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  • Now lets look at how the network is shared by multiple users. The sharing of resources on a link among multiple users is referred to as multiplexing. Here is an example where three hosts are trying to share a common link between switch 1 and switch 2. There are two common strategies for sharing. One is called time division multiplexing (TDM) and the other is called frequency division multiplexing (FDM). Under time division multiplexing hosts take turns in using the link. In TDM, the time is divided into frames of fixed duration and each frame is divided into a fixed number of time slots. Each host is assigned a specific time slot in each frame and that slot is dedicated to that host. The slot remains unused if there is no data to send. Under FDM, the frequency spectrum of the link is divided into multiple bands and each host is assigned a dedicated frequency band. So under FDM multiple hosts use the link simultaneously without interfering with each other. It may be easy to understand this with sharing a road analogy. If different types of traffic want to share the road, we can either dedicate the road to a specific type of traffic for certain hours in the day. This is like TDM. Or we can have multiple lanes with each lane dedicated to specific traffic. This is like FDM. Both these strategies dedicate a slot or a band to each host. That slot or band remains unused if there is no data to be sent by that host even of other hosts have something to send. This is known as circuit switching.
  • Statistical multiplexing is like time division multiplexing but on demand rather than fixed. Instead of having a dedicated slot for each source, the link is rescheduled on a per-packet basis. The link is never kept idle whenever there is data to send. Packets from different sources are interleaved on the link. Its is not possible to figure out the source from its time slot. Each packet should carry its identity. All the packets contending for a link are buffered. If the link is busy, buffer fills up. The buffer size is finite and if the buffer is full, some packets have to be discarded. This is due to congestion. This per-packet scheduling of link is known as packet switching.
  • Why use packet switching and share resources statically. Because it results in efficient utilization of the network resources which also means we can support more calls Lets look at an example. Suppose a link bandwidth is 1 Mbps and that each call requires 100 Kbps when transmitting. Lets assume that each call has data to send only 10% of the time. Now lets say we use circuit switching. Since each call requires 100Kbps, we can support at most 10 calls simultaneously. What happens when we use packet switching. We need probability theory to show that packet switching is good. The probability that a call is active is 0.1 and the probability that it is not active is 0.9. Given this we can use binomial distribution to compute the probability that more than 10 calls are active simultaneously out of 35 calls is less than 0.0017. This shows that packet switching can support many more calls with some small probability of contention. It has been shown that if the traffic sources are bursty, that is, if they have on and off periods, then packet switching is advantageous.
  • Is packet switching is always preferable? Ideally we want circuit switching type service with the efficiency of packet switching. Computer networks use packet switching.
  • The purpose of a network is to enable communication between end hosts. It has to resolve two fundamental issues. How to find the address of the party we would like to communicate with and how to reach there. In networks, address is a byte string that identifies the node. Different types of addresses possible, unicast, broadcast, multicast. Unicast address is specific to a node. When you want to communicate with a particular node, you use its unicast address. By using a broadcast address, we can communicate with all the nodes in the network. You may use broadcast address to find out whether there exists any server in the network that provides a specific service. Multicast address is used to communicate with a specific subset of nodes in the network. Routing is the process of deciding where to send the packets such that they reach the destination. The destination address should provide enough information on how to reach the destination. It’s the job of a router to find out its neighbors and build routing tables such that it can forward a packet in the direction of the destination. Later in the course we will be looking at how different routing protocols and algorithms are used to perform this task.
  • The purpose of a network is to enable communication between end hosts. It has to resolve two fundamental issues. How to find the address of the party we would like to communicate with and how to reach there. In networks, address is a byte string that identifies the node. Different types of addresses possible, unicast, broadcast, multicast. Unicast address is specific to a node. When you want to communicate with a particular node, you use its unicast address. By using a broadcast address, we can communicate with all the nodes in the network. You may use broadcast address to find out whether there exists any server in the network that provides a specific service. Multicast address is used to communicate with a specific subset of nodes in the network. Routing is the process of deciding where to send the packets such that they reach the destination. The destination address should provide enough information on how to reach the destination. It’s the job of a router to find out its neighbors and build routing tables such that it can forward a packet in the direction of the destination. Later in the course we will be looking at how different routing protocols and algorithms are used to perform this task.
