Token Ring

Token Ring is becoming less popular with many organizations moving to Ethernet. Token Ring is discussed here because of it's importance in the history of NetBIOS and understanding of NetBIOS.

When IBM introduced Token-Ring, an emulator for NetBIOS was produced. The NetBIOS Extended User Interface (NetBEUI) was introduced in 1985. NetBIOS was no longer implemented only on a set of propriety protocols, but also on 802.2 frames. The implementation on Token-Ring was the first implementation over 802.2 and provides a reference model. Detailed information can be found in the IBM manual: IBM LAN Technical Reference, see Bibliography IBM LAN Technical Reference IEEE 802.2 and NetBIOS Application Program Interfaces.

A full description of Token Ring is beyond the scope of this document; some basic information on Token Ring and its use with NetBIOS is given below.

There are two kinds of Token Ring frames: Media Access Control (MAC) frames and Non-MAC frames. MAC frames carry Token Ring management information between nodes, Non-MAC frames carry user data. The non-MAC frames contain IEEE 802.2 Logical Link Control frames which in turn can contain NetBIOS frames.

Non-MAC Frame Structure

Table 1. Non-MAC Token Ring Frame Structure

Token Ring frame 802.2 Frame detail NBF frame
Start Delimiter (SDEL) 1 octet    
Access Control (AC) 1 octet
Frame Control (FC) 1 octet
Destination Address 6 octets
Source Address 6 octets
IEEE 802.2 Logical Link Control DSAP 2 octets
SSAP 2 octets
Control 1 or 2 octets
Data 46-1500 octets NetBIOS header
Optional data
Frame Check sequence (FCS) 4 octets
End Delimiter (EDEL) 1 octet    
Frame Status (FS) Check sequence 1 octet

Further information

Many manuals and documents describe Token-Ring in detail including

Novell's Guide to NetWare LAN Analysis, see Bibliography