NAME: __________________________ DATE: _____________
CISC231 - CCNA 1
Final Exam Review

1. When connectionless protocols are implemented at the lower layers of the OSI model, what is usually used to acknowledge that the data was received and to request the retransmission of missing data?
Upper-layer connection-oriented protocols 2. What type of cable should be used to connect to different devices? like devices?
Straight through Cross-over 3. Which OSI layer does IP rely on to determine whether packets have been lost and to request retransmission?
Transport
4. Describe the 7 layers of the OSI model.
Application Layer 7
This top layer defines the language and syntax that programs use to communicate with other programs. The application layer represents the purpose of communicating in the first place. For example, a program in a client workstation uses commands to request data from a program in the server. Common functions at this layer are opening, closing, reading and writing files, transferring files and e-mail messages, executing remote jobs and obtaining directory information about network resources.
Presentation Layer 6
When data are transmitted between different types of computer systems, the presentation layer negotiates and manages the way data are represented and encoded. For example, it provides a common denominator between ASCII and EBCDIC machines as well as between different floating point and binary formats. Sun's XDR and OSI's ASN.1 are two protocols used for this purpose. This layer is also used for encryption and decryption.

Session Layer 5
Provides coordination of the communications in an orderly manner. It determines one-way or two-way communications and manages the dialog between both parties; for example, making sure that the previous request has been fulfilled before the next one is sent. It also marks significant parts of the transmitted data with checkpoints to allow for fast recovery in the event of a connection failure.
In practice, this layer is often not used or services within this layer are sometimes incorporated into the transport layer.
Transport Layer 4
This layer is responsible for overall end-to-end validity and integrity of the transmission. The lower layers may drop packets, but the transport layer performs a sequence check on the data and ensures that if a 12MB file is sent, the full 12MB is received.
"OSI transport services" include layers 1 through 4, collectively responsible for delivering a complete message or file from sending to receiving station without error.
Lower Layers
Layers 3 through 1 are responsible for moving packets from the sending station to the receiving station.
Network Layer 3
The network layer establishes the route between the sender and receiver across switching points, which are typically routers. The most ubiquitous example of this layer is the IP protocol in TCP/IP (see TCP/IP). IPX, SNA and AppleTalk are other examples of routable protocols, which means that they include a network address and a station address in their addressing system. This layer is also the switching function of the dial-up telephone system. If all stations are contained within a single network segment, then the routing capability in this layer is not required. See layer 3 switch.
Data Link Layer 2
The data link is responsible for node to node validity and integrity of the transmission. The transmitted bits are divided into frames; for example, an Ethernet, Token Ring or FDDI frame in local area networks (LANs). Frame relay and ATM are also at Layer 2. Layers 1 and 2 are required for every type of communications. For more on this layer, see data link protocol.
Physical Layer 1
The physical layer is responsible for passing bits onto and receiving them from the connecting medium. This layer has no understanding of the meaning of the bits, but deals with the electrical and mechanical characteristics of the signals and signaling methods. For example,