  • What are the fundamental problems in networking. There are many things that can go wrong. Due to noise and interference, it is possible that a bit transmitted as 0 is interpreted as 1 at the receiver. As we discussed earlier, in packet switching it is possible that buffers at a congested link may overflow. This results in packet loss. We will see later that it is not necessary that all the packets to a destination follow the same path. Each packet is routed in isolation and so it possible that two packets take two different paths, experience different delays and reach the destination out of order. How do we deal with link and node failures. The cable may get cut. This is not as unusual as it seems. The systems may crash. So what can be done. Lets look some potential solutions. One way to deal with bit level errors is to add redundancy in the packet so that we can detect such bit errors and discard the packet. Or we can add enough redundancy such that we know how to correct/repair the error. We can use selective retransmission with timeout to recover the lost packets. If each packet received is acknowledged, sender can retransmit a packet if the acknowledgement doesn’t reach within the timeout period. To deal with out of order delivery, we can assign each packet a sequence number and buffer the packets reached out of order at the receiver and reorder them at the receiver. A router can send are you alive packets to its neighbors periodically to confirm that the link and the node are up. If it doesn’t get a response, it can declare them down and reset the routing tables such that failed links and nodes are avoided. These are not the only problems. This is just a small representative list of problems. The basic goal of networking software is to fill the gap between expectations of applications and the capabilities of the underlying technology. For example, if applications expect a reliable transmission and underlying channel is noisy, it’s the job of networking software to add error correction bits or error detection bits with retransmission. The networking software that addresses these problems is generally designed in a modular way to make the complexity manageable.
  • What are the fundamental problems in networking. There are many things that can go wrong. Due to noise and interference, it is possible that a bit transmitted as 0 is interpreted as 1 at the receiver. As we discussed earlier, in packet switching it is possible that buffers at a congested link may overflow. This results in packet loss. We will see later that it is not necessary that all the packets to a destination follow the same path. Each packet is routed in isolation and so it possible that two packets take two different paths, experience different delays and reach the destination out of order. How do we deal with link and node failures. The cable may get cut. This is not as unusual as it seems. The systems may crash. So what can be done. Lets look some potential solutions. One way to deal with bit level errors is to add redundancy in the packet so that we can detect such bit errors and discard the packet. Or we can add enough redundancy such that we know how to correct/repair the error. We can use selective retransmission with timeout to recover the lost packets. If each packet received is acknowledged, sender can retransmit a packet if the acknowledgement doesn’t reach within the timeout period. To deal with out of order delivery, we can assign each packet a sequence number and buffer the packets reached out of order at the receiver and reorder them at the receiver. A router can send are you alive packets to its neighbors periodically to confirm that the link and the node are up. If it doesn’t get a response, it can declare them down and reset the routing tables such that failed links and nodes are avoided. These are not the only problems. This is just a small representative list of problems. The basic goal of networking software is to fill the gap between expectations of applications and the capabilities of the underlying technology. For example, if applications expect a reliable transmission and underlying channel is noisy, it’s the job of networking software to add error correction bits or error detection bits with retransmission. The networking software that addresses these problems is generally designed in a modular way to make the complexity manageable.
  • Lets look at the relation between services, protocols and interfaces. The interface of a layer defines the service provided by that layer and protocols are used to implement the service according to the interface specification. The protocol is between peer entities and they communicate with each other using the service provided by the lower layer. Here is an example of communication between peer layers. It is important to understand the difference between logical vs physical communication. For example, layer 4’s communicate with each other using a layer 4 protocol. They exchange messages as if they can talk to each other directly. But in reality, messages go thru the router. Layer 4 uses the services offered by layer 3 to send the message to layer 4 on the other side. The dotted line shows the logical communication path and the solid line, physical communication path. This approach allows design, implementation and testing of a layer software independent of other layers.
  • Now lets look at the protocols used in the Internet. There are tons of protocols and not all the protocols are listed here. Why so many? Each protocol serves a specific purpose. There so many link layer protocols and application layer protocols. There are two transport protocols namely TCP and UDP. But there is only one network layer protocol called Internet Protocol (IP). This protocol in the middle is the glue that holds the whole thing together. That’s why Internet protocol stack is said to resemble an hour glass. This architecture makes it easy to interface with new technologies and support new applications. They only need to interact with IP. This Internet protocol stack is also referred to as TCP/IP protocol stack as these two are most popular protocols. We will briefly look at some of these protocols and cover them in more detail later in the semester.
