T-110.5110 Computer Networks II Quality of Service 20.10.2008 Dr. Matti Siekkinen [email protected] (Primary sources: C. Hota: “Quality of Service in.

T-110.5110 Computer Networks II

Quality of Service

20.10.2008

Dr. Matti [email protected]

(Primary sources: C. Hota: “Quality of Service in the Internet” and J. Manner: IP Quality of Service)

22.10.20072 April 19, 2023

Outline

What is QoS?

QoS mechanisms

QoS architectures Integrated Services (IntServ) Differentiated Services (DiffServ) Multiprotocol Label Switching (MPLS) Generalized Multiprotocol Label Switching (GMPLS) QoS architectures for mobile networks Next Steps in Signaling (NSIS)

22.10.20073 April 19, 2023

What is Quality of Service?

Many applications are sensitive to delay, jitter, and packet loss Too high values makes utility drop to zero

Some mission-critical applications cannot tolerate disruption VoIP high-availability computing

Charge more for business applications vs. consumer applications Related concept is service availability

How likely is it that I can place a call and not get interrupted? requires meeting the QoS requirements for the given application

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QoS Requirements

Personal voice over IP

Network monitoring

CEO Video conference with analysis

Financial Transactions

Interactive whiteboard

Unicast radio

Network management traffic

Extranet web traffic

Public web traffic

Push news

Personal e-mail

Businesse-mail

Server backups

Sensitive

Insensitive

Casual Critical

Delay

Mission Criticality

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The existing Internet architecture provides a best effort service. All traffic is treated equally (generally, FIFO queuing with tail drop) No mechanism for distinguishing between delay sensitive and best

effort traffic No guarantees for end-to-end QoS

Originally IPv4 has TOS (type-of-service byte) in packet header RFC 795: defined multiple axes (delay, throughput, reliability) rarely used in practice (DiffServ)

We try to minimize delay and loss …and try to mitigate the effects with different techniques E.g. adapt application (video stream) based on QoS feedback (RTCP)

QoS and the Internet

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Outline

What is QoS?

QoS mechanisms


22.10.20077 April 19, 2023

QoS Mechanisms

Packet Scheduling

Admission Control

Traffic Shaping

(Users get their share of bandwidth)(Amount of traffic

users can inject into the network)

(To accept or reject a flow based on flow specifications)

Core

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QoS Mechanisms: classification

Provisioning Admission control

o Prohibit or allow new flows to enter the nw Resource reservation

o E.g. Over provisioning

Control Operate on short time scales Real-time traffic or flow control

o E.g. scheduling, shaping, policing...

Management Monitor the QoS Longer time scales than control

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QoS Control Mechanisms

Application-level techniques Application adapts to network conditions E.g. adapt media stream to a lower quality based on RTCP feedback

Transport-layer techniques Adapt transport protocols to application requirements and network

conditions TCP, DCCP

Network-layer techniques QoS routing Non-FIFO scheduling (like WFQ) Something else than tail drop (like RED)

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QoS Control Mechanisms (cont.)

Packet Classifier

IP addresses, net mask, port numbers, protocol id

Flow identifier

Full ProcessorArrival

Discard

N

Queue

Departure

Scheduling (FIFO Queuing)

ClassifierArrival

N

Discard

Full

Y

Full

Y

N

Discard

High Priority Queue

Low Priority Queue

ProcessorDeparture

The switch turns to other queue when the current one is empty

Scheduling (Priority Queuing)

Y

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ClassifierArrival

N

Discard

Full

Y

Full

Y

N

Discard

Weight: 2

Weight: 1

ProcessorDeparture

The turning switch selects 2 packets from 1st queue, then 1 packet from 2nd queue and the cycle repeats

Scheduling (Weighted Fair Queuing)

Leaky Bucket (Regulate the traffic) Token Bucket (Credit an idle host)

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Arriving Packet Queue

Dropped

Full

(Tail-drop scheme)

Arriving Packet Queue

Dropped from front

Full

(Drop-from-front scheme)

Accepted

Queue

Drop

(Random Early Detection with Drop function)

Avg. TCP Traffic

MAXth MINth

MINth MAXth

1

MAXdrop

Drop probability

Avg. queue size

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QoS routing Routing based on QoS related metrics, not just shortest path

o E.g. available bandwidth

(Multi-)constrained path computationo Can be computationally complex

Widest-Shortest Patho Select the shortest path that is feasible according to the bandwidth

constraint

Shortest-Widest Patho Find paths with the most available bandwidth (i.e. widest paths)o Break ties by selecting the shortest path (#hops or delay)

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Where to implement QoS mechanisms?

