TCP, UDP and Router

Trigun

Folks, quick question regarding TCP/IP and UDP.

Is UDP part of TCP/IP protocols or is it a lone ranger?

I tend to get confused because UDP does use IP addresses to communicate and send packets right, so why isn't it called UDP/IP? Since IP itself is connectionless?

I know all the besics like TCP (bigger header, error detection) and is connection orianted and UDP is connectionless. Also, in saying that another question about UDP... what happens if there is an error in UDP, what does it do? Just dropps the packets or delivers the packets in error to the recipient?

What are some of examples that use UDP, I know that PING command is one.

With regards to routers... a router is located on the L3 Network layer... and a Gateway is essentially a router (or part of router functionallity) right?

Well, on this site we see that
http://www.geocities.com/SiliconValley/Monitor/3131/ne/osimodel.html

A gateway is L4 - L7, while a router is only L3. What gives?

Also, a brouter is on Layers 3, 4 but a bridge is on a data link layer 2. Becasue a brouter is just a router with bridgeing capabilities shouldn't it be on L2 and L3?

All this is really really confusing, but fun in a nerdy way!!! Thanks to all who are willing to help.

hypnotoad

With regards to TCP and UDP...

UDP is a layer-4 protocol, just like TCP. It uses IP for routing (and therefore IP addresses) -- it sits "on top" of IP. The UDP segment carries the data, just like TCP does, and IP sits at a lower level, handling where the UDP segments go.

The TCP Segment has some extra fields compared to the UDP segment. An error in UDP doesn't require a re-transmit. The packets go out, and they're gone. You don't get an ACKnowledgement of a UDP packet.

Protocols that use UDP:
- TFTP
- DNS (zone transfers from one server to another are done with TCP, but requests use UDP)
- SNMP
- DHCP
- VoIP (by the time an error is detected and corrected, it's too late to retransmit, because the other party already 'heard' the drop, so inserting it in the conversation doesn't make any sense)
- Video Games (probably not on your test though)

Plantwiz

nlabelle wrote:

The TCP Segment has some extra fields compared to the UDP segment. An error in UDP doesn't require a re-transmit. The packets go out, and they're gone. You don't get an ACKnowledgement of a UDP packet.

Nicely done

EdTheLad

nlabelle wrote:

The TCP Segment has some extra fields compared to the UDP segment. An error in UDP doesn't require a re-transmit. The packets go out, and they're gone. You don't get an ACKnowledgement of a UDP packet.

Just to add, generally the upper layer application will request a retransmit if some data is missing or corrupt.So the error recovery is done at the application layer rather than the transport layer.