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Networks

Henry Stockdale Inglés 193 fichas

Fichas del conjunto (193)

  1. 1What is routing?The technique needed to enable networks to cater for these differing connectivitty characteristics and to determine an appropriate path
  2. 2What are the two main activities in the router?A - Forwarding – Determining which output line to send a packet to using a routing table
    B- Routing – Adding and deleting entries to the routing table & using network information to determine what to add and what to delete
  3. 3What is shortest path?A method that we can create network algorithms for to compute the shortest path from source to destination
  4. 4Why do we need multiple routes in a network topology?Because some may not be available at particular times, such as a link developing a fault or organisational policy reasons.
  5. 5Define "Best route" in networking termsWhen we say best route for a packet to take, we mean that it should be correct, should be the simplest or most direct, that it minimises network failures or be robust and that the algorithm should quickly arrive a stable view of appropriate routes and apply them
  6. 6What factors does the network consider when using Shortest Route?It can measure this in ways such as distance, delay, financial cost, hops and we can use metrics in these ways. They can be calculated from link properties, such as make metric proportional to bandwidth
  7. 7What does DV Routing stand for?Distance Vector Routing
  8. 8What are the 3 steps of DVR High Level Process?1 – Wait for update from a neighbour router
    2 – Calculate the new distance vector
    3 – Distribute new distance vector to neighbours
  9. 9What does a routing table maintain?Entries for each router on the network, preferred output line (port) for the destination and the estimated cost of reaching the destination (E.G. number of hops)
  10. 10Why does DVR need the information from the Routing Table?It can estimate the cost of reaching a lot of destinations
  11. 11What is "Convergence" in DVR?A process where DVR updates occur in parallel, several times, as information circulates through the network. Multiple updates to the estimates may be made over time and eventually, the “correct” answer will be reached via this process.
  12. 12What are the main issues with DVR?DV routing was found to be an inefficient process, as time to converge was found to be too slow after a change to the network topology
  13. 13What does LSR stand for?Link State Routing
  14. 14What are the 5 main activities of LSR?• Discover neighbours and learn their network address
    • Set the distance or cost metric to each neighbiur
    • Construct a packet with all of this information
    • Send this to other routers, and receive such packets from other routers
    • Compute the shortest path to every other router
  15. 15Where does LSR differ from DVR?Rather than maintaining a model in each router of destinations, best known distance (Cost), and output port, LSR uses a different technique
  16. 16What is the packet structure across the network in LSR?Sender ID – Sequence Number – Age – Neighbour- Associated Cost
  17. 17What is an Autonomous System (AS)?The unit of routing policy in the modern world of exterior routing
  18. 18What are the main characteristics of AS?They operate inter- and intra-routing protocols. Operate as entities and communicate between themselves to establish routes. Each operating under single organisational control (e.g. PLC). Generally created in a multi-homed situation and lead to the emergence of graphical networks where each vertex (point) represents an AS
  19. 19What is the routing policy of AS?* Flows of packets can be considered from two directions
    * Generally both directions of flow transit across the same route, though this is not necessarily always so. Policies & Technologies (e.g. SATCOM)
    * Path information flows take across the AS graphical network is dependent on a variety of factors, such as Commercial interests, Economic considerations and Policies in general
  20. 20What is Switching?Switching forwards packet from input port to output port. Port selected based on address in packet header. Has the advantage in that it covers a large geographic area (tolerate latency) and support large numbers of hosts (scalable bandwidth)
  21. 21What is Forwarding?Forwarding is the relaying of packets from one network segment to another by nodes in a computer network. The Network Layer of the OSI Layer is responsible for Packet Forwarding. The simplest forwarding model — unicasting — involves a packet being relayed from link to link along a chain leading from the packet's source to its destination
  22. 22Name two forms of internal switchingBuses, Interconnects
  23. 23What is interconnection?The physical linking of a carrier's network with equipment or facilities not belonging to that network. The term may refer to a connection between a carrier's facilities and the equipment belonging to its customer, or to a connection between two (or more) carriers
  24. 24What is, in Network terms, a Bus?A communication system that transfers data between components inside a computer, or between computers. This expression covers all related hardware components (wire, optical fiber, etc.) and software, including communication protocols
  25. 25What is OSPF?Open Shortest Path First. A routing protocol for Internet Protocol (IP) networks. It uses a link state routing algorithm and falls into the group of interior routing protocols, operating within a single autonomous system (AS)
  26. 26What is IS-IS?Intermediate System to Intermediate System - A routing protocol designed to move information efficiently within a computer network, a group of physically connected computers or similar devices. It accomplishes this by determining the best route for datagrams through a packet-switched network.
  27. 27Define RIPRouting Information Protocol (RIP) . It's one of the oldest distance-vector routing protocols, which employs the hop count as a routing metric. RIP prevents routing loops by implementing a limit on the number of hops allowed in a path from the source to a destination
  28. 28Explain Static RoutingA form of routing that occurs when a router uses a manually-configured routing entry, rather than information from a dynamic routing protocol to forward traffic. In many cases, static routes are usually manually configured by a network administrator by adding in entries into a routing table, though this may not always be the case. Unlike dynamic routing, static routes are fixed and do not change if the network is changed or reconfigured
  29. 29Describe the OSI ModelThe OSI model is a conceptual model that characterizes and standardizes the internal functions of a communication system by partitioning it into abstraction layers. The model groups communication functions into seven logical layers. A layer serves the layer above it and is served by the layer below it.
  30. 30What are the seven layers of the OSI Model?Physical
    Data Link
    Network
    Transport
    Session
    Presentation
    Application
  31. 31Describe a Socket, in network termsAn endpoint of an inter-process communication flow across a computer network. Today, most communication between computers is based on the Internet Protocol; therefore most network sockets are Internet sockets
  32. 32Please detail a Socket APIAn application programming interface (API), usually provided by the operating system, that allows application programs to control and use network sockets
  33. 33Define a Socket AddressThe combination of an IP address and a port number, much like one end of a telephone connection is the combination of a phone number and a particular extension. Based on this address, internet sockets deliver incoming data packets to the appropriate application process or thread
  34. 34What is the Internet Protocol Suite?Its the computer networking model and set of communications protocols used on the Internet and similar computer networks. It is commonly known as TCP/IP, because of its most important protocols, the Transmission Control Protocol (TCP) and the Internet Protocol (IP)
  35. 35What are the four main layers of TCP/IP?Application
    Transport
    Internet
    Link
  36. 36Where does TCP/IP differ from OSI?The three top layers in the OSI model—the application layer, the presentation layer and the session layer—are not distinguished separately in the TCP/IP model where it is just the application layer
  37. 37What are 3 ways that TCP implements congestion controls? Slow start – Part of the congestion control strategy used by TCP. Used with other algorithms to avoid sending more data than the network is capable of transmitting
     Congestion avoidance – Uses various aspects of an additive increase/multiplicative decrease (AIMD) scheme, with other schemes such as slow-start to achieve congestion avoidance. As this is still a developing area with on-going research, there are a variety of algorithms currently in use as none in the industry are universally accepted as the best.