Core routers Link speeds fast Lot of trafficCannot do much more than over provisioning or treat limited nb of

flow classes

Access routers Generally, not so high rates Feasible to do complex operations (filtering, classification, policing…)Could do per-flow packet handling

22.10.200715 April 19, 2023

Outline

What is QoS?

QoS mechanisms


22.10.200716 April 19, 2023

QoS Architectures

Use the QoS mechanisms to provide application to application QoS Many different proposals over the years

YESSIR, IntServ, DiffServ, Mobile RSVP, OMEGA, QoS-A... We will look at a few ones in more detail

Integrated Services (IntServ)

Differentiated Services (DiffServ)

Multiprotocol Label Switching (MPLS)

Generalized MPLS (GMPLS)

QoS for mobile networks

Next Steps in Signaling (NSIS)

22.10.200717 April 19, 2023

IntServ

Resource reservation and admission control Source describes its desired flow rate and sends this information

to the routers and the receiver Network admits requests and reserves resources Source must send at this rate (controlled by network) Provides a sort of “dedicated” connection within an IP packet-

switched network Reservation of resources is done with the Resource Reservation

Protocol (RSVP)

22.10.200718 April 19, 2023

RSVP

Supports both multicast and unicast Sender-to-network signaling

path message: make sender presence known to routers path teardown: delete sender’s path state from routers

Receiver-to-network signaling reservation message: reserve resources from senders to receiver reservation teardown: remove receiver reservations

Network-to-end-system signaling path error, -reservation error

Soft state protocol Need to refresh state

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RSVP (cont.)

Reservations are for unidirectional data flows Provides several reservation models or "styles" to fit a variety of

applications (shared and dedicated reservations) Transparent to routers that do not support it

RSVP packets are just normal IP packets

Not a routing protocol but depends upon present and future routing protocols

Supports both IPv4 and IPv6

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IntServ: Scalability Issues

RSVP signaling Overhead

One PATH/RESV per flow for each refresh period

Processing overhead

Routers have to classify, police and queue each flow

State information stored in routers

Flow identification (using IP address, port etc)

Previous hop identification

Reservation Status

Reserved Resources

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DiffServ

No signalling, no resource reservation

Complex processing is moved from core to edge

Per flow service (IntServ) is replaced by per aggregate or per class

service with a SLA with the provider

Mark packets with a code (DSCP) to differentiate between

pkts/flows e.g. a priority stamp

Uses IP type of service field (TOS)

Core uses the codes to select appropriate service level Premium, priority, best effort

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DiffServ

Two types of services standardized, operators may define other services and code points

Does not necessarily provide end-to-end QoS: Operators may have different meanings and implementations for classes

and code points, The code points can change, thus, may not remain the same on the whole

end-to-end path.

22.10.200723 April 19, 2023

DiffServ Schema

Source sends request message to first hop router

First hop router sends request to Bandwidth Broker (BB) that replies with either

accept or reject

If the request is accepted, either the source or the first hop router will mark DSCP

and will start sending packets

Edge router checks compliance with the SLA and will do policing. It may drop or

mark the packet with low priority to match the SLA

Core routers will look into DSCP and decide the PHB

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Expedited Forwarding

• Expedited packets experience a traffic-free network (low loss, low latency, low jitter,

and assured bandwidth (premium service)

• Strict priority queuing

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Assured Forwarding

• A possible implementation of the data flow for assured forwarding is shown below.

