Wireless Networks and Protocols MAP-Tele Manuel P. Ricardo - - PowerPoint PPT Presentation

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Wireless Networks and Protocols

MAP-Tele Manuel P. Ricardo

Faculdade de Engenharia da Universidade do Porto

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Topics Scheduled for Today

…

♦ Convergence and interoperability of wireless systems: bringing

all together

» 4G wireless networks » 3GPP approach » Mobile IPv6 approach

– Basics on Mobile IP – 3GPP plans for adopting Mobile IPv6 – Media Independent handover

» Wireless mesh

– Basics on ad-hoc networks – The IEEE 802.11 mesh networks

» Research issues

…

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Basics on Mobile IP

♦ How to move between IP networks while maintaining a

connection active?

♦ What are the differences between MIPv4 and MIPv6? ♦ How is route optimization performed in MIPv6 ♦ How does the Dual Stack MIPv6 work?

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Mobile IPv4

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Motivation

♦ IP datagram forwarding is based on IP destination address ♦ IP network address  physical network ♦ Changing network  changing IP address ♦ How to implement mobility at the IP layer? ♦ Possible solution

» Register new IP address near the DNS server » Problems

– DNS registration takes time – TCP connections will break

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Mobile IPv4 - Terminology

♦ MN, Mobile Node ♦ HA, Home Agent

registers MN location

♦ FA, Foreign Agent

agent in the visited network

♦ COA, Care-of Address

MN’s IP address in the visited network

♦ CN, Correspondent Node

host which communicates with the MN

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Example

mobile end-system Internet router router router end-system

FA HA MN

home network foreign network (physical home network for the MN) (current physical network for the MN)

CN

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Data transference to MN

Internet sender

FA HA MN

home network foreign network receiver

1 2 3

• 1. Sender sends to the IP address of MN,

HA intercepts packet

• 2. HA tunnels packet to COA (FA)

by encapsulation

• 3. FA forwards the packet to the MN

CN

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Data transference from MN

Internet receiver

FA HA MN

home network foreign network sender

1

• 1. Sender sends to the IP address
• f the receiver as usual,

FA works as default router

CN

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Mobility phases

CN router HA router FA Internet router 1. 2. 3. home network MN foreign network 4. CN router HA router FA Internet router home network MN foreign network COA

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MN – Agents communication

♦ MN identifies the network

» Mobility agents send regularly messages to their networks

ICMP Router Advertisement messages

» MN listens messages; determines the network

– Its home network, or – A visited network  MN obtains new address – the CoA

♦ In the visited network, after obtaining CoA, MN

» MN sends COA to HA (via FA)  new location registered at the HA » At the home network

– HA assumes the MN home IP address – Packets destined to the MN IP home address are intercepted by HA and tunnelled to the MN (CoA address)

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ICMP Router Advertisment – Mobility Extensiom

preference level 1 router address 1 #addresses type

• addr. size

lifetime checksum COA 1 COA 2 type sequence number length 7 8 15 16 31 24 23 code preference level 2 router address 2 . . . registration lifetime . . .

R B H F M G r

reserved

R – registration required B – FA busy H – agent is HA F – agent is FA M – minimal encaspulation accepted G – GRE encapsulation accepted r – not used T – FA supports reverse tunneling

Message sent by mobility agents (HA and FA)

T

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To think about

♦ Can we remove the Foreign Agent from MIPv4? What are the

consequences of it?

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MN registration in the Home Agent

t MN HA t MN FA HA

• Co-located address
• Tunnel ends at the MN
• Address obtained by DHCP, for instance

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Registration messages

Type – registration request, registration reply S – Maintain old binding B –broadcast messages shall be forwarded D – co-located address M – minimal encapsulation accepted G – GRE encapsulation accepted r – not used T – FA supports reverse tunneling x - ignored

home agent home address type lifetime 7 8 15 16 31 24 23 identification COA extensions . . .

S B DMG r T x

port UDP 434

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Tunnels

• riginal IP header
• riginal data

new data new IP header

• uter header

inner header

• riginal data

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IP in IP (mandatory)

Care-of address COA IP address of HA TTL IP identification IP-in-IP IP checksum flags fragment offset length TOS ver. IHL IP address of MN IP address of CN TTL IP identification

• lay. 4 prot.

IP checksum flags fragment offset length TOS ver. IHL TCP/UDP/ ... payload

Tunnel HA  COA

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To think about

♦ What is NAT (Network Address Translation)?

