Webcam streaming using gstreamer over UDP

Maybe packets are too large for udp? They are limited to 64K. Try resizing frames to really small size to check if this is the reason. If so, you may be interested in some compression and payloaders/depayloaders (gst-inspect | grep pay).

Try these (You may have to install gstreamer-ugly plugins for this one)

UDP streaming from Webcam (stream over the network)

gst-launch v4l2src device=/dev/video0 ! 'video/x-raw-yuv,width=640,height=480' !  x264enc pass=qual quantizer=20 tune=zerolatency ! rtph264pay ! udpsink host=127.0.0.1 port=1234

UDP Streaming received from webcam (receive over the network)

gst-launch udpsrc port=1234 ! "application/x-rtp, payload=127" ! rtph264depay ! ffdec_h264 ! xvimagesink sync=false

Update

To determine the payload at the streaming end simply use verbose option with gst-launch -v ...