• AF PHB delivers the packet with high assurance as long as its class does not exceed the a

subscribed rate

• Use e.g. WFQ scheduling with RED

22.10.200726 April 19, 2023

Bandwidth Brokers

Server 3

Server 2Core Network

ISP 1 ISP 2

BBBB BB

BB

BB

U1

U2

U1

U2 U3

Server 1

S1

S2

C1

C2 C3

C4C5

C6 C7

D

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Integrated Solution

22.10.200728 April 19, 2023

Multiprotocol Label Switching (MPLS)

Traffic engineering tool

Allocate specific path and network resources to specific types of traffic ensuring QoS

Supports multiple protocols

IPv4, IPv6, IPX, AppleTalk at the network layer

Ethernet, Token Ring, FDDI, ATM, Frame Relay, PPP at the link layer

Forwarding behavior independent of layer 2 and layer 3

Data transmission occurs on Label Switched Paths (LSP)

Labels are distributed using Label Distribution Protocol (LDP), or RSVP, or piggybacked on

BGP and OSPF

FEC (Forward Equivalence Class) is a representation of group of packets that share the same

requirements for their transport

Assignment of FEC to a packet is done once only as it enters into the network

22.10.200729 April 19, 2023

Model for MPLS Network• Convergence of connection oriented forwarding techniques and Internet’s routing protocols

LSR = Label Switched RouterLER = Label Edge RouterLSP = Label Switched Path

Route at edge and Switch at core

LSP

LSP

LSR

LER

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Separate forwarding and control

Forwarding:

Label Swapping

Control:

IP Router Software

Control:

IP Router Software

Forwarding:

Longest-match Lookup

Control:

ATM Forum Software

Forwarding:

Label Swapping

IP Router MPLS ATM Switch

• Exact match instead of longest prefix match (like IP) faster forwarding

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MPLS Forwarding

22.10.200732 April 19, 2023

MPLS Operation1a. Routing protocols (e.g. OSPF-TE) exchange reachability to destination networks

1b. Label Distribution Protocol (LDP) establishes label mappings to destination network

2. Ingress LER receives packet and “label”s packets

IP

IP 10

3. LSR forwards packets using label swapping

IP 20IP 40

4. LER at egress removes label and delivers packet

IP

MPLS Domain

Ingress

Egress

22.10.200733 April 19, 2023

MPLS Labels• Label assignment decisions are based on forwarding criteria like

•Destination unicast routing

•Traffic engineering

•Multicast

•Virtual Private Network

•Quality of Service

A Label could be embedded in the header of the DL layer like ATM (VPI/VCI) and FR (DLCI) or could be between DL and IP as shown below:

Bottom of Stack (first label in stack)

22.10.200734 April 19, 2023

Label and FEC Relationship

•FEC (Forwarding Equivalence Class): Assigned on the basis of IP addresses, port numbers or TOS bits.

•FEC could be associated with all the flows destined to an egress LSR.

Assignment of FEC to a packet is done by ingress router

R4 could send a packet with Label=L1, but it would mean a different FEC

22.10.200735 April 19, 2023

Label Merging Label Switched Path (LSP): A unidirectional connection through multiple LSRs.

A B C D

E F

6 3 27

5

8

6

5 A B C D

E F

6 3 8

56

5

Multi-point to Single point tree routed at Egress router

22.10.200736 April 19, 2023

LSP Hierarchy A Packet can have several labels one after the other before the IP header.

(Why? Tunneling)

(Multiple Levels of Nesting)(Tunnel 1 may be for the Enterprise with 1a for VoIP data, 1b for billing, and 1c for alarm & provisioning)

R1 R2 R3 R4

IP

3

R2A R2B R2C

72 62 82 4IP

Push Swap & Push Swap Pop & Swap Pop

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Label Distribution Establishes and Maintains a LSP that includes establishment of Label/FEC bindings between LSRs

in the LSP.

A downstream LSR can directly distribute Label/FEC (unsolicited downstream).

An upstream LSR requests a downstream for Label/FEC (downstream on demand).

