Understanding the network.pdf - Back to Home

• Ring timing maintenance—The AM provides two ring time-related functions.
The first is to maintain the ring's master reference clock for timing data
transmission and management functions. On a 4Mbps ring, the transmission
clock rate is 8MHz. On a 16Mbps ring, the transmission clock is 32MHz. The
token, which is originated by the AM, is used by each station to maintain ring
timing and its local transmitter clock. The AM is responsible for adjusting the
ring's reference clock to accommodate for jitter, which phase shifts in the
ring's timing due to environmental characteristics that exist in the ring. Many
of the Token Ring operations are managed through the use of different
protocol timers to measure essential ring communication functions on the
ring. So, accurate timing is essential for the ring's proper operation.
• In addition to maintaining the ring's reference clock, the AM is also
responsible for maintaining the ring's transmission delay. In order to ensure
that the entire transmitted token reaches the destination station before
being returned to the sending station, a transmission delay is needed. The
AM inserts a 24-bit delay pattern into the ring to provide enough delay to
ensure proper token processing.
After the ring has an active monitor, the remaining stations on the ring function as
standby monitors (SMs). As each station completes the ring insertion process,
verifying the existence of an active monitor, it assumes the role of an SM. The SM's
primary function is to monitor the ring for errors and the presence of an active
monitor. If an SM fails to detect an active monitor at any time, the SM can initiate
the token claiming process.
The Ring Error Monitor (REM) is the one of the more important management server
definitions in the IBM Token Ring architecture. The REM collects ring error reports
from stations that have detected ring error conditions. Its purpose is to provide a
central point for collecting troubleshooting information on types of errors that occur
on the ring. The REM is typically not a normal ring station; rather, the REM is a
dedicate station running management software, like IBM's LAN Manager or a
dedicated network monitoring probe or protocol analyzer.
The Ring Parameter Server (RPS), like the REM, is defined as part of the IBM Token
Ring architecture specification. The RPS's function is to provide ring initialization
parameters to each new station that is inserted into the ring. One of the RPS most
important functions is the monitoring of the ring's station density. In the event that
a new station inserted into the ring exceeds the maximum numbers of stations
permitted on the ring, the RPS notifies the station and the station removes itself
from the ring. Additionally, the RPS maintains a list of all the active stations
according to their station address, mircocode level, and NAUN address.
The Configuration Report Server (CRS) is essentially the IBM LAN Manager console.
Its role is to collect information on the overall operation of the ring. This information