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Foundation. Outline Requirements Network Architecture Implementing Network Software. Problem: Building a Network. How to build a network: Requirements Architecture Key elements in the implementation. Requirements. Outline Statistical Multiplexing Inter-Process Communication

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foundation

Foundation

Outline

Requirements

Network Architecture

Implementing Network Software

problem building a network
Problem: Building a Network
  • How to build a network:
    • Requirements
    • Architecture
    • Key elements in the implementation
requirements

Requirements

Outline

Statistical Multiplexing

Inter-Process Communication

Performance Metrics

building blocks

Building Blocks
  • Nodes: PC, special-purpose hardware…
    • hosts
    • switches
  • Links: coax cable, optical fiber…
    • point-to-point
    • multiple access
switched networks
Switched Networks
  • A network can be defined recursively as...
  • two or more nodes connected by a link, or
  • two or more networks connected by two or more nodes
strategies
Strategies
  • Circuit switching: carry bit streams
    • original telephone network
  • Packet switching: store-and-forward messages
    • Internet
addressing and routing
Addressing and Routing
  • Address: byte-string that identifies a node
    • usually unique
  • Routing: process of forwarding messages to the destination node based on its address
  • Types of addresses
    • unicast: node-specific
    • broadcast: all nodes on the network
    • multicast: some subset of nodes on the network
multiplexing

L1

R1

L2

R2

Switch 1

Switch 2

L3

R3

Multiplexing
  • Use multiplexing to efficiently share a network
  • Time-Division Multiplexing (TDM)
  • Frequency-Division Multiplexing (FDM)
statistical multiplexing
Statistical Multiplexing
  • On-demand time-division
  • Schedule link on a per-packet (limited-size block of data) basis
  • Packets from different sources interleaved on link
  • Buffer packets that are contending for the link
  • Buffer (queue) overflow is called congestion
  • FIFO or round-robin to make flow in a fair maner
statistical multiplexing10
Statistical Multiplexing
  • A network that allow flows not to be delayed for more than certain length of time is said to support qualify of service (QoS).

inter process communication

Host

Host

Application

Host

Channel

Application

Host

Host

Inter-Process Communication
  • Turn host-to-host connectivity into process-to-process communication.
  • Fill gap between what applications expect and what the underlying technology provides.
  • Provide a logical channel.
ipc abstractions
IPC Abstractions
  • Stream-Based
    • video: sequence of frames
      • 1/4 NTSC = 352x240 pixels
      • (352 x 240 x 24)/8=247.5KB
      • 30 fps = 7500KBps = 60Mbps
    • video applications
      • on-demand video
      • video conferencing
  • Request/Reply
    • distributed file systems
    • digital libraries (web)
what goes wrong in the network
What Goes Wrong in the Network?
  • Bit-level errors (electrical interference)
  • Packet-level errors (congestion)
  • Link and node failures
  • Messages are delayed
  • Messages are deliver out-of-order
  • Third parties eavesdrop
performance metrics
Performance Metrics
  • Bandwidth (throughput)
    • data transmitted per time unit
    • link versus end-to-end
    • notation
      • KB = 210 bytes
      • Mbps = 106 bits per second
  • 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 / SpeedOfLight

Transmit = Size / Bandwidth

bandwidth versus latency
Bandwidth versus Latency
  • Relative importance
    • 1-byte: 1ms vs. 100ms dominates 1Mbps vs. 100Mbps
    • 25MB: 1Mbps vs. 100Mbps dominates 1ms vs. 100ms
  • Infinite bandwidth
    • RTT dominates
      • Throughput = TransferSize / TransferTime
      • TransferTime = RTT + 1/Bandwidth x TransferSize
    • 1-MB file to 1-Gbps link as 1-KB packet to 1-Mbps link
delay x bandwidth product
Delay x Bandwidth Product
  • Amount of data “in flight” or “in the pipe”
  • Example: 100ms x 45Mbps = 560KB
osi vs internet architecture
OSI vs. Internet Architecture
  • Countless debates on the technical advantages of the ISO protocols versus the Internet protocols are no longer relevant.
    • ISO protocols are largely ignored.
    • An implementation of the TCP/IP protocol suite was bundled with the Unix operating system.
    • The ISO/ITU culture has always been to specify first and implement later.
    • In 1988, the NIST approved a mandate that required government agencies to procure equipment that could run the ISO protocols.
    • In reality, computers were shipped with ISO-compliant code, but people kept using TCP/IP. This mandate was rescinded in September 1994.
network architecture
Network Architecture
  • A computer network must provide general, cost-effective, fair, robust, and high-performance connectivity among a large number of computers.
  • To deal with the complexity, designers developed a network architecture.
  • OSI and Internet architecture are two widely referenced architectures.
layering
Layering
  • Use abstractions to hide complexity
  • Abstraction naturally lead to layering
  • Alternative abstractions at each layer

Application programs

Request/reply

Message stream

channel

channel

Host-to-host connectivity

Hardware

protocols
Protocols
  • 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
  • Term “protocol” is overloaded
    • specification of peer-to-peer interface
    • module that implements this interface
interfaces
Interfaces

Host1

Host2

Service

High-level

High-level

interface

object

object

Protocol

Protocol

Peer-to-peer

interface

protocol machinery
Protocol Machinery
  • Protocol Graph
    • most peer-to-peer communication is indirect
    • peer-to-peer is direct only at hardware level

Host 2

Host 1

Digital

Digital

Video

Video

File

File

library

library

application

application

application

application

application

application

RRP

MSP

RRP

MSP

HHP

HHP

machinery cont
Machinery (cont)
  • Multiplexing and Demultiplexing (demux key)
  • Encapsulation (header/body)

Host 1

Host 2

Application

Application

program

program

Data

Data

RRP

RRP

RRP

Data

RRP

Data

HHP

HHP

HHP

RRP

Data

iso 7 layer reference model
ISO 7-Layer Reference Model

End host

End host

Application

Application

Various applications (FTP,HTTP,…)

Presentation

Presentation

Present data in a meaningful format

Session

Session

Provide session semantics (RPC)

Transport

Transport

Reliable, end-to-end byte stream (TCP)

Network

Network

Network

Network

Unreliable end-to-end tx of packets

Data link

Data link

Data link

Data link

Reliable transmission (tx) of frames

Physical

Physical

Physical

Physical

Unreliable transmission (tx) of raw bits

One or more nodes

within the network

internet architecture

FTP

HTTP

NV

TFTP

UDP

TCP

IP

NET

NET

NET

2

1

n

Internet Architecture
  • Defined by Internet Engineering Task Force (IETF)
  • Hourglass Design
  • Application vs. Application Protocol (FTP, HTTP)
osi vs internet architecture26
OSI vs. Internet Architecture
  • Countless debates on the technical advantages of the ISO protocols versus the Internet protocols are no longer relevant.
    • ISO protocols are largely ignored.
    • An implementation of the TCP/IP protocol suite was bundled with the Unix operating system.
    • The ISO/ITU culture has always been to specify first and implement later.
    • In 1988, the NIST approved a mandate that required government agencies to procure equipment that could run the ISO protocols.
    • In reality, computers were shipped with ISO-compliant code, but people kept using TCP/IP. This mandate was rescinded in September 1994.
open issue ubiquitous networking
Open Issue – Ubiquitous Networking
  • Networking has become a big business. Three major players are:
    • Computing industry
    • Telephone carriers
    • TV industry
  • A ubiquitous networking is to bring the network into every household.