UDP was chosen as a first CLA because of it’s simplicity in framing the initial development of the kernel modules and developing the bundle protocol. The use of BP over UDP is not recommended as bundle protocol does not incorporate an effective retransmission mechanism. Other reasons include the following:
- UDP checksums are required, and even then there is a small probability of UDP packet corruption.
- UDP offers no congestion control which can interfere with other traffic in the network.
- The sending of large IP datagrams that must be fragmented by the network carries enormous efficiency penalties.
For more info on dealing with fragmentation and other issues related to BP over UDP, see UCP Convergence Layers for the DTN Bundle and LTP Protocols
However, unlike UDP, DGR and LTP do provide acknowledgement and retransmission facilities making either of these possible candidates.