Model Co Networks

The Differences Between SAN and NAS

Storage Area Networks (SANs) and Network Attached Storage (NAS) both provide networked storage solutions. A NAS is a single storage device that operates on data files, while a SAN is a local network of multiple devices.

The differences between NAS and SAN can be seen when comparing their cabling and how they’re connected to the system, as well as how communication to the device occurs.

SAN vs. NAS Technology

A NAS unit includes a dedicated hardware device that connects to a local area network, usually through an Ethernet connection.

This NAS server authenticates clients and manages file operations in much the same manner as traditional file servers, through well-established network protocols.

To reduce the costs that occur with traditional file servers, NAS devices generally run an embedded operating system on simplified hardware and lack peripherals like a monitor or keyboard.

A SAN commonly utilizes Fibre Channel interconnects and connects a set of storage devices that are able to share data with one another.

SAN vs. NAS Usage Models

The administrator of a home or small business network can connect one NAS device to their local area network. The NAS maintains its own IP address comparable to computers and other TCP/IP devices. Using a software program that is provided with the NAS hardware, the network administrator can set up automatic or manual backups and file copies between the NAS and all the other connected devices.

The NAS holds many gigabytes or terabytes of data. Administrators can add additional storage capacity to their network by installing additional NAS devices, although each NAS operates independently.

Administrators of large enterprise networks may require many terabytes of centralized file storage or extremely high-speed file transfer operations.

Where installing an army of many NAS devices is not a practical option, administrators can instead install a SAN containing a high-performance disk array to provide the needed scalability and performance.

SAN/NAS Convergence

As internet technologies like ​TCP/IP and Ethernet have proliferated worldwide, some SAN products are making the transition from Fibre Channel to the same IP-based approach NAS uses. Also, with the rapid improvements in disk storage technology, today’s NAS devices now offer capacities and performance that once were only possible with SAN.

These two industry factors have led to a partial convergence of NAS and SAN approaches to network storage.

KEY TERMS in Computer Networks

Following are some important terms, which are frequently used in context of Computer Networks.

Terms Definition
1. ISO The OSI model is a product of the Open Systems Interconnection project at the International Organization for Standardization. ISO is a voluntary organization.
2. OSI Model Open System Interconnection is a model consisting of seven logical layers.
3. TCP/IP Model Transmission Control Protocol and Internet Protocol Model is based on four layer model which is based on Protocols.
4. UTP Unshielded Twisted Pair cable is a Wired/Guided media which consists of two conductors usually copper, each with its own colour plastic insulator
5. STP Shielded Twisted Pair cable is a Wired/Guided media has a metal foil or braided-mesh covering which encases each pair of insulated conductors. Shielding also eliminates crosstalk
6. PPP Point-to-Point connection is a protocol which is used as a communication link between two devices.
7. LAN Local Area Network is designed for small areas such as an office, group of building or a factory.
8. WAN Wide Area Network is used for the network that covers large distance such as cover states of a country
9. MAN Metropolitan Area Network uses the similar technology as LAN. It is designed to extend over the entire city.
10. Crosstalk Undesired effect of one circuit on another circuit. It can occur when one line picks up some signals travelling down another line. Example: telephone conversation when one can hear background conversations. It can be eliminated by shielding each pair of twisted pair cable.
11. PSTN Public Switched Telephone Network consists of telephone lines, cellular networks, satellites for communication, fiber optic cables etc. It is the combination of world’s (national, local and regional) circuit switched telephone network.
12. File Transfer, Access and Management (FTAM) Standard mechanism to access files and manages it. Users can access files in a remote computer and manage it.
13. Analog Transmission The signal is continuously variable in amplitude and frequency. Power requirement is high when compared with Digital Transmission.
14. Digital Transmission It is a sequence of voltage pulses. It is basically a series of discrete pulses. Security is better than Analog Transmission.

Comparison of OSI Reference Model and TCP/IP Reference Model

Following are some major differences between OSI Reference Model and TCP/IP Reference Model, with diagrammatic comparison below.

