page 1 hans peter schwefel phd course: umts lecture 2, fall03 phd course: umts and ip based mobile...

Hans Peter Schwefel

PhD Course: UMTS Lecture 2, Fall03

PhD Course: UMTS and IP based mobile networksWerner Mohr, Ljupco Jorguseski, and Hans-Peter Schwefel

• Day 1 Architecture and Core Network Aspects (HPS)

• Day 2 Radio Resource Management and Radio Planning (LJ)

• Day 3 Radio Propagation (WM)

• Day 4 W-CDMA & TD-CDMA (WM)

• Day 5 Cell Structure & Outlook Beyond 3G (WM)

Organized by Ramjee Prasad

Hans Peter Schwefel


Content1. Performance & Network Planning

• Performance Impacting Factors, circuit switched planning approaches, packets switched planning

2. IP Quality of service and performance optimizations• Basic methods, implementation approaches• Protocol Enhancements (RoHC)

3. Session Initiation Protocol (SIP)• Architectures & Entities• Methods

4. IP based multimedia subsystems (IMS)• Architecture & components• Registration & Call Routing

5. Services6. Outlook: Beyond 3G Networks

Hans Peter Schwefel


Core Network PlanningDetermine topology, # and type of network elements and link capacities• Plus planning of radio cells (topic in subsequent lecture)

Based on operator requirements on:• Security • Availability/Reliability• Performance (Transmission-, Processing-, Queueing delays)

Input data for planning:• Traffic and Mobility models

– # subscribers, # active users during busy hours, # active PDP contexts, traffic characterisation

• Functional Requirements– E.g. number of supported APNs, supported security features, redundancy for high

availability

Hans Peter Schwefel


IP Protocol: Packet-Based Transport• 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)

... and it makes performance modeling harder!!

Main motivation for Performance Modeling:• Network Planning• Evaluation/optimization of methods for congestion control & QoS provisioning

queueing

+

Hans Peter Schwefel


The circuit switched scenario

• K channels• Users allocate one channel per call for certain call duration• If all channels are allocated additional starting calls are blocked• How many channels are necessary to achieve a call certain maximal

blocking probability?

Common Model Assumptions:• Calls are arriving according to a Poission Process (justified for large user

population, limit theorems for stochastic processes) with rate • Call durations are exponentially distributed with mean T (okay for voice

calls)

Hans Peter Schwefel


Computation of Blocking Prob.: M/M/K/K model

• Poisson arrival of calls (first ’M’ Markovian) with rate – ti : arrival time of call i

– Xi:=ti+1-ti : interarrival time

– Poisson process of rate lambda: • Xi independent and

• Pr(Xi<x)=1 - exp(- x)

• Exponentially distributed call holding times of rate 1/T per call (second ’M’)

• K ’Servers’ • No additional waiting room for calls beyond K

Illustration of exponential distribution (Prob. that call longer than x, leftmost curve)

Hans Peter Schwefel


Computation of blocking probabilities:M/M/K/K models

• Finite Birth-Death Process (see e.g. [Cassandras & Lafortune]):

– Probability of i calls active [using Chapman-Kolmogorov Equations]

pi := Pr(n=i) = p0 (T)i /i! , i=1,…,K

where p0 = 1/[(T)i /i!] (sum taken over i=0 to K)

– Probability of blocked call:

p(B) = pK = p0 (T)K /K!

[also known as Erlang-B formula]

2/T1/T 3/T K/T

K

Hans Peter Schwefel


Challenges in IP networks:• Multiplexing of packets at nodes (L3)

• Burstiness of IP traffic (L3-7)

• Impact of Routing (L3)

• Performance impact of transport layer, in particular TCP (L4)

• Wide range of applications different traffic & QoS requirements (L5-7)

+ Feedback: performance traffic model, e.g. for TCP traffic, adaptive applications (cross-layer optimization)

Challenges in Packet Switched Setting

HTTP

TCP

IP

Link-Layer

L5-7

L4

L3

L2

Traffic Model

Mobility Model

Network Model

Performance Values (Delay, Loss, etc.)

TCP / adaptive applics.

