On an IP RAN shown in Figure 1, NodeBs need to implement only frequency synchronization rather than phase synchronization; devices on an MPLS backbone network do not support 1588v2; the RNC-side device is connected to an IPCLK server; closed subscriber groups (CSGs) support 1588 ACR.
NodeB2 transmits wireless services along an Ethernet link to the other CSG.
On the preceding network, CSGs support 1588 ACR and function as clients to initiate requests for Layer 3 unicast connections to the upstream IPCLK server. The CSGs then exchange 1588v2 messages with the IPCLK server over the connections, achieving frequency recovery. BITS1 and BITS2 are configured as clock servers for the CSGs to provide protection.
The CSG transmits NodeB2 frequency information either along a synchronous Ethernet link or by sending 1588v2 messages. In this manner, both NodeBs connected to the CSGs can achieve frequency synchronization.