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Media-Aware Network Elements on Legacy Devices
1. Media‐Aware Network Elements
on Legacy Devices
m16695
Ingo Kofler, Robert Kuschnig, and Hermann Hellwagner
Chris:an Timmerer
Klagenfurt University (UNIKLU) Faculty of Technical Sciences (TEWI)
Department of Informa:on Technology (ITEC) Mul:media Communica:on (MMC)
h;p://research.@mmerer.com h;p://blog.@mmerer.com mailto:chris@an.@mmerer@itec.uni‐klu.ac.at
Acknowledgement: Part of this work is supported by the European Commission in the
context of the and ENTHRONE (contract no. 038463) project. Further informa@on is
available at h;p://www.ist‐enthrone.org.
3. Mo@va@on and Introduc@on
• Adapta@on of an SVC bitstream
– Achieved by removing certain NALUs ➙ filtering of NALUs
– Steered by a (TID, DID, QID) tuple ➙ filter criteria
– Computa@onally cheap (compared to transcoding etc.)
• Idea
– Perform real‐@me in‐network adapta@on of the SVC bitstream
on an ordinary, low‐cost WiFi router
– Media‐aware Network Element (MANE)
• Applica@ons of in‐network adapta@on
– Cross‐layer adapta@on on the access point
– Adapta@on for different end‐devices
2009/07/01 Chris@an Timmerer, Klagenfurt University, Austria 3
4. Media‐aware Network Element
On‐the‐fly adapta@on of scalable coded video content in a media‐
aware network element (MANE).
Source: h;p://ip.hhi.de/imagecom_G1/savce/
2009/07/01 Chris@an Timmerer, Klagenfurt University, Austria 4
5. List of Technologies
• Scalable Video Coding (SVC)
• Real‐@me Streaming Protocol (RTSP)
– Establishing and controlling the streaming session
– VCR‐like control of the streaming (Start, Stop, Pause)
• Real‐@me Transport Protocol (RTP)
– Encapsulates the video and/or audio content
– Mostly used on top of the unreliable UDP protocol
– Offers sequence number, @mestamps for syncing the
playback
– Generic header with content‐specific payload format
(AVC, SVC, …)
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6. Proxy Approach
server router with proxy
router client
RTSP RTP/RTCP RTSP RTP/RTCP RTSP RTP/RTCP
TCP UDP TCP UDP TCP UDP
IP IP IP
MAC/PHY MAC/PHY MAC/PHY
• Proxy on network device between client & server
– Intercepts the RTSP / RTP communication
– Proxy is transparent for the client
– Acts as client for initial server and as server for the client
• Implications
– Proxy has to modify parts of the request (e.g. port numbers)
– Proxy can then adapt the SVC video stream carried over RTP
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7. Proxy Approach (cont’d)
Benefits Drawbacks
• Session‐ and stream‐/ • Proxy is running as user‐
media‐awareness space process
• Enables stateful inspec@on • RTP packets have to be
and processing of packets passed (copied) from the
• Allows adapta@on on a per‐ kernel‐space to the user‐
session basis space and vice versa
• Consistent RTCP receiver • Decreases theore@cal
and sender reports throughput compared to
kernel‐internal solu@on (e.g.
filtering on IP level)
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8. Architecture
Handles incoming RTSP requests (554
redirect to proxy using iptables)
SDP stored in LRU‐based cache un@l
session established
Maintains state: seq#, @mestamps,
SVC params, monitoring, etc.
Forwards non‐SVC packets
Adapts SVC packets
Acts as server for client
Acts as client for server
Retrieve monitoring informa@on
Modify adapta@on/SVC parameters
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9. Performance Evalua@ons
• Hardware: Linksys WRT 54 GL
– Broadcom System‐on‐Chip BCM5352EL
– MIPS32 200 MHz CPU
– 16 MB RAM
– 4 MB Flash Memory
– IEEE 802.11b/g WLAN
– Fast Ethernet switch with 5 ports
– price ~ 45 Euros (May 2008)
• Sonware: OpenWrt
– Linux‐based firmware for Broadcom‐based WiFi routers
– gcc-based SDK for OpenWrt available
– Proxy implementa@on in ANSI C
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10. Performance Evalua@ons (cont’d)
• Evalua@on of the implementa@on on the target plaporm
– Server – proxy – client deployment
– Inves@ga@on of worst‐case scenario (no adapta@on)
• Performance metrics
– CPU usage for different number of streams
– Delay introduced by the proxy on a complete access unit (frame)
• Three different SVC streams for evalua@on
– Foreman, CIF, 30 Hz, 715 kbps
– City, 4CIF, 30 Hz, 1247 kbps
– Harbour, 4CIF, 30 Hz, 2056 kbps
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14. Conclusions
• Proxy approach for in‐network adapta@on on a per‐packet
basis
– Aware of sessions and individual streams (media‐aware)
– Stateful, not a simple packet dropper
• Applica@ons
– Adapta@on according to device capabili@es
– Cross‐layer adapta@on
– NAT traversal
• Performance sufficient for typical home deployments
– 4 parallel streams with 30 percent CPU load and < 100 ms delay
➙SVC adapta@on can be done on exis@ng off‐the‐shelf
network devices
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15. References
• I. Kofler, J. Seidl, C. Timmerer, H. Hellwagner, I. Djama and T. Ahmed,
“Using MPEG‐21 for cross‐layer mul@media content adapta@on”, Journal
on Signal, Image and Video Processing, Springer, vol. 2, no. 4, Dec. 2008.
• R. Kuschnig, I. Kofler, M. Ransburg, H. Hellwagner, “Design op@ons and
comparison of in‐network H.264/SVC adapta@on”, Journal of Visual
Communica@on and Image Representa@on, Sept. 2008.
• I. Kofler, M. Prangl, R. Kuschnig, and H. Hellwagner, “An H.264/SVC‐based
adapta@on proxy on a WiFi router”, Proceedings of the 18th Interna@onal
Workshop on Network and Opera@ng Systems Support for Digital Audio
and Video (NOSSDAV 2008), Braunschweig, Germany, May 2008.
• I. Kofler, C. Timmerer, H. Hellwagner, and T. Ahmed: “Towards MPEG‐21‐
based Cross‐layer Mul@media Content Adapta@on”, Proc. 2nd
Interna@onal Workshop on Seman@c Media Adapta@on and
Personaliza@on (SMAP 2007), London, UK, Dec. 2007.
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