Hans Peter Schwefel


Network model example: M/M/1/K queue

• Poisson arrival of packets (first ’M’ Markovian) with rate • Exponentially distributed service times

of rate (second ’M’)• Single Server (1)• Finite waiting room (buffer) for K packets• Often also specified: service discipline

– Default: First-In-First-Out– Others: Processor Sharing, Last-In-First-Out,

Earliest Deadline First,...

Finite buffer (size K)

Hans Peter Schwefel


M/M/1/K queue: Performance

• Finite Birth-Death Process (see e.g. [Cassandras & Lafortune]):

– Probability of i packets in queue [using Chapman-Kolmogorov Equations]

pi := Pr(n=i) = (1-)/(1- K+1) * i , where = /

1, i=0,…,K

– Probability of packet loss:

p(loss) = pK = (1-)/(1- K+1) * K

– Average Delay:

Ď = 1/[ (1-pK)] * /(1- K+1) * [(1- K)/ (1-) – K K ]

K

Hans Peter Schwefel


More realistic models: ON/OFF Models

Parameters:

• N sources, each average rate

• During ON periods: peak-rate p

• Mean duration of ON and OFF times

ON & OFF Times exponential MMPP representation with N+1 states

Hans Peter Schwefel


Traffic models: General hierarchical models

• Mathematical /stochastic description of traffic• Frequently used: Several levels with increasing granularity

– E.g. 3 levels: sessions, connections, packets– Or: 5-level model:

Hans Peter Schwefel


Example: HTTP traffic model • ‘Main’ objects contain zero or more embedded objects that the browser retrieves

Correlated requests for embedded objects within retrieval of main object

HTTP Session (User A)

HTTP Session (User B)

HTTP Session (User C)...

Session Level

Download Phase 1 Download Phase 2 Dld. Phase 3 ...Idle timeRead time

’exit browser’’click’ ’click’

Dld. Phase K

’click’’start browser’

Get Main Object Get embedded Obj. 1 Get emb. Obj. 2 Get emb. Obj. N...

Connection/ Flow Level

Packet Level, TCP dynamics (not shown here)

• Statistics:– Session arrivals: Renewal process (Poisson)– Idle time: heavy-tail

– # embedded objects: geometric (measurements e.g. mean 5)

– Object size: heavy-tailed

Hans Peter Schwefel








Hans Peter Schwefel


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)

Hans Peter Schwefel


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

treatment at routers 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

Boundary Router

Host

EdgeRouter SLA: Service Level Agreement

Hans Peter Schwefel


QoS Solutions III: 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

Hans Peter Schwefel


QoS Solutions III: IntServ/RSVP (cont`d)• Signalling by Resource Reservation Protocol (RSVP)

– Path Message: sender initiated, description of traffic parameters and path

– Resv Message: receiver initiated, causes connection admission/reservation along path; specifies QoS parameters

– Other messages for reservation teardown and error treatment– 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.)

Hans Peter Schwefel


Protocol Enhancements: Motivation

• Wireless links tend to show poor performance– Large delays– Low throughput– Bit errors / packet losses due to radio transmission

• Protocols in IP family not originally designed for such links– Increased volume due to headers– Deficiencies of TCP flow control– ... many more (e.g. applications HTTPWAP)

• Protocol Enhancements are required, two examples discussed here– Robust Header Compression (RoHC)– Enhancements for Wireless TCP

Hans Peter Schwefel


Robust Header Compression (RoHC)• Motivation

– IP voice packets: header 40/60Bytes, average payload 25Bytes

– TCP ACK packets: header 40/60 Bytes, payload often 0Bytes

• Data in many header fields …

– … hardly ever changes e.g. source/destination address within same IP flow

– … or changes in a regular pattern

• Idea: reduce header length by compression, e.g.

