Computer Networking - Chapter 1

• This is Chapter 1 from "Computer Networking: A Top-Down Approach", 6th edition, by Jim Kurose and Keith Ross, Addison-Wesley, March 2012.
• Chapter 1 provides an introduction to computer networking concepts.

Chapter 1 Goals

• To get a "feel" and terminology for the field
• To go into more depth and detail later in the course
• The internet will be used as an example.

Chapter 1 Overview

• What's the Internet?
• What's a protocol?
• Network edge, hosts, access net, physical media
• Network core, packet/circuit switching, Internet structure
• Performance: loss, delay, throughput
• Security
• Protocol layers, service models
• History

Chapter 1 Roadmap

• What is the Internet?
• Network edge: end systems, access networks, links
• Network core: packet switching, circuit switching, network structure
• Delay, loss, throughput in networks
• Protocol layers, service models
• Networks under attack: security
• History

What's the Internet: "Nuts and Bolts" View

• Millions of connected computing devices exist, including PCs, servers, laptops, and smartphones
• Hosts are end systems and run network applications
• Communication links include fiber, copper, radio, and satellite
• These links have a transmission rate called bandwidth
• Packet switches forward packets (chunks of data)
• Routers and switches are examples of packet switches
• The Internet is a "network of networks" and consists of interconnected ISPs
• Protocols control sending and receiving messages, like TCP, IP, HTTP, Skype, and 802.11
• Internet standards are defined by RFCs (Request for Comments) and the IETF (Internet Engineering Task Force)

Fun Internet Appliances

• Internet appliances include IP picture frames, Internet refrigerators, web-enabled toasters with weather forecasting, Tweet-a-watt energy monitors, Slingboxes for remote cable TV control, and Internet phones.

What's the Internet: A Service View

• The internet Provides services to applications like the Web, VoIP, email, games and social networks
• Programming interfaces allow sending and receiving app programs to connect to the internet and provide service options analogous to postal service

What's A Protocol?

• Human protocols involve messages and actions taken upon receipt, such as asking for the time
• Network protocols are for machines rather than humans govern communication activity on the Internet
• Protocols define the format and order of messages sent/received among network entities and actions taken on message transmission/receipt

A Closer Look at Network Structure

• The network edge contains Hosts like clients and servers often located in data centers
• Access networks and physical media are wired and wireless communication links
• The network core Consists of interconnected routers that form a network of networks

Access Networks and Physical Media

• The question: is How to connect end systems to the edge router?
• This can be done through Residential access networks, institutional access networks (school, company), and mobile access networks
• Bandwidth (bits per second) of the access network, and if it's shared or dedicated
• Digital Subscriber Line (DSL): Uses existing telephone lines to connect to the central office DSLAM
• Data over DSL phone line goes to the Internet and Voice goes to the telephone network
• Upstream transmission rate is less than 2.5 Mbps, downstream < 24 Mbps (can vary)
• Cable network: Homes share access network to cable headend, unlike DSL
• HFC (hybrid fiber coax): Asymmetric, up to 30Mbps downstream and 2 Mbps upstream
• Home network: can consist of Wireless devices or Wired Ethernet connected to a modem
• Enterprise access networks (Ethernet): typically used in companies, universities etc., connects into Ethernet switch
• Transmission rates range from 10 Mbps to 10 Gbps
• Wireless access networks connect end systems to routers via base stations also know as access points
• In wireless LANs, connections are within buildings at 11-54 Mbps via 802.11b/g (WiFi)
• Wide-area wireless access is provided by cellular operators over 10s of km at 1-10 Mbps via 3G or 4G (LTE)

Host Sending Function

• The Host takes some application message, and breaks it to size L chunks (Packets)
• capacity Transmission rate R which is measured in bits
• packet transmission delay = time needed to transmit L-bit packet into link = L (bits) / R (bits/sec)

Physical Media

• A bit propagates between transmitter/receiver with Physical links lying between them
• Guided media: signals propagate in solid media like copper, fiber, or coax
• Unguided media: signals propagate freely, like radio waves
• two insulated copper wires forms a twisted pair - TP
• Ethernet uses Category 5 with 100 Mbps / 1 Gbps or Category 6 with 10Gbps
• Fiber optic cable carries light pulses to represent bits enabling high speed point to point transmission
• Coaxial cable has two concentric copper conductors, it is bidirectional, and broadband with multiple channels

Radio

• Radio signals travel with electromagnetic spectrum and do not need a physical "wire"
• Bidirectional, environmental effects like reflection and interference affect the signal
• Terrestrial microwave radio can transmit over 45 Mbps channels
• Wireless LANs (e.g., WiFi) can achieve 11-54 Mbps
• Cellular wide-area connections can achieve around 3G speeds
• Satellite links can offer Kbps to 45Mbps channels but suffer from 270 msec end-end delay

