Computer Networks and Internet Protocols Flashcards

Objectives of the Course

• Understand how two computers in the Internet talk to each other.
• Basic functionalities of the computer networks.
• Learn how to program the network.
• Future of the computer network – Do we need any further changes in the design?
• Functionalities
• Protocols
• Network Architecture

Network Architecture

• A way to visualize how two remote computers talk to each other.
• Network Protocol Stack.
• Requirement: Convert digital data to analog signal and vice versa using Physical Layer.
• Requirement: Ensure proper scheduling in media access using Data Link Layer, L2 Switch.
• Requirement: Find out a suitable path to forward data using Network Layer, L3 Switch or Routers.
• Requirement: End to end traffic control in the network using Transport Layer.
• Network Protocol Stack includes Application, Transport, Network, Data Link, and Physical Layers.

Data Transfer Between Two Remote Machines

• Source and Destination communicate through Application, Transport, Network, Data Link and Physical Layers.

Protocols at Different Layers

• Application: HTTP, FTP, SMTP
• Transport: TCP, UDP, RTP
• Network: IPv4, IPv6, MPLS
• Data Link: Ethernet, WiFi, Bluetooth, UMTS, LTE
• Physical

Network Management and Control – Cross Layer Protocols

• Physical: Ethernet, WiFi, Bluetooth, UMTS, LTE
• Data Link: ARP, DHCP
• Network: IPv4, IPv6, MPLS
• Transport: TCP, UDP, RTP
• Application: HTTP, FTP, SMTP, DNS, SNMP

Two Ways to Learn Computer Networks

• Application, Transport, Network, Data Link, Physical Layers displayed in a diagram.

History of Computer Networks

• Internet History resources: https://www.internetsociety.org/internet/history-internet

History of Internet - Year and Event

• 1836: Telegraph by Cooke and Wheatstone revolutionized human communications. Morse Code (series of dots/dashes) is similar to binary (0/1).
• 1858-1866: Transatlantic cable allowed direct instantaneous communication across the Atlantic. Cables connect all continents and are still a main telecommunications hub.
• 1876: Telephone by Alexander Graham Bell. Telephone exchanges provide the backbone of Internet connections today. Modems provide Digital to Audio conversions for computers to connect over the telephone network.
• 1957: US forms ARPA (Advanced Research Projects Agency) within the DoD to build US skills in computer technology. USSR launches Sputnik.
• 1962: ARPA's contracts from the private sector to universities laid the foundations for what would become the ARPANET.
• 1962-1968: Packet-switching (PS) networks developed. The Internet relies on packets to transfer data, which is split into tiny packets that may take different routes to a destination.
• 1969: ARPANET commissioned by DoD for research into networking. Four nodes: UCLA, SRI, UCSB, and Univ of Utah.
• 1971: Ray Tomlinson invents Email program to send messages across a distributed network. 15 nodes (23 hosts) on ARPANET.
• 1973: Global Networking becomes a reality with First international connections to the ARPANET: University College of London (England) and Royal Radar Establishment (Norway).
• 1974: Packets become mode of transfer - Transmission Control Program (TCP) specified. Packet network Intercommunication is the basis of Internet Communication. Telenet, a commercial version of ARPANET, opened as the first public packet data service.
• 1977: E-mail becomes a reality with 100+ hosts.
• 1979: News Groups formed and USENET established using UUCP - A collection of discussions groups, news groups.
• 1982: establishes the Transmission Control Protocol (TCP) and Internet Protocol (IP), as the protocol suite, commonly known as TCP/IP, for ARPANET. TCP/IP defines future network communication.
• 1983: Name server developed.
• 1984: Domain Name Server (DNS) introduced. 1,000+ Hosts. NSFNET created, with NSF establishing 5 super-computing centers to provide high-computing power for all - This allows an explosion of connections, especially from universities.
• 1987: Commercialization of Internet. UUNET is founded with Usenix funds to provide commercial UUCP and Usenet access, with ~30,000 Hosts.
• 1989: First relays between a commercial electronic mail carrier and the Internet with 100,000+ Hosts. WWW concept by Tim Berners-Lee.
• 1990: First search-engine (Archie) with 300,000 Hosts and 1,000 News groups. ARPANET ceases to exist. First browser/editor program.
• 1991: User Friendly Interface to Internet established using Gopher released by Paul Lindner and Mark P. McCahill from the U of Minnesota - Text based, menu-driven interface to access internet resources.
• 1992: Multimedia changes the face of the Internet, with 1+ Million Hosts and 4,000 News groups. The term "Surfing the Internet" is coined by Jean Armour Polly.
• 1993: The WWW Revolution truly begins with 2 Million Hosts and 600 WWW sites. The Mosaic Web browser is released on the Net.
• Web exploded…
  • 1994 – 3,2 million hosts and 3,000 websites
  • 1995 – 6,4 million hosts and 25,000 websites
  • 1997 – 19,5 million hosts and 1,2 million websites
  • January 2001 – 110 million hosts and 30 million websites
  • Expansion continues….
• Some Facts
  • 1994 – Hotmail starts web based email
  • 1994 – World Wide Web Consortium (W3C) was founded
  • 1995 – JAVA source code was released
  • 1996 – Mirabilis (Israel) starts ICQ
  • 1998 – Google is founded