     Fast retransmit – An enhancement to TCP which reduces the time a sender waits before retransmitting a lost segment. A TCP sender uses a timer to recognize lost segments. If an acknowledgement is not received for a particular segment within a specified time (a function of the estimated Round-trip delay time), the sender will assume the segment was lost in the network, and will retransmit the segment
  38. 38What were some early restrictions of HTTP? Restricted by use of the modem at first because it limited data transfer speeds
     No capability to resume a previous transfer
     Terminated connections after each request, which was costly
     Error handling was poor because responses are HTML, not features of the protocol
  39. 39Hows has HTTP become more efficient? Implementing of extensions for better caching
     Increased performance for certain operations, like requesting multiple items from a single socket connection
     Persistent connections, and the client indicates when the server can close it and this led to improved network utilisation, higher speed and reduced latency and less load on the client and server.
  40. 40What is the basic definition of DNS?DNS provides the basis for referring to hosts on the Internet by use of a human-friendly naming scheme. These host names form part of the URL used by web browsers and therefore are instantly recognisable.DNS names are translated into IP addresses that we are all familiar with, to enable UDP datagrams and TCP connections to be established (typically using sockets)
  41. 41What is the design purpose of DNS?To provide a way of referring to systems on a network in a human-readable way. It establishes a hierarchy of names, with the root derived from a series of top level domains (TLDs)
  42. 42What are the benefits of DNS?It is a distributed system, and in doing so avoids the limitations presented by the largely ad-hoc distribution of the original HOSTS.TXT file
  43. 43What are some security issues with DNS? DNS spoofing relies on this basic process to insert false entries into a nameserver cache. DNS makes use of sequence numbers that can be obtained by malicious operators of DNS servers. Once obtained, sequences can be predicted and used to generate false responses to DNS queries and thus poison a DNS cache
  44. 44What is DNSSEC?DNSSEC, developed by the IETF, Incorporates public key infrastructure into the DNS system. Primary aim is to provide authentication functionality into DNS to verify the sender of DNS records, Private and public keys, Co-existence with ordinary DNS and the now familar pattern to you of applying PKI to insecure protocols
  45. 45What is the difference between Recursive and Non-Recursive resolutions? Recursive - Where the local nameserver handles the search for the correct response
     Non-recursive - (iterative) Where the resolving party must search the DNS system for the required response
  46. 46Describe ARP. What is the basic concept of ARP?Address Response Protocol. Common protocol on large networks; applies to a subnet and was intended for multiple protocol types originally. It helps translate protocol-address pairs into the corresponding Ethernet address so we can build (Ethernet) frames at link-layer. Network layers use IP addresses (with routing) and IP datagrams. At lower layers such as Ethernet we need to use Ethernet frames for transmission
  47. 47What information does the ARP Packet contain?Ethernet address of the destination & sender, Protocol type (address resolution), Hardware address space (e.g. Ethernet), Protocol address space, Byte length of each hardware and protocol address, Opcode (request or reply), Hardware and protocol address of the sender and Hardware and protocol address of the target of this packet
  48. 48Describe the seven steps of ARP Packet Generation1.Packet travels down through network layers
    2.Lower layer consults ARP module to convert from the specific protocol address to the Ethernet address
    3.Looks up in table to see if has already done this before
    4. Returns Ethernet address if found in table
    5.Discard the packet if the mapping is not found It will likely be retransmitted
    6.Generate an ARP request packet to determine the hardware address of the target
    7. Broadcasts ARP request packet
  49. 49What are the 3 parts of the ARP reception process?o ARP Reception Process
    1. Process Hardware and protocol check
    2. Record sender addresses in table (A)
    3. If the target protocol address matches ours (B) Generate a new ARP packet and send this out onto the network
  50. 50What is ARP functionality in an OS?OS maintain IP address to MAC address pairings. Table is constructed automatically upon connection, Various commands possible in OS to view table
    On windows
    • - arp –a: Displays current ARP entries
    • - arp –a IPV4A: Displays entry associated with IPv4 address
    • - arp –d IPV4A: Deletes entry associated with IPv4 address
    • - arp –s IPV4A ETHADDR: Add static entry associating IP address with specified Ethernet address
  51. 51What are some issues with ARP Security?The ARP packet reception process automatically updates tables when ARP packets are seen. No authentication steps to verify if sender is legitimate. ARP spoofing is possible and can lead to redirection of traffic and MITM attack
  52. 52Describe the basic attributes of SSL/TLSEvolution of Secure Sockets Layer (SSL) into Transport Layer Security (TLS). A secure and authenticated communications channel between web browser and web server, provides foundation for confidentiality and integrity needed in web applications such as emails and banking. It is not the same as HTTP or Secure HTTP
    It provides a means to authenticate the server from the client perspective. It can be viewed as residing at the intersection between the application and transport layers. Protocols used with SSL are effectively encapsulated in an encrypted, authenticated communication link between client and server
  53. 53How does SSL work?o SSL begins with a negotiation phase which establishes the parameters of the connection (many). The client communicates to the server the desired compression and cryptographic algorithm settings. A subsequent phase is used to exchange data securely. Public key cryptography is used to authenticate the server. Server can either send the public key signed by a known authority (e.g. VeriSign) or by providing a certificate chain back to a known authority
  54. 54What are the 4 protocols used by SSL? Record Protocol - carries messages and data
     Alert Protocol - indicates errors, warnings
     Cipher Change Spec Protocol - indicates a special message after which parameters and secrets can be used for encryption
     Handshake Protocol - negotiation of the cryptosystem and establishment of secrets for encryption
  55. 55How does data transportation work in SSL? Fragmentation - Data stream is split into chunks of 16KB
     Compression - Data fragment is compressed (if enabled)
     Integrity - added onto end (a hash value)
     Encryption - encrypted using the secret key
     Header - to manage fragmentation stream
  56. 56Where does TLS differ from SSL?TLS does not differ much from SSL version 3 but does not interoperate with it either. Key generation process has been changed to be more resistant to cryptanalysis
  57. 57What does TLS achieve?Achieves a high level of security suitable for transport of sensitive data such as credit cards, personal information, financial details, commercial data and more.
