Computer Networking
Suppose that a Web server runs in Host C on port 80. Suppose this Web server uses persistent connections, and is currently receiving requests from two different Hosts, A and B. Are all of the requests being sent through the same socket at Host C? If they are being passed through different sockets, do both of the sockets have port 80? Discuss and explain.
. For each persistent connection, the Web server creates a separate "connection socket". Each connection socket is identified with a four-tuple: (source IP address, source port number, destination IP address, destination port number). When host C receives and IP datagram, it examines these four fields in the datagram/segment to determine to which socket it should pass the payload of the TCP segment. Thus, the requests from A and B pass through different sockets. The identifier for both of these sockets has 80 for the destination port; however, the identifiers for these sockets have different values for source IP addresses. Unlike UDP, when the transport layer passes a TCP segment's payload to the application process, it does not specify the source IP address, as this is implicitly specified by the socket identifier.
How are different RTP streams in different sessions identified by a receiver? How are different streams from within the same session identified?
. RTP streams in different sessions: different multicast addresses; RTP streams in the same session: SSRC field; RTP packets are distinguished from RTCP packets by using distinct port numbers.
What are the ICMP Types/Codes
0/0 - Echo Reply 8/0 - Echo Request 3/0 - Network Unreachable 3/1 - Host unreachable 3/3 - Port Unreachable 3/4 - Fragmentation needed but DF set 3/9 - Destination Network prohibited 3/10 - Destination host prohibited 4/0 - Source quench 5/0 - Redirect for network 5/1 - Redirect for host 11/0 - TTL Exceeded during transit 17/0 - Address Mask Request 18/0 - Address Mask Reply
What does CIDR do?
1) makes large blocks of networks that can be summarized, or aggregated, into single routes 2)Circumvents Classful System
What are the 7 Layers of Computer Networking
Application, Presentation, Session, Transport, Network, Data-Link, and Physical
How does the polling protocol work?
The polling protocol eliminates the collisions and empty slots that plague random access protocols. This allows polling to achieve a much higher efficiency. But it also has a few drawbacks. The first drawback is that the protocol introduces a polling delay—the amount of time required to notify a node that it can transmit. If, for example, only one node is active, then the node will transmit at a rate less than R bps, as the master node must poll each of the inactive nodes in turn each time the active node has sent its maximum number of frames. The second drawback, which is potentially more serious, is that if the master node fails, the entire channel becomes inoperative. The 802.15 protocol and the Bluetooth protocol we will study in Section 6.3 are examples of polling protocols.
What is the role of a SIP registrar? How is the role of an SIP registrar different from that of a home agent in Mobile IP?
The role of a SIP registrar is to keep track of the users and their corresponding IP addresses which they are currently using. Each SIP registrar keeps track of the users that belong to its domain. It also forwards INVITE messages (for users in its domain) to the IP address which the user is currently using. In this regard, its role is similar to that of an authoritative name server in DNS.
What are the decisions made when routing?
The routing table is queried for the destination network. The entry with the smallest network mask that qualifies is returned The TTL in the packet is decremented by the metric number If the TTL is now zero, the packet is discarded and an ICMP time exceeded message is sent back to the source If the packet size is greater than the MTU of the network, the packet is fragmented The hardware address of the next-hop is determined and the DLC header is applied to the packet(s) If the HA cannot be determined and the route is still active in the table, send an ICMP Host/Network unreachable message to the source The packet(s) are sent to the next-hop.
What is the IP broadcast address 255.255.255.255
When a host sends a datagram with destination address 255.255.255.255, the message is delivered to all hosts on the same subnet. Routers optionally forward the message into neighboring subnets as well (although they usually don't).
Repeat R12, but now with the Selective Repeat Java applet. How are Selective Repeat and Go-Back-N different?
When a packet was lost, GO-Back-N retransmitted all the packets whereas Selective Repeat retransmitted the lost packet only. In case of lost acknowledgement, selective repeat sent a duplicate ACK and as GO-Back-N used cumulative acknowledgment, so that duplicate ACK was unnecessary. The packet loss caused a time out after which all the five packets were retransmitted.
What is the mainly used distributed algorithm?
Whereas the LS algorithm is an algorithm using global information, the distance vector (DV) algorithm is iterative, asynchronous, and distributed. It is distributed in that each node receives some information from one or more of its directly attached neighbors,
What does BGP do?
1. Obtain subnet reachability information from neighboring ASs. 2. Propagate the reachability information to all routers internal to the AS. 3. Determine "good" routes to subnets based on the reachability information and on AS policy. Most importantly, BGP allows each subnet to advertise its existence to the rest of the Internet. A subnet screams "I exist and I am here," and BGP makes sure that all the ASs in the Internet know about the subnet and how to get there. If it weren't for BGP, each subnet would be isolated—alone and unknown by the rest of the Internet.
What does the CSMA/CD Protocol do?
1. The adapter obtains a datagram from the network layer, prepares a link-layer frame, and puts the frame adapter buffer. 2. If the adapter senses that the channel is idle (that is, there is no signal energy entering the adapter from the channel), it starts to transmit the frame. If, on the other hand, the adapter senses that the channel is busy, it waits until it senses no signal energy and then starts to transmit the frame. 3. While transmitting, the adapter monitors for the presence of signal energy coming from other adapters using the broadcast channel. 4. If the adapter transmits the entire frame without detecting signal energy from other adapters, the adapter is finished with the frame. If, on the other hand, the adapter detects signal energy from other adapters while transmitting, it aborts the transmission (that is, it stops transmitting its frame). 5. After aborting, the adapter waits a random amount of time and then returns to step 2.
How many hosts were in a class C subnet
254
How many hosts were in a class B subnet
65,634
What port does DHCP run on
67 and 68
What port does TCP HTTP protocol use?