– differential encoding of fields

– and/or variations of Huffman compression

• Compression can be applied to several protocol headers, e.g. RTP/UDP/IP

Hans Peter Schwefel


Robust Header Compression (RoHC)

• Synchronized compression context required in compressor and decompressor

• Lost packets Synchronization disturbed Additional mechanisms for context synchronisation required: Robustness

– Error detection by Cyclic Redundancy Codes (CRC)

– Loss detection through sequence numbers

Reduced compression efficiency price for error robustness

• Current RoHC methods: 40 Bytes RTP/UDP/IP header on average 1 or 2 bytes

Hans Peter Schwefel


RoHC in UMTS

• RoHC optional part of Packet Data Convergence Protocol (PDCP) headers compressed only over radio link (RNC-UE)

• In principle compression already in GGSN possible, but– Flow identification/separation necessary– Large number of flows (up to 104 active flows)

L1

RLC

PDCP

MAC

IPv4 or v6

Application

L1

RLC

PDCP

MAC

ATM

UDP/IPv4 or v6

GTP‑U

AAL5

Relay

L1

UDP/IPv4 or v6

L2

GTP‑U

IPv4 or v6

3G‑SGSNUTRANMS

Iu-PSUu Gn Gi

3G‑GGSN

ATM

UDP/IPv4 or v6

GTP‑U

AAL5

L1

UDP/IPv4 or v6

GTP‑U

L2

Relay

L1

L2

IPv4 or v6

Hans Peter Schwefel








Hans Peter Schwefel


Session Initiation Protocol -- SIP

SIP: Application layer signalling protocol (RFC 3261) Provides call control for multi-media services

initiation, modification, and termination of sessions terminal-type negotiation and selections call holding, forwarding, forking, transfer media type negotiation (also mid-call changes) using Session Description Protocol (SDP)

Provides personal mobility support Independent of transport protocols (TCP, UDP, SCTP,…) ASCII format SIP headers Separation of call signalling and data stream

Application types/examples: Interactive Voice over IP (VoIP) Multimedia conferences (multi-party, e.g. voice & video) Instant messaging Presence service Support of location-based services

Hans Peter Schwefel


SIP – Basic messages

• Selected Requests (Methods)– INVITE: initiate call– ACK: confirm final response (after ‘invite’)– BYE: terminate call– CANCEL: cancel pending requests– OPTIONS: queries features supported by

other side– REGISTER: register with location service

• Responses– 1xx Intermediate results

e.g. 180 Ringing– 2xx Successful Responses

e.g. 200 OK– 3xx Redirections

e.g. 302 Moved Temporarily– 4xx Request Failures– 5xx Server Failures– 6xx Global Errors

Hans Peter Schwefel


SIP Addressing and header formatAddressing:• Addresses specified SIP URL, in the format: user@host. • Examples of SIP URLs:

• sip:[email protected]• sip:[email protected]• sip:[email protected]

INVITE sip:[email protected] SIP/2.0Via: SIP/2.0/UDP 192.168.6.21:5060From: sip:[email protected]: <sip:[email protected]>Call-ID: [email protected]: 100 INVITEExpires: 180User-Agent: Cisco IP Phone/ Rev. 1/ SIP enabledAccept: application/sdpContact: sip:[email protected]:5060Content-Type: application/sdp

• Example: SIP Header

Hans Peter Schwefel


SIP: Architecture & Entities

User agent: An application program which initiates SIP requests (User agent client) and also acts upon (accepts, rejects or re-directs) incoming SIP requests (User agent server)

Location server provides SIP redirect or proxy servers information about a callee's possible location(s).

Proxy server takes requests on behalf other user agents or servers and forwards them to the next hop.

Redirect server accepts a SIP request, maps the address into zero or more new addresses and returns these addresses to the client. Unlike a proxy server, it does not initiate its own SIP request.

Registrar is a server that accepts REGISTER requests. A registrar is typically co-located with a proxy or redirect server and may offer location services.