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NAT – Network Address Translation

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To think about

♦ Does this version of MIPv4 work when MN has a private CoA

address?

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Mobile IPv6

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Mobile IPv6 – working principles

♦ Differences to MIPv4

» No ForeignAgent » Registration signalling (HomeAddress  CareOfAddress )

– Sent as an IPv6 extension header  Mobility Header – Binding relations (HomeAddress  CareOfAddress ) recorded also in the CNs

♦ Binding messages

» BindingUpdate

– MN informs HA/CN of its CareOfAddress

» BindingAcknowledgement

– Received by MN. Confirms BindingUpdate

» BindingRefreshRequest

– Sent by HA/CN. Requests MN to refresh binding

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Binding

♦ MN moves to a visited network

– MN auto-configures new address  COA – COA network prefix == prefix of the visited network – MN request the registration of COA in HA MN sends IPv6 packet with BindingUpdate (extension header) – HA registers MN and replies with BindingAcknowledgment

♦ Tunnel MN - HA

– HA, in home networks

 Intercepts packet to MN  Sends packet to COA; by tunnel

– MN

 Sends packet in tunnel to HA

– Tunnel terminates in the MN

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CoA autoconfiguration, in the visited network

♦ MN

» Listens RouterAdvertisment messages

– In mobility routers  up to 50 msg/s – Obtains network prefix

» Builds address in the visited network, the CareOfAddress

♦ DHCPv6 may be used by MN to obtain CoA

Routing Prefix MAC address

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Route optimization

♦ When MN receives a tunnelled packet

» it sends BindingUpdate to CN

♦ HomeAddress  CareOfAddress binding

– also known at the CN

♦ Then, packets are exchanged directly between MN e CN

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Route optimization

♦ IPv6 packets in direction CN  MN

» CN

– Before sending a packet to MN, reads its Bindings cache – Is there is no entry  packet sent as usual – If there is an entry

 Sends packet to CareOfAddress (destination address = CareOfAddress)  Includes in the packet a RoutingHeader having 2 hops

(list of addresses to be visited) – 1º hop  CareOfAddress; 2º hop  MN HomeAddress

» MN

– Receives packet in CareOfAddress – Forwards packet to itself (MN home address)

♦ IPv6 packets in the MN  CN direction

– Source address = CareOfAddress – Inclusion of DestinationHeader with information about HomeAddress – CN replaces HomeAddress in the packet source address so that the socket structure may contain the correct information  HomeAddress

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Routing Header – Packet sent from S to D, passing by I1, I2, I3

As the packet travels from S to I1: Source Address = S Hdr Ext Len = 6 Destination Address = I1 Segments Left = 3 Address[1] = I2 Address[2] = I3 Address[3] = D As the packet travels from I1 to I2: Source Address = S Hdr Ext Len = 6 Destination Address = I2 Segments Left = 2 Address[1] = I1 Address[2] = I3 Address[3] = D As the packet travels from I2 to I3: Source Address = S Hdr Ext Len = 6 Destination Address = I3 Segments Left = 1 Address[1] = I1 Address[2] = I2 Address[3] = D As the packet travels from I3 to D: Source Address = S Hdr Ext Len = 6 Destination Address = D Segments Left = 0 Address[1] = I1 Address[2] = I2 Address[3] = I3

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cn ha mn router novo mn | | | | no no' mo moves ves | | | | | | | | + +---

• ->|

>| | | | | | | |r |rad adv | | | | | | | | + +---

• ->|

>| | | | | bind inding ing u upd pdate ate | | | | | | |< |<----

• --+

| | |b |bindi nding ng ac ack k | | | | | | | | +-----

• ->|

>| |ec |echo ho re requ quest est| | | | | | | | + + ----

• --==

====== ====== ===== ==== ===== ===== ====== ====== ===== ==== ===== ===== ====== ====== ===== ==== ==>| >| | e | echo cho r rep eply ly | | | | | | | | |< |<----

• --==

====== ====== ===== ==== ===== ===== ====== ====== ===== ==== ===== ===== ====== ====== ===== ==== ===+ =+ |ho |home me te test st in init it | | | | | | |< |<----

• --==

====== ====== ===== ==== ===== ===== ====== ====== ===== ==== ===== ===== ====== ====== ===== ==== ===+ =+ | c | care are o

