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VTU 6TH SEM CSE COMPUTER NETWORKS 2 NOTES 10CS64, Study notes of Computer Networks

Visvesvaraya Technological UniversityComputer Networks

VTU 6TH SEM CSE COMPUTER NETWORKS 2 NOTES 10CS64

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COMPUTER NETWORKS - II
Subject Code: 10CS64 I.A. Marks : 25
Hours/Week : 04 Exam Hours: 03
Total Hours : 52 Exam Marks: 100
PART - A
UNIT – 1 6 Hours
Packet Switching Networks - 1: Network services and internal network operation, Packet network topology,
Routing in Packet networks, Shortest path routing: Bellman-Ford algorithm.
UNIT – 2 6 Hours
Packet Switching Networks – 2: Shortest path routing (continued), Traffic management at the Packet level,
Traffic management at Flow level, Traffic management at flow aggregate level.
UNIT – 3 7 Hours
TCP/IP-1: TCP/IP architecture, The Internet Protocol, IPv6, UDP.
UNIT – 4 7 Hours
TCP/IP-2: TCP, Internet Routing Protocols, Multicast Routing, DHCP, NATand Mobile IP.
PART – B
UNIT – 5 6 Hours
Applications, Network Management, Network Security: Application layer overview, Domain Name System
(DNS), Remote Login Protocols, E-mail, File Transfer and FTP, World Wide Web and HTTP, Network
management, Overview of network security, Overview of security methods, Secret-key encryption protocols,
Public-key encryption protocols, Authentication, Authentication and digital signature, Firewalls.
UNIT – 6 7 Hours
QoS, VPNs, Tunneling, Overlay Networks: Overview of QoS, Integrated Services QoS, Differentiated
services QoS, Virtual Private Networks, MPLS, Overlay networks.
UNIT – 7 7 Hours
Multimedia Networking: Overview of data compression, Digital voice and compression, JPEG, MPEG, Limits
of compression with loss, Compression methods without loss, Overview of IP Telephony, VoIP signaling
protocols, Real-Time Media Transport Protocols, Stream control Transmission Protocol (SCTP)
UNIT – 8 6 Hours
Mobile Ad-Hoc Networks, Wireless sensor Networks: Overview of wireless adhoc networks; Routing in
adhoc networks; Routing protocols for adhoc networks; security of adhoc networks. Sensor networks and
protocol structures; Communication energy model; Clustering protocols; Routing protocols; Zigbee technology
and IEEE 802.15.4
Text Books:
1. Alberto Leon-Garcia and Indra Widjaja: Communication Networks – Fundamental Concepts and Key
architectures, 2nd Edition, Tata McGraw-Hill, 2004.
(Chapters 7, 8, 9, 11, Appendix B)
2. Nader F. Mir: Computer and Communication Networks, Pearson Education, 2007.
(Chapters 12, 16, 17, 18, 19, 20)
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Download VTU 6TH SEM CSE COMPUTER NETWORKS 2 NOTES 10CS64 and more Study notes Computer Networks in PDF only on Docsity!

Subject Code: 10CS64 I.A. Marks : 25

Hours/Week : 04 Exam Hours: 03

Total Hours : 52 Exam Marks: 100

PART - A

UNIT – 1 6 Hours

Packet Switching Networks - 1: Network services and internal network operation, Packet network topology,

Routing in Packet networks, Shortest path routing: Bellman-Ford algorithm.

UNIT – 2 6 Hours

Packet Switching Networks – 2: Shortest path routing (continued), Traffic management at the Packet level,

Traffic management at Flow level, Traffic management at flow aggregate level.

UNIT – 3 7 Hours

TCP/IP-1: TCP/IP architecture, The Internet Protocol, IPv6, UDP.

UNIT – 4 7 Hours

TCP/IP-2: TCP, Internet Routing Protocols, Multicast Routing, DHCP, NATand Mobile IP.

