Differentiated Services Slide

Wednesday, November 5, 2003 1

Differentiated Services (DiffServ)

Seminar on transport of multimedia streams over the wireless internet

University of Helsinki

Cristiano di FloraUniversity of Naples “Federico II”

[email protected]


Presentation Outline

♦ Introduction to QoS♦ Differentiated Services Network (DiffServ)♦ Diffserv Router Architecture♦ Bandwidth Brokers♦ Conclusion


Quality of Service (QoS) - 1/3

♦ What is it?– When you can measure what you are talking about

and express it in numbers, you know something about it - Lord Kelvin


Quality of Service (QoS) – 2/3♦ Performance observed by the end user

– Combination of Delay, Jitter, Loss, Throughput– Two most important for QoS: Delay + Loss– Jitter is important for real-time live streaming (no

buffering)♦ QoS for different applications

– Real-time applications need assurance from the network for timely delivery

– Non-real-time applications need correctness of information delivery


Quality of Service (QoS) – 3/3

♦ What causes poor QoS?– Lack of resources in network or hosts

♦ Techniques to provide proper QoS– Overprovisioning: huge link bandwidth and high

performance routers/switches– Resource management (IntServ and DiffServ)

• Traffic control• Generic switch architecture => ATM


QoS via overprovisioning

♦ Fiber links can now support 1.6 Tbps♦ Bottleneck is electronic switches/routers♦ Optical switching currently switches paths, not

packets (say av length 8000 bits)

Optical(1.6 Tbps)

Electrical(160 M packets/s)

Optical(1.6 Tbps)


QoS via resource management

♦ Traffic differentiation and prioritization♦ Resource negotiation and Service Level

Agreement (SLA) – Network availability– Guaranteed service level = predictable QoS– But guaranteed in a statistical sense


QoS via resource management

♦ Congestion control (reactive)♦ Admission control (proactive)

– Traffic policing• Leaky bucket

– Traffic shaping• Improves predictability of flow, but introduces delay

and reduces statistical multiplexing gains


Congestion control

♦ Reactive congestion control– Differentiate traffic

• ATM => CLP bit, FR =>DE bit, IP => ToS field

– Act immediately to relieve congestion by discarding low value packets

=> Utility of low priority traffic cushion

– Take steps to limit congestion by getting sources to reduce transmission rate


Internet structure

♦ Past = classic IP with no QoS♦ Present = IntServ, DiffServ

– IntServ: end-to-end QoS but does not scale– DiffServ: scales well, but coarse grained

♦ Future = IPv6, all optical core, IntServ over DiffServ, Internet2, and things coming out of this conference!


DiffServ - Differentiated Services network

Effort by IETF to provide end-to end QoSResult of reaction against the scalability problem faced by IntServ/RSVP

Eliminates storing soft state information about individual flows in the router

Aims to provide differentiation among variety of traffics by aggregating flows into a small number of groups (the so-called Class Of Service, CoS)Based on a classify – conditioning – forwarding approach


DiffServ and IPv4

♦ IPv4 Packet header format

8-bit type of service (TOS)

3-bitprecedence

1-bitunused

4-bit type of service

Total Length in bytes (16)

Time to Live (8)

Options (if any)

Bit 0 Bit 31Version

(4)Hdr Len

(4) TOS (8)

Indication (16 bits) Flags (3) Fragment Offset (13)

Source IP Address

Destination IP Address

Header Checksum (16)Protocol (8)


DiffServ Code Point (DSCP)♦ DiffServ Code point (DSCP)♦ Use of ToS field of IPv4,Traffic class field of IPv6♦ Defined in early 1980s, but was largely unused until

introduction of prioritization into IP header0 5 7

♦ CU: Currently UnusedPool Codepoint space Allocation

1 XXXXX0 Standard activity2 XXXX11 Experiment/local action3 XXXX01 Experiment/local action

DSCP CU


DiffServ domains

♦ A DiffServ domain (DS) is defined as a set of contiguous DS compliant networks having DS compliant nodes

♦ DS is implemented in individual routers by queuing and forwarding packets based on the DSCP

♦ DS is not based on priority, application or flow but on possible forwarding behavior of packets called Per Hop Behavior (PHB)


Per Hop Beavior - 1/2

♦ PHB defines the set of rules for a particular class of traffic

♦ Does not require a particular queuing discipline

♦ 6-bit DSCP identifies a particular PHB to be applied to a packet


Per Hop Behavior – 2/2♦ PHB defines behavior of individual routers rather

than end-to-end services♦ PHB provides a particular service level (bandwidth,

queuing and dropping decisions) in accordance with network policy

♦ 2 primary PHBs defined by the DiffServ working group– Expedited and Assured Forwarding

♦ One additional default PHB (Best-effort, traditional internet, DCSP)


Expedited Forwarding (EF) PHB♦ Premium service♦ Meant for traffic sensitive to delay and loss ♦ Provides bandwidth guarantees (Virtual Leased Line

service): bwidth cannot be exceeded but can be left idle♦ Router guarantees performance if the arrival rate of

packets is lower than the forwarding rate♦ Implementation strategy:

