Offloading Multimedia Proxies using Network Processors A presentation by Øyvind Hvamstad 19. Nov. 2004

19. nov 2004Offloading Multimedia Proxies using Network Processors 2 Domain overview  Distributed media on demand (MoD)  Standarized protocols (RTSP/RTP)  Utilizing proxies  -with Network processing units. Stream setup with RTSPStream transport with RTP OUR FOCUS IXP1200

19. nov 2004Offloading Multimedia Proxies using Network Processors 3 Multimedia stream characteristics  High data-rates Requires much bandwith and storage space. Depending on codec, quality and length.  Soft real-time requirements Percieved quality is sensitive to jitter.  Access Patterns Zipf distribution (10% requested 90% of the time) Newly published material tend to be popular. Consumed from start to end or quickly aborted. ”write-once-read-many” A one hour long MPEG-2 movie at an average bit-rate Of 3.5 Mbps takes up 1.6 GB worth of storage. DivX can reduce this by a factor of 6.5. Thus reducing the size to 246 MB

19. nov 2004Offloading Multimedia Proxies using Network Processors 4 The MoD Proxy  Deployed in client vicinity to: Reduce client startup latency Reduce server load Reduce network load  Must face the challenges of: Many concurrent clients Possible high aggregate network load CPU intensive tasks

19. nov 2004Offloading Multimedia Proxies using Network Processors 5  Caching  Protocol translation  Transcoding  Re-encoding  Encryption  General functions Access control QoS mechanisms Traffic engeneering MoD proxy tasks OUR FOCUS  Forwarding data and requests

19. nov 2004Offloading Multimedia Proxies using Network Processors 6 Traditional proxy data-path  Reception Interrupt and bus transfer Processing Memory copy  Transmission Memory copy Processing Bus transfer  Application layer forwarding Reception and transmission for every packet application processing. Communication system Application (RTSP/RTP) Transport (TCP/UDP) Network (IP) Link User space Kernel space

19. nov 2004Offloading Multimedia Proxies using Network Processors 7 IXP1200 Network processor and the ENP-2505 card  IXP1200 Features One embedded StrongARM RISC processor Six Microengines Interfaces for external memory and I/O devices On-chip scratchpad memory  ENP-2505 Devices 256 MB SDRAM 8 MB SRAM 8 MB FLASH ROM 4 Ethernet (10/100 Mbit/s)

19. nov 2004Offloading Multimedia Proxies using Network Processors 8 Exactly what?  Offload application layer packet forwarding. Free cycles on the host CPU for other tasks.  Show improvements compared to a traditional architecture. Reduced latency  Provide a basis for future work in the area. Extensions  Caching  Zero copy

19. nov 2004Offloading Multimedia Proxies using Network Processors 9 Design RTSP client RTSP server RTP server RTP client Cache control Session Mgmt. Cacher control-plane data-plane write_through(async)fetch() fast_forward() insert() remove() lookup() insert() remove() lookup() signal() lookup() From server To/from server To client To/from client lookup()

19. nov 2004Offloading Multimedia Proxies using Network Processors 10 Prototype implementation RTSP Proxy Linux run-time IXA run-time StrongARM Microengines Ingress coreACE Ingress microACE Classifer/ RTP-fwd microACE Egress microACE Classifer/ RTP-fwd coreACE Egress coreACE StackACE µe 0µe 1 control-plane data-plane Intel ACEs

19. nov 2004Offloading Multimedia Proxies using Network Processors 11 Experiments  Measure the processing overhead during RTP-forwarding.  Cycle precision Probes at different locations in the code. Minimal probe overhead. Switch Dell GX260 Darwin streaming server rclient.py Proxy eth0 IXP1200 Ingress microACE Process microACE Egress microACE Probe

19. nov 2004Offloading Multimedia Proxies using Network Processors 12 Results  Offloading effect 100% of all network traffic processed by the StrongARM and the microengines.  Prototype performance Processes every RTP packet using about a tenth of the cycles compared to a traditional architecture. (Delay reduced from ~80 µs to ~8 232 Mhz)

19. nov 2004Offloading Multimedia Proxies using Network Processors 13 Extensions  Write-through caching Make a multicaster by copying packets Use a lazy-copy strategy to reduce copy operations pr. packet. Send payload copy to the host.  Zero-copy-path Batched transfer to the host. Scatter-gather DMA to assemble packet payloads in host memory. Large disk-requests.

19. nov 2004Offloading Multimedia Proxies using Network Processors 14 Conclusion  Prototype relevance Data will always flow through the proxy The forwarder processes an RTP packet efficiently compared to a traditional architecture. Is thus an orthogonal way to improve MoD proxies.  Low resource utilization leaves room for extensions.

19. nov 2004Offloading Multimedia Proxies using Network Processors 15 Other applications  The idea might be more applicable in other, more real-time areas.  Online games Proxy holds game state Might also need to forward real-time data while playing.  Live voice communication  Other urgent game data  Video conferences Node that handles overlay multicasting. Real-time data forwarded with low latency.

19. nov 2004Offloading Multimedia Proxies using Network Processors 16 Linear modulo operator #macro Mod[out_z, in_x, in_y].local xm alu[xm, --, B, in_x] Loop#: alu[out_z, xm, -, in_y] br =0[Loop#] End#: alu[out_z, --, B, xm].endlocal #endm int mod(int x, int y) { int z; top: z = y – x; if (z 0) goto top return z; } Intel Assembler macroANSI C function

19. nov 2004Offloading Multimedia Proxies using Network Processors 17 Basic hash function #macro Hash[out_z, in_x, in_seed].local x start immed[start,START] alu[x, in_x, -, start] ; alu_shf[x, --, B, x, >>1] Mod[out_z, x, in_seed].endlocal #endm int hash(int x, int y) { x = x – START; x = x / 2; return x % seed; } Intel Assembler macroANSI C function

19. nov 2004Offloading Multimedia Proxies using Network Processors 18 Incremental checksumming #macro IncrementCksum[out_newsum, oldsum, old, new].local sum tmp mask immed[mask, 0xffff] alu[sum, --, ~B, oldsum] alu[sum, sum, -, old] alu[sum, sum, +, new] alu[tmp, sum, AND, mask] alu_shf[sum, tmp, +, sum, >>16] alu[tmp, sum, AND, mask] alu_shf[sum, tmp, +, sum, >>16] alu[sum, --, ~B, sum] alu[out_newsum, sum, AND, mask].endlocal #endm sum = ~oldsum; sum = sum - old; sum = sum + new; tmp = sum & 0xffff sum = tmp + (sum >> 16); tmp = sum & 0xffff; sum = ~sum; sum = tmp + (sum >> 16);

19. nov 2004Offloading Multimedia Proxies using Network Processors 19 Just can’t get enough, huh?  /hom/~oyvindh/thesis.pdf  CVS repository :pserver:hic.no/cvs  Module: thesis  User: anonymous  Pwd: Should be up in a few days  Have just moved to a new location