Data Communication - 1 | Computer Networks - Computer Science Engineering (CSE) PDF Download

1. INTRODUCTION TO NETWORKS

1. Network Definition

• A network can be defined as two or more computers connected together in such a way that they can share resources. The purpose of a network is to share resources.

A resource may be:

• A file
• A folder
• A printer
• A disk drive
• Or just about anything else that exists on a computer

• A network is simply a collection of computers or other hardware devices that are connected together, either physically or logically, using special hardware and software, to allow them to exchange information and cooperate. Networking is the term that describes the processes involved in designing, implementing, upgrading, managing and otherwise working with networks and network technologies

Advantages of networking.

• Connectivity and Communication
• Data Sharing
• Hardware Sharing
• Internet Access
• Internet Access Sharing
• Data Security and Management
• Performance Enhancement and Balancing
• Entertainment

2. NETWORK ARCHITECTURE

Layered system with alternative abstractions available at a given layer

Protocols

• Protocol defines the interfaces between the layers in the same system and with the layers of peer system
• Building blocks of a network architecture
• Each protocol object has two different interfaces
  • service interface: operations on this protocol
• peer-to-peer interface: messages exchanged with peer
• Term “protocol” is overloaded
• specification of peer-to-peer interface
• module that implements this interface

Interfaces

• Protocol Specification: prose, pseudo-code, state transition diagram
• Interoperable: when two or more protocols that implement the specification accurately
• IETF: Internet Engineering Task Force

Description of Layers

Physical Layer

• Handles the transmission of raw bits over a communication link

Data Link Layer

• Collects a stream of bits into a larger aggregate called a frame
• Network adaptor along with device driver in OS implement the protocol in this layer
• Frames are actually delivered to hosts

Network Layer

• Handles routing among nodes within a packet-switched network
• Unit of data exchanged between nodes in this layer is called a packet

The lower three layers are implemented on all network nodes

Transport Layer

• Implements a process-to-process channel
• Unit of data exchanges in this layer is called a message

Session Layer

• Provides a name space that is used to tie together the potentially different transport streams that are part of a single application

Presentation Layer

• Concerned about the format of data exchanged between peers

Application Layer

• Standardize common type of exchanges

The transport layer and the higher layers typically run only on end-hosts and not on the intermediate switches and routers

Internet Architecture

  Three main features

• Does not imply strict layering. The application is free to bypass the defined transport layers and to directly use IP or other underlying networks
• An hour-glass shape – wide at the top, narrow in the middle and wide at the bottom. IP serves as the focal point for the architecture
• In order for a new protocol to be officially included in the architecture, there needs to be both a protocol specification and at least one (and preferably two) representative implementations of the specification

Application Programming Interface

• Interface exported by the network
• Since most network protocols are implemented (those in the high protocol stack) in software and nearly all computer systems implement their network protocols as part of the operating system, when we refer to the interface “exported by the network”, we are generally referring to the interface that the OS provides to its networking subsystem
• The interface is called the network Application Programming Interface (API)
• Interface exported by the network
• Since most network protocols are implemented (those in the high protocol stack) in software and nearly all computer systems implement their network protocols as part of the operating system, when we refer to the interface “exported by the network”, we are generally referring to the interface that the OS provides to its networking subsystem
• The interface is called the network Application Programming Interface (API)
• Socket Interface was originally provided by the Berkeley distribution of Unix

Now supported in virtually all operating systems

• Each protocol provides a certain set of services, and the API provides a syntax by which those services can be invoked in this particular OS

Socket

Socket Family

• PF_INET denotes the Internet family
• PF_UNIX denotes the Unix pipe facility
• PF_PACKET denotes direct access to the network interface (i.e., it bypasses the TCP/IP protocol stack)
• Socket Type
• SOCK_STREAM is used to denote a byte stream
• SOCK_DGRAM is an alternative that denotes a message oriented service, such as that provided by UDP 

Creating a Socket

int sockfd = socket(address_family, type, protocol);

• The socket number returned is the socket descriptor for the newly created socket

 int sockfd = socket (PF_INET, SOCK_STREAM, 0);

 int sockfd = socket (PF_INET, SOCK_DGRAM, 0);

•  The combination of PF_INET and SOCK_STREAM implies TCP

Bind

•  Binds the newly created socket to the specified address i.e. the network address of the local participant (the server)
• Address is a data structure which combines IP and port

Listen

• Defines how many connections can be pending on the specified socket

Accept

• Carries out the passive open
• Blocking operation
• Does not return until a remote participant has established a connection
• When it does, it returns a new socket that corresponds to the new established connection and the address argument contains the remote participant’s address

Client

o     Application performs active open

o     It says who it wants to communicate with

Client invokes

•  int connect (int socket, struct sockaddr *address, int addr_len)

 Connect

•  Does not return until TCP has successfully established a connection at which application is free to begin sending data
• Address contains remote machine’s address

 4. NETWORK PERFORMANCE