Guaranteed QoS Synthesiser
(GQS)
Bob Briscoe, Peter Hovell
BT Research
Jan 2005
GQS goals (realised)
• v cheap Internet-wide statistical guarantees for inter-domain μflows
• cores rarely congest but if/when they do you’re screwed
• uses existing protocols, but not their architectures
• RSVP (other signalling possible),
DSCP,
ECN
• not Intserv,
not Diffserv,
not e2e ECN
• neither path signalling nor state…
• …on core AND border routers
• incremental deployment
• scales better as more networks join
• no-one has to trust anyone else
• incentives against inter-provider cheating
IP routers
Reservation
enabled
RSVP/ECN
gateway
ECN only
GQS
system arrangement
Data path processing
1
Reserved flow processing
2
Policing flow entry to G
4
Meter congestion per peer
3
Bulk ECN marking
G prioritised over N
table of
ECN fraction
per previous
RSVP hop
aggregate
reservation signalling
1
2
guaranteed
3
guaranteed
3
guaranteed (G)
non-guaranteed
(N)
3
3
4
1
guaranteed
legend
heterogeneity
connectionoriented (CO)
connectionless
gateways
GQS
GQS/core CO
core CO/core CO
access CO/core CO
assume
app layer
signalling (SIP)
initiates out of
band
various
QoS signalling
access networks
b/w
broker
ECN
ECN
ECN
MPLS
RSVP-TE
PSTN
ECN
ECN
ECN
data plane functions:
ingress GQS
explanation easier if we start by assuming
we have already admitted a flow
reserved flow table
filterspec : flowspec
packet
arrives
Y
filterspec
matches reservation
and passes
policer
set traffic class G and
set ECN-capable transport
1
2
3
3
3
3
4
1
N
re-mark any spoof G to BE
data plane functions:
ECN marking
probability
virtual queue mgmt
(VQM)
1 Pg
virtual
queue
q
vg+qn
CoSg
G
virtual
X output
 ~ 99%
vg
priority
queuing
1
traffic
class?
2
CoSn CoSg
qn
N
qg
1 Pn
qn
drop (or ECN marking)
probability
3
3
3
line rate,
X
3
4
1
data plane functions: egress
reserved flow table
filterspec : prev RSVP hop
lookup
prev hop
G
previous hop load
prev RSVP hop : ECN fraction
maintain
moving ave
ECN fraction
clear traffic class G
clear ECN-capable transport
1
2
traffic
class?
N
GQS
3
3
3
3
4
1
Q wot, no inter-domain signalling gateway?
A no 
1
2
X
Q wot, no per session
inter-domain charging?
Y
3
3
3
3
4
1
A no 
could by intercepting signalling, but not necessary,
so if you did I’d hide it 
Q can’t X admit calls
despite congestion in Y?
transp
QoS
IP
S1
QoS
IP
IP
NA
A emulate inter-domain policing
monthly charge for bulk ECN counter at each border
dead simple to meter & account
IP
IP
IP
NB
QoS
IP
transp
QoS
IP
R1
ND
summary
• it works
• it’s simple
• it’s cheap
• it’s robust
• it’s secure
• it’s deployable
• what else do you want?
status
• two implementations (2000-4)
• FreeBSD & Linux
•
extensive simulation
•
full design documentation
•
looking for vendor take-up
Guaranteed QoS Synthesiser
(GQS)
spare slides
no time for…
• probing when no active flows between gateway pair
• robustness during re-routes
• ECN mechanisms for incentives
• ingress setting of ECT(0) & ECT(1)
• VBR
• preventing starvation
• policy-based admission control
inter-class load self-balancing
Guaranteed
admission
threshold
Non-Guaranteed
TCP
#flows
op. point