Ch05� Layers 3&4

Ch05� Layers 3&4 - Layer 2 Mini-Quiz Review...

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Copyright © 2008 Thomas W. Bajzek Layer 2 Mini-Quiz Review End-of-frame may be indicated by a bit-pattern, a byte pattern, or a byte-count (e.g., Ethernet) When two or more messages interfere with each other, it is a collision. This cannot happen on a ring. To manage transmission errors requires transmission of redundant info (so the receiver can detect an error), feedback to the sender (so the sender can know of the error), and sender awareness of transmission history so it can re-send what is required. CRC is an example of polynomial correction. It is better than parity checking because it can detect more types of errors. Sliding window is a Fow-control method associated with ARQ error management. It controls Fow by specifying the amount of data it is willing to accept from the sender. A collision domain is the set of devices connected to a bus network (the devices whose messages are subject to collisions with each other). The concept is relevant in CSMA networks.
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Copyright © 2008 Thomas W. Bajzek Layer-4: Transport Layer (e.g., TCP, UDP) Provides a network interface to serve the Application Layer Assures delivery of data from end-to-end, in sequence Manages Fow-control and error recovery Manages virtual circuits for connection-based applications Layer-3: Network Layer (IP) Handles network addressing Handles the routing of packets through the network, i.e. beyond the local subnet Handles fragmentation as required by Layer-2 Helps resolve symbolic names Other protocol suites exist, which we won’t cover IPX/SPX, SNA, X.25, etc.
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Copyright © 2008 Thomas W. Bajzek Connectionless & Connection-oriented Protocols UDP (User Datagram Protocol) For isolated transactions, not sequential processes Query-response transactions Domain name queries, time queries, etc. TCP (Transmission Control Protocol) Connection-oriented, for sequential processes Session-oriented applications Interactive sessions, ±le transfers, etc.
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Thomas W. Bajzek Transmission Control Protocol (TCP) Links the Application Layer(5) to the Network Layer(3) Responsible for end-to-end delivery of message streams Integrity and sequencing of messages Used for connection-oriented applications (telnet, FTP, HTTP, etc.) Performs segmentation, reassembly and sequencing of messages longer than one packet Manages error detection and correction (where needed) to assure reliable delivery of the data stream Header length Source port
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Ch05� Layers 3&4 - Layer 2 Mini-Quiz Review...

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