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Goals: review key topics from intro networks course equalize backgrounds identify remedial work ease into course. Review (by yourself): overview error control flow control congestion control routing LANs addressing synthesis: “a day in the life” control timescales.

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networking review
Goals:

review key topics from intro networks course

equalize backgrounds

identify remedial work

ease into course

Review (by yourself):

overview

error control

flow control

congestion control

routing

LANs

addressing

synthesis:

“a day in the life”

control timescales

Networking Review

Readings:

Review your csci5211 or csci4211 textbooks

CSci5221: Introduction

what s a network key features
What’s a Network: Key Features
  • 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

CSci5221: Introduction

what s a network nuts and bolts view
network edge: millions of end-system devices:

pc’s workstations, servers

PDA’s, phones, toasters

running network apps

network core: routers, switches forwarding data

packets: packet switching

calls: circuit switching

communication links

fiber, copper, radio, …

What’s a Network: “Nuts and Bolts” View

router

workstation

server

mobile

local net

regional net

company

net

CSci5221: Introduction

a taxonomy of communication networks

Communication Network

SwitchedCommunication Network

BroadcastCommunication Network

Packet-SwitchedCommunication Network

Circuit-SwitchedCommunication Network

Virtual Circuit Network

Datagram Network

A Taxonomy of Communication Networks
  • Communication networks can be classified based on the way in which the nodes exchange information:

CSci5221: Introduction

broadcast vs switched communication networks
Broadcast vs. Switched Communication Networks
  • Broadcast communication networks
    • Information transmitted by any node is received by every other node in the network
      • E.g., LANs (Ethernet, Wavelan)
    • Problem: coordinate the access of all nodes to the shared communication medium (Multiple Access Problem)
  • Switched communication networks
    • Information is transmitted to a sub-set of designated nodes
      • E.g., WANs (Telephony Network, Internet)
    • Problem: how to forward information to intended node(s)
      • Done by special nodes (e.g., routers, switches) running routing protocols

CSci5221: Introduction

data computer networks
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 3rd world countries

CSci5221: Introduction

circuit switching
End-end resources reserved for “call”

link bandwidth, switch capacity

dedicated resources: no sharing

circuit-like (guaranteed) performance

call setup required

Circuit Switching

CSci5221: Introduction

packet switching
each end-end data stream divided into packets

user A, B packets share network resources

each packet uses full link bandwidth

resources used as needed,

Bandwidth division into “pieces”

Dedicated allocation

Resource reservation

Packet Switching

resource contention:

  • aggregate resource demand can exceed amount available
  • congestion: packets queue, wait for link use
  • store and forward: packets move one hop at a time
    • transmit over link
    • wait turn at next link

CSci5221: Introduction

packet switching vs circuit switching why
“reliability” – no congestion, in order data in circuit-switching

packet switching: better bandwidth use

state, resources: packet switching has less state

good: less control-plane processing resources along the way

More dataplane (address lookup) processing

failure modes (routers/links down):

packet switching routing reconfigures sub-second timescale;

circuit-switching: more complex recovery – need to involve all (downstream) switches on path

Packet Switching vs Circuit Switching: Why?

filled in during class!

CSci5221: Introduction

the internet
The Internet
  • Global scale, general purpose, heterogeneous-technologies, public, computer network
  • Internet Protocol
    • Open standard: Internet Engineering Task Force (IETF) as standard body ( http://www.ietf.org )
    • Technical basis for other types of networks
      • Intranet: enterprise IP network
  • Developed by the research community

CSci5221: Introduction

services provided by the internet
Services Provided by the Internet
  • Shared access to computing resources
    • Telnet (1970’s)
  • Shared access to data/files
    • FTP, NFS, AFS (1980’s)
  • Communication medium over which people interact
    • Email (1980’s), on-line chat rooms (1990’s)
    • Instant messaging, IP Telephony (2000’s)
  • A medium for information dissemination
    • USENET (1980’s)
    • WWW (1990’s)
      • Replacing newspaper, magazine
    • Audio, video (2000’s): peer-to-peer systems
      • Replacing radio, telephony, TV, …

CSci5221: Introduction

origin of internet
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

CSci5221: Introduction

brief history of the internet
Brief History of the Internet
  • 70’s: started as a research project, 56 kbps, < 100 computers
  • 80-83: ARPANET and MILNET split,
  • 85-86: NSF builds NSFNET as backbone, links 6 Supercomputer centers, 1.5 Mbps, 10,000 computers
  • 87-90: link regional networks, NSI (NASA), ESNet(DOE), DARTnet, TWBNet (DARPA), 100,000 computers
  • 90-92: NSFNET moves to 45 Mbps, 16 mid-level networks
  • 94: NSF backbone dismantled, multiple private backbones
  • Today: backbones run at >10 Gbps, >300 millions computers in 150 countries

CSci5221: Introduction

growth of the internet
Growth of the Internet
  • Number of Hosts on the Internet:

Aug. 1981 213

Oct. 1984 1,024

Dec. 1987 28,174

Oct. 1990 313,000

Oct. 1993 2,056,000

Apr. 1995 5,706,000

Jan. 1997 16,146,000

Jan. 1999 56,218,000

Jan. 2001 109,374,000

Jan. 2003 171,638,297

Jul 2004 285,139,107

Jul 2005 353,284,187

CSci5221: Introduction

today s internet
Today’s Internet

Internet: “networks of networks” at global scale!