• f

f tes test t init nit | | | | | | |< |<----

• --+

|ca |care re of

• f t

test est| | | | | | | | +--

• ->|

>| |ho |home me te test st | | | | | | | | +--

• --==

====== ====== ===== ==== ===== ===== ====== ====== ===== ==== ===== ===== ====== ====== ===== ==== ==>| >| | b | bind indin ing g upd updat ate | | | | | | |< |<----

• --+

| b | bind indin ing g ack ack | | | | | | +--

• ->|

>| |ec |echo ho re requ quest est| | | | | | | | +--

• ->|

>| | e | echo cho r rep eply ly | | | | | | | | |< |<----

• --+

| | | | | | | | | | pin ping pin ping

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Dual Stack Mobile IPv6 (DSMIPv6)

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DSMIPv6

♦ DSMIPv6

» Assumes MN and HA are both IPv4 and IPv6-enabled » Uses only MIPv6 signalling

♦ Extends MIPv6 to allow

» registration of IPv4 addresses » transport of both IPv4 and IPv6 packets in the tunnel MN-HA » MN to roam between IPv6 and IPv4 (public and private) networks

DS-HA

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DSMIPv6 – Mobility Management

Visited network supports IPv6

» MN sends regular MIPv6 BindingUpdate » MN registers IPv6 CoA to HA » HA creates two binding cache entries, both pointing to MN-CoA-IPv6

– MN-home-address-IPv6  MN-CoA-IPv6 – MN-home-address-IPv4  MN-CoA-IPv6

» HA tunnels traffic to MN-CoA-IPv6

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DSMIPv6 – Mobility Management

Visited network supports IPv4 only - public addresses

» MN tunnels MIPv6 BindingUpdate message to the HA IPv4 address » HA creates two binding caches entries, both pointing to the MN-CoA-IPv4

– MN-home-address-IPv6  MN-CoA-IPv4 – MN-home-address-IPv4  MN-CoA-IPv4

» All the packets addressed to MN-home-addresses (IPv4 or IPv6) are encapsulated in an IPv4 tunnel HAv4MN-CoA-IPv4

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DSMIPv6 – Mobility Management

Visited network supports IPv4 only - private addresses

» HA listens in an UDP port, over a public IPv4 address » MN tunnels MIPv6 BindingUpdate message to HA IPv4/port addresses » HA creates two binding caches entries, both pointing to the public-MN-CoA-IPv4/port (recall NAT)

– MN-home-address-IPv6  public-MN-CoA-IPv4/port – MN-home-address-IPv4  public-MN-CoA-IPv4/port

» At the HA, the packets addressed to MN home addresses (IPv4 or IPv6)

– are first encapsulated in UDP packet (port to port), – then encapsulated in an IPv4 tunnel ending at the public-MN-CoA-IPv4 (recall the NAT functionality)

IPv4/IPv6 UDP IPv4

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To think about

♦

Is the IPv4/IPv6 packet received in (linux) user or kernel space?

♦

How can the contents of this packet be delivered to, for instance, the Web-browser running on top of TCP/IPv4? IPv4/IPv6 UDP IPv4

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DSMIPv6 – Route Optimization

♦ Visited network supports IPv6  similar to MIPv6 ♦ Visited network supports IPv4 only

not possible; communication always through the Home Agent

♦ Not possible

for traffic addressed to the Mobile Node's IPv4 home address

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3GPP plans for adopting Mobile IP

♦ What MIP based solutions are currently being studied in 3GPP? ♦ How are these solutions expected to work?

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Mobility between 3GPP-WLAN Interworking and 3GPP Systems

♦ Plans for Release 8 ♦ Requirements

» Smooth migration from legacy network with minimal impacts on dual mode UEs, I-WLAN and 3GPP systems » Architecture, functions and procedures shall be re-used » Both IPv4 and IPv6 addresses shall be supported » Service continuity between 3GPP PS network and I-WLAN with IP address preservation

