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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: [email protected]