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P13ITE05
High Speed Networks

UNIT - IV

Dr.A.Kathirvel
Professor & Head/IT - VCEW
UNIT - IV


Integrated services architecture



Approach, components and services



Queuing discipline: FQ, PS, BRFQ, WFQ



Random early detection



Differentiated services
Introduction





New additions to Internet increasing traffic
 High volume client/server application
 Web
 Graphics
 Real time voice and video
Need to manage traffic and control congestion
IEFT standards
 Integrated services
 Collective service to set of traffic demands in domain
 Limit demand & reserve resources
 Differentiated services
 Classify traffic in groups
 Different group traffic handled differently
3
Integrated Services Architecture (ISA)‫‏‬






IPv4 header fields for precedence and type of service
usually ignored
ATM only network designed to support TCP, UDP and
real-time traffic
 May need new installation
Need to support Quality of Service (QoS) within TCP/IP
 Add functionality to routers
 Means of requesting QoS

4
Internet Traffic – Elastic








Can adjust to changes in delay and throughput
E.g. common TCP and UDP application
 E-Mail – insensitive to delay changes
 FTP – User expect delay proportional to file size
 Sensitive to changes in throughput
 SNMP – delay not a problem, except when caused by congestion
 Web (HTTP), TELNET – sensitive to delay
Not per packet delay – total elapsed time
 E.g. web page loading time
 For small items, delay across internet dominates
 For large items it is throughput over connection
Need some QoS control to match to demand
5
Internet Traffic – Inelastic










Does not easily adapt to changes in delay and throughput
 Real time traffic
Throughput
 Minimum may be required
Delay
 E.g. stock trading
Jitter - Delay variation
 More jitter requires a bigger buffer
 E.g. teleconferencing requires reasonable upper bound
Packet loss

6
Inelastic Traffic Problems







Difficult to meet requirements on network with
variable queuing delays and congestion
Need preferential treatment
Applications need to state requirements
 Ahead of time (preferably) or on the fly
 Using fields in IP header
 Resource reservation protocol
Must still support elastic traffic
 Deny service requests that leave too few resources
to handle elastic traffic demands

7
ISA Approach






Provision of QoS over IP
Sharing available capacity when congested
Router mechanisms
 Routing Algorithms
 Select to minimize delay
 Packet discard
 Causes TCP sender to back off and reduce load
Enahnced by ISA

8
Flow


IP packet can be associated with a flow
 Distinguishable stream of related IP packets
 From single user activity
 Requiring same QoS
 E.g. one transport connection or one video stream
 Unidirectional
 Can be more than one recipient
 Multicast
 Membership of flow identified by source and destination IP
address, port numbers, protocol type
 IPv6 header flow identifier can be used but isnot
necessarily equivalent to ISA flow
9
ISA Functions








Admission control
 For QoS, reservation required for new flow
 RSVP used
Routing algorithm
 Base decision on QoS parameters
Queuing discipline
 Take account of different flow requirements
Discard policy
 Manage congestion
 Meet QoS

10
ISA Implementation in Router




Background
Functions

Forwarding
functions

11
ISA Components – Background Functions







Reservation Protocol
 RSVP
Admission control
Management agent
 Can use agent to modify traffic control database and
direct admission control
Routing protocol

12
ISA Components – Forwarding




Classifier and route selection
 Incoming packets mapped to classes
 Single flow or set of flows with same QoS
E.g. all video flows
 Based on IP header fields
 Determines next hop
Packet scheduler
 Manages one or more queues for each output
 Order queued packets sent
 Based on class, traffic control database, current
and past activity on outgoing port
 Policing
13
ISA Services





Traffic specification (TSpec) defined as service for flow
On two levels
 General categories of service
 Guaranteed
 Controlled load
 Best effort (default)‫‏‬
 Particular flow within category
TSpec is part of contract

14
Token Bucket







Many traffic sources can be defined by token
bucket scheme
Provides concise description of load imposed by
flow
 Easy to determine resource requirements
Provides input parameters to policing function

