Internet Quality of Service (QoS) issues in competitive commercial network operation Bjørn Jæger...

Internet Quality of Service (QoS) issues in competitive commercial

network operation

Bjørn Jæger Talk on given topic for the

Dr. Scient. dissertationSeptember 4, 2000

Department of InformaticsUniversity of Bergen

Jæger: given topic 2000

Overview

Introduction Internet Quality of Service (QoS)

– Overlay networks– Integrated Services– Differentiated Services– Multi Protocol Label Switching

Competitive network operation Summary


Internet development milestones

Humans communicate by phone1876

Computers communicateFirst computer network: SAGE Semi-Automatic Ground Equipment (MIT, USA)

1950’s

ARPANET: Advanced Research Projects Agency NETworkFirst network to use layered protocols, flow control, and fault-tolerance.Introduced the term “Packet” for units of data sent: Packet Switched Network

1969

1973

1983

First ARPANET connection outside USDirect Link: Virginia - Kjeller, Norway

1986

ARPANET starts using TCP/IP protocol connecting different networksBecame known as the Internet.

IETF: Internet Engineering Task Force establishedOpen international community developing Internet standardsNow developing QoS related standards.


Internet has become a world-wide data network1990’s

1991

1996

2000

1. Commercial Internet Operation(NSF lifts restrictions on the commercial use)

2. World Wide Web (HTTP, HTML)

Internet phones catch the attention of US telecommunication

companies who ask the US Congress to ban the technology

(which has been around for years)

High Demand for QoS sensitive services. Internet Service Providers

(ISPs) want to provide Voice, Video and Data over the Internet in

order to maximize revenue. Require new technology.

Internet development milestones

First Internet audiocast (radio)1992

First Internet video conference1993


Traffic Handling in the Present-Day Internet

Each node broadcast Link State information

– Part of IGP: Interior Gateway Protocol

Administrative Domain

Each node obtains a complete picture of all links

and routers (topology information)

Aggregation of states over Administrative Domains



Each router use the topology information to compute

the Shortest Path to every destination in the network

Based on this each router builds a Forwarding Table

associating an address prefix with the next hop linkMolde-Bergen Prefix: Use link Molde-Trondheim

… ...

Molde-Ålesund: Molde-ÅlesundMolde-Kristiansund: Molde-KristiansundMolde-Trondheim: Molde-Trondheim Molde-Bergen: Molde-Trondheim-BergenMolde-Oslo: Molde-Trondheim-Oslo

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When a packet arrives at a router the Forwarding Table is consulted, and packets are forwarded out on the appropriate link based on the destination Internet Protocol (IP) address

Each router makes an autonomous decision about how to forward a packet

Forwarding proceeds in a connectionless way at every hop


Can cause imbalance of network load since it use the

shortest path

Problems with the Present-Day Internet

It is desirable to have routing which optimize the

traffic distribution for a given network topology

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congested Alternative paths:

underutilized


No Traffic Management standardized: A router handles all packets in the same way as fast as it can: Best Effort Service

Problems with the Present-Day Internet

Consequently, there is no way to predict a priori or guarantee the Quality of Service (QoS) that a particular flow will receive

Voice, Video, and other real time services will not meet users expectation of quality

Also, in case of link failures, link state is distributed slowly: Slow convergence of routing to avoid failed device.

Need to be able to control the network resources in order to provide a specified Quality of Service (QoS)


What is Quality of Service (QoS)?