  58. 58What is HTTPS?HTTP Secure (HTTPS) uses standard HTTP over SSL/TLS, making use of an alternative port number and requires the use of HTTPS in the protocol part of a url in a web browser
  59. 59Explain SSHSSH envisaged as a secure means of remote sessions to a variety of operating systems (primarily UNIX based). Version 2 is recommended because of security shortfalls in version 1
     SSH attempts to establish a secure connection over an insecure medium (TCP) and uses similar processes to our earlier discussion of SSL & TLS
     SSH-TRANS provides the secure layer above TCP by ensuring confidentiality and data integrity checks are in place
     SSH-AUTH is an authentication protocol for client/server
     SSH-CONN provides connection services over the SSH-TRANS layer
  60. 60Where is SSH good for?Capable of compressing the connection (using gzip compression). Good for slow links such as modems. Users can generate public/private keypairs that can be used to authenticate and log into sessions automatically (without UN/PW). Server provides fingerprint of public key on first connection
  61. 61What does NAT do?provides a method of modifying network address information in Internet Protocol (IP) datagram packet headers while they are in transit across a traffic routing device for the purpose of remapping one IP address space into another. Network administrators originally used network address translation to map every address of one address space to a corresponding address in another space, such as when an organization changed Internet service providers without having a facility to announce a public route to the network
  62. 62What are the advantages/disadvantages of NAT?Advantages - Public IP address sharing, easier expansion, greater local control, greater flexibility in ISP service, transparent
    Disadvantages - Complexity, problems due to lack of public addresses, poor support for client access, performance reduction
  63. 63Why do we need Firewalls?Firewalls are a form of filter that assess incoming packets and outgoing packets and make decisions about them. These decisions can be made based on the header information in the packet (e.g. originating IP, destination IP, ports, etc.) but also the content of the packet. Firewalls are generic concepts, and can be applied at any layer of the OSI, and to any type of traffic – they are not restricted or limited to the network layer. More advanced firewalls can provide functionality for authentication and implementation of VPNs
  64. 64How does Packet Filtering in Linux work?It focuses on the management of packets as they enter, transit through, and then exit the network stack. Prior to the 2.4 series of the Linux kernel, ipchains was the predominant mechanism for filtering network packets
  65. 65In a kernel, how many tables comprise the chain of rules? Please elaborate as to their functions Filter - default table, contains chains for INPUT and OUTPUT
     NAT - for packets that create new connections
     Mangle - for packet alteration
     Raw
  66. 66Each chain is composed of a series of rules. Rules have associated targets specified, that are triggered when a match is detected. What are matches typically made against?Multiple rules may apply to a packet as the rules are evaluated against the packet. Matches are typically made against
     Destination
     Source address (e.g. IP address, or MAC address)
     Interface the packet was received upon
     Interface the packet is going to be sent out on
  67. 67What are some of the other targets in packets?Rule Targets
     ACCEPT - let the packet proceed as normal
     DROP - drop the packet (don't do anything further with the packet)
     LOG - save info. on matching packet in log files
    Other targets - QUEUE, RETURN
  68. 68Describe the issues surrounding a Stateless FirewallFiltering individual packets is fine to operate, but it can create problems when we try to use connections (rather than datagrams). Consider when we allow all outbound packets to be sent, but then we block all inbound packets received.
  69. 69Why is a Stateful Firewall better?They introduce some form of memory into the firewall logic, so that it can keep track of the connections. On future filtering decisions, the firewall can use this contextual information to make a better decision. Most firewall implementations of any sophistication are stateful. A firewall for a large corporate network would almost certainly have to be a stateful firewall
  70. 70Why does FTP create issues for Firewalls?Most protocols make a single outbound connection. FTP in one mode of operation can make one OUTBOUND connection (SYN), but then the server makes a further INBOUND connection (SYN). Most basic firewall rule sets will not permit the inbound connection to take place, and thus the FTP session will fail. Providing functionality in the firewall to understand how protocols operate in this respect is the solution
  71. 71What is Virtualisation?the creation of a virtual (rather than actual) version of something, such as an operating system, a server, a storage device or network resources.
  72. 72What is Network Virtualisation?A method of combining the available resources in a network by splitting up the available bandwidth into channels, each of which is independent from the others, and each of which can be assigned (or reassigned) to a particular server or device in real time. The idea is that virtualization disguises the true complexity of the network by separating it into manageable parts, much like your partitioned hard drive makes it easier to manage your files.
  73. 73Describe Storage VirtualisationThe pooling of physical storage from multiple network storage devices into what appears to be a single storage device that is managed from a central console. Storage virtualization is commonly used in storage area networks (SANs).
  74. 74Please detail Server VirtualisationThe masking of server resources (including the number and identity of individual physical servers, processors, and operating systems) from server users. The intention is to spare the user from having to understand and manage complicated details of server resources while increasing resource sharing and utilization and maintaining the capacity to expand later
  75. 75Network Components: What is the function of the server?They are computers that hold shared files, programs, and the network operating system. Servers provide access to network resources to all the users of the network. There are many different kinds of servers, and one server can provide several functions
  76. 76Network Components: What is the function of clients?Clients are computers that access and use the network and shared network resources. Client computers are basically the customers(users) of the network, as they request and receive services from the servers.
  77. 77Network Components: What is the function of transmission media?Transmission media are the facilities used to interconnect computers in a network, such as twisted-pair wire, coaxial cable, and optical fiber cable. Transmission media are sometimes called channels, links or lines.
  78. 78Network Components: What is the function of shared data?Data that file servers provide to clients such as data files, printer access programs and e-mail.
  79. 79Network Components: What is the function of shard printers and peripherals?Shared printers and peripherals are hardware resources provided to the users of the network by servers. Resources provided include data files, printers, software, or any other items used by clients on the network.
  80. 80Network Components: What is the function of the Network interface card?Each computer in a network has a special expansion card called a network interface card (NIC). The NIC prepares(formats) and sends data, receives data, and controls data flow between the computer and the network. On the transmit side, the NIC passes frames of data on to the physical layer, which transmits the data to the physical link. On the receiver's side, the NIC processes bits received from the physical layer and processes the message based on its contents.
  81. 81Network Components: What is the function of a local operating system?A local operating system allows personal computers to access files, print to a local printer, and have and use one or more disk and CD drives that are located on the computer
  82. 82Network Components: What is the function of a Network Operating System?The network operating system is a program that runs on computers and servers, and allows the computers to communicate over the network.
  83. 83Network Components: What is the function of a Hub?Hub is a device that splits a network connection into multiple computers. It is like a distribution center. When a computer request information from a network or a specific computer, it sends the request to the hub through a cable. The hub will receive the request and transmit it to the entire network. Each computer in the network should then figure out whether the broadcast data is for them or not.
