Introduction to Networking Chapter 1

Introduction to Networking: Key Concepts

• Free access to PowerPoint slides provided for educational purposes; attribution requested when used.
• Slides cover foundational topics in networking, including the structure and protocols of the Internet.

Understanding the Internet

• The Internet comprises millions of connected devices, including PCs, servers, laptops, smartphones, and more.
• Key components include end systems (hosts), communication links (fiber, copper, radio, satellite), and packets for data transfer.

Internet Structure and Functionality

• Defined as a "network of networks" created by interconnected Internet Service Providers (ISPs).
• Protocols (e.g., TCP, IP, HTTP) govern the sending and receiving of messages across the network.
• Internet standards established through Requests for Comments (RFC) by the Internet Engineering Task Force (IETF).

Network Architecture

• Network edge involves end systems such as clients and servers, often located in data centers.
• Access networks use varied physical media (wired and wireless) to connect end systems to the network core.
• The core consists of interconnected routers that manage data traffic.

Access Networks

• Residential, institutional, and mobile access networks exist to connect users to the Internet.
• Transmission rates and bandwidth can vary significantly among different access methods.

Types of Access Networks

• DSL (Digital Subscriber Line): Utilizes existing telephone lines; offers upstream speeds <2.5 Mbps and downstream speeds <24 Mbps.
• Cable Network: Hybrid fiber coaxial (HFC) cable provides asymmetric speeds with up to 30 Mbps downstream.
• Wireless Networks: Include wireless LANs (WiFi) with speeds of 11-54 Mbps and cellular networks (3G, 4G).

Packet Transmission

• End systems break application messages into packets for transmission.
• Packet transmission delays depend on link transmission rates and sizes, defined as transmission and propagation delay.

Types of Delay in Networks

• Four primary sources of packet delay:
  • Nodal Processing Delay: Time for routers to check errors and determine output links.
  • Queueing Delay: Time packets spend waiting in queues when network congestion occurs.
  • Transmission Delay: Time required to push packet bits onto the outgoing link.
  • Propagation Delay: Time taken for a signal to traverse the physical link.

Impact of Congestion and Delay

• Packet loss can occur when incoming packets exceed the router's capacity to handle them, resulting in dropped packets.
• Average queueing delay is affected by traffic intensity, calculated as La/R (arrival rate over transmission rate).

Real-World Internet Performance

• Tools like traceroute measure actual Internet delays and paths, helping assess performance.
• Real Internet conditions can significantly influence both delay and data loss during transmission.

Comparison Analogies

• The caravan analogy illustrates how packets move through the network, emphasizing the importance of processing and propagation times.
• Variations in transmission and propagation speeds affect overall performance, exemplifying the intricate balancing act of networking delays.### Internet Delay Measurements
• Traceroute from gaia.cs.umass.edu to www.eurecom.fr provides metrics for the journey through the network.
• Nodes and their respective delays (in milliseconds):
  • cs-gw (128.119.240.254): 1 ms, 1 ms, 2 ms
  • border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145): Consistent delays around 1-2 ms
  • Various nodes display increasing delays, peaking at 135 ms at eurecom-valbonne.r3t2.ft.net.

Packet Loss

• Packet loss occurs when a packet arrives at a full queue (buffer) and is dropped.
• Lost packets may be retransmitted by:
  • Previous node in the route
  • Source end system
  • Not retransmitted at all

Understanding Throughput

• Throughput: The rate of bits transferred over time (bits/time unit).
• Two types of throughput:
  • Instantaneous: Rate at a specific moment.
  • Average: Rate over an extended period.
• Key elements affecting throughput include:
  • Rs: Sending rate of the server.
  • Rc: Capacity of the link/pipeline.

Average End-to-End Throughput

• When Rs (sending rate) is less than Rc (link capacity), the average end-to-end throughput is determined by Rs.
• When Rs is greater than Rc, average throughput is limited by Rc, highlighting potential bottlenecks.

Bottleneck Links in Internet Context

• The bottleneck link is the constraining factor on end-to-end throughput across the network path.
• Per-connection end-to-end throughput is often calculated as:
  • min(Rc, Rs, R/10), where R represents the capacity of the backbone link.
• In practice, the bottleneck typically arises from either Rc or Rs, which limits data transfer rates.
• For 10 connections sharing a backbone link, throughputs are distributed based on overall capacity.

Network Edge

• End systems include devices like PCs, laptops, smartphones, and servers that run network applications.
• Access networks connect end systems to the Internet, utilizing wired (fiber, copper) and wireless (radio, satellite) communication links.
• Packets, the fundamental units of data, are forwarded by devices like routers and switches.

Internet Structure

• The Internet is regarded as a "network of networks," interlinking various Internet Service Providers (ISPs).
• Communication adheres to protocols, governing the sending and receiving of messages, such as TCP, IP, and HTTP.
• Internet standards are developed and maintained by organizations like the Internet Engineering Task Force (IETF) and through Requests for Comments (RFC).

Protocols

• Protocols are essential for communication, outlining how messages are formatted, sent, and acted upon by network entities.
• Examples of human protocols can include greetings, while network protocols manage all communication activities over the Internet.

Network Edge Infrastructure

• Hosts in the network edge include both clients and servers, often located in data centers.
• Access networks are classified into residential, institutional (like schools and companies), and mobile networks.

Access Network Characteristics

• Bandwidth varies by access type: wired networks can offer higher bandwidth (up to 45 Mbps), while mobile networks typically provide lower bandwidth (e.g., 3G ~ few Mbps).
• Additional influences on network performance include propagation environment, signal interference, and physical obstacles.

Delay and Loss in Networks

• Packet delay occurs when the arrival rate of packets exceeds the output capacity of a link, leading to queuing.
• Types of delays include:
  • Transmission Delay (dtrans): Time taken to push all packet bits onto the wire.
  • Propagation Delay (dprop): Time for a signal to traverse the physical link.
  • Processing Delay (dproc): Time spent checking for errors and deciding on routing.
  • Queueing Delay (dqueue): Time spent waiting in line to be transmitted.

Queueing and Packet Loss

• Queueing delay intensifies with the level of router congestion; limits exist on the size of the buffer (queue), leading to packet loss when no space is available.
• Packet loss can result in the need for retransmission by the source or previous nodes in the network.

Throughput

• Throughput refers to the rate at which data is successfully transferred from sender to receiver, typically measured in bits per time unit.
• Average throughput is influenced by the capacity of the link along with the sender's transmission rate, factoring into the overall network performance.

Traceroute Utility

• Traceroute is a diagnostic tool that measures delays along the path to a destination, providing a list of routers and their respective response times.

Real Internet Attributes

• Environmental factors affect both delay and loss, making it crucial for networking applications to account for variations in real-world conditions and performance metrics.