1. Accelerating Service Discovery in Ad Hoc Zero Configuration Networking
Se Gi Hong, Suman Srinivasan, and Henning Schulzrinne
Columbia University

2. Contents Wireless mobile ad-hoc networks
Overview of Zeroconf (Zero Configuration Networking)
Zeroconf in Mobile Ad Hoc Networks
Analysis of the mean service loss probability
Overview of joining process in
Accelerating Zeroconf
Implementation and performance

3. wireless mobile ad-hoc networks
No Infrastructure
Allocate IP addresses without a DHCP server
Translate between domain names and IP addresses without a DNS Server
Find service without a directory service
Service discovery
The usage of service discovery has been increasing
e.g., iTunes (Apple’s music file sharing), iChat
Solution
Zeroconf (Zero Configuration Networking)

4. What is Zeroconf? IETF Zero Configuration Networking (Zeroconf) WG
4 requirements
IP interface configuration
Auto-configuration of IPv4 link-local address without a central server (DHCP server) within the /16 subnet
Translation between host name and IP address
Auto-configuration of a host name without a central server (DNS server)
IP multicast address allocation
Range of IP multicast: to
Service discovery
Implementation
Bonjour
Apple’s implementation of zero-configuration networking
iTunes, iChat
Avahi
Open source for Linux

5. What is Zeroconf? Service discovery
Users can discover available service instances of a service types.
Bonjour
Multicast DNS-Based service discovery (mDNS-SD)
PTR, SRV and TXT records
PTR lookup: <Service type>.<Domain>
SRV records: port number, host name
TXT records: additional information

6. What is Zeroconf? Service discovery SRV – 0 0 3689 segihong.local.
TXT – txtvers=1
segihong.local. A
segi._daap._tcp.local. SRV?
segi._daap._tcp.local. TXT?
MDNS standard query:
_daap._tcp.local. PTR?
MDNS standard query response PTR:
segi._daap._tcp.local.
MDNS standard query response PTR:
suman._daap._tcp.local.

7. Zeroconf in Mobile Ad Hoc Networks
High mobile environment – frequently join/leave for a short time
Zeroconf does not include algorithm to detect network topology changes
To discovery services, services should be announced and looked up frequently -> overhead

8. Analysis of the mean service loss probability
Assumption:
Node arrival rate to a local ad-hoc area follows an exponential distribution with rate 
Node residence time follows exponential distribution with rate 
Service announcing and browsing interval follows exponential distribution with rate 
Current number of nodes in an area is n
Service
browsing
of node k
Service
browsing
of node i T
Time X
Node A
arrives
Node A’s next
Service announcing Y
Node A
leaves

9. Analysis of the mean service loss probability
The service loss probability
The mean service loss probability

10. Analysis of the mean service loss probability
Average number of users
Average number of users
(a) Average residence time is 60 minutes
(b) Average residence time is 10 minutes

11. What do we need?
Current Service Discovery of Zeroconf is not enough for high mobile environment since Zeroconf does not have the algorithm for detecting network topology changes
We need a method to recognize new peers (services) in real-time while reducing overhead.
Solution
We can use the existing Beacon frames of

12. What happens when a device joins in a local ad-hoc network?
BSSID (Basic service set identification) is required for communication each other.
TSF (Time Synchronization Function) keeps the timer for all node in same BSS for beacon period.
BSSID and TSF timer value are same for all nodes in the same BSS (Basic Service Set)
Beacon frames contains BSSID and TSF timer value
How to join in the group?
Initially, each device randomly chooses BSSID
Sending probe request and scanning (listening) Beacon frames in all channels
Adopt the information, such as BSSID and the TSF timer, only if the SSID is matched and the value of timestamp in the received beacon frames or probe requests is later than the node’s TSF timer

13. What happens when a device joins in a local ad-hoc network?
Node A joins
BSS2
BSS1
Node A
Node B
Node C
802.11
MAC/PHY
BSSID = 02:02:2D:0D:6B:0E
TSF timer = 1000
BSSID = 00:35:0E:3S:5D:5E
TSF timer = 2000

14. What happens when a device joins in a local ad-hoc network?
Node A joins
802.11
MAC/PHY
Node B
Node C
Node A
BSS2
BSSID = 00:35:0E:3S:5D:5E
TSF timer = 2000

15. Accelerating Zeroconf
Monitoring current BSSID
Changes of BSSID means that it joins in a new local ad-hoc network.
If (old_BSSID != current_BSSID), then re-trigger service discovery.
Standard wireless extensions in Linux
ioctl(): SIOCGIWAP option – get BSSID
Windows WLAN API
WlanGetNetworkBssList()

16. Accelerating Zeroconf
Accelerating service discovery architecture
User A
User B
Zeroconf Software
Zeroconf Software
Application
Layer
IP assign
Naming
Service Discovery
Monitoring
BSSID
IP assign
Naming
Service Discovery
Monitoring
BSSID
Data Link
Layer
Beacon Frames
Beacon Frames

17. Performance Scenarios
Three laptops (A, B, and C)
Laptop A joins a local ad-hoc networks
Laptop A announces a service and B and C browse for the service
Compare to theoretical analysis of delay in Zeroconf with periodic service announcing and browsing
Service announcing and browsing interval: exponential distribution with rate
D is the delay
is the next announcing or browsing time of A, B and C
Mean of the delay is

18. Performance
Delay measurement of the service discovery protocol