2. Comparing Communication Types
Basic communication vocabulary
Synchronous Communication
Asynchronous communication
Broadcast
Multicast
Point-to-point communication

3. General Communication
Synchronous communication
Both sender and receiver active at same time
Example?
Asynchronous communication
Sending and receiving occur at different times

4. General Communication
Based on number of receivers
Broadcast communication: single sender and many receivers (example?)
Multicast: many receivers, but usually a specific group (mailing list)
Point-to-point communication: one specific sender and one specific receiver (example?)

5. Internet’s Communication Properties
Internet supports point-to-point, asynchronous communication
Internet provides a general communication “fabric”

6. Internet’s Communication Properties
Internet is fast enough to mimic synchronous communication
Multicasting is also possible
Chat rooms
Streaming video accessible by anyone (broadcasting)

7. Internet Schematic Diagram

8. Client/Server Structure
Server stores info; client requests it
Most interactions (like loading web page) over the Internet use client/server interaction protocol
Click Web link
Client, requests page (file) from server
Web server responds with page contents
Client/server relationship ends

9. Basic Client/Server Interaction

10. Client/Server Structure
Relationships are brief, so a server can serve many clients “at the same time”
Ask, receive, done
Yahoo, Google, eBay…
One client computer can ask for services from many servers

11. Client/Server Relationships

12. Getting More Connected
Internet is primarily a point-to-point asynchronous communication system
Software has been built to implement the many forms of communication
E.g., Skype “slices up” signals from computer’s microphone and video camera into packet-size blocks

13. Getting More Connected
Content is transferred to other party, whose client reassembles sound and image
Process relies on fast and reliable transmission

14. Computer Addresses IP Addresses
Each computer connected to Internet has unique address
Series of four numbers separated by dots
E.g.,
Range of each number is 0–255
How many possible addresses?

15. IP Addresses

16. Computer Addresses Domain Names IP addresses hard to remember
Internet uses symbolic names for computers based on a hierarchy of domains
A domain is a related group of networked computers

17. Computer Addresses Domain Names Example: turing.cs.millersville.edu
Name of computer is turing
Part of the CS department domain (cs)
Part of the MU domain (millersville)
Which is part of the educational domain (edu)

18. Computer Addresses Domains are hierarchical
Each is a member of the next larger domain
edu is a peer of other top-level domains such as com

19. The .edu Domain

20. The .edu Domain

21. DNS Servers
Domain Name System (DNS) translates hierarchical, human-readable names into IP addresses
Every Internet host knows the IP address of its nearest DNS name server
Hostname needs to be translated to IP address by DNS server for communications

22. DNS Servers DNS uses client/server model
Name is sent to closest DNS server
If not on DNS server, it contacts an authoritative name server (ANS)
ANS has complete list of IP address/domain name mappings for all computers in its domain
Server returns address

23. DNS Servers
Root name servers know addresses of name servers for edu, com, org, etc. domains
Their addresses are preprogrammed into your computer’s net software
Servers listed at (13 + mirrors)

24. Top-Level Domains Top-level domain names (TLDs)
.edu for educational groups
.com for commercial enterprises
.org for organizations
.net for networks
.mil for the military
.gov for government agencies

25. Top-Level Domains
TLDs were expanded to include biz, info, name, travel, etc.
Full list can be found at (ICANN is Internet Corporation for Assigned Names and Numbers)

26. Top-Level Domains Also country code TLDs (ccTLDs)
ca (Canada)
uk (United Kingdom)
fr (France)
Allow domain names to be grouped by their country of origin

29. Following Protocol
Protocol describes the specific technical steps involved in a communication
TCP/IP (Transmission Control Protocol/Internet Protocol) is key protocol used on Internet

30. TCP/IP TCP/IP Postcard Analogy
Internet communication is like sending a novel to your publisher using postcards
Novel is broken into small units that fit on a postcard
“postcards” are numbered to indicate where each belongs in the novel
As each postcard is completed, it is mailed

32. TCP/IP TCP/IP Postcard Analogy
Your publisher eventually receives postcards, but not necessarily in sequential order
Nor do they take the same route
Cards are finally ordered
These “postcards” are really IP packets
They hold: one unit of information, the destination IP, and their sequence number (which packet they are)

34. Packets Are Independent
Each TCP/IP packet can take different route
Congestion and service interruptions do not delay transmissions
The TCP/IP protocol works under adverse conditions
Under heavy traffic packets may be “dropped”

35. Packets Are Independent
If a packet is dropped, recipient can request a resend
Packets can arrive out of order

36. Moving Packets: Wires & More
Internet uses
telephone carriers for long-distance connections
fiber optics (e.g., see
dedicated lines for connections
Transmissions may rely on multiple technologies

37. Far and Near: WAN and LAN
Internet is a collection of wide area networks (WAN)
Machines aren’t geographically close
Internet is a collection of point-to-point channels
Packets take several must visit a sequence of computers (or hops) before they reach their destination

38. A ping is a “please reply” message
See ping.eu
or network-tools.com

39. Far and Near: WAN and LAN
Local area network (LAN)
Computers are geographically close
Usually linked by a single cable or pair of wires
Ethernet is the main technology
Used in labs or buildings