80
What is an interface?
A host typically has only a single link into the network; when IP in the host wants to send a datagram, it does so over this link. The boundary between the host and the physical link is called an interface.
What is a global routing algorithm?
A global routing algorithm computes the least-cost path between a source and destination using complete, global knowledge about the network. That is, the algorithm takes the connectivity between all nodes and all link costs as inputs. They are also called Link State Algorithms.
Congestion control
A TCP mechanism, also available from other protocols, that permits network hosts to exchange information about their ability to handle traffic volumes and thereby causes senders to decrease or increase the frequency and size of their upcoming communications. regulates the amount of data that an application can send into the network. TCP uses a congestion window in the sender side to do congestion avoidance. The congestion window indicates the maximum amount of data that can be sent out on a connection without being acknowledged. TCP detects congestion when it fails to receive an acknowledgement for a packet within the estimated timeout. In such a situation, it decreases the congestion window to one maximum segment size (MSS), and under other cases it increases the congestion window by one MSS. There also exists a congestion window threshold, which is set to half the congestion window size at the time when a re-transmit was required.
What is the difference between packet switching and circuit switching and the Pros/Cons of each
A circuit-switched network can guarantee a certain amount of end-to-end bandwidth for the duration of a call. Most packet-switched networks today (including the Internet) cannot make any end-to-end guarantees for bandwidth. In a packet switched network, the packets from different sources flowing on a link do not follow any fixed, pre-defined pattern. In TDM circuit switching, each host gets the same slot in a revolving TDM frame.
What is a link layer address called?
A link-layer address is variously called a LAN address, a physical address, or a MAC address.
P2P network
A locally managed network in which each node can communicate directly with every other node in the network
IP Address
A number assigned to any item that is connected to the Internet. 32-bit quantity that we can think of as uniquely identifying the host.
Why is a packet that is received after its scheduled playout time considered lost?
A packet that arrives after its scheduled play out time cannot be played out. Therefore, from the perspective of the application, the packet has been lost.
How does RIP work?
A router can also request information about its neighbor's cost to a given destination using RIP's request message. Routers send RIP request and response messages to each other over UDP using port number 520. The UDP segment is carried between routers in a standard IP datagram. The fact that RIP uses a transport-layer protocol (UDP) on top of a networklayer protocol (IP) to implement network-layer functionality (a routing algorithm) may seem rather convoluted (it is!). Looking a little deeper at how RIP is implemented will clear this up.
What is a forwarding table?
A router forwards a packet by examining the value of a field in the arriving packet's header, and then using this header value to index into the router's forwarding table. The value stored in the forwarding table entry for that header indicates the router's outgoing link interface to which that packet is to be forwarded.
Another difference between HTTP and FTP
A second difference, which we alluded to earlier, is that SMTP requires each message, including the body of each message, to be in 7-bit ASCII format. If the message contains characters that are not 7-bit ASCII (for example, French characters with accents) or contains binary data (such as an image file), then the message has to be encoded into 7-bit ASCII. HTTP data does not impose this restriction.
What are the rules of ICMP?
An ICMP error message is never sent in response to an ICMP error message An ICMP error message will never be sent in response to a packet destined for a broadcast address An ICMP error message will never be sent in response to a fragment other than the first.
Describe why an application developer might choose to run an application over UDP rather than TCP.
An application developer may not want its application to use TCP's congestion control, which can throttle the application's sending rate at times of congestion. Often, designers of IP telephony and IP videoconference applications choose to run their applications over UDP because they want to avoid TCP's congestion control. Also, some applications do not need the reliable data transfer provided by TCP.
What is a type-3 ICMP message
An error
Give an example of intra-AS routing protocols. These are routing protocols used over the internet.
An intra-AS routing protocol is used to determine how routing is performed within an autonomous system (AS). Intra-AS routing protocols are also known as interior gateway protocols. Historically, two routing protocols have been used extensively for routing within an autonomous system in the Internet: the Routing Information Protocol (RIP) and Open Shortest Path First (OSPF). A routing protocol closely related to OSPF is the IS-IS protocol [RFC 1142, Perlman 1999]. We first discuss RIP and then consider OSPF.
What is The Internet's address assignment strategy is known as
Classless Interdomain Routing
What does CDN stand for?
Content Delivery Network
What else does BGP do?
BGP allows each AS to learn which destinations are reachable via its neighboring ASs. In BGP, destinations are not hosts but instead are CIDRized prefixes, with each prefix representing a subnet or a collection of subnets. Thus, for example, suppose there are four subnets attached to AS2: 138.16.64/24, 138.16.65/24, 138.16.66/24, and 138.16.67/24. Then AS2 could aggregate the prefixes for these four subnets and use BGP to advertise the single prefix to 138.16.64/22 to AS1. As another example, suppose that only the first three of those four subnets are in AS2 and the fourth subnet, 138.16.67/24, is in AS3. Then, as described in the Principles and Practice in Section 4.4.2, because routers use longest-prefix matching for forwarding datagrams, AS3 could advertise to AS1 the more specific prefix 138.16.67/24 and AS2 could still advertise to AS1 the aggregated prefix 138.16.64/22.
What is BootP?
Boot Strap Protocol. DHCP uses BOOTP as its transport protocol (port 67 on server, 68 on client)
What is BGP?
Border Gateway Protocol (BGP) is a standardized exterior gateway protocol designed to exchange routing and reachability information between autonomous systems (AS) on the Internet.[1] The protocol is often classified as a path vector protocol, Border Gateway Protocol makes routing decisions based on paths, network policies or rule-sets configured by a network administrator, and is involved in making core routing decisions. BGP may be used for routing within an AS. In this application it is referred to as Interior Border Gateway Protocol, Internal BGP or iBGP. In contrast, the Internet application of the protocol may be referred to as Exterior Border Gateway Protocol, External BGP or EBGP.