Network Core

• The network core contains a mesh of interconnected routers that use packet-switching
• Hosts break application-layer messages into packets that are forwarded across links from source to destination at full link capacity

Packet Switching: Store-and-Forward

• L/R provides the time to transmit L-bit packet into link at R bps
• Store and forward: Entire packet must arrive at a router before it can be transmitted on the next link
• End-end delay = 2L/R assuming zero propagation delay

Packet Switching: Queueing Delay, Loss

• Arriving bits exceeding the links transmission rate for a short period of time will result in Queuing
• If memory or buffer is full Packets will be dropped
• Two key network core functions are Routing and Forwarding

Routing vs Forwarding

• Routing determines the source-destination route taken by packets, using routing algorithms
• Forwarding transfers packets from a router's input to the appropriate router output

Alternate Network Core: Circuit Switching

• End-end resources are allocated and reserved for a "call" between source and destination
• A call gets 2nd circuit in top link and Ist circuit in right link
• Dedicated resources result in guaranteed performance unlike packet switching
• Circuit segments are idle if unused by a call (no sharing) which is common in traditional telephone networks

Circuit Switching: FDM versus TDM

• FDM and TDM are multiplexing techniques where FDM divides the frequency band, and TDM divides time.

Packet Switching vs Circuit Switching

• packet switching Allows more users to use a network
• Given an example of a 1 Mb/s link with users needing 100kb/s when active 10%,
• Circuit-switching can only support 10 users
• Packet switching has a probability of >35 users
• Packet switching, with resource sharing and no call setup complexity, is great for bursty data
• Packet delay and loss are possible when there is excessive congestion
• Protocols, bandwidth guarantees are needed for reliable applications

Internet Structure: Network of Networks

• End systems connect to the Internet through access ISPs (Internet Service Providers)
• These consist of Residential, company, and university ISPs or mobile networks.
• Access ISPs are interconnected.
• To allow any two hosts to communicate, this results in a complex network
• Evolution was driven by economics and national policies for economics
• Instead of connecting each access ISP to every other access ISP (doesn't scale), the internet is structured in layers
• The options are connecting each access ISP to a global transit ISP with customer and provider ISPs having economic agreement
• In practice there are typically competitors each global ISP is viable this is known as the Internet Exchange Point

Tiered Structure

• Tier 1 are well-connected large networks forming the basis of the internet
• A content provider network is also present providing the best experience for content providers

How do Loss and Delay Occur?

• Packets queue in router buffers when the packet arrival rate (temporarily) exceeds output link capacity
• The packets queue while waiting for their turn, resulting in delay
• When buffers are full, packets are dropped, resulting in loss

Four Sources of Packet Delay

• Nodal processing (d_proc): time to check for bit errors and determine output link
• Queueing delay (d_queue): time waiting at the output link for transmission
• Transmission delay (d_trans): L(packet length (bits)) / R(link bandwidth (bps))
• Propagation delay (d_prop): d(length of physical link) / s(propagation speed in medium (~2x10^8 m/sec))
• The total nodal delay is d_nodal = d_proc + d_queue + d_trans + d_prop

Caravan Analogy

• A "caravan analogy" is an example of a ten-car caravan traveling a distance of 100 km at a speed of 100 km/hr.
• the cars "propagate" at a speed of 100 km/hr
• The toll booth takes 12 seconds to service a single vehicle. The packet analog is bit transmission time
• The time to “push” the entire caravan through the toll booth onto the highway equals 120 seconds
• Time for last car to propagate from 1st toll both = 1 hour, or 62 minutes
• Now consider suppose cars “propagate” at 1000km/hr and suppose toll booth now takes 1 min to service a car the number of arriving cars will be higher then the number of cars serviced

Analysing Delay

• In Queueing delay traffic intensity (La/R) becomes a key factor
• La/R ~ 0: If a graph can be formed, the average queueing delay is small
• La/R -> 1: average queueing delay is Large
• La/R > 1: average delay will go to infinite

"Real" Internet Delays and Routes

• The traceroute program provides delay measurement from a source to a router along an end-to-end Internet path
• Traceroute sends three packets to each router on the path towards the destination with the router i will return packets to sender and the sender times interval between transmission and reply.