International lines

NAP

Internic

3G cellular networks

regional

network

national network

on-line services

ISP

ISP

company

university

access via modem

company

LANs

WiFi

CSci5221: Introduction

slide16

MAE-West

Exchange Point

Pacific Bell

Exchange Point

Ameritech Exchange Point

Sprint Exchange Point

MAE-East

Exchange Point

Private

Peering

Private

Peering

Private

Peering

Private

Peering

Private

Peering

Private

Peering

Private

Peering

Private

Peering

InternetNetwork

Leveraging Sprint’s SONET-based, gigabit switch Internet backbone

CSci5221: Introduction

slide17

SprintNetwork

DS3

OC3

OC12

OC48

Legend

Click here for a closer look at theSprint network in Washington state

Click here fora closer lookat the Sprintnetwork on theEast Coast

Seattle

Tacoma

New York

Stockton

Cheyenne

Chicago

Pennsauken

Relay

Wash. DC

San Jose

Roachdale

Kansas City

Anaheim

Click here fora closer lookat the Sprintnetwork inNorthern

California

Atlanta

Fort Worth

Pearl City in Hawaii is

a future network location

Orlando

CSci5221: Introduction

slide18
CSci5221: Introduction

OC1 (45 Mbps), OC2 (155 Mbps), …, OC192 (10 Gbps)

uunet global backbone
UUNET Global BackBone

CSci5221: Introduction

uunet north america backbone
UUNET North America Backbone

CSci5221: Introduction

fundamental issues in networking
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

CSci5221: Introduction

uunet europe
UUNET Europe

CSci5221: Introduction

other key issues in networking
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,
  • ……

CSci5221: Introduction

fundamental problems in networking
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

CSci5221: Introduction

fundamental problems in networking1
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 Challenges in Internet:

large, complex, decentralized, ever-evolving, distributed network of networks!

CSci5221: Introduction

key performance metrics
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

  • Reliability, availability, …
  • Efficiency/overhead of implementation, ……

CSci5221: Introduction

network architecture and structure
Network components: (edge/core) nodes and linksNetwork Architecture and Structure

How do we talk about “structure” of network and its architecture?

  • layered architecture
    • structure allows identification, relationship of complex system’s pieces: layered reference model for discussion
    • layer N builds on services provided by layer N-1
    • Layer N provides service to layer N+1
      • Notions of protocol, service and peer interfaces
  • physical topology, interconnection

CSci5221: Introduction

what s a protocol
human protocols:

“what’s the time?”

“I have a question”

introductions

… specific msgs sent

… specific actions taken when msgs received, or other events

network protocols:

machines rather than humans

all communication activity in Internet governed by protocols

What’s a Protocol?

protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt

CSci5221: Introduction

what s a protocol1
a human protocol and a computer network protocol:

Hi

TCP connection

req.

Hi

TCP connection

reply.

Get http://gaia.cs.umass.edu/index.htm

Got the

time?

2:00

<file>

time

What’s a Protocol?

CSci5221: Introduction

protocols and interfaces
Protocols and Interfaces
  • Protocols: specification/implementation of a “service” or “functionality”
  • Each protocol object has two different interfaces
    • service interface: operations on this protocol
    • peer-to-peer interface: messages exchanged with peer

CSci5221: Introduction

internet protocol stack
application: supporting network applications

ftp, smtp, http

transport: host-host data transfer

tcp, udp

network: routing of datagrams from source to destination

ip, routing protocols

link: data transfer between neighboring network elements

ppp, ethernet

physical: bits “on the wire”

application

transport

network

link

physical

Internet Protocol Stack

CSci5221: Introduction

layering logical communication
E.g.: transport

take data from app

add addressing, reliability check info to form “datagram”

send datagram to peer

wait for peer to ack receipt

analogy: post office

network

link

physical

application

transport

network

link

physical

application

transport

network

link

physical

application

transport

network

link

physical

application

transport

network

link

physical

data

data

data

ack

Layering: Logical Communication

transport

transport

CSci5221: Introduction

layering physical communication

network

link

physical

application

transport

network

link

physical

application

transport

network

link

physical

application

transport

network

link

physical

application

transport

network

link

physical

data

data

Layering: Physical Communication

CSci5221: Introduction

internet hourglass architecture
Internet Hourglass Architecture

CSci5221: Introduction

implications of 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

CSci5221: Introduction

internet names and addresses
Internet Names and Addresses
  • host and domain names
    • other “names”: email addresses, URLs, …
  • IP addresses: logical, with global reachability
    • IPv4: 32 bits, IPv6: 128 bits, “global”
    • two-level hierarchy: network part and host part
      • CIDR: network prefixes, e.g., 128.101.0.0/24
    • Network Address Translation (NAT) complicates global reachability
  • MAC (and other physical-layer) addresses
    • used and understood by “native” physical technologies!