Books/Resources to Follow

• Computer Networking: A Top-Down Approach by Kurose and Ross (Fifth Edition).
• Computer Networks by Andrew S. Tanenbaum (FOURTH EDITION).
• Computer Networks: A Systems Approach by Larry L. Peterson & Bruce S. Davie (SECOND EDITION).
• TCP/IP Tutorial and Technical Overview, IBM Redbooks (http://www.redbooks.ibm.com/abstracts/gg243376.html)
• The TCP/IP Guide (http://www.tcpipguide.com/)

Internet Resources

• The Internet Engineering Task Force (IETF) - The goal of the IETF is to make the Internet work better. (https://www.ietf.org/)
• RFC Editor - RFCs contain technical and organizational notes about the Internet.

Protocol Stacks – OSI and TCP/IP

• Protocol: A controlled sequence of messages exchanged between systems to accomplish a task. Protocol specifications define this sequence and message format.

• OSI Model Layers:

  • Physical: Transmission of binary data.
  • Data Link: Transfer of information units, framing, error checking.
  • Network: Delivery of packets; routing.
  • Transport: End-to-end reliable/unreliable delivery.
  • Session: Establishment and maintenance of sessions.
  • Presentation: Data formatting and encryption.
  • Application: Network applications (file transfer, terminal emulation).

• Transmission Control Protocol/Internet Protocol (TCP/IP): A dominant standard for inter-networking that specifies how information packets are exchanged between computers over one or more networks.

• Comparison of OSI and TCP/IP models:

  • OSI: Application, Presentation, Session, Transport, Network, Data link, Physical
  • TCP/IP: Application, Transport, Network, Data link, Physical

• TCP/IP

  • Telenet, Trace
  • Ping
  • FTP
  • SMTP
  • SNMP
  • Rlogin
  • route
  • DNS
  • TFTP
  • BOOTP
  • RIP
  • OSPF
  • TCP
  • UDP
  • ICMP
  • IP
  • LLC
  • HDLC
  • PPP
  • Ethernet 802.3 X.25 Token Ring Frame Relay ATM SMDS etc.
  • Fiber Optics
  • UTP
  • Coax
  • Microwave
  • Satellite
  • STP

• OSI & TCP/IP Protocol-Stacks and Protocols

  • OSI: SMTP, FTP, HTTP, POP3, IMAP4, SNMP (Application), Presentation, Session, TCP & UDP (Transport), IP (Networking), Ethernet (Datalink), Physical
  • TCP/IP: Application, Transport, Networking, Datalink And Physical, Protocols

• TCP/IP - Packet Encapsulation

  • Application - Telnet, FTP, TFTP, HTTP,BOOTP, DHCP, SNMP - Socket API - User Data (Messages or Streams)

  • Transport - TCP, UDP - Transport Protocol Messages

  • Network - IP, ARP, ICMP - IP Datagrams

  • Data Link - PPP, SLIP, Ethernet - Network-Specific Frames

  • Physical - Physical Devices

  • Ethernet \ Frame = Ethernet \ Header(14) + IP \ Header(20) + TCP \ Header(20) + \ Application \ Data(46 \ to \ 1500 \ bytes) + Ethernet \ Trailer(4)

Local Area Network (LAN) – Typical Components

• Clients – workstations
• Servers – usually have more computing resources
• Network devices
  • Repeaters
  • Hubs
  • Transceivers
  • NICs
  • Bridges
  • Switches
  • Routers

Wide Area Networks

• A WAN is a data communications network covering a large geographic area.
• Unlike LANs, a WAN connection is generally rented from a service provider.
• WANs connect various sites at different geographic locations so that information can be exchanged.

