Communication Networks (4)

Application architectures

Possible structure of applications:

• Client-server
• Peer-to-peer (P2P)
• Hybrid

Client-server architecture

server

• always-on host
• permanent IP address

client

• may be intermittently connected
• may have dynamic IP addresses

P2P architecture

• no always-on server
• peers request service from other peers, provide service in return to other peers
• self scalability – new peers bring new service capacity, as well as new service demands

Hybrid of client-server and P2P

• Finding address of remote party: centralized server(s)
• Client-client connection is direct (not through server)

Processes communicating

• client process: process that initiates communication
• server process: process that waits to be contacted

Sockets

• process sends/receives messages to/from its socket
• socket analogous to mailbox

Transport service requirements

Application	Data Loss	Throughput	Time Sensitive
file transfer	no loss	elastic	no
e-mail	no loss	elastic	no
Web documents	no loss	elastic	no
real-time audio/video	loss-tolerant	audio: 5kbps-1Mbps	yes, 100’s msec
		video:10kbps-5Mbps	yes, few secs
stored audio/video	loss-tolerant	same as above	yes, 100’s ms
interactive games	loss-tolerant	few kbps up	yes and no
text messaging	no loss	elastic	no