IEEE 802 3AS-2006 pdf free download – IEEE Standard for Information technology— Telecommunications and information exchange between systems— Local and metropolitan area networks— Specific requirements Part 3: Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications.
b) If the value of this field is greater than or equal to 1536 decimal (equal to 0600 hexadecimal), then the Length/Type field indicates the nature of the MAC client protocol (Type interpretation). 19 The Length and Type interpretations of this field are mutually exclusive. When used as a Type field, it is the responsibility of the MAC client to ensure that the MAC client operates properly when the MAC sublayer pads the supplied MAC client data, as discussed in 3.2.7.
Regardless of the interpretation of the Length/Type field, if the length of the MAC Client Datadata field is less than the minimum required for proper operation of the protocol, a PADPad field (a sequence of octets) will be added at the end ofafter the MAC Client Datadata field but prior to the FCS field, specified below. The procedure that determines the size of the PADPad field is specified in 4.2.8. The Length/Type field is transmitted and received with the high order octet first.
NOTE—Clause 12 of IEEE Std 802a-2003 (an amendment to IEEE Std 802) defines a set of Type values and associated mechanisms for use in prototype and vendor-specific protocol development.
Change subclause 3.2.7 as follows: 3.2.7 MAC Client Data fieldData and PAD fields The MAC Client Datadata field contains a sequence of n octets. Full data transparency is provided in the sense that any arbitrary sequence of octet values may appear in the MAC Client Datadata field up to a maxi- mum field lengthnumber specifieddetermined by the particular implementation of the standard that is used. A minimum frame size is required for correct CSMA/CD protocol operation and is specified by the par- ticular implementation of the standard. If necessary, the data field is extended by appending extra bits (that is, a pad) in units of octets after the data field but prior to calculating and appending the FCS. The size of the pad, if any, is determined by the size of the data field supplied by the MAC client and the minimum frame size and address size parameters of the particular implementation. The maximum size of the data field is determined by the maximum frame size and address size parameters of the particular implementation. Ethernet implementations shall support at least one of three maximum MAC Client Data field sizes defined as follows: a) 1500 decimal—basic frames (see 1.4.x) b) 1504 decimal—Q-tagged frames (see 1.4.344) c) 1982 decimal—envelope frames (see 1.4.y) If layer management is implemented, frames with a MAC Client Data field larger than the supported maxi- mum MAC Client Data field size are counted. It is recommended that new implementations support the transmission and reception of envelope frames, item c) above.
NOTE 1 —The envelope frame is intended to allow inclusion of additional prefixes and suffixes required by higher layer encapsulation protocols (see 1.4.x) such as those defined by the IEEE 802.1 working group (such as Provider Bridges and MAC Security), ITU-T or IETF (such as MPLS). The original MAC Client Data field maximum remains 1500 octets while the encapsulation protocols may add up to an additional 482 octets. Use of these extra octets for other pur- poses is not recommended, and may result in MAC frames being dropped or corrupted as they may violate maximum MAC frame size restrictions if encapsulation protocols are required to operate on them.
NOTE 2 — All IEEE 802.3 MAC frames share a common format. The processing of the three types of MAC frames is not differentiated within the IEEE 802.3 MAC, except for management. However, they may be distinguished within the MAC client.IEEE 802 pdf download.