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streaming applications vs. traditional web page delivery
humans consume audio and video streams in a continuous manner, and discontinuity. By contrast, a regular (nonstreaming) page can be delivered and read in bits and pieces.
what characterizes real-time audio and video applications
tighter timing constraints than streaming applications
during the initial years of internet access, how did most people obtain internet connectivity
work, school, dial-up modem at home
network
term used to describe physical links connecting two or more computers directly
what distinguishes multiple-access links from point-to-point links
the physical links of point-to-point are limited by a pair of nodes while multiple-access links can have more than a pair of nodes sharing a single link
characteristic of packet-switched networks
the nodes send discrete blocks of data to each other.
what is one of the most crucial functions that a network must provide
connectivity among a set of computers
what is multiplexing in network communication
a system resource is shared among multiple users
synchronous time-division multiplexing (STDM)
divides time into equal-sized quanta to share the physical link among multiple flows
what distinguishes statistical multiplexing from STDM
data are transmitted from each flow on demand rather than during a predetermined time slot
how does the concept of layering relate to logical process-to-process channels
implemented on top of a collection of physical host-to-host channels.
what happens when a switch receives packets faster than the shared link can accommodate
the switch is forced to buffer these packets in its memory. After an extended period of time, the switch will eventually run out of buffer space, and some packets will have to be dropped.
what functionality characterizes the request/reply channel used by file transfer and digital library applications
guarantees that every message sent by one side is received by the other side and that only one copy of each message is delivered.
purpose of abstraction in system design
to manage complexity
what are the 2 interfaces defined by a protocol
service
peer
body (payload)
the part of the message that contains the application’s data
what is the fundamental idea of packet switching
to multiplex multiple flows of data over a single physical link
what is the purpose of a demultiplexing key in a protocol’s header
determine which messages to pass up to RRP and which to pass up to MSP
7 layer OSI model
physical
data link
network
transport
session
presentation
application
which layer of the OSI model implements process-to-process channels
transport
what is the primary function of the physical layer in the OSI model
handles the transmission of raw bits over a communications link
message
the unit of data exchanged at the transport layer
which layer of the OSI model manages the format of data exchanged between peers
presentation
which layer of the OSI model is responsible for tying together different transport streams in a single application
session
what is the purpose of the application layer in the OSI model?
enables web browsers to request pages from web servers
what is the fundamental unit of data exchanged at the data link layer
frame
what is the role of protocols in network communication
provides a communication service that higher-level objects (such as application processes, or perhaps higher-level protocols) use to exchange messages
what is the purpose of a protocol graph
the suite of protocols that make up a network system
how does the process of encapsulation work in a protocol graph
the process repeats on each level of the protocol graph;
HHP encapsulates RRP’s message by attaching a header of its own, then arrives to destination host
what happens when a message arrives at the destination host in terms of encapsulation
it is processed in the opposite order
latency in terms of propagation
propagation = distance/speed of light
latency in terms of transmit
transmit = size/bandwidth
latency in terms of queue delay
time packets are stored before forwarding them on an outbound link;
time taken for a signal to propagate from one end of a link to another
latency
propagation + transmit + queue
what does it mean when bits in the pipe are said to be “in flight”
if the receiver tells the sender to stop transmitting, it might receive up to one RTT × bandwidth's worth of data before the sender manages to respond.
what remains constant as bandwidth increases in high-speed networks
the speed of light
how does the RTT compare between 1-Gbps and a 1-Mbps network
Gbps link is the same 100 ms as Mbps
latency
starts to dominate network design thinking as bandwidth increases
jitter
variation in latency experienced by packets in a network
what is the purpose of storing frames in a buffer in the presence of jitter
receiver delays the frame, effectively smoothing out the jitter
how are links characterized
by the medium they use:
copper wire, twisted pair, coaxial cable, optical fiber
what is the main purpose of a network architecture
to provide a common abstraction of something as complex and diverse as a link.
what technology is likely to become an important part of the 5G mobile network
mmWave band
what is the role of modulation in the context of encoding binary data onto electromagnetic signals
vary the amplitude of a single wavelength
which technology is commonly used to connect homes and businesses over recently deployed fiber
PON (passive optical network)
what is the main task when turning nodes and links into usable building blocks
understand how to connect them in such a way that bits can be transmitted from one node to the other
which encoding scheme maps the data value 1 onto the high signal and 0 onto the low signal
nonreturn to zero (NRZ)
what problem is associated with long strings of consecutive 1s or 0s in NRZ encoding
several consecutive 1s means that the signal stays high on the link for an extended period of time; similarly, several consecutive 0s mean that the signal stays low for a long time;
baseline wander: too many consecutive 1s or 0s cause this average to change, making it more difficult to detect a significant change in the signal.
clock recovery: both the encoding and decoding processes are driven by a clock—every clock cycle, the sender transmits a bit and the receiver recovers a bit. If the receiver's clock is even slightly faster or slower than the sender's clock, then it does not correctly decode the signal.
