1. FDM is a multiplexing scheme which divides the bandwidth into equalsized portions, with each user being assigned to one portion.
2. ALOHA is a protocol that let users transmit whenever they have a frame to
be sent, And if collision happens, it retransmits the frame again after waiting
a random amount of time.
3. CSMA are protocols in which stations listen to the channel and send their
data if the channel is idle.
4. CSMA/CD is a protocol in which stations listen to the channel for collision
while it is transmitting.
5. Collision-Free Protocols are protocols that ensure totally no collision could
happen.
6. A Bit Map Protocol is a protocol in which there are contention slots to
decide the order of stations that are going to make transmission.
7. Token Passing is a protocol in which the station that has a token
(permission to send), it has the right to start transmission, otherwise it must
pass this token to another station.
8. Binary Countdown is a protocol in which higher- numbered stations have a
higher priority.
9. Limited-Contention Protocols
are protocols combine the best properties
of the contention protocols and collision-free protocols.
10.Wireless LAN Protocols (MACA) is a protocol in which the sender must
send a (Request to Send) and wait for (Clear to send) before start
transmission.
11.The hidden terminal problem
is a wireless Lan problem of a station not
being able to detect a potential competitor for the medium because the
competitor is too far away.
12.The exposed terminal problem is a wireless Lan problem that happened
when a station falsely concludes that it may not start transmission while it is
possible.
13.Describe the static channel allocation (e.g. FDM ) problem.
If Number of spectrum portions > number of users
Problem : some of users will be denied permission for lack of bandwidth.
If Number of spectrum portions < number of users
Problem : a large piece of valuable spectrum will be wasted.
if Number of spectrum portions = number of users
Problem : some of users will be denied permission for lack of bandwidth.
14.Compare between ALOHA and SLOTTED ALLOHA ?
Pure ALOHA: Let users transmit whenever they have data to be sent, if the frame
was destroyed ,the sender just waits a random amount of time and sends it again.
Slotted ALOHA: Time is divided into intervals, Each interval corresponding to one
frame , it is required to wait for the beginning of the next slot.
15.Compare between 1-persistent CSMA , nonpersistent CSMA , by (a)how
they work, (b) channel utilization, (c) delay?
1-persistent CSMA
nonpersistent CSMA
how they work
If the channel is busy,
If the channel is busy,
continuously sense it for waits a random period of
collision.
time before sense it again.
channel utilization
Better channel utilization
(less collisions) than 1persistent CSMA
delay
lower delay than
nonpersistent CSMA
16.Compare between 1-persistent CSMA , CSMA/CD , by (a)how they work,
(b) channel utilization (c) delay?
1-persistent CSMA CSMA/CD
how they work It doesn’t sense the It stops transmitting when it detect
channel for collision a collision
while transmitting
channel
Better channel utilization (less
utilization
collisions) than 1-persistent
CSMA
delay
lower delay than 1-persistent
CSMA
17.Compare between ALOHA and CSMA protocols by (a)how they work, (b)
channel utilization, (c) delay?
ALOHA
CSMA
how they work
It doesn’t sense the
It senses the channel for
channel for collisions
collisions
channel utilization
Better channel utilization
(less collisions) than
ALOHA
delay
lower delay than ALOHA
18.Compare between Contention Protocols (e.g CSMA, ALOHA), CollisionFree Protocols , Limited-Contention Protocols by (b) channel utilization, (c)
delay?
Collision-Free Contention Limited-Contention
channel utilization Better channel
Better channel
utilization
utilization (less
(0% collisons)
collision) than
than others
contention protocols
delay
lower delay Lower delay than
than others Collision-free
protocols
1. Reprater is a physical layer device that receives, amplifies, and transmits
in both directions.
2. Repraters or hubs are devices that do not understand frames, packets, or
headers. They understand the symbols that encode bits as volts.
3. Hub is a physical layer device connects all attached wires electrically
together, and all stations connected to are in the same collision domain.
4. Bridges is a data link layer device like switch but used to connect two or
more LANs
5. Switch is a device that outputs frames to the station for which those frame
are destined and each station connected to its own independent collision
domain.
6. Switch is a data link layer device that examines the physical addresses in
the frame header to use them to outputs frames to their destinations.
7. Router is a network layer device that examines the logical addresses (IP
addresses) in the packet header to forward data packets between computer
networks.
8. Fast Ethernet is the Ethernet model that keeps the entire old frame formats
interfaces, and procedural rules, but reduce the bit time from 100 nsec to 10
nsec (increase the speed from 10Mbps to 100 Mbps) by improving its cable
technology.
9. Gigabit Ethernet is the Ethernet model that keeps the entire old frame
formats interfaces, and procedural rules, but reduce the bit time from 10 nsec
to 1 nsec (increase the speed from 100Mbps to 1 Gbps) by improving its
cable technology.
10.10-Gigabit Ethernet is the Ethernet model that keeps the entire old frame
formats interfaces, and procedural rules, but reduce the bit time from 1 nsec
to 100 psec (increase the speed from 1 Gbps to 10 Gbps) by improving its
cable technology.
