Page 1 Hans Peter Schwefel Wireless Networks II: Lecture 3, Spring04 Wireless Networks II: Performance & Cross-Layer Aspects by Hans Peter Schwefel Mm1

Page 1Hans Peter Schwefel

Wireless Networks II: Lecture 3, Spring04

Wireless Networks II: Performance & Cross-Layer Aspects

by Hans Peter Schwefel

• Mm1 Cellular Networks: GSM, GPRS, and UMTS

• Mm2 Network Performance: Methodology

• Mm3 Quality of Service

• Mm4 Security aspects of wireless networks

• Mm5 Reliability aspects, content & header compression

www.kom.auc.dk/~hps/WN2_Sp04/



Motivation: Quality of Service• Advantages of Packet-Based Transport (as opposed to circuit switched)

– Flexibility– Optimal Use of Link Capacities, Multiplex-Gain for bursty traffic

• Drawbacks– Buffering/Queueing at routers can be necessary– Delay / Jitter / Packet Loss can occur – Overhead from Headers (20 Byte IPv4, 20 Byte TCP)

Protocol Improvements for Real-Time Applications necessary– Packet Prioritization (DiffServ, TypeOfService field in IPv4)– Resource Reservation (IntServ)– Traffic Engineering (QoS Routing, static/dynamic MPLS paths)– Connection Admission / Traffic Policing / Shaping– Header Compression

queueing

+



Quality of Service: Scope / Parameters• User Plane QoS

– End-2-End Packet Delay (in particular interactive applications)

– Delay Jitter – Packet Loss– Throughput/Goodput

• Application Level QoS– e.g. Video/Voice Quality (depending on codecs)

• Signalling Plane– Call Setup Delays– Fraction of blocked Calls

• Behavior at Handover– Dropped Calls– Delayed / Lost packets

• Reliability Aspects– Failure probablities of entities– Downtime distribution

Main Focus here

See MM5

Realtime Applications: VoIP, Video, etc.



QoS and User perception

L3: Network Layer: IP

L2: MAC/LLC

L4: Transport: TCP, UDP, RTP/UDP

Application

(L5) Session Control, e.g. SIP

Middleware

User Interface

User

L1: PHYS

User Environment

Netw

ork Q

oS

Ap

plication Q

oS

User p

erceived QoS



Real-Time Transport Protocol: RTP

RTP

UDP

IP

Link-Layer

L5-7

L4

L3

L2

Application • Defined in RFC 1889• Uses UDP: multiple RTP messages can be multiplexed in one UDP datagram

• Provides Time-stamps, sequence numbers• Supports:

– Standard Codec descriptions– codec translation– mixing of multi-media streams

• Header

VERsion=2

P=Padding

X=Extension Header

CC=Source Count

M=Marker

PayloadTYPE



Real-time transmission control protocol: RTCP• Control Protocol for RTP

flows• Message Types

– 200 Sender Report– 201 Receiver Report– 202 Source Description– 203 BYE– 204 Application specific



Content

1. Introduction/Motivation• Network QoS, User-perceived QoS, QoS Parameters,

Transport of real-time applications

2. Basic IP QoS Provisioning Methodsa. Network Design/Overprovisioningb. Integrated Servicesc. Differentiated Servicesd. Traffic Engineering/QoS Routing/MPLS

3. QoS in cellular networksa. GPRSb. Outlook on UMTS

4. Summary/Exercises



IP QoS Solution I: Over-Provisioning

• Design network to be able to deal with worst-case traffic scenario• Advantage:

– no impact on architecture, protocols and user equipment– simplicity

• Problems:– Traffic depends on number of active users, user mobility, type of

application, daily utilization profile difficult forecasting– Data traffic tends to be very bursty (even `self-similar´)

waste of resources if planned for worst-case scenario can be very expensive

– Unforseeable events can occur (new applications; changes in user behavior, e.g. always-on)



QoS Solutions II: IntServ/RSVP• Fundamental Idea: Reserve necessary resources for each traffic flow along its

transmission path, which requires:

– Connection Admission Control (CAC): traffic specification + info about available resources at router admission decision (if no, then re-routing)

– Packet Classification: which flow does it belong to?

– Packet Scheduling: make sure, flow obtains resources as specified



IntServ/RSVP (cont`d)• Signalling by Resource Reservation Protocol (RSVP)

– Path Message: sender initiated, description of traffic parameters (Tspec) and path– Resv Message: receiver initiated, causes connection admission/reservation along

path; specifies QoS parameters (Rspec)– Other messages for reservation teardown and error treatment– Principles

• In-path signalling• Multi-cast support• Soft-State concept: periodic refresh of reservation required

• Advantages:– Fine Granularity: per flow treatment, flexible set of QoS parameters– Able to provide QoS guarantees (if admission, classification, scheduling is

performed correctly)• Disadvantages

– Scalability problem: management of state for each single flow– Complexity (already connection admission can be complex, e.g. effective

bandwidths, etc.)



