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114 Chapter 3: OSI Reference Model & Layered Communication
Figure 3-19 provides a visual representation of the same-layer interaction concepts.
Figure 3-19
Same-Layer Interactions on Different Computers
Table 3-14 summarizes the concepts behind error recovery and lists the behavior of three
popular error-recovery protocols.
Table 3-13
Protocol Characteristics: Recovery and Connections
Connected?
Reliable?
Examples
Connection-oriented
Yes
LLC type 2 (802.2), TCP (TCP/IP), SPX
(NetWare), X.25
Connection-oriented
No
Frame Relay virtual circuits, ATM virtual
connections, PPP
Connectionless
Yes
TFTP, NetWare NCP (without Packet Burst)
Connectionless
No
UDP, IP, IPX, AppleTalk DDP, most Layer 3
protocols, 802.3, 802.5
Table 3-14
Examples of Error-Recovery Protocols and Their Features
Feature
TCP
SPX
LLC2
Acknowledges data in both directions?
Yes
Yes
Yes
Provides forward acknowledgment?
Yes
Yes
Yes
Counts bytes or frame/packets?
Bytes
Packets
Frames
Necessitates resending of all data, or
just one part and wait when resending?
One and wait
Resend all
Resend all
Host A
Application
Presentation
Session
Transport
Network
Data Link
Physical
Network
Data Link
Physical
Router 1
Host B
Application
Presentation
Session
Transport
Network
Data Link
Physical
ch03.fm Page 114 Monday, March 20, 2000 4:58 PM