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Protocols and the TCP/IP Suite Introduction Modern Internet applications demand services not provided by a best-effort service model Two complementary, yet fundamentally different, traffic management frameworks have evolved: Integrated Services (IS, ISA, IntServ): reserve resources per session and limit total demand to the capacity that can be handled by the network Differentiated Services (DS, DiffServ): classify traffic into a number of traffic groups and handle traffic based on its group Traffic control mechanisms: queuing discipline, packet discard policy Services are specified within a given domain Chapter 17: Integrated and Differentiated Services Chapter 2
Citation preview
Integrated Services & Differentiated Services
Protocols and the TCP/IP Suite Integrated Services
&Differentiated Services Chapter 2 Protocols and the TCP/IP
Suite
Introduction Modern Internet applications demand services not
provided by a best-effort service model Two complementary, yet
fundamentally different, traffic management frameworks have
evolved: Integrated Services (IS, ISA, IntServ):reserve resources
per session and limit total demand to the capacity that can be
handled by the network Differentiated Services (DS, DiffServ):
classify traffic into a number of traffic groups and handle traffic
based on its group Traffic control mechanisms:queuing discipline,
packet discard policy Services are specified within a given domain
Chapter 17:Integrated and Differentiated Services Chapter 2
Protocols and the TCP/IP Suite
Internet Traffic Elastic Traffic traffic that can adapt, over a
wide range, to delay and throughput changes typically TCP/UDP QoS
perceived based on application Inelastic Traffic traffic does not
adapt well requires guarantees on:throughput, delay, jitter, packet
loss e.g. traffic generated by real-time applications elastic
traffic must still be supported Chapter 17:Integrated and
Differentiated Services Chapter 2 Protocols and the TCP/IP
Suite
IntServ Approach Two key features form core of architecture
Resource reservation routers must maintain state of available
resource reserved for each session Call/session setup each router
on the sessions path must verify availability of required resources
for a session and admit sessions only if requirements can be met
Call Admission process (more later) Traffic characterization
(Tspec) Desired QoS characterization (Rspec) Reservation signaling
(RSVP, RFC 2210) Per-element call admission per Tspec and Rspec
Chapter 17:Integrated and Differentiated Services Chapter 2 IntServ
Implementation
Protocols and the TCP/IP Suite IntServ Implementation Associate
each packet with a flow a distinguishable stream of related IP
packets that result from a single user activity and demand the same
QoS (per RFC 1633) unidirectional, can have multiple recipients
typically identified by: source & destination IP addresses,
port numbers and protocol type Provide for enhanced router
functions to manage flows: Admission control based on requested QoS
and availability of required network resources Routing protocol
based on QoS (like OSPF/MOSPF) Queuing/scheduling disciplines based
on QoS Packet discard policy based on QoS Chapter 17:Integrated and
Differentiated Services Chapter 2 IntServ Architecture (ISA) -
requirements at each router
Protocols and the TCP/IP Suite IntServ Architecture (ISA) -
requirements at each router RSVP Background Functions Primary
Forwarding Functions Chapter 17:Integrated and Differentiated
Services Chapter 2 ISA: 3 Categories of Service
Protocols and the TCP/IP Suite ISA: 3 Categories of Service
Guaranteed Service assured capacity (data rate) specified upper
bound on queuing delay through the network no queuing loss (i.e.,
no buffer overflow) Controlled Load roughly equivalent to
best-effort under no-load conditions (dprop + dtrans) no specified
upper bound on queuing delay, but will approximate minimum expected
transit delay almost no queuing loss Best Effort Chapter
17:Integrated and Differentiated Services Chapter 2 Protocols and
the TCP/IP Suite
Leaky Bucket Scheme Used to: Characterize traffic in a flow.