Compare between a Router , a Switch,a Hub by (a) function (b)device type.
router
switch
hub
function
examines the IP examines the
It does not
addresses in the
physical
understand
packet header to addresses in the frames’ or
forward data
frame header to packets’ headers.
packets between use them to
it understands
computer
outputs frames
the symbols that
networks
to their
encode bits as
destinations
volts
device type
Network layer
Data link layer
Physical layer
11.A switch improves performance over a hub in two ways. Mention them.
1-There are no collisions, the capacity is used more efficiently.
2-With a switch multiple frames can be sent simultaneously (by different
stations).
12.In the switched Ethernet that uses a switch and full duplex connections; does
it need to apply CSMA protocol, Yes or No?
No , Not needed
13.What is the IEEE numbers that represent Ethernet, wireless LAN, broadband
wireless, Bluetooth?
Ethernet : 802.3
wireless LAN : 802.11
broadband wireless ( MAN ) : 802.16
Bluetooth ( PAN ) : 802.15
14.What is the basic idea behind fast Ethernet and other later Ethernets ?
- keep all the old frame formats, interfaces, and procedural rules (make it
compatible with older Ethernet systems)
- increase speed connection
o (10Mbps to 100 Mbps for fast Ethernet,
100Mbps to 1 Gbps for Gigabit Ethernet,
1Gbps to 10 Gbps for 10- Gigabit Ethernet)
15.CSMA/CD is no longer part of the 10-Gigabit Ethernet design, why?
The design uses switch and full dublex operations .
1. compare between infrastructure mode and ad hoc mode in wireless Lanby their
architecture?
The infrastructure mode has AP ( Access Point )
2. What is the LLC sublayerjob ?What is the service-specific convergence
sublayer job ?
LLC ( logical link control ) or service-specific convergence: hide the
differences between the different 802 variants technologies and provide an
interface to the network layer.
3. What is the MACsublayerjob ?
MAC (Medium Access Control) sublayer : determines how the channel
is allocated, that is , who gets to transmit next or who gets access to the
channel.
4. match between the Service name and its main Task?
Service name
1.
association service
Task
4. lets stations transmit and receive data
2.
integration
2. 2.connecting the wireless LAN to the Internet
3.
Reassociation
6. provides higher-layer timer synchronization
4.
Data delivery
1. Used to connect stations to APs
5.
Privacy
5. manages the details of encryption and decryption
6.
Companion
3. lets a station change its preferred AP
5. What is the main technology that used by wireless LAN and broadband
wireless? OFDM
6. ,
7. ,
8. Mention the three data link sublayers of wimax protocol stack, and what is their
jobs?
- Security layer : deal with privacy and security . It manages encryption,
decryption, and key management.
MAC common layer : determines how the channel is allocated .
- The service-specific convergence sublayer ( LLC layer) : hide the
differences between the different 802 variants technologies and provide
an interface to the network layer.
9. Mention the key features of Bluetooth technology?
- Short Range and Small Networks
- low power
- low cost
10.What is the basic unit of Bluetooth architecture? What does it consist of?
- A Piconet : it consists of a master node (for synchronization purposes)
and up to seven active slave nodes.
11.how are piconets interconnected ?
- bridge node
12.What does scatternet consist of ?
- is interconnected collection of piconets
13.Why is direct slave-slave communication not possible?
- Because slave nodes just do whatever the master tells them to do.
1. Compare between connectionless service and connection-oriented service
by network name of each service, circuit setup requiring, Addressing,
routing, effect of router failure.
connectionless service
network name
datagram network
circuit setup requiring Not needed
Addressing
Each packet contains full
source and destination
address
routing
Each packet is routed
independently
effect of router failure None, except for packets
lost
during the crash
connection-oriented service
a virtual-circuit network
required
Each packet contains a
short VC number
Router chosen when VC is
set up , all packets follow it
All VCs that passed
through
the failed router are
terminated
2. Compare between Nonadaptive algorithms and Adaptive algorithms by
how the routing decision is done.
1. Nonadaptive algorithms (static routing) : their routing decisions are
computed in advance, offline.
2. Adaptive algorithms (dynamic routing): change their routing decisions to
reflect changes in the topology, and the traffic.
3. Mention three metrics to measure the path length between routers.
• the number of hops
• the geographic distance in kilometers
• The propagation delay
4. Find the shortest path from the router A to the router D, and determine the
propagation delay and the outgoing line at each router.
A --> G --> E --> F --> C --> D
5. Mention the measures that are taken to stop generating vast numbers of
duplicate packets In flooding routing algorithm
a. to have a hop counter in the header of each packet that is
decremented at each router, with the packet being discarded when the
counter reaches zero.
b. to have a sequence number in the header of each packet , to make
sure the router not to send the same packet second time.
6. What are the 2 parts that each entry in the routing table has?
a. the best outgoing line
b. the best distance.