IntServ: RSVP Messages I• Path Message

– Tspec: Traffic specification• Token Bucket Rate• Token Bucket Size• Peak Data Rate• Minimum Policed Unit• Packet Size

– Adspec: Network Resources on Path• Non QoS Hop-count• Available Path Bandwidth• Minimum Path Latency• Path MTU

– Sender Template: Filter Specification• IP source address, protocol type, port number, etc.

– Previous router on path



IntServ: RSVP Messages II• Resv Message

– Next hop in path (receiver sender)

– Flow-spec• Tspec• Rspec

– List of Filter Specs (description of sender for which the reservation is intended)

– Reservation style• Wildcard filter: shared, one reservation for all senders• Fixed filter: distinct, one per sender• Shared explicit: one reservation for specified list of senders



RSVP Messages: FlowSpec (Controlled Load) 31 24 23 16 15 8 7 0

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1 | 0 (a) | reserved | 7 (b) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2 | 5 (c) |0| reserved | 6 (d) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3 | 127 (e) | 0 (f) | 5 (g) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 4 | Token Bucket Rate [r] (32-bit IEEE floating point number) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 5 | Token Bucket Size [b] (32-bit IEEE floating point number) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 6 | Peak Data Rate [p] (32-bit IEEE floating point number) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7 | Minimum Policed Unit [m] (32-bit integer) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 8 | Maximum Packet Size [M] (32-bit integer) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ (a) - Message format version number (0) (b) - Overall length (7 words not including header) (c) - Service header, service number 5 (Controlled-Load) (d) - Length of controlled-load data, 6 words not including per-service header (e) - Parameter ID, parameter 127 (Token Bucket TSpec) (f) - Parameter 127 flags (none set) (g) - Parameter 127 length, 5 words not including per-service header

Reservation Types:

•Guaranteed Service: Bandwidth and Delay Guarantees, No Loss

•Controlled Load: Only Bandwidth Guarantee



Additional Issues in QoS signalling• Inter-domain signaling• Off-path signaling• Arbitrary placement of initiator and receiver • Bi-directional signaling/ sender-initiated signaling• Mobility support• Implementation size & complexity (~own transport protocol on top of

IP, multicast support, etc.)• How to secure RSVP in a real-world environment



QoS signalling scenarios

QoS

midcom

QoS QoS

Host A

Host B

State kept at more than two entities.

Protocol requires interaction with other protocols (routing, security, AAA, mobility, etc.)

AS 1249 AS15465 AS17

Bandwidth

broker

QoS Signalling

data

Bandwidth

broker

Bandwidth

broker

IN-Path

OFF-Path



QoS Solutions III: DiffServ• Basic Idea: reduce queueing delay/loss for critical traffic by preferential

treatment at routers (multiple queues) improve per-hop transmission behavior

• Packets marked by DiffServ Code Points (DSCPs, 6bit)

• Various scheduling disciplines at routers possible (e.g. static priority, weighted fair queueing)

• Advantage: Simple and scalable

• Problem: No performance guarantees unless used in conjunction with connection admission and traffic shaping/policing at ingress routers

SLA

CustomerNetwork

CustomerNetwork

SLA

SLA DiffServDomain

Border Router

Host

EdgeRouter SLA: Service Level Agreement



Per Hop Behaviour

Differentiated Services (DS) Byte

CurrentlyUnused

Version IHL Total LengthIdentification Flags Fragment Offset

Time to Live Protocol Header ChecksumSource Address

Destination Address

Destination Address

Source Address

Version Flow LabelPayload Length Next Header Hop Limit

IPv4 IPv6

Traffic ClassTOS

17

DiffServ Code Points (DSCP)



DiffServ: Influencing QoS• At Border Routers

– Traffic classification and Marking DiffServ Class (e.g. EF, AF, BE)

– Traffic Policing/Shaping/Conditioning, e.g.• (Token) Leaky Bucket• Time-sliding window 3 color marker

• Two thresholds: Commited Information Rate,Peak Information Rate

• Time-sliding window for measurement of average rate

• At Interior DiffServ Router– Scheduling: Strict Priority, Weighted Fair Queueing, etc.

– Buffer Management, e.g. Random Early Drop RED, RIO• Possibly different drop precedence



47.1

47.247.3

12

1

2

1

23

3

IP 47.1.1.1

IP 47.1.1.1

QoS Solutions IV: Traffic Engineering

• TE = distribute traffic over network links in order to avoid congestion• IP routing (OSPF, IS-IS, RIP, etc.)