Evolution of LAN Devices

• NICs, Repeaters, & Hubs
• Bridges
• Switches
• Routers

NIC Specifics

• NICs provide hosts with access to media by using a MAC address.
• MAC stands for Media Access Control
• NICs operate at Layer 2 !!

NICs, Repeaters, & Hubs

• To connect two computers, you must Install a NIC card in each computer, and attach computers using a crossover cable.
• Repeaters can be used to increase the distance. Repeaters amplify and retime signals. approximately 100 \ meters ([
  300 \ feet).
• Hub: A multi-port repeater.

A Dilemma!

• As businesses expanded their networks, they began to cascade hubs.

What’s The Problem?

1. Hubs share bandwidth between all attached devices.
2. Hubs are stupid, Layer 1 devices. They cannot filter traffic.
3. Most LANs use a “broadcast topology,” so every device sees every packet sent down the media.

Broadcast Topology

• All hubs forward all traffic to all devices.
• If Host 1 wants ping Host 2, all hosts see the ping. Only Host 2 will respond.

What’s The Solution?

• We need a smarter hub!
• What’s a “smarter hub” called?
• A Bridge!
• Bridges filter network traffic based on MAC addresses.

Bridge

• To lessen the amount of LAN traffic, businesses began to uses bridges to filter frames based on MAC addresses.
• Now, if Host 1 pings Host 2, only the hosts on that LAN segment see the ping. The bridges stop the ping.

Switch

• A switch (also know as a multi-port bridge), can effectively replace these four bridges.
• Another benefit of a switch is that each LAN segment gets dedicated bandwidth.
• Each LAN segment gets bandwidth of 10 \ Mbps .

Router

• Routers filter traffic based on IP addresses. The IP address tells the router which LAN segment the ping belongs to.
• Host 1 send ping to host 16.

Devices Function at Layers

• 7 Application (Host)
• 6 Presentation
• 5 Session
• 4 Transport
• 3 Network (Router)
• 2 Data Link (NIC Card)
• 1 Physical
• Each device not only works at its layer, but all layers below it.
• For example, a router is a layer 3 device but also uses MAC addresses (layer 2) and repeats the signal (layer 1).

Hierarchical Design Model

• A layered model for network design.
• Consists of 3 tiers
  • Access layer - for end user connectivity
  • Distribution layer - for policy based routing and access control
  • Core layer- for switching packets as fast as possible across the internetwork.

Few points to note

• Routers, by default, break up broadcast domain
• Broadcast domain – Set of all devices on a network segment that hear all the broadcasts sent on that segment
• Breaking-up of network broadcast is important – because when a host or server sends a network broadcast, every device on the network “must” read and process that broadcast.
• When a router’s interface receives this broadcast – it discards the broadcast without forwarding it on to other network
• Router also breaks up “collision domain” as well !
• Switches aren’t used to create internetworks, they’re employed to add functionality to an internetwork LAN
• Switches only “switches” frames from one port to other within a “switched network”
• Switches break-up collision domains.
• Collision domain – Ethernet term! – used to describe a network scenario in which one particular device sends a packet on a network segment, forcing other devices on the same segment to pay attention to it. At the same time, a different device tries to transmit, leading to collision, then both the devices must re-transmit – a situation found in a Hub
• Each and every port on a switch represent its own collision domain (Hub represents only one collision domain and only one broadcast domain)

Circuit Switching and Packet Switching

• Switched Network
  • Communication between distant stations/ end-devices is typically done over a network of switching nodes.
  • Switching nodes do not concern with content of data. The purpose is to provide a switching facility that will communicate/transmit the data from source to destination via intermediate node(s).
  • A collection of nodes and connections forms a communications network.
  • In a switched communications network, data entering the network from a source station are routed to the destination by being switched from node to node.
• Switching Technologies
  • Switching nodes may connect to other nodes, or to some stations.
  • Network is usually partially connected – However, some redundant connections are desirable for reliability
  • Two different switching technologies: Circuit switching and Packet switching

Circuit Switching

• Dedicated communication path between two stations.
• Three phases: Establish, Transfer, Disconnect.
• Must have switching capacity and channel capacity to establish connection.
• Must have intelligence to work out routing.

