IEEE 802.5 Token Ring |
Description | Glossary | RFCs | Publications | Obsolete RFCs |
Type: | Physical and Data Link Layers. |
SNMP MIBs: | iso.org.dod.internet.mgmt.mib-2.dot5SrMIB (1.3.6.1.2.1.42). |
In IEEE 802.5, the token passing scheme is used in place of Carrier Sense Multiple Access with Collision Detection (CSMA/CD) on a ring topology local area network (LAN). A token is circulated around a network. The computer that has possession of the token has the right to transmit packets for a certain period of time. If that computer has no packets to transmit then the token is passed to the next computer. Only one computer at a time can transmit packets so this helps to avoid collision problems.
Token:
00 | 01 | 02 | 03 | 04 | 05 | 06 | 07 |
---|---|---|---|---|---|---|---|
Start Delimiter | |||||||
Access Control | |||||||
End Delimiter |
Abort:
00 | 01 | 02 | 03 | 04 | 05 | 06 | 07 |
---|---|---|---|---|---|---|---|
Start Delimiter | |||||||
End Delimiter |
IEEE 802.5 Frame:
Start Frame Delimiter and Control | IEEE 802.5 packet | FCS | Frame Delimiter and Status |
SFD, Start Frame Delimiter.
8 bits.
Js and Ks are infractions.
Js of ones. Ks of zeros. Signals the start of a token or packet.
00 | 01 | 02 | 03 | 04 | 05 | 06 | 07 |
---|---|---|---|---|---|---|---|
J | K | 0 | J | K | 0 | 0 | 0 |
Access Control. 8 bits.
00 | 01 | 02 | 03 | 04 | 05 | 06 | 07 |
---|---|---|---|---|---|---|---|
P2 | P1 | P0 | TI | M | PR2 | PR1 | PR0 |
Frame Control.
8 bits.
The frame contains data or control information.
00 | 01 | 02 | 03 | 04 | 05 | 06 | 07 |
---|---|---|---|---|---|---|---|
F1 | F0 | 0 | 0 | PC3 | PC2 | PC1 | PC0 |
Value Physical Control Field 0 Normal Buffer. 1 Express Buffer. 2 Purge. 3 Claim Token. 4 Beacon. 5 Active Monitor. 6 Standby Monitor.
IEEE 802.5. Packet for token networks:
00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15
Destination Address
Source Address
Data :::
Destination Addresses. 6 bytes.
Some specific format variations in MAC addressing scheme.
- Group addresses when the group/specific bit is set to 1. Broadcast addresses go to entire group on a network. Multicast addresses go to a subset group.
- Functional/nonfunctional addresses.
- Global/Local assigned addresses.
Source Addresses. 6 bytes.
Physical address.
Data Field. Variable length.
MAC or non-MAC information about the frames.
- Token Ring Hold Time. The maximum time a station may hold a token before transmitting the data.
- Adapter Driver Limit.
- Packet Size Limit.
FCS, Frame Check Sequence.
4 bytes.
Cyclic redundancy check (CRC) value.
EDEL, End Frame Delimiter.
10 bits.
Signals the end of a token or packet.
00 | 01 | 02 | 03 | 04 | 05 | 08 | 09 |
---|---|---|---|---|---|---|---|
J | K | 1 | J | K | 1 | IF | ED |
IF, Intermediate Frame.
If more frames follow in logical sequence, then this bit is set to 1. Otherwise it is cleared to zero.ED, Error Detection Indicator.
Set to 1 if a CRC error is detected in the frame.
Frame Status Field. 1 byte.
00 | 01 | 02 | 03 | 04 | 05 | 06 | 07 |
---|---|---|---|---|---|---|---|
ARI | FCI | 0 | 0 | ARI | FCI | 0 | 0 |
Good Frame.
(RFC 1513, page 5)
The 802.5 specification [Token Ring Access Method and Physical Layer
Specifications, Institute of Electrical and Electronic Engineers, IEEE Standard
802.5-1989, 1989.] defines the term "good frame" as a frame that is bounded by a
valid SD and ED, is an integral number of octets in length, is composed of only 0 and 1
bits between the SD and the ED, has the FF bits of the GC field equal to 00 or 01, has a
valid FCS, and has a minimum of 18 octets between the SD and the ED.
RFCs:
[RFC 1042] A Standard for the Transmission of IP Datagrams over IEEE 802 Networks.
[RFC 1239] Reassignment of Experimental MIBs to Standard MIBs.
[RFC 1271] Remote Network Monitoring Management Information Base.
[RFC 1469] IP Multicast over Token-Ring Local Area Networks.
[RFC 1513] Token Ring Extensions to the Remote Network Monitoring MIB.
[RFC 1748] IEEE 802.5 MIB using SMIv2.
[RFC 1749] IEEE 802.5 Station Source Routing MIB using SMIv2.
[RFC 948] TWO METHODS FOR THE TRANSMISSION OF IP DATAGRAMS OVER IEEE 802.3 NETWORKS.
[RFC 1231] IEEE 802.5 Token Ring MIB.
[RFC 1743] IEEE 802.5 MIB using SMIv2.
Description | Glossary | RFCs | Publications | Obsolete RFCs |