  84. 84Network Components: What is the function of a switch?Switch is a telecommunication device grouped as one of computer network components. Switch is like a Hub but built in with advanced features. It uses physical device addresses in each incoming messages so that it can deliver the message to the right destination or port.
  85. 85Describe the purpose of Mobile IPMobile IP was developed as a way of allowing mobile devices to use IP across different networks but to do so in a way that minimises the effects of switching to different networks
  86. 86How was IP traditionally designed?o In the traditional IP vision, stations and the network infrastructure is largely fixed and devices do not change networks often. The addressing scheme in IP reflects this, where packets are forwarded on the basis of IP addressing information contained in the packet. Because of the way IP addresses are allocated and managed, the address has implied network structuring information and host addressing data. Most importantly, the IP addressing scheme represents the network address of the device and not the device itself
  87. 87How do mobile devices connect to networks?They do so when required and can obtain a wide variety of network related settings via DHCP. DHCP servers allocate addresses statically or dynamically from a central pool
  88. 88Why is DCHP not the best solution for mobile networks?Its more designed to provide a rapid, easy way of deploying configurations across networks from a central location (It’s a network management protocol).
  89. 89For a TCP or UDP flow to operate at the application layer, IP addresses and ports are needed at the endpoints and these are specified in the packets sent/received via the network. If this is interrupted, what could happen?This could lead to an aborted connection leading to various problems depending on how the application layer protocol handles the condition. In situations where the device may change networks fairly often this is not ideal and becomes a problem for effective mobile use. It is clear this is not 'true' mobile connectivity as the infrastructure is not managing mobility
  90. 90Would using a fixed mobile device IP address fix the issue?No. That would remain the same as the device connects to various networks. This does not work efficiently at all. One feature of the way routing is achieved within the Internet is route aggregation. Routers aggregate prefixes and know where to punt a packet on the basis of these IP address prefixes
    Onn top of this, o Aggregated routes are designed for efficiency but would no longer be valid when making routing decisions. The only way of accommodating a fixed mobile IP address would be to still allow aggregated routes, but to store exceptions to them. Imagine thousands or millions of users using these special IP addresses, and it becomes obvious: it will not be scalable or manageable. The routing tables used by routers would get too big
  91. 91What does Mobile IP do?Enables users to keep the same IP address regardless of location. Built on the IP standard so compatible with IP networks. Mobile IP tackles the addressing problem by introducing the concept of a home address. The home address is the notional permanent home of the mobile device/user
  92. 92How does Mobile IP support mobility?A second concept of a care of address is introduced (COA). This second address is temporary and is part of the network the mobile device is associated with at a particular point in time. The name for the general scheme in Mobile IP is indirect routing
  93. 93What are the 3 comnponents of Mobile IP? Please elaborateMobile Node
    • A host that attaches to various networks over time
    Home agent
    • Provides the permanent location to which data is sent to
    • Relays by encapsulation packets to the mobile host
    Foreign agent
    • Accepts encapsulated packets from the home agent via a tunnel
    • Participates in the registration process where a mobile host registers via the foreign agent with the home agent
  94. 94What address does Mobile IP use to send IP datagrams?The home address is used as the source address. Routing algorithms are in place to route packets destined for the home address to the home network at all times
  95. 95Mobility nodes advertise themselves on their networks. What happens if the mobile nodes detect these and determine whether they are in a home network?No special procedures are used, the standard routing and addressing can be used using the home address
  96. 96Mobility nodes advertise themselves on their networks. What happens if the mobile nodes detect these and determine whether they are in a foreign network?The mobile node will obtain a care-of-address. The COA is registered with the home agent. The tunnel hides addressing from routers, preventing packets from being mis-routed
  97. 97What does ICMP do?Advertises routers that are able to act as foreign agents. Mobile devices use a registration request and will then receive a registration reply
  98. 98Why will Mobile IP require more conversion from network to link-layer addressing spaces as well?When a mobile node is on a foreign network, the home agent uses Proxy ARP (announcing their own MAC address as the destination for the home address). When a switch to a foreign network takes place, the home agent uses Gratuitous ARP to associate it's own MAC address with the IP of the home address for the mobile node
  99. 99What are the costs associated with use of Mobile IP?Encapsulated packets in the tunnel between the home agent and the foreign agent will attract an overhead, and in general the protocol will attract an overhead cost for advertisement and registration. Triangle routing problem & Double crossing problem. We can't get away from these problems as they're inherent in the basic design approach
  100. 100What is SATCOM?Short for Satellite Communications. For fixed (point-to-point) services, communications satellites provide a microwave radio relay technology complementary to that of communication cables. Can be used to provide connectivity for telephones, television, radio, internet and military purposes
  101. 101What is a WAN?Wide Area Network that covers a large geographical area and often compositions or inter-networks of other networks
  102. 102What does WAN Provide?Connectivity between devices, protocols for information to exchange between devices. Often has less bandwidth compared to LANs and MANs. They can also make use of existing national infrastructure
  103. 103What technologies can be used in WANs?Asynchronous Transfer Mode (ATM), Frame Relay, Cellular Technologies, Broadband Communications technologies
  104. 104What is the difference between circuit switching and packet switching?Circuit switching introduces the concept of a circuit or path across the network topology
    Established during a call set up phase, with each node identifying an appropriate follow-on node, eventually leading to an end-to-end path. Data transits via the nodes established in the circuit set up phase (contrasting with packet switching) The circuit or path is finally closed and resources are freed
    In packet switching though, data messages are fragmented into packets, more addressing information is introduced and routers have greater capability to identify appropriate destinations for them
  105. 105What are the issues with circuit switching?Results in potentially low utilisation of resources within the network as circuits may be left idling
    The data rate is often pre-specified in the circuit set up phase; client requirements may change or network conditions may permit more efficient alternatives
    Can lead to higher speed for the end parties in the circuit compared to packet switching
    A failure of a router within a circuit switched network can be severe
  106. 106Why is packet switching more effective?Shares resources such as bandwidth more efficiently
    Data rate conversion
    More flexible as it uses all available resources within the network
    More robust in the event of network congestion or component failure, accepting packets but providing lower throughput
    Packets may arrive out of sequence requiring greater reassembly functionality at the end-points
  107. 107What is Frame Relay?Telecommunicatiosn service designed for cost-efficient data transmission for intermittent traffic between local LANs and between end-points in a WAN
  108. 108Why do we use Frame Relay?It has a lower overhead and offers simplicity when it comes to implementing and it's better suited for links with lower error rates. This allows FR to provide higher data rates, though it has reduced flow and error control
  109. 109Describe the Frame Relay addressing schemeWhen using multiple frame relay connections the data link connection identifier (DLCI) is used. Only applies on a link basis and so DLCI values can be reused across links. Each FR node must maintain a routing table to determine for an incoming frame
  110. 110Please detail Asynchronous Transfer Mode (ATM)Heavily used in major carrier networks for the internet and is the connection-based standard. Doesn't need addressing data in each item of data. It's concerned with the transmission of fixed size packets called Cells
  111. 111What does ATM offer?It offers higher data rates compared to alternative protocols. It's used extensively in broadband access connections for supporting AAL5, PPP and IP. Addressing is not used within cells, rather a virtual circuit (VCI) identifier is used to route packets to the appropriate destination
  112. 112What are the two main categories of service in ATM?Non-Real-Time Service & Real-Time Service.