15
Token Bucket Diagram

16
ISA Services - Guaranteed Service







Assured capacity level or data rate
Specific upper bound on queuing delay through
network
 Must be added to propagation delay or latency to
get total delay
 Set high to accommodate rare long queue delays
No queuing losses
 I.e. no buffer overflow
E.g. Real time play back of incoming signal can use
delay buffer for incoming signal but will not tolerate
packet loss

17
ISA Services - Controlled Load








Tightly approximates to best efforts under unloaded conditions
No upper bound on queuing delay
 High percentage of packets do not experience delay over
minimum transit delay
 Propagation plus router processing with no queuing
delay
Very high percentage delivered
 Almost no queuing loss
Adaptive real time applications
 Receiver measures jitter and sets playback point
 Video can drop a frame or delay output slightly
 Voice can adjust silence periods

18
Queuing Discipline







Traditionally first in first out (FIFO) or first come first
served (FCFS) at each router port
No special treatment to high priority packets (flows)‫‏‬
Small packets held up by large packets ahead of them
in queue
 Larger average delay for smaller packets
 Flows of larger packets get better service
Greedy TCP connection can crowd out altruistic
connections
 If one connection does not back off, others may
back off more

19
Fair Queuing (FQ)‫‏‬


Multiple queues for each port
 One for each source or flow
 Queues services round robin
 Each busy queue (flow) gets exactly one packet per
cycle
 Load balancing among flows
 No advantage to being greedy
 Your queue gets longer, increasing your delay
 Short packets penalized as each queue sends one
packet per cycle

20
FIFO and FQ

21
Processor Sharing







Multiple queues as in FQ
Send one bit from each queue per round
 Longer packets no longer get an advantage
Can work out virtual (number of cycles) start and
finish time for a given packet
However, we wish to send packets, not bits

22
Bit-Round Fair Queuing (BRFQ)‫‏‬





Compute virtual start and finish time as before
When a packet finished, the next packet sent is the
one with the earliest virtual finish time
Good approximation to performance of PS
 Throughput and delay converge as time increases

23
Examples
of PS and
BRFQ

24
Comparison of FIFO, FQ and BRFQ

25
Generalized Processor Sharing (GPS)‫‏‬








BRFQ can not provide different capacities to different
flows
Enhancement called Weighted fair queue (WFQ)‫‏‬
From PS, allocate weighting to each flow that determines
how many bots are sent during each round
 If weighted 5, then 5 bits are sent per round
Gives means of responding to different service requests
Guarantees that delays do not exceed bounds

26
Weighted Fair Queue




Emulates bit by bit GPS
Same strategy as BRFQ

27
FIFO And WFQ

Chapter 17 Integrated and Differentiated
Services

28
Proactive Packet Discard


Congestion management by proactive packet discard
 Before buffer full
 Used on single FIFO queue or multiple queues for
elastic traffic
 E.g. Random Early Detection (RED)‫‏‬

29
Random Early Detection(RED) Motivation






Surges fill buffers and cause discards
On TCP this is a signal to enter slow start phase, reducing load
 Lost packets need to be resent
 Adds to load and delay
 Global synchronization
 Traffic burst fills queues so packets lost
 Many TCP connections enter slow start
 Traffic drops so network under utilized
 Connections leave slow start at same time causing burst
Bigger buffers do not help
Try to anticipate onset of congestion and tell one connection to slow
down

30
RED Design Goals







Congestion avoidance
Global synchronization avoidance
 Current systems inform connections to back off
implicitly by dropping packets
Avoidance of bias to bursty traffic
 Discard arriving packets will do this
Bound on average queue length
 Hence control on average delay

31
RED Algorithm – Overview
Calculate average queue size avg
if avg < THmin
queue packet
else if THmin  avg  Thmax
calculate probability Pa
with probability Pa
discard packet
else with probability 1-Pa
queue packet
else if avg  THmax
discard packet

