Because 852 is a full featured tunneling protocol, it can be repurposed to solve some uncommonly difficult integration problems. The 852 protocol is not limited merely for routing from a CN channel over IP to another CN channel. But can be used to build multi-tier backbones on IP with routers that route from one IP-852 channel to another IP-852 channel. This can be used to support backbones with more than the maximum number of 852 devices on a single 852 channel. The maximum number of 852 devices on a channel is 256 but practical bandwidth limitations of the individual devices means the practical limit is much lower. The block diagram of an 852 to 852 bridging router is shown below.
Fig. 2.5: 852 Bridging Router Architecture
If both 852 channels share the same IP channel then this is called an 852 to 852 bridging router. In this mode one 852 bridging router is an IP bridge between two logical 852 channels. So it looks like a CN router to any CN devices. When acting in bridging router mode, the router is a member of two logical 852 channels sharing one ethernet interface. The router bridges traffic between the two 852 IP channels. This allows one to overcomes limitations on the number of 852 devices per channel and provides for enhanced scalability by partitioning the 852 traffic seen by any given router. Moreover on a WAN where some IP channels are very low bandwidth such as a cellular network and some high bandwidth, this allows partitioning of the high bandwidth 852 devices from the low bandwidth 852 devices. The Adept GR4 uniquely supports 852 bridging router mode.