Quality of Service can be characterized by:– Bandwidth (bits per second)

– Delay: End-to-End

– Packet Loss probability

– Jitter (variation in delay among packets)

Human ear and eye are sensitive to delay and delay variation (Voice & Video services)

Data applications are sensitive to data loss Generally: Unequal allocation of resources among

connections are needed to provide QoS Mechanisms: Routing, Classifying, Scheduling, Queuing,

Admission Control, Policing, Capacity Planning


Approaches to provide Internet QoS

Overlay networks

Integrated Services

Differentiated Services

MPLS


The Overlay Solution

Run IP traffic over a circuit switched network, like e.g. ATM Connect IP backbone by a complete mesh of permanent virtual circuits

ATM Core

Logical network topology (mesh)

- PVCs serve as Point-to-Point IP links

ATM PVCs

Physical network topology

- IP over ATM



Advantages:

– Layer 2 (ATM) manage bandwidth

– Mesh of VCs: prevents hop-by-hop aggregation

– IP traffic can be individually routed through the layer 2 (ATM) topology.

– Can move traffic from overloaded links to underutilized links

Disadvantages:

– Need to build and manage two networks with different technologies

– Increased complexity of design and management

– Inefficient due to packing and encapsulation overhead associated with

Layer 2 (ATM)



Disadvantages continued:

An edge router represents a User

Domain (many connections) ATM PVCs

Problem: How to do the mapping between IP-connections and the PVC’s:

Is IP-connections aggregated by the user domain before transmission on a PVC?

Or

Is IP-connections routed over PVCs which are aggregated in the ATM-network?


Integrated Services - IntServ

Applications set up paths and reserve resources before any user data is sent

Four components:– Signaling– Admission control– Classification– Scheduling



Signaling: Resource ReSerVation Protocol - RSVP:Carries resource reservation requests through the network with

characteristics of source traffic and QoS specifications required by

receiver (receiver oriented)

Sender ReceiverNetworkPATH w/Traffic Spec

Available Resources

RESV w/QoS Spec

PATH w/Traffic Spec

RESV w/QoS Spec

Admission Control:– Intermediate routers can reject or accept reservations

– Accept: Each router installs Flow State information


Classification:– Upon receiving a packet each router perform a

classification based on Flow State, and places the packet in a specific queue

Scheduling:– The scheduler will schedule the packet for transmission

according to its QoS requirements



Problems with IntServ

Flow State information needed for each flow in each router

Huge memory and processing capabilities in core routers needed ==> does not scale

Requirement on routers are high, all need:– RSVP, admission control, classification, scheduling


Differentiated Services - DiffServ

The IPv4 header:

Type of Service Precedence

3 b 4 b 1 b

Unused HdrLen

4 b 4 b

Ver Total Length

16 b

Previously: Precedence bits used to indicate– low-delay, high throughput, low loss service, but Not Standardized

IETF DiffServ working Group Charter:

– Define a set of classes by defining the layout of IPv4 DS-field

– Define packet forwarding rules: Per-Hop-Behavior, PHB


By marking DS-fields of packets differently and handling packets based on their DS-field several differentiated service classes can be created

Relative Priority Scheme A customer get Differentiated Service from an

Internet Service Provider (ISP) by getting a Service Level Agreement (SLA) with the provider– Static SLA long term negotiation (months)

– Dynamic SLA needs signaling to request services on demand (e.g. RSVP)



Customers mark DS-field of each packet

Classification, policing, shaping:– At the ingress of an ISP domain (at edge) based on the SLA

– In core: behavioral aggregate

Service is allocated by granularity of a class==> scaleable

Core routers must be simple and fast, boundary routers need not forward packets very quickly since customer links are relatively slow



Problems with DiffServ

Per-Hop-Behavior (PHB) / Relative Priorities

Designing end-to-end services with weighted guarantees at individual hops is difficult

Can not ensure resource availability inside the network– based on assumption that arrival rate of Guaranteed Service is far

below the service rate - can not hold in general

– statistical guarantees only

Guarantees require stability of paths -- route pinning needed


A label is inserted in IP packets at the ingress of an MPLS-capable domain– Mapping between IP-packets and labels is described by Forwarding

Equivalence Classes (FECs). Done only once, at the ingress.