Redirect Server

Location Server

Registrar Server

User Agent Proxy ServerProxy Server User Agent

Hans Peter Schwefel


SIP Call Signalling: Example

302 (Moved Temporarily)

INVITE

200 (OK)200 (OK)

ACK

INVITE

180 (Ringing)180 (Ringing)180 (Ringing)

200 (OK)ACKACK ACK

RTP MEDIA PATH

BYEBYE BYE

200 (OK)200 (OK) 200 (OK)Call Teardown

MediaPath

Call Setup

INVITE

Location/Redirect ServerProxy Server Proxy Server User AgentUser AgentINVITE

Hans Peter Schwefel


SIP: Separation of signalling and data

• Route of SIP messages (proxy chain) different than media stream route:

Potential Problems with Firewalls & NATs

Hans Peter Schwefel


SIP: Mobility support

User Mobility (change of terminal)• Registration via SIP ‘REGISTER’• mid-session mobility (application mobility):

call transfer, SIP method ‘REFER’ (RFC3515)

Host Mobility (change of IP address)• Pre-call: re-register, routing of ‘INVITE’ based

on SIP-URL• mid-call: re-invite

Hans Peter Schwefel


SIP: additional topics

Not touched in this lecture, see IETF SIP WG:• Multitude of SIP extensions: new methods (e.g. instant messages)• SIP over NAT/FW• Authentication and security aspects• Support of location based services• Discovery of SIP entities (e.g. DNS SRV records)• Service Discovery (e.g. SLP)• Reliability aspects of SIP-based call control

Hans Peter Schwefel








Hans Peter Schwefel


IP based Multimedia Subsystem (IMS)

Additional domain in UMTS Rel. 5, based on Packet-switched domainEstablishment and Control of IP based multimedia calls based on SIP

Standardized interfaces to applicationsAuthentication and authorisation of service accessService based chargingQoS controlGlobal roaming and access to home services

Originally planned to be based on IPv6‘Network centric’ approach (as opposed to IETF SIP)In principle access independent (e.g. also WLAN access)No Network layer mobility support in IMS (mobility via SIP or in access networks)

Hans Peter Schwefel


SIP

Network Entities and Protocols

IM SubsystemApplicationsand

Services

MultimediaIP

Networks

CS Domain-or-

PSTN-or-

Legacy-or-

External

PS Domain

HSS

R-SGW

CSCF

CSCF

GGSN

MRF-CSCP

MGCF

MGW

SGSN

Cx

Sh

Sc

Gr

Mm

Mw

Mc

Gc

Mg

Gn

BGCF

T-SGW

BGCFMi

GoGm

SLF

Dx

AS

AlternativeAccess Networks

„Gi-Cloud“

PCF

OSA-SCS

IM-SSF

MRF-PMp

Sr

ISC

SIPSI

P

?

?

Dia

met

er

H248

SIP

H248

CO

PS

TCP/IP/UDP/RTP/…

SIP

?

MAP

CAP SIP

SIP

Mj

SIP TCP UDP

HTTP Others

? ?

SIP

?

R-SGW

CA

PO

SA

UE

UTRANMT TE

Uu IuR

GERAN

Mr

SIP Mk

Hans Peter Schwefel


Network Entities

• CSCF (Call State/Service Control Function)• PCF (Policy Control Function)• HSS (Home Subscriber Service)• SLF (Subscription Locator Function)• MRF (Multimedia Resource Function)• BGCF (Breakout Gateway Control Function)• MGCF (Median Gateway Control Function)• MGW (Media Gateway)• T-SGW (Transport Signaling Gateway)• R-SGW (Roaming Signaling Gateway)• AS (Application Server)• SCP (Service Content Provider)• IM-SSF (Service Switching Function)• OSA-SCS (Service Capability Server)

Additionally:- Charging Entities- Security Entities- Lawful Interception- Firewalls- DNS, DHCP, TRIP, …- QoS Entities- OAM and NM- …

Hans Peter Schwefel


IMS: Important Network ElementsHSS : Home Subscriber ServiceDatabase for subscriber related information• Identification (SIP, Mail, E.164, Label, IMSI, ...)• Location management (P-CSCF, S-CSCF, IP address)• List of authorized services, List of subscribed services• Quintuplets for Security

Proxy Call State Control Function (P-CSCF)First contact point of an operator‘s network (for the mobile terminal)• Forwarding of SIP messages between terminal and core network• Generation of charging records• Translation of IDs other than SIP URIs into SIP URIs

(e.g. E.164 numbers)• Termination of confidentiality and integrity, Lawful interception• Authorisation of bearer resources and QoS management• Detection of emergency calls and selection of a emergency S-CSCF• Translation of SIP URIs for local services• SIP header compression