Packet Switching

• A station breaks long message into packets.
• Packets are sent out to the network sequentially, one at a time
• The stream of packets are routed through the network and are delivered to the intended destination?
• Two approaches: Datagram approach & Virtual circuit approach

Circuit Switching

• Approaches

  • Space-Division Switch
  • Time-Division Switch
    • TDM Bus
  • Combinations

• Long-distance office

• End Office

• Subscriber Loop

• Connecting Trunk

• Intercity Trunk

• Digital PBX

• Circuit Switching - Space Division Switch

  • Crosspoint

  • To control station

  • Multi-stage Space Division Switch

• Circuit Switching - Time Division Multiplexing

  • a. No switching
  • b. Switching

• Circuit Switching – Time Slot Interchange

Circuit Switching - Properties/Issues

• Once connected, transfer is transparent
• Developed for voice traffic (phone).
• Inefficient
  • Channel capacity dedicated for duration of connection
  • If no data, capacity wasted
• Set up (connection) takes time
• Data rate is fixed - Both ends must operate at the same rate

Packet Switching – Basics

• Data transmitted in small packets
  • Typically 1000 octets (8 bit byte)
  • Longer messages split into series of packets
  • Each packet contains a portion of user data plus some control info
• Control info
  • Routing (addressing) info
• Packets are received, stored briefly (buffered) and passed on to the next node
  • Store and forward

Packet-Switching Network

• Application data, control information, and packet header

Packet Switching – Advantages

• Line efficiency
  • Single node to node link can be shared by many packets over time
  • Packets queued and transmitted as fast as possible
• Data rate conversion
  • Each station connects to the local node at its own speed
  • Nodes buffer data if required to equalize rates
• Packets are accepted even when network is busy
  • Delivery may slow down
• Priorities can be used

Packet Switching – Techniques

• Station breaks long message into packets
• Packets sent one at a time to the network
• Packets are handled in two ways
  • Datagram
  • Virtual circuit

Packet Switching – Datagram

• Each packet treated independently
• Packets can take any practical route
• Packets may arrive out of order
• Packets may get lost or delayed
• Up to receiver to re-order packets and recover from missing packets

Packet Switching – Virtual Circuit

• Preplanned route established before any packets sent
• Call request and call accept packets establish connection (handshake)
• Each packet contains a virtual circuit identifier instead of destination address
• No routing decisions required for each packet
• Clear request to drop circuit
• Not a dedicated path

Packet Switching - VC Switching Table

• Contains Incoming and Outgoing ports and VCIs (Virtual Circuit Identifier)

Packet Switching – Virtual Circuits vs Datagram

• Virtual circuits
  • Network can provide sequencing and error control
  • Packets are forwarded more quickly
    • No routing decisions to make
  • Less reliable
    • Loss of a node loses all circuits through that node
• Datagram
  • No call setup phase
    • Better if few packets
  • More flexible
    • Routing can be used to avoid congested parts of the network

Circuit vs. Packet Switching

Circuit Switched

• Bandwidth guaranteed
• Circuit capacity not reduced by other network traffic
• Circuit costs independent of amount of data transmitted, resulting in wasted bandwidth
• Suitable for voice communication

Packet Switched

• Bandwidth dynamically allocated on as-needed basis
• May have concurrent transmissions over physical channel
• May have delays and congestion
• More cost-effective, offer better performance
• Suitable for data communication

Protocol Stack – Layered Services

• Protocol defines the interfaces between the layers in the same system and with the layers of peer system
• Building blocks of a network architecture
• Each protocol object has two different interfaces
  • service interface: operations on this protocol
  • peer-to-peer interface: messages exchanged with peer
• “Protocol” includes
  • specification of peer-to-peer interface
  • module that implements this interface
• Features:
  • Protocol Specification: prose, pseudo-code, state transition diagram
  • Interoperable: when two or more protocols that implement the specification accurately
  • IETF: Internet Engineering Task Force

Key Elements of a Protocol

• Syntax: Data formats, Signal levels
• Semantics: Control information, Error handling
• Timing: Speed matching, Sequencing

Interfaces

• Service and Peer Interfaces
• High-level object linked by Service interface to Protocol
• Protocols link to each other via Peer-to-peer interface.

