Networking Guide
Chapter 4, Administering SCO IPX/SPX

medium-access protocols

medium-access protocols

Medium-access protocol implementations define the addressing that distinguishes each node on a NetWare network. This addressing is implemented within the hardware of each network interface controller (NIC).

A number of medium-access protocols are defined, many of which are used with NetWare. The focus within this document is on the implementations of medium-access protocols, the most common of which are:

The 802.x protocols are defined by the Institute of Electrical and Electronic Engineers (IEEE). Ethernet version 2.0 was co-developed by XEROX and Digital Equipment Corporation. These medium-access protocol implementations are primarily concerned with the transport of packets from one node to another on a single network segment. 

To move a packet to the proper node on a network, a medium-access control (MAC) header is placed at the beginning of every packet. This header contains address fields for both the source and destination nodes to indicate where the packet originated and where it is going. Each NIC checks the destination address in the MAC header of each packet sent on the network segment to which it is attached. If the destination address matches the NIC's own address, or if the packet is a broadcast packet intended for all nodes, the NIC will copy the packet. 

Error-checking

Two types of error-checking can be performed:

Medium-access protocols provide bit-level error-checking in the form of a cyclic redundancy check (CRC). This CRC, which is appended to every packet that is transmitted, assures that virtually all of the packets successfully received will be free of corruption. In view of this level of integrity, NetWare does not provide any additional bit-level error-checking within any of its upper-level protocols. Bit-level error-checking and node-addressing are provided by the majority of medium-access protocol implementations.