Hans Peter Schwefel


IMS: Important Network Elements (cntd.)Interrogating Call State Control Function (I-CSCF)First contact point of an operator‘s network (for other operators)• Forwarding of SIP messages (proxy functionality)• Assignment of a S-CSCF

– during registration and during invite (for services for not registered subscribers)• Generation of charging records• Hiding of internal network configuration/capacity/topology

Serving Call State Control Function (S-CSCF)Performs session control and service triggering• Acts as a registrar according to RFC2543• May behave as a Proxy Server as defined in RFC2543, i.e. it accepts requests and services them

internally or forwards them on, possibly after translation.• May behave as a User Agent as defined in RFC2543, i.e. it may terminate and independently

generate SIP transactions.• Interaction with service platform(s), provides endpoints with service event related information • Authentication (based on quintuplets from HSS), Generation of charging records

Hans Peter Schwefel


Levels of Registration

UE xGSN

Visited Network Home Network

UMS

CSCFDHCP AS

HLR

Bearer Level

IM Subsystem

Application?

DHCP

CSCF HSS

Hans Peter Schwefel


Registration in a Roaming Scenario

Home Network of MS B

Network visited by MS B

MS B

P-CSCF-B

S-CSCF-B

2

1

Home Network of MS A

Network visited by MS A

MS A

P-CSCF-A

S-CSCF-A

REG

ISTE

R

I-CSCF-A

HSS-A User Profile

1

2

4

5

REG

ISTE

R

I-CSCF-A4

HSS-AUser Profile

5

Hans Peter Schwefel


Routing of Mobile-To-Mobile Calls



Home Network of MS B

Network visited by MS B

MS A MS B

P-CSCF-A

I-CSCF-B

P-CSCF-B

HSS-B

S-CSCF-A S-CSCF-B

REG

ISTE

R

User Profile

1 2

34

5

6

7

INVI

TE

Call C

ontro

l

REG

ISTE

R

I-CSCF-A

HSS-A User Profile

Hans Peter Schwefel


Foreign Network

Routing of Mobile Calls to CS or PSTN (3GPP)



MS A

PSTN

P-CSCF-A

I-CSCF-A

HSS-A

User Profile

S-CSCF A

MGCF-B T-SGW-B

MGW-B

I-CSCF-B

BGCF-BBGCF-ARE

GIS

TER

INVI

TE

Call C

ontro

l

GatewayControl

1 2

3

4

5

7

User Profile

A

B

6

Hans Peter Schwefel


SIP in IMS• Mandatory existence of P-CSCF as first point of contact• Network initiated call release (e.g. due to missing coverage or administrative reasons)

– Proxies are able to send BYE

• Network Control of Media Types– P/S-CSCF checks the SDP in the SIP body– If SDP contains invalid parameters (e.g. not supported codecs), P/S-CSCF rejects the SIP request by sending a

488 (“not acceptable here”) response that contains a SDP body indicating parameters that would be acceptable by the network

• Network Hiding (Encryption of Route and Via Headers)• Additional Signaling Information

– For example Cell-ID, Mobile Network/Country Code, Charging-IDs – Information transported P-header based solution

• Compression– SIP Compression is mandatory as radio interface is a scarce resource– Compression / decompression of SIP will be performed by the UE and the P-CSCF

• Authentication & Integrity protection– S-CSCF performs the Authentication using AKA – P-CSCF checks the integrity of messages received via the air interface via IPsec ESP

Hans Peter Schwefel


IMS: Services are Home Controlled

3rd Party ServiceProvider

Visited Network Home Network

UEServingCSCF

ApplicationServer

ProxyCSCF

ApplicationServer

SIP

ISC

SIPSIP

ApplicationServer

The Serving CSCF (S-CSCF) is located in the Home Network The Visited Network only provides a proxy (P-CSCF): all calls are always first

routed to the Home Network.

??