Before packet leaves MPLS domain its label is removed

Multi Protocol Label Switching - MPLS

MPLS-domainIP-networkLSR

LSR

MPLS capable router examines only the label when forwarding a packet: Label Switched Router (LSR)



Labels are distributed by a signaling protocol– Label Distribution Protocol (LDP) or RSVP

Explicit Route decided by source possible– IETF work to extend IGP Link State information w/link capacity– Facilitates Traffic Management

When a packet arrives at a router the label is used as an index into the forwarding table which specifies the QoS ==> FAST

The incoming label is swapped with the outgoing label and the packet is switched to the next LSR.


Can provide Guaranteed Quality of Service (QoS)– Explicit Routes & Traffic Engineering

Labels can be stacked in a LSR:– Allows an arbitrary number of labels giving possibility for multiple

control planes to act on a packet (contrast with two in ATM: VPI, VCI, one in Frame Relay, DLCI)

Fast Recovery Possible– by pushing and popping a backup path label on the stack in order to

make a backup LSP around the failure.



Mixing IntServ, DiffServ and MPLS?

By definition, the internet is a set of networks connected to each other, each typically by one ISP

DiffServ

IntServ MPLS

Combinations, e.g.

DiffServ/MPLS

IPv4

Network Access Point

A mapping between the “QoS islands” is needed Not standardized, work in progress


Mixing IntServ and DiffServ?

Intserv: not scalable, per flow DiffServ scalable, aggregate

CoreIP Network

Regional/AccessIP Network

Regional/AccessIP Network

IntServ IntServ

DiffServ

QoS Translations: Flow State <--> Relative Priority– Service Level Agreement (SLA) which includes

Traffic Conditioning Agreement (TCA)

Edge Core Routers must apply mapping


Mixing DiffServ and MPLS?

DiffServ (modifies IP packet) MPLS Encapsulate IP packets

MPLS domain can be seen as a link by DiffServ MPLS can use DiffServ’s DS-field to define FEC

MPLS-domainDiffServ

DiffServ


Mixing IntServ and MPLS?

IntServ (Flow State) use RSVP signalling MPLS (Labels) can use RSVP -signaling to set

up Labels and at the same time reserve resources for the labels as in IntServ

In case LDP: translation LDP <--> RSVP needed

MPLS-domainIntServ

IntServ


Pricing, Accounting and Charging

Previously:– Best Effort Service

– Fixed price for Internet connection, unlimited usage

Future:– Differentiated QoS services

– Pricing mechanism needed or else everybody will use highest quality possibly (tragedy of the commons).

» Several schemes proposed, work in progress.

– Accounting and charging, IETF work in progress

– Management could be done by connecting to the well established telecommunication management system


What technology to choose?

Overlay, IntServ, DiffServ, or MPLS?

Today: 80 % of the large ISP providers in US use the overlay approach. (Although mostly for data services)

Tradeoffs exists among the technologies and type of Internet Service Provider– Regional ISP

– Enterprise ISP

– Backbone ISP


What is the incremental cost of doing QoS in my network?

Consider short term / long run perspective– Short term:

» Does statistical guarantees suffice?

» What QoS upgrades does my equipment manufacturer offer?

– Long term: » Some users need absolute guarantees

» Maybe change equipment provider



Regional ISP vs. Backbone ISPs– Regional: Scaling not a major issue, can use IntServ/RSVP

– Backbone: Scaling important, aggregation needed

» DiffServ if statistical guarantees suffices

» MPLS if guaranteed service is required

Network Management functions– Short/long term (partly vs. full management support)

– Regional/backbone (partly vs. full management support)



Summary

Technologies for guaranteed Internet Quality of Service (QoS) are available

Unresolved issues– Standards for QoS translations among QoS technologies

– Standards for QoS translations among administrative domains

– Standards for Network Management needed: Especially: Pricing, Accounting and Charging

What technology to choose depend upon several factors including: time perspective, size of network, and current manufacturer used

Internet Quality of Service (QoS) issues in competitive commercial network operation Bjørn Jæger...

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