Layering Models Flashcards
What are the Internet Standard Bodies?
- ISOC (Internet Society): oversees the Internet standard development process
- IAB (Internet Architecture Board): oversees the IETF and IRTF
- IETF (Internet Engineering Task Force): develops standards and publishes RFCs.
- IESG (Internet Engineering Steering Group): approves RFCs
- ICANN (Internet Corporation for Assigned Names and Numbers): Sets policy on the Internet
- IANA (Internet Assigned Numbers Authority): manages domains and IP addresses
What is packet switching?
Data is split into small chunks called ‘packets’ and each packet is sent individually.
Individual packets might get lost but others will get through.
Each packet’s header contains information such as ‘source’, ‘destination’ and ‘number of packets’.
Why does the OSI and Internet Model use layers and encapsulation?
Layers are used for flexibility and interoperability
Modularity: Dividing the network process into layers, making it easier to update and modify without changing other layers
Interoperability: Different devices and systems are able to communicate with each other, even by different vendors
Scalability: Allows new technologies to be added to the network without changing the underlying infrastructure
Reliability: If a problem occurs, it can be easily isolated without affecting other layers
What are the advantages of the OSI Model?
It is a generic model and acts as a guidance tool to develop any networking model.
It is a layered model – changes in one layer do not affect other layers
It supports both connectionless and connection-oriented services.
What are the disadvantages of the OSI Model?
It restricts practical implementation
It is a theoretical model – it does not consider the availability of current technology
The Session and Presentation layer have very little functionality
There is duplication of services present in layers – there are more than one layers offering addressing, flow control, error control
The TCP/IP Model was preferred by academia
OSI was from Europe and Americans hesitated to adopt it
What are the layers of the OSI Model?
- Physical Layer: hardware layer
- Data Link Layer: creates channels for the physical layer without errors
- Network Layer: controls operations of the network and handles routing
- Transport Layer: accepts data from the Session Layer and responsible for packetisation and congestion control
- Session Layer: manages sessions between source and destination
- Presentation: responsible for representation of data and its encodings
- Application Layer: holds user-created applications and protocols, such as FTP, Telnet, SMTP, HTTP
What are the advantages of the Internet Model?
TCP/IP is wildly successful
It is so successful that its standards (RFCs) are open and freely available – anyone can join in
It is an industry-standard model that can be effectively deployed in practical networking problems
It is interoperable – it allows cross-platform communications among heterogenous networks
It is an open protocol suite, and it is not owned by any particular institute – anyone can use it
It is a scalable, client-server architecture. This allows networks to be added without disrupting the current services
It assigns an IP address to each computer on the network, thus making each device identifiable over the network
It assigns each site a domain name and provides a name and address resolution services
What are the disadvantages of the Internet Model?
It was created after TCP/IP
It is only good for describing TCP/IP
It is not generic in nature – it fails to represent any protocol stack other than the TCP/IP suite. Example: it cannot describe the Bluetooth protocol
It does not clearly separate the concepts of services, interfaces, and protocols. It is not suitable to describe new technologies in new networks.
It does not distinguish between the data link and the physical layers, which have very different functionalities. The data link layer should be concerned with the transmission of frames. The physical layer should lay down the physical characteristics of transmission, such as data encoding.
It was initially designed and implemented for wide-area networks. It is not optimised for small networks like LAN and PAN
TCP/IP was carefully designed and well-implemented. Other protocols were developed ad hoc and proved unsuitable in the long run. However, they are still being used due to the popularity of the model
It is fuzzy in nature – it does not make a distinction between model and implementation
Why does TCP/IP have no security features?
Internet protocols were mainly designed and developed in Academia. This had a significant effect on the security of the Internet, and little regard was given to issues of privacy or authentication.
The management and use of cryptography have an overhead – this is an extra workload on servers, and some people are unwilling to pay this price.
There are newer protocols and secure extensions to existing protocols, such as HTTPS for the Web and SMTPS for email.
