Advanced satellite infrastructures in
future global Grid computing: network
solutions to compensate delivery delay
Blasco Bonito, Alberto Gotta and Raffaello Secchi
ISTI – CNR
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
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
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 allows bidirectional channels
over satellite links (Meshed Networks)
with a generic MF-TDMA access
scheme
Concept of Demand
Assignment Multiple Access
Processing time
Master Station
safe frame
period
allocation delay
DAMA steps
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
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
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.
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.
Basic QS mechanism
QS router
QS request
sent
the sender
can transmit
data up to the
approved rate
QS request
accepted
QS
response
sent
TFRC Performance (with/without QS) in
terms of end-to-end delay
NO QS
QS
QS improves performance but we want more!!
QS problems due to the interaction with
DAMA (Skyplex Data® platform)
TFRC receiver
TFRC sender
QS request
sent
Source
quick starts
Source
reduces
Tx rate
QS request
accepted
Receiver
sends
QS resp
Packets
queued
Receiver
sends
low
feedback
report
Proposed Solution: Delaying the QS
request
TFRC receiver
TFRC sender
QS request
accepted
QS request
sent
Tq
Receiver
sends
QS resp
Source
quick starts
TFRC Performance (with/without QS +DAMA
improvement) in terms of end-to-end delay
QS
Delay further reduced!!
QS with
Forward Delay
Delayed QS request
Estimation of the
minimum delay
to impose to QS
request
Conclusions and Future works
 Congestion control algorithms will be probably a
MUST in future internet and Grid networks
 QS protocol supply 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