Hans Peter Schwefel


IM Core Network Subsystem

IMS Security Architecture

HSS

I-CSCF S-CSCF

Home / Serving Network

P-CSCF

Visited / Home Network

ISIM

UA

UE

Mutualauthentication

IMS AKA

IPSec:IntegrityProtection

IPSec: Confidentiality and Integrity Protection

IPSec: Confidentiality and Integrity Protection

Hans Peter Schwefel


Entertainment

•m-Gaming

•Gambling

•Audio

•Video

•Unified Messaging

•MMS

•Chat

•Conferencing

•Voice over IP

•Buddy list

•Presence configuration

•Availability configuration

Information

•Dynamic Info Svcs.

•Static Info Svcs.

Commerce

•m-Banking

•m-Shopping

•m-ticketing & reservations

•m-advertisement

End User Services: Categorization

Communication

Hans Peter Schwefel


Service Market Analysis

Willing to Use (W2U) / Willing to Pay (W2P)

Source: Adopted from Siemens End-User Survey 2000

Commerce Entertainment

Communication Information

Commerce27 %

Entertainment14 %

Information29 %

Communication30 %

Service Desirability (W2U)

Commerce Entertainment

Communication Information

Commerce12 %

Information3 %

Communication57 %

Entertainment28 %

Source: Durlacher UMTS Report

Service Revenue Potential (W2P)

Hans Peter Schwefel


Within the next six years data and multimedia traffic will overrule voice

In 2008 Multimedia Communication will account for ¼ of mobile traffic

Mbit/

User/

Month

Browsing & Download

Messaging

Real-Time Multimedia

Voice (Minutes of Use x 9,6 kb/s)50

100

150

200

250

300

350

2003 2004 2005 2006 2007 2008

0

Prediction: services in mobile NWs

Hans Peter Schwefel


Summary1. Performance & Network Planning






Hans Peter Schwefel


Outlook: Beyond 3G networks• Unifies different

access technologies• IP as convergence

layer• Mobility support on

the network layer• Ad-hoc networks can

extend geographic reach of cellular wireless technologies

• Personal Area Networks (PAN)

• Ubiquitous Computing

Services andapplications

IP based core network

IMT-2000UMTS

WLANtype

cellularGSM

short range

connectivity

WirelinexDSL

otherentities

DABDVB

return channel:e.g. GSM

download channel

New radiointerface

Hans Peter Schwefel


Problem: IP address identifies host as well as topological locationReason: IP Routing:

– Routes selected based on IP destination address– network prefix (e.g. 129.13.42) determines physical subnet– change of physical subnet change of IP address to have a topological correct address

• Solution? Host-based routing: Specific routes to each host– Handover change of all routing table entries in each (!) router– Scalability & performance problem

• Solution? Obtain new IP-address at hand-over– Problem: how to identify host after handover? DNS update performance/scalability problem– Higher protocol layers (TCP/UDP/application) need to ‘handle’ changing IP address

Development of mobile IP

Mobile IP Motivation: Host mobility & Routing

Subnet A

Subnet BIP network

Mobile Node

Hans Peter Schwefel


Mobile IP: Principles & Terminology

Underlying Approach: separate host identifier and location identifier maintain multiple IP addresses for mobile host

Terminology:• Mobile Node (MN) with fixed IP address IP1 (home address)• Home Network: subnet that contains IP1

• Home Agent (HA): node in home network, responsible for packet forwarding to MN• Visited Network: new subnet after roaming / handover• Care-of Address (CoA): temporary IP address within visited network• Foreign Agent (FA): node in visited network, responsible for packet forwarding to CoA

Home network

Visited network

IP network

Mobile Node Home Address IP1

HA

FA Home Address IP1

Care of Address: CoA1Correspondent Node

Hans Peter Schwefel


Home Network

Mobile IP: Tunneling &Triangle Routing

CN sends packets to the MN using its Home Address IP1

HA tunnels them to FA, using CoA1; FA forwards them to MN

MN sends packets back to the CN using IP2 (without any tunneling)

Home Agent needs to contain mapping of care-of address to home address (location register)

Mobile NodeIP1, CoA1

Home Agent

Subnet

Correspondent Node (CN) IP2

Visited Network

FA

IP1

CoA1

IP2

Source: Mobile IPv4 illustrated

Hans Peter Schwefel


Mobile IP: Agent Discovery & Registration

• Mobile Node finds out about FA through Agent Advertisements– FAs broadcast Advertisements in periodic intervals– Advertisements can be triggered by an Agent Solicitation from the MN

• Care of Address of the MN is determined, either– Dynamically, e.g. using Dynamic Host Configuration Protocol (DHCP)– Or: use IP address of FA as CoA

• MN registers at FA and HA: Registration Request & Reply– MN signals COA to the HA via the FA– HA acknowledges via FA to MN

• Registration with old FA simply expires (limited life-time, soft-state)

FAHA MN

[Agent Solicitation] (opt.)