PART – B

UNIT – 5 6 Hours

Applications, Network Management, Network Security: Application layer overview, Domain Name System

(DNS), Remote Login Protocols, E-mail, File Transfer and FTP, World Wide Web and HTTP, Network

management, Overview of network security, Overview of security methods, Secret-key encryption protocols,

Public-key encryption protocols, Authentication, Authentication and digital signature, Firewalls.

UNIT – 6 7 Hours

QoS, VPNs, Tunneling, Overlay Networks: Overview of QoS, Integrated Services QoS, Differentiated

services QoS, Virtual Private Networks, MPLS, Overlay networks.

UNIT – 7 7 Hours

Multimedia Networking: Overview of data compression, Digital voice and compression, JPEG, MPEG, Limits

of compression with loss, Compression methods without loss, Overview of IP Telephony, VoIP signaling

protocols, Real-Time Media Transport Protocols, Stream control Transmission Protocol (SCTP)

UNIT – 8 6 Hours

Mobile Ad-Hoc Networks, Wireless sensor Networks: Overview of wireless adhoc networks; Routing in

adhoc networks; Routing protocols for adhoc networks; security of adhoc networks. Sensor networks and

protocol structures; Communication energy model; Clustering protocols; Routing protocols; Zigbee technology

and IEEE 802.15.

Text Books:

1. Alberto Leon-Garcia and Indra Widjaja: Communication Networks – Fundamental Concepts and Key

architectures, 2nd^ Edition, Tata McGraw-Hill, 2004.

(Chapters 7, 8, 9, 11, Appendix B)

2. Nader F. Mir: Computer and Communication Networks, Pearson Education, 2007.

(Chapters 12, 16, 17, 18, 19, 20)

TABLE OF CONTENTS

  • UNIT 1: PACKET SWITCHING NETWORKS 1-
  • UNIT 2: PACKET SWITCHING NETWORKS(CONT.) 12-
  • UNIT 3: TCP/IP 26-
  • UNIT 5: APPLICATIONS & NETWORK MANAGEMENT 38-
  • UNIT 6: QUALITY OF SERVICE & RESOURCE ALLOCATION 59-

PACKET NETWORK TOPOLOGY

ACCESS NETWORK

  • The access multiplexer is used to combine the typically bursty traffic flows from the individual computers into aggregated flows so that the transmission line to the packet network is used more efficiently (Figure 7.4).
  • An example of an access multiplexer includes a DSLAM (Digital Subscriber Loop Access Multiplexer) located in a telephone central office.
  • The computer in the subscriber home is connected to the DSLAM in the central office via an ADSL modem.

Figure 7.4: Access network

CAMPUS NETWORK

  • LANs for a large group of users such as a department are interconnected in an extended LAN through the use of LAN switches(s).
  • Resources such as servers & databases that are primarily of use to this department are kept within the subnetwork. Thus, delays in accessing the resources can be reduced (Figure 7.5).
  • Each subnetwork has access to the rest of the organization through a router(R) that accesses the campus backbone network.
  • A subnetwork also uses the campus backbone to reach the "outside world" such as the Internet.
  • Servers containing critical resources that are required by entire organization are usually located in a data center → where they can be easily maintained & → where security can be enforced
  • The routers in the campus network are interconnected to form the campus backbone network(S).
  • Routers are interconnected by very high speed LANs. For example: Gigabit Ethernet or an ATM network.
  • Routers use IP which enables them to operate over various data link and network technologies.
  • Routers exchange information about the state of their links to dynamically calculate routing tables.

