1. Chapter 1: Introduction
Our goal:
get “feel” and terminology
more depth, detail later in course
approach:
use Internet as example
Overview:
what’s the Internet
what’s a protocol?
network edge
network core
access net, physical media
Internet/ISP structure
performance: loss, delay
protocol layers, service models
network modeling
Introduction

2. What’s the Internet: “nuts and bolts” view
millions of connected computing devices: hosts = end systems
running network apps
communication links
fiber, copper, radio, satellite
transmission rate = bandwidth
routers: forward packets (chunks of data)
local ISP
company
network
regional ISP
router
workstation
server
mobile
Introduction

3. ISPs –Internet service providers
e.g.Dial-up, Broadband,High speed LANs,wireless
protocols control sending, receiving of msgs
e.g., TCP, IP, HTTP, FTP, PPP
Internet: “network of networks”
router
workstation
server
mobile
local ISP
regional ISP
company
network
Introduction

4. What’s the Internet: a service view
communication infrastructure enables distributed applications:
Web, , games, e-commerce, file sharing
communication services provided to apps:
Connectionless unreliable
connection-oriented reliable
Introduction

5. 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
protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt
Introduction

6. What’s a protocol? a human protocol and a computer network protocol:Hi
TCP connection
request Hi
TCP connection
response
Got the
time?
Get
2:00
<file>
time
Introduction

7. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge
1.3 Network core
1.4 Network access and physical media
1.5 Internet structure and ISPs
1.6 Delay & loss in packet-switched networks
1.7 Protocol layers, service models
1.8 History
Introduction

8. A closer look at network structure:
network edge: applications and hosts
network core:
routers
network of networks
access networks, physical media: communication links
Introduction

9. The network edge: end systems (hosts): client/server model
run application programs
e.g. Web,
at “edge of network”
client/server model
client host requests, receives service from always-on server
e.g. Web browser/server; client/server
peer-peer model:
minimal (or no) use of dedicated servers
e.g. Skype,
Introduction

10. 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
Internet’s connection-oriented service
TCP service
reliable, in-order byte-stream data transfer
loss: acknowledgements and retransmissions
flow control:
sender won’t overcome receiver
congestion control:
senders “slow down sending rate” when network congested
Introduction

11. Network edge: connectionless service
Goal: data transfer between end systems
same as before!
UDP - User Datagram Protocol
connectionless
unreliable data transfer
no flow control
no congestion control
App’s using TCP:
HTTP (Web), FTP (file transfer), SMTP ( )
App’s using UDP:
streaming media, teleconferencing,
Introduction

12. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge
1.3 Network core
1.4 Network access and physical media
1.5 Internet structure and ISPs
1.6 Delay & loss in packet-switched networks
1.7 Protocol layers, service models
1.8 History
Introduction

13. 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
1-13 13

14. Circuit Switching
In circuit switched networks the resources needed along a path to provide for communication between the end systems are reserved for the duration of communication session
In packet switched networks these resources are not reserved
A sessions messages use the resources on demand & as a consequence may have to wait (that is , queue) for access to communication link

15. Telephone networks are examples of the circuit switched networks
When one person wants to send information to another over a telephone network
Before the sender can send information the network must establish a connection between sender & receiver this connection is called circuit

16. When networks established circuit it is also reserves a constant transmission rate in the networks links for duration of the connection
Since bandwidth has been reserved for this sender to receiver connection
The sender can transfer data to receiver at the guaranteed constant rate

17. 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
Introduction

18. 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
Introduction

19. Circuit Switching: FDM and TDM
4 users
Example:
FDM
frequency
time
TDM
frequency
time
Two simple multiple access control techniques.
Each mobile’s share of the bandwidth is divided into portions for the uplink and the downlink. Also, possibly, out of band signaling.
As we will see, used in AMPS, GSM, IS-54/136
Introduction

20. 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:
Node receives complete packet before forwarding
Introduction

21. Packet Switching: Statistical Multiplexing
100 Mb/s
Ethernet C A
statistical multiplexing
1.5 Mb/s B
queue of packets
waiting for output
link D E
Sequence of A & B packets does not have fixed pattern, shared on demand  statistical multiplexing.
Introduction

22. Packet-switching: store-and-forward
Store and forward transmission means that switch must receive entire packet before it can began to transmit first bit of the packet onto the link
Each packet switch has multiple links attached to it
For each attached link the packet switch has an output buffer also called an output queue which stores packets that router is about to send into link
Introduction