Protocol Hierarchy

• File, Digital library, Video Application linked to RRP
• RRP Linked to MSP
• MSP Linked to HHP

Encapsulation

• High-level messages are encapsulated inside of low-level messages

OSI (Open Systems Interconnection) Model

• End host: Application, Presentation, Session, Transport, Network, Data link, Physical
• One or more nodes within the network: Network, Data link, Physical

Protocol Layers - Functions

• Physical Layer
  • Handles the transmission of raw bits over a communication link
• Data Link Layer
  • Collects a stream of bits into a larger aggregate called a frame
  • Network adaptor along with device driver in OS implement the protocol in this layer
  • Frames are actually delivered to hosts
• Network Layer
  • Handles routing among nodes within a packet-switched network
  • Unit of data exchanged between nodes in this layer is called a packet
• Lower three layers are typically implemented on all network nodes
• Transport Layer
  • Implements a process-to-process channel
  • Unit of data exchanges in this layer is called a message
• Session Layer
  • Provides a name space that is used to tie together the potentially different transport streams that are part of a single application
• Presentation Layer
  • Concerned about the format of data exchanged between peers
• Application Layer
  • Standardize common type of exchanges
• Transport layer and the higher layers typically run only on end-hosts and not on the intermediate switches and routers

Internet Architecture

• Application, TCP UDP, IP, Subnetwork
• FTP, HTTP, NV, TFTP on Application Layer
• TCP,UDP on TCP UDP Layer
• IP on IP Layer
• NET₁, NET₂, NETn on Subnetwork Layer

Internet Architecture

• Defined by IETF
• Three main features
  • Does not imply strict layering. The application is free to bypass the defined transport layers and to directly use IP or other underlying networks
  • An hour-glass shape – wide at the top, narrow in the middle and wide at the bottom. IP serves as the focal point for the architecture
  • In order for a new protocol to be officially included in the architecture, there needs to be both a protocol specification and at least one (and preferably two) representative implementations of the specification

Network Application Programming Interface (API)

• Interface exported by the network
• Since most network protocols are implemented (those in the high protocol stack) in software and nearly all computer systems implement their network protocols as part of the operating system
• The interface is called the network Application Programming Interface (API)

TCP/IP Protocol Stack

• Applications, Transport, Internetwork, Network Interface and Hardware
• TCP/IP Layers - Group of functions in each layer
• Application layer
  • Provided by the program that uses TCP/IP for communication.
  • An application is a user process cooperating with another process usually on a different host (there is also a benefit to application communication within a single host).
  • Examples of applications include Telnet and the File Transfer Protocol (FTP).
  • The interface between the application and transport layers is defined by port numbers and “sockets”
• Transport layer
  • Provides the end-to-end data transfer by delivering data from an application to its remote peer. Multiple applications can be supported simultaneously.
  • Most-used transport layer protocol is the Transmission Control Protocol (TCP), which provides connection-oriented reliable data delivery, duplicate data suppression, congestion control, and flow control.
  • Another transport layer protocol: User Datagram Protocol (UDP) – It provides connectionless, unreliable, best-effort service.
  • As a result, applications using UDP as the transport protocol have to provide their own end-to-end integrity, flow control, and congestion control, if desired.
  • Usually, UDP is used by applications that need a fast transport mechanism and can tolerate the loss of some data.
• Internetwork layer (IP / Network Layer)
  • Provides the “virtual network” image of an internet (this layer shields the higher levels from the physical network architecture below it).
  • Internet Protocol (IP) is the most important protocol in this layer. It is a connectionless protocol that does not assume reliability from lower layers.
  • IP does not provide reliability, flow control, or error recovery. These functions must be provided at a higher level.
  • Provides a routing function that attempts to deliver transmitted messages to their destination.
  • A message unit in an IP network is called an IP datagram. This is the basic unit of information transmitted across TCP/IP networks.
  • Typical internetwork-layer protocols are IP, ICMP, IGMP, ARP, and RARP.
• Network interface layer
  • Is the interface to the actual network hardware.
  • This interface may or may not provide reliable delivery, and may be packet or stream oriented.
  • TCP/IP does not specify any protocol here but can use almost any network interface available, which illustrates the flexibility of the IP layer.
  • Examples are IEEE 802.2, X.25 (which is reliable in itself), ATM, FDDI, and even SNA.
  • There should be some underlying physical networks and interfaces
• TCP/IP specifications do not describe or standardize any network-layer protocols per se; they only standardize ways of accessing those protocols from the internetwork layer.

