Computer Networking - Chapter 1

• Computer Networking: A Top-Down Approach, 8th edition, by Jim Kurose and Keith Ross, published by Pearson in 2020 is the source material for the notes.

Chapter 1 Goal

• Get a feel for computer networking
• See the "big picture"
• Learn the terminology of computer networking
• More details will come later in the course

Overview/Roadmap

• Understand what the Internet is and the role of protocols
• Learn network edge concepts such as hosts, access networks, and physical media
• Learn network core concepts such as packet/circuit switching and internet structure
• Understand network performance factors such as loss, delay, and throughput
• Learn about protocol layers and service models
• Learn about security considerations
• Know the history of the Internet

The Internet: A "Nuts and Bolts" View

• Billions of connected computing devices make up the Internet
• Hosts are end systems that run network applications at the internet's edge
• Packet switches forward packets (chunks of data) using routers and switches
• Communication links involve fiber, copper, radio, and satellite, and their transmission rate is bandwidth
• Networks are a collection of devices, routers, and links managed by an organization

The Internet: 'Network of Networks'

• Internet is a network of interconnected ISPs
• Protocols are everywhere, controlling the sending and receiving of messages
• Examples of Internet protocols include HTTP for the web, streaming video protocols, Skype, TCP, IP, WiFi, 4G, and Ethernet
• Internet standards include RFCs (Request for Comments) and the work of the IETF (Internet Engineering Task Force)

The Internet: a “Services” View

• Infrastructure provides services to applications.
• Services include web, streaming video, multimedia teleconferencing, email, games, and e-commerce.
• The internet provides connection for interconnected devices and distributed applications.

What is a Protocol?

• A protocol defines the format and order of messages sent and received
• Protocols also determine the actions taken on message transmission and receipt
• Network protocols are for computers (devices) rather than humans
• All communication activity on the Internet is governed by protocols

Chapter 1 Roadmap

• The roadmap explores the Internet, protocols, network edges (hosts, access networks, physical media), and network cores (packet/circuit switching, internet structure)
• It also includes network performance, security, protocol layers, service models, and history

Internet Structure: Network Edge

• Hosts include clients and servers
• Servers are often in data centers
• Access networks and physical media include wired and wireless communication links

Network Core

• The network core has interconnected routers
• It is a network of networks

Access Networks and Physical Media

• Connecting end systems to the edge router involves residential access nets, institutional access networks, and mobile access networks (WiFi, 4G/5G).
• Cable-based access networks use frequency division multiplexing (FDM)
• FDM transmits different channels in different frequency bands

Access Networks: Cable-Based Access

• Hybrid fiber coax (HFC) is asymmetric with up to 40 Mbps – 1.2 Gbps downstream and 30-100 Mbps upstream
• Homes share access networks to cable headends
• The network of cable and fiber attaches homes to the ISP router

Access Networks: Digital Subscriber Line (DSL)

• Digital Subscriber Line (DSL) uses an existing telephone line to the central office DSLAM
• Data over a DSL phone line goes to the Internet, and voice goes to the telephone net
• DSL provides 24-52 Mbps dedicated downstream and 3.5-16 Mbps dedicated upstream transmission rates

Access Networks: Home Networks

• Home networks include wireless and wired devices
• They often combine cable or DSL modems, routers, firewalls, and NAT
• Wired Ethernet provides 1 Gbps, and WiFi wireless access points offer 54 to 450 Mbps

Wireless Access Networks

• Wireless access networks connect end systems to routers via a base station, also known as an "access point"
• Wireless Local Area Networks (WLANs) are typically within or around buildings (~100 ft)
• Wireless LANs use 802.11b/g/n (WiFi): connections at 11, 54, or 450 Mbps transmission rate
• Wide-area cellular access networks are provided by cellular network operators (over tens of kilometers)
• Wide-area cellular access networks typically offer 10's of Mbps: 4G cellular networks (with 5G coming)

Access Networks: Enterprise Networks

• Enterprise networks include companies, universities, etc.
• Enterprise networks mix wired and wireless link technologies
• Ethernet provides wired access at 100 Mbps, 1 Gbps, or 10 Gbps
• WiFi provides wireless access points at 11, 54, or 450 Mbps

Access Networks: Data Center Networks

• Data center networks use high-bandwidth links (10s to 100s Gbps)
• High bandwidth links connect hundreds to thousands of servers together, and to the Internet.

