Hello, dear friends!
Today, I'd like to share with you a knowledge point. The details are as follows:
Link-layer standard GFP (Generic Framing Procedure) (G.7041) overcomes IP over PPP/HDLC over SDH, IP over Multi-Link PPP over SDH can only avoid point-to-point logical topology Structure, need to have a specific frame delimiter byte, need to scramble the load in the frame and many other shortcomings. Compared with the original similar protocol (PPP/LAPS), GFP has the following main features: adopting a frame delimiting method similar to ATM technology, reducing the positioning byte overhead, avoiding the impact of transmission content on transmission efficiency; breaking the link-layer The adaptation protocol can only support the limitations of the point-to-point topology and can support different topologies. By introducing the concept of multiple service levels, GFP can implement the simple function of bandwidth control.
Compared with PPP, the technical advantages of GFP are:
1) Frame delimitation mode: The frame delimitation is implemented based on the frame length indicator in the frame header by the CRC capture method, similar to the method used in the ATM. This method is more efficient than de-frame delimitation with a special frame identifier.
2) Adapt the different topologies by extending the function of the frame header, ring or point to point. It is also possible to define different service levels for data streams in GFP without using the upper-layer protocol to view the service level of the data stream.
3) By extending the frame header, you can indicate the type of load to determine how to forward the load without opening the load and seeing its type
4) GFP has its own FCS domain so that the integrity of the transmitted load can be guaranteed, which is very effective for protecting the load without FCS domain.
5) Transmission performance is independent of the transmission content. This advantage comes from the fact that GFP adopts a specific frame delimiting method. In PPP, it checks every byte of the payload. If there are bytes with the same frame identifier, it will process this byte, making the load longer and unpredictable.
In the MSTP test, it is this point to determine whether the mapping protocol used by the device is GFP or PPP, and compare the transmission performance of the device when transmitting OX7E and other non-OX7E information. When the performance of the latter is significantly better than the former, The mapping protocol uses PPP, and when there is no significant difference in the transmission performance between the two, the mapping protocol uses GFP.
I hope it will be helpful for you. Thank you!