Protocols like LDP, RSVP-TE are used to distribute Labels in the LSP

22.10.200738 April 19, 2023

Label Distribution

Label Distribution Protocol (LDP) [RFC 3036]

An LSR sends HELLO messages over UDP periodically to its’ neighbors to discover LDP peers

(routing protocol tells about peers)

Upon discovery, it establishes a TCP connection to its peer

Two peers then may negotiate Session parameters (label distribution option, valid label ranges,

and valid timers)

They may then exchange LDP messages over the session (label request, label mapping, label

withdraw etc)

RSVP-TE (Resource Reservation Protocol-Traffic Extension) [RFC 3209]

Path message includes a label request object, and Resv message contains a label object

Follows a downstream-on-demand model to distribute labels

Path message could contain an Explicit Route Object (ERO) to specify list of nodes

Priorities can be assigned to LSPs, where a higher one can preempt a lower one

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MPLS Protection

Dynamic routing restores the traffic (upon a failure) based on the

convergence time of the protocol Convergence can be slow

Set up secondary backup paths in addition to primary working

paths End-to-end protection

May need really fast recovery for mission critical or high priority

data Fast reroute: Setup detour paths around failed links/nodes

Temporary recovery until backup path takes over

22.10.200740 April 19, 2023

IntServ, DiffServ and MPLS An RSVP request (say guaranteed service) from one domain could be mapped to an appropriate

DiffServ PHB at another domain that again could be mapped to a possible MPLS FEC at the edge of another MPLS domain.

22.10.200741 April 19, 2023

Generalized MPLS (GMPLS)

MPLS – the base technology (for packet switched nws) GMPLS – extension of MPLS to provide the control plane

(signaling and routing) for devices that switching in any of these domains: packet, time, wavelength and fiber.

22.10.200742 April 19, 2023

MPLS vs. GMPLS

For packet-switching nw only Focuses mainly on the data

plane

For packet switched capable (PSC) as well as non-PSC interfaces.

Focuses on the control plane that performs connection management for the data plane

MPLS GMPLS

22.10.200743 April 19, 2023

MPLS vs. GMPLS (cont.)

Requires Label Switched Path (LSP) to be set up b/w routers at both ends

LSP can be set up b/w any similar types of Label Switched Routers (LSR) e.g. b/w SONET/SDH ADM to form a TDM LSP

Scale better by forming a forwarding hierarchy

Functions specific to optical nw such as suggested label and bi-directional LSP setup

MPLS GMPLS

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Goals of GMPLS

A common control plane promises to simplify network operation and management by: Automating end-to-end provisioning of connections Managing network resources

22.10.200745 April 19, 2023

Summary of the GMPLS Protocol Suite

Extended the signaling (RSVP-TE, CR-LSP) and routing protocols (OSPF-TE, IS-IS-TE) to accommodate the characteristics of TDM/SONET & optical networks.

A new protocol, Link Management Protocol (LMP) has been introduced to manage and maintain the health of the control and data planes between two neighboring nodes.

22.10.200746 April 19, 2023

LSP Creation in GMPLS-Based Networks / Hierarchical LSP

1. LSP (LSPλ) is established between OXC1 and OXC2 and capable of delivering OC-192 wavelength to tunnel in TDM LSPs.

2. LSP (LSPtdi) is established between DCSi and DCSe.

3. LSP (LSPtdm) is established between DCS1 and DCS2.

4. LSP (LSPpi) is established between LSR2 and LSR3 (LSPpi).

5. LSP (LSPpc) is established between LSR1 and LSR4.

22.10.200747 April 19, 2023

QoS for Mobile Networks

Problems: Current IP QoS Signaling is not mobility aware (RSVP, DiffServ etc) Resources may not be available for the new path Handoff latency Different QoS mechanisms

Requirements/challenges: Minimize disruption in QoS during handover Localize the QoS re-establishment to only the effected parts of the packet path Release any old QoS state after handover as early as possible Deal with multiple QoS mechanisms deployed

Mobile RSVP (MRSVP) Use advance resource reservations Common path identification Mobile proxy: refresh RSVP state instead of energy constrained mobile device

22.10.200748 April 19, 2023

QoS for MANETs

More problems: No infrastructure, all mobile battery limited devices Frequent topology changes and high mobility

INSIGNIA Support for the delivery of adaptive services in mobile ad hoc

networks See Seoung-Bum Lee et al. INSIGNIA: An IP-Based Quality of

Service Framework For Mobile Ad Hoc Networks, Journal of Parallel and Distributed Computing, 2000.