32
RED Buffer

33
RED Algorithm Detail

34
Differentiated Services (DS)‫‏‬





ISA and RSVP complex to deploy
May not scale well for large volumes of traffic
 Amount of control signals
 Maintenance of state information at routers
DS architecture designed to provide simple, easy
to implement, low overhead tool
 Support range of network services
 Differentiated on basis of performance

35
Characteristics of DS






Use IPv4 header Type of Service or IPv6 Traffic Class field
 No change to IP
Service level agreement (SLA) established between provider
(internet domain) and customer prior to use of DS
 DS mechanisms not needed in applications
Build in aggregation
 All traffic with same DS field treated same
 E.g. multiple voice connections
 DS implemented in individual routers by queuing and
forwarding based on DS field
 State information on flows not saved by routers
36
DS Terminology

Chapter 17 Integrated and Differentiated
Services

37
Services









Provided within DS domain
 Contiguous portion of Internet over which consistent set of
DS policies administered
 Typically under control of one administrative entity
Defined in SLA
 Customer may be user organization or other DS domain
 Packet class marked in DS field
Service provider configures forwarding policies routers
 Ongoing measure of performance provided for each class
DS domain expected to provide agreed service internally
If destination in another domain, DS domain attempts to forward
packets through other domains
 Appropriate service level requested from each domain
38
SLA Parameters








Detailed service performance parameters
 Throughput, drop probability, latency
Constraints on ingress and egress points
 Indicate scope of service
Traffic profiles to be adhered to
 Token bucket
Disposition of traffic in excess of profile

39
Example Services


Qualitative
A: Low latency
 B: Low loss




Quantitative
C: 90% in-profile traffic delivered with no more than 50ms
latency
 D: 95% in-profile traffic delivered




Mixed
E: Twice bandwidth of F
 F: Traffic with drop precedence X has higher delivery
probability than that with drop precedence Y


40
DS Field v IPv4 Type of Service

41
DS Field Detail




Leftmost 6 bits are DS codepoint
 64 different classes available
 3 pools
 xxxxx0 : reserved for standards
 000000 : default packet class
 xxx000 : reserved for backwards compatibility with
IPv4 TOS
 xxxx11 : reserved for experimental or local use
 xxxx01 : reserved for experimental or local use but may
be allocated for future standards if needed
Rightmost 2 bits unused

42
Configuration Diagram

43
Configuration – Interior Routers




Domain consists of set of contiguous routers
Interpretation of DS codepoints within domain is consistent
Interior nodes (routers) have simple mechanisms to handle
packets based on codepoints
 Queuing gives preferential treatment depending on
codepoint
 Per Hop behaviour (PHB)‫‏‬
 Must be available to all routers
 Typically the only part implemented in interior routers
 Packet dropping rule dictated which to drop when buffer
saturated

44
Configuration – Boundary Routers



Include PHB rules
Also traffic conditioning to provide desired service
 Classifier
 Separate packets into classes
 Meter
 Measure traffic for conformance to profile
 Marker
 Policing by remarking codepoints if required
 Shaper
 Dropper

45
DS Traffic Conditioner

46
Per Hop Behaviour – Expedited forwarding


Premium service
 Low loss, delay, jitter; assured bandwidth end-to-end
service through domains
 Looks like point to point or leased line
 Difficult to achieve
 Configure nodes so traffic aggregate has well defined
minimum departure rate
 EF PHB
 Condition aggregate so arrival rate at any node is
always less that minimum departure rate
 Boundary conditioners
47
Per Hop Behaviour – Explicit Allocation












Superior to best efforts
Does not require reservation of resources
Does not require detailed discrimination among flows
Users offered choice of number of classes
Monitored at boundary node
 In or out depending on matching profile or not
Inside network all traffic treated as single pool of
packets, distinguished only as in or out
Drop out packets before in packets if necessary
Different levels of service because different number of
in packets for each user

