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22 Cards in this Set
- Front
- Back
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packet transmission delay formula
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delay = L/R
L = bits R = transmission rate |
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How long does it take to send a file of 640,000 bits from host A to host B over a circuit-switched network?
all link speeds: 1.536 Mbps each link uses TDM with 24 slots/sec 500 msec to establish end-to-end circuit |
640000 bits / (1.536 Mbps / 24) + 500msec = 10.5sec
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four sources of packet delay
(Dnodal = ? + ? + ? + ?) |
dproc: nodal processing
check bit errors determine output link typically < msec dqueue: queueing delay time waiting at output link for transmission depends on congestion level of router dtrans: transmission delay: L: packet length (bits) R: link bandwidth (bps) dtrans = L/R dprop: propagation delay: d: length of physical link s: propagation speed in medium (~2x108 m/sec) dprop = d/s |
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Q: How long until caravan is lined up before 2nd toll booth?
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time to “push” entire caravan through toll booth onto highway = 12*10 = 120 sec
time for last car to propagate from 1st to 2nd toll both: 100km/(100km/hr)= 1 hr =62mins |
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traffic intensity
= ? |
=La/R
L = packet length (bits) R = link bandwidth (bps) a = average packet arrival rate |
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throughput:
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rate (bits/time unit) at which bits transferred between sender/receiver
instantaneous: rate at given point in time average: rate over longer period of time |
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application layer
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supporting network applications
FTP, SMTP, HTTP *message |
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transport layer
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process-process data transfer
TCP, UDP *segment |
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network layer
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routing of datagrams from source to destination
IP, routing protocols *datagram |
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link layer
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data transfer between neighboring network elements
Ethernet, 802.111 (WiFi), PPP *frame |
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physical layer
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bits “on the wire”
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IP spoofing
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send packet with false source address
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record-and-playback:
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sniff sensitive info (e.g., password), and use later
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process:
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a program running within a host
within same host, two processes communicate using inter-process communication (defined by OS) processes in different hosts communicate by exchanging messages |
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client process:
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process that initiates communication
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server process:
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process that waits to be contacted
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does IP address of host on which process runs suffice for identifying the process?
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no, many processes can be running on same host
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to receive messages, process must have identifier
host device has unique 32-bit IP address |
identifier includes both IP address and port numbers associated with process on host.
example port numbers: HTTP server: 80 mail server: 25 |
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app-layer protocol defines
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1. types of messages exchanged
2. message syntax 3. message semantics (meaning) 4. when/how send/respond rules |
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what transport service does an app need?
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1. data integrity (file xfer)
2. timing (mmo's, phone) 3. throughput 4. security |
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TCP service:
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TCP service:
reliable transport between sending and receiving process flow control: sender won’t overwhelm receiver congestion control: throttle sender when network overloaded does not provide: timing, minimum throughput guarantee, security connection-oriented: setup required between client and server processes |
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UDP service:
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unreliable data transfer between sending and receiving process
does not provide: reliability, flow control, congestion control, timing, throughput guarantee, security, or connection setup, |
