What is the difference between a host and an end system?
List several different types of end systems.
Is a Web server an end system?
A host is an end system, and vice versa.
Types of end systems: desktops, laptops, smartphones, tablets, automobiles, various sensors, etc.
Yes, a Web server is an end system.
The word protocol is often used to describe diplomatic relations. How does Wikipedia describe diplomatic protocol?
A protocol is described as the rules of etiquette for heads of state, for example in what order diplomats address representatives of other nations often in order of decreasing importance and power.
Why are standards important for protocols?
Standards are important for protocols so that both communicating computers are sending and interpreting data in the same order and manner.
List six access technologies. Classify each one as home access, enterprise access, or wide area network access.
DSL(Digital Subscriber Line) - Home Access
Cable - Home Access
FTTH(Fiber to the Home) - Home Access
Dial-Up - Home Access
Satellite - Home Access
Ethernet - Enterprise (and Home) Access
WiFi - Enterprise (and Home) Access
3G - Wide Area Network Access
LT
Is HFC transmission rate dedicated or shared among users? Are collisions possible in a downstream HFC channel? Why or why not?
HFC (cable internet) transmission rate is shared among users. There are no collisions in the downstream channel because all packets come from a single source, the head end.
List the available residential access technologies in your city. For each type of access, provide the advertised downstream rate, upstream rate, and monthly price.
In most American cities, the current possibilities include: dial-up; DSL; cable modem; fiber- to-the-home.
HFC - 300 mbps - $65
- 100 mbps - $65
- 2 mbps - $15
What is the transmission rate of Ethernet LANs?
Users - 100 mbps
Servers - 1 gbps or even 10 gbps
Ethernet LANs have transmission rates of 10 Mbps, 100 Mbps, 1 Gbps and 10 Gbps.
What are some of the physical media that Ethernet can run over?
Today, Ethernet most commonly runs over twisted-pair copper wire. It also can run over fibers optic links.
Dial-up modems, HFC, DSL and FTTH are all used for residential access. For each of these access technologies, provide a range of transmission rates and comment on whether the transmission rate is shared or dedicated.
Dial up modems: up to 56 Kbps, bandwidth is dedicated; ADSL: up to 24 Mbps downstream and 2.5 Mbps upstream, bandwidth is dedicated; HFC, rates up to 42.8 Mbps and upstream rates of up to 30.7 Mbps, bandwidth is shared. FTTH: 2-10Mbps upload; 10-20 Mbps d
Describe the most popular wireless Internet access technologies today. Compare and contrast them.
There are two popular wireless Internet access technologies today:
a) Wifi (802.11) In a wireless LAN, wireless users transmit/receive packets to/from an base station (i.e., wireless access point) within a radius of few tens of meters. The base station is
Suppose there is exactly one packet switch between a sending host and a receiving host. The transmission rates between the sending host and the switch and between the switch and the receiving host are R1 and R2, respectively. Assuming that the switch uses
d(end to end) = N(L/R)
d - delay
N - Number of links
L - Number of bits in packets
R - rate
d(end to end) = (L/R1)+(L/R2)
What advantage does a circuit-switched network have over a packet-switched network?
What advantages does TDM(Time Division Multiplexing) have over FDM(Frequency Division Multiplexing) in a circuit-switched network?
A circuit-switched network can guarantee a certain amount of end-to-end bandwidth for the duration of a call. Most packet-switched networks today (including the Internet) cannot make any end-to-end guarantees for bandwidth.
In a packet switched network, t
Suppose users share a 2 Mbps link. Also suppose each user transmits continuously at 1 Mbps when transmitting, but each user transmits only 20 percent of the time. (See the discussion of statistical multiplexing in Section 1.3.)
a. When circuit switching i
a) two users can be supported because each user requires half of the bandwidth
b)Since each user requires 1Mbps when transmitting, if two or fewer users transmit simultaneously, a maximum of 2Mbps will be required. Since the available bandwidth of the sha
Why will two ISPs at the same level of the hierarchy often peer with each other? How does an ISP earn money?
If the two ISPs do not peer with each other, then when they send traffic to each other they have to send the traffic through a provider ISP (intermediary), to which they have to pay for carrying the traffic. By peering with each other directly, the two IS
Some content providers have created their own networks. Describe Google's network. What motivates content providers to create these networks?