48
PHB - Assured Forwarding





Four classes defined
 Select one or more to meet requirements
Within class, packets marked by customer or provider
with one of three drop precedence values
 Used to determine importance when dropping
packets as result of congestion

49
Codepoints for AF PHB

50
Questions
?

51

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HIGH SPEED NETWORKS

  • 1. P13ITE05 High Speed Networks UNIT - IV Dr.A.Kathirvel Professor & Head/IT - VCEW
  • 2. UNIT - IV  Integrated services architecture  Approach, components and services  Queuing discipline: FQ, PS, BRFQ, WFQ  Random early detection  Differentiated services
  • 3. Introduction    New additions to Internet increasing traffic  High volume client/server application  Web  Graphics  Real time voice and video Need to manage traffic and control congestion IEFT standards  Integrated services  Collective service to set of traffic demands in domain  Limit demand & reserve resources  Differentiated services  Classify traffic in groups  Different group traffic handled differently 3
  • 4. Integrated Services Architecture (ISA)‫‏‬    IPv4 header fields for precedence and type of service usually ignored ATM only network designed to support TCP, UDP and real-time traffic  May need new installation Need to support Quality of Service (QoS) within TCP/IP  Add functionality to routers  Means of requesting QoS 4
  • 5. Internet Traffic – Elastic     Can adjust to changes in delay and throughput E.g. common TCP and UDP application  E-Mail – insensitive to delay changes  FTP – User expect delay proportional to file size  Sensitive to changes in throughput  SNMP – delay not a problem, except when caused by congestion  Web (HTTP), TELNET – sensitive to delay Not per packet delay – total elapsed time  E.g. web page loading time  For small items, delay across internet dominates  For large items it is throughput over connection Need some QoS control to match to demand 5
  • 6. Internet Traffic – Inelastic      Does not easily adapt to changes in delay and throughput  Real time traffic Throughput  Minimum may be required Delay  E.g. stock trading Jitter - Delay variation  More jitter requires a bigger buffer  E.g. teleconferencing requires reasonable upper bound Packet loss 6
  • 7. Inelastic Traffic Problems     Difficult to meet requirements on network with variable queuing delays and congestion Need preferential treatment Applications need to state requirements  Ahead of time (preferably) or on the fly  Using fields in IP header  Resource reservation protocol Must still support elastic traffic  Deny service requests that leave too few resources to handle elastic traffic demands 7
  • 8. ISA Approach     Provision of QoS over IP Sharing available capacity when congested Router mechanisms  Routing Algorithms  Select to minimize delay  Packet discard  Causes TCP sender to back off and reduce load Enahnced by ISA 8
  • 9. Flow  IP packet can be associated with a flow  Distinguishable stream of related IP packets  From single user activity  Requiring same QoS  E.g. one transport connection or one video stream  Unidirectional  Can be more than one recipient  Multicast  Membership of flow identified by source and destination IP address, port numbers, protocol type  IPv6 header flow identifier can be used but isnot necessarily equivalent to ISA flow 9
  • 10. ISA Functions     Admission control  For QoS, reservation required for new flow  RSVP used Routing algorithm  Base decision on QoS parameters Queuing discipline  Take account of different flow requirements Discard policy  Manage congestion  Meet QoS 10
  • 11. ISA Implementation in Router   Background Functions Forwarding functions 11
  • 12. ISA Components – Background Functions     Reservation Protocol  RSVP Admission control Management agent  Can use agent to modify traffic control database and direct admission control Routing protocol 12
  • 13. ISA Components – Forwarding   Classifier and route selection  Incoming packets mapped to classes  Single flow or set of flows with same QoS E.g. all video flows  Based on IP header fields  Determines next hop Packet scheduler  Manages one or more queues for each output  Order queued packets sent  Based on class, traffic control database, current and past activity on outgoing port  Policing 13
  • 14. ISA Services    Traffic specification (TSpec) defined as service for flow On two levels  General categories of service  Guaranteed  Controlled load  Best effort (default)‫‏‬  Particular flow within category TSpec is part of contract 14