♦ Possible solution based on DSMIPv6

» 3GPP TS 23.327, TS 23.827

♦ Conclusions based on the SAE report may lead to other solutions

» See 3GPP TR 23.882

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UE

WLAN AccessNetwork GERAN/UTRAN

SGSN HA PDG/ AR 3GPP AAA Server HSS

External PDN

WAG Ww Wu Wn Wp Wx HGi Iu_ps/Gb Uu/Um H3 H1 H2 GGSN/ AR Gn H3

Home Mobility Service Architecture

Home Agent function at home PLMN

L2/L1

Transport IP Tunneling layer

WLAN UE WLAN AN WAG PDG L2/L1

Transport IP

L2/L1

Transport IP

L2/L1 L2/L1 L2/L1

Transport IP Remote IP

L2/L1

Transport IP Transport IP Remote IP Tunneling layer

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UE WLAN Access Network GERAN/UTRAN SGSN HA PDG/ AR External PDN WAG Ww Wu Wn Wp HGi Iu_ps/Gb Uu/Um H3

H1

H2 GGSN/ AR H3 Wx Wd* HSS 3GPP AAA server 3GPP AAA proxy HPLMN VPLMN Gn

Visited Mobility Service Architecture

Home Agent function outside the hPLMN

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H1 PDN Attach

UE HA 3GPP AAA Server

• 1. HA discovery
• 2. IKEv2 Security Association establishment

& IPv6 HoA allocation

• 2. Auth. & Authorization
• 3. Binding Update
• 4. Binding Acknowledgement

3GPP AAA Proxy

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H1 PDN Attach

• 1. UE discovers the Home Agent (e.g using the DNS service)
• 2. A security association is established between UE and HA

» to secure the DS-MIPv6 » HA communicates with AAA infrastructure to complete authentication » HA assigns IPv6 home address/prefix to UE » If HA@ vPLMN

– interaction HA@vPLMN  AAA/HSS@hPLMN involves AAA-Proxy@vPLMN

• 3. UE sends BindingUpdate

» UE may request an IPv4 home address from the HA

• 4. HA replies with BindingAck

» HA may assign IPv4 home address to UE

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To think about

♦ Why does HA “assign home addresses”? What about the IP

addresses gathered by the UE through the GPRS-attach and IWLAN-attach?

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Handover from IWLAN to 3GPP access

• 1. UE discovers the GPRS,

and decides to transfer sessions to GPRS

• 2. UE starts GPRS attach procedure, which includes

» GGSN selection, IP address assignment to the UE (CoA) » GTP tunnel establishment between UE and GGSN

• 3. UE sends BindingUpdate message to HA, registering the GPRS CoA
• 4. HA sends BindingAck to UE

UE GGSN HA SGS N

• 1. UE Discovers

3GPP access and initiates HO

• 2. GPRS Attach/PDP context activation
• 3. Binding Update
• 4. Binding Acknowledgement

GTP Tunnel PDG

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Handover from 3GPP access to IWLAN access

• 1. UE discovers the IWLAN,

and decides to transfer sessions to IWLAN

• 2. UE establishes an IPsec tunnel with PDG,

and gets new IP address (CoA)

• 3. UE sends BindingUpdate via IWLAN
• 4. DSMIPv6 tunnel established between UE and HA; UE can exchange data through IWLAN

UE GGSN HA PDG

• 6. UE Discovers

3GPP IWLAN access and initiates HO UE GGSN HA PDG

• 1. UE Discovers

3GPP IWLAN access and initiates HO

• 3. H1 PDN Attach or

BU/BA

• 8. DSMIPv6 Tunnel

8. DSMIPv6 Tunnel

• 2. IPsec tunnel establishment

IPsec Tunnel DSMIPv6 tunnel

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UE Initiated Detach

• 1. UE sends BindingUpdate to HA with Binding-Lifetime = 0
• 2. HA sends the BindingAck to UE
• 3. UE tears down security association between UE and HA
• 4. The HA communicates with AAA infrastructure to tear down the H2 session

UE HA 3GPP AAA Server

• 3. IKEv2 Security Association tear down
• 4. H2 session termination
• 1. Binding Update
• 2. Binding Acknowledgement

3GPP AAA Proxy

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IEEE 802.21

♦ What other efforts are being developed to help macro mobility? ♦ How does the 802.21 work?

