Network Support for Multimedia Applications

in Mobile Networks

Major Area ExamKimaya Sanzgiri

MOMENT Lab

Computer Science Dept., UCSB

Motivation Growing popularity of multimedia applications

Streaming music/videos Internet telephony Media-rich messaging

Growing popularity of mobile wireless networks Infrastructured Multi-hop (ad hoc)

Increasing support for multimedia content on wireless devices

Characteristics of Real-time Multimedia Applications

Sensitive to end-to-end delay and jitter Many applications can tolerate some

packet loss Different needs from other types of

applications, such as bulk data transfers

Network Support Due to diverse needs, packets belonging to

different types of applications need to be handled differently by the network

Network needs to offer different qualities of service

Availability of sufficient resources must be ensured in order to meet application requirements

Characteristics of Wireless Networks Shared nature of medium

Resource availability influenced by activities of neighboring nodes

Mobility and dynamic topology Resource constrained devices Higher error rates No defined network boundary Lack of central authority

Supporting Multimedia Applications

Solutions have been proposed for both wired and wireless networks that operate at different levels of the network stack

In this talk, we focus on network layer solutions

At the end, we will mention some proposed solutions at other layers

QoS support at the Network layer QoS-aware routing Admission control Resource reservation Packet classification and QoS-sensitive

packet forwarding Monitoring/Policing

Wired Network Solutions Often not directly applicable to wireless

networks due to the inherent difference in characteristics

Provide insight into the problem Are a good starting point to address the

problem in the wireless environment

Prominent Network-layer QoS Solutions for Wired Networks

IP Precedence and TOS Integrated Services (IntServ) Differentiated Services (DiffServ)

IP Precedence and Type of Service (TOS) Field in the IPv4 header Indicates that the need for QoS support was

recognized since the early days of the Internet The TOS field can be used to specify a

precedence value (0-7) or a TOS (delay/throughput/reliability/cost) for each IP packet

Interpretation of this field was left ambiguous Field remained largely unused

Integrated Services Attempt to modify Internet service model to

support diverse application requirements Any data flow that desires better than best-effort

delivery requests and reserves resources at routers along the path RSVP is the recommended reservation protocol

If insufficient resources are available, the flow is denied admission into the network

Integrated Services (cont.) Each router

Maintains reservation state for each flow Classifies every packet and decides forwarding

behavior Monitors the flow to ensure that it does not consume

more than the reserved resources Advantages

Enables fine-grained QoS and resource guarantees Disadvantages

Not scalable, harder to administer

Differentiated Services Moves admission control and flow monitoring to

the edge of the network Edge nodes classify and mark packets to receive a

particular type of service Diff Serv Code Point (DSCP) Finite set of DSCPs defined

Interior nodes determine the type of service for forwarded packets based on their DSCP values

Differentiated Services (cont.) Advantages

More scalable No per-flow state Easier to administer

Disadvantages Cannot provide the same per-flow guarantees

as IntServ

QoS support at the Network layer QoS-aware routing Admission control Resource reservation Packet classification and QoS-sensitive

packet forwarding Monitoring/Policing

Applicability of Wired Approaches to Wireless Networks Some ideas may be applicable directly,

while some need modification and others may be inapplicable

Additional challenges in wireless networks that are not encountered in wired networks have to be addressed

Applicability of Wired Approaches to Wireless Networks IntServ

Effectiveness of reservations in highly dynamic environment questionable

Per-flow state and monitoring may be resource exhaustive (depends on traffic)

DiffServ DSCP idea may be useful With dynamic topology and no defined network

boundary, some admission control/monitoring may be necessary at each node

Admission Control in Wireless Networks Determining available bandwidth at a

wireless node is a complex task due to the nature of the wireless medium Wireless medium is shared among multiple

nodes Bandwidth is affected by transmissions of

nodes that are not within transmission range Each node potentially has a different view of

the medium

Bandwidth is affected by nodes that are not within transmission range

A

Interference/Carrier-Sensing

Range

TransmissionRange

B

CC’s transmissions affect bandwidth at A

Different views of the wireless medium at different nodes

Y

XZ

P

R

S

Q

Carrier-Sensing Range of X

Carrier-Sensing Range of Q

Making an Admission Control Decision

Y

XZ

P

R

S

Q

T

400 kbps

400 kbps

Total bandwidth = 1 Mbps

If X admits a 400 kbps flow to Z, the medium will getcongested at Q

?

Contention-Aware Admission Control Protocol (CACP) [Yang 2003] Each node senses the medium to determine the

fraction of time that the medium is idle Local bandwidth availability is determined from

the idle fraction Further, each node queries all nodes within its

carrier sensing range for their local bandwidths. The minimum of these is the neighborhood available bandwidth

Admission control decisions are based on the neighborhood available bandwidth

CACP Admission Control

Y

XZ

P

R

S

Q

T

400 kbps

400 kbps

Total bandwidth = 1 Mbps

Neighborhood available bandwidth at X is 200 kbps, so X will not admit the 400 kbps flow

?