Host: Sends Packets of Data

• The host sending function takes an application message and breaks it into smaller chunks, known as packets, of length L bits
• It transmits the packet into an access network at transmission rate R
• Link transmission rate (capacity or bandwidth) = L (bits) / R (bits/sec)

Links: Physical Media

• A bit propagates between transmitter/receiver pairs
• Physical links lie between the transmitter and receiver
• Guided media contains signals that propagate in solid media like copper, fiber, and coax
• Unguided media contains signals that propagate freely, such as radio waves
• Twisted pair (TP) cable has two insulated copper wires
• Category 5: 100 Mbps, 1 Gbps Ethernet
• Category 6: 10Gbps Ethernet

Links: Physical Media - Coaxial and Fiber Optic Cables

• Coaxial cable has two concentric copper conductors
• Coaxial cable is bidirectional and broadband
• Fiber optic cable carries light pulses, each pulse transmits a bit
• High-speed fiber optic operation: point-to-point transmission (10's-100's Gbps)
• Fiber optic cables have a low error rate and use repeaters spaced far apart

Links: Wireless Radio

• Wireless radio transmits signals carried in various "bands" of the electromagnetic spectrum
• There is no physical "wire"
• Wireless radio is broadcast, "half-duplex" (sender to receiver)
• Wireless radio experiences propagation environment effects such as reflection, obstruction by objects, and interference/noise

Radio Link Types

• Wireless LAN (WiFi) radios transmit 10-100's Mbps over 10's of meters
• Wide-area (e.g., 4G cellular) radios transmit 10's Mbps over ~10 Km
• Bluetooth radios offer cable replacement over short distances with limited rates
• Terrestrial microwave radios offer point-to-point transmission at 45 Mbps channels
• Satellites transmit up to 45 Mbps per channel and incur a 270 msec end-end delay

Chapter 1 Roadmap: Network Core

• The network core involves packet/circuit switching and internet structure

The Network Core: Packet Switching

• The network core is a mesh of interconnected routers
• Packet-switching breaks application-layer messages into packets
• A network forwards packets from one router to the next, across links on a path from source to destination

Two Key Network-Core Functions

• Forwarding: The local action of moving arriving packets from a router's input link to the appropriate router output link
• Routing is a global action that determines the source-destination paths taken by packets, using algorithms

Packet-Switching: Store-and-Forward

• In packet switching, packet transmission delay takes L/R seconds to transmit (push out) an L-bit packet into a link at R bps
• Store and forward requires the entire packet to arrive at the router before it can be transmitted on the next link
• One-hop numerical example: L = 10 Kbits, R = 100 Mbps, one-hop transmission delay = 0.1 msec

Packet-Switching: Queueing

• Queueing occurs when work arrives faster than it can be serviced
• Packet queuing and loss results if the arrival rate (in bps) to a link exceeds transmission rate (bps) of the link for some time
• Packets will queue, waiting to be transmitted on output link
• Packets can be dropped (lost) if memory (buffer) fills up

Alternative to Packet Switching: Circuit Switching

• End-end resources are allocated to, and reserved for, the "call" between source and destination
• Dedicated resources mean that no sharing occurs, and performance is guaranteed
• In circuit switching, a circuit segment is idle if not used

Circuit Switching: FDM and TDM

• Frequency Division Multiplexing (FDM) divides optical, electromagnetic frequencies into (narrow) frequency bands
• each call is allocated its own band, can transmit at max rate of that narrow band
• Time Division Multiplexing (TDM) divides time into periodic slots; each call has a dedicated time slot
• Each call can transmit at maximum rate of (wider) frequency band (only) during its time slot(s).

Internet Structure

• Hosts connect to the Internet via access Internet Service Providers (ISPs)
• Access ISPs must be interconnected so any two hosts (anywhere!) can send packets to each other
• The resulting network of networks is complex due to evolution driven by economics and national policies

Protocol Layers

• Networks are complex due to hosts, routers, links of various media, applications, protocols, hardware, and software
• Layering helps organize network structure

Why Layering?

• Explicit structure allows identification and relationship of system's pieces
• Layering eases maintenance and updating of systems
• Changes in a layer's service is transparent to the rest of the system.

Layered Internet Protocol Stack

• Application Layer: Supports network applications (HTTP, SMTP, DNS)
• Transport Layer: Provides process-process data transfer (TCP, UDP)
• Network Layer: Routes datagrams from source to destination (IP, routing protocols)
• Link Layer: Transfers data between neighboring network elements (Ethernet, WiFi, PPP)
• Physical Layer: Transmits bits "on the wire".

Services, Layering and Encapsulation

• Application exchanges messages to implement some application service using services of transport layer
• Transport-layer protocol transfers M (e.g., reliably) from one process to another, using services of network layer
• Transport-layer protocol encapsulates application-layer message, M, with transport layer-layer header Ht to create a transport-layer segment

Packet Transmission Delay

• Packet Transmission Delay is the time it takes for a host to push all of the packets bits into the link.
• packets cannot be transmitted faster than the link bandwidth
• Packet Transmission Delay = L/R -L- packet length (bits) -R- link transmission rate (bits/sec)
• Real life caravan analogy of a tollbooth

Packet Queueing Delay

• Average Queueing Delay is La/R ~ 0: queueing delay -Small -L - is packet length bits -a - is packet arrival rate -R - is rate of bits intensity
• La/R -> 1. avg queueing delay -Large •La/R 1. more "work" arriving is more than can be serviced

"Real" Internet Delays and Routes

• Traceroute program to measure delay on Internet path to the destination
• Sends 3 packets which results in router, and router replies by time interval between transmission

Packet Loss

• A queue( or buffer) where packets precede the link, this buffer has finite capacity
• a packet that arrives to a buffer that is full, results in a packet drop (packet lost)
• A lost packet may be retransmitted by the previous mode or source end system.