  • 15. Token Bucket    Many traffic sources can be defined by token bucket scheme Provides concise description of load imposed by flow  Easy to determine resource requirements Provides input parameters to policing function 15
  • 17. ISA Services - Guaranteed Service     Assured capacity level or data rate Specific upper bound on queuing delay through network  Must be added to propagation delay or latency to get total delay  Set high to accommodate rare long queue delays No queuing losses  I.e. no buffer overflow E.g. Real time play back of incoming signal can use delay buffer for incoming signal but will not tolerate packet loss 17
  • 18. ISA Services - Controlled Load     Tightly approximates to best efforts under unloaded conditions No upper bound on queuing delay  High percentage of packets do not experience delay over minimum transit delay  Propagation plus router processing with no queuing delay Very high percentage delivered  Almost no queuing loss Adaptive real time applications  Receiver measures jitter and sets playback point  Video can drop a frame or delay output slightly  Voice can adjust silence periods 18
  • 19. Queuing Discipline     Traditionally first in first out (FIFO) or first come first served (FCFS) at each router port No special treatment to high priority packets (flows)‫‏‬ Small packets held up by large packets ahead of them in queue  Larger average delay for smaller packets  Flows of larger packets get better service Greedy TCP connection can crowd out altruistic connections  If one connection does not back off, others may back off more 19
  • 20. Fair Queuing (FQ)‫‏‬  Multiple queues for each port  One for each source or flow  Queues services round robin  Each busy queue (flow) gets exactly one packet per cycle  Load balancing among flows  No advantage to being greedy  Your queue gets longer, increasing your delay  Short packets penalized as each queue sends one packet per cycle 20
  • 22. Processor Sharing     Multiple queues as in FQ Send one bit from each queue per round  Longer packets no longer get an advantage Can work out virtual (number of cycles) start and finish time for a given packet However, we wish to send packets, not bits 22
  • 23. Bit-Round Fair Queuing (BRFQ)‫‏‬    Compute virtual start and finish time as before When a packet finished, the next packet sent is the one with the earliest virtual finish time Good approximation to performance of PS  Throughput and delay converge as time increases 23
  • 25. Comparison of FIFO, FQ and BRFQ 25
  • 26. Generalized Processor Sharing (GPS)‫‏‬      BRFQ can not provide different capacities to different flows Enhancement called Weighted fair queue (WFQ)‫‏‬ From PS, allocate weighting to each flow that determines how many bots are sent during each round  If weighted 5, then 5 bits are sent per round Gives means of responding to different service requests Guarantees that delays do not exceed bounds 26
  • 27. Weighted Fair Queue   Emulates bit by bit GPS Same strategy as BRFQ 27
  • 28. FIFO And WFQ Chapter 17 Integrated and Differentiated Services 28
  • 29. Proactive Packet Discard  Congestion management by proactive packet discard  Before buffer full  Used on single FIFO queue or multiple queues for elastic traffic  E.g. Random Early Detection (RED)‫‏‬ 29
  • 30. Random Early Detection(RED) Motivation     Surges fill buffers and cause discards On TCP this is a signal to enter slow start phase, reducing load  Lost packets need to be resent  Adds to load and delay  Global synchronization  Traffic burst fills queues so packets lost  Many TCP connections enter slow start  Traffic drops so network under utilized  Connections leave slow start at same time causing burst Bigger buffers do not help Try to anticipate onset of congestion and tell one connection to slow down 30
  • 31. RED Design Goals     Congestion avoidance Global synchronization avoidance  Current systems inform connections to back off implicitly by dropping packets Avoidance of bias to bursty traffic  Discard arriving packets will do this Bound on average queue length  Hence control on average delay 31
  • 32. RED Algorithm – Overview Calculate average queue size avg if avg < THmin queue packet else if THmin  avg  Thmax calculate probability Pa with probability Pa discard packet else with probability 1-Pa queue packet else if avg  THmax discard packet 32
