Software Tools and Techniques

Class Notes for Nov. 14, 2002

By: Jody Platt, Hongming Li

Contents:

Networks and Network Programming
1.1 Network Layers
1.2 Addressing
1.3 Domain Name Service
1.4 Ports
1.5 Sockets
Homework 9
2.1 Functional
2.2 Program
2.3 Data Flow

· Networks can enable machines to talk to each other (Machine A can talk to Machine B)

· Communication software was written to be used for network communication between different machines, and what path to take.

1.1 Network layers (OSI):

Application	Accomplishes using goals: File transfer: FTP,NFS Email: IMAP, POP Remote logon: telnet, ssh Time synchronization: NTP
Presentation	How Is Information Presented? Big Endin (e.g., ASCII)/ Little Endin(e.g., EBCIPIC)
Session	Organize and Synchronize Data Exchange. Ex. Getright Download Program
Transport	It provides end-to-end issues.. Is all the data being received ? Does it need to be resent? Ex. TCP, UPD, TP4
Network	Addressing + Routing Handling network wide connection Ex. IP, IPX, XNS, SNA.
Data link	It sends blocks of data (frames) with the necessary synchronization, error control and flow control
Physical	It deals with the mechanical, electrical, procedural characteristics to establish, maintain and deactivate the physical link. Ex. Ethernet, Frame relay, x.25, Token Ring, FDDI.

1.2 ADDRESSING: how are machines known to each other?

Each machine/node has an IP address. May have a separate address for each interface.
The IP address is 4 bytes within decimal
Format: xxx.xxx.xxx.xxx
Example: Paradox IP =136.142.118.6x
The address has 2 parts: Subnet address (S.) and Host address (H.).
32-bit addressing.
IP Address Classes:

v Class A: 127 networks of 16 million host addresses (S.H.H.H).--------0xxxxxxx

v Class B: 16,000 networks of 65,000 host addresses (S.S.H.H).-------10xxxxxx

v Class C: 2 million networks of 254 host addresses (S.S.S.H).---------110xxxxx

v Class D: Multicast address -------------------------------------------------------1110xxxx

v Class E: Experimental -------------------------------------------------------------11111xxx

                 Examples: Pitt has Class B. Anything on the internet 136.142.x.x is from Pitt.
                 Carlow College has 2 Class C's.

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1.3 DOMAIN NAME SERVICE: how are machines known to humans?

Used to convert name to IP
Each machine is configured for one or more name servers
Domain name servers have 1) a table to convert names to IP addresses; and 2) table with a list of other servers to request information from
Top Level Domains: .com, .org, .edu, .uk, .ir, .au

1.4 PORTS: enable simultaneous communication with machines

A port is a 16-bit number
A socket is a port number
Port numbers exist so that one machine can talk to several others at one time.
0-1023= "well known ports" which are commonly used ports that are agreed upon for specific tasks:

v 21=ftp

v 23=telnet

v 80=http

v 119=ntp

    For a list of port number assignments, see: /etc/services
    type netstat | more to list all connections in use

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    1.5 SOCKET: interface between a process and networking software

Creates one endpoint of a "virtual wire" between two processes
Identified by IP: port ↔ IP: port
Connection= 2 endpoints

2 . Homework 9

2.1 Functional

CLIENT	SERVER
1. send a name to server
	2. add the name on the list
3. get the list and print it

2.2 Program

CLIENT	SERVER
	1. Creates a master socket or passive socket . Listen and waits for connection to be accepted.
2. Read the name
3. Connect to server
4. Write the record to server
	5. Read record from client
	6. Append the record to the file
	7. Send entire file to client
8. Receive all the records from server
9. Read all record and print them
10 .Exit

2.3 Data Flow

CLIENT SERVER

webpage of homework 9

http://www2.sis.pitt.edu/~klynch/Homework9.html