Format

1
Format

• LAN Devices
• LAN Topologies
• Connectionless and connection-oriented services
• Packet switching and circuit switching

2
Hub

• A hub receives incoming packets, possibly
  amplifies the electrical signal, and broadcasts
  these packets out to all devices on the network
• Hubs can support little in the way of
  sophisticated networking.
• do not read any of the data passing through them
• are not aware of a packet's source or
  destination.

3
Hub OSI
Layer 1 devices in the OSI model Physical Layer
coordinates the functions required to transmit a
bit stream over a physical medium
Application
Application
Presentation
Presentation
Session
Session
Transport
Transport
Network
Network
Hub
Data link
Data link
Physical
Physical
1
1
4
Hub Application
5
Switch

• A switch contains more "intelligence" and a
  slightly higher price tag than a hub.
• Switches are capable of inspecting the received
  data packets-determining the source and
  destination device of that packet, and forwarding
  that packet appropriately.
• conserve network bandwidth and offer generally
  better performance than hubs.

6
Switch OSI

• Switch operate in Layer 1 2 of OSI model
• It given access to physical address of the data
  packet Source and destination address

Application
Application
Presentation
Presentation
Session
Session
Transport
Transport
Switch
Network
Network
2
2
Data link
Data link
Physical
Physical
1
1
7
Switch Application
8
Router

• Router responsible for the source to destination
  delivery of packet possibly across multiple
  network
• Routers are capable of inspecting the received
  data packets-determining the node of that packet,
  and forwarding that packet appropriately.

9
Router OSI

• Router operate in Layer 1,2 3 of OSI model
• It given access to physical logical address of
  the data packet nodes addresses

Application
Application
Presentation
Presentation
Session
Session
Router
Transport
Transport
3
3
Network
Network
2
2
Data link
Data link
Click here
Physical
Physical
1
1
10
Gateway

• A gateway is generally software installed within
  a router.
• It able to translate from one protocol to
  another.
• Eg It can accept a packet formatted for
  AppleTalk and convert it to a packet formatted
  for TCP/IP before forwarding it.

11
Gateway OSI

• Gateway operate in all Layers of the OSI model

Gateway
Application
Application
7
7
Presentation
6
6
Presentation
5
Session
Session
5
Transport
Transport
4
4
3
3
Network
Network
2
2
Data link
Data link
Physical
Physical
1
1
12
Encapsulation
source
message
application transport network link physical
segment
datagram
frame
switch
destination
application transport network link physical
router
13
Simple LAN Topologies

• Physical topology
• Physical layout of a network

• Bus topology consists of a single cable called a
  bus connecting all nodes on a network without
  intervening connectivity devices

Credit to White
14
Simple LAN Topologies

• Terminators stop signals after they have reached
  their destination
• Signal bounce
• Phenomenon in which signals travel endlessly
  between the two ends of a bus network

Terminated bus network
Credit to White
15
Simple LAN Topologies

• Star topology
• Every node on the network is connected through a
  central device
• The device could be a hub or a switch or a router!

Credit to White
16
Hybrid LAN Topologies

• Hybrid topology
• Complex combination of the simple physical
  topologies
• Star-wired ring
• Star-wired topologies use physical layout of a
  star in conjunction with token ring-passing data
  transmission method

Credit to White
17
Hybrid LAN Topologies

• Star-wired bus
• In a star-wired bus topology, groups of
  workstations are star-connected to hubs and then
  networked via a single bus

Credit to White
18
Hybrid LAN Topologies

• Daisy-Chained
• Daisy chain is linked series of devices

Daisy-chained star-wired bus topology
Credit to White
19
Simple LAN Topologies

• Ring topology
• Each node is connected to the two nearest nodes
  so the entire network forms a circle
• Active topology
• Each workstation transmits data
• Each workstation functions as a repeater

Credit to Fourozan
20
A closer look at network structure

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

21
The network edge

• end systems (hosts)
• run application programs
• e.g. Web, email
• at edge of network
• 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. Gnutella, KaZaA, Skype

22
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

23
Network edge connectionless service

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

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

24
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

25
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

26
Network Core Circuit Switching

• network resources (e.g., bandwidth) divided into
  pieces
• pieces allocated to calls
• resource piece idle if not used by owning call
  (no sharing)

• dividing link bandwidth into pieces
• frequency division
• time division

27
Network Core 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
• Node receives complete packet before forwarding

• 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
28
Packet switching versus circuit switching

• Is packet switching a slam dunk winner?

• Great for bursty data
• resource sharing
• simpler, no call setup
• Excessive congestion packet delay and loss
• protocols needed for reliable data transfer,
  congestion control
• Q How to provide circuit-like behavior?
• bandwidth guarantees needed for audio/video apps
• still an unsolved problem

Q human analogies of reserved resources
(circuit switching) versus on-demand allocation
(packet-switching)?