Related Concepts

DS Field

To implement DiffServ, the ToS field in an IPv4 header is redefined in relevant standards and then called the Differentiated Services (DS) field. In the DS field, higher two bits are reserved and lower six bits are the DS codepoint (DSCP).

PHB

Per-Hop Behavior (PHB) is used to describe the next action on packets with the same DHCP. Commonly, PHB contains traffic traits, such as delay and packet loss rate.

The IETF defines the existing three standard PHBs: Expedited Forwarding (EF), Assured Forwarding (AF), and Best-Effort (BE). BE is the default PHB.

CT

To provide differentiated services, DS-TE divides the LSP bandwidth into one to eight parts, each part corresponding to a CoS. Such a collection of bandwidths of an LSP or a group of LSPs with the same service class are called a CT. A CT can transmit only the traffic of a CoS.

Defined by the IETF, DS-TE supports up to eight CTs, marked CTi, in which i ranges from 0 to 7.

TE-Class

A TE-class refers to a combination of a CT and a priority, in the format of <CT, priority>.

The priority is the priority of a CR-LSP in a TE-class mapping table, not the EXP value in the MPLS header. The priority value is an integer ranging from 0 to 7. The smaller the value, the higher the priority is. When you create a CR-LSP, you can set the setup and holding priorities for it and CT bandwidth values. A CR-LSP can be established only when both <CT, setup-priority> and <CT, holding-priority> exist in a TE-class mapping table. Assume that the TE-class mapping table of a node contains only TE-Class [0] = <CT0, 6> and TE-Class [1] = <CT0, 7>, only the following three types of CR-LSPs can be successfully set up:

• Class-Type = CT0, setup-priority = 6, holding-priority = 6
• Class-Type = CT0, setup-priority = 7, holding-priority = 6
• Class-Type = CT0, setup-priority = 7, holding-priority = 7

The combination of setup-priority = 6 and hold-priority = 7 does not exist because the setup priority cannot be higher than the holding priority on a CR-LSP.

CTs and priorities can be in any combination. Therefore, there are 64 TE-classes theoretically. The NE20E supports a maximum of eight TE-classes, which are specified by users.

DS-TE Modes

DS-TE has two modes:

• IETF mode: The IETF mode is defined by the IETF and supports 64 TE-classes by combining 8 CTs and 8 priorities. The NE20E supports up to 8 TE-classes.

• Non-IETF mode: The non-IETF mode is not defined by the IETF and supports 8 TE-classes by combining CT0 and 8 priorities.

TE-class mapping table

The TE-class mapping table consists of a group of TE-classes. On the NE20E, the TE-class mapping table consists of a maximum of 8 TE-classes. It is recommended that the same TE-class mapping table be configured on all LSRs on an MPLS network.

BCM

The Bandwidth Constraints Model (BCM) is used to define the maximum number of Bandwidth Constraints (BCs), which CTs can use the bandwidth of each BC, and how to use BC bandwidth.