Title: Multimedia Wireless Networks: Technologies, Standards, and QoS Chapter 3. QoS Mechanisms
1Multimedia Wireless Networks Technologies,Standa
rds, and QoSChapter 3. QoS Mechanisms
- TTM8100
- Slides edited by Steinar Andresen
2QoS Mechanisms
3Traffic handling mechanisms
- (sometimes called In-traffic mechanisms) are
mechanisms that classify, handle, police, and
monitor the traffic across the network. The main
mechanisms are - classification,
- channel access,
- packet scheduling, and
- traffic policing.
4Bandwidth management mechanisms
- (sometimes called Out-of-traffic mechanisms) are
mechanisms that manage the network resources
(e.g., bandwidth) by coordinating and configuring
network devices' (i.e., hosts, base stations,
access points) traffic handling mechanisms. The
main mechanisms are - resource reservation signaling and
- admission control.
5Classification
6Classification Techniques related to OSI layers
OSI layer Classification Techniques
Application
User/Application Identification
Transport
Flow (5 tuplet IP Address)
Network
IPTOS, DSCP
Data Link
802.1p/Q Classification
Physical Layer
7Data Link Classification (ref. 3- bits field
IEEE 802 header)
8Network Layer Classification
- Network layer, or Layer 3 classification is
using Layer 3 header.s Layer 3 classification
enables service differentiation in Layer 3
network. - An example of Layer 3 classification is IPTOS
(Internet protocol type of service - IPv4 and IPv6 standard defined a prioritization
field in the IP header RFC 1349 defined a TOS
field in IPv4 header. The type of service field
consists of a 3-bit precedence subfield, a 4-bit
TOS subfield, and the final bit which is unused
and is set to be 0. The 4-bit TOS subfield
enables 16 classes of service. In IPv6 header
there is an 8-bit class of service field - and DSCP (Internet protocol differential service
code point). - Later IETFs differentiated services working
group redefined IPv4 IPTOS to be DSCP,. DSCP has
a 6-bit field enabling 64 classes of service.
9Structure of IPTOS and DSCP in IPv4
DSCP
6-bit DSCP
2-bit Unused
0 7
3-bit Precedence
4-bit TOS
0
IPTOS
0 31
16-bit total length (in bytes)
4-bit header l
4-bit version
8-bit TOS
16-bit identification
3-bit flag
13-bit fragment offset
8-bit TTL
8-bit Protocol
16-bit header checksum
32-bit source IP address
32-bit destination IP address
DATA
10Structure of IPTOS and DSCP in IPv6
0 31
Flow Label
4-bit version
8-bit traffic class
Payload Length
Next Header
Hop Limit
Payload Length
Payload length
11Transport Layer Classification
- A 5-tuplet IP header
- source IP,
- destination IP,
- source port,
- destination port, and
- protocol IP)
- can be used for transport layer classification.
12Transport Layer Classification
- A 5-tuplet IP header can uniquely identify the
individual application or flow. This
classification provides the finest granularity
and supports per-flow QoS service. - Limitations
- OK at the EDGE, but NOT Suitable to CORE
- Problems when passing firewalls using NAT
13Application or User Classfication
- The users or applications can be uniquely
identified by an ID and a central agency in the
network can be made responsible to - allow or reject
- requests for new sessions, depending on the
traffic situation. Normally each session also
will be given a unique ID number.
14Channel Access Mechanisms
- There is two options to channel access control
- Collision based access and
- Collision-free channel access
- Collision based access needs a MAC protocol that
tries to avoid and resolve collisions (in the
case they occur). E.g. CSMA/CD. Service level
can be improved by - Over-provisioning or
- Adding a priority scheme
15Collision-Free Channel Access
- Polling
- TDMA - illustrated here -static or dynamic
16Packet Scheduling Mechanisms
- Hierarchical
- or
- - Flat Packet scheduling
17FIFO Packet Scheduling
18Strict Priority Packet Scheduling
19Weight Fair Queue (WFQ)
20Traffic Policing Mechanisms
(A) Incoming traffic with rate R which is less
than the bucket rate r. The outgoing traffic
rate is equal to R.In this case when we start
with anempty bucket, the burstiness of the
incoming traffic is the same as the burstiness
of the outgoing trafficas long as R lt r.
21Traffic Policing Mechanisms
(B) Incoming traffic with rate Rwhich is
greater than the bucket rate r. The outgoing
traffic rate is equal to r (bucket rate).
22Traffic Policing Mechanisms
(C) Same as (B) but the bucket is full.
Non-conformant traffic is eitherdropped or sent
as best effort traffic.
23Token Bucket Mechanism (A)
The incoming traffic rate is less than the token
arrival rate. In this case the outgoing traffic
rate is equal to the incoming traffic rate.
24Token Bucket Mechanism (B)
The incoming traffic rate is greater than the
token arrival rate. In case there are still
tokens in the bucket, the outgoing traffic rate
is equal to the incoming traffic rate.
25Token Bucket Mechanism (C)
If the incoming traffic rate is still greater
than the token arrival rate (e.g., long traffic
burst), eventually all the tokens will be
exhausted. In this case the incoming traffic has
to wait for the new tokens to arrive in order to
be able to send out. Therefore, the outgoing
traffic is limited at the token arrival rate.
26Resource Reservation Signaling Mechanisms
- Provision of resource reservation signaling that
notifies all devices along the communication path
on the multimedia applications' QoS requirements.
- Delivery of QoS requirements to the admission
control mechanism that decides if there are
available resources to meet the new request QoS
requirements. - Notification of the application regarding the
admission result.
27Resource Reservation Signaling Mechanisms
28Admission Control
- Explicit admission control This approach is
based on explicit resource reservation.
Applications will send the request to join the
network through the resource reservation
signaling mechanism. The request that contains
QoS parameters is forwarded to the admission
control mechanism. The admission control
mechanism decides to accept or reject the
application based on the application's QoS
requirements, available resources, performance
criteria, and network policy. - Implicit admission control There is no explicit
resource reservation signaling. The admission
control mechanism relies on bandwidth
over-provisioning and traffic control (i.e.,
traffic policing).
29QoS Architecture
- Applications with quantitative QoS requirements
mostly require QoS guaranteed services.
Therefore, explicit resource reservation and
admission control are needed, also require strict
traffic control (traffic policing, packet
scheduling, and channel access). - Applications with qualitative QoS requirements
require high QoS levels but do not provide
quantitative QoS requirements. We can use
resource reservation and admission control. They
also require traffic handling which delivers
differentiated services. - Best effort There is no need for QoS guarantees.
The network should reserve bandwidth for such
services. The amount of reserved bandwidth for
best effort traffic is determined by the network
policy.
30QoS Architecture for Infrastructure based
Wireless Networks
31QoS Architecture for Ad Hoc Wireless Networks