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Problem Characterization

♦ Increasing number of interfaces on devices

» mostly radio interfaces

♦ Device has difficulties in finding its best connection

» connection at L2, but not at the network layer » connect to the wrong of many APs available

based on signal strength criteria alone

♦ Many (vertical) handover mechanisms available ♦ Unified mechanism for handover decisions would help

 new standard, IEEE 802.21

» common across, at least, 802 media » based on L2 Triggers to make Mobile IP like protocols to work fast » based on media independent information

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The Use Case

Desk Undocked & walking around Headed out of the building 802.3 802.11 802.16 Internet

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Handover Initiation Handover Preparation Handover Execution

Search New Link

Network Discovery Network Selection Handover Negotiation

Setup New Link

Layer 2 Connectivity IP Connectivity

Transfer Connection

Handover Signaling Context Transfer Packet Reception

IEEE 802.21 helps with Handover Initiation, Network Selection and Interface Activation Scope of 802.21

Genesis for 802.21

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The role of IEEE 802.21

I EEE

8 0 2 .1 1 r 8 0 2 .1 6 e

3 GPP/ 2

VCC I -W LAN SAE-LTE Horizontal Handovers

IP Mobility & Handover Signaling

Inter-working & Handover Signaling

I EEE 8 0 2 .2 1 I ETF

MI P FMI P SI P HI P NETLMM DNA MI PSHOP

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Link Layer Triggers

State Change Predictive Network Initiated

Network Information

Available Networks Neighbor Maps Network Services

Handover Commands

Client Initiated Network Initiated Vertical Handovers

802.21 MIH Function Protocol and Device Hardware

Applications (VoIP/RTP)

Connection Management

WLAN Cellular WMAN

L2 Triggers and Events Information Service

Mobility Management Protocols

Smart Triggers Information Service Handover Messages

Handover Management

Handover Policy

Handover Messages IEEE 802.21 IETF

802.21 - Key Services

WNP-MPR-mip-mesh 52 WLAN WWAN

Link Up Link Going Down Link Down Link Up

Link Switch Make before Break

Connected Disconnected

Time

L2 Triggers and Events

♦ State Change Events

» Link Up » Link Down » Link Parameters Change

♦ Predictive Events

» Link Going Down

♦ Network Initiated Events

» Load Balancing » Operator Preferences

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No

Event Type Event Name Description

1 State Change Link Up L2 Connection established 2 State Change Link Down L2 Connection is broken 3 Predictive Link Going Down L2 connection breakdown imminent 4 State Change Link Detected New L2 link has been found 5 State Change Link Parameters Change Change in specific link parameters has crossed pre- specified thresholds (link Speed, Quality metrics) 6 Administrative Link Event Rollback Event rollback 7 Link Transmission Link SDU Transmit Status Improve handover performance through local feedback as opposed to waiting for end-to-end notifications 8 Link Synchronous Link Handover Imminent L2 intra-technology handover imminent (subnet change). Notify Handover information without change in link state. 9 Link Synchronous Link Handover Complete Notify handover state

Link Layer Events

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802.21 Information Server

WMAN WLAN WWAN

Network Type SSID/ Cell ID BSSID Operator Security NW Channel QoS Physical Layer Data Rate

GSM 13989 N/A AT&T NA NA 1900 N/A N/A 9.6 kbps

Network Type SSID/ Cell ID BSSID Operator Security NW Channel QoS Physical Layer Data Rate

GSM 13989 N/A AT&T NA NA 1900 N/A N/A 9.6 kbps 802.11b Intel 00:00:… Intel .11i EAP-PEAP 6 .11e OFDM 11 Mbps

Network Type SSID/ Cell ID BSSID Operator Security EAP Type Channel QoS Physical Layer Data Rate

GSM 13989 N/A Oper-1 NA NA 1900 N/A N/A 9.6 Kbps 802.11n Enterprise 00:00:… Oper-2 .11i EAP-PEAP 6 .11e OFDM 100 Mbps 802.16e NA NA Oper-3 PKM EAP-PEAP 11 Yes OFDM 40 Mbps

Global Network Map

• List of Available Networks
• 802.11/16/22, GSM, UMTS
• Link Layer Information
• Neighbor Maps
• Higher Layer Services
• ISP, MMS, ….