– Based on destination IP address– No possibility for distinguishing traffic classes– Modification of link costs possible, but implications on link utilizations not straightforward

• Alternatives– QoS Routing: Use QoS parameters for path selection

– Establishment of explicite paths• Automatically• Via network management• Approaches:

• Tunneling: e.g.L2TP, PPP

• Multi-Protocol Label Switching (MPLS)



BR1

BR2

BR3

BR4

TR1 TR2

TR3TR4

AS1AS2 AS3

• Border Router (ingress) assigns label to packet• e.g. based on protocol type, DSCP, QoS demands, etc.

• Forwarding within MPLS domain based on assigned label• Necessary: establishment of Label Switched Paths (LSPs), using signalling protocols

• CR-LDP• RSVP-TE

• Egress router will remove label

Ingress routerreceives packetIngress router

receives packetPacket labeled

based onegress router

Packet labeled based on

egress router

Forwarding in the interiorbased on labels

Forwarding in the interiorbased on labels

Egress borderrouter pops

label and fwds.

Egress borderrouter pops

label and fwds.

MPLS: Principles



Dynamic MPLS paths for aggregated traffic• Dynamic MPLS path setup using source routing

• Question:

– Trigger events?

– Requirements/QoS parameters for new path?



QoS routing

• E.g. QoS routing based on RFC 2676 (Apostolopoulos, et al. - QoS Routing Mechanisms and OSPF Extensions; status: experimental)

• OSPF LSAs advertise

– Cost

– Residual bandwidth

– Delay of links

• Widest-shortest path algorithm:

– Among all paths with sufficient bandwidth

– choose among those with the lowest hop count

– If there are several feasible paths with identical hop count, choose the one with the highest residual bandwidth.

• Computation of routing tables at each node using a modified Bellman-Ford algorithm



Content








GPRS QoS management principles

3 radio block period

2 TBF

1 PDP context

t1 PDP context activation (SGSN/GGSN, CAC)2 resource allocation at TBF setup (BSS, RLC/MAC)

3 scheduling of RLC/MAC blocks within a TBF (BSS, RLC/MAC)

QoS management in GPRS follows a three-stage principle:

QoS negotiation at Packet Data Protocol (PDP) context activation

radio resource assignment at TBF setup

scheduling of radio blocks during ongoing TBF + QoS in IP transport (SGSNGGSN)



GPRS Release 97: QoS profilesQoS in GPRS Release 97 is described by the parameters of the QoS profile

precedence class (4 classes)

reliability class (9 classes)

delay class (4 classes)

peak throughput class (9 classes)

mean throughput class (19 classes)

QoS profile is negotiated between MS and SGSN/GGSN at PDP context activation

QoS profile is not available in the BSS

no efficient MAC scheduling can be performed



GPRS Release 99: Traffic classes

Conversational Audio Telephony 4-25 kbit/s < 150 ms

Data Telnet > 8 kbit/s < 250 ms

Streaming Audio Internet Radio (HQ) 32-128 kbit/s < 10 ms

Data FTP - < 10 ms

Interactive Data Web Browsing (HTML)

- < 4 s/Seite

Audio Voice Messages 4-13 kbit/s < 1 s

Background Data E-mail - -

besides the QoS profile four application-specific traffic classes are introduced (conversational, streaming, interactive, background)

Aggregate BSS QoS Profile (ABSQSP) is indicated to the BSS by the SGSN on demand

TypeTraffic class Application Data rate req. Delay req.



PDP context activation(PDP = Packet Data Protocol)

1) MS initiates the PDP context activation2) connection admission control (CAC) in

the SGSN checks the requested QoS profile

3) GGSN installs downlink Traffic Flow Template

4) QoS profile is delivered to BSS5) BSS indicates radio priority to MS

PDP context setup and QoS

Activate PDP Context Req (QoS Req)

...

...

RLC/MAC CACCAC

InstallDL TFT

GPRS

Set radio

MS SGSN GGSNBSS

Create BSS PFC Req (ABQS)

Create PDP Context Res (QoS Neg)

(Radio priority)

Radio Resource Request

DeleteDL TFT

Activate PDP Context Acc (QoS Neg)

Create BSS PFC Acc (ABQS)

Create PDP Context Req (QoS Neg)

Deactivate PDP Context ReqDelete PDP Context Req

Delete PDP Context ResDeactivate PDP Context Acc

Mapping to

PDP context

Delete PDPcontext

Admission control

Scheduling

setpriority



Limit I

Shared(priority to premium)

Premium andinteractivetraffic increase

Implementation example: CACLowtrafficload

Backgroundtraffic increases

Resources used by

traffic streams

Premium

Shared(priority to interactive)

Reserved tobackground

Interactive Background

Limit P

three traffic classes are regarded:

premium subscriber traffic

interactive traffic

background traffic

the aim of an optimized CAC policy is the compromise between:

efficient use of resources

guarantee of negotiated QoS

this can be achieved by suitable choice of the limits P and I



Implementation example: MAC scheduler

Best effort

Standard

Premium„Gold Card“ service

Background

Interactive

Conversational

Streaming

FIFO, RR, EDD, etc.

