Client-Server Architecture

Client-Server Architecture

• This model is the basis for all network applications.
• It involves a server process and one or more client processes.
• A server manages resources and provides services to clients.
• Web servers manage disk files.
• FTP servers manage and store disk files.
• Email servers manage and update spool files.

Client-Server Programming Model

• The client initiates transactions by sending requests to the server.
• Web browsers request files from Web servers.
• The server receives, interprets and manipulates resources relevant to the request.
• Web servers read disk files based on client requests.
• The server sends a response to the client.
• Web servers sends the requested file to the client.
• The client receives the response and processes it based on the request.
• Web browsers display pages after receiving them from the server.

Client-Server Operations (Four Steps)

• Step 1: Client requests service by sending a request to a server.
• Step 2: The server processes the request and manipulates the requested resource.
• Step 3: The server responds to the client request and waits for the next request.
• Step 4: The client receives the server response and processes it.

Client-Server Model

• Clients and servers are processes, not machines.
• A single host can run many clients and servers concurrently.
• Client-server transactions can run on the same or different hosts.

Network

• Clients and servers often run on separate hosts.
• Network communication utilizes hardware and software resources.

Ethernet

• Ethernet segments consist of wires and a hub.
• Segments are typically contained in small areas, like a room or floor.
• Each wire has a consistent maximum bit bandwidth (e.g., 100 Mb/s or 1 Gb/s).
• One end of the wire attaches to a host adapter, and the other end to a port on the hub.
• A hub copies data from each port to every other.
• Each Ethernet adapter has a unique 48-bit address.

Ethernet LAN

• Each Ethernet adapter has its unique 48-bit address.
• A host can send a chunk of bits (frame) to another host on the same segment.
• Frames contain header bits (source, destination, length) and a data payload.
• All hosts receive the frame, but only the destination host reads it.

Bridged LAN

• Two or more Ethernet segments can be connected with bridges.
• Bridges connect Ethernet segments with varying bandwidths.
• Hosts communicate across different LAN segments via bridges.

Internet

• The Internet connects multiple LANs together.
• Routers connect distinct LANs.
• Hosts communicate through routers when they are on separate LANs.

Client-Server Communication

• Hosts and routers use internet protocols to communicate across incompatible LANs.
• A request from a client on one LAN is routed to the server on another LAN.
• Data is encapsulated (wrapped) within multiple layers of protocols as it travels across the internet.

Client-Server Communication (Steps)

• Client invokes a system call to copy data in virtual address space to kernel buffer.
• The protocol software creates a LAN1 frame, adding an internet header addressed to the destination host.
• LAN1 frame header gets added; the frame is sent to the LAN1 adapter, and the corresponding router.
• The router checks the destination and passes the frame to the LAN2 adapter.
• The LAN2 adapter passes the frame to the destination host (server).
• The server's protocol software extracts the user data and places it in the server's virtual address space,.

Explore the fundamentals of client-server architecture with this quiz. Understand how client and server processes interact, the role of web servers, and the operational steps involved in client-server communications. Test your knowledge of network applications and server functionalities.