Media Independent Information Service

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Information Element Description Comments

List of networks available List all network types that are available given client location E.g., 802.11, 802.16, GSM, GPRS/EDGE, UMTS networks Location of PoA Geographical Location, Civic address, PoA ID E.g. GML format for LBS or network management purpose Operator ID Name of the network provider E.g. Could be equivalent to Network ID. Roaming Partners List of direct roaming agreements E.g. in form of NAIs or MCC+MNC Cost Indication of costs for service/network usage E.g, Free/Not free or (flat rate, hourly, day or weekly rate) Security Link layer security supported Cipher Suites and Authentication Methods, Technology specific, e.g. WEP in 802.11, 802.11i, PKM in 802.16, etc. Quality of Service Link QoS parameters 802 wide representation, application friendly PoA Capabilities Emergency Services, IMS Services, etc. Higher Layer Services Vendor Specific IEs Vendor/Operator specific information Custom information

Information Elements

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Handover

• Types of Handover Based on Control Model
• Terminal Controlled
• Terminal Initiated, Network Assisted
• Network Initiated and Network Controlled
• Handover Commands for Network Initiated Handovers

No Command Name MIHF <> MIHF Description

1 MIH Handover Initiate Client <> Network Initiates handovers and sends a list of suggested networks and suggested PoA (AP/BS). 2 MIH Handover Prepare Network <> Network This command is sent by MIHF on old network to MIHF on suggested new network . This allows the client to query for resources on new network and also allows to prepare the new network for handover 3 MIH Handover Commit Client <> Network In this case the client commits to do the handover based on selected choices for network and PoA. 4 MIH Handover Complete Client <> Network Network <> Network This is a notification from new network PoA to old network PoA that handover has been completed, new PoA has been established and any pending packets may now be forwarded to the new PoA.

WNP-MPR-mip-mesh 57 New items in scope of 802.21

SME

• r

NME

LLC MAC PHY PHY_SAP MAC_SAP MLME PLME MLME_PLME_SAP

MLME_SAP PLME_SAP

LSAP

Layer 3 or higher Mobility Protocol (L3MP) 802.21 Scope MIH_SAP MLME_SAP MIH Function MIH Event Service MIH Command Service MIH Information Service

No New Mobility Protocols Does Not handle Handover Execution No Redesign of Existing PHY/MAC

MIH Amendments for 802.11

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Management Plane MAC Common Part Sublayer MAC Security Sublayer

NCMS

Convergence Sublayer (CS) PHY PHY_SAP MAC_SAP

M_SAP

CS_SAP

C_SAP

New SAPs in scope of 802.21

L2.5

No Redesign of Existing PHY/MAC

Layer 3 or higher Mobility Protocol (L3MP) MIH Function MIH Event Service MIH Command Service MIH Information Service MIH_SAP 802.21 Scope

No New Mobility Protocols Does Not handle Handover Execution

MIH Amendments for 802.16

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Basics on ad-hoc networks

♦ What is an ad-hoc network? ♦ What are the differences between an ad-hoc wireless network

and a wired network?

♦ What are the characteristics of the most important ad-hoc

routing protocols?

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♦ Auto-configurable networks ♦ Having wireless links ♦ Mobile nodes  dynamic topology ♦ Isolated networks or interconnected to Internet ♦ Nodes forward traffic ♦ Routing protocols

A B C

Ad-Hoc Networks (Layer 3)

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IETF MANET - Mobile Ad-hoc Networking

Fixed Network Mobile Devices Mobile Router Manet Mobile IP, DHCP Router End system

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Route calculation in wired networks

♦ Distance vector

» Messages exchanged periodically with neighbours » Message indicates reachable nodes and their distance » Algorithm takes long time to converge » Eg. RIP

♦ Link state

» Router informs periodically the other routers about its links state » Every router gets information from all other routers » Lots of traffic » Eg. OSPF

4 3 6 2 1 9 1 1 D A F E B C

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Route calculation in Ad-Hoc Netoworks- Characteristics

Ad-hoc network

» Dynamic topology

– Depends on node mobility

» Interference

– Radio communications

» Asymmetric links

– Received powers and attenuation unequal in the two directions N1 N4 N2 N5 N3 N1 N4 N2 N5 N3 good link weak link time = t1 time = t2

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Routing in Ad-hoc Networks

♦ Conventional routing protocols

– Built for wired networks  whose topology varies slowly – Assume symmetric links

♦ In Ad-hoc networks

» Dynamic topology information required to be refreshed more frequently

– energy consumption – radio resources for with signaling information

» Wireless node may have scarce resources (bandwidth, energy) …

♦ New routing strategies / protocols for ad-hoc networks

– 2 type : reactive e pro-active

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To think about

♦ How can we avoid a large signaling overhead (number of

routing messages) in ad-hoc networks

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AODV – A needs to send packet to B

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AODV – A sends RouteRequest

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AODV – B replies with RouteReply

