Member Avatar for abhishek_s_n

heyy guys..

m implementing PEER TO PEER FILE TRANSFER..

What protocol should I use? TCP or UDP? And why?

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Dani AI

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is right for the payload: default to TCP for file bytes so you get built-in reliability, ordering, and congestion control without reinventing them. (datatracker.ietf.org)

Where teams still reach for UDP is when they need extra control. If you choose raw UDP, plan to implement your own loss recovery, ordering, and congestion control; that is non-trivial and the IETF explicitly recommends doing so if you go this route. In practice, most file-transfer apps avoid this unless they adopt a higher-level transport over UDP. (datatracker.ietf.org)

Two modern UDP-based options worth knowing:

  • QUIC: reliable, stream-multiplexed transport with built-in TLS 1.3 and faster handshakes, all over UDP. If your stack supports it, QUIC can be a solid alternative to TCP for bulk transfer, especially through NATs and on changing networks (Wi‑Fi to cellular, etc.). (ietf.org)
  • uTP (BitTorrent): an application-level reliable transport over UDP that uses LEDBAT congestion control to be friendly to other traffic. It is a proven choice in P2P ecosystems. (bittorrent.org)

P2P wrinkle that complements ’s overview: most peers sit behind NATs. Use ICE for connectivity checks and hole punching; it tries direct paths with STUN and falls back to a TURN relay only when needed. Many apps still move the actual file over TCP/QUIC once the path is found. (rfc-editor.org)

Drop-in workflow you can copy (works for TCP or QUIC):

  • Split the file into fixed pieces (eg 256 KiB), hash each piece.
  • Exchange a manifest, then request only missing pieces so resumes are trivial.
{ "type":"handshake", "file_id":"abcd", "size":104857600,
  "piece_size":262144, "pieces_sha256":["...","..."] }

{ "type":"request", "pieces":[0,3,5,7] }

If you do not need QUIC/uTP’s special strengths, ’s direction plus TCP is the simplest, safest path. (datatracker.ietf.org)

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Member Avatar for JamesCherrill

TCP.
UDP messages are sent, but there is no check or guarantee whether they arrive or not. Also if you send multiple UDP packets there's no guarantee that they will arrive in the same order as they were sent.

Member Avatar for dmanw100

Its important to understand how sending information over a connection works before deciding on a protocol. When you send data over a connection it is broken down into small, standard size chunks called packets. The difference in the two protocols you've described is how they handle packets.

UDP simply takes a file, breaks it up, and sends each packet out onto the network. This sounds good in theory, but problems in the network can easily cause some packets to be lost or arrive in a different order than they were sent (think of it like the mail).

TCP also breaks up a file, but it adds a little bit of information that tells the receiving client where it goes when the file gets put back together. This fixes the out of order problem. TCP also requires a client to tell the sender when it receives a packet, which means any lost packets will be resent (and so on until it reaches the client).

I would strongly recommend TCP for the application you are describing. My team used TCP for a similar system we made as a school project.

Member Avatar for Sofiia

When implementing peer-to-peer file transfer, the choice of protocol depends on your specific requirements. Here's a brief explanation of TCP and UDP to help you make an informed decision:

TCP (Transmission Control Protocol):
TCP provides reliable, ordered, and error-checked delivery of data packets.
It guarantees that all data packets are received in the correct order.
TCP is suitable for scenarios where data integrity and accuracy are crucial, such as downloading large files or streaming media.

UDP (User Datagram Protocol):
UDP is a lightweight protocol that offers fast and connectionless communication.
It does not guarantee reliable delivery or ordered data packets.
UDP is suitable for scenarios where real-time communication and low latency are more important than data reliability, such as online gaming or live video streaming.

Ultimately, the choice between TCP and UDP depends on your specific use case and priorities.

Edited by Dani because: Promotional link removed
commented: It’s for file transfer. UDP is only appropriate if you don’t care about getting a whole, uncorruped file -4
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