What is CSMA/CD Protocol?
Carrier Sense Multiple Access with Collision Detection When a node has data to transmit, it first listens If there is silence on the network, begin transmitting; otherwise wait for silence. If during transmission, the voltage on the line rises above +5v, stop transmitting, generate a random number and wait that amount of time Restart with step 1 as necessary
Design the simplest possible transport-layer protocol that will get application data to the desired process at the destination host. Assume the operating system in the destination host has assigned a 4-byte port number to each running application process.
Call this protocol Simple Transport Protocol (STP). At the sender side, STP accepts from the sending process a chunk of data not exceeding 1196 bytes, a destination host address, and a destination port number. STP adds a four-byte header to each chunk and puts the port number of the destination process in this header. STP then gives the destination host address and the resulting segment to the network layer. The network layer delivers the segment to STP at the destination host. STP then examines the port number in the segment, extracts the data from the segment, and passes the data to the process identified by the port number.
What does the network layer do in major computing architectures
Computer networks that provide only a connection service at the network layer are called virtual-circuit (VC) networks; computer networks that provide only a connectionless service at the network layer are called datagram networks.
What is Dynamic Host Configuration Protocol (DHCP)
DHCP is a protocol that is based on a client-server model that dynamically allocates the assignment of IP addresses. The DHCP server is a device that is configured to allocate IP addresses and network configuration. A DHCP client is a host that requests IP address, subnet mask, default gateway, and other information from a server.
What are some protocols that use DV algorithms?
DV-like algorithms are used in many routing protocols in practice, including the Internet's RIP and BGP, ISO IDRP, Novell IPX, and the original ARPAnet.
What does DHCP stand for?
Dynamic Host Configuration Protocol
What is SSL used for?
Encrypt data as it travels over a network. For TCP connections
What is the difference between end-to-end delay and packet jitter? What are the causes of packet jitter?
End-to-end delay is the time it takes a packet to travel across the network from source to destination. Delay jitter is the fluctuation of end-to-end delay from packet to the next packet.
CDNs typically adopt one of two different server placement philosophies. Name and briefly describe these two philosophies.
Enter Deep: This philosophy is to enter deep into the access networks of Internet Service Providers, by deploying server clusters in access ISPs all over the world. Bring Home: A second design philosophy is to bring the ISP's home by building large clusters at a smaller number of key locations and connecting these clusters using a private high-speed network.
What protocol does ethernet use?
Ethernet with a bus topology is a broadcast LAN—all transmitted frames travel to and are processed by all adapters connected to the bus. Recall that we covered Ethernet's CSMA/CD multiple access protocol with binary exponential backoff in Section 5.3.2.
What is it called when a control connection sends data over a separate connection
FTP is said to send its control information out-of-band
List the application layer protocols
FTP, IRC, IMAP, HTTP, MIME, POP3, Rlogin, SOAP, SSH, Telnet
Pros and Cons of Switches
First consider the pros and cons of switches. As mentioned above, switches are plug-and-play, a property that is cherished by all the overworked network administrators of the world. Switches can also have relatively high filtering and forwarding rates—as shown in Figure 5.24, switches have to process frames only up through layer 2, whereas routers have to process datagrams up through layer 3. On the other hand, to prevent the cycling of broadcast frames, the active topology of a switched network is restricted to a spanning tree. Also, a large switched network would require large ARP tables in the hosts and routers and would generate substantial ARP traffic and processing. Furthermore, switches are susceptible to broadcast storms—if one host goes haywire and transmits an endless stream of Ethernet broadcast frames, the switches will forward all of these frames, causing the entire network to collapse.
Section 7.3 describes two FEC schemes. Briefly summarize them. Both schemes increase the transmission rate of the stream by adding overhead. Does interleaving also increase the transmission rate?
First scheme: send a redundant encoded chunk after every n chunks; the redundant chunk is obtained by exclusive OR-ing the n original chunks. Second scheme: send a lower-resolution low-bit rate scheme along with the original stream. Interleaving does not increase the bandwidth requirements of a stream.
Using the solution to Problem R1 above as inspiration, describe a protocol that the delegates can use to deliver letters from a sending family member to a receiving family member.
For sending a letter, the family member is required to give the delegate the letter itself, the address of the destination house, and the name of the recipient. The delegate clearly writes the recipient's name on the top of the letter. The delegate then puts the letter in an envelope and writes the address of the destination house on the envelope. The delegate then gives the letter to the planet's mail service. At the receiving side, the delegate receives the letter from the mail service, takes the letter out of the envelope, and takes note of the recipient name written at the top of the letter. The delegate then gives the letter to the family member with this name.
What is forwarding is terms of the network layer
Forwarding involves the transfer of a packet from an incoming link to an outgoing link within a single router.
What does FDM stand for?
Frequency Division Multiplexing
What is it called when data is sent through the control connection?
HTTP, as you recall, sends request and response header lines into the same TCP connection that carries the transferred file itself. For this reason, HTTP is said to send its control information in-band.
What is the code for a universal MAC address
However, sometimes a sending adapter does want all the other adapters on the LAN to receive and process the frame it is about to send. In this case, the sending adapter inserts a special MAC broadcast address into the destination address field of the frame. For LANs that use 6-byte addresses (such as Ethernet and 802.11), the broadcast address is a string of 48 consecutive 1s (that is, FF-FF-FF-FF-FFFF in hexadecimal notation).