TCP/IP Architecture

• TCP/IP : Protocol Architecture and Communication Network has Computer A, Computer B, and Computer C communicate through applications, transport, and network access.
• TCP/IP : Protocol Architecture and Communication Network has Computer X and Computer Y communicate, with Application Protocol, Transport Protocol, Network access protocol, and Communications network.

TCP/IP : Protocol Architecture and Communication Network

• Computer X: Application, Transport, Network access
• Computer Y: Application Protocol, Application, Transport Protocol, Network access protocol, Communications network, Transport, Network access

TCP/IP : Operation

• Source X and Destination Y communication
• DSAP: destination service access point.
• DHost: destination host.

TCP/IP : Concept

• Host A: App X, App Y communicate through TCP, IP, and Network Access
• Host B: Port or service access point (SAP), App Y, Logical connection (TCP connection), Global network address, TCP, IP, Network Access
• Router J: IP, NAP 1 NAP 2, Network 1, Network 2, Protocol #2, Physical, Subnetwork attachment, Physical Logical connection. Network 1 is using NAP1, and Network 2 using NAP2

TCP/IP : Sample Protocols

• BGP, FTP, MIME, HTTP SMTP TELNET SNMP, TCP, IP, UDP, ICMP IGMP, OSPF, RSVP

Protocol Stack Implementation in a Host

• Application, Transport - Software, Kernel
• Network - Firmware, Device Driver
• Data Link, Physical - Hardware

How Application Data Passes Through Different Layers

• Application Layer: HTTP Data
• Transport Layer: HTTP Header, TCP Header, HTTP Data
• Network Layer: HTTP Header, TCP Header, IP Header, HTTP Data
• Data Link Layer: HTTP Header, TCP Header, IP Header, MAC Header, HTTP Data
• Physical Layer: HTTP Header, TCP Header, IP Header, MAC Header, PHY Header, HTTP Data, PHY Trailer

Application Layer Interfacing

• UDP: End to end packet delivery
• TCP: Connection Establishment, Reliable Data Delivery, Flow and Congestion Control, Ordered Packet Delivery

Responsibilities of Application Layer

• Identifying and establishing the availability of intended communication partners
• Synchronizing cooperating applications
• Establishing agreement on procedures for error recovery
• Controlling data integrity

Application Layer Examples

• Domain Name System (DNS)
• File Transfer Protocol (FTP)
• Hypertext Transfer Protocol (HTTP)
• Simple Mail Transport Protocol (SMTP)
• Simple Network Management Protocol (SNMP)
• Telnet
• ….

DNS

• Domain Name System (DNS) is a system used for translating names of domains into IP addresses.
• There are more than 200 top-level domains on the Internet
  • .in - India
  • .us – United States
  • .uk – United Kingdom
  • .edu – educational sites
  • .com – commercial sites
  • .gov – government sites
  • .org – non-profit sites
  • .net – network service

FTP and TFTP

• FTP is a reliable, connection-oriented service that uses TCP to transfer files between systems that support FTP.
• TFTP is a connectionless service that uses User Datagram Protocol (UDP).
  • TFTP is used on routers to transfer configuration files and Cisco IOS images.
  • TFTP is designed to be small and easy to implement.

HTTP

• Clients and Servers exchange messages using HTTP over TCP/IP
• Web Browser sends HTTP Request Message
• Web Server sends HTTP Response Message

SMTP

• E-mail servers communicate with each other using the Simple Mail Transport Protocol (SMTP) to send and receive mail.

SNMP

• Simple Network Management Protocol is an application layer protocol that facilitates the exchange of management information between network devices.
• Management entity, NMS
• Agent, Management database
• Managed devices

Telnet

• Telnet client software provides the ability to log in to a remote Internet host that is running a Telnet server application and then to execute commands from the command line.

Network API: “Socket”

• Server and Client exchange messages over the network through a common Socket API