Quality of Service in Networks

Presented by: Shatrunjay Rawat

Communication Group – R&D

CMC Limited

What does Users Expect?

Best service Whenever they want Minimum Price

Service Provider’s Limitations

Limited Resources High Requirements / Demand Cost of Resources Profit Moto

Meeting Point?

Quality of Service Provisioning

Quality of Service Parameters

Availability Reliability Bandwidth Delay and Response Time BER, etc Cost?

Popular Network Protocols

Ethernet Token Ring & Token Bus X.25 Frame Relay TDM ATM IP

Ethernet

Best Effort Mechanism Non deterministic Quality is

Traffic Dependent Bandwidth Dependent

Token Ring & Token Bus

Assured Response Known Delay Limited Control on QoS

Frame Relay

Reservation of Resources PVC & SVC Data and Voice Not Scalable:

Bandwidth limited to 2Mbps

TDM

Dedicated Links and Bandwidth Best Response Time Lowest Delay Voice, Data, Video Denial of Service Wastage of Bandwidth Limited Flexibility Costly

ATM

Good QoS features Various Classes Services

CBR, ABR, VBR, etc

Data, Voice, Video Scalable Bandwidth Denial of Service Costly

IP

Connection-less Best effort Service is not denied Primarily designed for data communication Most Popular i.e. widely used Cost effective Traditionally no QoS control

Present Scenario

Demand for Voice and Video over Internet

Needs Differential QoS for Data, Voice and Video to avoid jitter and packet loss

Needs Fundamental Change in the Internet Architecture

QoS - Types

Resource Reservation (Integrated Service)

Prioritisation (Differentiated Service)

Resource Reservation

network resources are apportioned according to an application's QoS request, and subject to bandwidth management policy.

Prioritisation

network traffic is classified and apportioned network resources according to bandwidth management policy criteria.

To enable QoS, network elements give preferential treatment to classifications identified as having more demanding requirements.

Type of QoS Characterisation

Per Flow Identified by five tuple: transport protocol,

source address, source port number, destination address, and destination port number

Per Aggregate An aggregate of two or more flows

QoS Protocols

ReSerVation Protocol (RSVP) Differentiated Services (DiffServ) Multi Protocol Labeling Switching (MPLS) Subnet Bandwidth Management (SBM)

These protocols are not mutually exclusive of one another

ReSerVation Protocol (RSVP) RFC2205, 1997 Is a Transport Layer Protocol Operates on top of IPv4 and IPv6 Internet control protocol like ICMP and

IGMP Not a routing protocol Operates with unicast and multicast routing

protocols

RSVP

Request resources for simplex flows Receiver is responsible for making

request for QoS IP fragmentation will cause problem for

QoS as some information may be lost that is used for identifying packets

RSVP

Implemented by mechanisms called ‘traffic control’ Packet classifier Admission control

Determines the availability of resources

Policy control Determines administrative rights for QoS

Packet scheduler

RSVP

Salient Features Reservations in each router are "soft," which means

they need to be refreshed periodically by the receiver(s).

Applications require APIs to specify the flow requirements, initiate the reservation request, and receive notification of reservation success or failure after the initial request and throughout a session.

Reservations are receiver-based, in order to efficiently accommodate large heterogeneous (multicast) receiver groups.

RSVP

Salient Features Multicast reservations are "merged" at traffic

replication points on their way upstream RSVP traffic can traverse non-RSVP routers, this

creates a "weak-link" in the QoS chain where the service falls-back to "best effort“

There are two types of RSVP Protocols: Native RSVP and UDP-encapsulated RSVP. The 802 "Subnet Bandwidth Manager" only supports Native RSVP.

RSVP

RSVP provides the highest level of IP QoS available

Comes at the price of complexity and overhead,

Differentiated Services (DiffServ) Provides a simple and coarse method

of classifying services of various applications

There are currently two standard per hop behaviors (PHBs) defined that effectively represent two service levels (traffic classes):

Expedited Forwarding (EF) Assured Forwarding (AF)

DiffServ:Expedited Forwarding

dedicated to low-loss, low-latency traffic Has a single codepoint (DiffServ value –

8 bits(upper 2 for ECN)). EF minimizes delay and jitter and provides the highest level of aggregate quality of service.

Any traffic that exceeds the traffic profile (which is defined by local policy) is discarded.

DiffServ: Assured Forwarding

Has various classes and drop-precedences within each class.

Excess AF traffic is not delivered with as high probability as the traffic "within profile," which means it may be demoted but not necessarily dropped.

DiffServ

Assumes the existence of a service level agreement (SLA) between networks that share a border.

The SLA establishes the policy criteria, and defines the traffic profile.

Traffic will be policed and smoothed at egress points according to the SLA.

DiffServ

Any traffic "out of profile" (i.e. above the upper-bounds of bandwidth usage) at an ingress point have no guarantees (or may incur extra costs, according to the SLA).

The policy criteria used can include time of day, source and destination addresses, transport, and/or port numbers (i.e. application Ids).

Any context or traffic content (including headers or data) can be used to apply policy.

Multi Protocol Labeling Switching (MPLS) marks traffic at ingress boundaries in a

network, and un-marks at egress points

MPLS markings (20-bit labels) are primarily designed to determine the next router hop (and not the priority within the router)

MPLS

MPLS is not application controlled (no MPLS APIs exist), nor does it have an end-host protocol component.

Unlike any of the other QoS protocols, MPLS resides only on routers.

Multi-Protocol: Both Above and Below

Possibly several ways to set up Routing/Control

Single Forwarding Paradigm based on Label Switching

Can run over different Link Layer technologies

IPv6 IPv4 IPXNetwork Layer

Protocols

Eth

ernet

FD

DI

AT

M

Fram

e Relay

Poin

t-to-Poin

t

Link Layer Protocols

Label Switching

AppleTalk

MPLS

MPLS is protocol-independent (i.e., "multi-protocol"), so it can be used with network protocols other than IP (IPX, ATM, PPP, FR) or directly over data-link layer as well.

MPLS routing is used to establish "fixed bandwidth pipes" analogous to ATM or Frame Relay virtual circuits.

QoS in LAN

Ethernet HUB Single collision domain No QoS

Ethernet Switches No collision domain Better throughput No QoS

QoS in LAN

Layer 3 Switches Port based VLAN IP address based VLAN

ATM Switches Voice, data, video Lack of ATM based application softwares

i.e. ATM to the desktop Costly

Thanks

My e-mail: rawat@ieee.org