  • This is what we learnt so far. We talked about statistical multiplexing and packet switching, why its better to use packet switching instead of circuit switching in computer networks. Also some of the fundamental issues that need to be addressed by the networking software are routing/forwarding and error/flow/congestion control. Next we looked at the layered architecture for addressing these issues using a modular approach. Finally, we briefly discussed TCP/IP protocol stack used in Internet
  • This is what we learnt so far. We talked about statistical multiplexing and packet switching, why its better to use packet switching instead of circuit switching in computer networks. Also some of the fundamental issues that need to be addressed by the networking software are routing/forwarding and error/flow/congestion control. Next we looked at the layered architecture for addressing these issues using a modular approach. Finally, we briefly discussed TCP/IP protocol stack used in Internet

[PPT] [PPT] Presentation Transcript

  • Introduction to Networking
    • What is a (computer/data) network?
    • Statistical multiplexing
      • Packet switching
    • OSI Model and Internet Architecture
    • Introduction to the Internet
    • Readings
      • Chapter 1
  • What is a Network?
    • There are many types of networks!
    • Transportation Networks
      • Transport goods using trucks, ships, airplanes, …
    • Postal Services
      • Delivering letters, parcels, etc.
    • Broadcast and cable TV networks
    • Telephone networks
    • Internet
    • “ Social/Human networks”
  • Key Features of Networks
    • Providing certain services
      • transport goods, mail, information or data
    • Shared resources
      • used by many users, often concurrently
    • Basic building blocks
      • nodes (active entities): process and transfer goods/data
      • links (passive medium): passive “carrier” of goods/data
    • Typically “multi-hop”
      • two “end points” cannot directly reach each other
      • need other nodes/entities to relay
    View slide
  • Data/Computer Networks
    • Delivery of information (“data”) among computers of all kinds
      • servers, desktops, laptop, PDAs, cell phones, ......
    • General-Purpose
      • Not for specific types of data or groups of nodes, or using specific technologies
    • Utilizing a variety of technologies
      • “ physical/link layer” technologies for connecting nodes
        • copper wires, optical links, wireless radio, satellite
      • or even “non-electronic” means: e.g., cars, postal services, humans -- e.g., recent “delay-tolerant networks” efforts for 3 rd world countries
    View slide
  • How to Build Data/Computer Networks
    • Two possibilities
    • infrastructure-less ( ad hoc, peer-to-peer )
      • (end) nodes also help other (end) nodes, i.e., peers, to relay data
    • infrastructure-based
      • use special nodes
      • (switches, routers, gateways)
      • to help relay data
  • Connectivity and Inter-networking
    • Point-to-point vs.
    • broadcast links/
    • wireless media
    • switched networks
    • connecting “clouds” (existing physical networks)
      • inter-networking using gateways, virtual tunnels, overlays
    (a) (b) base station
  • Resource Sharing in Switched Networks
    • Multiplexing Strategies
    • Circuit Switching
      • set up a dedicated route (“circuit”) first
      • carry all bits of a “conversation” on one circuit
        • original telephone network
        • Analogy: railroads and trains
    • Packet Switching
      • divide information into small chunks (“packets”)
      • each packet delivered independently
      • “store-and-forward” packets
        • Internet
    • (also Postal Service, but they don’t tear your mail into pieces first!)
        • Analogy: highways and cars
  • Common Circuit Switching Methods
    • Sharing of network resources among multiple users
    • Common multiplexing strategies for circuit switching
      • Time Division Multiplexing Access (TDMA)
      • Frequency Division Multiplexing Access (FDMA)
      • Code Division Multiplexing Access (CDMA)
    • What happens if running out of circuits?
  • Packet Switching & Statistical Multiplexing
    • Time division, but on demand rather than fixed
    • Reschedule link on a per-packet basis
    • Packets from different sources interleaved on the link
    • Buffer packets that are contending for the link
    • Buffer buildup is called congestion
    Packet Switching , used in computer/data networks, relies on statistical multiplexing for cost-effective resource sharing
  • Why Statistically Share Resources
    • Efficient utilization of the network
    • Example scenario
      • Link bandwidth: 1 Mbps
      • Each call requires 100 Kbps when transmitting
      • Each call has data to send only 10% of time
    • Circuit switching
      • Each call gets 100 Kbps: supports 10 simultaneous calls
    • Packet switching
      • Supports many more calls with small probability of contention
        • 35 ongoing calls: probability that > 10 active is < 0.0017!