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AODV - Characteristics

» Decision to request a route » Broadcast of Route-request » Intermediate nodes get routes to node A » Route-reply sent in unicast by same path » Intermediate nodes get also route to node B » Routes have Time-to-live, in every node » Needs symmetric graph

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Pro-active routing protocols

♦ Routes built using continuous control traffic ♦ Routes are maintained ♦ Advantages, disadvantages

» Constant control traffic » Routes always available

♦ Example – OLSR (RFC 3626)

» OLSR - Optimized Link-State Routing protocol

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OLSR – Main functions

♦ Detection of links to neighbour nodes ♦ Optimized forwarding / flooding (MultiPoint Relaying)

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OLSR – Detecting links to neighbour nodes

♦ Using HELLO messages ♦ All nodes transmit periodically HELLO messages ♦ HELLO messages group neighbour by their state

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OLSR – MultiPoint Relaying (MPR)

♦ MultiPoint Relaying (MPR)

» Special nodes in the network » Used to

– Limit number of nodes retransmiting packets – Reduce number duplicated retransmissions

♦ Each node selects its MPRs, which must

» Be at 1 hop distance » Have symmetric links

♦ MPR set selected by a node

» Must be minimum » Must enable communication with every 2-hop-away nodes

♦ Node is MPR if it has been selected by other node

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OLSR – Link State

♦ In wired networks, OSPF

» Every node floods the network » With information about its links state

♦ OLSR does the same, using 2 optimizations

» Only nodes associated to MPR are declared in link state message  Reduced message length » Only the MPR nodes send link state messages  Smaller number of nodes sending messages

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OLSR – Link state, example

♦ Messages which declare the links state

» “Topology Control Messages”

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The IEEE 802.11 mesh networks

♦ How will the 802.11s Mesh Network work?

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Note: This set of slides reflects the view of a 802.11s draft standard.

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IEEE 802.11s - Main Characteristics

♦ Network topology and discovery ♦ Inter-working ♦ Path Selection and Forwarding ♦ MAC Enhancements

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Elements of a WLAN Mesh Network

• MP - Mesh Point

– establishes links with neighbor MPs

• MAP - Mesh AP

– MP + AP

• MPP - Mesh Portal
• STA – 802.11 station

– standard 802.11 STA

Bridge

• r Router

Mesh Portal MP

MAP MAP

STA STA MP

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L2 Mesh Network - Emulates 802 LAN Segment

5 9 7 10 6 2 4 3

Support for connecting an 802.11s mesh to an 802.1D bridged LAN

• Broadcast LAN (transparent forwarding)
• Learning bridge
• Support for bridge-to-bridge communications: Mesh Portal participates in STP

802 LAN

Broadcast LAN

• Unicast delivery
• Broadcast delivery
• Multicast delivery

11

13 12

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To think about

♦ Suppose A sends a frame to B (MAC layer). What MAC

addresses are required for the frame transmitted between the two Ethernet switches?

♦ And what MAC addresses are required for the frame transmitted

between the two MAPs? Why are the 2 cases different?

ethernet switch ethernet switch

A B

MAP MAP

A B ))) ))) )))

I) II)

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Mesh Data Frames

♦ Data frames

» based on 802.11 frames - 4 MAC address format » extended with: 802.11e QoS header, and new Mesh Control header field

♦ Mesh Control Field

» TTL – eliminates possibility of infinite loops (recall these are mesh networks!) » Mesh E2E Seq

MAC Header

Frame Control Dur Addr 1 Addr 2 Addr 3 Seq Control Addr 4 QoS Control Mesh Control Body FCS

2 2 6 6 6 2 6 2 3 4 Mesh E2E Seq

Mesh Control

Mesh TTL 7 8 23

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Topology Formation

♦ Mesh Point discovers candidate neighbors

» based on beacons, which contain mesh information

– WLAN Mesh capabilities – Mesh ID

♦ Membership in a WLAN Mesh Network

» determined by (secure) association with neighbors

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Mesh Association

5 7 1 2 6 4 3 MeshID: mesh-A Mesh Profile: (link state, …) X

Capabilities:

Path Selection: distance vector, link state

• 1. MP X discovers Mesh mesh-A with

profile (link state, …)

• 2. MP X associates /

authenticates with neighbors in the mesh, since it can support the Profile

• 3. MP X begins participating in

link state path selection and data forwarding protocol

One active protocol in one mesh but alternative protocols in different meshes

8

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Interworking - Packet Forwarding