What does ICMP
ICMP (Internet Control Message Protocol) is an error-reporting protocol network devices like routers use to generate error messages to the source IP address when network problems prevent delivery of IP packets. ICMP creates and sends messages to the source IP address indicating that a gateway to the Internet that a router, service or host cannot be reached for packet delivery. Any IP network device has the capability to send, receive or process ICMP messages.
What happens when a message is fragmented?
IP considers everything in the ULP section of the packet as data which can be fragmented. If fragmentation is necessary perform the following: Decide how much data can be "stuffed" into the first packet. Consider the following equation: (MTU - IP Header) as an acceptable size for the new packet. Take the old header and apply it to the new packet, however change the flags to "001." Bit 0 must be set to 0, bit one says other routers may fragment, and bit 2 says this is not the last fragment. Send this packet immediatly. Take as much of the original data as is left up to the (MTU - IP Header), put it in a new packet with the same header as before except set the fragment offset to: count*(MTU-IP header) + original fragment offset where count is the number of packets sent before this one. If this is the last fragment set the flags to "000." Continue doing step 3 until no more data remains.
BGP works on which port?
In BGP, pairs of routers exchange routing information over semipermanent TCP connections using port 179.
Where is the link layer implemented?
In Network card in hardware
What is the random Access protocol?
In a random access protocol, a transmitting node always transmits at the full rate of the channel, namely, R bps. When there is a collision, each node involved in the collision repeatedly retransmits its frame (that is, packet) until its frame getsthrough without a collision. But when a node experiences a collision, it doesn't necessarily retransmit the frame right away. Instead it waits a random delay before retransmitting the frame. Each node involved in a collision chooses independent random delays. Because the random delays are independently chosen, it is possible that one of the nodes will pick a delay that is sufficiently less than the delays of the other colliding nodes and will therefore be able to sneak its frame into the channel without a collision.
What is VLAN trunking?
In the VLAN trunking approach shown in Figure 5.26(b), a special port on each switch (port 16 on the left switch and port 1 on the right switch) is configured as a trunk port to interconnect the two VLAN switches. The trunk port belongs to all VLANs, and frames sent to any VLAN are forwarded over the trunk link to the other switch. But this raises yet another question: How does a switch know that a frame arriving on a trunk port belongs to a particular VLAN? The IEEE has defined an extended Ethernet frame format, 802.1Q, for frames crossing a VLAN trunk. As shown in Figure 5.27, the 802.1Q frame consists of the standard Ethernet frame with a four-byte VLAN tag added into the header that carries the identity of the VLAN to which the frame belongs. The VLAN tag is added into a frame by the switch at the sending side of a VLAN trunk, parsed, and removed by the switch at the receiving side of the trunk. The VLAN tag itself consists of a 2-byte
What are the components of a router?
Input ports, Switching fabric, Output ports, Routing processor
What does ICMP stand for?
Internet Control Message Protocol
What does IP stand for?
Internet Protocol
What is ICMP?
Internet control message protocol - used for testing basic connectivity, diagnostics, control, and error messaging
What does the application layer do
It is the layer which interacts with the user to provide access to services and data that is sent/received over a network. Communication partners are identified. The set of services that an application makes usage of
What is a point-to-point link?
It refers to a direct connection between two computers on a network. A point to point connection does not need any other network devices other than connecting a cable to the NIC cards of both computers.
What is LDNS
LDNS stands for Local Domain Name Server (computer networking)
Differences between FTP and HTTP
Let's now briefly compare SMTP with HTTP. Both protocols are used to transfer files from one host to another: HTTP transfers files (also called objects) from a Web server to a Web client (typically a browser); SMTP transfers files (that is, e-mail messages) from one mail server to another mail server. When transferring the files, both persistent HTTP and SMTP use persistent connections. Thus, the two protocols have common characteristics. However, there are important differences. First, HTTP is mainly a pull protocol—someone loads information on a Web server and users use HTTP to pull the information from the server at their convenience. In particular, the TCP connection is initiated by the machine that wants to receive the file. On the other hand, SMTP is primarily a push protocol—the sending mail server pushes the file to the receiving mail server. In particular, the TCP connection is initiated by the machine that wants to send the file.
What is the OSFP?
Like RIP, OSPF routing is widely used for intra-AS routing in the Internet. OSPF and its closely related cousin, IS-IS, are typically deployed in upper-tier ISPs whereas RIP is deployed in lower-tier ISPs and enterprise networks. The Open in OSPF indicates that the routing protocol specification is publicly available (for example, as opposed to Cisco's EIGRP protocol). The most recent version of OSPF, version 2, is defined in RFC 2328, a public document.
Besides network-related considerations such as delay, loss, and bandwidth performance, there are many additional important factors that go into designing a cluster selection strategy. What are they?
Load on the cluster - clients should not be directed to overload clusters. ISP delivery cost - the clusters may be chosen so that specific ISPs are used to carry CDN-to-client traffic, taking into account the different cost structures in the contractual relationships between ISPs and cluster operators.
What is a bootstrap program?
Loaded at power-up, initializes all aspects of system, loads operating system kernel and starts execution
What does MSS stand for?
Maximum Segment Size
What is Network Throughput?
Network throughput is usually represented as an average and measured in bits per second (bps), or in some cases as data packets per second. Throughput is an important indicator of the performance and quality of a network connection. A high ratio of unsuccessful message delivery will ultimately lead to lower throughput and degraded performance.
In your protocol, does the mail service ever have to open the envelope and examine the letter in order to provide its service?
No, the mail service does not have to open the envelope; it only examines the address on the envelope.
In your protocols, does the transport layer "have to do anything" in the core of the computer network?
No, the transport layer does not have to do anything in the core; the transport layer "lives" in the end systems.
With HTTP streaming, are the TCP receive buffer and the client's application buffer the same thing? If not, how do they interact?