  • Circuit Switching vs Packet Switching Queuing delay Call blocking Effect of congestion On every packet At setup time When can congestion occur Not Needed Required Call setup Not necessarily Yes Each packet/bit always follows the same route Yes No Store-and-forward transmission No (not really!) Yes Potentially wasted bandwidth Dynamic Fixed Bandwidth available No Yes Dedicated “copper” path Packet-switched Circuit-switched Item
  • Fundamental Issues in Networking
    • Networking is more than connecting nodes!
    • Naming/Addressing
      • How to find name/address of the party (or parties) you would like to communicate with
      • Address: bit- or byte-string that identifies a node
      • Types of addresses
        • Unicast: node-specific
        • Broadcast: all nodes in the network
        • Multicast: some subset of nodes in the network
    • Routing/Forwarding:
      • process of determining how to send packets towards the destination based on its address
      • Finding out neighbors, building routing tables
  • Other Key Issues in Networking
    • Detecting whether there is an error!
    • Fixing the error if possible
    • Deciding how fast to send, meeting user demands, and managing network resources efficiently
    • Make sure integrity and authenticity of messages,
    • ……
  • Fundamental Problems in Networking …
    • What can go wrong?
    • Bit-level errors: due to electrical interferences
    • Packet-level errors: packet loss due to buffer overflow/congestion
    • Out of order delivery: packets may takes different paths
    • Link/node failures: cable is cut or system crash
    • Others: e.g., malicious attacks
  • Fundamental Problems in Networking
    • What can be done?
    • Add redundancy to detect and correct erroneous packets
    • Acknowledge received packets and retransmit lost packets
    • Assign sequence numbers and reorder packets at the receiver
    • Sense link/node failures and route around failed links/nodes
    • Goal: to fill the gap between what applications expect and what underlying technology provides
  • Key Performance Metrics
    • Bandwidth (throughput)
      • data transmitted per time unit
      • link versus end-to-end
    • Latency (delay)
      • time to send message from point A to point B
      • one-way versus round-trip time (RTT)
      • components
        • Latency = Propagation + Transmit + Queue
        • Propagation = Distance / c
        • Transmit = Size / Bandwidth
      • Delay Bandwidth Product: # of bits that can be carried in transit
      • RTT usually contains Transmit time plus Queuing delay
    • Reliability, availability, …
    • Efficiency/overhead of implementation, ……
    • Bridging the gap between
    • what applications expect
      • reliable data transfer
      • response time, latency
      • availability, security ….
    • what (physical/link layer) technologies provide
      • various technologies for connecting computers/devices
    How to Build Data Networks applications technologies Web Email File Sharing Multimedia Coaxial Cable Optical Fiber Wireless Radio
  • The Problem
    • Do we re-implement every application for every technology?
    • Obviously not, but how does the Internet architecture avoid this?
    Application Transmission Media Web Email Skype KaZaa Coaxial Cable Optical Fiber Wireless Radio
  • Architectural Principles
    • What is (Network) Architecture ?
      • not the implementation itself
      • “design blueprint” on how to “organize” implementations
        • what interfaces are supported
        • where functionality is implemented
    • Two (Internet) Architectural Principles
      • Layering
        • how to break network functionality into modules
      • End-to-End Arguments
        • where to implement functionality
  • Layering
    • Layering is a particular form of modularization
    • system is broken into a vertical hierarchy of logically distinct entities (layers)
    • each layer use abstractions to hide complexity
    • can have alternative abstractions at each layer
    without layering apps media Web Email Skype KaZaa Coaxial Cable Optical Fiber Wireless Radio Web Email Skype KaZaa Coaxial Cable Optical Fiber Wireless Radio intermediate layers with layering
  • Logical vs. Physical Communications
    • Layers interacts with corresponding layer on peer
    • Communication goes down to physical network, then to peer, then up to relevant layer
  • ISO OSI Network Architecture
  • OSI Model Concepts
    • Service : what a layer does
    • Service interface : how to access the service
      • interface for layer above
    • Peer interface ( protocol ): how peers communicate
      • a set of rules and formats that govern the communication between two network boxes
      • protocol does not govern the implementation on a single machine, but how the layer is implemented between machines
  • Protocols and Interfaces
    • Protocols: specification/implementation of a “service” or “functionality”
    • Each protocol object defines two different interfaces
      • service interface : operations on this machine
      • peer-to-peer interface : messages exchanged with peer
  • Who Does What?
