This attribute specifies the AND mask for the IP TOS byte for overwriting an IPv4 packet's TOS value or IPv6 packet's Traffic Class value. The IP packet TOS byte is bitwise ANDed with TosAndMask, then the result is bitwise ORed with TosORMask and the result is written to the IP packet TOS byte. A value of 'FF'H for TosAndMask and a value of '00'H for TosOrMask means that the IP Packet TOS byte is not overwritten.

This combination is reported if the referenced parameter is not present in a QOS Parameter Set. The IP TOS octet as originally defined in RFC 791 has been superseded by the 6-bit Differentiated Services Field (DSField, RFC 3260) and the 2-bit Explicit Congestion Notification Field (ECN field, RFC 3168). The IPv6 Traffic Class octet RFC 2460 is consistent with that new definition. Network operators SHOULD avoid specifying values of TosAndMask and TosORMask that would result in the modification of the ECN bits. In particular, operators should not use values of TosAndMask that have either of the least-significant two bits set to 0. Similarly, operators should not use values of TosORMask that have either of the least-significant two bits set to 1. Even though this attribute is only enforced by the CMTS, the CM reports the value as signaled in the referenced parameter.