Gstreamer streaming issue- laggy and choppy video (= succession of short freezings)

I'm using Gstreamer to stream video shot with a digital camera with a phone through a server to a PC app.

■ About the hard configuration:
Windows PC and Android are connected through LAN.
Android connects WiFi to router. PC connects thorugh wire to router.

■ Programs installed:
- On PC: 1. A streaming server app.
2. Gstreamer player
3. A user program that connects to the server, and uses the player (Gstreamer); it has a GUI and can display the streamed video in full screen.
- On Android: the streaming app. It sends mjpeg stream through LAN to the server program on PC.

■ Camera streams video to LAN. Android app connects to camera, captures the video streamed by the camera and re-streams it to a server app installed on PC.
The server sends video to a program installed on same PC, which displays it.

■ Technology used:
- Streamed data format is movie jpeg (this is the only one that cannot be changed).
- Streaming protocol is RTSP over UDP.

■ Gstreamer command is:
-v udpsrc caps="application/x-rtp,encoding-name=JPEG,payload=26" port=6000 ! rtpjpegdepay ! jpegdec ! videoconvert ! queue ! x264enc ! rtph264pay config-interval=10 pt=96 ! udpsink host=127.0.0.1 port=5000 sync=false

and configuration for VLC in SDP file:
v=0
m=video 5000 RTP/AVP 96
c=IN IP4 127.0.0.1
a=rtpmap:96 JPEG/90000

■ The problem is that streaming is far from being smooth; I get freezings on both Android and PC. There is a succession of these short freezings/unfreezings, sometimes PC/Android in the same time and sometime unrelated.
I shot a movie with the screens of both PC and Android, it can be downloaded from here:
http://www.mediafire.com/file/ah0m5m7msyce3sr/test01_0727.avi

I assume some packets may be lost or order is not kept right.
Any hint how this issue should be corrected? I welcome any suggestions about where I should look into and how to deal with this.

Thanks.