Understanding Packet Loss

• Queue which has a finite capacity, also known as buffer which is preceding a transmission
• A packet arriving too full will automatically will be dropped also known as loss

Throughput

• The throughput (bits/time unit) is the rate at which bits are transferred between sender and receiver
• Throughput can be instantaneous, meaning the rate at a single point in time, or rate over a longer period
• In a throughput mode with bits or rate the constrain is the bottleneck link
• The bottleneck link is the link on the end-end path that constrains end-end throughput

Internet Structure and Throughput

• throughput: the per-connection end-to-end throughput is determined by the minimum of Rc, Rs, and R/10
• meaning both rates between clients and server together with the bandwidth are the key factors to determine the throughout

Protocol Layers

• Networks are complex and have numerous hosts and routers to consider, Question has to be Asked if There is any hope of organizing it efficiently
• protocol layering - networks are organized with layering
• the "Layers: each layer implements a service for the network
• layering can be performed by both internal interactions or external
• relying on services provided by layer below

Organiziation of Air Travel Analogy

• Air travel is a series of steps, ticket purchase, baggage check, plane routing...
• Layers of airline functionality include: Ticket (purchase), Baggage (check), Gates (load), Runway (takeoff), and Airplane routing
• A Ticket complaint is similar to a TCP error
• Using Airplane routing is similar to network routing

Benefits of Layering

• Explicit structure allows identification and understanding of complex systems
• Modularization simplifies maintenance and updating
• Changes in implementation is transparent to the entire system

Protocol Stack

• Application Protocol Includes: FTP, SMTP, HTTP
• TCP uses: TCP and UDP
• Network includes :IP and routing protocols
• Data Linking is typically Ethernet, 802.11 -WIFI, PPP
• Physical: Cable/ Wireless the raw electrical signal

ISO/OSI Reference Model

• Presentation layer : allows applications to interpret data through Encryption and compression
• Session Layer: synchronization, checkpointing, recovery of data exchange
• Internet stack "missing" :these services, can be implemented in application, only if :Needed

Encapsulation

• Encapsulation describes how packets are wrapped as they flow through protocol layers, from source to destination

Network Security

• The field of network security studies how bad actors can attack computer networks, defending the networks and designing the structures
• Was designed to use with limited security due transparent network in which all users were trust
• Network security concerns are not originally designed with (much) security in mind Internet protocol designers playing “catch-up” the original design was an open network security considerations in all layers that exist, can be bypassed

Type of Attacks

• Malwares can get it through self by Object - Virus and Object passively - worm Object
• Infected host is enrolled, in botnet, spam
• Denial service attacks on resource, bandwidth by overwhelming
• Packet sniffing, the attacker can use broadcast and all packets
• Used to retrieve unhashed passwords
• Address being used to gain access and is being used , to do damage to the network address "src :B"
• spoofing Send a packet with a different address "src :B"

History of the Internet

• 1961-1972: Development of packet-switching principles
• Kleinrock's queueing theory showed effectiveness of packet-switching
• Baran implemented packet-switching in military networks
• The first ARPAnet node went operational in 1969
• ARPAnet public demo, Host-Host Protocol
• First Email Program
• ARPANet has only 15 Nodes
• 1972-1980: the development of the Internetworking, new and proprietary nets

Internet History - 1970s

• 1970: Created ALOHAnet satellite network
• 1974: Cerf and Kahn created architecture for interconnecting networks
• 1976: Creation of Ethernet at Xerox Parc
• late 70's ( switching fixed length packets ATN precursor):proprietary architectures: DECnet, SNA, XNA
• 1979: ARPAnet has 200 nodes
• Cerf and Kahn's internetworking principles: minimalism/autonomy, best effort, stateless routers, decentralized control defined modern Internet architecture
• 1980-1990: the development of new protocols, and a increasing proliferation of networks
• Creation of new national networks: Csnet, BITnet, NSFnet, Minitel, 100,000 hosts

Internet History - 1980s

• 1982: smtp E-Mail
• 1983: DNIS name-t- P- address
• 1985: TEP forocolo
• 1988: TOP for ololengerton control
• 1990,2000's: commercialization, the Web, and new applications

Internet History - 1990s and 2000s

• early 1990's: :web creation [Bush, 1945 Nelson,1960's]
• : ( HTMLHTTP) : Berners- lee ( late 1900's commercialization
• ARPAnet decommissioned
• More killer apps started emerging ( instant messaging, P2P file sharing )
• 1995 The network , security 50 million host , 100 m.i. user(S
• 1994; Mosaic -back bone links currently running in Gbps back-bon
• 2005 to Present: ~ 75 million hosts, increasing Ubiquity of high-speed wireless Access
• Service P( Googleicrosoft) create their own network ""Instantaneous Access to search, email etc
• E-, Commen-commerce, 2- university ECZ, etc. now in the ""d""