    RTS contains a constant bit rate (CBR) and Real-Time Variable Bit Rate (RT-VBR)
    NRTS however contains Available Bit Rate (ABR), Guaranteed Frame Rate (GFR), Unspecified Bit Rate (UBR) and non-real-time Variable bit Rate (NRT-VBR)
  113. 113In ATM, how do cells actually get produced?AAL5 - ATM Adaptation Layer 5, a commonly used protocol that sits as a layer above ATM. Performs segmentation and assembly of data into ATM cells as well as generates AAL5 frames
    It consists of two layers. SEAL - Simple and Efficient Adaptation Layer & the segmentation and reassembly (SAR) layer
  114. 114Describe Cell SwitchingThe result of the segmentation process adopted results in a series of cells. The effect of fixed sized cells is to split the bandwidth of the link between multiple VCs. The use of fixed sized cells also allows for efficiencies to be introduced into the handling of cells, particularly in terms of the speed of processing
    Fixed cell size allows use of dedicated hardware options to perform the cell switching function as opposed to slower software based solutions
    The time needed to interpret and decide what to do with a cell is similarly reduced as a result of a simplified cell structure and fixed sizing
  115. 115Please describe X.25Usually used to transfer large amounts of data at once and uses a connection oriented protocol using virtual circuits. Often used in banking computer systems.
  116. 116Why is X.25 not widely used?It has limitations in that its not easily usable across different link layer technologies
  117. 117How many layers are there in X.25?Three. Physical, data link and network later
  118. 118How many packet options does X.25 provide?Three
    * Virtual circuits providing virtual calls
    * Permanent virtual circuit, which is dedicated to interfaces to X.25
    * Fast select, simple datagram based service for limited data transfer
  119. 119Describe xDSLCovers both Asymmetric Digital Subscriber Lines (ASDL) and Symmetric Digital Subscriber Lines (SDSL). It allows the local loop to be adapted for high data rate provision. People used modems before this was developed
  120. 120Describe ASDLIt's an Orthogonal frequency-division multiplexing (OFDM) technology. Takes advantage of the fact that upload traffic is usually less over IP for a consumer than download traffic. It allocates the frequency spectrum accordingly, specifying a much smaller bandwidth for upstream compared to downstream
  121. 121What is ISDN?Integrated Services Digital Network. It supports three types of channel
    Bearer channel @ 64kbps (voice or data)
    Data channel @ 15kbps or 64kbps (packet)
    H channel @ 384kbps, bonded D channels
  122. 122Describe SATCOMSATCOM operates using electromagnetic waves through free space. A kind of wireless communications technology
    SATCOM has been widely adopted in broadcast industries such as radio and TV.
  123. 123What are the benefits of SATCOM?Viewed as a potential means to connect the third world to the Internet, good for disaster response, provides communication access across the globe
  124. 124What are the two main types of satellites used in SATCOM?Geostationary Satellites (GEO)
    Circa 35,000km, offering a (relatively high) latency of 270ms
    Few satellites needed for global coverage
    Low Earth Orbit Satellites (LEO)
    Circa 1000-2000km and below, offering low latency of around 5ms
    Many satellites needed to achieve global coverage
  125. 125What issues are there with GEO Satellites?They can be difficult to maintain a persistent data connection when the terminal is moving as the terminal must maintain a direct line of sight to the satellite. More sophisticated terminal equipment (e.g. Inmarsat FleetBroadband) can manage mobility and adverse weather conditions and correct for RF side effects of mobility
  126. 126In what situations would SATCOM be a viable option?Providing communications services in locations where communications are scarce.
    Providing corporate data services to staff in remote locations
    Teleconferencing to remote locations
    Internet access to rural or Third World regions
    Disaster response telephony (and data) in emergency situations
    Backup communications routes for increased resilience
    Broadcast services for radio, TV
    Amateur radio packet services
  127. 127What advantages does SATCOM offer?Potential to provide global coverage
    Providing connectivity in situations where other technologies are unusable/inadequate (e.g. DSL, cable, FTTH, dialup)
    Rural applications
    Not affected by land-based communications infrastructure problems (e.g. DSL) (resiliency, reliability)
    Only requires a power source in the immediate environment (e.g. battery, generator, alternator) (resiliency) at ground terminal end
    Cost to the user is the same anywhere in the world
    Addition of ground terminals is fast and does not require additional infrastructure
  128. 128What disadvantages are there to using SATCOM?Latency of communications can create issues and require workarounds
    Node to node communications can sometimes require a relay via a hub station (delays)
    Not as high a bandwidth compared to terrestrial networks
    Incurs a cost (can be substantial)
    Can be affected by local weather conditions (e.g. rain on the satellite dish)
  129. 129What affect does the Data Protection Act have on Networking in the UK?The act applies if personal or sensitive personal data is processed. The DPA addresses personal information processing. It has widespread relevance across information technology and computing. It also applies to generic information processing, be that on record cards, personal diaries, calendars, HR files, etc. The act introduces the concept of personal data, information that relates to an individual and it can exist in a variety of forms. The data controller is the person responsible for following the DPA requirements. Act regulates the processing of data
  130. 130What effect does RIPA have in the UK?Regulatory and Investigatory Powers Act 2000 (RIPA) - provided a clear framework for lawful interception of digital communications
  131. 131What effect does the Telecommunications Regulations have?The Telecommunications (Lawful Business Practice) (Interception of Communications) Regulations 2000 - provide clarity on when lawful interception can take place
  132. 132What is a common example of network monitoring policy in an organisation? Specifying clear terms of reference for staff undertaking network monitoring activity
     Spell out who has what responsibilities
     Provide reference to the relevant legislation
     Clear statements that are accessible to any member of staff
  133. 133What areas of networking does the law cover?Network congestion, Packets sent and received, Peak and average bandwidth, Live status of network components, Network error conditions, Email processing for detection of spam, Email processing for detection of viruses, malware, Records of transactions such as web traffic on a proxy, Logging all inbound and outbound TCP connections, SNMP, IDS
  134. 134Describe BGP SecurityBorder Gateway Protocol (BGP) is an Internet Engineering Task Force (IETF) standard, and the most scalable of all routing protocols. BGP is the routing protocol of the global Internet, as well as for service provider private networks. BGP has expanded upon its original purpose of carrying Internet reachability information, and can now carry routes for Multicast, IPv6, VPNs, and a variety of other data
  135. 135Why is BGP vulnerable?Unlike other routing protocols that typically provide their own transport layer (Layer 4) protocol, BGP relies on TCP as its transport protocol. BGP is susceptible to the same attacks that target any TCP-based protocol, and it must be protected similarly.
