Support for Bluetooth networking
Support for Wi-Fi networking (since 3.1)
Peer discovery
"Reliable but slower" data delivery
"Unreliable but faster" data delivery
"Chat room" client-server model

Connected iPhone Apps:
GameKit vs CFNetwork
presented by Peter Bakhirev      ByteClub.com
GameKit
Peer-to-peer*
Connectivity
Voice Chat
Ability to establish a voice chat
session between two devices
It's interesting, but
out of scope of this talk.
Sorry...
Peer Discovery in GameKit
2 ways:
Built-in peer discovery,
using Peer Picker
Custom peer discovery,
based on event handling
UI already implemented
Turns on Bluetooth(if necessary)
Only 2 peers can connect
Can implement own UI
No control over Bluetooth (user must turn it on manually)
More than 2 peers possible

* both of these are based on NetServices and Bonjour
"Reliable but slower"
"Unreliable but faster"
On top of UDP
Each message is acknowledged
Delivery is guaranteed
Order is guaranteed
Happens behind the scenes
On top of UDP
It's fire-and-forget
Might get lost
Might arrive out of order
Personal
Area
Network
Full support for TCP/IP networking over Bluetooth
Apple's proprietary implementation
Available to CFNetwork, too
*Data transfer is flakey when both Bluetooth and Wi-Fi are ON
For a simple "echo" round-trip message,
latency differs by anywhere between 5% and 20%
"Chat room"
client-server model
Server and clients are called "peers"
Server hosts and advertises a session
Clients discover and join the session
Each peer that joins or leaves is announced to others
A peer can send messages to all or some peers of the session
Server relays messages between peers
Connect to
server
Session join/leave events
are propagated to all peers
Peer 3
Server relays messages
between peers
This is not true peer-to-peer.
If server goes away,
the structure breaks.
1. Overview of networking APIs
2. Overview of GameKit
3. When to use GameKit
4. GameKit code patterns
5. GameKit-based app demo
NetServices
Implementation of the Bonjour protocol
Allows devices and apps to find each other on the network
Uses multicasting, works on local networks
Can also be used online, but requires extra infrastructure
Easy-to-use, high-level framework
CFNetwork
BSD sockets
UDP
Bonjour
Available in the
App Store
Online Multiplayer Gaming Technology
@byteclub
Twitter
Published by Apress
Quartz, OpenGL ES, positional audio, networking for iPhone games

Scheduled for December 2009
Peer 2
Peer 3
Peer 4
Peer 1
(server)
Message
from Peer 2
Peer 4
Peer 1
(server)
"Peer 4
connected"
"Peer 4
connected"
Peer 2
Connected iPhone Apps
GameKit
Good for:
Not good for:
Real-time and turn based games
Data exchange apps (contacts, pictures, etc)
Apps that require interactions between devices located nearby
Interactions with non-iPhone OS devices
Interactions beyond local Wi-Fi network or out of Bluetooth range
Wi-Fi support only in firmware 3.1!
Message to
Peer 4
Socket API: Integrates BSD sockets with run loop, making it easier to write asynchronous network code
Stream API: Makes it easier to exchange data over network 
Support for higher-level protocols such as HTTP and FTP
From the TCP/IP family
Connection-less
Fast
Simple
No guarantees
"User Datagram Protocol"
GameKit's
Peer-to-Peer Connectivity
glossary
class GKSession
Encapsulates the session used by peers to exchange data
sessionID property
Allows you to distinguish between different GameKit apps.
Clients connect only to servers that advertise matching sessionID
Type: NSString. Default value is based on app's Bundle ID.
peerID property
Unique identification of each peer in the session.
Type: NSString, but looks like a long number.
protocol GKSessionDelegate
Allows you to interact with GKSession by suppying a delegate that implements this protocol.
data receive handler
Object supplied by you that handles data received from other peers connected to the session.
class GKPeerPickerController
"Provides a standard UI to allow iPhone to discover and connect to another iPhone"
protocol GKPeerPickerControllerDelegate
Allows you to interact with GKPeerPickerController by supplying a delegate that implements this protocol
1 and 2
3
4
GameKit pattern: Using peer picker
User can dismiss the dialog,
but you still have to deallocate it
This is your chance to
do something great
But don't forget to clean up
after yourself
Optionally, you can customize the session
GameKit pattern: Creating server session,
no peer picker
Session creation
with sensible defaults
Set it in motion
Up to you whether to
accept or deny connection
GameKit pattern: Choosing a server and connecting, 
no peer picker
This will contain "readable" peer names
This will contain "unreadable" peer IDs
Set it in motion
Initial fill of the server list
Create a "client" session
Using "peer state changed" callback, keep track of available servers
Let user pick a server
Try connecting to the chosen server
Using callbacks, figure out whether your connection attempt was successful
peer's display name
Peers can have human-readable names. If you don't specify anything, GameKit uses name of the device by default.
GameKit pattern: Handling disconnects
Common GameKit coding patterns
Using peer picker
Creating server session, no peer picker
Choosing a server and connecting without peer picker
Detecting and handling disconnects
Exchanging data "efficiently"
Exchanging data "flexibly"
GKSession operates on NSData
It's up to you to come up with your own data format
You need to account for multiple types of messages
Conversion to and from NSData should be fairly efficient
It's a hypothetical shooting game with 2 kinds of network messages
Each message is a structure
Turn it into NSData
Fill in the details
Send it
reliably
Fill in the details
Turn it into NSData
Send it
UNreliably
Figure out message type
Handle different messages appropriately
You might want to verify
that message is legitimate
by checking it's size (or some magic value)
before attempting to process it
GameKit pattern: Exchanging data flexibly
You can also use a less rigid data format
Example: Pack your keys and values into a dictionary
Serialize and de-serialize dictionary using "archivers"
Tradeoffs: messages are bigger, more CPU used
GameKit pattern: Exchanging data efficiently
Time for
a demo!
5
Thank you!
Questions?
Peter Bakhirev

Twitter: @byteclub
Email: peter@byteclub.com