23. If the arriving packets needs to be transmitted across a link but finds the link busy with the transmission of another packet then arriving packet must wait in the output buffer
The amount of buffer space is finite an arriving packets may find that buffer is completely filled with other packets waiting for transmission
In this case packet loss will occur either the arriving packet or one of the already queued packets will dropped
Introduction
1-23 23

24. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge
1.3 Network core
1.4 Network access and physical media
1.5 Internet structure and ISPs
1.6 Delay & loss in packet-switched networks
1.7 Protocol layers, service models
1.8 History
Introduction

25. 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

26. Access networks and physical media
Access networks classified into three categories:
Residential Access: connecting home end system into network
Company Access: connecting end systems in a business or educational institution into network
Wireless Access: connecting end systems (i.e. mobile networks) into end system
Introduction
1-26 26

27. 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”
Residential access refers to connecting a home end system( typically a PCs) to an router
One form of residential access is the dial-up-modem
Introduction

28. 2.Company access: local area networks
company/univ local area network (LAN) connects end system to edge router
Ethernet:
shared or dedicated link connects end system and router
10 Mbs, 100Mbps,
Introduction

29. 3.Wireless access networks
shared wireless access network connects end system to router
via base station “access point”
wireless LANs:
54 Mbps
wider-area wireless access 3G
base
station
mobile
hosts
router
Introduction

30. Physical Media Twisted Pair (TP) two insulated copper wires
Category : traditional phone wires, 10 Mbps Ethernet
Category : 100Mbps Ethernet
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
Introduction

31. Physical Media: coax, fiber
Fiber optic cable:
glass fiber carrying light pulses, each pulse a bit
high-speed operation:
high-speed point-to-point transmission
low error rate: resistant to electromagnetic noise
Coaxial cable:
two concentric copper conductors
bidirectional
baseband:
single channel on cable
broadband:
multiple channels on cable
Introduction

32. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge
1.3 Network core
1.4 Network access and physical media
1.5 Delay & loss in packet-switched networks
1.6Protocol layers, service models
1.7 History
Introduction

33. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge
1.3 Network core
1.4 Network access and physical media
1.5 Delay & loss in packet-switched networks
1.6 Protocol layers, service models
Introduction

34. How do loss and delay occur?
packets queue in router buffers
packet arrival rate to link exceeds output link capacity
packets queue, wait for turn
packet being transmitted (delay) A
free (available) buffers: arriving packets
dropped (loss) if no free buffers
packets queueing (delay) B
Introduction

35. Four sources of packet delay
1. nodal processing:
check bit errors
determine output link
time it takes to process packet in network node (swith,router,hub)
2. queueing
time waiting at output link for transmission
depends on congestion level of router A B
propagation
transmission
nodal
processing
queueing
Introduction

36. Delay in packet-switched networks
3. Transmission delay:
R=link bandwidth (bps)
i.e.Tranmission Rate
L=packet length (bits)
time to send bits into link = L/R
4. Propagation delay:
d = length of physical link
s = propagation speed in medium
propagation delay = d/s A B
propagation
transmission
nodal
processing
queueing
Introduction

37. Protocol “Layers” Networks are complex! many “pieces”: hosts routers
links of various media
applications
protocols
hardware, software
Introduction

38. Internet protocol stack
application: where network applications & their application layer protocols reside
FTP, SMTP, HTTP (supporting network applications)
transport: transport application layer message between client & server
TCP, UDP
network: routing of datagrams from source to destination (moving network layer packets known as datagrams from one host to another) IP
application
transport
network
link
physical
Introduction

39. link: The internet’s network layer routes a datagram through a series of packet switches (called router in the internet) between the source & destination
data transfer between neighboring network elements (to move packets from one node (host or packet switch) to the next node in the route, the network layer relies on the services of the link layer)
(In link layer packets are known as frames)
Ex: PPP (ponit to point), Ethernet
physical: While the job of the link layer is to move entire frames from one network element to an adjacent network element
The job of the physical layer is to move the individual bits within the frame from one node to the next node
bits “on the wire”

40. Encapsulation source destination application transport network link
message M
application
transport
network
link
physical
segment Ht M Ht
datagram Ht Hn M Hn
frame Ht Hn Hl M
link
physical
switch
destination
network
link
physical Ht Hn M Ht Hn Hl M M
application
transport
network
link
physical Ht Hn M Ht M Ht Hn M
router Ht Hn Hl M
Introduction

41. Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge
1.3 Network core
1.4 Network access and physical media
1.5 Internet structure and ISPs
1.6 Delay & loss in packet-switched networks
1.7 Protocol layers, service models
Introduction