OSI(Open System Interconnection) TCP/IP(Transmission Control Protocol / Internet Protocol)
1. OSI is a generic, protocol independent standard, acting as a communication gateway between the network and end user. 1. TCP/IP model is based on standard protocols around which the Internet has developed. It is a communication protocol, which allows connection of hosts over a network.
2. In OSI model the transport layer guarantees the delivery of packets. 2. In TCP/IP model the transport layer does not guarantees delivery of packets. Still the TCP/IP model is more reliable.
3. Follows vertical approach. 3. Follows horizontal approach.
4. OSI model has a separate Presentation layer and Session layer. 4. TCP/IP does not have a separate Presentation layer or Session layer.
5. OSI is a reference model around which the networks are built. Generally it is used as a guidance tool. 5. TCP/IP model is, in a way implementation of the OSI model.
6. Network layer of OSI model provides both connection oriented and connectionless service. 6. The Network layer in TCP/IP model provides connectionless service.
7. OSI model has a problem of fitting the protocols into the model. 7. TCP/IP model does not fit any protocol
8. Protocols are hidden in OSI model and are easily replaced as the technology changes. 8. In TCP/IP replacing protocol is not easy.
9. OSI model defines services, interfaces and protocols very clearly and makes clear distinction between them. It is protocol independent. 9. In TCP/IP, services, interfaces and protocols are not clearly separated. It is also protocol dependent.
10. It has 7 layers 10. It has 4 layers

Diagrammatic Comparison between OSI Reference Model and TCP/IP Reference Model

between OSI (7 layers) and TCP/IP (4 layers) Model

The TCP/IP Reference Model

TCP/IP means Transmission Control Protocol and Internet Protocol. It is the network model used in the current Internet architecture as well. Protocols are set of rules which govern every possible communication over a network. These protocols describe the movement of data between the source and destination or the internet. These protocols offer simple naming and addressing schemes.

 

Diagram Representation of TCP/IP Model


Overview of TCP/IP reference model

TCP/IP that is Transmission Control Protocol and Internet Protocol was developed by Department of Defence’s Project Research Agency (ARPA, later DARPA) as a part of a research project of network interconnection to connect remote machines.

The features that stood out during the research, which led to making the TCP/IP reference model were:

  • Support for a flexible architecture. Adding more machines to a network was easy.
  • The network was robust, and connections remained intact untill the source and destination machines were functioning.

The overall idea was to allow one application on one computer to talk to(send data packets) another application running on different computer.


Description of different TCP/IP protocols

Layer 1: Host-to-network Layer

  1. Lowest layer of the all.
  2. Protocol is used to connect to the host, so that the packets can be sent over it.
  3. Varies from host to host and network to network.

 

Layer 2: Internet layer

  1. Selection of a packet switching network which is based on a connectionless internetwork layer is called a internet layer.
  2. It is the layer which holds the whole architecture together.
  3. It helps the packet to travel independently to the destination.
  4. Order in which packets are received is different from the way they are sent.
  5. IP (Internet Protocol) is used in this layer.

 

Layer 3: Transport Layer

  1. It decides if data transmission should be on parallel path or single path.
  2. Functions such as multiplexing, segmenting or splitting on the data is done by transport layer.
  3. The applications can read and write to the transport layer.
  4. Transport layer adds header information to the data.
  5. Transport layer breaks the message (data) into small units so that they are handled more efficiently by the network layer.
  6. Transport layer also arrange the packets to be sent, in sequence.

 

Layer 4: Application Layer

The TCP/IP specifications described a lot of applications that were at the top of the protocol stack. Some of them were TELNET, FTP, SMTP, DNS etc.

  1. TELNET is a two-way communication protocol which allows connecting to a remote machine and run applications on it.
  2. FTP(File Transfer Protocol) is a protocol, that allows File transfer amongst computer users connected over a network. It is reliable, simple and efficient.
  3. SMTP(Simple Mail Transport Protocol) is a protocol, which is used to transport electronic mail between a source and destination, directed via a route.
  4. DNS(Domain Name Server) resolves an IP address into a textual address for Hosts connected over a network.

Merits of TCP/IP model

  1. It operated independently.
  2. It is scalable.
  3. Client/server architecture.
  4. Supports a number of routing protocols.
  5. Can be used to establish a connection between two computers.

Demerits of TCP/IP

  1. In this, the transport layer does not guarantee delivery of packets.
  2. The model cannot be used in any other application.
  3. Replacing protocol is not easy.
  4. It has not clearly separated its services, interfaces and protocols.