Per-hop behaviour

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In computer networking, per-hop behaviour (PHB) is a term used in differentiated services (DiffServ) or multiprotocol label switching (MPLS). It defines the policy and priority applied to a packet when traversing a hop (such as a router) in a DiffServ network.

Rule that governs how packets are handled within a diffserv[1] network is called the Per-Hop Behavior (PHB). PHBs are defined to support the general properties controlled by IP precedence. DSCP Contains 6-bits, PHBs are created (one for each combination of the top 3 bits) of the form bbb000 to match the precedence behaviors and leaves the other DSCP values open where each b may take the value zero or 1.

DSCP Bit Settings Meaning
000000 Best effort
bbb000 Conforms to the requirements of Type of Service queuing precedence
bbbbb0 Available for standardization
bbbb11 For experimental of local network usage
bbbb01 For experimental of local network usage, but may be taken for standardization


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