QOS IN THE INTERNET Better than best-effort

Andreas Liaker

Feroz Zahid

Agenda

• Quality of Service – What is it and Why it is needed?• IntSrv, ST-II and RSVP• Differentiated Services• MPLS• Constraint Based Routing and Traffic Engineering• Difference between ST-II and RSVP

What is Quality of Service?

• Guarantees for the predictable results• Unlike Best-effort service

• What Guarantees?• Bandwidth• Latency• Robustness

• Methods• Resource Reservation (IntServ)• Resource Prioritization (Differentiated Services)

Integrated services (IntServ) and RSVP

• Basic Idea• Network components (routers) reserve resources to provide

Quality of Service to specific packet streams• Types

• Guaranteed• Most strict• IP possible version of dedicated virtual circuit

• Controlled-Load• Equivalent to best-effort service under unloaded conditions

Some TerminologiesTerm Description

Traffic Profile A description of the properties of a traffic stream e.g. rate and burst size

PHB Externally observable behavior of a packet

Admission Control

The decision process of whether to accept a request for resources or not

Classification The process of sorting packets based on the content of packet headers as per the rules defined

Marking The process of setting the DS field in a packet

Policing The process of handling out of profile traffic e.g. discarding excess packets

Shaping The process of delaying packets within traffic stream to cause it to conform to some defined traffic profile

Scheduling The process of deciding which packet to send first in a system of multiple queues

IntServ Components

RSVP Protocol

• Runs on top of the routing protocol• Implementation should be available on sender, receiver,

router• Carries resource requests all the way through the network• At each hop

• consults admission control • sets up reservation and packet filter. • If fails, inform sender

• Reservation Style• Wildcard• Fixed Filter• Dynamic Filter

RSVP Protocol – In IP Stack

ULPs

IP

Link layer modules

ICMP IGMP RSVP

IP service interface

Link layer service interface

RSVP Messages

• Sender• PATH message

• Traffic specification

• Receiver• RECV message containing

• Reservation specification• Guaranteed or Controlled

• Filter specification • Type of packets

RSVP Signaling Mechanism

PATH RESV

Quality-bound Communication

ST-II

• IP v5 (4 first bit Header)• Experimental protocol• Serves as an adjunct to, not a replacement for, IPv4• ST-II

• Multicast distribution tree• Unicast routing table

• ST-agent Connect (each hop)• Allocate resources• May reduce resource request.

• Receiver must Accept or Refuse• Accept can reduce resource requests

ST-II

• ST-II Hole stream is treated homogeneous. • Stream source must wait for all Accept/Refuse reply• Must adapt to lower QoS , or reject group participation

(Disconnect message)• Receivers can be added or deleted using IP.

• Must reduce QoS or reject if needed• Reliability and Robustness

• Manage Stream with hop-by-hop acknowledgment• Hello Message to neighboring ST Agents

• Only service model supported is homogeneous point to multipoint simplex distribution tree

ST-II Protocol – In IP Stack

ULPs

ST-II

Link layer modules

SCMP

ST-II service interface

Link layer service interface

IntServ - Conclusions

• Pros• Highest level service guarantees• Granularity of resource allocation• Feedback for QoS enabled applications

• Cons• Scalability?

• Amount of state information increases proportionally with the number of flows

• Huge storage and processing overhead on routers• Ubiquitous deployment is required (for Guaranteed Service)

Differentiated Services

• Basic Idea• All complex functionality shift to the edge routers

• Applied on flow aggregates• Services requirements are classified • A predefined per-hop behavior (PHB) is applied to every

service class• Traffic is smoothed according to PHB applied• Types

• Assured service• Premium service• Ordinary Best-effort service

Differentiated Services – Assured Service

• Defined in terms of user profile• how much assured traffic is a user allowed to inject into the

network• Network

• provides a lower loss rate than best-effort• In case of congestion

• best-effort packets are dropped first• User

• sends no more assured traffic than its profile• If it sends more, the excess traffic is converted to best-effort

End to End Service Delivery – Delivery of Assured Service with Static SLA

1. Host S sends a RSVP message to the local Bandwidth Broker (CN1-BB) requesting for Assured Service for its traffic.

RSVP

Granted

2. CN1-BB configure leaf router LR1 so that LR1 can set the A-bits of the packets of this flow. CN1-BB will also reply to the host S.3. Host S sends packets to leaf router LR1.4. LR1 mark A-bits of the packet.5. Every router from LR1 (excl) to ER1 (incl) does a BA classification. Packets with the A-bit set are considered as in .6. BR1 polices the traffic. If the in traffic exceeds its bit-rate, the excess packets’ A-bits will be reset.7. All routers between boundary router BR1 and BR2 (incl) perform BA classifications and apply RIO on their AQs.8. ER2 performs the same operations as BR1.9. The packets are eventually delivered to host D.