No. On the client side, the client application reads bytes from the TCP receive buffer and places the bytes in the client application buffer.
What does an IPv4 daragram look like?
Note that an IP datagram has a total of 20 bytes of header (assuming no options). If the datagram carries a TCP segment, then each (nonfragmented) datagram carries a total of 40 bytes of header (20 bytes of IP header plus 20 bytes of TCP header) along with the application-layer message.
What are the pros and cons of routers
Now consider the pros and cons of routers. Because network addressing is often hierarchical (and not flat, as is MAC addressing), packets do not normally cycle through routers even when the network has redundant paths. (However, packets can cycle when router tables are misconfigured; but as we learned in Chapter 4, IP uses a special datagram header field to limit the cycling.) Thus, packets are not restricted to a spanning tree and can use the best path between source and destination. Because routers do not have the spanning tree restriction, they have allowed the Internet to be built with a rich topology that includes, for example, multiple active links between Europe and North America. Another feature of routers is that they provide firewall protection against layer-2 broadcast storms. Perhaps the most significant drawback of routers, though, is that they are not plug-and-play—they and the hosts that connect to them need their IP addresses to be configured. Also, routers often have a larger per-packet processing time than switches, because they have to process up through the layer-3 fields. Finally, there are two different ways to pronounce the word router, either as "rootor" or as "rowter," and people waste a lot of time arguing over the proper pronunciation [Perlman 1999].
How does OSFP work?
OSPF was conceived as the successor to RIP and as such has a number of advanced features. At its heart, however, OSPF is a link-state protocol that uses flooding of link-state information and a Dijkstra least-cost path algorithm. With OSPF, a router constructs a complete topological map (that is, a graph) of the entire autonomous system. The router then locally runs Dijkstra's shortest-path algorithm to determine a shortest-path tree to all subnets, with itself as the root node. Individual link costs are configured by the network administrator (see Principles and Practice: Setting OSPF Weights). The administrator might choose to set all link costs to 1, thus achieving minimum-hop routing, or might choose to set the link weights to be inversely proportional to link capacity in order to discourage traffic from using low-bandwidth links. OSPF does not mandate a policy for how link weights are set (that is the job of the network administrator), but instead provides the mechanisms (protocol) for determining least-cost path routing for the given set of link weights.
What is he difference between frame forwarding and datagram forwarding?
One important difference is that switches forward packets based on MAC addresses rather than on IP addresses. We will also see that a switch table is constructed in a very different manner from a router's forwarding table.
What port does DNS use?
Port 53
What is routing
Process of identifying what path to have a packet take through a network from sender to receiver
What features does the link layer have
Provides a protocol for communication over the physical medium Provides error checking Provides primitive flow control
What is PCM
Pulse Code Modulation. Pulse-code modulation (PCM) is a method used to digitally represent sampled analog signals. It is the standard form of digital audio in computers, compact discs, digital telephony and other digital audio applications. In a PCM stream, the amplitude of the analog signal is sampled regularly at uniform intervals, and each sample is quantized to the nearest value within a range of digital steps.
Suppose an analog audio signal is sampled 16,000 times per second, and each sample is quantized into one of 1024 levels. What would be the resulting bit rate of the PCM digital audio signal?
Quantizing a sample into 1024 levels means 10 bits per sample. The resulting rate of the PCM digital audio signal is 160 Kbps.
What does the network layer do?
Responsible for addressing and routing of messages
What does the network layer do?
Responsible for addressing and routing of messages. sending it in the right direction to the right destination on outgoing transmissions and receiving incoming transmissions at the packet level.
What does the data link layer do?
Responsible for sending and receiving messages to and from other computers. Its job is to reliably move a message from one computer over one circuit to the next computer where the messages needs to go .Sets up links across physical networks.
What is RARP?
Reverse Address Resolution Protocol. RARP (Reverse Address Resolution Protocol) is a protocol by which a physical machine in a local area network can request to learn its IP address from a gateway server's Address Resolution Protocol (ARP) table or cache. A network administrator creates a table in a local area network's gateway router that maps the physical machine (or Media Access Control - MAC address) addresses to corresponding Internet Protocol addresses. When a new machine is set up, its RARP client program requests from the RARP server on the router to be sent its IP address. Assuming that an entry has been set up in the router table, the RARP server will return the IP address to the machine which can store it for future use.
Difference between router and switch
Router is like a gateway between networks. As we learned in Chapter 4, routers are store-and-forward packet switches that forward packets using network-layer addresses. Although a switch is also a store-andforward packet switch, it is fundamentally different from a router in that it forwards packets using MAC addresses. Whereas a router is a layer-3 packet switch, a switch is a layer-2 packet switch.
What is RIP?
Routing Internet Protocol. RIP is a distance-vector protocol that operates in a manner very close to the idealized DV protocol we examined in Section 4.5.2. The version of RIP specified in RFC 1058 uses hop count as a cost metric; that is, each link has a cost of 1. In the DV algorithm in Section 4.5.2, for simplicity, costs were defined between pairs of routers. In RIP (and also in OSPF), costs are actually from source router to a destination subnet. RIP uses the term hop, which is the number of subnets traversed along the shortest path from source router to destination subnet, including the destination subnet. Figure 4.34 illustrates an AS with six leaf subnets. The table in the figure indicates the number of hops from the source A to each of the leaf subnets.
What does SIP stand for? A. Standard Initiation Protocol B. System Internetworking Protocol C. Session Initiation Protocol D. Sector Information Protocol
Session Initiantion Protocol
Several cluster selection strategies were described in Section 7.2.4. Which of these strategies finds a good cluster with respect to the client's LDNS? Which of these strategies finds a good cluster with respect to the client itself?
