| Note: I FatFingered the SMAC/DMAC originally. Homework grades will not be affected by this but I hope | |||||||||||||
| everyone will resubmit the correct ones later for the practice. | |||||||||||||
| I apologize for this oversight. I have done it before and I have no idea why I insist on getting this one wrong | |||||||||||||
| IEEE (Ethernet) Frame Types | |||||||||||||
| DIX Ethernet II (non-802.3 Compliant) | |||||||||||||
| Preamble/SFD | DMAC | SMAC | Type | Data | FCS | ||||||||
| 8 Bytes | 6 Bytes | 6 Bytes | 2 Bytes | 1500 Bytes | 4 Bytes | ||||||||
| DIX E'net treats the Data Link Layer as a single entity: a Destination Address, a Source Address, and a Destination Protocol | |||||||||||||
| Novel 802.3 Frame (non-802.3 Compliant, also called Novell Raw) | |||||||||||||
| Preamble/SFD | DMAC | SMAC | Length | FF | FF | Data | FCS | ||||||
| 8 Bytes | 6 Bytes | 6 Bytes | 2 Bytes | 1 Byte | 1 Byte | 1498 Bytes | 4 Bytes | ||||||
| 802.2 Frame (802.3 Compliant) | |||||||||||||
| Preamble/SFD | DMAC | SMAC | Length | DSAP | SSAP | Control | Data | FCS | |||||
| 8 Bytes | 6 Bytes | 6 Bytes | 2 Bytes | 1 Byte | 1 Byte | I Byte | 1497 Bytes | 4 Bytes | |||||
| 802.2 SNAP (802.3 Compliant) | |||||||||||||
| Preamble/SFD | DMAC | SMAC | Length | DSAP = AA | SSAP = AA | Control = 01 | Type | OUI | Data | FCS | |||
| 8 Bytes | 6 Bytes | 6 Bytes | 2 Bytes | 1 Byte | 1 Byte | I Byte | 2 Bytes | 3 Bytes | 1492 Bytes | 4 Bytes | |||
| 802.3 splits the data link into two parts: the Media Access Control part (MAC sublayer) and the Logical Link Control part (LLC sublayer) | |||||||||||||
| MAC | Hardware addresses | ||||||||||||
| Packet payload size | |||||||||||||
| LLC | Upper layer protocol (IPX/SPX or TCP/IP) | ||||||||||||
| Upper layer service type (SAP type) | |||||||||||||
| Frame Constituents: | |||||||||||||
| Preamble | 7 Bytes: | 01010101 | |||||||||||
| SFD (Start Frame Delimiter) | 1 Byte: | 10101011 | |||||||||||
| SMAC (Source Media Access Control Address) | 6 Bytes: | 3 Bytes assigned to vendor by IEEE | |||||||||||
| 3 Bytes assigned by vendor as unit identifier | |||||||||||||
| DMAC (Destination Media Access Control Address) | 6 Bytes: | 3 Bytes assigned to vendor by IEEE | |||||||||||
| 3 Bytes assigned by vendor as unit identifier | |||||||||||||
| Type | Greater than 1500 (decimal) or 0x5DC | ||||||||||||
| 0x800 (2048 decimal) = TCP/IP | |||||||||||||
| 0x806 (2054 decimal) = ARP/RARP from TCP/IP suite | |||||||||||||
| 0x8137 (33079 decimal) = IPX/SPX | |||||||||||||
| Length | Less than 1500 (decimal) or 0x5DC | ||||||||||||
| DSAP (Destination Service Access Point) | ISO identification of Upper lever protocols | ||||||||||||
| SSAP (Source Service Access Point) | Usually the same for both fields | ||||||||||||
| 0xE0 = Novell | |||||||||||||
| 0xF0 = NetBIOS | |||||||||||||
| 0x06 = TCP/IP | |||||||||||||
| 0xAA = SubNetwork Access Protocol (SNAP) | |||||||||||||
| Control | Usually 0x01 (Unnumbered information, i.e., data) | ||||||||||||
| OUI (Organizationally Unique Identifier) | Allowed vendors to develop a wider array of | ||||||||||||
| upper level services | |||||||||||||
| FCS (Frame Check Sequence) | A CRC error check on the frame to detect transmission errors | ||||||||||||
| Note: The fields added after the length in the 802.3 frame are called the 802.2 sub-header. It is commonly called the Logical Link Control (LLC) header | |||||||||||||
| The ethernet implementation (LLC1) does not perform any session control functions. IBM uses another version (LLC2) that does perform such functions | |||||||||||||
| Standard ethernet (E'net) parameters (for 10BASE E'net): | |||||||||||||
| Minimum Frame Size: | 512 bits/64 bytes | ||||||||||||
| Maximum Frame Size: | 12144 bits/1518 bytes | ||||||||||||
| PDU (Protocol Data Unit or Payload) | 12000 bits/1500 bytes | ||||||||||||
| Interframe Gap | 96 bits/12 bytes (= 9.6 micros sec.) | ||||||||||||
| Fast ethernet uses the same bit restrictions but the interframe gap is reduced to 0.96 microseconds | |||||||||||||