  136. 136How can BGP be exploited? BGP Route Manipulation — This scenario occurs when a malicious device alters the contents of the BGP routing table, which can, among other impacts, prevent traffic from reaching its intended destination without acknowledgement or notification.
     BGP Route Hijacking — This scenario occurs when a rogue BGP peer maliciously announces a victim’s prefixes in an effort to reroute some or all traffic to itself for untoward purposes (for example, to view contents of traffic that the router would otherwise not be able to read).
     BGP Denial of Service (DoS) — This scenario occurs when a malicious host sends unexpected or undesirable BGP traffic to a victim in an attempt to expend all available BGP or CPU resources, which results in a lack of resources for valid BGP traffic processing.
  137. 137Describe symmetric algorithmsWhen using symmetric algorithms, both parties share the same key for en- and decryption. To provide privacy, this key needs to be kept secret. Once somebody else gets to know the key, it is not safe any more. Symmetric algorithms have the advantage of not consuming too much computing power. A few well-known examples are: DES, Triple-DES (3DES), IDEA, CAST5, BLOWFISH, TWOFISH.
  138. 138Describe asymmetric algorithmsAsymmetric algorithms use pairs of keys. One is used for encryption and the other one for decryption. The decryption key is typically kept secretly, therefore called ``private key'' or ``secret key'', while the encryption key is spread to all who might want to send encrypted messages, therefore called ``public key''. Everybody having the public key is able to send encrypted messages to the owner of the secret key. The secret key can't be reconstructed from the public key
  139. 139What are the advantages of asymmetric algorithms?o Asymmetric algorithms seem to be ideally suited for real-world use: As the secret key does not have to be shared, the risk of getting known is much smaller. Every user only needs to keep one secret key in secrecy and a collection of public keys, that only need to be protected against being changed. With symmetric keys, every pair of users would need to have an own shared secret key. Well-known asymmetric algorithms are RSA, DSA, ELGAMAL.
  140. 140What are the disadvantages of asymmetric algorithms?asymmetric algorithms are much slower than symmetric ones. Therefore, in many applications, a combination of both is being used. The asymmetric keys are used for authentication and after this is successful, one or more symmetric keys are generated and exchanged using the asymmetric encryption. This way the advantages of both algorithms can be used
  141. 141What does an IPS do?it has rules, maybe hundreds, maybe thousands. Most of those rules are "deny" rules: "block this known security problem." When a packet shows up at the IPS, the IPS looks through its rule list from top to bottom, looking for some reason to drop the packet. At the end of the list, though, is an implicit "pass" rule: "allow this packet through." Thus, in the absence of a reason to drop the traffic, the IPS passes it through.
  142. 142How does an IDS compare to an IPS?If an IPS is a control tool, then an IDS is a visibility tool. Intrusion Detection Systems sit off to the side of the network, monitoring traffic at many different points, and provide visibility into the security posture of the network. A good analogy is to compare an IDS with a protocol analyzer. A protocol analyzer is a tool that a network engineer uses to look deep into the network and see what is happening, in sometimes excruciating detail. An IDS is a "protocol analyzer" for the security engineer. The IDS looks deep into the network and sees what is happening from the security point of view.
  143. 143What are the needs that WiMAX helps address?Providers want to set up infrastructure without the expense of digging up roads and pavements to install cabling
    Customers want to increase their data rates substantially, or to achieve suitable connectivity where there are no other alternatives
    Customers who want to achieve broadband connectivity while on the move in a vehicle or on foot, where alternatives are scarce or perhaps expensive
  144. 144What does WiMAX stand for?Worldwide Interoperability for Microwave Access (WiMAX) helps address all of these needs by providing broadband connectivity
    Wirelessly. WiMAX is formally titled IEEE 802.16
  145. 145What does WiMAX do?Focused on providing broadband connectivity wirelessly, It provides an equivalent class of provision similar to the "last mile" of conventional POTS network DSL services.
    Intended for licensed spectrum usage (contrast with 802.11) but does not prescribe detailed spectrum usage. Has flexibility between 2GHz and 10GHz and uses more powerful transmission as a consequence. Intended to provide a foundation for a paid service. WiMAX is believed to be a technology through which competition for high data rate broadband connectivity within communities can be enhanced
  146. 146WiMAX Spectrum and Operating ModelUsers connect either via
    Mobile/portable stations - Can be any type of device that supports WiMAX, including laptops, desktops, mobile devices and even vehicles
    Fixed stations- Can be any type of device that supports WiMAX, such as a residential broadband router, desktop PC, etc.