how does NRZI address the issue of consecutive 1s in encoding
has the sender make a transition from the current signal to encode a 1 and stay at the current signal to encode a 0
what is the primary disadvantage of Manchester encoding
it doubles the rate at which signal transitions are made on the link, which means that the receiver has half the time to detect each pulse of the signal
which modulation scheme allows the encoding of 16 or even 64 different patterns during each clock interval
Quadrature Amplitude Modulation (QAM)
what is the relationship between bit rate and baud rate in Manchester encoding
bit rate is half the baud rate
what is the efficiency of the 4B/5B encoding
80% efficiency
how does 4B/5B encoding address the inefficiency of Manchester encoding
inserts extra bits into the bit stream so as to break up long sequences of 0s or 1s.
which of the following protocols uses only sentinel characters for framing
byte-oriented protocol
what is the problem with using sentinel characters for framing
one of the special characters might appear in the data portion of the frame
which protocol uses sentinels and character stuffing for framing
point-to-point protocol (PPP)
what action does the receiver take when it encounters five consecutive 1s during bit stuffing (HDLC protocol)
the receiver makes its decision based on the next bit it sees
if 0: receiver removes
if 1: error, whole frame discarded
how does the receiver determine the start and end of a frame in SONET
The first 2 bytes of the frame contain a special bit pattern
what is the purpose of scrambling the payload bytes in SONET
to ensure that there are plenty of transitions to allow the receiver to recover the sender's clock
how are packets transmitted in the PPP frame format
starting at the leftmost field
what action does the receiver take if the result of applying the error-detecting algorithm to the received message does not match the sender’s result
discarding the message of correcting it if possible
why is the term “checksum” sometimes used imprecisely in networking
it is used imprecisely to mean any form of error-detecting code, including CRCs
what combination of mechanisms is commonly used to achieve reliable delivery in networking
acknowledgments (ACK) and timeouts
what is the term for the general strategy of using acknowledgments and timeouts to implement reliable delivery
automatic repeat request (ARQ)
which ARQ algorithm is the simplest
stop-and-wait
what are the 3 roles that the sliding window algorithm can serve
reliably deliver frames across an unreliable link
to preserve the order in which frames are transmitted
support flow control (keep the sender from overrunning the receiver)
what is the distinguishing feature of the ARPANET protocol compared to the sliding window protocol
it is able to keep the pipe full while still using the simple stop-and-wait algorithm.
what does the term “carrier sense” mean in the context of CSMA/CD
all the nodes can distinguish between an idle and a busy link
what does it mean for hosts in an Ethernet network to be in the same collision domain
they are all competing for access to the same link
what is the purpose of the preamble in an Ethernet frame
allows the receiver to synchronize with the signal
why must an Ethernet frame contain at least 46 bytes of data
it’s long enough to detect a collision
how are Ethernet addresses typically represented
48-bit address
why did the switch-based variant of the Ethernet succeed in replacing multi-access Ethernet
it could be deployed incrementally
why is media access control a central issue for wireless links
it is hard to control who receives your signal when you transmit over the air, issues of eavesdropping may also have to be addressed
frequency hopping
spread spectrum technique involving transmitting the signal over a random sequence of frequency
what does MIMO stand for in the context of wireless networks
multiple-input multiple-output
what is the purpose of spread spectrum techniques in wireless communication
deals with possible interference in the band. Provides a natural time slot for Bluetooth to use for synchronous time division multiplexing.
which spread spectrum technique adds redundancy to transmitted bits for greater tolerance of interference
direct sequence
what is the purpose of the RTS-CTS mechanism in the 802.11 networks
tells the nodes within range of the receiver that they should not send anything for a while
what is a commonly used mechanism for controlling access to wireless networks and transmitted data
wireless security
how many devices can be connected to a master device in a Bluetooth piconet
225
frequency hopping
spread spectrum technique Bluetooth uses to mitigate interference
role of the four addresses in the 802.11 frame format
node sends probe frame
APs reply with probe response frame
node sends AP an association request frame
AP replies with an association response frame
what is the purpose of the distribution system in an 802.11 network
connects access points (APs)
what happens if two nodes sent RTS frames at the same time in 802.11 networks
RTS frames collide. Nodes wait for a CTS frame, and if not received, they retry after a random delay
which standard is based on Bluetooth but excludes application protocols? It is designed for situations where low bandwidth and power consumption are crucial
IEEE 801.15.1
what is the primary technology used for fiber-based broadband delivery to homes and businesses
PON (passive optical network)
how is upstream traffic managed in a PON network
it is time-division multiplexed on the upstream wavelength, with each ONU periodically getting a turn to transmit
what is the primary difference between 4G and 5G regarding waveforms
5G defines a family of waveforms while 4G defines only one
what is the main innovation of LTE’s air interface
the allocation of available radio spectrum to UEs
what is the primary purpose of the Broadband Network Gateway (BNG) in a PON network
gateway between the access network and internet
what is the current bandwidth supported by G-PON (Gigabit-PON)
2.25 Gbps
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