1. Lecture 30 QoS in WLAN / Mobile IP Dr. Ghalib A. Shah
Wireless Networks
Lecture 30
QoS in WLAN / Mobile IP
Dr. Ghalib A. Shah

2. Outlines Last lecture Limitations of QoS in IEEE 802.11
Overview of e
Traffic Categories
EDCF
HCF
Mobile IP
Care-of-address,
MIP Protocol (Discovery, Registration, Tunneling)
Routing
Inefficiencies
MIPv6

3. Last Lecture Types of Attack Goals of 802.11 Security WEP Protocol
Access control, data integrity, confidentality
WEP Protocol
WEP Authentication
Security flaws in original
Physical threat, impersonation, mutual authentication, dictionary attacks, DOS
802.1x Security
AKM Operations with AS
AKM operations with PSK
IBSS Security model

4. 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

5. Aim to support both IntServ and DiffServ New QoS mechanisms
Overview of e
Formed in Sep TheQoSbaseline document was approved in November 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

6. 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

7. 0 <= I <= j <= 3 I, j are AC [0,1,2,3]
CWmin[i] >= CWmin[j], CWmax[i] >= CWmax[j], AFIS[i] >= AFIS[j]

9. 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

11. HCF (Hybrid CF)
Provides policing and deterministic channel access by controlling the channel through the HC (Hybrid Coordinator)
Operate in CFP and CP

12. 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

13. 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 care-of address when it's away from home

14. slide by Konidala M. Divyan [3]
Example
Network B
Home
network A
Foreign Agent
Internet
Home Agent
Network C
Mobile Node
Corresp.
Node C
slide by Konidala M. Divyan [3]

15. Mobile IP: Basics, Cont.
Correspondent host 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

16. 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 remote network
foreign agent delivers packets forwarded from home agent to mobile host
care-of can be a temporary, foreign IP address obtained through, e.g., DHCP
home agent tunnels packets directly to the temporary IP address
Regardless, care-of address must be registered with home agent

17. slide by Konidala M. Divyan [3]
Mobile Node registers at its Home Agent
Network B 
Foreign Agent
Network A 
Internet
Mobile Node
Home Agent
Network C
Mobile Node sends Binding Update
Home Agent replies with Binding Acknowledgement
Corresp.
Node C
slide by Konidala M. Divyan [3]

18. In order to support mobility, Mobile IP includes three capabilities:
Protocol
In order to support mobility, Mobile IP includes three capabilities:
1. Discovery
2. Registration
3. Tunneling

19. 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.

20. 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.

21. Registration 2. Foreign agent relays this request to the home agent.
3. Home agent accepts or denies the request and sends registration reply to the foreign agent.
4. Foreign agent relays this reply to Mobile node.

22. 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.

23. 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.

24. IP-in-IP Tunneling
Packet to be forwarded is encapsulated in a new IP packet
In the new header:
Destination = care-of-address
Source = address of home agent
Protocol number = IP-in-IP
IP header
IP header
data
IP header
data

25. slide by Konidala M. Divyan [3]
Triangle Routing (Mobile IPv4)
Network B
Network A 
Internet
Mobile Node 
Network C
Home Agent 
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
slide by Konidala M. Divyan [3]

26. Routing Inefficiency Mobile host and correspondent host
might even be on the same
network!!
correspondent host
home agent

27. Route Optimizations Possible Solution: But!
Home agent sends current care-of address to correspondent host
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

28. 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.

29. 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)
Mobile IP: Security Issues [4]

30. 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

31. slide by Konidala M. Divyan [3]
Mobile IPv6 Roaming
Network B
Network D
Network A 
Internet
Network C
Home Agent
Mobile Node sends Binding Updates to Home Agent and all Corresp. Nodes, which already received a previous Binding Update from this Mobile Node
Corresp.
Node C
slide by Konidala M. Divyan [3]

32. Summary Last lecture Limitations of QoS in IEEE 802.11
Overview of e
Traffic Categories
EDCF
HCF
Mobile IP
Care-of-address,
MIP Protocol (Discovery, Registration, Tunneling)
Routing
Inefficiencies
MIPv6