Computer Networking Fundamentals
1) The Four Sources of Packet Delay and Key Factors
Total nodal delay = Processing delay + Queueing delay + Transmission delay + Propagation delay.
Processing Delay
Caused by processing in the node (e.g., router) for tasks like checking bit errors and determining the output link. This delay is minimal, usually less than 1 millisecond.
Queueing Delay
Occurs as packets stack up, waiting to be transmitted. The delay depends on node congestion, with higher congestion causing greater delay.
Transmission Delay
Caused by the node’s limitations in pushing packets into the network. Expressed as L/R (packet length / bandwidth). Larger packets and lower bandwidth increase transmission time.
Propagation Delay
Time to cover the physical distance over a transmission medium. Speed is typically near the speed of light, primarily affected by distance. Length / speed = propagation delay.
2) Layers of the IP Stack and Their Functions
Application Layer
Provides application-to-application services by transmitting messages. Protocols include HTTP, SMTP, and FTP.
Transport Layer
Transports application messages between endpoints using segments. Protocols include TCP (offers flow control, congestion control, and reliability) and UDP (does not).
Network Layer
Routes datagrams (containing a destination IP address) from source to destination using the IP protocol. Routing protocols determine packet travel across the network.
Link Layer
Transmits frames between node interfaces. Protocols include Ethernet and WiFi for device communication.
Physical Layer
Moves physical bits “on the wire.” Different protocols exist for each transmission method (e.g., twisted copper, coax, fiber).
3) IP Address, Socket, and Protocol in Process Communication
IP Address
A 32-bit quantity uniquely identifying a host on a network, acting like a mailing address for location.
Protocol
Defines the format, order of messages, and actions taken during transmission and receipt. Protocols govern information flow between hosts, ensuring interoperability.
Socket (API)
The interface between a process and the network. Processes send information through their socket for communication.
4) Primary Email Protocols
SMTP (Simple Mail Transfer Protocol)
Uses TCP for reliable email transfer between client and server. Stores messages on the mail server.
POP3 (Post Office Protocol)
Allows user authorization and message download from the server. Supports commands like delete. Email is not visible in other clients once downloaded.
IMAP (Internet Message Access Protocol)
Similar to POP3 but remembers state across sessions, stores all messages on the server, and uses a file storage structure. Commonly used for multi-device access.
5) Dedicated and Shared Access Networks
Dedicated Access
Provides a direct link between the ISP and the client (e.g., DSL, direct fiber).
Shared Access
Allows multiple connections over the same line (e.g., cable network). Packets travel through each node on the shared link to the central office.
6) FDM and TDM
Frequency Division Multiplexing (FDM)
Divides the link’s bandwidth into different frequencies, each providing a separate connection.
Time Division Multiplexing (TDM)
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7) Throughput vs. Bandwidth
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8) HTTP: Non-Persistent and Persistent
Non-Persistent HTTP
A TCP connection is established, a file request is made, HTTP messages are exchanged, and the connection is closed. This process repeats for each object, increasing overhead.
Persistent HTTP
The TCP connection remains open for multiple requests and transfers, reducing overhead and improving loading time.
9) Web Caching and Its Benefits
A web cache, located near clients, serves requests without involving the origin server. It stores recently requested objects, speeding up response times, reducing link traffic, and improving content delivery, especially for smaller providers without a CDN.