– strict priority over all other packets– drop “out-of-profile” packets– need for admission control and traffic shaping


Assured Forward (AF) PHB♦ More complex than EF♦ AF divides traffic into four different classes in three different

classes of service (Gold, Silver and Bronze)Drop Pref. Class 1 Class 2 Class 3 Class 4

Low 010000 011000 100000 101000Medium 010010 011010 100010 101010High 010100 011100 100100 101100

♦ During congestion, router may discard packets based on their drop preferences

♦ AF packets have higher priority than best-effort ones♦ Classes are managed seperately

– No packet-reordering within a single domain– A specifc queue for each class


DiffServ architecture♦ DiffServ Architecture:

DS Domain 1

DS Domain 2

Edge Routers mark packets(Ingress Router)

Core Routers only forward Egress Router


DiffServ and Autonomous Systems♦ Service Level Agreement (SLA): a set of parameters

and their values which together define the service offered to a traffic stream by a DS domain

♦ Traffic Conditioning Agreement (TCA): a set of parameters and their values which together specify a set of classifier rules and traffic profile

♦ Both inbound and outbound packets in a DS domain are marked according to SLA and TCAs

♦ DS may trigger accounting mechanism at network boundaries to track each service usage for quality level monitoring and billing purposes

♦ DS is rule based, hence good for policy based network management


Diffserv Router Architecture – Traffic entering into a DS domain are conditioned prior

to assignment of DSCP– Traffic classification and conditioning at the Edge

Router (Ingress)

– Specific SLAs are enforced at the ingress and egress nodes of the network by conditioning the aggregate traffic to fit the terms of the SLA.

Meter

Classifier Marker Shaper / Dropper

PACKETS

DROP

FORWARD


Diffserv Router Architecture

Behavior Aggregate: selects packets basedonly on the DSCPs.

Multi-Field: looks intocustomer-specific fields


Resource management♦ Resource management challenges

– How to decide what users get which type of service?– Where to implement bandwidth sharing policy?– Who will ensure proper resource management?– Interoperability of services between different domains– Different domains might use different PHBs for the same service– Same PHB – Different DSCP– Same PHB and DSCP – different charging mechanisms and policies

♦ Solution:– Manual or automatic configuration– Automatic: many (ongoing research) but we will emphasize only one

=> Bandwidth Broker (BB)


Bandwidth Broker - 1/3

♦ Bandwidth Broker (BB), initially proposed by Van Jacobson

♦ BB is a logical entity residing in each administrative domain:– internally keeps track of QoS requests from

individual users and applications and allocates resources according to some policy (intra-domain)

– working as an agent between BBs of neighbor domains for setting up & maintaining bilateral agreement (inter-domain)


Bandwidth Broker – 2/3♦ BB also manages resources for each class

– by keeping track of current allocation of marked traffic– interpreting new requests in the light of policies and

current allocation♦ Configures edge routers to deliver a particular service to

flows♦ Negotiation of SLAs with BBs of neighboring domains♦ Translation of SLAs into one or several TCAs for edge

devices♦ Delivery of the TCAs to the edge routers of the

administered domain, using one of many proposed protocols


Bandwidth Broker – 3/3Negotiation of SLAs with BBs of neighboring domains


Traffic conditioning and QoS in Wireless Diffserv♦ Huge Heterogeneity (connectivity, user devices, autonomous systems)♦ Different parameters for evaluating the perceived QoS♦ Support for next-generation applications (e.g. human-critical, security-

critical applications). ♦ Roaming Users: all edge routers must know user QoS profiles

– Scalability issues– Huge Database dimensions– Solutions based on a centralized repository are preferable

♦ J.C. Chen, A. McAuley, V. Sarangan, S. Baba, and Y. Ohba, DynamicService Negotiation Protocol (DSNP) and Wireless DiffServ, ICC'02, New York city, April 2002.

♦ Proposals for using diffserv in IP-Mobility environments:– Bongkyo Moon; Arhvami, H. , DiffServ extensions for QoS Provisioning in

IP mobility environments, in IEEE Wireless Communications, October 2003Page(s): 38- 44(a Drop-off strategy for managing hand-over is also presented)


Conclusions

♦ DiffServ provides a scalable solution for QoS over the Internet

♦ Provides coarse-grain end-to-end QoS♦ Cannot provide per-flow (fine-grain) QoS♦ Edge routers are configured to classify and mark ♦ Bandwidth Brokers play central role at the control

level of DiffServ architecture


Conclusion - QoS SongWe don’t need no reservationWe don’t need no admission controlAll applications must be adaptiveThe Net work’s just fine, so leave it aloneHey! Professor! Leave the Net alone!We don’t need no traffic managementOver-provision bandwidth for allThe only true god is TCP/IPThe Net isn’t broken, so leave it aloneHey! Professor! Leave the Net alone!All we want is flat rate pricing for all

– Keshav: “An Engineering Approach to Computer Networking”

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