Several cluster selection strategies were described in Section 7.2.4. Which of these strategies finds a good cluster with respect to the client's LDNS? Which of these strategies finds a good cluster with respect to the client itself?
What does ARP do?
Shows the IP address to MAC address mapping table (address cache). We'll also cover the Address Resolution Protocol (ARP), which provides a mechanism to translate IP addresses to link-layer addresses.
What does SMTP stand for?
Simple Mail Transfer Protocol
What is the difference between slotted and pure ALOHA?
Slotted ALOHA is not decetralized but it is twice as fast
socket
Software in an operating system that connects an application with a network protocol. a socket is the interface between the application layer and the transport layer within a host
Consider a TCP connection between Host A and Host B. Suppose that the TCP segments traveling from Host A to Host B have source port number x and destination port number y. What are the source and destination port numbers for the segments traveling from Host B to Host A?
Source port number y and destination port number x.
There are two types of redundancy in video. Describe them, and discuss how they can be exploited for efficient compression.
Spatial Redundancy: It is the redundancy within a given image. Intuitively, an image consists of mostly white space has a high degree of redundancy and can be efficiently compressed without significantly sacrificing image quality. Temporal Redundancy reflects repetition from image to subsequent image. If, for example, an image and the subsequent image are exactly the same, there is no reason to re-encode the subsequent image; it is instead more efficient simply to indicate during encoding that the subsequent image is exactly the same. If the two images are very similar, it may be not efficient to indicate how the second image differs from the first, rather than re-encode the second image
What is the binary exponential backoff algorithm?
Specifically, when transmitting a frame that has already experienced n collisions, a node chooses the value of K at random from {0, 1, 2, . . . . 2n 1}. Thus, the more collisions experienced by a frame, the larger the interval from which K is chosen. For Ethernet, the actual amount of time a node waits is K 512 bit times (i.e., K times the amount of time needed to send 512 bits into the Ethernet) and the maximum value that n can take is capped at 10.
Multimedia applications can be classified into three categories. Name and describe each category.
Streaming stored audio/video, Conversational Voice- and Video-over-IP, and Streaming Live Audio and Video.
What are different ways to implement router switching
Switching via memory, Switching via a bus, Switching via an interconnection network.
What Transport layer protocol does IP usually get associated with?
TCP
what is cwnd and rwnd
TCP can use the congestion window (cwnd) and the receiver window (rwnd) to control and avoid network congestion. The amount of data that can be transmitted through a TCP connection is dependent on the congestion window, which is maintained by the source. The receiver window is maintained by the destination.
What is in a routing table?
The *routing table* contains only the best routes from every routing protocol. Routing tables are composed of: A Destination Address, either host or network in nature The IP Address of the next "hop" The Metric, or cost of sending to that router The network interface which is closest to the next hop
Who is DARPA and why were they relevant
The Advanced Research Projects Agency Network (ARPANET) was an early packet switching network and the first network to implement the protocol suite TCP/IP. Both technologies became the technical foundation of the Internet. The ARPANET was initially funded by the Advanced Research Projects Agency (ARPA) of the United States Department of Defense.
What are the two important taking-turns protocols?
The first one is the polling protocol. and The second taking-turns protocol is the token-passing protocol.
What address space is reserved for private networks?
The address space 10.0.0.0/24 is one of three portions of the IP address space that is reserved in [RFC 1918] for a private network or a realm with private addresses, such as the home network in
What is classful addressing?
The concept that an IPv4 address has three parts—network, subnet, and host—as defined by the mask and Class A, B, and C rules.
What does the data protocol do?
The data connection is used to actually send a file.
How does ARP work?
The important question addressed in this section is, How does the sending host determine the MAC address for the destination host with IP address 222.222.222.222? As you might have guessed, it uses ARP. An ARP module in the sending host takes any IP address on the same LAN as input, and returns the corresponding MAC address. In the example at hand, sending host 222.222.222.220 provides its ARP module the IP address 222.222.222.222, and the ARP module returns the corresponding MAC address 49-BD-D2-C7-56-2A. So we see that ARP resolves an IP address to a MAC address. In many ways it is analogous to DNS (studied in Section 2.5), which resolves host names to IP addresses. However, one important difference between the two resolvers is that DNS resolves host names for hosts anywhere in the Internet, whereas ARP resolves IP addresses only for hosts and router interfaces on the same subnet. If a node in California were to try to use ARP to resolve the IP address for a node in Mississippi, ARP would return with an error.
What is the mainly used LS algorithm?
The link-state routing algorithm we present below is known as Dijkstra's algorithm, named after its inventor. A closely related algorithm is Prim's algorithm; see [Cormen 2001] for a general discussion of graph algorithms. Dijkstra's algorithm computes the least-cost path from one node (the source, which we will refer to as u) to all other nodes in the network. Dijkstra's algorithm is iterative and has the property that after the kth iteration of the algorithm, the least-cost paths are known to k destination nodes, and among the least-cost paths to all destination nodes, these k paths will have the k smallest costs.
What is the main difference between HTTP Protocol and FTP Protocol
The most striking difference is that FTP uses two parallel TCP connections to transfer a file, a control connection and a data connection.
How does the token protocol work?
The second taking-turns protocol is the token-passing protocol. In this protocol there is no master node. Asmall, special-purpose frame known as a token is exchanged among the nodes in some fixed order. For example, node 1 might always send the token to node 2, node 2 might always send the token to node 3, and node N might always send the token to node 1. When a node receives a token, it holds onto the token only if it has some frames to transmit; otherwise, it immediately forwards the token to the next node. If a node does have frames to transmit when it receives the token, it sends up to a maximum number of frames and then forwards the token to the next node. Token passing is decentralized and highly efficient. But it has its problems as well. For example, the failure of one node can crash the entire channel. Or if a node accidentally neglects to release the token, then some recovery procedure must be invoked to get the token back in circulation.