  147. 147What are the principles of WiMAX?WiMAX is an all-data IP based technology
    Compare to cellular circuit switched standards, legacy
    All data transfer, including telephony, must be carried over IP
    Provides two physical layer implementations
    Fixed WiMAX
    Mobile WiMAX (released later)
    WiMAX borrows principles from other established protocols
    Design of WiMAX similar to competing 4G technologies (e.g. LTE-A)
  148. 148What are the unique characteristics of WiMAX?WiMAX is heavily engineered and designed to provide a foundation for a billable broadband service, differing from 802.11
    It does support point to point and an infrastructure-like mode, but predominant mode expected to be point-to-multipoint
  149. 149What are the 4 layers in WiMAX?WiMAX Physical Layer
    WiMAX Data Link Layer
    Data Link Layer Sub-Layers
    WiMAX Above Data Link Layer
  150. 150Why would we use WiMAX over other options?Where the cost of deploying underground fixed cabling (e.g. FTTH, FFTK or POTS) is uneconomic
    Where there are few subscribers to justify a capital cost intensive alternative (e.g. xDSL, cable)
    Where the subscribers are using portable equipment or are mobile (such as in a vehicle)
    Where high data rate is required over a long distance wirelessly
  151. 151Describe WLAN technologyWireless LAN (WLAN) technology primarily address the use case where mobile (and fixed devices) can connect to existing network infrastructure without the use of cabling
  152. 152What does WLAN Rely on?WLAN relies on radio transmission and reception capabilities added to devices and the infrastructure
    IEEE 802.11 was developed in the late 1990s and includes standards that are the cornerstone of current WLAN use
  153. 153There are two predominant frequency regions that are used by the various 802.11 standards. What are they?2.4GHz, an ISM band - Used by a variety of standards, not just 802.11. This is an unlicensed band, thus operators of ISM band equipment do not have to obtain a license from the spectrum licensing authority (in the UK - Ofcom) to TX/TX in this band
    5GHz, also an ISM band
  154. 154Used in the latest 802.11n standard, what are the three bands provided within the 5GHz band?5150-5350 MHz (Band A)
    All devices must comply with ERC Decision 99(23) and IR 2006, all devices must be nomadic/mobile, for indoor use only
    5470-5725 MHz (Band B)
    All devices must comply with ERC Decision 99(23) and IR 2006, all devices must be nomadic/mobile
    5725-5875 MHz (Band C)
    Licensed band
    To achieve unlicensed usage, equipment must meet the standards specified for Bands A and B; Band C requires a license
  155. 155Describe 802.11Physical layer is implemented according to the 802.11 release being used
    802.11 layered model
    Upper layers
    Data link layer (incorporating the LLC & MAC)
    Physical layer (implementation varies)
    Mobility support (nomadic)
    Medium Access Control
  156. 156Describe Carrier Sense Multiple Access Collision Avoidance (CSMA/CA)One of the more complex parts of 802.11 is deciding how multiple devices can TX & RX on a common spectrum band
    Similarities with Ethernet
    Difficulty of detecting collision (i.e. none)
    Hidden terminal problem
  157. 157Describe 802.11 Ad Hoc ModeFormation of ad hoc network
    Does not use an AP
    Communication is directly between nodes in the AHN
    Users specify
    An SSID for the AHN
    Joins automatically
    Optional encryption settings
    Static address or dynamic allocation via DHCP, APIPA
  158. 158Talk about Service Set Identification (SSID)ID
    Limited size
    Requirement for interoperation
    Incorrectly classed as a security mechanism
    The SSID is advertised by an AP via beacon messages
    SSID broadcast within beacon messages can be disabled, but this should not be viewed as a security countermeasure
  159. 159What are some security issues with 802.11?You need to disable SSID broadcast in beacon messages - Cannot be relied upon and it reduces visibility of the network
    MAC authentication - 802.11 AP checks the MAC address of the connecting devices against a list of authorised devices. This list may be dynamically updated in response to client activities (e.g. acceptance of a web page describing terms and conditions, or requesting payment). MAC addresses can be spoofed
    Encryption key authentication - Knowledge of the key implies authentication of the parties. Running without encryption exposes data but also provides no authentication of end user devices
  160. 160What is (Wired Equivalent Privacy) WEP?Provides encryption facilities for communications between the hosts and the AP
    WEP employs a challenge-response protocol to authenticate the client to the AP
    RC4 stream cipher used to encrypt payload
  161. 161Name the security issues revolving around WEPDuplicate key vulnerability and payload decryption
    Weak key vulnerabilities
    Lack of message integrity checking
    Unlikely to gain assurance in a new deployment unless additional security measures are implemented (e.g. encrypted VPN)
  162. 162What do 802.11i and Wi-Fi Protected Access (WPA/WPA2) do?802.11i addresses the security problems of WEP. It provides an option for an authentication server (AS). Clients, APs and ASs undertake a dialogue to discover security capabilities and establish security keys to protect subsequent data traffic
    Once the Temporal Key (TK) is established, the host and AP switch to encrypted communication. Several algorithms supported, the most well-known being the Advanced Encryption Standard (AES) a.k.a. WPA2
  163. 163What are some typical applications of 802.11?Residential broadband
    Provision of broadband connectivity to fixed and mobile devices in a residential setting (killer application)
    Temporary Internet access for customers
    Providing Internet access for customers for example in hotels, bars, aircraft, many other settings
    Events
    Providing access to the Internet at festivals, including outdoor events
    Connectivity in the workplace
    Providing connectivity to internal and external networks within a corporate environment
  164. 164Describe the RF SpectrumThe radio spectrum underlies all wireless communication
    It's regulation and management is therefore of growing importance in the UK and internationally as wireless technology expands
    While effective schemes for transmitting information are essential for gaining maximum utility from spectrum, data rates is ultimately proportional to the amount of the radio spectrum allocated
    Regulated by OFCOM in the UK and the ITU worldwide
  165. 165Describe the RF Spectrum in greater detailThis ranges from 3 Hz up to 300 GHz
    Allocation and management of spectrum is essential to help avoid harmful interference
    Radio use in the UK must be authorised by Ofcom under the Wireless Telegraphy Act 2006
  166. 166Why use Zigbee and Bluetooth over 802.11?802.11 is more suited for long distance connection, whilst Zigbee and Bluetooth cater to shorter range, lower data rate connections
  167. 167Talk to me about Radio Frequency Identification (RFID) and Near Field Communication (NFC)RFID provides a short-range equivalent to traditional bar codes, however the technology has had much broader applications in commerce and research
    For example, in research via the Internet of Things
    Many applications in commerce such as inventory management, payments
    For shorter range wireless requirements, near-field communication (NFC) technologies have been developed that provide such capability
    NFC can be considered a variant of the general approach of RFID, supporting bi-directional communication and is finding particular use in financial payments
  168. 168Describe Personal Area Networks (PAN) and Wireless PANs (WPAN)Personal Area Networks (PANs) are a class of networking technology that do not offer the range supported by LAN technologies (and variants thereof, such as WLAN)
    Instead PANs are focussed on providing similar types of functionality over much shorter distances
    Wireless PANs, where the PAN is implemented using wireless technology, are well known types of PAN
  169. 169What type of area network do Zigbee and Bluetooth come under?Personal Area Network
  170. 170Describe Bluetooth in it's most basic formBluetooth provides a suite of functionality (profiles) for communicating in various ways between devices
    Bluetooth has an ad-hoc networking capability in the form of piconets and scatter nets
