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