Information Technology Reference
In-Depth Information
Early Token Release (ETR)
In a normal token ring operation, the station that transmitted the data frame removes it and then
generates a free token.
With ETR, a token is released immediately after the sending station transmits its frame. The
sending station does not wait for the data frame to circle the ring. ETR is only available on
16 Mbps rings. Stations running ETR can coexist with stations not running ETR. With ETR,
a free token can circulate the ring with multiple data frames.
On supported router platforms, early token release is configured as follows:
interface token 0
early-token-release
Ring Insertion
The process for a station to insert into the token ring follows five phases:
•
Phase 0—Lobe media test
•
Phase 1—Physical insertion
•
Phase 2—Address verification
•
Phase 3—Participation in ring poll
•
Phase 4—Request initialization
Phase 0: Lobe Media Test
The first step when a token ring device is inserted is the lobe media test. The transmitter and
receiver of the adapter and the cable between the adapter and the MSAU are tested in this phase.
Phase 1: Physical Insertion
In phase 1, the adapter opens a relay on the MSAU. After the MSAU opens, the adapter
determines an AM is present on the ring, which indicates successful completion of phase 1.
Phase 2: Address Verification
This phase verifies that the MAC address is unique to the ring. This phase can detect if two
Locally Administered Addresses (LAAs) are configured with the same MAC address. This
phase is also called the
duplicate address test
.
Phase 3: Participation in Ring Poll
In this phase, the station learns its upstream neighbor's address and informs its downstream
neighbor of the inserting adapter's address and produces a station list. If the adapter success-
fully participates in a ring poll, it proceeds into the final phase of insertion.
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