Throughput

• Throughput Is the rate (bits/ time unit) that bits are being sent from the sender to the receiver
• Can be instantaneous rate or average rate over a long period

Throughput: Network Scenario

• Per-connection end-end throughput: min(Rc,Rs,R/10)
• In practice: Rc or Rs is often the bottleneck
• **

Network Security

• The Internet was not originally designed with security in mind
  • Security has been added later
• We now need to consider how bad guys hack computer networks
• how to defend against attacks
• how to set up safe architectures that are immune to attacks

Bad Guys: Packet Interception

• Broadcast media "sniffing" are packet interceptions
• Promiscuous network interfaces read/ record all packets passing by, like passwords
• Wireshark can be used to prevent packet access
• **

Bad Guys: Fake Identity

• There is IP Spoofing, or packet injection with false source addresses
• **

Bad Guys: Denial of Service

• Denial of Service ( DOS): hackers overwhelm a network with bogus traffic and make the resources unavailable
  • They break into hosts around the network
  • Send Packets to the target from the compromised hosts.***

Lines of Defense

• authentication - proving you are who you say are
• Confidentiality - via encryption
• Integrity Checks - digital signatures prevent/ detect tampering -Access Restrictions - password protected VPN's
• Firewalls - specialized "middleboxes" in access and core networks
  • detecting/ reacting to DOS attacks

Internet History: Early Packet-Switching Principles

• 1961: Kleinrock's queueing theory shows the effectiveness of packet-switching
• 1964: Baran's packet-switching in military nets
• 1967: ARPAnet conceived by Advanced Research Projects Agency
• 1969: First ARPAnet node is operational
• 1972: ARPAnet public demo. NCP (Network Control Protocol) is the first host-host protocol; first e-mail
• ARPAnet has 15 nodes

Internet History: Internetworking, New and Proprietary Networks

• 1970: ALOHAnet satellite network in Hawaii
• 1974: Cerf and Kahn's architecture interconnecting networks
• 1976: Ethernet at Xerox PARC
• Late 70s: proprietary architectures such as DECnet, SNA, and XNA
• 1979: ARPAnet has 200 nodes
• Cerf and Kahn's internetworking principles define today's Internet architecture
  • minimalism and autonomy
    • best-effort service model, stateless routing, decentralized control
  • no internal changes were required to interconnect networks

Internet History: New Protocols, a Proliferation of Networks

• 1983: Deployment of TCP/IP
• 1982: SMTP e-mail protocol defined
• 1983: DNS defined for name-to-IP-address translation
• 1985: FTP protocol defined
• 1988: TCP congestion control
• New national networks proliferated CSnet, BITnet, NSFnet, and Minitel. 100,000 hosts connected to networks.

History: Commercialization, the Web, New Applications

• Early 1990s: ARPAnet decommissioned -
• 1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995)
• Early 1990s: Web
  • Hypertext links: 1945, hypertext links were created. -HTML, HTTP: Berners-Lee: made hypertext links to the web
  • 1994: Mosaic- Berners Lee creates Netscape
    • Late1990s
      • commercialization of the Web

Timeline of Internet Technology and Throughput(cont.)

• Late 1990s – 2000s:
  • more killer apps: instant messaging, P2P file sharing, network security to forefront
  • About 50 million hosts with 100 million + users with backbone links running at Gbps

Internet History: Recent Developments

• 2005 to Present): the latest timeline of developments
  • aggressive deployment of broadband home access (10-100's Mbps), software-defined networking (SDN)
  • greater presence of high-speed wireless access: -4G/5G, WiFi, increase in cloud services like Google, service providers create their own networks to connect to end users. -18B devices attached to internet by 2017

ISO/OSI Reference Model

• Presentation - enables applications to understand of data ( ie encryption, and machine specific agreements)
• Session - data control, recovery( ie, restart transmission from Checkpoint.)
• note- some services like security may need to function at app level
• the 7 Layer OSI / ISO Model of layers exists as well. - Application (network process to application) - Layer 7 - Presentation (data representation, encryption) -Layer 6 - Session (interhost connection) - Layer 5 - Transport (reliable data transfer) - Layer 4 - Network (logical addressing and routing) - Layer 3 - Link (physical addessing) - Layer 2 - Physical (bit transmission) - Layer 1

Wireshark

• Software used to precent packet sharing( analyzer)
• captures different network - Application - Transport - Network - Link - Physical