Nokia 7705 - 6.4.4.1 DCR Frequencies

System Management
228
Basic System Configuration Guide
3HE 11010 AAAC TQZZA Edition: 01
In each direction, the service clock is compared to the common clock and the
difference is encoded into the RTP header in the TDM PW overhead. At the other
end of the network, the original service clock is reproduced by comparing the
common clock to the frequency difference in the RTP header. Figure 12 shows an
example of a network using DCR.
Figure 12 Differential Clock Recovery on a Network
RTP headers are disabled by default and must be enabled for all circuit emulation
services that require DCR. RTP must be enabled for the TDM PW that uses channel
group 1. All channel groups on the same DS1 or E1 channel must be configured for
the same mode of operation.
To achieve the best DCR performance, it is recommended that you use a Layer 1
network synchronization method to ensure the common clock has the best stability.
If a timing-over-packet technique is used to transfer the common clock, then the
number and type of nodes, the traffic profile, and the temperature variations will
affect DCR synchronization performance. As well, a packet rate of at least 200 pps
is recommended (up to 4000 pps is supported). Packet rates lower than 200 pps may
affect system performance.
6.4.4.1 DCR Frequencies
Each DS1, E1, DS3, or E3 circuit configured with DCR executes its own clock
recovery from the packet stream. This allows each circuit to have an independent
frequency.
TDM
Service
Clock
PRC
22418
IWF
CE CE
TDM TDM
Recovered
TDM timing
based on the
differential
timing
messages
Packet
Switched
Network
Synchronization
Network
PRC
IWF
Synchronization
Network