OSI Model

Name 4 protocols that operate at Application layer 7?

1. Email protocols SMTP and POP3 2. Telnet 3. HTTP 4. FTP 5. SNMP

What is the function of Physical Layer 1?

Anything to do with cable, physical pins etc. or electrical signals is the physical layers 1 function.

What is a PDU?

Protocol Data Unit. It is a combination of the dat and the header. E.g. A layer 5 data and header would be known as L5 PDU

What is windowing?

Windowing refers to the amount of data the sender is allowed to transmit without waiting for an ACK

Name the four primary tasks of the Presentation layer 6?

1. Compatibility with operating system 2. Encapsulation of data for network transmission 3. Data formatting (ASCII, binary) 4. Data encryption, compression, translation E.g. File types that are used at the presentation layer are JPEG, GIF, MPEG etc.

What are the four main specifications that run on the Data link layer 2?

1. Ethernet 2. High Data Link Control (HDLC) 3. Point-to-Point Protocol (PPP) 4. Frame Relay

In the OSI model what is a header?

As data flows down an OSI model each layer adds a header that will be removed by the same layer on the other end. The Data Link Layer 2 adds both a header and a trailer.

What is the function of Network Layer 3?

It is the IP layer sometimes called the routing layer. It checks what valid pathes exist between the router and the destination and what is the optimum path.

What is the function of Session Layer 5?

It is the manager of the two-way communication between the two remote hosts. It handles the creation, maintenance and tear down of communication between the two hosts.

What is the function of Application Layer 7?

It is where the end user interacts with the network. It ensures that the remote commucication partner is available and that the needed communications resources exist.

What is the function of Data Link Layer 2?

MAC addresses and error detection (not recovery) operate at this layer. Switches, AP's and DSL modems operate on this layer.

What does the term OSI mean?

Open Systems Interconnection

What is the function of Presentation Layer 6?

Performs data transformations to provide a common interface for user applications, including encryption

What is PAR?

Positive Acknowledgement with Retransmission. The sender is waiting for a positive message the the data was received. If that message isn't received, the data is retransmitted.

What is meant by the term "Sliding Window"?

Refers to the dynamic adjustment of the window size. (TCP)

What is the function of Transport Layer 4?

To establish a logical end to end connection between the two hosts, segment the data received from the upper layers, this layer provides error recovery. Desides between TCP / UDP