Are there any protocol specifications that allow either TCP or UDP to be utilized?

If you examine a Windows' services file you will see a number of protocols registered for both TCP and UDP. Path: C:\Windows\System32\drivers\etc In fact, most of the listings in the services file use both TCP and UDP protocols.

If you examine a Windows' services file you will see a number of protocols registered for both TCP and UDP. Path: C:\Windows\System32\drivers\etc In fact, most of the listings in the services file use both TCP and UDP protocols. As far as well known apps that use both, I would think that most chat applications use both.

Sms-chat definitely does but probably most others. Edit: From that file, here's a few of the protocols that can be sent over either TCP or UDP (there are exactly 100 listed protocols that use both in the file, many internal MS protocols): echo discard daytime qotd (Quote of the day) chargen (Character generator) time.

OTOH, that doesn't necessarily mean that the protocol can actually use both TCP and UDP, just that the port is assigned to the protocol for both TCP and UDP. – Anomie May 16 at 15:56 @Anomie: that is true. In the end it just a file of port/protocol registrations.

Though it might be a useful reference to figure out what apps may actually make use of of both. – Paul Sasik May 16 at 16:12 @Anomie It does mean that. You can get an ECHO response via either the TCP or the UDP port.

The protocol is the same, the transport is different. Same applies to daytime, qotd, time, etc. – EJP May 17 at 0:20 @EJP: How about ssh, http, bootps, bootpc, pop3, imap2, etc?– Anomie May 17 at 1:30 @Anomie, bottom line, this file is a great list and from it I was able to find several protocols that are defined by spec as supporting both TCP and UDP, which is exactly what I was looking for. This is the best answer of the group, particularly after my edit.

– Samuel Neff May 17 at 3:28.

DNS can use either UDP or TCP; TCP is required when the response data exceeds 512 bytes.

SIP can be either UDP or TCP. However, the reality is that UDP is mostly used for this protocol.

SIP can use UDP, TCP or SCTP. Using a reliable transport becomes important in SIP if your messages get to be at all large (i.e. , significantly larger than the smallest MTU in between user agents).

A good example is shared- or bridged-line appearances, which use a form of presence with XML bodies. The larger the number of SIP clients in the shared-line group, the larger the packets are likely to be, making fragmentation and retransmission an issue.

SNMP almost always runs over UDP, but it can and does run over TCP. Theory says that it's a bad idea to do SNMP over an error-correcting transport because because some of the very errors that SNMP intends to detect are masked.

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