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