Figure 7.5: Campus network

DATAGRAMS AND VIRTUAL CIRCUITS

CONNECTIONLESS PACKET SWITCHING (DATAGRAM)

  • This is analogous to postal system (Figure 7.11).
  • Each packet is routed independently through the network.
  • Each packet has a header attached to it to provide source and destination addresses.
  • Each switch examines the header to determine the next hop in the path to the destination.
  • If the transmission line is busy then the packet is placed in the queue until the line becomes free.
  • Advantage: High utilization of transmission-line can be achieved by sharing among multiple packets.
  • Disadvantage: 1) Packets may arrive out-of-order, and re-sequencing may be required at the destination
  1. Loss of packets may occur when a switch has insufficient buffer
  • If the path followed by a sequence of packets consists of L hops with identical propagation delays P and transmission speeds (Figure 7.12), then the delay incurred by a message that consists of k packets is given by

Figure 7.11:Datagram packet switching

Figure 7.12:Delays in datagrams packet switching

STRUCTURE OF A PACKET-SWITCH

  • A packet-switch performs 2 main functions:
    1. Routing function uses algorithms to find a path to each destination and store the result in a routing table.
    2. Forwarding function processes each incoming packet from an input port and forwards the packet to the appropriate output port (based on the information stored in the routing table).
  • A line card contains several input/output ports (Figure 7.19). The line card also contains some buffers and the associated scheduling algorithms. The line card is concerned with symbol timing, line coding, framing, physical layer addressing & error checking.
  • Programmable network processor performs packet-related tasks such as table lookup and packet scheduling.
  • A controller contains a general-purpose processor which is used for control & management functions depending on the type of packet switching. The controller acts as a central coordinator, as it communicates with each line card and the interconnection fabric.
  • Interconnection fabric is used to transfer packets between the line cards.
  • Problem: Interconnection fabric is likely to be the bottleneck if there are many high-speed line cards, since all traffic from the input line cards have to go through to the interconnection fabric (Figure 7.20).
  • Buffers need to be added to the crossbar interconnection fabric to accommodate packet contention
  • How to eliminate head-of-line(HOL) blocking? Solution: Provide N separate input buffers at each input port so that each input buffer is dedicated to a particular output. Such an input buffer is called a virtual output buffer.

Figure 7.19:a)components of a generic packet switch b)organization of a line card

Figure 7.20: Input buffering versus output buffering

ROUTING IN PACKET NETWORKS

  • Routing means determining feasible paths for packets to follow from each source to each destination.

ROUTING ALGORITHM SHOULD SEEK ONE OR MORE OF THE FOLLOWING GOALS 1)Rapid and accurate delivery of packets

  1. Adaptability to changes in network topology resulting from node or link failures
  2. Adaptability to varying source-destination traffic loads
  3. Ability to route packets away from temporarily congested links
  4. Ability to determine the connectivity of the network
  5. Ability to avoid routing loops
  6. Low overhead: The control messages represent an overhead on bandwidth usage that should be minimized.

ROUTING ALGORITHM CLASSIFICATION Static (Non-adaptive) Routing

  • Paths are precomputed based on the network topology, link capacities and other information.
  • A dedicated host is used to perform computation offline.
  • The precomputed paths → are loaded to the routing-table & → remain fixed for a relatively long period of time
  • Static routing is suitable if → network size is small → network topology is relatively fixed
  • Disadvantage: 1) Inability to react rapidly to network failures.
    1. Static routing may become cumbersome, as the network size increases. Dynamic (Adaptive) Routing
  • Each node continuously learns state of the network by communicating with its neighbors. Thus, a change in a network-topology is eventually propagated to all nodes
  • Based on the information collected, each node computes the best path to the destination.
  • Disadvantage: Added complexity in the node. Centralized Routing
  • A network control center → computes all paths & → then uploads this information to the nodes in the network. Distributed Routing
  • Nodes cooperate by means of message exchanges and perform their own routing computations.
  • Advantage: These algorithms scales better than centralized algorithm Disadvantage: More likely to produce inconsistent results.

DATAGRAM PACKET SWITCHING

  • The routing table identifies the next hop to which to forward a packet based on the destination address of the packet (Figure 7.25).
  • How to route from node 1 to node 6(Figure 7.22)?
    1. The packet is first forwarded to node 3 based on the corresponding entry in the routing table at node
    1. Node 3 then forwards the packet to node 6.