Differentiated Service – Premium Service

• Provides the abstraction of a virtual pipe between an ingress and an egress router

• Network• Guarantees that premium packets are not dropped and they

experience low delay• User

• does not send more than the size of the pipe• If it sends more, excess traffic is delayed, and dropped when

buffer overflows

Delivery of Premium Service with Dynamic SLAPhase I - Signaling

1. Host S sends RSVP PATH message to the local bandwidth broker CN1-BB.

PATH

2. CN1-BB makes an admission control decision.

Granted

3. If request is accepted, CN1-BB sends PATH message to ISP1-BB.4a. ISP1-BB makes an admission control decision.

Granted

4b. If request is accepted, ISP1-BB sends PATH message to CN2-BB.5a. CN2-BB makes an admission control decision.

Granted

5b. If request is accepted, CN2-BB set the classification and policing rules on router ER2 using LDAP or RSVP.

RESV

5c. CN2-BB then sends RSVP RESV message to ISP1-BB.6a. ISP1-BB configures classification and policing rules on router BR1, and the policing and reshaping rules on router ER2.6b. ISP1-BB then sends RESV message to CN1-BB.7a. CN1-BB will set classification and shaping rules on router LR1 and router ER1.7b. CN1-BB will then set RESV message to host S.8. Host S may now start transmitting data packets.

Delivery of Premium Service with Dynamic SLAPhase II - Data Transmission

1. Host S sends packets to the leaf router LR1.2. Leaf router LR1 performs a MF classification. If the traffic is non-conformant, LR1 will shape it. It will also set the P-bits of the packets.3. Each intermediate router between leaf router LR1 and ER1 performs a BA classification, puts the packet in PQ and sends them out.4. ER1 performs a BA classification and reshapes the traffic to make sure that the negotiated peak rate is not exceeded.5. BR1 classifies and polices the premium traffic. Excess premium packets are dropped.6. Intermediate router between BR1 and BR2 (incl) performs BA classification. BR2 also reshapes the premium traffic.

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7. ER2 classifies and polices the premium traffic. Excess premium packets are dropped.8. The premium packets are delivered to host D.

Differentiated Services - Conclusions

• Pros• Scalable• Edge routers maintain per aggregate state• Core routers maintain state only for a few traffic classes• Easier implementation• Incremental deployment

• Cons• Provide weaker service than IntServ

Quality of Service Pyramid

Best-effort

DiffServ

IntServNot Strict

Less Strict

Very Strict

Multi Label Protocol Switching (MPLS)

• Basic Idea• Header of the packet contains a label that is used to advance

the packet toward its destination• The label simplifies the forwarding decision a node must

make for the packet• A group of packets forwarded in the same manner are

said to belong to the same Forwarding Equivalence Class (FEC)

Multi Label Protocol Switching (MPLS)

• Label Switched Paths (LSPs)• Within an MPLS domain, a path is set up for a given packet to

travel based on a Forwarding Equivalence Class (FEC)• The LSP is set up prior to data transmission

Multi Label Protocol Switching (MPLS)

• MPLS improves packet forwarding performance• Enhances and simplifies packet forwarding through routers

• Layer-2 switching• Simplicity allows for easy implementation

• MPLS supports QoS for service differentiation• Use traffic-engineered path set-up and support QoS

guarantees• Classification and QoS service are determined by the labels

Multi Label Protocol Switching (MPLS)

Picture Source: http://itknowledgeexchange.techtarget.com/network-engineering-journey/how-mpls-works/

Constraint Based Routing and Traffic Engineering

• Traffic Engineering• Process of arranging traffic flows so congestion caused by

uneven network utilization could be avoided

• Constraint-Based Routing• Compute routes that are subject to rules

• Multiple constraints possible

Traffic Engineering

• Network congestion • Lack of network resources• Uneven distribution of traffic

• Lack of network Resources• All routers and links are overloaded• Only solution is to add more resources

• Uneven traffic distribution • Dynamic Routing protocols such as RIP and OSPF always

select the shortest paths to forward packets• Traffic Engineering can be utilized to:

• Avoid congestion• Provide graceful degradation in case of congestion

Picture Source: http://www.geoexpertsolutions.com/

Constraint Based Routing

• With DiffServ• Select those routes that most likely are to satisfy

QoS requirements

• Constraint-Based Routing with RSVP• Select the path for RSVP messages

• Constraint-Based Routing with MPLS• MPLS as a forwarding scheme• Constraint-based routing as a routing scheme

Differences between ST-II and RSVP

• Static Analysis• Self-limiting applications• Support heterogeneous groups• Support channel selection

