Advanced satellite infrastructures in future global Grid computing: network solutions to compensate delivery delay ISTI CNR

Transcription

1 Advanced satellite infrastructures in future global Grid computing: network solutions to compensate delivery delay Blasco Bonito, Alberto Gotta and Raffaello Secchi ISTI CNR

2 Outline Introduction Grid Networks Architecture to Access Remote Equipments Technology Overview DVB-RCS overview and TCP-friendly protocols and their related startup problems Numerical Results Current TFRC performance TFRC performance using Quick Start Integration between QS and DAMA

3 Introduction GEO SATELLITE HOST B Grid Network typically require high speed connection to transfer significant amount of data Remote equipments may be difficult to reach with high speed connections New satellite links (DVB-RCS) may provide reliable and high speed connectivity to these sites

4 DVB-RCS architecture DVB-RCS architecture DVB-RCS (ETSI EN 301) RETURN LINK DVB-RCS FORWARD LINK DVB-S/S2 DVB-RCS is maintained by the DVB project is an industry-led consortium of broadcasters, manufacturers, network operators and regulatory bodies in over 35 countries DVB-RCS defines MAC and PHY specifications for a satellite network DVB-RCS permits bidirectional channels over satellite links (Meshed Networks) with a generic MF-TDMA access scheme

5 Concept of Demand Assignment Multiple Access Processing time Master Station DAMA steps BWreq BTP allocation delay safe frame period 1. The Traffic Terminal (TT) sends a Bandwidth request 2. The Master Station (MS) receive the message, Traffic Terminal computes the value of the bandwidth to be allocated and broadcast the BTP 3. Once the TT has received the reply from the MS, it waits its turn of transmission Internet congestion control algorithm (e.g. TCP or TFRC) may suffer of long end-to-end delay due to DAMA latency

6 DVB-RCS Bandwidth Allocation Methods DVB-RCS Bandwidth Allocation Methods Constant Rate Assignment (CRA) Bandwidth is negotiated between the traffic terminal and the allocator at the beginning of each connection Rate Based Dynamic Capacity (RBDC) Each Traffic terminals submits to the allocator a bandwidth request message based on the rate of local incoming traffic Volume Based Dynamic Capacity (VBDC) Each terminal dynamically signals the data volume needed to empty its buffer Free Capacity Assignment (FCA) No explicit request comes from the terminals. Unused bandwidth is assigned automatically by the allocator to the traffic terminals according to some fairness criteria

7 TCP-friendly Rate Control TCP-friendly Rate Control TFRC is an equation-based & paced-based protocol that provides congestion control to multimedia applications. It is designed to be reasonably fair when competing for bandwidth with TCP connections. In TFRC, the receiver periodically sends a feedback report informing the sender of received throughput and recent loss event rate that a connection experiences. TFRC slow start phase Initial Slow Start: TFRC starts with 4 packets per RTT and doubles the rate at each RTT. Due to satellite delays, the sending rate reaches the encoding rate in a long time (without congestion). Sending rate limit: TFRC sending rate can be at most twice the current receiver rate. This growth rate is not sufficient to keep up with the encoding rate when the application oscillates between silence and talk periods.

8 Quick Start (RFC 4782) Quick Start (RFC 4782) Quick Start is a protocol that provides a lightweight signaling of congestion level between the routers of a network and a pair of communicating end hosts. QS was proposed to work with TCP but it can be used with any congestion control protocol that would prefer to inflate their sending rates without effectively slow starting from a small initial rate. Using QS with Internet protocols can effectively and efficiently work over a wide range of links including those with satellite delay. QS may also be useful for multimedia flows.

9 Basic QS mechanism Basic QS mechanism QS router QS request sent the sender can transmit ata up to the pproved rate QS request accepted QS response sent

10 TFRC Performance (with/without QS) in terms of end-to-end delay NO QS QS QS improves performance but we want more!! QS improves performance but we want more!!

11 QS problems due to the interaction with DAMA (Skyplex Data platform) TFRC sender TFRC receiver QS request sent Source quick starts Source reduces Tx rate QS request accepted Packets queued BWreq BTP Receiver sends QS resp Receiver sends low feedback report

12 Proposed Solution: Delaying the QS request TFRC sender TFRC receiver QS request sent QS request accepted T q BWreq BTP Receiver sends QS resp Source quick starts

13 TFRC Performance (with/without QS +DAMA improvement) in terms of end-to-end delay QS QS with Forward Delay Delay further reduced!! Delay further reduced!!

14 Delayed QS request Delayed QS request Estimation of the minimum delay to impose to QS request

15 Conclusions and Future works Conclusions and Future works Congestion control algorithms will be probably a MUST in future internet and Grid networks QS protocol supplies a considerable support to networks with large propagation delay (such in case of SAT networks) The proposed solution really improves the performance of a DAMA base satellite platform when QS is adopted Find an analytical backing of the imposed delay in relation with the satellite architecture