  • 35. Differentiated Services (DS)‫‏‬    ISA and RSVP complex to deploy May not scale well for large volumes of traffic  Amount of control signals  Maintenance of state information at routers DS architecture designed to provide simple, easy to implement, low overhead tool  Support range of network services  Differentiated on basis of performance 35
  • 36. Characteristics of DS    Use IPv4 header Type of Service or IPv6 Traffic Class field  No change to IP Service level agreement (SLA) established between provider (internet domain) and customer prior to use of DS  DS mechanisms not needed in applications Build in aggregation  All traffic with same DS field treated same  E.g. multiple voice connections  DS implemented in individual routers by queuing and forwarding based on DS field  State information on flows not saved by routers 36
  • 37. DS Terminology Chapter 17 Integrated and Differentiated Services 37
  • 38. Services      Provided within DS domain  Contiguous portion of Internet over which consistent set of DS policies administered  Typically under control of one administrative entity Defined in SLA  Customer may be user organization or other DS domain  Packet class marked in DS field Service provider configures forwarding policies routers  Ongoing measure of performance provided for each class DS domain expected to provide agreed service internally If destination in another domain, DS domain attempts to forward packets through other domains  Appropriate service level requested from each domain 38
  • 39. SLA Parameters     Detailed service performance parameters  Throughput, drop probability, latency Constraints on ingress and egress points  Indicate scope of service Traffic profiles to be adhered to  Token bucket Disposition of traffic in excess of profile 39
  • 40. Example Services  Qualitative A: Low latency  B: Low loss   Quantitative C: 90% in-profile traffic delivered with no more than 50ms latency  D: 95% in-profile traffic delivered   Mixed E: Twice bandwidth of F  F: Traffic with drop precedence X has higher delivery probability than that with drop precedence Y  40
  • 41. DS Field v IPv4 Type of Service 41
  • 42. DS Field Detail   Leftmost 6 bits are DS codepoint  64 different classes available  3 pools  xxxxx0 : reserved for standards  000000 : default packet class  xxx000 : reserved for backwards compatibility with IPv4 TOS  xxxx11 : reserved for experimental or local use  xxxx01 : reserved for experimental or local use but may be allocated for future standards if needed Rightmost 2 bits unused 42
  • 44. Configuration – Interior Routers    Domain consists of set of contiguous routers Interpretation of DS codepoints within domain is consistent Interior nodes (routers) have simple mechanisms to handle packets based on codepoints  Queuing gives preferential treatment depending on codepoint  Per Hop behaviour (PHB)‫‏‬  Must be available to all routers  Typically the only part implemented in interior routers  Packet dropping rule dictated which to drop when buffer saturated 44
  • 45. Configuration – Boundary Routers   Include PHB rules Also traffic conditioning to provide desired service  Classifier  Separate packets into classes  Meter  Measure traffic for conformance to profile  Marker  Policing by remarking codepoints if required  Shaper  Dropper 45
  • 47. Per Hop Behaviour – Expedited forwarding  Premium service  Low loss, delay, jitter; assured bandwidth end-to-end service through domains  Looks like point to point or leased line  Difficult to achieve  Configure nodes so traffic aggregate has well defined minimum departure rate  EF PHB  Condition aggregate so arrival rate at any node is always less that minimum departure rate  Boundary conditioners 47
  • 48. Per Hop Behaviour – Explicit Allocation         Superior to best efforts Does not require reservation of resources Does not require detailed discrimination among flows Users offered choice of number of classes Monitored at boundary node  In or out depending on matching profile or not Inside network all traffic treated as single pool of packets, distinguished only as in or out Drop out packets before in packets if necessary Different levels of service because different number of in packets for each user 48
  • 49. PHB - Assured Forwarding   Four classes defined  Select one or more to meet requirements Within class, packets marked by customer or provider with one of three drop precedence values  Used to determine importance when dropping packets as result of congestion 49