    • Seven layers
      • Lower three layers are implemented everywhere
      • Next four layers are implemented only at hosts
    Application Presentation Session Transport Network Datalink Physical Application Presentation Session Transport Network Datalink Physical Network Datalink Physical Physical medium Host A Host B Router
  • Physical and Data Link layers
    • Physical Layer: Transmit and receive bits on physical media
      • analog and digital transmission
      • a definition of the 0 and 1 bits
      • bit rate (bandwidth)
    • Data Link Layer: Provide error-free bit streams across physical media
      • Error detection/correction
      • reliability
      • flow control
  • Network Layer
    • Controls the operations of the network
    • Routing : determining the path from the source of a message to its destination
    • Congestion Control : handling traffic jams
    • Internetworking of both homogeneous and heterogeneous networks.
  • Transport Layer
    • Provides end–to–end (host–to–host) connections
    • Packetization : cut the messages into smaller chunks (packets)
    • An ensuing issue is ordering : the receiving end must make sure that the user receives the packets in the right order
    • Host–to–host flow control
  • Upper Layers
    • Session Layer
      • user–to–user connection
      • synchronization, checkpoint, and error recovery
    • Presentation Layer
      • data representation/compression
      • cryptography and authentication
    • Application Layer
      • file transfer, email, WWW, and so on
  • Data Communication based on OSI
  • Data Encapsulation in OSI Headers tell the peer how to do the job
  • Shortcomings of the OSI Model
    • Just because someone says it is a model/standard does not mean you have to follow it
    • All layers do not have the same size and importance
      • session and presentation layers seldom present
      • data link, network, and transport layers often very full
    • Little agreement on where to place various features
      • Encryption, network management
    • Large number of layers increases overheads
  • Internet Protocol Suite Reference Model Host to Network Internet Transport Application Host to Network Internet Transport Application Physical Link
    • There are no presentation and session layers in the Internet model.
    • The internet layer is the equivalent of the network layer in the OSI model.
    • The physical and data link layers in the OSI model are merged to the “Host to Network” layer.
  • OSI vs. Internet
    • OSI: conceptually define services, interfaces, protocols
    • Internet: provide a successful implementation
    Application Presentation Session Transport Network Datalink Physical Internet Net access/ Physical Transport Application OSI (formal) Internet (informal) IP LAN Packet radio TCP UDP Telnet FTP DNS
  • Hourglass
  • Implications of Hourglass
    • A single Internet layer module:
    • Allows all networks to interoperate
      • all networks technologies that support IP can exchange packets
    • Allows all applications to function on all networks
      • all applications that can run on IP can use any network
    • Simultaneous developments above and below IP
  • Internet Protocol “Zoo” application SMTP Telnet NFS/Sun RPC FTP DNS HTTP RealAudio RealVideo
  • Benefits/Drawbacks of Layering
    • Benefits of layering
      • Encapsulation/informing hiding
        • Functionality inside a layer is self-contained;
        • one layer does not need to know how other layers are implemented
      • Modularity
        • can be replaced without impacting other layers
        • Lower layers can be re-used by higher layer
      • Consequences:
        • Applications do not need to do anything in lower layers;
        • information about network hidden from higher layers (applications in particular)
    • Drawbacks?
      • Obviously, too rigid, may lead to inefficient implementation
  • What’s the Internet: “nuts and bolts” view
    • millions of connected computing devices: hosts = end systems
      • running network apps
    Introduction 1-
    • communication links
      • fiber, copper, radio, satellite
      • transmission rate = bandwidth
    • routers: forward packets (chunks of data)
    Home network Institutional network Mobile network Global ISP Regional ISP router PC server wireless laptop cellular handheld wired links access points
  • What’s the Internet: “nuts and bolts” view
    • protocols control sending, receiving of msgs
      • e.g., TCP, IP, HTTP, Skype, Ethernet
    • Internet: “network of networks”
      • loosely hierarchical
      • public Internet versus private intranet
    • Internet standards
      • RFC: Request for comments
      • IETF: Internet Engineering Task Force
    Introduction 1- Home network Institutional network Mobile network Global ISP Regional ISP
  • What’s the Internet: a service view
    • communication infrastructure enables distributed applications:
      • Web, VoIP, email, games, e-commerce, file sharing
    • communication services provided to apps:
      • reliable data delivery from source to destination
      • “ best effort” (unreliable) data delivery
    Introduction 1-
  • A closer look at network structure:
    • network edge: applications and hosts
    Introduction 1-
    • access networks, physical media: wired, wireless communication links
    • network core:
      • interconnected routers
      • network of networks
  • The network edge:
    • end systems (hosts):
      • run application programs
      • e.g. Web, email
      • at “edge of network”
    Introduction 1-
    • client/server model
      • client host requests, receives service from always-on server
      • e.g. Web browser/server; email client/server
    • peer-peer model:
      • minimal (or no) use of dedicated servers
      • e.g. Skype, BitTorrent
    client/server peer-peer
  • Access networks and physical media
    • Q: How to connect end systems to edge router?
