Telecom Exam Two

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  1. What's the three way handshake and when do we use it?
    • Connection-oriented messaging sets up a TCP connection (also called a session) between the sender and receiver. To establish a connection, the transport layer on both the sender and the receiver must send a SYN
    • (synchronize) and receive a ACK (acknowledgement) segment. This process starts with
    • the sender (usually a client) sending a SYN to the receiver (usually a server). The server
    • responds with an ACK for the sender’s/client’s SYN and then sends its own SYN. SYN
    • is usually a randomly generated number that identifies a packet. The last step is when
    • the client sends an ACK for the server’s SYN. This is called the three-way handshake
    • and this process also contains the segment size negotiation. Once the connection is established, the segments flow between the sender and receiver. TCP uses the continuous ARQ (sliding window) technique described in Chapter 4 to make sure that all segments arrive and to provide flow control.
  2. What's the transport layer and what does it do?
    • The transport layer links the application software in the application layer with the network
    • and is responsible for segmenting large messages into smaller ones for transmission and
    • for managing the session (the end-to-end delivery of the message). When the transport layer receives an incoming message,
    • the transport layer must decide to which application program it should be delivered.


    • It is therefore up to the sender’s transport layer to break
    • the data into several smaller segments that can be sent by the data link layer across the
    • circuit. At the other end, the receiver’s transport layer must receive all these separate
    • segments and recombine them into one large message. Segmenting means to take one outgoing message from the application layer and
    • break it into a set of smaller segments for transmission through the network.


    And Session Management
  3. What's connection oriented and connectionless circuits and when do we use one over the other?
    Connection-oriented messaging sets up a TCP connection (also called a session) between the sender and receiver (three way handshake). Connectionless messaging means each packet is treated separately and makes its own way through the network. Unlike connection-oriented routing, no connection is established. The sender simply sends the packets as separate, unrelated entities, and it is possible that different packets will take different routes through the network, depending on the type of routing used and the amount of traf- fic. Because packets following different routes may travel at different speeds, they may arrive out of sequence at their destination. The sender’s network layer, therefore, puts a sequence number on each packet, in addition to information about the message stream to which the packet belongs. The network layer must reassemble them in the correct order before passing the message to the application layer. Quality of Service (QoS) routing is a special type of connection-oriented messaging in which different connections are assigned different priorities. For example, videoconferencing requires fast delivery of packets to ensure that the images and voices appear smooth and continuous; they are very time dependent because delays in routing seriously affect the quality of the service provided. Email packets, on the other hand, have no such requirements. With QoS routing, different classes of service are defined, each with different priorities. When the transport layer software attempts to establish a connection (i.e., a session), it specifies the class of service that connection requires. Each path through the network is designed to support a different number and mix of service classes. When a connection is established, the network ensures that no connections are established that exceed the maximum number of that class on a given circuit.

    • Connectionless is most commonly used when the application data or message can fit
    • into one single message.

