session qos vs bulk qos bob briscoe chief researcher, bt group oct 2008
TRANSCRIPT
session QoS vs bulk QoS
Bob Briscoe
Chief Researcher, BT Group
Oct 2008
2
End usersEnd users
ISPsas ASPs
ISPsas ASPs
QoS bypass
• QoS = differentiated congestion delay & bandwidth
• as link rates increase, congestion delay becoming a non-problem
• all the bandwidth-demanding applications are taking the QoS they need• just taking a larger than average cost share of the best efforts service
policingpeak access ratepeak access rate vol capvol cap DPIDPI TCATCA flowspecflowspec
FIFOFIFO DiffservedgeAC
edgeAC local
e2eAC
locale2eAC
IPIP
link technologieslink technologies
resourcesharing /scheduling
ASPsASPs
I S
P s
endpoint transport resource sharingendpoint transport resource sharing
€ €€€€/b
Q. bulk or session QoS?A. bulk, but BE bulk QoS
3
the information supermarket
aislesaisles
self check-outself check-out check-outscheck-outs
$100/wk take what you
need
4
QoS interconnect
• evolution by company death is too slow• years
• need market evolution (by financial perf) • months or weeks
aislesaisles
self check-outself check-out check-outscheck-outs
aislesaisles
self check-outself check-out check-outscheck-outs
aislesaisles
self check-outself check-out check-outscheck-outs
$10,000/wk
take what
you need
€10,000/wk
take what
you need
$100/wktake what
you need
¥1,000/wk
take what
you need
ISPsas ASPs
ISPsas ASPs
cross-subsidy
5
Future of the Internet
5.0%
15.0%20.0% 20.0%
40.0%45.3%
27.8%
15.7%
7.5%3.8%
Hogs Pow er Users Up & Comers Middle Children Barely Users
% of Total Subscribers % of Traff ic % of Cost
SuperpowerUsers
QoS interconnection includes BE QoS
• QoS interconnection is not just about explicit QoS mechanisms
• starts with visibility of BE costs
• including at interconnect [Laskowski06, Briscoe05]...
• this is how to get to this future • where apps minimise cost, even if they transfer large volumes
• (limiting peak volume will wrongly cap BitTorrent DNA)
State of the Internet
5.0%
15.0%20.0% 20.0%
40.0%45.3%
27.8%
15.7%
7.5%3.8%
Hogs Pow er Users Up & Comers Middle Children Barely Users
% of Total Subscribers % of Traff ic % of Cost
6
legend:legend:re-ECNdownstreamcongestionmarking [%]
NA
NDNB
NC
receiverreceiver
sender marks 3%of packetssender marks 3%of packets
automatic interconnectusage cost allocation
highly congested link marking 2.8%
of packets
highly congested link marking 2.8%
of packets
lightly congested link marking 0.2%
of packets
lightly congested link marking 0.2%
of packets
marking in 2.8%of packets crossing
interconnect
marking in 2.8%of packets crossing
interconnect
a single flow of packets
7
ND
NA
NB
NC
solution
legend:legend:interconnect aggregation simple internalisation of all externalities'routing money'
re-ECNdownstreamcongestionmarking [%]
bit ratearea =instantaneousdownstream
congestion volume
area =instantaneousdownstream
congestion volume
just two counters at border,one for each direction
meter monthly bulk volumeof packet markings
= aggregate downstreamcongestion volume in flows
without measuring flows
just two counters at border,one for each direction
meter monthly bulk volumeof packet markings
= aggregate downstreamcongestion volume in flows
without measuring flows
0|0|2|7|6|0|5 €€
€
8
• as an attribute of the customer contract, not the network
• customer can roam without changing network
• as an attribute of the customer contract, not the network
• customer can roam without changing network
differentiated services& admission control
just happen
bulkcongestion
policer
Internet
0.3%congestion
0%
0.1%
2 Mb/s0.3Mb/s6 Mb/s
Acceptable Use Policy
Your 'congestion volume' allowance: 1GB/month (= 3kb/s continuous)This only limits the traffic you can try to transfer above the maximum the Internet can take when it is congested.
Under typical conditions this will allow you to transfer about 70GB per day.
If you use software that seeks out uncongested times and routes, you will be able to transfer a lot more.
