1. Quality-of-Service
ECE1545

2. Quality of Service What is Quality-of-Service?
QoS refers to traffic control mechanisms that seek to either differentiate performance based on application or network-operator requirements, or provide predictable or guaranteed performance to applications, sessions, or traffic aggregates.
Why is this an issue?
The default service in many packet networks is to give all applications the same service, and not consider any service requirements to the network This is called a best-effort service.

3. QoS: History QoS for packet networks was a big issue in the 1990s
IntServ and DiffServ architectures for the Internet
QoS has not played an important role in 2000s until 2019s
Recently it has become increasingly important (not under “QoS” label):
IEEE TSN working group in 802.1Q (Time sensitive networking)
IETF DetNet working group (Deterministic Networking)
Driving factors:
Ultra-reliable and low-latency communication of 5G
Internet of Things
ECE1545

4. Slide from Ericsson Research

5. Quality of Service Who needs Quality-of-Service?
Video and audio conferencing  bounded delay and loss rate
Video and audio streaming  bounded packet loss rate
Time-critical applications (real-time control)  bounded delays
“valuable applications”  better service than less valuable applications
How are Quality-of-Service requirements specified?
QoS parameters are
Delay
Delay Variation (Jitter)
Throughput
Error Rate

6. Quality of Service What is the granularity of QoS? Per-flow QoS
 Guarantees are specified and enforced for single end-to-end data flow
Class-based QoS
 Guarantees are specified and enforced for groups of flows

7. Granularity of QoS Per-flow guarantees
Transition: there is in fact a trade-off between per-flow and per-class architectures.
Per-flow architectures GRAPH
Provide strict bounds on delays, loss rates and throughputs
Require per-flow reservations in the network
Require per-flow classification at routers
Per-class architectures
Bundle traffic flows with similar service requirements into a small number of aggregates (classes)
Provide service differentiation to aggregates
Per-class guarantees do not immediately translate into per-flow guarantees
Per-flow reservations are not needed
Per-flow guarantees
Require per-flow reservations in the network
Require per-flow classification at routers

8. Granularity of QoS Per-class guarantees2 1 1 2 1 1 2 1 2 1 2 2 1 2
Transition: there is in fact a trade-off between per-flow and per-class architectures.
Per-flow architectures GRAPH
Provide strict bounds on delays, loss rates and throughputs
Require per-flow reservations in the network
Require per-flow classification at routers
Per-class architectures
Bundle traffic flows with similar service requirements into a small number of aggregates (classes)
Provide service differentiation to aggregates
Per-class guarantees do not immediately translate into per-flow guarantees
Per-flow reservations are not needed
Per-class guarantees
Bundle traffic flows with similar service requirements into “classes”
No per-flow reservations
Per-class guarantees do not immediately translate into per-flow guarantees

9. Levels of QoS guarantees
Absolute QoS guarantees
Assumes per-flow guarantees
The QoS of a flow is independent of QoS of other flows
Objective of service: “Isolation”
Guarantees can be deterministic or statistical
Needs resource reservation mechanism

10. Levels of QoS guarantees
Adaptive QoS guarantees
Adapts QoS to load conditions in the network; potentially with upper and lower bounds.
Objective of Service: “Fairness”
Does not need resource reservation
Needs adaptive feedback mechanism
No QoS guarantees (Best Effort)
- Objective of Service: “Sharing”
- Always works

11. Components of QoS in a NetworkU t i l y
Application needs
 absolute QoS
QoS U t i l y
Application can
adapt utility
 adaptive QoS
QoS U t i l y
Application toler-
ates QoS variations
 best effort

12. Types of QoS guarantees
Deterministic QoS
Service guarantees are enforced for all traffic
For example, deterministic delay guarantees have the form:
Delay of a packet from flow X < D
(D is called a delay bound)
Statistical QoS
Allows a certain fraction of traffic to violate the service guarantees Prob [ Delay of a packet from flow X < D ] > 1 - e
Where e is a small number (e.g., e = 10-6)

13. Quality of Service Network
Admission
Control
Switch
Receiver
Sender
Policing
and
Shaping
Traffic description: 1 Mbps throughput, 100 kB max. burst
Quality of Service parameters: 10-5 loss rate, 50 msec delay

14. Traffic Contract
An application submits to network a reservation request for a new flow with a traffic specification and desired QoS
Network performs admission control functions which determines if sufficient resources are available to
(a) satisfy the desired QoS of new flow
(b) without violating QoS of existing flows
If sufficient resources are available, network reserves resources for flow; Otherwise, it rejects the flow
Network performs policing and shaping at the network entrance to ensure that application adheres to its specification

