Transcript Data link control protocols

Data link control
protocols
HDLC & Point to point
protocol
HDLC
High-level Data Link Control (HDLC) is a bit-oriented
protocol for communication over point-to-point and
multipoint links. It implements the ARQ mechanisms.
HDLC Protocol explanation divided into
following parts:
Configurations and Transfer Modes
Frames
Control Field
Types of Transmission modes:
Normal response mode
Asynchronous balanced mode
TYPES OF FRAMES
Information frame: Used to transport data and
control information (Piggybacking)
Supervisory frame: used only to transport only
control information
U Frame: Reserved for system management
TYPES OF FRAMES HDLC frames
Frame check sequence
Control field format for the different frame types
N(S) = Sequence number of the
Frame
N(R) = Acknowledgement number
If Piggybacking is used
P/F Bit =1 means poll, address
Field contain the address of receiver
P/F Bit =0 means Final, address
Field contain the address of sender
Control field format for S-Frame
00 ( Receive ready) : This kind of frame
Acknowledges the receipt of safe frame
10 ( Receive not ready) : It announces
That receiver is busy and can not receive
More frames
01 (Reject REJ) : Negative
Acknowledgement
11 (Selective reject) : Negative
Acknowledgement for repeat
Control field format for U-Frame
How U-frames can be used for connection establishment and connection release. Node A
asks for a connection with a set asynchronous balanced mode (SABM) frame; node B
gives a positive response with an unnumbered acknowledgment (UA) frame. After these
two exchanges, data can be transferred between the two nodes. After data transfer, node A
sends a DISC (disconnect) frame to release the connection; it is confirmed by node B
responding with a UA (unnumbered acknowledgment).
11 100 : Set Asynchronous
Balanced mode
00 110 : Unnumbered
Acknowledgement
00 010 : Disconnect
Example of piggybacking without error
00 ( Receive ready) : This kind of frame
Acknowledges the receipt of safe frame
10 ( Receive not ready) : It announces
That receiver is busy and can not receive
More frames
01 (Reject REJ) : Negative
Acknowledgement
11 (Selective reject) : Negative
Acknowledgement for repeat
Example of piggybacking with error
00 ( Receive ready) : This kind of frame
Acknowledges the receipt of safe frame
10 ( Receive not ready) : It announces
That receiver is busy and can not receive
More frames
01 (Reject REJ) : Negative
Acknowledgement
11 (Selective reject) : Negative
Acknowledgement for repeat
POINT-TO-POINT PROTOCOL
Although HDLC is a general protocol that can be used
for both point-to-point and multipoint configurations,
one of the most common protocols for point-to-point
access is the Point-to-Point Protocol (PPP). PPP is a
byte-oriented protocol.
Explanation of protocol divided
Into following parts:
Framing
Transition Phases
Multilink PPP
PPP frame format
All stations are to
accept the frame
Unnumbered
frame
PPP can support multiple network
protocols simultaneously
Specifies what kind of packet is contained
in the payload
e.g. LCP, NCP, IP, OSI CLNP, IPX...
CRC 16 or CRC 32
Note
PPP is a byte-oriented protocol using
byte stuffing with the escape byte
01111101.
Transition phases
Multiplexing in PPP
LCP (LINK CONROL PROTOCOL)
It is responsible for establishing, maintaining,
configuring and terminating Links.
AUTHENTICATION PROTOCOLS
It is used where verification of user identity is Necessary.
PAP: Password Authentication protocol
*User sends an authentication identification and a
password.
*The system checks the validity of the identification
and password and either accepts or denies connection.
CHAP: Challenge Handshake Authentication protocol
*System sends a challenge packet containing challenge value.
*User applies a predefined function that takes the challenge
value and the user’s own password and create a result. The
user sends result in response packet to the system which
will be checked.
NETWORK CONTROL PROTOCOLS
Configure the link at the network layer for the incoming data.
IPCP: Internet protocol Control Protocol
•Configures the link for carrying IP packets.
•After the network layer configuration is completed by one of
the NCP protocols the user can exchange the packets.
Multilink PPP
An example of communication using PPP Protocol
example (continued)