request message. The label TLV is the same as in LDP (see Figure 7.8). The label request message id TLV is used as follows. If this label mapping message is a response to a label request message, then it must include the label request message id parameter. This parameter is carried in the label request message id TLV. The traffic parameters TLV is described in the next section.
7.2.4 The Traffic Parameters TLV
The traffic parameters TLV is used in the label request and label mapping messages. It is used to describe the traffic parameters of the CR-LSP that is being established. The traffic parameters TLV is shown in Figure 7.15. The traffic parameters TLV type is 0x0810, and the length of the value field is 24 bytes. The following fields have been defined: flags, frequency, weight, peak data rate (PDR), peak burst size (PBS), committed data rate
0 12 3
Label mapping (0x0400)
Label request message id TLV
LSPID TLV (optional)
Traffic parameters TLV (optional)
Figure 7.14 The label mapping message.
LABEL DISTRIBUTION PROTOCOLS
0 12 3
Peak data rate (PDR)
Peak burst size (PBS)
Committed data rate (CDR)
Committed burst size (CBS)
Excess burst size (EBS)
Figure 7.15 The traffic parameters TLV.
(CDR), committed burst size (CBS) and excess burst size (EBS). The PDR and the PBS parameters are used to define the traffic sent to the CR-LSP. The parameters CDR, CBS, and EBS, are used to specify how the network will police the traffic submitted to the CD-LSP. Finally, the flags, frequency, and weight fields are used to provide additional information as will seen below.
Peak data rate (PDR) and peak burst size (PBS)
The peak rate is the maximum rate at which traffic is sent to the CR-LDP, and is expressed in bytes/sec. The equivalent parameter in ATM is the peak cell rate (PCR). Unlike the PCR, which is specified by a single value, the peak rate in CR-LDP is specified in terms of token bucket P. The maximum token bucket size of P is set equal to the peak burst size (PBS), expressed in bytes, and the token bucket is replenished at the peak data rate (PDR), expressed in bytes/sec. The PBS defines the maximum packet size that can be sent to the CR-LSP, and the PDR gives the maximum rate at which traffic is transmitted by the user. The peak rate, is the output from the token bucket P , which is sent to the CR-LSP.
The token bucket operates as follows:
• Initially, the token count (i.e., the number of tokens in the token bucket) is TP = PBS.
• Let PDR = N bytes/sec. Then, if TP < PBS, the token count TP is incremented every second by N (it should not exceed PBS).
• When a packet of size B bytes arrives, if TP — B > 0, then the packet is not in excess of the peak rate, and TP = TP — B.