Your bit-rate is otherwise unlimited
0|0|2|7|6|0|5
• operators can synthesise a carrier grade admission control service out of this
• see pre-congestion notification (PCN) working group at the IETF
• operators can synthesise a carrier grade admission control service out of this
• see pre-congestion notification (PCN) working group at the IETF
9
summary
• everyone's got their eye on the wrong balls
• volume cost (congestion)
• AF, EF & session QoS BE QoS cost policing
• intra-domain & inter-domain
session QoS vs bulk QoS
Q&Arefsspare slides
11
more info
interconnected visibility of BE cost• The Internet's missing link: rest of path metrics at interconnect
[Laskowski06] Paul Laskowski and John Chuang, "Network Monitors and Contracting Systems: Competition and Innovation" In: Proc. ACM SIGCOMM'06, Computer Communication Review 36 (4) pp. 183--194 (September, 2006)
• A way to do rest of path metrics[Briscoe05] Bob Briscoe, Arnaud Jacquet, Carla Di-Cairano Gilfedder, Andrea Soppera and Martin Koyabe, "Policing Congestion Response in an Inter-Network Using Re-Feedback“ In: Proc. ACM SIGCOMM'05, Computer Communication Review 35 (4) (September, 2005)
pre-congestion notification (PCN)• Diffserv’s scaling problem
[Reid05] Andy B. Reid, Economics and scalability of QoS solutions, BT Technology Journal, 23(2) 97–117 (Apr’05)
• PCN interconnection for commercial and technical audiences:[Briscoe05] Bob Briscoe and Steve Rudkin, Commercial Models for IP Quality of Service Interconnect, in BTTJ Special Edition on IP Quality of
Service, 23(2) 171–195 (Apr’05) <www.cs.ucl.ac.uk/staff/B.Briscoe/pubs.html#ixqos>
• IETF PCN working group documents<tools.ietf.org/wg/pcn/> in particular:[PCN] Phil Eardley (Ed), Pre-Congestion Notification Architecture, Internet Draft <www.ietf.org/internet-drafts/draft-ietf-pcn-architecture-06.txt>
(Sep’08)
[re-PCN] Bob Briscoe, Emulating Border Flow Policing using Re-PCN on Bulk Data, Internet Draft <www.cs.ucl.ac.uk/staff/B.Briscoe/pubs.html#repcn> (Sep’08)
these slides<www.cs.ucl.ac.uk/staff/B.Briscoe/present.html>
12
best efforts (b)best efforts (b)
strict priority (g)strict priority (g)qg+qb
qbweak competitionprice of expectation of better servicearbitrarily higher pg >> pb
perfect competitionprice differential cost differentialpg pb
pg
pb
markingprobability
shouldn't network charge more for lower congestion?
• apologies for my sleight of hand• actually aiming to avoid congestion impairment (loss / delay)
• congestion marking = congestion avoidance marking
• alternatively, congestion marking = price marking
• clearly should charge more for higher 'price marking'
• Diffserv example may help [Gibbens02]
13
callserver
SIP
PCN system arrangementhighlighting 2 flows
(P)expedited forwarding,PCN-capable traffic
(P)
(P)
non-assured QoS(N)
RSVP/RACF per flow reservation signalling
reserved
1
2
4
3
Reservationenabled
RSVP/PCNgateway
PCN & Diffserv EF
Reserved flow processing
Policing flow entry to P
Meter congestion per peer
Bulk pre-congestion markingP scheduled over N
IP routersData path processing
table of PCN fractionper aggregate (per previous
big hop)
b/wmgr
2
4
33
33
1
1
14
Pre-Congestion Notification(algorithm for PCN-marking)
PCN pkt?PCN pkt?
Yes
No
virtual queue(bulk token bucket)
virtual queue(bulk token bucket)
PCN marking
probability ofPCN
packets
PCN marking
probability ofPCN
packets
1
Prob
X = configured admission control capacity
for PCN traffic
X = configured admission control capacity
for PCN traffic
X ( < 1)
• virtual queue (a conceptual queue – actually a simple counter):– drained somewhat slower than the rate configured for adm ctrl of PCN traffic
– therefore build up of virtual queue is ‘early warning’ that the amount of PCN traffic is getting close to the configured capacity
– NB mean number of packets in real PCN queue is still very small
PCN packet queue
Non-PCN packet queue(s)
2
4
3 3 3 3
1
1
P
N
Expedited
Forwarding
15
value-based chargesover low cost floor• over IP, currently choice between
A. “good enough” service with no QoS costs (e.g. VoIP)– but can brown-out during peak demand or anomalies
B. fairly costly QoS mechanisms – either admission control or generous sizing
• this talk: where the premium end of the market (B) is headed• a new IETF technology: pre-congestion notification (PCN)
• service of ‘B’ but mechanism cost competes with ‘A’
– assured bandwidth & latency + PSTN-equivalent call admission probability
– fail-safe fast recovery from even multiple disasters
• core networks could soon fully guarantee sessions without touching sessions• some may forego falling session-value margins to compete on cost
the Internet
cost-
based
revenue
value-base
d
revenue
designed for competitive pressuretowards true marginal cost
app signal (SIP)QoS admissionpriority forwarding& PCN
NANA
NBNB
NDND
RS
per session
bulk data