Issues with CACP approach How does a node communicate with its carrier-

sensing neighbors? High power transmissions

May increase collisions Local multi-hop flood

May reach nodes that are outside CS range May not reach some nodes in CS range

Considering neighborhood bandwidth as defined by CACP may sometimes be overly conservative and prevent spatial reuse

Y

XZ

P

R

S

Q

T

700 kbps

?

Preventing Spatial ReuseTotal bandwidth = 1 Mbps

Neighborhood available bandwidth at X is 700 kbps, so X will not admit the 400 kbps flow, although it could be admitted

Bandwidth Availability Determination Other approaches have been proposed

Different trade-offs between accuracy and efficiency Perceptive Admission Control (PAC) [Chakeres

2004] reduces overhead and improves spatial reuse compared to CACP

However, even PAC could be overly conservative in some situations

Open Question: How can bandwidth availability be determined more accurately with low overhead?

Multi-hop Admission ControlIn a multi-hop route, there could be interference between multiple hops

BC

X

D

E

UP

Q

RS

Y

T

A

FCS Range of X CS Range of Y

Multi-hop Admission Control Due to the interference between multiple

hops, the bandwidth required at a node is some multiple of that requested by the application

The exact value depends on the Contention Count at the node Contention Count at a node is the number of

other nodes on the route that are contending with this node for medium access

Multi-hop Admission ControlContention Count at a node is determined by the number of nodes on the route that are within the nodes carrier-sensing range

BC

X

D

E

UP

Q

RS

Y

T

A

FContention Count at X = 5 Contention Count at Y = 7

V

Determining Contention Count Node must know the identities of its carrier-sensing

neighbors CACP does either high power periodic broadcasts or

multi-hop broadcasts - Collision, overhead and inaccuracy problems

Node must know the identities of all other nodes on any route Requires source routing or path accumulation in routing

packets – overhead Open Questions: Is there a better way? Can

approximations be made that could reduce overhead?

QoS Routing Several QoS routing protocol have been

proposed. Each exhibits one or more of the following features Extend a corresponding best-effort routing protocol

(AODV/DSR/DSDV) Find one or more QoS-satisfactory paths between

source and destination Admission control may be integrated with route

discovery Resource reservations may be established along the

route

QoS-sensitive extensions of AODV

S D

RREQ

RREP

• QoS information is added to the RREQ packet

• Intermediate nodes forward the RREQ only if they have sufficient resources to meet

the QoS requirement• Resource information is updated in the RREQ by intermediate nodes

• Destination sends resource information back to source in the RREP message

Other Challenges for QoS Routing and Admission Control

X

R S

P Q

Simultaneous Intersecting Requests

Simultaneous Parallel Requests

QoS Monitoring Resource availability may change over

time due to mobility and changing topology

There is a need for monitoring and renegotiation of QoS parameters

Monitoring can be performed in various ways

QoS Monitoring Approaches INSIGNIA [Lee 2000] uses in-band

signalling QoS parameters added to every data packet

using IP options in the IP header Intermediate nodes appropriately set the

values for the parameters based on their current resource availability

Destination gathers the information from the data packets and gives feedback to the source

QoS Monitoring Approaches SWAN [Ahn 2002] does monitoring at

intermediate nodes and uses Explicit Congestion Notification (ECN) to regulate flow

AQOR [Xue 2003] does no monitoring at intermediate nodes. Destination does the monitoring based on the received data characteristics and gives feedback to the source

Open Questions: Can these approaches be used in combination for an effective solution? Is there a better new approach?

Hybrid Network

InternetInternet

Gateway

Mobile Network

Hybrid networks A hybrid network is formed when the mobile

network extends the wired Internet To run multimedia applications in hybrid

networks, QoS needs to be ensured in both the wired and wireless parts of the network

QoS mechanisms in wired and wireless networks can be very different

Open Question: How can this be addressed? Network layer QoS gateways? Needs exploration

Solutions at other layers MAC layer

Priority-based medium access Transport layer

QoS monitoring, rate control Application layer

Adaptive streaming, layering techniques Open Question: How do mechanisms at

different layers interact?

Other Open Questions Most of the proposed QoS solutions have

been validated through simulations or analytical models. Do the observations and results hold true in real deployments?

Can special characteristics of wireless networks, such as mobility, be leveraged in any way to improve QoS?

Conclusions Multimedia applications require QoS support

from the network This is particularly difficult in wireless networks

owing to their special characteristics Several solutions have been proposed at the

network layer for admission control, QoS routing and monitoring in wireless networks

Many open questions still remain and there is significant scope for further research

Thank you!

Questions/Comments?