Wireless networks - Lecture 30: QoS in WLAN/Mobile IP

Wireless networks - Lecture 30: QoS in WLAN/Mobile IP. The main topics covered in this chapter include: limitations of QoS in IEEE 802.11; overview of 802.11e; traffic categories; EDCF; HCF; Mobile IP; distributed coordination function (DCF); point coordination function (PCF);...

Wireless Networks

Lecture 30 QoS in WLAN / Mobile IP

Dr Ghalib A Shah

 Security flaws in original 802.11

► Physical threat, impersonation, mutual authentication,

dictionary attacks, DOS

 802.1x Security

► AKM Operations with AS

► AKM operations with PSK

 IBSS Security model

QoS Limitations of 802.11

 DCF (Distributed Coordination Function)

► Only support best-effort services

► No guarantee in bandwidth, packet delay and jitter

► Throughput degradation in the heavy load

 PCF (Point Coordination Function)

► Inefficient central polling scheme

► Unpredictable beacon frame delay due to

incompatible cooperation between CP and CFP modes

► Transmission time of the polled stations is unknown

Overview of 802.11e

 Formed in Sep 1999 TheQoSbaseline

document was approved in November 2000 The first draft was available in late 2001.

 Aim to support both IntServ and DiffServ

 New QoS mechanisms

► EDCF (Enhanced DCF)

► HCF (Hybrid Coordination Function)

 Backwardly compatible with the DCF and PCF

 QoS is realized by introducing traffic categories

(TCs)

 MSDUs are delivered through multiple backoff

instances running as virtual stations

► Each instance is parameterized with TC specific

parameters

• AIFS, CWmin, CWmax, Persistance factor (PF)

► For legacy DCF, AIFS=DIFS, PF=2, CWmin < 15

► CWnew[TC] = (CWold[TC]+1) x PF -1

 0 <= I <= j <= 3 I, j are AC [0,1,2,3]

 CWmin[i] >= CWmin[j], CWmax[i] >= CWmax[j], AFIS[i] >= AFIS[j]

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EDCF (Enhanced DCF)

 Enhanced DCF

 Also support bursting

 Different parameters for different TC/AC

 Replace DIFS with AIFS (AIFS>DIFS) which is shorter

for audio and video traffic

► Audio = Video < Data

 CWmin and CWmax

► Audio < Video < Data

 Different Persistence Factor (PF)

 For EDCF, AIFS>=DIFS, PF=1-16, CWmin=0-255

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HCF (Hybrid CF)

 Provides policing and deterministic channel

access by controlling the channel through the

HC (Hybrid Coordinator)

 Operate in CFP and CP

 Detecting the channel as being idle for PIFS,

shorter than DIFS, gives the HC high priority over EDCF

 HCF model can provide Guaranteed Services

with a much higher probability than pure EDCF

 A signaling protocol can be used to facilitate

admission control and specify service rate

requirement

Mobile IP: Basics

 Proposed by IETF (Internet Engineering Task

Force)

► Standards development body for the Internet

 Mobile IP allows a mobile host to move about

without changing its permanent IP address

 Each mobile host has a home agent on its home 

network

 Mobile host establishes a care­of address when it's

away from home

slide by Konidala M Divyan [3]

Example

Internet Home Agent

Mobile Node

Mobile IP: Basics, Cont.

 Corres pondent hos t  is a host that wants to send

packets to the mobile host

 Correspondent host sends packets to the mobile

host’s IP permanent address

 These packets are routed to the mobile host’s

home network

 Home agent forwards IP packets for mobile host to

current care-of address

 Mobile host sends packets directly to

correspondent, using permanent home IP as

source IP

Mobile IP: Care-of Addresses

 Whenever a mobile host connects to a remote

network, two choices:

► care-of can be the address of a foreign agent on the

 Regardless, care-of address must be regis tered

with home agent

slide by Konidala M Divyan [3]

Internet

Mobile Node sends Binding Update

Home Agent replies with Binding Acknowledgement

Corresp.

Node C

Mobile Node registers at its Home Agent

Foreign Agent

Protocol

 In order to support mobility, Mobile

IP includes three capabilities:

1 Discovery

2 Registration

3 Tunneling

Discovery

 Mobile Agents send ICMP router advertisements with

mobility agent advertisement extension periodically informing mobile nodes of its presence

 Mobile node is responsible for the discovery process

 In order to receive an advertisement, the mobile node

may optionally request one from an agent or simply wait for the next advertisement

Registration

 Mobile node recognizes that it is on a foreign network,

acquires a Care-of-Address and requests its home

agent to forward its data packets to the foreign agent

 The process of registration requires 4 steps:

1 Mobile node request forwarding service by

sending registration request to the foreign agent.

Tunneling

 After registration, an IP tunnel is set up between the

home agent and care-of-address of the mobile node

 Home agent broadcasts gratuitous ARP request which

causes all nodes in the subnet to update their ARP

caches to map the mobile nodes IP address to the

home agents link level address

 Thus home agent receives packets destined to the

mobile node, and forwards the packets to the foreign agent through the IP tunnel.

Tunneling

 In the foreign network, decapsulation is done by the

foreign agent or by the mobile node itself

 A correspondent node assumes that the reply from the

mobile node is coming from its home network and

continues to send the packet to the home agent

► Source = address of home agent

► Protocol number = IP-in-IP

IP header

data

slide by Konidala M Divyan [3]

Triangle Routing (Mobile IPv4)

Internet

 Corresp Node C initiates communication with Mobile

Node and sends packets to MN‘s home address

 Home Agent intercepts packets and forward them to

the Mobile Node (proxy functionality)

 Mobile Node replies directly to Corresp Node C

Corresp Node C

Routing Inefficiency

home agent correspondent host

Mobile host and correspondent host might even be on the same

network!!

► Correspondent host caches care-of address

► Future packets tunneled directly to care-of address

 But!

► An instance of the cache consistency problem arises

► Cached care-of address becomes stale when the mobile

host moves

► Potential security issues with providing care-of address to

correspondent

Issues in Mobile IP

1 Handoff:

 When mobile node changes its point of attachment, a

handoff sequence is initiated

 During or immediately after the handoff , packet losses

may occur due to delayed propagation of new location information which degrades the quality of service

 Solved by introducing access point probing functionality

in the mobile node to identify the current access point it

is attached with

Mobile IP: Security Issues [4]

Issues in Mobile IP

2 Replay attacks:

 A Bad Guy could obtain a copy of a valid Registration 

Request, store it, and then “replay” it at a later time,

thereby registering a bogus care-of address for the

mobile node

 To prevent that the Identification field is generated is a

such a way as to allow the home agent to determine

what the next value should be

 In this way, the Bad Guy is thwarted because the

Identification field in his stored Registration Request will

be recognized as being out of date by the home agent (timestamps or nonces are used for Identification field)

Issues in Mobile IP

 Redundancy: What if the home agent doesn't

answer a registration request?

► Registration request to broadcast address

► Rejection carries new home agent ID

 "Ingress" filtering

► Routers which see packets coming from a direction

from which they would not have routed the source address are dropped

slide by Konidala M Divyan [3]

Internet

 Mobile Node sends Binding Updates to Home Agent and

all Corresp Nodes, which already received a previous

Binding Update from this Mobile Node

Mobile IPv6 Roaming