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Network

Network consists of:

1. Circuit-switched network (CSW).
2. Packet-switched network (PSW).
   1. X.25
   2. Frame relay (FR)
   3. Leased line (LL)

Serial line encapsulation:

1. Link Access Procedure Balanced (LAPB)
   1. Provides a connection-oriented, reliable data-link protocol.
   2. Used for unreliable analog media.
   3. Support link compression.
2. Poing-to-Point Protocol (PPP)
   1. Based on RFCs 1332 and 1661.
   2. Provides support for authentication through PAP and CHAP.
   3. Includes a protocol type field along with a Link Control Protocol.
   4. Frame Format: Flag Address Control (FAC) - Protocol - Data
3. High-level Data Link Control (HDLC)
   1. Cisco default for synchronous serial lines.
   2. Implemented differently by different vendors.
   3. Does not provide windowing or flow control.
   4. Flag Address Control (FAC)
4. Synchronous Data Link Control (SDLC)
   1. Initial standard for encapsulation.
   2. Basis for HDLC and PPP.
   3. Used in SNA environments as a connection-oriented service.

Frame field format:

1. Flag (7Fh)
2. Address
3. Control
   1. Unnumbered
   2. Supervisory
   3. Information-type
4. Data
5. FCS (Frame Check Sequence)
6. Flag (7Eh)