Google's private network connects together all its data centers, big and small. Traffic between the Google data centers passes over its private network rather than over the public Internet. Many of these data centers are located in, or close to, lower tie
Consider sending a packet from a source host to a destination host over a fixed route. List the delay components in the end-to-end delay. Which of these delays are constant and which are variable?
The delay components are processing delays, transmission delays, propagation delays, and queuing delays. All of these delays are fixed, except for the queuing delays, which are variable
Visit the Transmission Versus Propagation Delay applet at the companion Web site. Among the rates, propagation delay, and packet sizes available, find a combination for which the sender finishes transmitting before the first bit of the packet reaches the
a) 1000 km, 1 Mbps, 100 bytes
b) 100 km, 1 Mbps, 100 bytes
How long does it take a packet of length 1,000 bytes to propagate over a link of distance 2,500 km, propagation speed 2.5 � 108 m/s, and transmission rate 2 Mbps? More generally, how long does it take a packet of length L to propagate over a link of dista
10msec;
d/s;
no;
no
Suppose Host A wants to send a large file to Host B. The path from Host A to Host B has three links, of rates R1 = 500 kbps, R2 = 2 Mbps, and R3 = 1 Mbps.
a. Assuming no other traffic in the network, what is the throughput for the file transfer?
b. Suppos
a) 500 kbps
b) 64 seconds
c) 100kbps; 320 seconds
Suppose end system A wants to send a large file to end system B. At a very high level, describe how end system A creates packets from the file. When one of these packets arrives to a packet switch, what information in the packet does the switch use to det
End system A breaks the large file into chunks. It adds header to each chunk, thereby generating multiple packets from the file. The header in each packet includes the IP address of the destination (end system B). The packet switch uses the destination IP
Visit the Queuing and Loss applet at the companion Web site. What is the maximum emission rate and the minimum transmission rate? With those rates, what is the traffic intensity? Run the applet with these rates and deter- mine how long it takes for packet
The maximum emission rate is 500 packets/sec and the maximum transmission rate is 350 packets/sec. The corresponding traffic intensity is 500/350 =1.43 > 1. Loss will eventually occur for each experiment; but the time when loss first occurs will be differ
List five tasks that a layer can perform. Is it possible that one (or more) of these tasks could be performed by two (or more) layers?
Five generic tasks are error control, flow control, segmentation and reassembly, multiplexing, and connection setup. Yes, these tasks can be duplicated at different layers. For example, error control is often provided at more than one layer.
What are the five layers in the Internet protocol stack? What are the principal responsibilities of each of these layers?
The five layers in the Internet protocol stack are - from top to bottom - the application layer, the transport layer, the network layer, the link layer, and the physical layer. The principal responsibilities are outlined in Section 1.5.1.
What is an application-layer message? A transport-layer segment? A network- layer datagram? A link-layer frame?
Application-layer message: data which an application wants to send and passed onto the transport layer; transport-layer segment: generated by the transport layer and encapsulates application-layer message with transport layer header; network-layer datagra
Which layers in the Internet protocol stack does a router process? Which layers does a link-layer switch process? Which layers does a host process?
Routers process network, link and physical layers (layers 1 through 3). (This is a little bit of a white lie, as modern routers sometimes act as firewalls or caching components, and process Transport layer as well.) Link layer switches process link and ph
What is the difference between a virus and a worm?
A virus requires some form of user interaction to infect a system.
A worm on the other hand, requires no interaction. Instead a hacker may send a piece of malware to a vulnerable network application, and have the application run it, creating the worm.
a)
Describe how a botnet can be created, and how it can be used for a DDoS attack.
Creation of a botnet requires an attacker to find vulnerability in some application or system (e.g. exploiting the buffer overflow vulnerability that might exist in an application). After finding the vulnerability, the attacker needs to scan for hosts tha
Suppose Alice and Bob are sending packets to each other over a computer network. Suppose Trudy positions herself in the network so that she can capture all the packets sent by Alice and send whatever she wants to Bob; she can also capture all the packets
Trudy can pretend to be Bob to Alice (and vice-versa) and partially or completely modify the message(s) being sent from Bob to Alice. For example, she can easily change the phrase "Alice, I owe you $1000" to "Alice, I owe you $10,000". Furthermore, Trudy