According to Shoch (IEEE COMPCON’78)

    • name: identifies what you want
    • address: identifies where it is
    • route: identifies how to get there

CSci5221: Introduction

a closer look at network structure
network edge: applications and hosts

network core:

routers

network of networks

access networks, physical media: communication links

A Closer Look at Network Structure:

CSci5221: Introduction

the network edge
end systems (hosts):

run application programs

e.g., WWW, email

at “edge of network”

client/server model

client host requests, receives service from server

e.g., WWW client (browser)/ server; email client/server

peer-peer model:

host interaction symmetric

e.g.: Gnutella, KaZaA

The Network Edge:

CSci5221: Introduction

network edge connection oriented service
Goal: data transfer between end sys.

handshaking: setup (prepare for) data transfer ahead of time

Hello, hello back human protocol

set up “state” in two communicating hosts

TCP - Transmission Control Protocol

Internet’s connection-oriented service

TCP service[RFC 793]

reliable, in-order byte-stream data transfer

loss: acknowledgements and retransmissions

flow control:

sender won’t overwhelm receiver

congestion control:

senders “slow down sending rate” when network congested

Network Edge: Connection-Oriented Service

CSci5221: Introduction

network edge connectionless service
Goal: data transfer between end systems

same as before!

UDP - User Datagram Protocol [RFC 768]: Internet’s connectionless service

unreliable data transfer

no flow control

no congestion control

App’s using TCP:

HTTP (WWW), FTP (file transfer), Telnet (remote login), SMTP (email)

App’s using UDP:

streaming media, teleconferencing, Internet telephony

Network Edge: Connectionless Service

CSci5221: Introduction

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?

Access Networks and Physical Media

CSci5221: Introduction

example access net home network
Typical home network components:

ADSL or cable modem

router/firewall

Ethernet

wireless access

point

wireless

laptops

to/from

cable

headend

cable

modem

router/

firewall

wireless

access

point

Ethernet

(switched)

Example Access Net: Home Network

CSci5221: Introduction

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”

The Network Core

CSci5221: Introduction

network core routing
Goal: move data among routers from source to dest.Network Core: Routing

datagram packet network:

  • destination address determines next hop
  • routes may change during session
  • analogy: driving, asking directions
  • No notion of call state

virtual circuit network:

  • packet carries tag, tag determines next hop
  • fixed path (for call) determined at call setup time
  • routers maintain little per-call state; resources not allocated

circuit-switched network:

  • call allocated time slots of bandwidth at each link
  • fixed path (for call) determined at call setup
  • switches maintain lots of per call state (what?): resource allocation

CSci5221: Introduction

internet structure network of networks
roughly hierarchical

at center: “tier-1” ISPs (e.g., UUNet, BBN/Genuity, Sprint, AT&T), national/international coverage

treat each other as equals

NAP

Tier-1 providers also interconnect at (public/private) Internet exchange points, or private peering links

Tier-1 providers interconnect (peer) privately

Internet Structure: Network of Networks

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

CSci5221: Introduction

internet structure network of networks1
“Tier-2” ISPs: smaller (often regional) ISPs

Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs

IXP

Tier-2 ISPs also peer privately with each other, interconnect at IXPs

  • Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet
  • tier-2 ISP is customer of

tier-1 provider

Tier-2 ISP

Tier-2 ISP

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

Tier-2 ISP

Tier-2 ISP

Tier-2 ISP

Internet Structure: Network of Networks

CSci5221: Introduction

internet structure network of networks2
“Tier-3” ISPs and local ISPs

last hop (“access”) network (closest to end systems)

Tier 3

ISP

local

ISP

local

ISP

local

ISP

local

ISP

local

ISP

local

ISP

local

ISP

local

ISP

Local and tier- 3 ISPs are customers of

higher tier ISPs

connecting them to rest of Internet

Tier-2 ISP

Tier-2 ISP

Tier 1 ISP

NAP

Tier 1 ISP

Tier 1 ISP

Tier-2 ISP

Tier-2 ISP

Tier-2 ISP

Internet Structure: Network of Networks

CSci5221: Introduction

internet structure network of networks3
a packet passes through many networks!

Tier 3

ISP

local

ISP

local

ISP

local

ISP

local

ISP

local

ISP

local

ISP

local

ISP

local

ISP

NAP

Tier-2 ISP

Tier-2 ISP

Tier 1 ISP

Try a

traceroute!

Tier 1 ISP

Tier 1 ISP

Tier-2 ISP

Tier-2 ISP

Tier-2 ISP

Internet Structure: Network of Networks

host/network edge:

IP addresses, port no’s

network core:

intra-domain vs.

inter-domain routing

CSci5221: Introduction

who runs the internet
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, …;

CSci5221: Introduction

internet governing bodies
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)

CSci5221: Introduction

internet names and addresses1
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)

CSci5221: Introduction

internet standardization process
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.”

CSci5221: Introduction

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