Advanced Data Communications - Lecture 1 Notes

Advanced Data Communications - Lecture 1

Course Overview

Course Code: MCS 1304
Instructor: Dr. Dinuni Fernando
Based on: Computer Networking: A Top-Down Approach Featuring the Internet, 8th edition

Learning Objectives

LO1: Understand different types of protocols in wired and wireless networks.
LO2: Appreciate trends in large-scale networks such as virtualization and software-defined capability.
LO3: Conceptualize and design networks of sufficient complexity.
LO4: Model and analyze network performance through simulation.

Covered Topics

Computer Networks and the Internet
Link Layer and Protocols
Routing
Data Center Design and Virtualization

Course Structure

Assignments: 40%
Final Paper: 60%
In-Class Activities: Assignments, Pop-up Quizzes, Practical Labs

Chapter 1: Introduction

Goal: Get a feel for the big picture and introduction to terminology.
Overview/Roadmap:
- What is the Internet?
- What is a protocol?
- Network edge: hosts, access network, physical media
- Network core: packet/circuit switching, internet structure
- Performance: loss, delay, throughput
- Security
- Protocol layers, service models

What is the Internet?

A "nuts and bolts" view:
- Billions of connected computing devices (hosts/end systems) running network apps at the Internet’s "edge". Includes mobile networks, home networks, enterprise networks, national or global ISPs, local or regional ISPs, data center networks, content provider networks
- Packet switches (routers, switches) forward packets (chunks of data).
- Communication links (fiber, copper, radio, satellite) with transmission rate (bandwidth).
Networks: Collection of devices, routers, links managed by an organization.
"Network of networks": Interconnected ISPs.
Protocols: Control sending and receiving of messages (e.g., HTTP, streaming video, Skype, TCP, IP, WiFi, 4G, Ethernet).
Internet standards:
- IETF (Internet Engineering Task Force).
- RFC (Request for Comments).
Protocols examples: Ethernet, HTTP, Skype, IP, WiFi, 4G, TCP, Streaming video

Internet-Connected Devices

IP picture frame
Web-enabled toaster + weather forecaster
Internet phones
Internet refrigerator
Slingbox: remote control cable TV
Tweet-a-watt: monitor energy use
Sensorized bed mattress
Security Camera
Amazon Echo
Pacemaker & Monitor
Fitbit
AR devices

The Internet: A "Service" View

Infrastructure providing services to applications:
- Web, streaming video, multimedia teleconferencing, email, games, e-commerce, social media, interconnected appliances.
Provides a programming interface to distributed applications:
- "Hooks" allowing sending/receiving apps to connect to and use Internet transport service.
- Provides service options analogous to postal service.

What's a Protocol?

Human protocols:
- Specific messages sent.
- Specific actions taken when a message is received or other events occur.
- Examples: "What's the time?", "I have a question", introductions.
Network protocols:
- Computers (devices) rather than humans.
- All communication activity on the Internet is governed by protocols.
Protocols define:
- Format and order of messages sent and received among network entities.
- Actions taken on message transmission and receipt.
Examples of protocols
- Human Protocol: HI - HI; Got the time? - 2:00 Time
- Computer Protocol: TCP connection request - TCP connection response; GET http://gaia.cs.umass.edu/kurose_ross -

Internet Structure - A Closer Look

Network Edge:
- Interface that connects internal to external network.
- First/last points of communication.
- Hosts: clients and servers.
- Servers often in data centers.
Access Networks, Physical Media:
- Wired, wireless communication links.
Network Core:
- Interconnected routers.
- Network of networks.

Access Networks and Physical Media

How to connect end systems to edge router?
- Residential access nets.
- Institutional access networks (school, company).
- Mobile access networks (WiFi, 4G/5G).
What to look for:
- Transmission rate (bits per second) of access network.
- Shared or dedicated access among users.

Access Networks: Cable-Based Access

*Different types of cable-based access networks:
* DSL (Digital Subscriber Line) – Uses telephone lines for internet access.
* Coaxial Cable (Cable Internet) – Uses TV cable lines for broadband internet.
* Fiber-Optic Networks – Uses light signals for ultra-fast data transfer.
* Ethernet (LAN Access) – Uses twisted-pair cables (Cat5, Cat6) for high-speed connections.

HFC (Hybrid Fiber Coax):
- Asymmetric: up to 40 Mbps – 1.2 Gbps downstream, 30-100 Mbps upstream.
- Network of cable, fiber attaches homes to ISP router.
- Homes share access network to cable headend.
  *Important terminology
- Frequency division multiplexing (FDM): different channels transmitted in different frequency bands
  *Diagram depicting channels for VIDEO, DATA and CONTROL.

Access Networks: Digital Subscriber Line (DSL)

Use existing telephone line to central office DSLAM.
Data over DSL phone line goes to Internet.
Voice over DSL phone line goes to telephone net.
24-52 Mbps dedicated downstream.
3.5-16 Mbps dedicated upstream.