ApplicationQoS profile

SubscriberQoS profile

Priority

differentiation by subscriber QoS classes differentiation by application QoS classes scheduling of the different traffic class queues (priority-based) scheduling of TBFs within the traffic class queues (round robin)



UMTS QoS: Bearer Hierarchy

TE MT UTRAN/GERAN

CN IuEDGENODE

CNGateway

TE/AS

End-to-End Service(IP Bearer Service)

TE/MT LocalBearer Service

UMTS BearerService

External BearerService

UMTS Bearer Service

Radio Access BearerService

CN BearerService

BackboneBearer Service

Iu BearerService

Radio BearerService

PhysicalRadio

Service

PhysicalBearer Service

Air Interface

3G GGSN3G SGSNRAN

User Equipment

Mapping of Parameters between bearer levels is implementation dependent!



UMTS Bearer: Traffic Classes (Source TS23.107, V5.2.0)



UMTS Bearer: Parameters (Source TS23.107, V5.2.0)

Selected Traffic/QoS Parameters• Maximum Bitrate (kb/s)

Token bucket: bucket size = MaxSDUsize; token rate=Maximum Bitrate• Guaranteed Bitrate (kb/s)

Token bucket: bucket size = k*MaxSDUsize; token rate=guaranteed bitratek=1 in Rel. 99; Note: for speech traffic, maximum bitrate = guaranteed bitrate (TS 25.413)

• Source statistics descriptor (`speech´, `unknown´)Could be used to compute effective bandwidths (multiplex gain)

• Transfer delay (ms)limit 95percentile of delay distribution of all delivered SDUs

• SDU error ratiofraction of lost or detected erroneous SDUs

• Maximum SDU size (bytes)



UMTS Bearer: Range of Traffic/QoS Parameters(Source TS23.107, V5.2.0)

AMR: SDU size 100-200 bit (20 ms inter-SDU time)

Subflows on Radio Access Bearer (25.413, 26.xxx)



Mapping GPRS/UMTS classes to DiffServ classes

UMTS QoS class DiffServ class ReasonConversational class Expedited forwarding class low latency and jitter

Streaming class Assured forwarding Class 4

low variation of delay

Interactive class Assured forwardingClass 3

low latency(but not as low as in conversational class)

Background class Assured forwardingClass 2 or class 1 or best effort (class 0)

no special requirement for this class except reliability



UMTS QoS Signalling: 3GPP ArchitectureNew Entities in UMTS Rel‘5:• Policy Control Function (co-located to P-CSCF)• IP Bearer Service Manager (Policy Enforcement

Point)

Adm/Cap.Control

UMTS BSManager

UMTS BSManager

UMTS BSManager

Radio BSManager

Radio BSManager

Iu BSManager

Iu BSManager

CN BSManager

CN BSManager

UTRAph. BS M

UTRAph. BS M

Iu NSManager

Iu NSManager

BB NSManager

BB NSManager

RABManager

Adm/Cap.Control

Adm/Cap.Control

Subsc.Control

Adm/Cap.Control

Protocol interface Service primitive interface

IP BSManager

Transl. Transl.

IP BSManager

LocalSIP proxy

Policy ControlFunction

P-CSCF

ExternalNetwork

ExternalService Control

UE UTRAN SGSN GGSN--[COPS]



Summary








Topics not treated here

• QoS aware wireless MAC protocols (random access)– QoS in WLAN 802.11 and Bluetooth (MOB 9)

• End-to-end QoS signalling in UMTS (SIP/IMS) (MOB 9)• Mapping of QoS Parameters (ApplicL3L2PHY)

• Coupling of Mobility support and QoS• Service Level Agreements (SLAs)• ATM QoS



Acknowledgements• Student work (all TU Munich)

– Raimund Brandt (Seminar)

– Sunhwei Shen (Seminar)– Stefan Rank (Master Thesis)

• Presentations of H. Schulzrinne (Columbia University) and H. Tschofenig (Siemens Corporate Technologies)

• InfotechLecture notes: IP Based Networks and Applications, Chapter 3 (J. Charzinski), www.jcho.de/jc/IPNA

• Tutorial: IP Technology in 3rd Generation mobile networks, Siemens AG (J. Kross, L. Smith, H. Schwefel)

• Peter Stuckmann: Differentiated Service for Mobile Core Networks, WPMC 2001.

Documents

Page 1 Hans Peter Schwefel Wireless Networks II: Lecture 3, Spring04 Wireless Networks II: Performance & Cross-Layer Aspects by Hans Peter Schwefel Mm1