Beyond Best-Effort Beyond Best-Effort ServiceService

Advanced Multimedia

University of PalestineUniversity of Palestine Eng. Wisam ZaqootEng. Wisam Zaqoot November 2010November 2010

Ref: Computer Networking: A Top Down Approach, 4th ed., Kurose & Ross

QoS PrinciplesQoS Principles

Was our bag of tricks Was our bag of tricks enoughenough??

We learned in previous lectures how We learned in previous lectures how sequence UDP, numbers, timestamps, FEC, sequence UDP, numbers, timestamps, FEC, CDN, RTP and RTCP can be used by CDN, RTP and RTCP can be used by multimedia networking applications to multimedia networking applications to enhance the internet best-effort service.enhance the internet best-effort service.

But are these techniques alone enough to But are these techniques alone enough to support reliable and robust multimedia support reliable and robust multimedia applications, like an IP telephony ??applications, like an IP telephony ?? NoNo. An application will receive whatever level of . An application will receive whatever level of performance (e.g., end-end packet delay and loss) that performance (e.g., end-end packet delay and loss) that thethe network is able to provide at that moment.network is able to provide at that moment.

In addition, the internet today In addition, the internet today does not allow delay-does not allow delay-sensitive multimedia applications to request any special sensitive multimedia applications to request any special treatment.treatment.

Providing Multiple Classes Providing Multiple Classes of Serviceof Service

thus far: making the best of best effort servicethus far: making the best of best effort service one-size fits all service modelone-size fits all service model

alternative: multiple classes of servicealternative: multiple classes of service partition traffic into classespartition traffic into classes network treats different classes of traffic network treats different classes of traffic

differently (analogy: VIP service vs regular differently (analogy: VIP service vs regular service)service)

0111

granularity: granularity: differential service differential service among multiple among multiple classes, not among classes, not among individual individual connectionsconnections

history: Type of history: Type of Service (ToS) bits in Service (ToS) bits in IPv4IPv4

In fact, many alternatives like In fact, many alternatives like diffservdiffserv, , intservintserv, and , and rsvprsvp were were proposed.proposed.

Multiple classes of service: Multiple classes of service: scenarioscenario

R1 R2H1

H2

H3

H41.5 Mbps linkR1 output

interface queue

The basic scenario: The basic scenario: two application packet flows originate on two application packet flows originate on hosts H1 and H2 on one LAN and are destined for hosts H3 and hosts H1 and H2 on one LAN and are destined for hosts H3 and H4 on another LAN. The routers on the two LANs are connected H4 on another LAN. The routers on the two LANs are connected by a 1.5 Mbps link.by a 1.5 Mbps link. We have to We have to focus on the output queue of router R1; it is here focus on the output queue of router R1; it is here

that packet delay and packet loss will occur if the aggregate that packet delay and packet loss will occur if the aggregate sending rate of the H1 and H2 exceeds 1.5 Mbps.sending rate of the H1 and H2 exceeds 1.5 Mbps.

Scenario 1: mixed FTP Scenario 1: mixed FTP and audioand audio Example: 1Mbps IP phone, FTP share 1.5 Example: 1Mbps IP phone, FTP share 1.5

Mbps link. Mbps link. bursts of FTP can fill the queue, congest router and bursts of FTP can fill the queue, congest router and

cause audio losscause audio loss want to give priority to audio over FTPwant to give priority to audio over FTP

packet marking needed for router to distinguish between different classes; and new router policy to treat packets accordingly

Principle 1

R1 R2

Scenario 2: mixed audio and high Scenario 2: mixed audio and high priority FTPpriority FTP

Example: 1Mbps IP phone, FTP share 1.5 Mbps Example: 1Mbps IP phone, FTP share 1.5 Mbps link. link. Suppose FTP user has purchased "platinum

service“ While audio user has purchased cheap service

packet classification needed for router to distinguish between different classes; and new router policy to treat packets accordingly

Principle 1

R1 R2

Scenario 3: A Misbehaving Audio Application and an FTP Transfer

what if applications misbehave (audio sends higher what if applications misbehave (audio sends higher than declared rate)than declared rate) policing: force source adherence to bandwidth allocationspolicing: force source adherence to bandwidth allocations

marking and policing at network edge:marking and policing at network edge: similar to ATM UNI (User Network Interface)similar to ATM UNI (User Network Interface)

provide protection (isolation) for one class from others, so that one flow is not adversely affected by another misbehaving flow.

Principle 2

R1 R2

1.5 Mbps link

1 Mbps phone

packet marking and policing

Scenario 3: A Misbehaving Audio Application and an FTP Transfer

(cont.) It is possible to "police" traffic flows and a traffic

flow must meet certain criteria, for example that the audio flow not exceed a peak rate of 1 Mbps. In the case of a misbehaving application, drop or

delay packets that are in violation of the criteria. The marking and policing mechanisms are located at

the "edge" of the network, either in the end system, or at an edge router.

An alternate approach for providing isolation among traffic flows is for the link-level packet scheduling mechanism to explicitly allocate a fixed amount of link bandwidth to each application flow. i.e. allocate 1Mbps at R1 for audio and 0.5 Mbps

allocated for the ftp flow. This is as if there were logical links with capacity 1.0 and 0.5 Mbps.

Scenario 4: Allocating fixed bandwidth to flows

Allocating Allocating fixed fixed (non-sharable) bandwidth to flow: (non-sharable) bandwidth to flow: inefficientinefficient use of bandwidth if flows doesn’t use its use of bandwidth if flows doesn’t use its allocationallocation

While providing isolation, it is desirable to use resources as efficiently as possible

Principle 3

R1R2

1.5 Mbps link

1 Mbps phone

1 Mbps logical link

0.5 Mbps logical link

Scenario 5: Two 1 Mbps Audio Applications over an Overloaded

1.5 Mbps Link two 1 Mbps audio connections transmit

their packets over the 1.5 Mbps link. The combined data rate of the two flows (2 Mbps) exceeds the link capacity. If the two applications equally share the

bandwidth, each would only receive 0.75 Mbps. This is an unacceptably low quality.

there's no need even to transmit any audio packets in the first place.

A call admission process is needed in which flows declare their QoS requirements and are then either

admitted to the network (at the required QoS) or blocked from the network (if the required QoS can

not be provided by the network.)

Principle 4