22.10.200749 April 19, 2023

Next Steps in Signaling (NSIS)

RSVP not widely used for resource reservation Used for MPLS path setup Security an open issue Limited support for IP mobility

IETF NSIS working group is looking at new ways to do QoS signaling Re-use, where appropriate, the mechanisms of RSVP See e.g. rfc4080

22.10.200750 April 19, 2023

References1. Andrew S. Tanenbaum, Computer Networks, Fourth Edition, Pearson Education, 2006.

2. James F. Kurose, and Keith W. Ross: Computer Networking: A Top-Down Approach Featuring the Internet, Third Edition, Pearson Education, 2006.

3. Alberto Leon-Garcia and Indra Widjaja, Communication Networks: Fundamental Concepts and Key Architectures, Second Edition, Tata McGraw-Hill, 2005.

4. IP QoS Architectures and Protocols, Packet Broadband Network Handbook, Digital Engineering Library, McGraw Hill, 2004.

5. Congestion Control and Quality of Service, Data Communication and Networking, Digital Engineering Library, McGraw Hill, 2006.

6. Curado, M. and Monteiro, E. , "A Survey of QoS Routing Algorithms", in Proc. of the International Conference on Information Technology (ICIT2004),

December 2004

7. Manner Jukka, Lopez A, Mihailovi A, Velayos H, Hepworth E, and Y Khouaja, Evaluation of Mobility and QoS Interaction, Computer Networks Volume 38,

Issue 2, 5 Feb 2002, pp. 137-163.

8. Anup Kumar Talukdar, B. R. Badrinath, and Arup Acharya, MRSVP: A Resource Reservation Protocol for an Integrated Services Network with Mobile Hosts,

Wireless Networks, 7, 5–19, 2001.

9. Rajeev Koodli, and Charles E. Perkins, Fast Handovers and Context Transfers in Mobile Networks, ACM SIGCOMM Computer Communications Review,

Special Issue on Wireless Extensions to Internet, 2001.

10. J. Hillebrand, C.Prehofer, R. Bless, M. Zitterbart, Quality-of-Service Signaling for Next-Generation IP-based Mobile Networks, IEEE Communications

Magazine, June 2004.

11. Seoung-Bum Lee, G. Ahn, X. Zhang and A. T. Campbell, INSIGNIA: An IP-Based Quality of Service Framework For Mobile Ad Hoc Networks, Journal of

Parallel and Distributed Computing, 2000.

12. Chittaranjan Hota, Sanjay Jha, G Raghurama, Distributed Dynamic Resource Management in IP VPNs to Guarantee Quality of Service, IEEE ICON 2004,

Singapore.

13. RFC 2205: Resource Reservation Protocol, Braden, Zhang et al.

14. RFC 3031: Multiprotocol Label Switching (MPLS), Rosen, Viswanathan and Callon.

15. RFC 2475: An Architecture for Differentiated Services, S. Blake, D. Black et al.

16. RFC 4080: Next Steps in Signaling (NSIS): Framework, R. Hancock, G. Karagiannis et al., 2005.

17. RFC 2326: Real Time Streaming Protocol (RTSP), H. Schulzrinne et al., 1998

18. GMPLS tutorial: http://www.iec.org/online/tutorials/gmpls/

T-110.5110 Computer Networks II Quality of Service 20.10.2008 Dr. Matti Siekkinen [email protected] (Primary sources: C. Hota: “Quality of Service in.

Documents

qos requirements

endtoend qos

qos control mechanisms

qos feedback rtcp

ip quality of service

service byte

best effort service

application requirements