Agent Advertisement

Registration Request

Registration ReplyTime

Obtain c/o address

Hans Peter Schwefel


type = 16R: registration requiredB: busy, no more registrationsH: home agentF: foreign agentM: minimal encapsulationG: GRE encapsulationr: =0, ignored (former Van Jacobson compression)T: FA supports reverse tunnelingreserved: =0, ignored

MIP messages:Agent advertisement

preference level 1router address 1

#addressestype

addr. size lifetimechecksum

COA 1COA 2

type = 16 sequence numberlength

0 7 8 15 16 312423code

preference level 2router address 2

. . .

registration lifetime

. . .

R B H F M G r reservedT

Procedure:

• HA and FA periodically broadcast advertisement messages into their subnets

• MN listens to these messages and detects, if it is in the home or a (new?) foreign network

• when new foreign network: MN reads a COA from the advertisement (opt.)

ICMP Router Discovery extension:

Hans Peter Schwefel


MIP messages: registration request & reply

home agenthome address

type = 1 lifetime0 7 8 15 16 312423

T x

identification

COA

extensions . . .

S B D MG rS: simultaneous bindingsB: broadcast datagramsD: decapsulation by MNM mininal encapsulationG: GRE encapsulationr: =0, ignoredT: reverse tunneling requestedx: =0, ignored

Registration Request (via UDP)

home agenthome address

type = 3 lifetime0 7 8 15 16 31

code

identification

extensions . . .

Registration Reply (UDP)

Example codes:registration successful• 0 registration accepted• 1 registration accepted, but simultaneous mobility bindings unsupportedregistration denied by FA•65 administratively prohibited•66 insufficient resources•67 mobile node failed authentication

•68 home agent failed authentication•69 requested Lifetime too longregistration denied by HA•129 administratively prohibited•131 mobile node failed authentication•133 registration Identification mismatch•135 too many simultaneous mobility bindings

Hans Peter Schwefel


MIP: Care-of addressesMN obtains local care-of address either• from FA Advertisement (see before)

• Or via Dynamic Host Configuration Protocol (DHCP)– supplies systems with all necessary information, such as IP address, DNS server

address, domain name, subnet mask, default router etc.– Client/Server-Model: client sends request via L2 broadcast

time

server(not selected)

client server(selected)

initialization

collection of replies

selection of configuration

initialization completed

confirmation ofconfiguration

determine the configuration

DHCPDISCOVER

DHCPOFFER

DHCPREQUEST(reject)

DHCPACK

DHCPDISCOVER

DHCPOFFER

DHCPREQUEST(options)

determine the configuration

Hans Peter Schwefel


The future of mobile networks

“Much of the initial enthusiasm for the concept appears to have evaporated and the original launch target of autumn this year has been slipping. When the government asked companies to apply for licences, international consortia rushed to compete.

(…) Since then, the economy has sunk into recession, forecasts of the number of subscribers have been scaled down and the need for heavy investment has scared many of the original shareholders.”

Financial Times: September 1992 “The Future of GSM Mobile Communications”

Hans Peter Schwefel


Acknowledgements (Lectures 1 & 2)• Tutorial: IP Technology in 3rd Generation mobile networks,

Siemens AG (J. Kross, L. Smith, H. Schwefel)• Lecture notes: Wireless Data Communication, MM5,

www.kom.auc.dk/~hps/teaching• Tutorial: Voice over IP Protocols – An Overview, www.vovida.org

• Various 3GPP slide-sets• Siemens ICM N PG U SE and Siemens CT IC 3

Other References• IETF (www.ietf.org)

– WGs: MMUSIC (old), SIP

• 3GPP: www.3gpp.org

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