Describe the load imposed by a flow. Traffic policing. Note that,
during any time period T, the amount of data sent cannot exceed
RT+B, and Maximum queuing delay by a packet is B/R. Chapter
17:Integrated and Differentiated Services Chapter 2 Protocols and
the TCP/IP Suite
Queuing Disciplines Single FIFO queues have numerous drawbacks
relative to QoS demands no special treatment based on priority
larger packets get better service connections can get an unfair
share of resources IntServ allows for multiple queues one per flow
separate discipline per flow fair queuing policy Chapter
17:Integrated and Differentiated Services Chapter 2 Queuing
Disciplines (Scheduling)
Protocols and the TCP/IP Suite Queuing Disciplines (Scheduling)
FIFO (First-Come-First-Served) Round Robin (Fair Queuing)
Drawbacks? Drawbacks? Flows with busy (greedy) sources crowd out
others Flows with shorter packets are penalized Flows with shorter
packets are penalized Chapter 17:Integrated and Differentiated
Services Chapter 2 Processor Sharing Approach
Protocols and the TCP/IP Suite Processor Sharing Approach Processor
Sharing (PS) ideal, but not a practical policy transmit only one
bit per round per queue with N queues, each queue receives exactly
1/N of the available capacity consider each queue independently to
calculate virtual start and finish times for each transmission
EXAMPLE QUEUE QUEUE QUEUE Packet 1 Packet Packet 1 Packet Packet 1
Real arrival time, i Transmission time, Pi Virtual start time, Si
Virtual finish time, Fi Chapter 17:Integrated and Differentiated
Services Chapter 2 Bit-Round Fair Queuing
Protocols and the TCP/IP Suite Bit-Round Fair Queuing Bit-Round
Fair Queuing (BRFQ) emulates PS round-robin approach for packets
and multiple synchronous queues uses packet length and flow
identification (queue) to schedule packets calculate Si and Fias
though PS were running when a packet finishes transmission, send
next packet based on smallest value of Fi over all queues algorithm
is fair on the basis of amount of data transmitted instead of
number of packets Chapter 17:Integrated and Differentiated Services
Chapter 2 Protocols and the TCP/IP Suite
PS vs. BRFQ Example Drawback? No precedence or priority weighting
of flows. Chapter 17:Integrated and Differentiated Services Chapter
2 Queuing Discipline Examples
Protocols and the TCP/IP Suite Queuing Discipline Examples Load
equals capacity Chapter 17:Integrated and Differentiated Services
Chapter 2 Queuing Discipline Examples
Protocols and the TCP/IP Suite Queuing Discipline Examples Load
exceeds capacity Drawbacks? Chapter 17:Integrated and
Differentiated Services Chapter 2 Queuing Discipline Priority
Queuing
Protocols and the TCP/IP Suite Queuing Discipline Priority Queuing
Data Communications and Networking, Forouzan, 2004 Chapter
17:Integrated and Differentiated Services Chapter 2 Queuing
Discipline Weighted Fair Queuing
Protocols and the TCP/IP Suite Queuing Discipline Weighted Fair
Queuing Data Communications and Networking, Forouzan, 2004 Chapter
17:Integrated and Differentiated Services Chapter 2 Weighted Fair
Queue (WFQ)
Protocols and the TCP/IP Suite Weighted Fair Queue (WFQ) Guaranteed
Rate (weight) = .5 Guaranteed Rate = .05 Fi = Si + Pi , = weight
Maximum delay for flow i Di Bi(Ki-1)Li Ki Lmax Ri Ri m=1Cm Di =
max. delay for flow i Bi = token bucket size for flow i Ri= token
rate for flow i Ki = number of nodes in flow i path Li= max. packet
size for flow i Lmax = max. packet length for all flows through all
nodes on flow i path Cm = outgoing link capacity at node m Chapter
17:Integrated and Differentiated Services Chapter 2 Scheduling vs.
