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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
Jæger: given topic 2000
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.
Jæger: given topic 2000
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
Jæger: given topic 2000
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
Jæger: given topic 2000
Traffic Handling in the Present-Day Internet
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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Jæger: given topic 2000
Traffic Handling in the Present-Day Internet
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
Jæger: given topic 2000
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
Jæger: given topic 2000
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)
Jæger: given topic 2000
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
Jæger: given topic 2000
Approaches to provide Internet QoS
Overlay networks
Integrated Services
Differentiated Services
MPLS
Jæger: given topic 2000
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
Jæger: given topic 2000
The Overlay Solution
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)
Jæger: given topic 2000
The Overlay Solution
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?
Jæger: given topic 2000
Integrated Services - IntServ
Applications set up paths and reserve resources before any user data is sent
Four components:– Signaling– Admission control– Classification– Scheduling
Jæger: given topic 2000
Integrated Services - IntServ
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
Jæger: given topic 2000
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
Integrated Services - IntServ
Jæger: given topic 2000
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
Jæger: given topic 2000
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
Jæger: given topic 2000
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)
Differentiated Services - DiffServ
Jæger: given topic 2000
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
Differentiated Services - DiffServ
Jæger: given topic 2000
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
Jæger: given topic 2000
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)
Jæger: given topic 2000
Multi Protocol Label Switching - MPLS
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.
Jæger: given topic 2000
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.
Multi Protocol Label Switching - MPLS
Jæger: given topic 2000
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
Jæger: given topic 2000
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
Jæger: given topic 2000
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
Jæger: given topic 2000
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
Jæger: given topic 2000
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
Jæger: given topic 2000
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
Jæger: given topic 2000
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
What technology to choose?
Jæger: given topic 2000
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)
What technology to choose?
Jæger: given topic 2000
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
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