7. How are the routing tables updated using the distance vector routing
algorithm?
- by exchanging information with the neighbor routers
8. ,
9. How is the propagation delay measured?
- the propagation delay is measured by calculating the difference
between the departure time and the arrival time of the a special
ECHO(timestamp) packet.
10.What the packet type that is used to measure the propagation delay with
neighbors routers?
- special ECHO (Timestamp)packet
11.And what the packet type that is used to learn who the router neighbors are?
- HELLO packet
12.How can hierarchical routing reduce the routing table size?
- By dividing the network into regions; so a router does not need to
know each station IP address, it just needs to know the network
address of each region
13.Give 2 methods of broadcasting routing.
• Sending a distinct packet to each destination.
• reverse path forwarding method
• flooding method
14.Flooding
is a simple local technique, in which every incoming packet is
sent out on every outgoing line except the one it arrived on.
15.broadcastingis sending a packet to all destinations simultaneously.
16. Determine the propagation delay and the outgoing line using Distance
Vector Routing
A 8
A
B 22
I
C 27
K
D 14
K
E 19
H
F 25
K
G 12
K
H 12
H
I 10
I
J K 6
K
L 15
K
1. Mention the two solutions of congestions.
• increase the resources
• decrease the load.
17.Match between the congestion approach and its definition?
congestion approach
1. Provisioning
(e)
2. traffic-aware routing (b)
3. admission control
(d)
4. Traffic Throttling
(a)
5. load shedding
(c)
Definition
a) To deliver feedback to the sources whose traffic
flows are responsible for the congestion, to stop or
slow down the traffic.
b) to shift traffic away from heavily used paths by
changing the shortest path weights.
c) to discard packets that it cannot deliver.
d) To refuse new connections in a virtual-circuit
network, if they would cause the network to become
congested.
e) to build a network that is well matched to the traffic
that it carries.
18.Mention the four primary parameters that determine the Quality of Service.
• bandwidth,
• delay,
• jitter,
• loss.
19. What’s the difference between delay and jitter?
- Jitter: The variation in the delay or packet arrival times
20.which parameters is each of the following application sensitive to.(there
would be more than one answer for each)
application
Audio
Video
Stream (on demand)
Real-time
Sensitive to
Jitter
Jitter , bandwidth
Jitter
Jitter , delay
21.Bandwidth (computing) is the rate of data transfer, bit rate or throughput,
measured in bits per second (bit/s)
22.Jitter is the variation in the delay or packet arrival times.
23.Tunneling is a technique used to send an IP packet containing an IPv6
address through IPv4 network.
24.Packet Fragmentation
is the solution when a large packet wants to travel
through a network whose maximum packet size is too small.
25.What are the three field of packet header are needed for fragmentation?
• the packet number (Identification)
• fragment offset
• the end-of-packet flag
3. Compare between subnetting and supernetting (Classless InterDomain
Routing). Mention the advantage of using these techniques.
- Subnetting : split large prefixes into smaller ones
- supernetting : combine multiple small prefixes into a single larger prefix .
4. Mention the advantage of Network Address Translation.
- Solution of the limited number of IP.V4 addresses
5. What are the purposes of these control protocols (ICMP, ARP, DHCP)
- ICMP : is a control protocol used for reporting unexpected events occur
during packet processing.
- ARP : is a control protocol used to find the destination’s physical address
(Ethernet address) by its IP address.
- DHCP : Is a control protocol to request new IP address and other
configurations.
6. IP
is the protocol that is used for data transfer.
7. ICMP is a control protocol used for reporting unexpected events occur
during packet processing.
8. ARP is a control protocol used to find the destination’s physical address
(Ethernet address) by its IP address.
9. DHCP
Is a control protocol to request new IP address and other
configurations.
1- Compare between Data Link layer, Network layer and Transport layer by
Types of data deliveries, Addressing
data deliveries
Addressing
Data Link layer node-to-node
a MAC address ( a physical
Address)
Network layer
host-to-host
IP address (a Logical Address)
Transport layer process-toa port number
process
2- What’s the socket address?
an IP address + a port number
3- Compare between UDP and TCP by connection services, reliability, flow
control and error control mechanisms
UDP
TCP
connection
reliability
services
connectionless no
connectionyes
oriented
flow control
no
sliding
window
error control
mechanisms
Checksum
Checksum,
acknowledgment,
time-out
4- Why does TCP need buffers to store packets?
because the sending and the receiving processes may not write or read data at the
same speed.
5- Mention the three TCP numbering system, and explain each of them. Slide 22
6- What does TCP do if a segment arrives out of order?
it stores them temporarily and flag them as out-of-order segments until the
missing segment arrives.
7- What is the technique that TCP uses for flow control?
Sliding window,
8 - Mention the three mechanisms that are used for Error detection and correction
checksum, acknowledgment, and time-out.
9- Mention the two occasions when a segment is needed to be retransmitted.
a- when a retransmission timer expires (time-out)
b- when the sender receives three duplicate ACKs