What is a broadcast link?
The second type of link, a broadcast link, can have multiple sending and receiving nodes all connected to the same, single, shared broadcast channel. The term broadcast is used here because when any one node transmits a frame, the channel broadcasts the frame and each of the other nodes receives a copy. Ethernet and wireless LANs are examples of broadcast link-layer technologies.
Modify this protocol so that it provides a "return address" to the destination process.
The segment now has two header fields: a source port field and destination port field. At the sender side, STP accepts a chunk of data not exceeding 1192 bytes, a destination host address, a source port number, and a destination port number. STP creates a segment which contains the application data, source port number, and destination port number. It then gives the segment and the destination host address to the network layer. After receiving the segment, STP at the receiving host gives the application process the application data and the source port number.
What is IP Datagram Fragmentation?
The solution is to fragment the data in the IP datagram into two or more smaller IP datagrams, encapsulate each of these smaller IP datagrams in a separate link-layer frame; and send these frames over the outgoing link. Each of these smaller datagrams is referred to as a fragment.
List three disadvantages of UDP streaming.
The three significant drawbacks of UDP Streaming are: 1. Due to unpredictable and varying amount of available bandwidth between server and client, constant-rate UDP streaming can fail to provide continuous play out. 2. It requires a media control server, such as an RTSP server, to process client-toserver interactivity requests and to track client state for each ongoing client session. 3. Many firewalls are configured to block UDP traffic, preventing users behind these firewalls from receiving UDP video
What is the most well known ICMP message?
The well-known ping program sends an ICMP type 8 code 0 message to the specified host. The destination host, seeing the echo request, sends back a type 0 code 0 ICMP echo reply.
How does ARP affect routers with multiple addresses
There are several interesting things to note about Figure 5.19. Each host has exactly one IP address and one adapter. But, as discussed in Chapter 4, a router has an IP address for each of its interfaces. For each router interface there is also an ARP module (in the router) and an adapter. Because the router in Figure 5.19 has two interfaces, it has two IP addresses, two ARP modules, and two adapters. Of course, each adapter in the network has its own MAC address.
What are the ideas behind CSMA?
These two rules are embodied in the family of carrier sense multiple access (CSMA) and CSMA with collision detection (CSMA/CD) protocols [Kleinrock 1975b; Metcalfe 1976; Lam 1980; Rom 1990]. Many variations on CSMA and CSMA/CD have been proposed. Here, we'll consider a few of the most important, and fundamental, characteristics of CSMA and CSMA/CD.
What port carries the DHCP discover message?
This is done using a DHCP discover message, which a client sends within a UDP packet to port 67. The UDP packet is encapsulated in an IP datagram.
What does the link layer do?
This layer controls the transmission and reception of packets of data to/from a local network
Why is FTP server not stateless?
Throughout a session, the FTP server must maintain state about the user. In particular, the server must associate the control connection with a specific user account, and the server must keep track of the user's current directory as the user wanders about the remote directory tree. Keeping track of this state information for each ongoing user session significantly constrains the total number of sessions that FTP can maintain simultaneously
In an FTP connection are the data connections persistent or not?
Thus, with FTP, the control connection remains open throughout the duration of the user session, but a new data connection is created for each file transferred within a session (that is, the data connections are non-persistent).
What does TDM stand for?
Time Division Multiplexing
What does the physical layer do
Timing and synchronization of bits. This layer conveys the bit stream across the network.
What is modern ethernet?
To deal with these collisions, the Ethernet standard included the CSMA/CD protocol, which is particularly effective for a wired broadcast LAN spanning a small geographical region. But if the prevalent use of Ethernet today is a switch-based star topology, using store-and-forward packet switching, in a switch-based Ethernet LAN there are no collisions and, therefore, there is no need for a MAC protocol!
What is the purpose of DNS?
To provide a human-friendly address for internet destinations. DNS is commonly employed by other application-layer protocols—including HTTP, SMTP, and FTP—to translate user-supplied hostnames to IP addresses
What does TCP stand for?
Transmission Control Protocol
When to use either?
Typically, small networks consisting of a few hundred hosts have a few LAN segments. Switches suffice for these small networks, as they localize traffic and increase aggregate throughput without requiring any configuration of IP addresses. But larger networks consisting of thousands of hosts typically include routers within the network (in addition to switches). The routers provide a more robust isolation of traffic, control broadcast storms, and use more "intelligent" routes among the hosts in the network.
Streaming video systems can be classified into three categories. Name and briefly describe each of these categories.
UDP Streaming, HTTP Streaming, Adaptive HTTP Streaming (DASH)
What port is RIP on?
UDP on 520.
We saw that streaming video systems can be classified into three categories:
UDP streaming, HTTP streaming, and adaptive HTTP streaming. Although all three types of systems are used in practice, the majority of today's systems employ HTTP streaming and adaptive HTTP streaming.
What are the FTP commands
USER username: Used to send the user identification to the server. • PASS password: Used to send the user password to the server. • LIST: Used to ask the server to send back a list of all the files in the current remote directory. The list of files is sent over a (new and non-persistent) data connection rather than the control TCP connection. • RETR filename: Used to retrieve (that is, get) a file from the current directory of the remote host. This command causes the remote host to initiate a data connection and to send the requested file over the data connection. • STOR filename: Used to store (that is, put) a file into the current directory of the remote host.
What is a VLAN?
VLAN is short for Virtual Area Network, in which virtual subnets are segregated using switch ports, eliminating the need for physical moves, adds and changes.
What does CDMA do?
