NETWORK GOALS:
The two main benefits of networking computers are…
The two main benefits of networking computers are…
Communications
Information can be distributed very quickly, such as email and video conferencing.
Saving Money
Resources such as information, software, and hardware can be shared.
CPUs and hard disks can be pooled together to create a more powerful machine.
APPLICATIONS:
A lot of things we take for granted are the result of computer networks.
• Email • Chat
• Web sites
• Sharing of documents and pictures
• Accessing a centralized database of information
• Mobile workers
NETWORK STRUCTURE
The subnet interconnects hosts.
Subnet
Carries messages from host to host. It is made up of telecommunication lines (i.e. circuits, channels, trunks) and switching elements (i.e. IMPs, routers).
Hosts
End user machines or computers.
Q: Is the host part of the subnet?
NETWORK ARCHITECTURES
A set of layers and protocols is called the network architecture.
1. Protocol Hierarchies
Networks are organized as layers to reduce design complexity. Each layer offers services to the higher layers. Between adjacent layers is an interface.
Services – connection oriented and connectionless.
Interface – defines which primitives and services the lower layer will offer to the upper layer.
Primitives – operations such as request, indicate, response, confirm.
2. Design Issues for the Layers
• Mechanism for connection establishment • Rules for data transfer • Error control • Fast sender swamping a slow receiver • Inability of processes to accept long messages • Routing in the case of multiple paths.
OSI REFERENCE MODEL:
The Open Systems Interconnection is the model developed by the International Standards Organization.
Benefits
• Interconnection of different systems (open) • Not limited to a single vendor solution
Negative Aspect
• Systems might be less secure
. Systems might be less stable.
OSI REFERENCE MODEL
7.Application
6.Presentation
5.Session
4.Transport
3.Network
2.Datalink
1.Physical
1. Physical Layer
a) Convert the logical 1’s and 0’s coming from layer 2 into electrical signals.
b) Transmission of the electrical signals over a communication channel.
Main topics:
• Transmission mediums
• Encoding
• Modulation
• RS232 and RS422 standards
• Repeaters Hubs (multi-port repeater)
2. Data Link Layer
a) Error control to compensate for the imperfections of the physical layer.
b) Flow control to keep a fast sender from swamping a slow receiver.
Main topics:
• Framing methods
• Error detection and correction methods
• Flow control • Frame format
• IEEE LAN standards
• Bridges
• Switches (multi-port bridges) e:en-US;font-style:italic’>
3. Network Layer
a) Controls the operation of the subnet.
b) Routing packets from source to destination.
c) Logical addressing.
Main topics:
• Internetworking
• Routing algorithms
• Internet Protocol (IP) addressing
• Routers
4. Transport Layer
a) Provides additional Quality of Service.
b) Heart of the OSI model.
Main topics:
• Connection-oriented and connectionless services
• Transmission Control Protocol (TCP)
• User Datagram Protocol (UDP)
5. Session Layer
a) Allows users on different machines to establish sessions between them.
b) One of the services is managing dialogue control.
c) Token management.
d) Synchronization.
6. Presentation Layer
a) Concerned with the syntax and semantics of the information.
b) Preserves the meaning of the information.
c) Data compression.
d) Data encryption.
7. Application Layer
a) Provides protocols that are commonly needed.
Main topics:
• File Transfer Protocol (FTP)
• HyperText Transfer Protocol (HTTP)
• Simple Mail Transfer Protocol (SMTP)
• Simple Network Management Protocol (SNMP)
• Network File System (NFS)
• Telnet
