Micro IPv6 protocol stack

We have briefly explained and introduced some of the main protocol types in the Embedded IPv6 protocol. I believe you have some knowledge about the protocol types contained in the entire system. Now, we will mainly discuss how to streamline the IPv6 protocol stack in the system.

A simplified IPv6 protocol stack

The core of streamlining is "miniaturization". We cut down the protocol module and simplify a single protocol on the protocol stack.

IPv6 protocol module reduction

Protocol Module reduction means removing some protocol modules as much as possible while ensuring basic communication functions to save system resources. Network Interface Layer we only consider 802.3 Ethernet protocol CSMA/CD, MAC, LLC), do not consider for CAN, RS-232, RS-485, RF, Bluetooth and other related support modules. In the access mode, only the vro access mode is considered. The peer-to-peer PPP and SLIP protocols related to the dial-up connection mode are removed, regardless of the dial-up connection method, the two protocols occupy a large amount of code at the network interface layer. The IP layer only implements basic headers, but does not implement extended headers, remove the IPsec protocol based on the authentication header and the security load header encapsulation option, and send the security control to other layers. ICMPV6 and ND are the core protocols that must be retained. The Transport Layer TCP and UDP can be implemented in all or only one way. The adaptability is considered and implemented in this design. Therefore, after the Protocol Module is reduced, the core protocol families are 802.3, IPv6, ICMPV6, ND, TCP, and UDP.

Simplify a single protocol

Single protocol simplification refers to the simplification of functions and data structures targeting a single protocol. For the IPv6 protocol, only receive and send packets. packet fragmentation and reorganization are not supported, and the header extension option is not supported. For reliable connection transmission, the packet size is too large to be confirmed, based on the congestion control mechanism and retransmission mechanism, the Data Group length will be reduced and re-sent. This will not cause other serious problems for most applications.

For ICMPV6, only the destination of the error message is inaccessible. The response packet in the information packet is not timeout. The packet is too large and the response packet is usually too large, timeout packets are implemented by the vro, and the response request packets are used at one end of the PC in the active test. For the Neighbor Discovery ND module, only the neighbor request and neighbor response packets are implemented. The embedded device is just connected to the network and can wait for the route announcement packets sent by the router on the network statically, instead of actively sending route request packets, you do not need to implement route request/route response packets.

The neighbor connection of the embedded device. The route is generally simple, with a small amount of transmission and does not need to be redirected. The simplified protocol is TCP, which is the most complex and code-intensive in the entire protocol cluster.

Its functional modules include sliding window, traffic control, congestion control, TCP connection state machine, round-trip time estimation, and retransmission protocol.

The objective of this IPv6 protocol stack is an embedded system supported by the operating system. The speed and storage capacity are higher than those of 8-bit and 16-bit single-chip microcomputer, instead of allocating a fixed buffer to receive a frame and process a frame, you can consider allocating a large buffer to implement a sliding window mechanism to improve transmission efficiency, the improvement in transmission efficiency is obvious. The round-trip time estimation and retransmission mechanism are relatively simple, and the amount of code is small. It can be implemented. The TCP state machine indicates the status migration of TCP Process Communication, it is the core of TCP and does not implement the traffic control mechanism, because the traffic is not very large.

Therefore, the functions implemented by the TCP module include: TCP finite automatic machine, sliding window, round-trip time estimation, and retransmission protocol.

Ignore the traffic control and congestion control modules. In a reliable connection, when data is lost due to congestion, the sender will re-send the data if it fails to receive the data.