    • Transmission Control Protocol/Internet Protocol can operate either as
    • connection-oriented or connectionless. When connection-oriented messaging is
    • desired, TCP is used. When connectionless messaging is desired, the TCP segment
    • is replaced with a User Datagram Protocol (UDP) packet. The UDP packet is much
    • smaller than the TCP packet (only 8 bytes). UDP is most commonly
    • used for control messages such as addressing (DHCP [Dynamic Host Configuration Protocol],
    • discussed later in this chapter), routing control messages (RIP [Routing Information
    • Protocol], discussed later in this chapter), and network management
  4. Various levels of addressing; he's going to give examples and you have to identify if it's application or data link layer?
    • application software that used Internet
    • addresses (e.g., www.indiana.edu). This is an application layer address (or a server
    • name). When a user types an Internet address into a Web browser, the request is passed
    • to the network layer as part of an application layer packet formatted using the HTTP
    • protocol. The network layer software, in turn, uses a network layer address. The network
    • layer protocol used on the Internet is IP, so this Web address (www.indiana.edu) is
    • translated into an IP address that is 4 bytes long when using IPv4 (e.g., 129.79.127.4) The network layer then determines the best route through the network to the final
    • destination. On the basis of this routing, the network layer identifies the data link layer
    • address of the next computer to which the message should be sent. If the data link
    • layer is running Ethernet, then the network layer IP address would be translated into
    • an Ethernet address.  a possible address might be 00-0F-00-81-14-00 (Ethernet addresses are usually
    • expressed in hexadecimal)
  5. IP addressing scheme-4 octets, what is each one used for?
  6. What is subnetting, when do you use it? (no arithmetic questions)
    • However, it is not
    • efficient to assign every computer to the same network. Rather, subnetworks or subnets
    • are designed on the network that subdivide the network into logical pieces. Two addresses on this subnet cannot be assigned as IP address to any
    • computer. The first address is 128.192.56.0 and this is the network address. The second
    • address is 128.192.56.255 is the broadcast address. Subnets are created to separate areas of your network for security and/or to hold down broadcasts if you have a large network. With routers, subnets can talk.
  7. Routing, what is a router, what is the difference between static and dynamic routing, the advantages and disadvantages between them.
    • Routing is the process of determining the route or path through the network that a message
    • will travel from the sending computer to the receiving computer. Routers are usually found at the
    • edge of subnets because they are the devices that connect subnets together and enable
    • messages to flow from one subnet to another as the messages move through the network
    • from sender to receiver. 
    • Static routing is decentralized, which means that all computers or
    • routers in the network make their own routing decisions following a formal routing
    • protocol. With static routing, routing decisions are made in a fixed manner by individual
    • computers or routers. The routing table is developed by the network manager, and it
    • changes only when computers are added to or removed from the network. Static routing is commonly used in networks that have few routing
    • options that seldom change.