15. Why is QoS Hard ?
QoS is easy to achieve if the network over allocates resources for each flow
Allocating bandwidth at the peak rate, yields deterministic QoS, but is very inefficient
Challenge of QoS Networking:
Build a network that can provide QoS with the least amount of resources  Using better algorithms has the same effect as adding bandwidth (or other resources)  Exploit multiplexing gain in packet networks
Problem: Complexity and scalability of QoS techniques

16. Designing Networks for Multiplexing Gain
Scheduling
Earliest-Deadline-First
GPS
Static Priority
FCFS
Peak Rate
Peak Rate Allocation
Token Bucket
Deterministic service
Multiple Buckets
Statistical service
Average Rate
Traffic
Characterization/
Conditioning
Service / Admission Control

17. Designing Networks for Multiplexing Gain
Scheduling
Earliest-Deadline-First
GPS
Static Priority
FCFS
Peak Rate
Peak Rate Allocation
Token Bucket
Deterministic service
Multiple Buckets
Statistical service
Average Rate
Traffic
Characterization/
Conditioning
Service / Admission Control

18. Designing Networks for Multiplexing Gain
Scheduling
Earliest-Deadline-First
GPS
Static Priority
FCFS
Peak Rate
Peak Rate Allocation
Token Bucket
Deterministic service
Multiple Buckets
Statistical service
Average Rate
Traffic
Characterization/
Conditioning
Service / Admission Control

19. ? Designing Networks for Multiplexing Gain Scheduling Traffic
Earliest-Deadline-First
GPS
Static Priority ?
FCFS
Peak Rate
Peak Rate Allocation
Token Bucket
Deterministic service
Multiple Buckets
Statistical service
Average Rate
Traffic
Characterization/
Conditioning
Service / Admission Control

20. Classification and Scheduling
Routers need to be able to
classify arriving packets according to their QoS requirements
 Packet Classification
isolate traffic flows and provide requested QoS
 Packet Scheduling

21. Packet Classification
Packet classification is done before routing table lookup
HEADER
----
Predicate
Action
Classifier (Policy Database)
Packet Classification
Forwarding Engine
Action
Incoming Packet
CS757

22. Packet Scheduling Allocating output bandwidth Controlling packet delay
Packet scheduling algorithm determines the order in which backlogged packets are transmitted on an output link
Allocating output bandwidth
Controlling packet delay
scheduler
CS757

23. Traffic Conditioning
Traffic conditioning mechanisms at the network boundary need to enforce that traffic from a flow adheres to its specification
Policing
Drop traffic that violates the specification
Shaping
Buffer traffic at network entrance that violates specification
Marking
Mark packets with a lower priority or as best effort, if the traffic specification is violated

24. Admission Control
Admission Control Conditions determine if the network can support the QoS requirements for a given set of flows
Example: End-to-end delay must be less than delays at all nodes 3 1 2
d1,j
d2,j
d3,j
Dj = d1,j + d2,j + d3,j

25. Distributed Admission Control
Example: End-to-end delay must be less than a delay bound D
Calculate smallest possible delay bound at each node: d1,d2 ,d3 and reserve resources
At receiver:
If D < d1+d2+d3 , reject flow, send reject message to sender and release resources
If D > d1+d2+d3 , accept flow, commit resource reservation and notify sender
D,d1,d2,d3 R
D,d1
D,d1,d2 3 D 1 2 S
Reject
D < d1+d2+d3  Reject
Accept
D > d1+d2+d3  Accept

26. Centralized Admission Control
Example: End-to-end delay must be less than a delay bound D
Calculate smallest possible delay bound at each node: d*1,d*2 ,d*3 and reserve resources
At receiver:
If D < d1+d2+d3 , send reject message to sender
If D > d1+d2+d3 , accept flow and reserve resources R 3 D 1 2 S
D < d1+d2+d3  Reject
Reject
server
D > d1+d2+d3  Accept
Accept
Reserve

27. Quality-of-Service Architectures for the Internet Integrated Services (IntServ)

28. QoS Service Architectures for the Internet
Two QoS architectures have been defined for Internet.
Integrated Services (IntServ)
Proposed in 1994
Per-flow Quality of Service
Resource reservation/admission control
Can support delay guarantees
Differentiated Services (DiffServ)
Proposed in 1998
Class-based QoS
Resource reservation not always needed

29. Integrated Services IntServ specifies two types of services:
Guaranteed Service
Guaranteed bandwidth
End-to-end delay bounds
No loss due to buffer overflows
Controlled Load Service
Provides a service that is equivalent to a best effort service in a lightly loaded netework
Low loss
Low delay
No absolute guarantees

30. Integrated Services in IntServ
At network entrance: Policing and Shaping
Somewhere in the network: Admission Control
At switches: Classification, Scheduling
Between hosts and routers: Signaling
FlowSpec (TSpec, RSpec)
Distributed or Centralized
Weighted Fair Queuing or
other latency-rate algorithm
RSVP

