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94 Cards in this Set
- Front
- Back
Connection-Oriented
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Befre applications can send data they must handshake with eachother and start the transfer
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Full Duplex Service
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Both hosts can send data back and forth to each other at the same time
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Point to Point
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Connection between single receiver ansender. Only two hosts
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How does the three way handshake work
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1.) Client sends syn segment with initial sequence value
2.) Server sends synack with initial sequence value 3.) Client sends ack with possible data |
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Send buffer
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On the sender side, application data is stored here and sent intermittently
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MSS
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Maximum Segment Size, the maximum amount of data in a tcp segment. Not including header information
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MTU
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Maximum Transmission Unit - Largest link layer frame that can be sent by sending host
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TCP Segment
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Combination of data and header information
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Sequence numbers in TCP
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Are based on bytes of data and what the receiver is expecting to get next
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What is the receive window used for
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flow control on the receiver side
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How do ACKS work in TCP
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Send ack for next byte you are expecting. Cumulative
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RTT
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round trip time, time from when a segment is sent until it is acknowledged
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How is Sample RTT taken?
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Oldest segment is timed for RTT. Not affter retransmit
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Timeout Interval equation
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EstimatdRTT + 4 * DevRTT
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Fast Retransmit
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After receiving triple ACK, the sender will resend Acked segment before the timer goes of
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Selective Acknowledgment
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Allows a receiver to acknowledge out of order segments selecitvly rather than just cumulatively acknowleding the last correctly received in order segment
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Receive Window
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Sender variable that gives an idea to sender about how much free buffer space is available at the receiver
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Receive Buffer
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The amount of data a client is willing to receive for this connection
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Last Byte Read
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The number of the last byte in the data stream read from the buffer by the client process
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LastByteRcvd
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The number o the last byte in the data stream that has arrived from the network and has been placed in the receive buffer at the client
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LastByteSent
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The last byte the sender has sent
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LastyteAcked
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The last byte the sender has received an ack for
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What does the server make sure of for flow control
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LastByteSent - LastByteAcked < rcvwindow
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What does the client do when its rwnd becomes 0 and it has nothing to send to the server?
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Server sends 1 byte data (with seq of ack) packages to client so client acks with rcvwindow size
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How is a TCP connection initiated
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1.) Client sends SYN packet with no data and segment it wants to start at
2.) Server allocates variables. Respons with SYN, ACKS segment #+1 and sends own segment 3.) Client allocates variables sends regular data with ack set to client + 1 |
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How is a TCP connection closed
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1.) Client sends Fin
2.) Server Acks 3.)Server sends Fin 4.) Client Acks 5.) Client waits for time after time is up, clears connection |
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Offered load
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The rate at which the transport layer sends segments (containing original and retransmitted data) into the network
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End-to-End congestion Control
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Networ layer provides no explicit support and the end system must control it
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Network-Assisted Congestion Control
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Routers provide feedback to the sender regarding congestion.
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What are the two ways Network-assisted congestion control work
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1.) Choke Packet - Router sends information to process
2.) Router modifies a bit in packet |
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congestion window
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A sender side value that constrains the rate at which a sender can send traffic into the network
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slow start
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cwnd starts at 1 and increases by 1 for each received ack
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3 Ways to leave slow start
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1.) CWND >= ssthresh
congestion avoidance 2.) Timeout. Start slow start but set cwnd to 1 and ssthresh to cwnd/2 3.) 3 duplicate acks. Set ssthres to cwnd/2 and cwnd to ssthresh + 3 and go to faast recovery |
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When is congestion avoidance entered?