Access Networks: Home Networks

Cable or DSL modem.
Router, firewall, NAT.
Wired Ethernet (1 Gbps).
WiFi wireless access point (54, 450 Mbps).
Wireless devices often combined in a single box.

Wireless Access Networks

Shared wireless access network connects end system to router via base station (access point).
Wireless LANs (WLANs):
- Typically within or around a building (~100 ft).
- 802.11b/g/n (WiFi): 11, 54, 450 Mbps.
Wide-area cellular access networks:
- Provided by mobile, cellular network operator (10’s km).
- 10’s Mbps.
- 4G cellular networks (5G coming).

Access Networks: Enterprise Networks

Companies, universities, etc.
Mix of wired, wireless link technologies connecting a mix of switches and routers.
Ethernet: wired access at 100Mbps, 1Gbps, 10Gbps.
WiFi: wireless access points at 11, 54, 450 Mbps.

Host Sending Packets of Data

Host sending function:
- Takes application message.
- Breaks it into smaller chunks (packets) of length L bits.
- Transmits packet into access network at transmission rate R.
  - R: link transmission rate, aka link capacity, aka link bandwidth.
Packet transmission delay: Time needed to transmit L-bit packet into link.
- \frac{L (bits)}{R (bits/sec)}

Links: Physical Media

Bit: propagates between transmitter/receiver pairs.
Physical link: what lies between transmitter & receiver.
Guided media: Signals propagate in solid media (copper, fiber, coax).
Unguided media: Signals propagate freely (e.g., radio).

Physical Media Types

Twisted Pair (TP):
- Two insulated copper wires.
- Category 5: 100 Mbps, 1 Gbps Ethernet.
- Category 6: 10Gbps Ethernet.
Coaxial Cable:
- Two concentric copper conductors.
- Bidirectional.
- Broadband: Multiple frequency channels on cable, 100’s Mbps per channel.
Fiber Optic Cable:
- Glass fiber carrying light pulses (each pulse is a bit).
- High-speed operation: 10’s-100’s Gbps.
- Low error rate: Repeaters spaced far apart, immune to electromagnetic noise.
Wireless Radio:
- Signal carried in the electromagnetic spectrum.
- No physical “wire”.
- Broadcast and “half-duplex” (sender to receiver).
- Propagation environment effects: reflection, obstruction by objects, interference.
  - Terrestrial microwave: up to 45 Mbps channels.
  - Wireless LAN (WiFi): Up to 100’s Mbps.
  - Wide-area (e.g., cellular): 4G cellular (~10’s Mbps).
  - Satellite: up to 45 Mbps per channel, 270 msec end-end delay, geosynchronous versus low-earth-orbit.

The Network Core

Mesh of interconnected routers
Packet-switching: hosts break application-layer messages into packets
- Forward packets from one router to the next, across links on path from source to destination
- Each packet transmitted at full link capacity

Packet-Switching: Store-and-Forward

Transmission delay: Takes L/R seconds to transmit (push out) L-bit packet into link at R bps
Store and forward: Entire packet must arrive at the router before it can be transmitted on the next link
End-end delay: 2L/R (assuming zero propagation delay)
Numerical Example
- L = 10 Kbits
- R = 100 Mbps
- One-hop transmission delay = 0.1 msec

Packet-Switching: Queueing Delay, Loss

Packet queuing and loss: If arrival rate (in bps) to link exceeds transmission rate (bps) of link for a period of time:
- Packets will queue, waiting to be transmitted on the output link
- Packets can be dropped (lost) if memory (buffer) in router fills up

Two Key Network-Core Functions

Forwarding:
- Local action: move arriving packets from router’s input link to the appropriate router output link
Routing:
- Global action: determine source-destination paths taken by packets

Alternative to Packet Switching: Circuit Switching

End-end resources allocated to, reserved for “call” between source and destination
- In diagram, each link has four circuits.
- Call gets 2nd circuit in the top link and 1st circuit in the right link.
Dedicated resources: no sharing
- Circuit-like (guaranteed) performance
Circuit segment idle if not used by call (no sharing)
Commonly used in traditional telephone networks

Circuit Switching: FDM and TDM

Frequency Division Multiplexing (FDM):
- Optical, electromagnetic frequencies divided into (narrow) frequency bands
- Each call allocated its own band, can transmit at the max rate of that narrow band
Time Division Multiplexing (TDM):
- Time divided into slots
- Each call allocated periodic slot(s), can transmit at a maximum rate of (wider) frequency band, but only during its time slot(s)

Packet Switching Versus Circuit Switching

Great for “bursty” data – sometimes has data to send, but at other times not
- Resource sharing
- Simpler, no call setup
Excessive congestion possible: packet delay and loss due to buffer overflow
- Protocols needed for reliable data transfer, congestion control
Q: How to provide circuit-like behavior?
- Bandwidth guarantees traditionally used for audio/video applications
Is packet switching a “slam dunk winner”?