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11 Fragmentation and Reassembly (Segmentation – OSI) Exchange data between two entities Characterized as sequence of PDUs of some bounded size — Application level message Lower-level protocols may need to break data up into smaller blocks Communications network may only accept blocks of up to a certain size — ATM 53 octets — Ethernet 1526 octets More efficient error control — Smaller retransmission Fairer — Prevent station monopolizing medium Smaller buffers Provision of checkpoint and restart/recovery operations Disadvantages of Fragmentation Make PDUs as large as possible because — PDU contains some control information — Smaller block, larger overhead PDU arrival generates interrupt — Smaller blocks, more interrupts More time processing smaller, more numerous PDUs Reassembly Segmented data must be reassembled into messages More complex if PDUs out of order PDUS and Fragmentation (Copied from chapter 2 fig 2.4) Connection Control Connectionless.
11 Fragmentation and Reassembly (Segmentation – OSI) Exchange data between two entities Characterized as sequence of PDUs of some bounded size — Application level message Lower-level protocols may need to break data up into smaller blocks Communications network may only accept blocks of up to a certain size — ATM 53 octets — Ethernet 1526 octets More efficient error control — Smaller retransmission Fairer — Prevent station monopolizing medium Smaller buffers Provision of checkpoint and restart/recovery operations Disadvantages of Fragmentation Make PDUs as large as possible because — PDU contains some control information — Smaller block, larger overhead PDU arrival generates interrupt — Smaller blocks, more interrupts More time processing smaller, more numerous PDUs Reassembly Segmented data must be reassembled into messages More complex if PDUs out of order PDUS and Fragmentation (Copied from chapter 2 fig 2.4) Connection Control Connectionless.
Communications network may only accept blocks of up to a certain ______
Communications network may only accept blocks of up to a certain ______
size
Lower-level protocols may need to break data up into smaller ______
Lower-level protocols may need to break data up into smaller ______
blocks
More efficient error control — Smaller ______
More efficient error control — Smaller ______
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More complex if PDUs out of ______
More complex if PDUs out of ______
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Segmented data must be reassembled into ______
Segmented data must be reassembled into ______
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Fragmentation and Reassembly is part of which layer of the OSI model?
Fragmentation and Reassembly is part of which layer of the OSI model?
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Communications network may only accept blocks of up to a certain ______
Communications network may only accept blocks of up to a certain ______
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Make PDUs as large as possible because — PDU contains some control ______
Make PDUs as large as possible because — PDU contains some control ______
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Connection Control and Connectionless are types of ______
Connection Control and Connectionless are types of ______
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Study Notes
Protocol Functions
- A small set of functions form the basis of all protocols
- Not all protocols have all functions, which reduces duplication of effort
- The same type of function may be present in protocols at different levels
Encapsulation
- Data is usually transferred in blocks called protocol data units (PDUs)
- Each PDU contains data and control information
- Some PDUs only contain control information
- There are three categories of control:
- Address: of sender and/or receiver
- Error-detecting code: e.g. frame check sequence
- Protocol control: additional information to implement protocol functions
- Encapsulation is the addition of control information to data
- Data accepted or generated by an entity is encapsulated into a PDU containing data and control information
- Examples of encapsulation protocols: TFTP, HDLC, frame relay, ATM, AAL5, LLC, IEEE 802.3, IEEE 802
Other Protocol Functions
- Fragmentation and reassembly
- Connection control
- Ordered delivery
- Flow control
- Error control
- Addressing
- Multiplexing
- Transmission services
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Description
Test your knowledge of the small set of functions that form the basis of all internet protocols. From encapsulation to error control, this quiz covers the essential protocol functions defined by William Stallings in Data and Computer Communications 7th Edition Chapter 18.