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1.) When CWND >= ssthresh
2.) New ack is received when in fast recovery |
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How does congestion avoidance work
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For each new ack, cwnd is incremented by cwnd + mss * (mss /cwnd)
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What happens for congestion control when 3 duplicate acks are encountered
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ssthresh = cwnd /2
cwnd = ssthresh + 3 |
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What happens in fast recovery / how do get out
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1.) Every duplicate ack increases cwnd by mss
EXITING 2.) ON timeout go to slow start ssthresh = cwnd/2 cwnd = 1 3.) ON new ack go to congestion cwnd = ssthresh |
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What is the difference between tahoe and reno
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TCP reno has fast recovery after a triple ack, tahoe goes to slow start stage
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AIMD
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Additive-increase, multiplicative-decrease. Sawtooth graph
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Forwarding
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Local action of transferring a packet from an input link interface to the appropriate output link interace
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Routing
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Network-wide process that determines the end-to-end paths that packets take from source to destination
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Forwarding Table
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Router reads the value in the packets header and determines which out going link to put the packet to
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How are forwarding tables populated (3 things)
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1.) By routing algorithms
2.) Central cerver routing alogortihms decentralized routing algorithms |
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Link Layer Switches
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Base forwarding decision on value in link-layer field
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Routers (forwarding decisions)
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Base decision on network layer-field
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Network Service model
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The characteristics of end-to-end transport of packets between sending and receiving end systems
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best effort service
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1.) Timing between packets isn't guranteed
2.) Packet order isn't guranteed 3.) Delivery of packets isn't guranteed |
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CBR ATM
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(Constant Bit Rate) Network service that provides constant bit rate
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ABR
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(Avaiable Bit Rate) Minimum throughput provided
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VC Network
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Virtual Circuit Networks - provide a connection service at the network layer
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Datagram Network
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Provides a connectionless service
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Signaling messages
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Messages that the end systems send into the network to initiate or terminate a VC, and the messages passed between the routers to set up the VC
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Longest Prefix matching rule
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longest matching entry in the table is the match
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Switching Fabric ways
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memory, crossbarr, bus
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Packet Scheduler
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Output port must queue requests and determine which to transmit
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Drop Tail
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Drop the remove one of already queued packets to make room for a new one
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HOL
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Head of line blocking - queued packet in input queue must wait for transfer through the fabric (even though its output port is free) because it is blocked by another packet at the head of the line
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Why is the header length field needed in the IP datagram
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Can contain a variable number of options
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What is the datagram length field in the ip datagram
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The total length of the datagram (header plus data) in bytes
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Interface
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Boundary between the host and physical link
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Subnet
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Network that interconectes other host interfaces and one router interface
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Subnet mask
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Denoted as ip with /* where all front bits are required
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CIDR
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Classless interdomain Routing . Generalized the notion of subnet addressing.
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Broadcast address
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255.255.255.255 Broadcasts information to all hosts on a subnet
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DHCP
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Dynamic Host Configuration Protocol. Allows a host to obtain an ip address automatically
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NAT
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network address translation
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realm
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A network whose addresses only have meaning to devices within that network
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ICMP
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Internet Control message Protocol
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TCP Header - Header length Field
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Since the options field makes it so TCP headers can be variable size, the header field is required to indicate how many bytes are in the header
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TCP Header - ACK bit
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Indicates that the value carried in the ack field is valid
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TCP Header - RST, SYN, FIN bits
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Used for connetion setup and teardown
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TCP Header - PSH bit
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indicates that the receiver should pass the data to the upper layer immediately
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TCP Header - URG bit
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used to indicate that there is data in this segment that the sending-side upper-layer has marked urgent
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RDT 1.0
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Reliable data transfer over perfectly reliable channel
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RDT 2.0
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Bit errors, send ack or nak to determine if we got a corrupted/uncorrupted piece of data
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Stop and Wait protocol
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Sender will not send new packet until it is sure previous packet has been received correctly
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RDT 2.1
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Add sequence numbers
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rdt 3.0
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Can lose packets. add timers
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Memorize TCP header
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SDSA
HUFR IUOD source port dest port sequence number ack number header length unusued flags receive window internet checksum urgent data point options data |
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IPv4 Datagram header - version number
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4 bits that indicate what version is being used
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IPv4 Datagram header - header length
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the length of the variable length header. Indicates where the data begins
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IPv4 Datagram header - type of service
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used to distinguish if application is real time or what
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IPv4 Datagram header - datagram length
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total length of the datagram (header plus data) measured in bytes
16 bits |
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IPv4 Datagram header - identifier, flags, fragmentation offset
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used for fragmentation
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IPv4 Datagram header - ttl
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time to live, used to ensure datagrams are dropped if this value reaches 0
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IPv4 Datagram header - protocol
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used when the datagram reaches its final destination. 17 for udp and 6 for tcp
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IPv4 Datagram header - header checksum
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checksum used for the ip datagram header
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IPv4 Datagram header - Ip addresses
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indicate where to deliver the datagram
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IPv4 Datagram header - options
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allow the header options to be extended
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IPv4 Datagram header - data
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where the actual data is held
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how does CIDR work
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First portion of bits indicate network. next part indicates inside an organization
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How are ICMP packets carried
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As IP data payload
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How is ICMP read
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it is demultiplexed to ICMP
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ipv4 datagram format
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VHTD
IFF TUH S D O D 1.) version, haeder length, type of service, datagram length 2.) identifier, flags, fragmentation offset 3.) time to live, upper layer protocol, checksum 4.) soruce ip 5.) destination ip 6.) options 7.) data |