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Internet Services Final
final
54
Computer Science
Undergraduate 4
04/29/2010

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Term
Media Access Control Protocols
Definition
Arbitrate access if multiple hosts wish to transmit at the same time
Term
Carrier Sense
Definition
listen before transmitting (Media Access Control)
Term
Collision Detection
Definition
listen while transmitting and stop on detecting collision (Media Access Control)
Term
Multiple Access
Definition
Multiple nodes plugged into common 'bus' medium
Term
MACAW Protocol
Definition
Multiple Access With Collision Avoidance for Wireless LANs. Basically: don't do collision avoidance. Sender sends RTS(Request to Send) with length of data frame. Receiver then replies with Clear to Send with echo of frame length. If sender gets CTS frame it sends data frame, if not it does exponential back-off before trying again. Receiver then sends ACK.
Term
RIP
Definition
distance vector-like algorithm. measures number of hops, up to 15, 16=infinity.Routing tables are exchanged with adjacent nodes every 30 seconds. If no communication happens after 180 seconds, the node/link is declared 'failed'
Term
OSPF
Definition
Publicly available. Uses the link state minimum cost path computation algorithm. Advertisement carries one entry per adjacent node. Advertisements disseminate to an entire AS via flooding. All messages are authenticated to prevent malicious intrusion. Multiple same-cost paths allowed. For each link, multiple cost metrics for different network-layer 'services'. Hierarchical.
Term
BGP
Definition
Border Gateway Protocol. Send messages like:OPEN, UPDATE, KEEPALIVE, NOTIFICATION. Used in Inter-AS Routing.
Term
Inter vs Intra AS routing
Definition
Inter- between networks. administrator wants control over how its traffic routed and who routes through its network. policy over performance.
Intra- in the same network. No policy decisions, but focus on performance.
Term
IP address
Definition
32-bit network-layer address. It identifies a host or router's interface. Used to get datagram to destination network. Not portable. The upper bits are the network part, host part is the lower bits
Term
MAC address
Definition
Ethernet address. Used to get datagram from one interface to another physically-connected interface in the same network. 48 bit MAC address burned into the adapter Read- only Memory. Address administration administered by IEEE. Manufactures buy some portion of MAC address space. MAC unstructured address is useful for portability.
Term
Ethernet switches
Definition
Like routers. They use the MAC address to forward frames. Large number of interfaces. Switches learn MAC addresses of hosts on each link.
Term
ARP
Definition
Address resolution protocol. ARP cache contains IP/MAC address mappings, along with TTL (Time to live; time after whch address mapping will be forgotten, like 20 mins). If a host, A, wants another host's, B, MAC address from B's IP address, it can broadcast a query, to which the B responds to with the MAC address to put into the A's ARP cache
Term
IP datagram
Definition
The protocol data unit at the IP network layer.
Term
Interface
Definition
connection between host or router and a physical link. Routers typically have multiple interfaces. IP addresses are associated with an interface, not the host or router.
Term
Class-biased addressing
Definition
Inefficient use of address space, address space exhaustion.
Term
Classless addressing
Definition
network portion of address has an arbitrary length. address format:a.b.c.d/x where x is the number of bits in network portion of address called the network mask. Used in routing tables, not IP datagram source/destination
Term
IP datagram format
Definition
made up of IP protocol version, Header length, total IP datagram length, fragmentation info, Maximum number of remaining hops, Transport layer protocol, and the data.
Term
MTU
Definition
maximum transmission unit. Used to fragment IP datagrams. Fragments only reassemble at final destination.
Term
ICMP
Definition
Internet control message protocol. Used by hosts, routers and gateways to communicate network-level information. Error reporting/echo request-reply.
Term
IPv6
Definition
changed to fixed-length 40 byte header. No fragmentation allowed. Helps high speed processing. New 'anycast': route to 'best' of several replicated servers. chooses priority among datagrams in flow. Has an upper layer protocol for data.
Term
Global routing algorithms
Definition
all routers maintain the complete graph of the network. "link state" algorithms.
Term
Decentralized routing algorithms
Definition
router knows link costs to physically connected adjacent nodes. Run iterative algorithm to exchange information with adjacent nodes. has distance vector algorithms.