Queue Management (see RFC 2309)
Protocols and the TCP/IP Suite Scheduling vs. Queue Management (see
RFC 2309) Closely related, but different performance issues
Scheduling:managing allocation of bandwidth between flows by
determining which packet to send next (queuing discipline) Queue
Management: managing the length of packet queues by proactively
dropping packets when necessary (packet discard policy) Chapter
17:Integrated and Differentiated Services Chapter 2 Random Early
Detection (RED)
Protocols and the TCP/IP Suite Random Early Detection (RED) Queuing
discipline with proactive packet discard anticipate congestion and
take early avoidance action improved performance for elastic
traffic by not penalizing bursty traffic avoids global
synchronization phenomenon at congestion onset control average
queue length (buffer size) within deterministic bounds therefore,
control average queuing delay Chapter 17:Integrated and
Differentiated Services Chapter 2 Protocols and the TCP/IP
Suite
RED Buffer Management Discard probability is calculated for each
packet arrival at the output queue based on: the current weighted
average queue size, and the number of packets sent since the
previous packet discard Chapter 17:Integrated and Differentiated
Services Chapter 2 Generalized RED Algorithm
Protocols and the TCP/IP Suite Generalized RED Algorithm calculate
the average queue size, avg if avg < THmin queue the packet else
if THmin avg < THmax calculate probability Pa with probability
Pa discard the packet else with probability 1 Pa else if avg THmax
See Figure 17.8, page 489 Chapter 17:Integrated and Differentiated
Services Chapter 2 Protocols and the TCP/IP Suite
RED Algorithm avg lags considerably behind changes in actual queue
size (weight, wq, is small typ ) avg (1 wq)avg + wqq prevents
reaction to short bursts count, number of packets passed without
discard, increases incrementally while Thmin < avg < Thmax
probability of discard, Pa, increases as count increases helps
ensure fairness across multiple flows Chapter 17:Integrated and
Differentiated Services Chapter 2 RED Probability Function
(Increasing F)
Protocols and the TCP/IP Suite RED Probability Function (Increasing
F) Pa = 1/(F x Pmax) - count 1 F = THmax - THmin avg - THmin
Chapter 17:Integrated and Differentiated Services Chapter 2 RED
Probability Function (Constant F)
Protocols and the TCP/IP Suite RED Probability Function (Constant
F) avg - THmin Fconst = THmax - THmin Pb = FxPmax 1 Pa = 1/Pb -
count Chapter 17:Integrated and Differentiated Services Chapter 2
RED Performance (vs. Drop Tail Queuing Policy)
Protocols and the TCP/IP Suite RED Performance (vs. Drop Tail
Queuing Policy) Pmax = 0.02 Chapter 17:Integrated and
Differentiated Services Chapter 2 Protocols and the TCP/IP Suite
Differentiated Services
Chapter 17 continued Differentiated Services Chapter 2
Differentiated Services (DS)
Protocols and the TCP/IP Suite Differentiated Services (DS) ISA and
RSVP deployment drawbacks relatively complex may not scale well for
large traffic volumes DiffServ solution (RFC2475, 3260) designed as
a simple, easily-implemented, low-overhead tool offers a range of
services in differentiated service categories scalable and flexible
service classification Key characteristics uses existing IPv4 TOS
field or IPv6 Traffic Class field (for DS field) SLA established in
advance no application changes required built-in aggregation
mechanism based on traffic category routers queue and forward based
on information carried in the DS Chapter 17:Integrated and
Differentiated Services Chapter 2 Protocols and the TCP/IP
Suite
DS Domains Contiguous portion of the Internet over which a
consistent set of DS policies are agreed and administered Typically
under control of a single management entity Services in a domain
defined by a Service Level Agreement (SLA) a contract between
service provider and user/another domain which specifies QoS
parameters detailed service parameters: throughput, drop
probability, latency ingress/egress constraints service-based
traffic profiles disposition of excess (in violation of SLA)
traffic DS field carries a traffic class as specified by the SLA
Chapter 17:Integrated and Differentiated Services Chapter 2
Protocols and the TCP/IP Suite
DiffServ Terminology Traffic conditioning functions Chapter