  171. 171Describe Zigbee in its most basic formZigBee is focused on lower data rate usage applications, such as the transmission of information from sensors to a centralised control system (such as a central heating system)
    ZigBee is also suited to low power applications, operating in the 2.4GHz band as IEEE 802.15.4 and also operating in regional bands (915MHz in the Americas, and 868MHz in Europe)
  172. 172Why are PANs seeing a surge in growth?Personal area networks are closely intertwined with innovations in the mobile computing space, and are likely to grow and gain in importance as users seek greater levels of connectivity between devices they own or operate
  173. 173What are some activities common to PAN?PANs often have to provide more autonomous behaviour compared to alternative technologies such as WiFi
    Discovering new devices either connected or in the vicinity of the querying device
    Connecting to known devices automatically or with user approval
    Transferring data of various types between devices
    Forming ad-hoc networks (AHNs) to relay information
  174. 174How does PAN compare to 802.11 in detail?802.11 is focused on longer-range connectivity as a replacement for Ethernet fixed networks in buildings
    Kurose and Ross refer to 802.11 as more of an "access" technology
    802.11 typically provides far higher bandwidth to clients
    802.11, in it's most common mode of operation, requires the use of fixed infrastructure to provide the WLAN service to mobile clients
    PANs typically provide lower data rates over shorter distances and do not use fixed infrastructure, creating their networks entirely dynamically
  175. 175Describe Ad Hoc Networks (AHNs)AHNs are networks that can operate without infrastructure and have no centralised administration
    Can be implemented using a variety of technologies, typically wireless
    Devices within the AHN possess the ability to route packets across the network themselves
    Versus having distinct infrastructure that performs this function (i.e. routers)
    Ability to dynamically reconfigure to suit changing environmental circumstances
  176. 176Name the different versions of BluetoothBluetooth was developed as a connection technology to link mobile phones to other devices and as a replacement for IrDA
    IrDA has a limitation being a point-to-point mode of operation
    Is a short range communications standard (shorter distances than 802.11) that does not require fixed infrastructure (AHNs)
    Several versions of the standard have since been released
    Version 2.0 added support for Enhanced Data Rate (EDR)
    Version 3.0 added high speed
    Version 4.0 provided lower power consumption features
    Variety of different classes of data can be exchanged via protocols
  177. 177Detail Bluetooth in the spectrumOperates in the unlicensed ISM band. Works at 2.4 GHz - the Industrial, Scientific and Medical Band. Operates across 79 channels within ISM band of 1MHz each
    By virtue of using the ISM band, Bluetooth is vulnerable to co-channel interference from other users of the band. Basic bit rate is 1 Mbps raising to 2 or 3 Mbps with EDR, high speed offers a rate up to 24 Mbps. Interference with 802.11 addressed by using adaptive frequency hopping
  178. 178How does bluetooth combat fading and interference?Frequency hopping regime used in Bluetooth sees the technology hop between channels at a fast rate. 1600 hops per second across the 79 channels
    Has a dwell time of 625 micro-seconds
    Sits on the frequency for that length of time before hopping once more. The master node determines the hopping sequence needed and sets the clock
  179. 179What are the two main link types in PANs between Primary and Secondary Nodes?Synchronous Connection Oriented (SCO)
    Low latency, reserved slots in transmission, good for audio e.g. voice calls
    Asynchronous Connectionless Link (ACL)
    Better data integrity (retransmission), more potential latency, suited to data
  180. 180Describe Bluetooth Packet StructureBluetooth uses packets as the core item of data exchange. These are transmitted, received and then the frequency hopping process takes effect
    Transmission window is split into a number of slots under a TDD scheme. Slots are allocated to packets as necessary. Links and pairing
  181. 181How does Bluetooth provide security?Bluetooth provides for support for encrypting the payload of the packet. Both the slaves and the master nodes know the key to encrypt and decrypt the payload
    Two approaches undertaken during the pairing process. Pre-shared PIN entered into the devices established before communication
  182. 182How does the Bluetooth Protocol stack work?It does not adhere to widely used schemes such as the OSI model. At the outer level, composed of physical, datalink, and upper layers
    Other aspects include Link control, Link manager, L2CAP, Applications, Profiles
  183. 183Describe Logical Link Control and Adaptation Protocol (L2CAP)When using ACL links L2CAP is needed. This provides services for upper layers regarding segmentation and reassembly of Bluetooth frames
    Determines which upper layer protocol to hand frames to. Error control and retransmission amongst other properties. Bluetooth groups supported
  184. 184Talk about synchronisation and PiconetsDevices must synchronise their clocks and frequency hopping pattern. One device takes on the role of "master" to provide a common reference, or primary node
    All other devices are called "slaves" or secondary nodes. The group is collectively termed a piconet with up to 8 active devices. Some nodes can take on a parked state to allow for power saving measures (up to 255 parked devices)
  185. 185Discuss ProfilesProfiles specify particular requirements for specific applications. Even specify protocol stacks required for each. Large amount of complexity is involved and this covers things like PANs,
  186. 186Bluetooth supports two types of frame for basic and enhanced rate. Please detail themIt has the capability to send data part of ER frame at enhanced rate, but header and guard part sent at BR
  187. 187What applications is Bluetooth suited for?Bluetooth is also suited to establishing connections in a more convenient way compared to alternative technologies such as 802.11
    Sharing files on a train, in a conference or in a meeting. Interfacing with specialised devices such as medical devices (such as blood glucose monitors). Connecting peripherals, providing an alternative to USB tethering, sharing an Internet connection
  188. 188What are some of the advantages of using Zigbee?Energy efficient. Of reasonable bandwidth (but not "huge"). With longer range
  189. 189What are some of the characteristics of Zigbee?Focused on lower data rate usage.Wide variety of networking applications are suitable for ZigBee. Two implementations have been developed: ZigBee and ZigBee PRO
    Good for low-power applications. Reduced demand from battery subsystems on mobile devices. Not all applications require the capabilities offered by, say, 802.11. Carrier-sense, random access protocols
  190. 190Where does ZigBee operate in the Spectrum?Operates in the 2.4GHz band as IEEE 802.15.4
    Also operates in regional bands
    915MHz (Americas)
    868MHz (Europe)
  191. 191How does Zigbee fare when it comes to Data Rates?Dependent on channel freq.. Data rates are small in comparison to Bluetooth and 802.11 however.
    Supports AES 128 encryption
    Sufficient for all potential applications in terms of assurance
  192. 192Describe ZigBee Device TypesZigBee End Devices are similar to slave devices. Coordinator and router devices are similar to master device
    ZigBee can form a network topology of the same general nature to that achievable in Bluetooth, using coordinator and router devices
    Coordinators and router devices are capable of forming mesh networking topologies in a way similar to BT
  193. 193Talk about Zigbee Scalability Options. How many different devices can it support on a single network?ZigBee can support up to 64,000 devices on a single network. This provides a good basis to support numerous low-power devices sending data intermittently
    Much higher scalability than Bluetooth piconets (max 8 devices active, 255 sleeping)

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Fichas sobre Networks, creado por Henry Stockdale el 18/01/2015.
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