Chapter 11
In bit-oriented protocols, the delimiter is a special bit pattern
01111110
In ____, If the data frames arrive at the receiver site faster than they can be processed, the frames must be ___ until their use
Stop-and-Wait protocol, stored
In Selective Repeat ARQ, window size must be at most one half of 2^m
*
PPP Services
* Format of the frame * How two devices negotiate link establishment * How network layer data are encapsulated in the data link frame * How two devices authenticate each other * Provides connections over multiple links * Provides network address configuration - No flow control - No sophisticated addressing mechanism to handle flames in a multipoint configuration - Very simple mechanism for error control using CRC
Stop-and-Wait ARQ
- If the received frame is corrupted, silently discard - Corrupted and lost frames, timer expired must be resent - Sender maintains a copy of sent frame and starts a time - Sequence numbers start from 0 to 2^m - 1 (uses modulo 2)
Go Back N-ARQ
- Like in Stop-and-Wait ARQ, the copy of the frames in transit are being kept until acknowledgment arrives - If timer expired, sender needs to resend all frames previously in transit
Volume of pipe in bits and measures the number of bits we can send out of our system while waiting news from the receiver
Bandwidth-delay product (BDP)
A very large frame makes flow and error control very inefficient
A single bit error requires retransmission
Specialized frames used in flow control and error control
ACK, NAK
In Stop-and-Wait ARQ, the receiver announces the next sequence number to the sender. What is this next sequence number called?
Acknowledgment numbers
In Stop-and-Wait protocol, when the frame just sent a frame, when will it send the next frame?
After it receives confirmation from the receiver
A transfer mode wherein each station can function as primary and secondary
Asynchronous Balanced Mode (ABM)
Any time an error is detected in an exchange, specified frames are retransmitted
Automatic Repeat Request (ARQ)
Adds one extra 0 whenever five consecutive 1s follow a 0 in the data
Bit stuffing
In this set of protocols, data section of frame is a sequence of bits to be interpreted by the upper layer as text, graphics, audio, video, etc.
Bit-oriented protocols
In character oriented protocols, this prevents the data from being interpreted as flag
Byte stuffing by using a special byte (escape character) to the data section of the frame when there is a character with the same pattern as the flag
Two types of variable-size framing
Character oriented and bit oriented
In this type of protocol, data to be carried are 8-bit characters from a coding system such as ASCII. The header and trailer are also multiples of 8 bits. An 8-bit flag is added at the beginning and end of a frame
Character-oriented protocols
1-or 2-byte segment used for flow and error control; depends on the type of frame
Control field
This address tells where the frame is to go
Destination address
Components of I-Frames
First bit: 0 N(S) - sequence number of the frame N(R) - acknowledgment number when piggybacking is used P/F bit - Poll or Final bit
U-Frames
First two bits: 11
Framing wherein there is no need to define the boundaries of the frames
Fixed-size framing
PPP Frame
Flag - 01111110 Address - 11111111; broadcast Control - 1100 0000 ; not needed Protocol - defines what is being carried in payload Payload - user data or control information Frame Check Sequence - 2 byte or 4-byte standard CRC ESC byte for stuffying: 01111101
This service of data link layer coordinates the amount of data to be sent before receiving an acknowledgment
Flow control
2- or 4-byte ITU-T CRC
Frame Check Sequence
In this noisy channel protocol, this uses the concept of pipelining - multiple frames must be in in transit while waiting for ACK
Go-Back-N ARQ
Bit-oriented protocol for communication over point-to-point and multiple links and implements the ARQ mechanism discussed
High-level Data Link Control (HDLC)
Three types of frames
I(nformation)-frames, S(upervisory)-frames, U(unnumbered)-frames
Performance of Stop-and-Wait ARQ
Inefficient if channel is thick (large bandwidth) and long (round trip delay is long)
data
Information field
Other protocols
Link Control Protocol, Password Authentication Protocol, Challenge Handshake Authentication Protocol, Internet Protocol Control Protocol
PPP transition phases
Network -> Open -> Terminate -> Dead -> Establish -> Authenticate -> Network
A transfer mode that involves One primary station and multiple secondary stations
Normal Response Mode
Two types of transfer modes
Normal Response Mode and Asynchronous Balanced Mode
When ACKs or NAKs are included in the data frame, it is called ___
Piggybacking
A byte oriented protocol used in home computers connecting to ISPs and traditional modem connection through a telephone line. - Most common data link layer protocol
Point-point protocol
What are the state/s of the sending and receiving node in SImplest Protocol?
Ready Events: Packet came from network layer, Frame arrived
Control codes of S-Frames
Receive Ready (RR) - 00 Receive not ready (RNR) - 10; receiver is busy Reject (REJ) - 01; NAK in Go-Back-N ARQ Selective reject(SREJ) - 11; NAK used in Selective Repeat * First two bits of S-Frames: 10
In this noisy channel protocol, only damaged frames are resent thus, more efficient for noisy links
Selective Repeat ARQ
Receive window is the same as the number of send window
Selective Repeat ARQ
This address helps the recipient acknowledge the receipt
Sender address
State/s of the sending node and receiving node in Stop-and-Wiat protocol
Sending Node: Ready, Block Receiving Node: Ready
In this noiseless channel protocol, there is no flow or error control
Simplest Protocol
What are the protocols of flow control in a Noiseless Channel?
Simplest, Stop and Wait
Defines the range of sequence numbers that is the concern of the sender and receiver in Go-Back-N ARQ
Sliding window * sender and receiver deals only with a part of the range of sequence numbers
This protocol in Noisy channel adds redundancy bits to data frame
Stop-and-Wait ARQ
What are the protocols of flow control in Noisy Channel
Stop-and-Wait ARQ, Go-Back-N-ARQ, Selective Repeat ARQ
How does Stop-and-Wait ARQ allow detection of lost frames?
Through numbering frames (sequence numbers)
Framing wherein there is a need to define the end of the frame and beginning of the next; used in most networks
Variable-size framing
Error control
both error detection and error correction
In Go-Back-N ARQ, ACKs are ___
cumulative - more than one frame can be acknowledged by a single ACK
Framing
separates a message from one source to destination, or from other messages to other destinations by adding a sender address and a destination address
The last bit of the last byte always ends with 1 (Frame field address)
signals the last byte of the address field