17:Integrated and Differentiated Services Chapter 2 Protocols and
the TCP/IP Suite
DS Terminology Service Level Agreement (per RFC 3260): A Service
Level Specification (SLS) is a set of parameters and their values
which together define the service offered to a traffic stream by a
DS domain. A Traffic Conditioning Specification (TCS) is a set of
parameters and their values which together specify a set of
classifier rules and a traffic profile. A TCS is an integral
element of an SLS. Chapter 17:Integrated and Differentiated
Services Chapter 2 Protocols and the TCP/IP Suite
DS and IPv4 TOS Fields IP ECN Field, per RFC 3168 & RFC 3260
Replaces 6-bit DS code point, in three pools Pool 1:xxxxx0-
standards-based use (e.g , xxx000) Pool 2:xxxx11 experimental/local
use Pool 3:xxxx01 experimental/local use, future standards Chapter
17:Integrated and Differentiated Services Chapter 2 Protocols and
the TCP/IP Suite
DS Domains/Regions Border node: Per Hop Behavior (PHB) plus traffic
conditioning mechanisms Interior node: typically only PHB
mechanisms Chapter 17:Integrated and Differentiated Services
Chapter 2 DS Traffic Classifier/Conditioner
Protocols and the TCP/IP Suite DS Traffic Classifier/Conditioner
Conformance test per SLA (e.g peak rate, burstiness, ) Regulate
traffic flow to achieve a specified traffic rate (e.g. with a token
bucket) Separate traffic into classes based on fields as specified
in the TCS (source IP, dest. IP, source port #, dest. port #, )
Mark with a DS codepoint, or re-mark as necessary (at domain
ingress node, or at boundary between domains) Police traffic and
drop packets if rate exceeds that specified in the SLA (per
metering function) Chapter 17:Integrated and Differentiated
Services Chapter 2 Protocols and the TCP/IP Suite
Per-Hop Behavior RFC 2475 definition: a description of the
externally observable forwarding behavior of a DiffServ node
applied to a particular DiffServ behavior aggregate. Two standard
PHBs defined: Expedited Forwarding (RFC 2598) Assured Forwarding
(RFC 2597) Expedited Forwarding Premium service with low delay,
low-loss, low jitter, and assured bandwidth Domain boundary nodes
control traffic aggregate to limit its characteristics (i.e.
controlled rate and burstiness) Interior nodes ensure that the
aggregates maximum arrival rate is less than its minimum departure
rate (i.e. limit the queuing effect) Chapter 17:Integrated and
Differentiated Services Chapter 2 Per-Hop Behavior (cont.)
Protocols and the TCP/IP Suite Per-Hop Behavior (cont.) Assured
Forwarding designed to offer a service level that is superior to
best-effort service based on explicit allocation concept choice of
classes offered, each with different traffic profile monitor
traffic at boundary nodes, and mark as in or out based on
conformance to profile interior nodes handle packets based only on
in or out mark in congestion, drop outs before ins implementation
defines four AF classes and replaces in/out mark with a drop
precedence codepoint simple and easy to implement in nodes Chapter
17:Integrated and Differentiated Services Chapter 2 Differentiated
Services Assured Forwarding PHB
Protocols and the TCP/IP Suite Differentiated Services Assured
Forwarding PHB ECN Designated AF1x, AF2x, AF3x, AF4x RFC 2597
Chapter 17:Integrated and Differentiated Services Chapter 2
Differentiated Services Assured Forwarding PHB
Protocols and the TCP/IP Suite Differentiated Services Assured
Forwarding PHB AF AF AF AF4 Low Medium High 001010 010010 011010
100010 001100 010100 011100 100100 001110 010110 011110 100110
Chapter 17:Integrated and Differentiated Services Chapter 2
Real-Time Traffic Flow
Protocols and the TCP/IP Suite Real-Time Traffic Flow Chapter
17:Integrated and Differentiated Services Chapter 2 Real-Time
Packet Transmission
Protocols and the TCP/IP Suite Real-Time Packet Transmission
fixed-size packets, generated at fixed intervals data too important
for lossy compression Examples: ATC or RT simulations on/off source
alternates between fixed size packets with fixed intervals and
inactivity Examples: voice telephony or audio conferencing variable
packet size at uniform intervals Examples: compressed video as in
video conferencing Chapter 17:Integrated and Differentiated
Services Chapter 2
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