Bit Oriented Protocol Flashcards
(21 cards)
Uses bit sequences to control information
Bit Oriented Protocols
The data sequence of the frame is a sequence of bits to be
interpreted by the upper layer as text, graphic, audio, video,
and so on
Bit Oriented Protocols
A group of communication protocols of the data link layer for
transmitting data between network points or nodes.
High Level Data Link Control (HDLC)
Two types of stations are present, the primary station
sends commands and the secondary station can respond
to received commands
Normal Response Mode (NRM)
Used for both point-to-point and multipoint
communications
Normal Response Mode (NRM)
balanced, which means each station can
both send command and respond to commands
Asynchronous Balanced Mode (ABM)
This type of transfer mode is only for point-to-point
communications
Asynchronous Balanced Mode (ABM)
A bit - oriented protocol where each frame contains up to six fields. The
structure varies according to the type of frame.
HDLC Frame
It is an 8-bit sequence that marks the beginning and the end of the frame. The bit pattern of the flag is 01111110
Flag
It contains the address of the receiver. If the frame is sent by the primary station, it contains the address(es) of the secondary station(s). If it is sent by the secondary station, it contains the address of the primary station. The address field may be from 1 byte to several
bytes
Address
(sometimes referred to as the frame header) It is 1 or 2 bytes containing flow and error control information
Control
carries the data from the network layer. Its length may vary from one network to another.
Payload
It is a 2 byte or 4 bytes frame check sequence for error detection. The standard code used is CRC
(cyclic redundancy code)
FCS (Frame Check Sequence)
Types of HDLC Frames
I Frame
S Frame
U Frame
carry user data from the network layer. They also include flow
and error control information that is piggybacked on user data. The first bit of control field
of I-frame is 0.
I Frame −Information frames
do not contain information field. They are used for flow and
error control when piggybacking is not required. The first two bits of control field of S-frame
is 10.
S-frame −Supervisory frames
used for myriad miscellaneous functions, like link
management. It may contain an information field, if required. The first two bits of control
field of U-frame is 11.
U-frame −Un-numbered frames
In bit stuffing, if A ZERO (0) and FIVE CONSECUTIVE (1) BITS are
encountered, no matter the value of the next bit, an extra 0 will be added.
This is to ensure that the receiver will not misinterpret the values
resembling the flag within the data as real flags.
Stuffing
Asynchronous or synchronous link (dials in to
ISP, links between routers)
PPP - Point to Point Control
Encapsulated signaling messages on ISDN D channel
LAPD - Link Access Procedure - D Channel