11

5 9 7 10 6 2 4 3 13 12

Destination inside or outside the Mesh? Portal forwards the message Use path to the destination

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Hybrid Wireless Mesh Protocol (HWMP)

Combines

» on-demand route discovery

– based on AODV

» proactive routing to a mesh portal

– distance vector routing tree built and maintained rooted at the Portal

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HWMP Example 1: No Root, Destination Inside the Mesh

• Communication: MP4  MP9
• MP4

– checks its forwarding table for an entry to MP9 – If no entry exists, MP4 sends a broadcast RREQ to discover the best path to MP9

• MP9 replies with unicast RREP
• Data communication begins

5 9 7 10 6 4 3 2 1 8

X On-demand path

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HWMP Example 3: No Root, Destination Outside the Mesh

♦ Communication: MP4  X ♦ MP4

» first checks its forwarding table for an entry to X » If no entry exists, MP4 sends a broadcast RREQ to discover the best path to X » When no RREP received, MP4 assumes X is

• utside the mesh and sends messages destined to

X to Mesh Portals

♦ Mesh Portal that knows X may respond

with a unicast RREP

5 9 7 10 6 4 3 2 1 8

X On-demand path

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HWMP Example 2: Root, Destination Inside the Mesh

♦ Communication: MP 4  MP 9 ♦ MPs learn Root MP1 through Root Announcement

messages

♦ MP 4 checks its forwarding table for an entry to

MP9

♦ If no entry exists, MP4 forwards message on the

proactive path to Root MP1

♦ When MP1 receives the message, it forwards on the

proactive path to MP9

♦ MP9, receiving the message, may issue a RREQ

back to MP 4 to establish a path that is more efficient than the path via Root MP1

5 9 7 10 6 4 3 2 1 8

X Proactive path

Root

On-demand path

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HWMP Example 4: Root, Destination Outside the Mesh

♦ Communication: MP4  X ♦ MPs learn Root MP1 through Root Announcement

messages

♦ If MP4 has no entry for X in its forwarding table,

MP 4 may forward the message on the proactive path toward the Root MP1

♦ When MP1 receives the message, if it does not have

an active forwarding entry to X it may assume the destination is outside the mesh

♦ Mesh Portal MP1 forwards messages to other LAN

segments

5 9 7 10 6 4 3 2 1 8

X Proactive path

Root

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Radio Aware OLSR (RA-OLSR)

♦ OLSR may be used in alternative to AODV ♦ RA-OLSR proactively maintains link-state for routing

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MAC Enhancements for Mesh

♦ Intra-mesh Congestion Control ♦ Common Channel Framework (Optional)

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Need for Congestion Control

♦ Mesh characteristics

» Heterogeneous link capacities along the path of a flow » Traffic aggregation: Multi-hop flows sharing intermediate links

♦ Issues with the 802.11 MAC for mesh

» Nodes blindly transmit as many packets as possible, regardless of how many reach the destination » Results in throughput degradation and performance inefficiency

2 1 7 6 3 High capacity link Low capacity link Flow 4 5

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Intra-Mesh Congestion Control Mechanisms

♦ Local congestion monitoring (informative)

» Each node actively monitors local channel utilization » If congestion detected,

notifies previous-hop neighbors and/or the neighborhood

♦ Congestion control signaling

» Congestion Control Request (unicast) » Congestion Control Response (unicast) » Neighborhood Congestion Announcement (broadcast)

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Common Channel

♦ Common channel

» Unified Channel on which MPs jointly operate

» Using RTX, the transmitter suggests a destination channel » Receiver accepts/declines the suggested channel using CTX » The transmitter and receiver switch to the destination channel » Data is transmitted » Then they switch back

RTX MP1 MP2 MP3 MP4 Common Channel Data Channel n Data Channel m CTX SIFS CTX SIFS RTX ≥ DIFS DIFS DATA Switching Delay ACK SIFS CTX SIFS RTX ≥ DIFS Switching Delay DATA Switching Delay DIFS ACK SIFS

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Control Frames

♦ Request to Switch (RTX) Frame ♦ Clear to Switch (CTX) Frame

Frame Control Duration/ ID RA TA Destination Channel Info. FCS 2 2 6 6 2 4 Frame Control Duration/ ID RA Destination Channel Info. FCS 2 2 6 2 4