Computer and Software

1
The TCP/IP Stack and Methods of Access
Nathan A. Webers
2
TCP/IP

• Native to the UNIX Environment
• Does not require any translation.
• Not Native to Windows
• requires the use of Winsock to implement TCP/IP
  functions

3
TCP/IP Stack Layers

• Consists of four layers
• Link Layer
• Network Layer
• Transport Layer
• Application Layer

4
Link Layer

• Lowest layer of the stack
• Composed of hardware device drivers
• Handles incoming packets and passes them on to
  the Network Layer

5
Network Layer

• Home of Internet Protocol (IP)
• ICMP for Ping Traceroute
• IP is used for all other internet functions.
• IP Addresses- unique numbers
• IP Routing- getting items to the right
  destination.

6
Transport Layer

• Home of Transmission Control Protocol (TCP)
• User Datagram Protocol (UDP)
• TCP creates a virtual circuit
• TCP has specific port access
• Certain ports reserved for specific functions

7
Application Layer

• Point where user interacts with the network
• Includes telnet, ftp, mail, www applications
• Applications in this layer use either TCP or UDP
  to communicate with other machines

8
An Application Example with Telnet

• Convert name to IP number
• Telnet tells transport layer to connect via TCP
• TCP initiates conversation with remote user
• Packets go from IP layer to Link layer then go on
  through routers
• Distant users TCP layer replies in similar
  fashion
• Information gets exchanged between users

9
TCP/IP Stack Diagram
10
Winsock

• Short for Windows Socket
• Was borne from Berkeley Socket Distribution (BSD)
• Designed to implement TCP/IP protocols for
  Windows systems
• Provides an open API standard

11
Why use Winsock?

• Winsock is as close to TCP/IP protocols as you
  can get without implementing them yourself
• Minimizes number of layers of software needed to
  access internet services
• First-hand access to error values and
  incoming/outgoing data gt more control

12
Winsock for Windows CE

• Windows CE uses ver. 1.1 subset
• Can be implemented in 16 or 32-bits (winsock.dll
  or wsock32.dll)
• Does not support asynchronous functions

13
Winsock Function Examples

• WSAStartup()
• Called before any other WSA function is used
• WSACleanup()
• When through using Windows Sockets, use this to
  free allocated resources used by the application
• Must be used 11 with WSAStartup()

14
Winsock Function Examples

• WSAGetLastError()
• Gets the last error message in the thread
• Database Routines
• Used to get information on the host, protocol,
  and server
• Do not use asynchronous functions in Windows CE

15
Communications Model in Windows CE
16
Basic SRES interaction with TCP/IP
17
Additional Information

• http//www.stardust.com/winsock/index.htm
• provides information on the Winsock API,
  including header file information and description
  of functions involved with Winsock
• http//www.msdn.microsoft.com/library/
  backgrnd/html/msdn_comm_mod.htm
• Discusses the communication involved in Windows
  CE
• http//info.acm.org/crossroads/xrds1-1/tcpjmy.html
  
• Under the hood of the Internet An overview of
  the TCP/IP Protocol Suite -by Jason Yanowitz