    • residential access nets
    • institutional access networks (school, company)
    • mobile access networks
    • Keep in mind:
    • bandwidth (bits per second) of access network?
    • shared or dedicated?
    Introduction 1-
  • Residential access: point to point access
    • Dialup via modem
      • up to 56Kbps direct access to router (often less)
      • Can’t surf and phone at same time: can’t be “always on”
    Introduction 1-
    • DSL: digital subscriber line
      • deployment: telephone company (typically)
      • up to 1 Mbps upstream (today typically < 256 kbps)
      • up to 8 Mbps downstream (today typically < 1 Mbps)
      • dedicated physical line to telephone central office
  • Residential access: cable modems
    • HFC: hybrid fiber coax
      • asymmetric: up to 30Mbps downstream, 2 Mbps upstream
    • network of cable and fiber attaches homes to ISP router
      • homes share access to router
    • deployment: available via cable TV companies
    Introduction 1-
  • Company access: local area networks
    • company/univ local area network (LAN) connects end system to edge router
    • Ethernet:
      • 10 Mbs, 100Mbps, 1Gbps, 10Gbps Ethernet
      • modern configuration: end systems connect into Ethernet switch
    Introduction 1-
  • Wireless access networks
    • shared wireless access network connects end system to router
      • via base station aka “access point”
    • wireless LANs:
      • 802.11b/g (WiFi): 11 or 54 Mbps
      • 802.11a
    • wider-area wireless access
      • provided by telco operator
      • ~1Mbps over cellular system (EVDO, HSDPA)
      • WiMAX (10’s Mbps) over wide area
    Introduction 1- base station mobile hosts router
  • Home networks
    • Typical home network components:
    • DSL or cable modem
    • router/firewall/NAT
    • Ethernet
    • wireless access
    • point
    Introduction 1- wireless access point wireless laptops router/ firewall cable modem to/from cable headend Ethernet
  • Physical Media
    • Bit: propagates between transmitter/rcvr 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
    • Twisted Pair (TP)
    • two insulated copper wires
      • Category 3: traditional phone wires, 10 Mbps Ethernet
      • Category 5: 100Mbps Ethernet
    Introduction 1-
  • Physical Media: coax, fiber
    • Coaxial cable:
    • two concentric copper conductors
    • bidirectional
    • baseband:
      • single channel on cable
      • legacy Ethernet
    • broadband:
      • multiple channels on cable
      • HFC
    Introduction 1-
    • Fiber optic cable:
    • glass fiber carrying light pulses, each pulse a bit
    • high-speed operation:
      • high-speed point-to-point transmission (e.g., 10’s-100’s Gps)
    • low error rate: repeaters spaced far apart; immune to electromagnetic noise
  • Physical media: radio
    • signal carried in electromagnetic spectrum
    • no physical “wire”
    • bidirectional
    • propagation environment effects:
      • reflection
      • obstruction by objects
      • interference
    Introduction 1-
    • Radio link types:
    • terrestrial microwave
      • e.g. up to 45 Mbps channels
    • LAN (e.g., Wifi)
      • 11Mbps, 54 Mbps
    • wide-area (e.g., cellular)
      • 3G cellular: ~ 1 Mbps
    • satellite
      • Kbps to 45Mbps channel (or multiple smaller channels)
      • 270 msec end-end delay
      • geosynchronous versus low altitude
  • The Network Core
    • mesh of interconnected routers
    • the fundamental question: how is data transferred through net?
      • circuit switching: dedicated circuit per call: telephone net
      • packet-switching: data sent thru net in discrete “chunks”
    Introduction 1-
  • Packet Switching: Statistical Multiplexing
    • Sequence of A & B packets does not have fixed pattern, bandwidth shared on demand  statistical multiplexing .
    • TDM: each host gets same slot in revolving TDM frame.
