Client-Server Architecture Overview

Client-Server Architecture

• This model forms the basis of every network application
• It consists of a server process and one or more client processes
• A server manages resources and provides services to clients
• Web servers manage disk files, retrieving and executing files on clients' behalf
• FTP servers manage disk files, storing and retrieving them for clients
• Email servers manage spool files, reading and updating for clients

Client-Server Operations

• A client-server transaction has 4 steps
• Step 1: A client initiates a transaction by sending a request to a server (e.g., a web browser requesting a file)
• Step 2: The server receives the request, interprets it, and manipulates resources appropriately (e.g., a web server reads a disk file)
• Step 3: The server sends a response to the client and waits for the next request (e.g., a web server sends the file back to the client)
• Step 4: The client receives the response and uses it (e.g., a web browser displays the received page)

Client-Server Model

• Clients and servers are processes, not machines
• A single host can run multiple clients and servers concurrently
• Client-server interactions can occur on the same or different hosts
• The mapping of clients and servers to hosts doesn't affect the client-server model

Network Communication

• Clients and servers typically run on separate hosts
• They communicate using hardware and software resources in a computer network
• Ethernet segments are made up of wires (usually twisted pairs) and a hub
• Each Ethernet wire has the same bandwidth (e.g., 100 Mb/s or 1 Gb/s)
• One end of a wire connects to a host's adapter, the other to a hub port
• Hubs copy data received on any port to all other ports
• Each Ethernet adapter has a unique 48-bit address

Ethernet LAN

• Ethernet adapters have globally unique 48-bit addresses
• A host can send a "frame" (a chunk of bits) to any other host on the same segment
• Frames include header bits for source, destination, and length, followed by data bits
• Every host adapter sees the frame, but only the destination host reads it

Bridged LAN

• Bridges connect Ethernet segments, allowing communication between them
• Bridges have higher bandwidth (e.g., 1 Gb/s) compared to Ethernet wires
• Frames can pass between different segments through bridges

Internet

• The Internet is a network of networks
• Routers connect LANs to facilitate communication across various LANs

Client-Server Communication (Detailed)

• Clients and routers use Internet protocols to transfer data across heterogeneous LANs
• Step 1: Client invokes a system call, data moved to kernel buffer
• Step 2: Protocol software creates a LAN frame with an internet header for destination and a LAN frame header for the router
• Step 3: LAN adapter copies frame to the network
• Step 4: Router adapter receives frame, passes to protocol software
• Step 5: Router fetches destination address, uses routing table to choose next LAN (LAN2 in example), removes old header, prepends new
• Step 6: Router's LAN2 adapter copies the frame to the network
• Step 7: Host B's adapter receives frame, passes to protocol software
• Step 8: Protocol software strips headers, resulting data moved to server's virtual address space after the server invokes the system call to read the data

This quiz explores the fundamentals of client-server architecture, which forms the backbone of network applications. It delves into the roles of servers and clients, the types of servers like web and FTP, and the four steps in a client-server transaction. Understanding these concepts is crucial for grasping how networked systems function effectively.