The 7705 SAR-A, 7705 SAR-Ax, 7705 SAR-H, 7705 SAR-Hc, 7705 SAR-M, 7705 SAR-Wx, and 7705 SAR-X are able to fragment packets between Ethernet ports (which support jumbo frames) and TDM ports (which do not support jumbo frames). In this case, when a packet arrives from a port that supports jumbo frames and is routed to a port that does not support jumbo frames (that is, a TDM port) the packet will get fragmented to the port MTU of the TDM port.
For example, if a packet arrives on a 7705 SAR-A and is to be forwarded to a TDM port that has a maximum port MTU of 2090 bytes and a channel group configured for PPP with the port MTU of 1000 bytes (PPP port MTU), the following may occur.
If the arriving packet is 800 bytes, then forward the packet.
If the arriving packet is 1400 bytes and the DF bit is 0, then forward the packet, which will be fragmented to the PPP port MTU size.
If the arriving packet is 2500 bytes and the DF bit is 0, then forward the packet, which will be fragmented to the PPP port MTU size.