By: Ashley OwensChelsey James

Dannielle Turmon

ProtocolsConsist of

1) Forward Channels(for data)2)Reverse Channels(for acknowledgements)

For better usageUse links for data in both directions, why

Allows the receiver to wait until network layer passed to next packet.

Acknowledgement then attached to the outgoing data frame. Causing piggybacking to act.

PiggybackingThe technique of temporarily delaying

outgoing acknowledgements so they can be hooked onto the next outgoing data frame.

It gives a positive acknowledgement with retransmission protocol.

Example:When data layer waits for a long period of time

then the sender wants, the frames then get resubmitted, defeating the purpose of having acknowledgements.

Advantages of PiggybackingAllows the privilege of having distinct

acknowledgement frames.It gives better use of available channel

bandwidth.The ack field acts as an acknowledger and a

checksum.

Ack FieldFrame header cost only a few bits( One bit in

frame header)Fewer frames means a lighter processing

load of receiver.

Protocol 3Allows unidirectional data flow over an

unreliable channel.Goes in a number of sequences describing

each protocol with the framesframe_to send-tells which frames the sender is

trying to sendframe_expected- tells which frames the

receiver is expecting

Bidirectional ProtocolsConsist of a sequence numbers Stop-and-wait sliding window n=1

This restricts the numbers from 0 and 1Consist of three class

1)Efficiency 2)Complexity 3)Buffer Requirements

Sending/Receiving WindowSender maintains a set of sequence numbers

corresponding to frames it is permitted to send. The receiving end corresponds to the set of frames permitted to be acceptedMust maintain the same lower and upper limitsMust maintain the same sizeSome are fixed in size, but grow and shrink

over time frame of being sent and receivedGives date link more freedom about order of

sending and receiving

Purpose of Sequence of NumbersRepresent frames that have been sent or can

be sentNewest packet is sent at highest sequence

numberMaintains a list of acknowledgment frames

One-Bit Sliding Window ProtocolBidirectionalUse the stop-and-wait protocol as discussed

in slide 8It starts by defining variables

Frame_to_send- tells frames the sender is trying to send

Frame_expected- tells which frame the receiver is expecting.

O and 1 are the only possibilities

Protocol Using Go-Back_NAllows sender to transmits w frames before

blocking, instead of just one.With the large variety of w the sender will be

able to continuously transmit frames since the acknowledgements will arrive for previous frames.

Before the windows become full, it prevents the sender from blocking.

Receiver would discard all subsequent frames, sending no acknowledgements for the discarded frames.

Bandwidth-delay productIn order to find the appropriate value for w we

need to know how many frames can fit inside the channel.

Bandwidth in bits/sec multiplied by one-way transit time

2BD+1Link utilization-< w/1+2BD

This value is an upper bound because it does not allow for any frame processing time and treats the acknowledgement frame as having zero length, since its usually short.

PipeliningTechnique of keeping multiple frames in

flightCan cause serious issues

Unreliable communication channelFrame can become lost of damaged

Approaches To Dealing With Errors In PipeliningTo aid in the recovery the frames are

discarded by data link layerWhen the window size is to large the frames

are buffered by data link layer

Selective RepeatAnother strategy for handling errors of framesWhen bad frame that is received is discarded,

but any good frames received after it are accepted and buffered.

Only the oldest unacknowledged frames are retransmitted.

Often combined with having receiver send a negative acknowledgement(NAK)

There are a few approaches to if NAK becomes lost, or is timed out

Alternative Approaches Bandwidth and data link layer buffer spaceThe network_layer_ready- is used when the

network layer has packet it wants to sendThe library procedures include:

disable_network_layer enable_network_layer

Cumulative AcknowledgementUses protocol 5Extremely important when frames were lost

or garbledWhenever acknowledgements come in, the

data link layer check to see if any buffers can be released

Has multiple outstanding frames, and needs multiple timers

Protocol Using Selective RepeatAllows receiver to accept and buffer the

frames following a damaged or lost oneBoth sender and receiver maintain a window

of outstanding and acceptable sequence number

Data Link ProtocolsPoint to point lines in the internet with two

common situationsUsed to send packets over these links

SONETIt provides a bitstream that runs at a well-

defined rateThe bitstream is organized as fixed-sized byte

payloads that recur every 125msec whether or not there is data sent

Examples of data link protocolsSLIP(serial line internet protocol)- is used to handle

error detection link configuration, support multiple protocols, permit authentication, and more.

LCP(link control protocol)- a link control that brings lines up, testing them, negotiating options, and bringing them down again gracefully when they are no longer needed.

NCP(network control protocol)- a way to negotiate network-layer options in a way that is independent of the network layer protocol to be used.

HDLC( high-level data link control)- provides reliable transmission with a sliding window, acknowledgements, and timeouts.

ADSL( Asymmetric Digital Subscriber Loop)Connects million of home subscribes to

the internet at megabit/sec rates over same telephone local loop used for plain old telephone service

It sends bits over a local loop to a device called DSLAM( DSL Access Multiplexer)

ATM(Asynchronous Transfer Mode)Link layer based on the transmission of fixed-

length cells of informationMeans that cells do not always need to be sent in

the way that bits are continuously sent over synchronous lines

Connection-Oriented technologyTo send data over network it needs to be mapped

into a sequence of cellsEach cell carries a virtual circuit identifier in its

header and devices use this identifier to forward cells along the paths of established connections

They can divide the bandwidth of physical layer link into slices sending both voice and data

Adaption Layers To send data over an ATM network, it needs

to be mapped into a sequence of cells, this is done with an ATM adaption layer in a process called segmentation and reassembly.

Several are defined for different servicesPeriodic voice samplesPacket data

AAL5 (ATM Adaption Layer 5) is the main one used for packet data

SummaryThe purpose of sliding protocols is to convert

the raw bit stream offered by the physical layer into a stream of frames for use by the network layer

It also provides error correction and detection