TCP packet sticking refers to the phenomenon where multiple data packets are merged into a continuous data stream during network transmission, making it difficult for the application layer to correctly parse the original data boundaries. This phenomenon is akin to parcels being bundled in disorder, making it challenging for the receiving party to accurately separate different package contents, directly affecting data processing accuracy and system stability.

Analysis of the Causes of TCP Packet Sticking

Sender-side merging mechanism

The Nagle algorithm delays sending small packets to reduce the number of network transmissions, which may lead to multiple data packets being merged and sent together. For example, multiple operation commands sent per second by a game client may be merged into a single large packet.

Receiver-side read delay

When the application layer fails to read data from the receive buffer promptly, subsequently arriving data continues to be written into the buffer, resulting in packet sticking. Typical code example:

# Failure to read the buffer in time leading to packet stickingdata = socket.recv(1024)# Processing logic delayprocess(data)

Network transmission characteristics

Ethernet defaults to an MTU (Maximum Transmission Unit) of 1500 bytes. Packets exceeding the MTU are fragmented for transmission, and these fragments may be incorrectly merged at intermediate nodes, causing packet sticking. Additionally, network congestion control mechanisms, such as the sender merging small packets during slow start and adjusting window sizes during congestion, can change packet merging and transmission order, leading to packet sticking.

Solutions for TCP Packet Sticking

Fixed-length protocol

Agree on fixed-length data packets to recognize data boundaries, suitable for scenarios where data length is known:

Sender-side:

data = b'hello'packet = data.ljust(10)  # Pad to a fixed length of 10 bytessocket.send(packet)

Receiver-side:

while True:    packet = socket.recv(10)    process(packet.strip())

Suitable for scenarios with fixed data lengths, such as monitoring system data collection and industrial control command transmission.

Delimiter marker method

Append a special delimiter (e.g., ) at the end of data packets for text protocol parsing:

Sender-side:

message = "data1

data2

"socket.send(message.encode())

Receiver-side:

buffer = b''while True:    buffer += socket.recv(1024)    while b'

' in buffer:        line, buffer = buffer.split(b'

', 1)        process(line)

Length prefix method

Add a 4-byte length field at the beginning of data packets to explicitly identify subsequent data lengths:

Sender-side:

data = b'important_data'length = len(data).to_bytes(4, 'big')socket.send(length + data)

Receiver-side:

def recv_all(sock, size):    data = b''    while len(data) < size:        chunk = sock.recv(size - len(data))        data += chunk    return datalength_data = recv_all(socket, 4)length = int.from_bytes(length_data, 'big')data = recv_all(socket, length)

Protocol stack optimization

• Adjust Nagle algorithm parameters (TCP_NODELAY)

• Use more efficient serialization protocols (e.g., Protobuf)

• Application-layer heartbeat mechanism to maintain connection activity

Solution Selection Recommendations

In practical development, it is recommended to prioritize the length prefix method for its versatility while supporting efficient parsing. For performance-sensitive systems, combine protocol stack optimization measures to enhance transmission efficiency.

TCP packet sticking is a classic issue in network programming, stemming from semantic differences between transport and application layer protocols. By understanding sender/receiver mechanisms and network transmission characteristics, selecting the appropriate solution can effectively resolve packet sticking issues. In practical development, consider using packet capture tools (such as Wireshark) for traffic analysis and design optimal solutions based on specific scenarios.