Data net

1. 05/01/09 MCSE201 : Communication Network 1
Layered Architecture
Layered Architecture
Anjan.K
II Sem M.Tech
Dept of CSE
M.S.R.I.T
1

2. 05/01/09 MCSE201 : Communication Network 2
Outline
Outline
 Layered Architecture
• Need For Layering
◦OSI Reference Model
◦TCP/IP Model
◦Problems
◦Socket Programming
◦ TCP
◦ UDP
◦ Sockets Demo
 Applications
FTP
• IP Utilities
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MCSE201 : Communication Network

3. 05/01/09 MCSE201 : Communication Network 3
Need For Layering
 Allows Complex problems are decomposed in to
small manageable units.
 Implementation details of the layer are abstracted.
Separation of implementation and specification
 Layers are work as one by sharing the services
provided by each other.
 Layering allows reuse functionality i.e., lower layers
implement common once.
 Provide framework to implement multiple specific
protocols per layer

4. 05/01/09 MCSE201 : Communication Network 4
05/01/09 MCSE201 : Communication Network 4
The ISO/OSI Reference Model
Need For Standard Architecture is various
vendors with various architectures. Hence ISO:
International Standards Organization
(Estd in 1947)
(
OSI: Open Systems Interconnection
(1970’s)
(
Oneor m
orenodes
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ithin thenetw
ork
Endhost
Application
Presentation
Session
Transport
Netw
ork
Datalink
Physical
Netw
ork
Datalink
Physical
Netw
ork
Datalink
Physical
Endhost
Application
Presentation
Session
Transport
Netw
ork
Datalink
Physical
Copyright © Computer Networks by Larry Peterson
 Physical
• Transmit raw bits over the
medium.
 Data Link
◦ Abstraction of an error free
medium (frame)
m
◦ Flow Control
 Network
◦ Routing (Packets)
R
◦ Addressing (IP address)
A
 Transport
◦ Error free end to end, type of
service
◦ Port Addresses
 Session
◦ establishing Sessions,
◦ dialog Control & token
management
 Presentation - Handles Syntax and
semantics
 Application- Protocols commonly
needed by applications (http,ftp
,etc.,).

5. 05/01/09 MCSE201 : Communication Network 5
TCP/IP Reference Model
 Also called the Internet
Architecture
 No Strict enforcement of
layering
 Usually shown as a 4 or 5
layer model
Copyright © Communication Networks by Leon Garcia

6. Problem
05/01/09 MCSE201 : Communication Network
 Suppose that the TCP entity receives a
1.5 megabyte file from the application
layer and that the IP layer is willing to
carry blocks of maximum size 1500
bytes. Calculate the amount of
overhead incurred from segmenting
the file into packet-sized units.
 Solution:
• MTU=1500 MSS= 1460
• 1.5 Mbyte / 1460 byte = 1027.4,
therefore 1028 blocks are needed to
transfer the file.
• Overhead = ((1028 x 1500 -
1.5M)/1.5M) x 100 = 2.8%
Copyright © Communication Networks by Leon Garcia
1.5MB File
Application
1.5MB File
MTU 1
MSS+
Header
MTU 2 MTU 1028
………..

7. 05/01/09 MCSE201 : Communication Network 7
7
Application Programming Interfaces(API)- Sockets
Application Programming Interfaces(API)- Sockets
 API are required to implement an Network application
 Socket interface, part of Berkeley Unix, is now supported
by all OS.
 Socket - point where a local abstraction process
attaches to the network.
 Interface defines operations
◦ Creating a socket
◦ Attaching the socket to the network,
◦ Sending/Receiving messages and
◦ closing the socket.
05/01/09 MCSE201 : Communication Network

8. 05/01/09 MCSE201 : Communication Network 8
Socket System Calls
Socket System Calls
 Create a socket
int socket(int family, int type, int protocol);
 Bind –binds socket to local address
int bind(int socket,struct sockaddr *address, int addr.len);
 Listen defines how many connections can be pending
int listen(int socket,int backlog);
 Accept carries out the passive operation
int accept( int socket,struct sockaddr *address,int
addr.len)
a
int connect(int socket,struct sockaddr *address, int addr.len);
int send(int socket, char *message, int msg.len, int flags);
int recv(int socket, char *buffer, int buf.len, int flags);
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9. 05/01/09 MCSE201 : Communication Network 9
Socket Calls
Socket Calls
05/01/09 MCSE201 : Communication Network 9
Copyright © Communication Networks by Leon Garcia
TCP Socket Calls UDP Socket Calls

11. 05/01/09 MCSE201 : Communication Network 11
Application Protocol Examples
Application Protocol Underlying
Transport
Protocol
Electronic Mail SMTP [RFC 2821] TCP
Web HTTP [RFC 1945] TCP
File Transfer FTP [RFC 959] TCP
Streaming
Multimedia
RTP [RFC 1889] TCP/UDP
Internet Telephony SIP [RFC 3261] UDP
Remote terminal
access
Telnet [RFC 854] TCP
Domain Name
server
DNS[RFC 883] UDP

12. 05/01/09 MCSE201 : Communication Network 12
File Transfer Protocol (FTP) [RFC 959]
 FTP client contacts FTP server at
port 21, specifying TCP as transport
protocol
 Client obtains authorization over
control connection
 Client browses remote directory by
sending commands over control
connection.
 When server receives a command
for a file transfer, the server opens
a TCP data connection to client
 After transferring one file, server
closes connection.
FTP
client
FTP
server
TCP control
connection
port 21
TCP data connection
port 20

13. 05/01/09 MCSE201 : Communication Network 13
IP Utilities
IP Utilities
05/01/09 MCSE201 : Communication Network 13
 PING
◦ Determines whether a host
is online and available and
make use of ICMP messages
◦ Inform the sending host
about errors in IP datagram
◦ Used to measure round-trip
delay between hosts
 NETSTAT
◦ Queries about its TCP/IP
network status
◦ Finds status of network
drivers and their interface
cards
 TRACEROUTE – debugging tool
◦ Used to track route of packet
from local host to remote host
◦ Informs about latency and
reachability
◦ Makes use of both ICMP and
UDP
 IPCONFIG
◦ Utility to display TCP/IP
information about a host
available in Windows
◦ Simplest form returns IP
address, subnet mask, default
gateway, DNS servers
◦ Available with various options

14. 05/01/09 MCSE201 : Communication Network 14
Summary
Summary
 Layered Architecture
◦ OSI Reference Model
◦ TCP/IP Model
◦ Socket Programming with Demo
◦ TCP
• UDP
 Applications
◦ FTP
◦ IP Utilities
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MCSE201 : Communication Network

15. 05/01/09 MCSE201 : Communication Network 15
References
References
[1] Larry L Peterson, “Communication
Networks”,3rd
Edition
[2] S.keshav, “An Engineering Approach to
Computer Networking”,Pearson
Education
[3] Andrew.S Tannenbaum, “Computer
Network”, 4th Edition
[4] Leon Garcia et.al., “Communication
Networks”, 2nd
Edition
[5] RFC’s From http://www.ietf.org
[6] Leslie Miller, “ISO Reference Model of OSI”
ACM transaction in Nov 1981
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