    • With dynamic routing (or adaptive routing), routing decisions are
    • made in a decentralized manner by individual computers. This approach is used when
    • there are multiple routes through a network, and it is important to select the best route.
    • Dynamic routing attempts to improve network performance by routing messages over the
    • fastest possible route, away from busy circuits and busy computers. There are two drawbacks to dynamic routing. First, it requires more processing by
    • each computer or router in the network than does centralized routing or static routing.
    • Computing resources are devoted to adjusting routing tables rather than to sending messages,
    • which can slow down the network. Second, the transmission of routing information
    • “wastes” network capacity. Some dynamic routing protocols transmit status information
    • very frequently, which can significantly reduce performance
  8. What is a routing table?
    • Every router has a routing table that specifies how messages will travel through the
    • network. In its simplest form, the routing table is a two-column table. The first column
    • lists every network or computer that the router knows about and the second column lists
    • the interface that connects to it.
    • A router uses its routing table to decide where to send the messages it receives. Suppose a computer in the 10.10.43.x subnet sends an HTTP request for a Web page that
    • is located on the company’s Web server, which is in the 10.10.20.x subnet (let’s say the
    • Web server has an IP address of 10.10.20.10). The computer would send the message to its router, R2. R2 would look at the IP address on the IP packet and search its routing
    • table for a matching address. It would search through the table, from top to bottom, until
    • it reached the third entry, which is a range of addresses that contains the Web server’s
    • address (10.10.20.10). The matching interface is number 2, so R2 would transmit the
    • message on this interface.
  9. What are the advantages and disadvantages of centralized and decentralized routing?
    • With centralized routing, all routing decisions are made by one
    • central computer or router. Centralized routing is commonly used in host-based networks  and in this case, routing decisions are rather simple. All computers are
    • connected to the central computer, so any message that needs to be routed is simply sent
    • to the central computer, which in turn retransmits the message on the appropriate circuit
    • to the destination. Static routing is decentralized, which means that all computers or
    • routers in the network make their own routing decisions following a formal routing
    • protocol. In MANs and WANs, the routing table for each computer is developed by its
    • individual network manager (although network managers often share information). In
    • LANs or backbones, the routing tables used by all computers on the network are usually
    • developed by one individual or a committee. Most decentralized routing protocols are
    • self-adjusting, meaning that they can automatically adapt to changes in the network
    • configuration (e.g., adding and deleting computers and circuits).
  10. Know the 2 ways of designing a network and their steps: 1) Traditional and 2)Contemporary (simpler and quicker)
    • The traditional network design process follows a very structured systems analysis and
    • design process similar to that used to build application systems. First, the network analyst
    • meets with users to identify user needs and the application systems planned for the network.
    • Second, the analyst develops a precise estimate of the amount of data that each user
    • will send and receive and uses this to estimate the total amount of traffic on each part of the
    • network. Third, the circuits needed to support this traffic plus a modest increase in traffic
    • are designed and cost estimates are obtained from vendors. Finally, 1 or 2 years later, the
    • network is built and implemented
  11. Know the building blocks to build a network-what is the most important step? (User requirements)
    • This process begins with needs analysis, during
    • which the designer attempts to understand the fundamental current and future network
    • needs of the various users, departments, and applications. This is likely to be an educated
    • guess at best. Users’ access needs and the needs of applications drive the network design
    • process from the top into the center of the network. These needs are classified as typical or
    • high volume. Specific technology needs are identified (e.g., the ability to dial in with current
    • modem technologies).
    • The next step, technology design, examines the available technologies and assesses
    • which options will meet users’ needs. The designer makes some estimates about the network
    • needs of each category of user and circuit in terms of current technology (e.g., 1 Gbps
    • Ethernet) and matches needs to technologies. Because the basic network design is general, it
    • can easily be changed as needs and technologies change. The difficulty, of course, lies in predicting
    • user demand so one can define the technologies needed. Most organizations solve
    • this by building more capacity than they expect to need and by designing networks that can
    • easily grow and then closely monitoring growth so they expand the network ahead of the
    • growth pattern.
    • In the third step, cost assessment, the relative costs of the technologies are considered.
    • The process then cycles back to the needs analysis, which is refined using the technology and
    • cost information to produce a new assessment of users’ needs. This in turn triggers changes
    • in the technology design and cost assessment, and so on. By cycling through these three
    • processes, the final network design is established
  12. Common network protocols. (Ethernet is most common, know 10BaseT, what they are, and how to do them.
    • Figure 7-6 summarizes the many different types of Ethernet in use today. The 10Base-T
    • standard revolutionized Ethernet and made it the most popular type of LAN in the world.
    • Today, 100Base-T and 1000Base-T are the most common forms of Ethernet.
    • Other types of Ethernet include 1000Base-F (which runs at 1 Gbps and is sometimes
    • called 1 GbE), 10 GbE (10 Gbps), 40 GbE (40 Gbps), and 100 GbE (100 Gbps).They can use
    • Ethernet’s traditional half-duplex approach, but most are configured to use full duplex. Each
    • is also designed to run over fiber-optic cables, but some may also use traditional twisted-pair
    • cables (e.g., Cat 5e). For example, two common versions of 1000Base-F are 1000Base-LX and
    • 1000Base-SX, which both use fiber-optic cable, running up to 440 and 260 meters, respectively;
    • 1000Base-T, which runs on four pairs of category 5 twisted-pair cable, but only up to
    • 100 meters;2 and 1000Base-CX, which runs up to 24 meters on one category 5 cable. Similar
    • versions of 10 and 40 GbE that use different media are also available.
  13. Simulate network what and how Carlo technique?
  14. Design phase in network design - includes technology component, how do you know what technology is available? RFP and tradeshows
  15. Relationship  protocol, speed in technology design phase, how they interrelate.Is there an advantage to purchasing things off the shelf or from a vendor; know the advantages and disadvantages.
  16. If you were selling your network design to management, what is important in your sales pitch?
    • The key to gaining the acceptance of senior management lies in speaking management’s
    • language. It is pointless to talk about upgrades from 100 Mbps to 1 Gbps on the backbone
    • because this terminology is meaningless from a business perspective. A more compelling argument is to discuss the growth in network use. For example, a simple graph that shows
    • network usage growing at 25% per year, compared with the network budget growing at
    • 10% per year, presents a powerful illustration that the network costs are well managed, not
    • out of control.
    • Likewise, a focus on network reliability is an easily understandable issue. For example,
    • if the network supports a mission-critical system such as order processing or moving
    • point-of-sale data from retail stores to corporate offices, it is clear from a business perspective
    • that the network must be available and performing properly, or the organization will
    • lose revenue.
  17. What are the five servers and how are they used?
  18. Know the advantages and disadvantages of media category 5, also with fiber optics.
    • Most LANs are built with unshielded twisted-pair (UTP) cable, shielded
    • twisted-pair (STP) cable, or fiber-optic cable. (Common cable standards are discussed on
    • the next page. We should add that these cable standards specify the minimum quality cable
    • required; it is possible, for example, to use category 5e UTP cable that is rated for 1000 Mbps
    • in a LAN that runs at 100 Mbps.)
    • Many LANs use UTP cable. Its low cost makes it very useful. STP is only used in special
    • areas that produce electrical interference, such as factories near heavy machinery or
    • hospitals near MRI scanners.
    • Fiber-optic cable is even thinner than UTP wire and therefore takes far less space when
    • cabled throughout a building. It also is much lighter, weighing less than 10 pounds per 1,000
    • feet. Because of its high capacity, fiber-optic cabling is perfect for BNs, although it is beginning
    • to be used in LANs.
  19. Various categories of network (LAN, BBN) how are they related, their design, protocol, speed.
  20. Know the several components of a network (network, server, media, NOS)
  21. How does a NOS differ from a regular OS?
    • The network operating system (NOS) is the software that controls the network. Every NOS
    • provides two sets of software: one that runs on the network server(s) and one that runs on
    • the network client(s). The server version of the NOS provides the software that performs
    • the functions associated with the data link, network, and application layers and usually the
    • computer’s own operating system. The client version of the NOS provides the software that
    • performs the functions associated with the data link and the network layers and must interact
    • with the application software and the computer’s own operating system. Most NOSs
    • provide different versions of their client software that run on different types of computers,
    • so that Windows computers, for example, can function on the same network as Apple computers.
    • In most cases (e.g., Windows and Linux), the client NOS software is included with
    • the operating system itself.
  22. List all the resources available on server
  23. Know logical and physical design.
  24. Bus, star network for logical and physical.
    • A logical topology is how the network works conceptually, much
    • like a logical data flow diagram (DFD) or logical entity relation diagram (ERD) in systems
    • analysis and design or database design. Aphysical topology is how the network is physically
    • installed, much like a physical DFD or physical ERD.

