11.4. Differentiated Services
As shown in Figure 11-3, DiffServ redefines the 8-bit TOS field in IPv4 (or traffic class octet in IPv6) to enable as many as 64 classes of service to be defined. As specified in RFC 2474 and RFC 2475, class of service is expanded from simple priority labeling to become a policy-based system. Class-of- service forwarding decisions are made at every network node or hop through the network according to per-hop-behavior (PHB) rules.
Figure 11-3. DiffServ redefinition of the IPv4 IP header TOS field.
To provide backward compatibility with IP routers that use the TOS precedence bits, DiffServ defines those bits as class ...
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