• Dynamic Analysis• Network dynamics• Group membership dynamics

Self-Limiting Applications

• Multipoint-to-multipoint applications • Application-level constraints

• Few simultaneous senders

• Audio conference• Simulate

• 60 routers • 82 Links • 2-65 participants

Self-Limiting Applications

0 10 15 20 25 35 45 60 650

50000

100000

150000

200000

250000

ST-IIRSVP WildCard (1 resv)RSVP WildCard (2 resv)RSVP WildCard (3 resv)

Self-Limiting Applications

• RSVP uses Wildcard Reservation style• Resources are reserved only for new links

• ST-II Independent distribution tree from new participant to all existing members

• ST-II Maximum Group Size

Supporting heterogeneous groups

• Global Scale InterNetwork different demand for QoS• Wide-spread distribution services

• Cable-TV distribution• Broadcasting of an audio/video lecture

• Multiple data streams/signal quality level to receiver.

• ST-II• Entire stream as a homogeneous• Maximum requested resource along all links.

• RSVP • Support for heterogeneous reservations

Supporting heterogeneous groups

• Heterogeneous mix of receivers listening to an audio lecture.

• Sending the entire data stream on a single multicast tree most efficient.

• High quality – 64Kb/s• Low quality – 16Kb/s

Number Of Low Quality Receivers

ST-II Resource Allocation (Kb/S)

RSVP Resource Allocation (Kb/S)

0 2944 2944

10 2944 2656

20 2944 2176

30 2944 1600

40 736 736

Link reservations for RSVP heterogeneous audio lecture (40 receivers).

Supporting channel selection

• Large multiparty conferences• Unable to receive from all active participants simultaneously• Select dynamically a subset of the sources

• Assured channel selection• Independent reservation for each source (ST-II & RSVP)• Dynamic Filter Reservation (RSVP)

• Non-assured Channel Selection (ST-II & RSVP)

Channel selection resource overheadGroupSize

Chosen Source (4 Res)

Dynamic Filter(4-Res)

Independent Streams(N-1 Reservations)

Resource Allocation (KB/S) Resource Allocation (KB/S)

Overhead Ratio Resource Allocation (KB/S)

Overhead Ratio

5 3200 3200 1 3200 1.00

10 6592 8704 1,32 12032 1,83

15 9728 13184 1,36 23808 2,45

20 11840 18432 1,56 36224 3.06

25 14400 22720 1,58 52480 3,64

35 20160 32704 1,62 89152 4,42

45 26368 42048 1,59 140352 5,32

60 36416 57024 1,57 226432 6.22

Network Dynamics

• Reliability and robustness in the face of network dynamics.• ST-II Reliable control message protocol and a Hello protocol• RSVP Datagram control message protocol in combination

with a soft state refresh mechanism• Difficulty to compare because they rely heavily on

timers. • Compare the design philosophies• Recovery

• ST-II Requires that the network be responsible for correctness

• RSVP leaves the final responsibility for maintaining reservations with the ends. “Fate-sharing”

Network Dynamics

• Overhead• ST-II: ST agent periodically exchanging one Hello message

with each active neighbor.• RSVP: Path and Reservation refreshes• RSVP incorporates a protocol overhead reduction mechanism

(merging)

Group membership dynamics

• Global distribution of a conference• Participants tuning into and leaving the conference.

• ST-II Overhead• Connect and Accept message between source and receiver• Overhead proportional to the number of downstream receivers• HotSpots• Bottleneck

• RSVP Overhead • Assuming homogeneoues recievers. One protocol message on

each link in each direction• Heterogeneous. Splices and sufficient resource allocated for

more demanding requests

Protocol overhead for independent group joins for audio lecture

0 5 10 20 30 40 500

10000

20000

30000

40000

50000

60000

70000

80000

ST-IIRSVP

Group membership dynamics

• Latency• ST-II Setup/teardown – One roundtrip source and receiver.• RSVP Setup.

• One initial delay for Path refresh • One hop to end to end depending possibility for «spliced»

• RSVP teardown• Can release the resource immediately

Some thoughts…

• Internet QoS: A Bigger Picture• 2007 - TM Bohnert et al.• New Generation Networks, Wireless Networks

• Net Neutrality• Internet service providers and governments should treat all

data on the Internet equally• Talk: Concept of QoS in the Internet

• Geoff Huston from APNiC, September 2012• Why QoS?

• Operators believe that this will allow them to extort revenues from Content service providers

• Solution?• Add more bandwidth• Adaptive behavior in applications

Picture Source: http://1.bp.blogspot.com/

Summary

• Integrated Services• Not Scalable• Difficult to implement even in corporate networks

• Differentiated Services• No per flow resource reservations• No assured outcome• Can’t guarantee fixed service response• Can’t measure performance

• Internet QoS still not experimented much!