Part 0: Networking Review

1
Part 0 Networking Review

• Goals
• review key topics from intro networks course
• equalize backgrounds
• identify remedial work
• ease into course

• Overview
• overview
• error control
• flow control
• congestion control
• routing
• LANs
• addressing
• synthesis
• a day in the life
• control timescales

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Whats a network nuts and bolts view
router
workstation

• network edge millions of end-system devices
• pcs workstations, servers
• PDAs, phones, toasters
• running network apps
• network core routers, switches forwarding data
• packets packet switching
• calls circuit switching
• communication links
• fiber, copper, radio,

server
mobile
local net
regional net
company net
3
Whats a protocol?

• a human protocol and a computer network protocol

4
Whats a protocol?

• human protocols
• whats 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

protocols define format, order of msgs sent and
received among network entities, and actions
taken on msg transmission, receipt
5
A closer look at network structure

• network edge applications and hosts
• network core
• routers
• network of networks
• access networks, physical media communication
  links

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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

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Network edge connection-oriented service

• Goal data transfer between end systems
• 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
• Internets connection-oriented service

• TCP service RFC 793
• reliable, in-order byte-stream data transfer
• loss acknowledgements and retransmissions
• flow control
• sender wont overwhelm receiver
• congestion control
• senders slow down sending rate when network
  congested

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Network edge connectionless service

• Goal data transfer between end systems
• same as before!
• UDP - User Datagram Protocol RFC 768
  Internets connectionless service
• unreliable data transfer
• no flow control
• no congestion control

• Apps using TCP
• HTTP (WWW), BitTorrent (file transfer), Telnet
  (remote login), SMTP (email)
• Apps using UDP
• streaming media, teleconferencing, Internet
  telephony

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The Network Core

• mesh of interconnected routers
• 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

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Network Core Circuit Switching

• End-end resources reserved for call
• link bandwidth, switch capacity
• dedicated resources no sharing
• circuit-like (guaranteed) performance
• call setup required

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Network Core 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,

• 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

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Network core routing

• Goal move data among routers from source to dest.

• 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

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Packet switching vs circuit switching why?

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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?

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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)
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We have seen pieces of network

• edge, core, links
• protocols

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

• layered architecture
• structure allows identification, relationship of
  complex systems pieces layered reference model
  for discussion
• layer N builds on services provided by layer N-1
• layer N provides service to layer N1
• physical topology, interconnection

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Internet protocol stack

• application supporting network applications
• ftp, smtp, http, BitTorrent
• 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

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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

transport
transport
19
Layering physical communication
20
Internet structure network of networks

• roughly hierarchical
• at center tier-1 ISPs (e.g., UUNet,
  BBN/Genuity, Sprint, ATT), national/international
  coverage
• treat each other as equals

Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
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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

Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
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Internet structure network of networks

• Tier-3 ISPs and local ISPs
• last hop (access) network (closest to end
  systems)

Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
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Internet structure network of networks

• a packet passes through many networks!

Tier 1 ISP
Try a traceroute!
Tier 1 ISP
Tier 1 ISP