31. Guaranteed Service
A flow must perform a reservation request during a flow setup phase
Uses RSVP
Traffic Specification (T-SPEC):
E(t) = min (M + pt, rt + b)
M is max. packet size
p is peak rate
r is average rate
b is burst size
Routers along a path accept or reject reservation
This follows LeBoudec textbook

32. Latency-rate Schedulers
Guaranteed service assumes that routers implement a latency-rate service curve with delay T and rate R:
S(t) = R · (t – T)+
with
T = L /R + D
L is the maximum packet size of this flow
D = Lall / C is the maximum packet transmission time
Lall is maximum packet size at this link
C is the link capacity
Router implementations (some in software):
Cisco – WFQ
Extreme Networks – WFQ, CBQ, DRR
Nortel - CBQ

33. RSVP Functional Diagram
Host
Router
RSVPD
RSVPD
Application
Routing
Process
Policy
Control
Policy
Control D A T
Admissions
Control
Admissions
Control
Packet
Classifier
Packet
Scheduler
Packet
Classifier
Packet
Scheduler
DATA
DATA
Source: Gordon Chaffee, UC Berkeley

34. Resource Reservation Senders advertise using PATH message
Receivers reserve using RESV message
Flowspec + filterspec + policy data
Travels upstream in reverse direction of Path message
Merging of reservations
Sender/receiver notified of changes
Source: Gordon Chaffee, UC Berkeley
© Jörg Liebeherr,
CS757

35. RSVP in IntServ Flow set-up:
advertisement with PATH message from source
contains TSPEC (p,M,r,b) of the source
contains ADSPEC (Ltot, Dtot) which is updated on the path
ADSPEC contains: Ltot = i Ci Dtot = i Di
PATH do not result in reservations !
(p,M,r,b)
(p,M,r,b)
( )
Sender
(p,M,r,b)
(L1, D1 )
(L1+L2, D1+D2)
Receiver
Source: P. Thiran

36. RSVP in IntServ ( ) (p,M,r,b) (L1, D1 ) (L1+L2, D1+D2) R’ R’ R’
Flow set-up: Receiver responds with a RESV message.
RESV messages make the reservations at the node
Receiver writes the service level requested by receiver in an R-SPEC
R-Spec specifies the reserved rate R’
R’ is determined at the receiver using the formla:
((b-M)/R’) (p-R)+/(p-r) + (M + i Li)/R’ + i Di
This assumes that all nodes reserve the same rate Rn= R’.
R’ is computed so that end-to-end delay bound <= delay objective.
(p,M,r,b)
( )
(L1, D1 )
(L1+L2, D1+D2) R’ R’ R’
Source: P. Thiran

37. RSVP UDP Reservation (1)
PATH 2
2. The Host A RSVP daemon generates a PATH message that is sent to the next hop RSVP router, R1, in the direction of the session address, R4
PATH
1. An application on Host A creates a session, /4078, by communicating with the RSVP daemon on Host A. 1 R1
PATH 3
3. The PATH message follows the next hop path through R5 and R4 until it gets to Host B. Each router on the path creates soft session state with the reservation parameters.
PATH
Host B
Host A R5
Source: Gordon Chaffee, UC Berkeley

38. RSVP UDP Reservation (2)
PATH
4. An application on Host B communicates with the local RSVP daemon and asks for a reservation in session /4078. The daemon checks for and finds existing session state. 4
RESV 5
5. The Host B RSVP daemon generates a RESV message that is sent to the next hop RSVP router, R4, in the direction of the source address,
PATH R1
Host B
RESV
PATH
PATH
Host A
RESV 6
6. The RESV message continues to follow the next hop path through R5 and R1 until it gets to Host A. Each router on the path makes a resource reservation.
RESV R5
Source: Gordon Chaffee, UC Berkeley

39. RSVP Flowspecs Source: Gordon Chaffee, UC Berkeley
Sender TSpec, Controlled Load Flowspec
. . .
Token Bucket Rate [r]
Token Bucket Size [b]
Peak Data Rate [p]
Minimum Policed Unit [m]
Maximum Policed Unit [M]
Guaranteed Flowspec
. . .
Token Bucket Rate [r]
Token Bucket Size [b]
Peak Data Rate [p]
Minimum Policed Unit [m]
Maximum Policed Unit [M]
Rate [R]
Slack Term [S]
Source: Gordon Chaffee, UC Berkeley

40. Reservation Merging (3) 50Kbs (7) 100 Kbs (6) 100 Kbs (2) 50Kbs
Reservations merge
as they travel up tree.
(6) 100 Kbs R3
(2) 50Kbs
(5) 100 Kbs
(9) 60Kbs R4 R6 R7
(1) 50Kbs
(8) 60Kbs
(4) 100 Kbs
Receiver #1
Receiver #2
Receiver #3