Term
distance vector routing
Definition
Iterative, meaning nodes exchange cost information until each node has the current route cost, and the algorithm is self-terminating. Each iteration is caused by local link cost change or message from adjacent node that its least cost path to some destination has changed. It's asynchronous, meaning nodes don't have to exchange info at the same time. Each node communicates with directly attached adjacent nodes. Nodes can advertise incorrect path cost. each node's table used by others.
Term
Network layer function
Definition
-addressing: the means by which end systems identify each other. -path determination- the route taken by packets from source to destination. -Switching- the movement of packets from an input interface to an appropriate output interface. Call setup- the establishment of a virtual circuit from sender to receiver.
Term
link state flooding algorithm
Definition
The data stored for an edge in the graph made up of the cost from end to end, and a unique timestamp for the last update to each cost. A node that discovers a change in cost for one of its attached links forwards the update to all adjacent nodes. A node receiving an update forwards it based on a comparison of the update timestamp and the timestamp on its local data for the link.
Term
latency at TCP
Definition
2RTT+O/R
R-transmission speed.
Sometimes +total stall time.
Term
flow control
Definition
sender adjusts its transmission rate so as not to overwhelm the receiver.
Term
Congestion control
Definition
the senders adjust their transmission rate so as not to overwhelm routers in the network. Congestion can lead to lost packets and long delays
Term
congestion collapse
Definition
all the links are fully utilized but no data is delivered to applications
Term
End-to-end congestion control
Definition
end-systems receive no feedback from network. Congestion inferred by observing loss and/or delay.
Term
hop-by-hop congestion control
Definition
routers provide feedback to end systems. Network determines an explicit rate that a sender should transmit at. Network signals congestion by setting a bit in a packet's header.
Term
MSS
Definition
maximum segment size, for segments in windows.
Term
slow start congestion control
Definition
ramp up the transmission rate until loss occurs. The window size increase exponentially each RTT until a loss occurs or the size of the window equals threshold. If there's a loss, it starts back over.
Term
congestion control
Definition
keep connection close to sustainable bandwidth. It increases the window size by 1 segment each RTT, decrease by a factor of 2 when packet loss is detected.
Term
slow start vs. congestion avoidance
Definition
threshold is an estimate of a safe level of throughput that is sustainable in the network. This determines whether a window uses slow start or congestion avoidance according to it.
Term
TCP Tahoe
Definition
loss signaled by timeout.
Term
TCP Reno
Definition
Fast retransmit-receipt of 3 duplicate ACKs also signals a packet loss
Fast recovery-skips slowstart and continue in congestion avoidance new slowstart threshold.
Term
TCP
Definition
point to point transport layer protocol. Bi-directional, reliable, in-order, connection oriented, pipelined, congestion controlled, flow controlled
Term
Sequence numbers
Definition
Byte stream index of the first byte in the segment's payload.
Term
ACKs
Definition
Sequence number of next byte expected from the other side.
Term
Sample RTT
Definition
to avoid premature timeouts and keep high performance, the sample RTT is calculated to set the time for the timeout. Timeout is estimated RTT plus safety margin
Term
Go back n protocols
Definition
The whole window (size n) is sent. If a NACK is received, then the last n packets will be sent again.
Term
transport layer vs network layer
Definition
transport layer: data transfer between end systems Network layer: data transfer between network components
Term
Transport layer
Definition
multiplexing, demultiplexing. Error detection, reliable data delivery. pipelining. flow control. congestion control
Term
UDP
Definition
uses destination IP addr, destination port number to identify the socket. Socket it owned by some processes, allocated by the OS. fast. No handshaking, best effort sending. DNS, SNMP, and routing protocols use it.
Term
TCP
Definition
TCP uses source IP and port number, and destination IP address and port #. Connection and socket are owned by some process
Term
metainfo file
Definition
contains all the info about a torrent. It has tracker-info, creation date, comment, created by. hash of all pieces are present in info field.
Term
FTP
Definition
transfer transfer protocol. Uses client/server model. FTP maintains state.
Term
HTTP
Definition
uses TCP sockets. stateless.
Term
SMTP
Definition
email. push protocol . Uses HTTP. persistent connections
Term
transmission delay
Definition
time to put bits onto the link. packet length/link bandwidth
Term
propagation delay
Definition
time to get from one end to the other. length of physical link/signal propagation speed.
Term
traffic intensity
Definition
La/R
L-packet length
a-average packet arrival rate
R-link transmission speed
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