While TDM and FDM assign time slots and frequencies, respectively, to the nodes, CDMA assigns a different code to each node. Each node then uses its unique code to encode the data bits it sends. If the codes are chosen carefully, CDMA networks have the wonderful property that different nodes can transmit simultaneously and yet have their respective receivers correctly receive a sender's encoded data bits (assuming the receiver knows the sender's code) in spite of interfering transmissions by other nodes.
Give examples of load-sensitive and load-insensitive algorithms.
While early ARPAnet routing algorithms were load-sensitive [McQuillan 1980], a number of difficulties were encountered [Huitema 1998]. Today's Internet routing algorithms (such as RIP, OSPF, and BGP) are load-insensitive, as a link's cost does not explicitly reflect its current (or recent past) level of congestion.
Who gives the ISP the IP addresses?
While obtaining a set of addresses from an ISP is one way to get a block of addresses, it is not the only way. Clearly, there must also be a way for the ISP itself to get a block of addresses. Is there a global authority that has ultimate responsibility for managing the IP address space and allocating address blocks to ISPs and other organizations? Indeed there is! IP addresses are managed under the authority of the Internet Corporation for Assigned Names and Numbers (ICANN) [ICANN 2012], based on guidelines set forth in [RFC 2050].
Suppose a process in Host C has a UDP socket with port number 6789. Suppose both Host A and Host B each send a UDP segment to Host C with destination port number 6789. Will both of these segments be directed to the same socket at Host C? If so, how will the process at Host C know that these two segments originated from two different hosts?
Yes, both segments will be directed to the same socket. For each received segment, at the socket interface, the operating system will provide the process with the IP addresses to determine the origins of the individual segments.
What is packet switching?
a mode of data transmission in which a message is broken into a number of parts that are sent independently, over whatever route is optimum for each packet, and reassembled at the destination.
What does the presentation layer do
deals with formatting of data at the coding or syntax level. Converts data from one presentation format to another
What do CSMA and CSMA/CD stand for?
carrier sense multiple access (CSMA) and CSMA with collision detection (CSMA/CD) protocols
What are the three categories of multiple access protocols?
channel partitioning protocols, random access protocols, and taking-turns protocols.
What does the transport layer do
covers end-to-end movement of data in a reliable manner. This layer manages packetization of data, then the delivery of the packets, including checking for errors in the data once it arrives.
What does the session layer do?
deals with establishment, management and dissolution of sessions (periods of time which systems exchange data). Sets up and terminates most conversations. Its services include authentication and reconnection after an interruption.
Make a UDP Client
from socket import * serverName = 'hostname' serverPort = 12000 clientSocket = socket(socket.AF_INET, socket.SOCK_DGRAM) message = raw_input('Input lowercase sentence:') clientSocket.sendto(message,(serverName, serverPort)) modifiedMessage, serverAddress = clientSocket.recvfrom(2048) print modifiedMessage clientSocket.close()
Make a UDP server
from socket import * serverPort = 12000 serverSocket = socket(AF_INET, SOCK_DGRAM) serverSocket.bind(('', serverPort)) print "The server is ready to receive" while 1: message, clientAddress = serverSocket.recvfrom(2048) modifiedMessage = message.upper() serverSocket.sendto(modifiedMessage, clientAddress)
Make a python TCP Client
import socket; sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM); sock.connect(("www.google.com",80)); sock.sendall(b"GET / HTTP/1.0\r\n\r\n"); data=''; buffer = sock.recv(1024); while buffer: data +=repr(buffer); buffer = sock.recv(1024); print("Server said: "); print(data,sep='',end=''); sock.close();
Make a python server TCP Server
import socket; sock = socket.socket(socket.AF_INET,socket.SOCK_STREAM); sock.bind(("", 6543)); #could be sock.bind(("",6543)) sock.listen(); while True: (conn,(ip,port)) = sock.accept(); #returns with a connection print("Got a connection from",ip,"from port",port); conn.sendall(b"Thanks for stopping by, but now you have to leave.\r\n"); conn.close();
What does the control protocol do?
is used for sending control information between the two hosts—information such as user identification, password, commands to change remote directory, and commands to "put" and "get" files.
Flow control
makes sure that neither end of a connection overwhelms the buffers in the other end of the connection by sending to many packets to fast.
TCP (Transmission Control Protocol)
provides reliable, ordered, and error-checked delivery of a stream of packets on the internet. TCP is tightly linked with IP and usually seen as TCP/IP in writing.
What is a decentralized routing algorithm?
the calculation of the least-cost path is carried out in an iterative, distributed manner. No node has complete information about the costs of all network links. Instead, each node begins with only the knowledge of the costs of its own directly attached links. Then, through an iterative process of calculation and exchange of information with its neighboring nodes (that is, nodes that are at the other end of links to which it itself is attached), a node gradually calculates the least-cost path to a destination or set of destinations.
What does the routing algorithm do?
the routing algorithm determines the values that are inserted into the routers' forwarding tables. The routing algorithm may be centralized (e.g., with an algorithm executing on a central site and downloading routing information to each of the routers) or decentralized (i.e., with a piece of the distributed routing algorithm running in each router).
What is network address translation?
the translation of an IP addressused within one network to a different IP address known within another network. One network is designated the inside network and the other is the outside.
How does slotted ALOHA protocol work?
• When the node has a fresh frame to send, it waits until the beginning of the next slot and transmits the entire frame in the slot. • If there isn't a collision, the node has successfully transmitted its frame and thus need not consider retransmitting the frame. (The node can prepare a new frame for transmission, if it has one.) • If there is a collision, the node detects the collision before the end of the slot. The node retransmits its frame in each subsequent slot with probability p until the frame is transmitted without a collision.
