Introduction

Internet is a Network of Networks

In your office or at your home, there is a private network
In your universities, there is a wide area private network
In HK, there is a wide area network
In Asia / Europe / America / Africa , there are regional networks
And then there is a Internet in our blue planet

Internet is PC + server + wireless laptop + access point + wired links + router ...

1. Millions of connected computing devices (Where hosts = end systems) and they are running network applications
2. There are communication links - fiber, copper, radio, satellite using rate = bandwidth (bit per second)
3. There are routers to forward packets

When you are on the Internet

1. You have an IP address
2. You are speaking with a protocol [http / https / ftp / MSN ...]
3. Your computer is using a IP Format

What is Protocols

1. Protocols control sending / receiving of messages
2. E.g. TCP / IP / Http / Skype ...
3. Normally undergoes Internet standards [RFC / IETF]
4. Protocols define format, order of messages sent and received among network entities, and actions taken on message transmission, receipt

What services do Internet offer?

1. Communication infrastructure - Web, VoIP, email, games, e-commerce, file sharing
2. Reliable data delivery from source to destination - TCP, Transmission Control Protocol
3. Best effort data transfer service - Unreliable data transfer, no flow control, no congestion control - UDP, User Datagram protocol
   

How hosts connect ?

1. end systems (hosts) run application programs like Web & email
2. Client / Server model - client host requests, receives service from always-on server
3. Peer-Peer model - minimal use of dedicated server E.g. BT, Foxy, Skype
4. Handshaking before TCP - setup "state" in two communicating hosts

TCP / UDP

1. Applications using TCP - http (web), FTP (file transfer), Telnet (remote login), SMTP (email)
2. Applications using UDP - streaming media, teleconferencing, DNS, Internet telephony

How to connect to Internet?

1. residential access nets
2. institutional access networks (school, company)
3. mobile access networks
4. You are in shared or dedicated network?

Local area network

1. company/univ local area network (LAN) connects end system to edge router
2. Ethernet: 10 Mbs, 100Mbps, 1Gbps, 10Gbps
3. modern configuration: end systems connect into Ethernet switch
4. G= Giga, bps=bit per second *not byte per second
5. Home network component - Modem, router/firewall/NAT, Ethernet, Wifi Access point

Wireless network

1. Wireless LAN: 802.11a/b/g/n: 11 or 54 or 300Mbps http://zh.wikipedia.org/wiki/IEEE_802.11
2. Wider-area wireless network - WiMax (10 Mbps), GPRS / HSDPA

Physical media

1. Bit: propagates between transmitter/receiver pairs
2. physical link: what lies between transmitter & receiver
3. guided media: signals propagate in solid (copper, fiber, coax)
4. unguided media: signals propagate freely e.g. radio
5. two insulated copper wires
   Category 3: traditional phone wires, 10 Mbps Ethernet
   Category 5: 100Mbps Ethernet
6. Fiber optic cable: glass fiber carrying light pulses, each pulse a bit
   high-speed operation: high-speed point-to-point transmission (e.g., 10’s-100’s Gbps)
   low error rate: repeaters spaced far apart ; immune to electromagnetic noise
7. Radio link types:
   • terrestrial microwave e.g. up to 45 Mbps channels
   • LAN (e.g., Wifi) 11Mbps, 54 Mbps
   • wide-area (e.g., cellular) 3G cellular: ~ 1 Mbps
   • satellite 1Kbps to 45Mbps channel

Network core concept

Network is a cloud

Network contains cloud of routers and we are usually at the end-host.

Switching concept

1. Circuit switching - Dedicated circuit E.g. Telephone
   • Dedicated resource: No sharing
   • Guaranteed performance
   • Call setup required
   • FDM / TDM
2. Packet-switching - discrete "chunks" E.g. Skype
   • Statistical Multiplexing
   • TDM
   • packets: data + metadata (header) = self-describing data
   • store and forward: Metadata allows us to forward packets when we
     want
   • Message segmenting
3. Packet-switching vs circuit switching
   • Packet switching allows more users to use network!
   • Circuit switching is more stable

Internet structure

We are using local ISP as our Internet provider in HK. Like HKBN, netvigator, i-Cable

For business, we have 01link, pacnet

For International, we have HKIX

Since there are many connecting device, delay is a must in Internet.

Measuring delay:

1. Throughput = (bits/time unit)
2. Always use Round trip time (RTT)
   

Delay checking software:

1. Traceroute
2. Ping

Network layering

We divide the network in 7-level layer

1. OSI model, 7-layer protocol
2. Physical layer- wires and Ethernet card
3. Link Layer - Mac address
4. Network layer - IP address
5. Transport - Protocols
6. session & presentation & Application - E.g. Web browser

Internet History

1970: ALOHAnet satellite network in Hawaii
1974: Cerf and Kahn - architecture for interconnecting networks
1976: Ethernet at Xerox PARC
late70’s: proprietary architectures: DECnet, SNA, XNA
late 70’s: switching fixed length packets (ATM precursor)
1979: ARPAnet has 200 nodes
1983: deployment of TCP/IP
1982: smtp e-mail protocol defined
1983: DNS defined
for name-to-IPaddress translation
1985: ftp protocol defined
1988: TCP congestion control

Early 1990’s: ARPAnet decommissioned
1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995)
early 1990s: Web hypertext [Bush 1945, Nelson 1960’s] HTML, HTTP: Berners-Lee
1994: Mosaic, later Netscape
late 1990’s: commercialization of the Web
1990-2000: more killer apps: instant messaging, P2P file sharing network security to
forefront
est. 50 million host, 100 million+ users
backbone links running at Gbps

2007:
~500 million hosts
Voice, Video over IP
P2P applications: BitTorrent (file sharing) Skype (VoIP), PPLive (video)
more applications: YouTube, gaming
wireless, mobility