    • When we use hubs, Ethernet’s logical topology is a bus topology. All
    • computers are connected to one half-duplex circuit running the length of the network that is
    • called the bus. The top part of Figure 7-4 shows Ethernet’s logical topology. All frames from
    • any computer flow onto the central cable (or bus) and through it to all computers on the
    • LAN.


    • When we use switches, Ethernet’s topology is a logical star and a
    • physical star (Figure 7-5). From the outside, the switch looks almost identical to a hub, but
    • inside, it is very different. A switch is an intelligent device with a small computer built in that
    • is designed to manage a set of separate point-to-point circuits. That means that each circuit
    • connected to a switch is not shared with any other devices; only the switch and the attached
    • computer use it. The physical topology looks essentially the same as Ethernet’s physical
    • topology: a star. On the inside, the logical topology is a set of separate point-to-point circuits,
    • also a star. Many switches support full duplex circuits, meaning that each circuit can
    • simultaneously send and receive.
  25. How to detect collision in bus, star(no collision in star ), and ring?
    • With hubs, all computers share the same multipoint circuit and must take turns using
    • it. This shared multipoint circuit is often called a collision domain, because if two computers
    • ever did accidentally transmit at the same time, there would be a collision. When one
    • computer transmits, all the other computers must wait, which is very inefficient. Because
    • all frames are sent to all computers in the same collision domain, security is a problem
    • because any frame can be read by any computer. Most companies don’t use hub-based Ethernet
    • today, but products are still available and are very cheap. Wireless Ethernet, which we
    • discuss in a later section, works much the same as hub-based Ethernet. 