    Introduction 1- A B C 100 Mb/s Ethernet 1.5 Mb/s statistical multiplexing queue of packets waiting for output link D E
  • Packet-switching: store-and-forward
    • takes L/R seconds to transmit (push out) packet of L bits on to link at R bps
    • store and forward: entire packet must arrive at router before it can be transmitted on next link
    • delay = 3L/R (assuming zero propagation delay)
    • Example:
    • L = 7.5 Mbits
    • R = 1.5 Mbps
    • transmission delay = 15 sec
    Introduction 1- R R R L
  • Internet structure: network of networks
    • roughly hierarchical
    • at center: “tier-1” ISPs (e.g., Verizon, Sprint, AT&T, Cable and Wireless), national/international coverage
      • treat each other as equals
    Introduction 1- Tier 1 ISP Tier 1 ISP Tier 1 ISP Tier-1 providers interconnect (peer) privately
  • Tier-1 ISP: e.g., Sprint Introduction 1- … to/from customers peering to/from backbone … . … … … POP: point-of-presence
  • Internet structure: network of networks
    • “ Tier-2” ISPs: smaller (often regional) ISPs
      • Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs
    Introduction 1- Tier 1 ISP Tier 1 ISP Tier 1 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP
    • Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet
    • tier-2 ISP is c ustomer of
    • tier-1 provider
    Tier-2 ISPs also peer privately with each other.
  • Internet structure: network of networks
    • “ Tier-3” ISPs and local ISPs
      • last hop (“access”) network (closest to end systems)
    Introduction 1- Tier 1 ISP Tier 1 ISP Tier 1 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP local ISP local ISP local ISP local ISP local ISP Tier 3 ISP local ISP local ISP local ISP Local and tier- 3 ISPs are customers of higher tier ISPs connecting them to rest of Internet
  • Internet structure: network of networks
    • a packet passes through many networks!
    Introduction 1- Tier 1 ISP Tier 1 ISP Tier 1 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP Tier-2 ISP local ISP local ISP local ISP local ISP local ISP Tier 3 ISP local ISP local ISP local ISP
  • Summary
    • Computer networks use packet switching
    • Fundamental issues in networking
      • Addressing/Naming and Routing/Forwarding
      • Error/Flow/Congestion control
    • Layered architecture and protocols
    • Internet is based on TCP/IP protocol suite
      • Networks of networks!
      • Shared, distributed and complex system in global scale
      • No centralized authority
  • Readings for Next Week
    • Review Chapter 1
    • Read Chapter 9: sections 9.1 -9.3; 9.4.2-3
      • Review how web/email and other applications work
      • Learn how p2p and CDN work
      • Understand what Domain Name System does for us
    • Read Chapter 7 if interested/needed
  • Who Runs the Internet
    • “ nobody” really!
    • standards: Internet Engineering Task Force (IETF)
    • names/numbers: The Internet Corporation for Assigned Names and Numbers (ICANN)
    • operational coordination: IEPG(Internet Engineering Planning Group)
    • networks: ISPs (Internet Service Providers), NAPs (Network Access Points), ……
    • fibers: telephone companies (mostly)
    • content: companies, universities, governments, individuals, …;
  • Internet “Governing” Bodies
    • Internet Society (ISOC): membership organization
      • raise funds for IAB, IETF& IESG, elect IAB
    • Internet Engineering Task Force (IETF):
      • a body of several thousands or more volunteers
      • organized in working groups (WGs)
      • meet three times a year + email
    • Internet Architecture Board
      • architectural oversight, elected by ISOC
    • Steering Group (IESG): approves standards,
      • Internet standards, subset of RFC
    • RFC: “Request For Comments”, since 1969
      • most are not standards, also
        • experimental, informational and historic(al)
  • Internet Standardization Process
    • All standards of the Internet are published as RFC
    • But not all RFCs are Internet Standards
    • A typical (but not only) way of standardization is:
      • Internet Drafts
      • RFC
      • Proposed Standard
      • Draft Standard (requires 2 working implementation)
      • Internet Standard (declared by IAB)
    • David Clark, MIT 1992: “We reject: kings, presidents, and voting. We believe in: rough consensus and running code.”
  • Internet Names and Addresses
    • Internet Assigned Number Authority (IANA):
      • keep track of numbers, delegates Internet address assignment
      • designates authority for each top-level domain
    • InterNIC, gTLD-MOU, CORE:
      • hand out names
      • provide “root DNS service”
    • RIPE, ARIN, APNIC:
      • hand out blocks of addresses
      • Many responsibilities (e.g., those of IANA) are now taken over by the Internet Corporation for Assigned Names and Numbers (ICANN)
  • Origin of Internet?
    • Started by U.S. research/military organizations:
    • Three Major Actors:
      • DARPA : Defense Advanced Research Projects Agency
        • funds technology with military goals
      • DoD : U.S. Department of Defense
        • early adaptor of Internet technology for production use
      • NSF : National Science Foundation
        • funds university
  • A Brief History of Internet
    • The Dark Age before the Internet: before 1960
      • 1830: telegraph
      • 1876: circuit-switching (telephone)
      • TV (1940?) , and later cable TV (1970s)
    • The Dawn of the Internet: 1960s
    • early 1960’s: concept of packet switching (Leonard Kleinrock, Paul Baran et al)
    • 1965: MIT’s Lincoln Laboratory commissions Thomas Marill to study computer networking
    • 1968: ARPAnet contract awarded to Bolt Beranek and Newman (BBN)
      • Robert Taylor (DARPA program manager)
      • BoB Kahn (originally MIT) and the team at BBN built the first router (aka IMP)
  • A Brief History of Internet …
    • 1969: ARPAnet has 4 nodes (UCLA, SRI, UCSB, U. Utah)
      • UCLA team: Len Kleinrock, Vincent Cerf, Jon Postel, et al
    • Early Days of the Internet: 1970s
        • multiple access networks (i.e., LANs): ALOHA, Ethernet(10Mb/s)
        • companies: DECnet (1975), IBM SNA (1974)
    • 1971: 15 nodes and 23 hosts: UCLA, SRI, UCSB, U. Utah, BBN, MIT, RAND, SDC, Harvard, Lincoln Lab, Stanford, UIUC, CWRU, CMU, NASA/Ames
    • 1972: First public demonstration at ICCC
    • 1973: TCP/IP design
    • 1973: first satellite link from California to Hawwii
  • A Brief History of Internet …
    • 1973:first international connections to ARPAnet: England and Norway
    • 1978: TCP split into TCP and IP
    • 1979: ARPAnet: approx. 100 nodes
    • The Internet Coming of Age: 1980s
        • proliferation of local area networks: Ethernet and token rings
        • late 1980s: fiber optical networks; FDDI at 100 Mbps
    • 1980’s: DARPA funded Berkeley Unix, with TCP/IP
    • 1981: Minitel deployed in France
    • 1981: BITNET/CSNet created
    • 1982: Eunet created (European Unix Network)
    • Jan 1, 1983: flag day , NCP -> TCP
  • A Brief History of Internet …
    • 1983: split ARAPNET (research), MILNET
    • 1983: Internet Activities Board (IAB) formed
    • 1984: Domain Name Service replaces hosts.txt file
    • 1986: Internet Engineering/Research Task Force created
    • 1986: NSFNET created (56kbps backbone)
    • 1987: UUNET founded
    • Nov 2, 1988: Internet worm, affecting ~6000 hosts
    • 1988: Internet Relay Chat (IRC) developed by Jarkko Oikarinen
    • 1988: Internet Assigned Numbers Authority (IANA) established
    • 1989: Internet passes 100,000 nodes
    • 1989: NSFNET backbone upgraded to T1 (1.544 Mpbs)
    • 1989: Berners-Lee invented WWW at CERN
  • A Brief History of Internet …
    • The Boom Time of the Internet: 1990s
        • high-speed networks: ATM ( 150 Mbps or higher ), Fast Ethernet ( 100Mbps ) and Gigabit Ethernet
        • new applications: gopher, and of course WWW !
        • wireless local area networks
        • commercialization
        • National Information Infrastructure (NII) (Al Gore, “father” of what?)
    • 1990: Original ARPANET disbanded
    • 1991: Gopher released by Paul Lindner & Mark P. McCahill, U.of Minnesota
    • 1991: WWW released by Tim Berners-Lee, CERN
    • 1991: NSFNET backbone upgrade to T3 (44.736 Mbps)
    • Jan 1992: Internet Society (ISOC) chartered
  • A Brief History of Internet …
    • March 1992: first MBONE audio multicast
      • MBONE: multicast backbone, “overlayed” on top of Internet
    • Nov 1992: first MBONE video multicast
    • 1992: numbers of Internet hosts break 1 million
      • The term &quot; surfing the Internet &quot; is coined by Jean Armour Polly
    • 1993: Mosaic takes the Internet by storm
    • 1993: InterNIC (Internet information center) created by NSF
      • US White House, UN come on-line
    • 1994: ARPANET/Internet celebrates 25th anniversary
    • 1994: NSFNET traffic passes 10 trillion bytes/month
    • Apr 30 1995: NSFNET backbone disbanded
      • traffic now routed through interconnected network providers