    • The solution to this is to listen while transmitting, better known as collision detection
    • (CD). If the NIC detects any signal other than its own, it presumes that a collision has
    • occurred and sends a jamming signal. All computers stop transmitting and wait for the
    • circuit to become free before trying to retransmit. The problem is that the computers
    • that caused the collision could attempt to retransmit at the same time. To prevent this,
    • each computer waits a random amount of time after the colliding frame disappears before
    • attempting to retransmit. Chances are both computers will choose a different random
    • amount of time and one will begin to transmit before the other, thus preventing a second
    • collision. However, if another collision occurs, the computers wait a random amount of
    • time before trying again. This does not eliminate collisions completely, but it reduces them
    • to manageable proportions.
  26. Differences and advantages in switch (star) and hub (bus) based Internet?
    • When a switch receives a frame from a computer, it looks at the address on the frame
    • and retransmits the frame only on the circuit connected to that computer, not to all circuits
    • as a hub would.Therefore, no computer needs to wait because another computer is transmitting;
    • every computer can transmit at the same time, resulting in much faster performance.
    • Today, no one buys a hub unless she or he can’t afford a switch.
  27. Know the three types of switches and their advantages and disadvantages
  28. Wireless Ethernet access points,what are their strengths and weaknesses and why we want to use them?
  29. How routers and switches are different.
  30. BBN what are they, and how are they designed (switched or nonswitched?)
    • Switched backbones are probably the most common type of BN used in the distribution
    • layer (i.e., within a building); most new building BNs designed today use switched backbones.
    • Switched backbone networks use a star topology with one switch at its center. Figure 8-1
    • shows a switched backbone connecting a series of LANs. There is a switch serving each
    • LAN (access layer) that is connected to the backbone switch at the bottom of the figure
    • (distribution layer). Most organizations now use switched backbones in which all network
    • devices for one part of the building are physically located in the same room, often in a rack
    • of equipment. This has the advantage of placing all network equipment in one place for easy
    • maintenance and upgrade, but it does require more cable. In most cases, the cost of the cable
    • is only a small part of the overall cost to install the network, so the cost is greatly outweighed
    • by the simplicity of maintenance and the flexibility it provides for future upgrades.

    • Routed backbones move packets along the backbone on the basis of their network layer
    • address (i.e., layer-3 address). Routed backbones are sometimes called subnetted backbones
    • or hierarchical backbones and are most commonly used to connect different buildings on
    • the same enterprise campus backbone network (i.e., at the core layer). There are a series of LANs (access layer) connected to a switched backbone (distribution
    • layer). Each backbone switch is connected to a router. Each router is connected to a core
    • router (core layer). These routers break the network into separate subnets. The LANs in one
    • building are a separate subnet from the LANs in a different building. Message traffic stays
    • within each subnet unless it specifically needs to leave the subnet to travel elsewhere on
    • the network, in which case the network layer address (e.g., TCP/IP) is used to move the
    • packet.
  31. Know VLANs
    • Virtual LANs are networks in which computers are assigned to LAN segments by software
    • rather than by hardware. In the first section, we described how in rack-mounted collapsed
    • BNs a computer could be moved from one hub to another by unplugging its cable
    • and plugging it into a different hub. VLANs provide the same capability via software so that
    • the network manager does not have to unplug and replug physical cables to move computers
    • from one segment to another.
    • Often, VLANs are faster and provide greater opportunities to manage the flow of traffic
    • on the LAN and BN than do the traditional LAN and routed BN architectures. However,
    • VLANs are significantly more complex, so they usually are used only for large networks.
  32. TCP/IP (give it) what it is, when we use it
    • Transmission Control Protocol/Internet Protocol can operate either as
    • connection-oriented or connectionless. When connection-oriented messaging is
    • desired, TCP is used. When connectionless messaging is desired, the TCP segment
    • is replaced with a User Datagram Protocol (UDP) packet. The UDP packet is much
    • smaller than the TCP packet (only 8 bytes).
  33. IP address scheme, when we use it and connectionless transmission when to use TCP or IP

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Telecom Exam Two
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