Figure 7.22: Multiple paths in a packet switching network

Figure 7.25: Routing tables for datagram network in figure 7.

HIERARCHICAL ROUTING

  • Hierarchical approach can be used to reduce size of routing table in the routers (Figure 7.26).
  • Hosts that are near each other should have addresses that have common prefixes.
  • In this way, routers need to examine only part of address in order to decide how a packet should be routed.

Figure 7.26: Address assignment a) Hierarchical b)flat

SPECIALIZED ROUTING

FLOODING

  • Switch forwards an incoming-packet to all ports except the one packet was received from (Fig 7.27).
  • Flooding is an effective routing approach → when the information in the routing tables is not available such as during system-startup → when the source needs to broadcast a packet to all nodes in the network
  • Problem: Flooding generates large number of duplicate packets, which may easily swamp the network.
  • Solution: To reduce resource consumption in the network, following mechanisms can be used:
    1. Use a TTL(time-to-live) field in each packet: When source sends a packet, TTL is initially set to some number. Each node decrements TTL value by 1 before flooding the packet. If TTL reaches zero, the node discards the packet.
    2. Add an identifier before flooding: Each node adds its identifier(ID) to the header before flooding the packet. If the node receives a packet that contains it’s own ID, it will discard the packet
    3. Have a unique sequence number: Each packet is assigned a unique sequence number. When a node receives a packet, the node records source address and sequence number of the packet. If the node discovers that the packet has already visited the node, it will discard the packet.

Figure 7.27: Flooding is initiated from node 1: a)hop-1 transmission b)hop-2 transmission and c)hop-3 transmission

SHORTEST PATH ROUTING

  • The shortest path from node 2 to node 6 is 2-4-3-6, and the path cost is 4 (Figure 7.30).
  • Following metrics can be used to assign a cost to each link:
    1. Cost~1/capacity: Here, one assigns higher costs to lower capacity links. The objective is to send a packet through a path with the highest capacity.
    2. Cost~delay: Delay includes queuing-delay in switch-buffer and propagation-delay in the link. Shortest path represents the fastest path to reach the destination.
    3. Cost~congestion: The shortest path tries to avoid congested links.

Figure 7.30: A network with associated link costs

BELLMAN-FORD ALGORITHM

  • If each neighbor of node A knows the shortest path to node Z, then node A can determine its shortest path to node Z by calculating the cost to node Z through each of its neighbors and picking the minimum.
  • Let Dj = current estimate of the minimum cost from node j to the destination Let Cij = link cost from node i to node j. (For example C 13 =C 31 =2) The link cost from node i to itself is defined to be zero (Cii=0). The link cost between node i & node k is infinite if node i & node k are not directly connected.(for example C 15 =C 23 =~ )
  • If the destination node is node 6, then the minimum cost from node 2 to the destination node 6 can be calculated in terms of distances through node 1, node 4 or node 5(Figure 7.31): D 2 = min{C 21 +D 1 ,C 24 +D 4 ,C 25 +D 5 } = min{3+3,1+3,4+2} = 4

Table 7.1: simple processing of Bellman Ford algorithm. Each entry for node represents the next node and cost of the current shortest path to destination 6

Figure 7.31: shortest path to node 6

UNIT 2: PACKET SWITCHING NETWORKS(CONT.)

DIJKSTRA'S ALGORITHM

  • This is used to find the shortest paths from a source node to all other nodes in a network (Figure 7.32).
  • Main idea: Progressively identify the closest nodes from the source node in order of increasing path cost.

Table 7.5: execution of Dijkstra's algorithm

Figure 7.32: shortest path tree from node 1 to other nodes

Table 7.6: routing table for fig 7.

TRAFFIC MANAGEMENT AT THE PACKET LEVEL

  • Traffic management is concerned → with delivery of QoS to the end user & → with efficient use of network resources.
  • Based on traffic granularity, we can classify traffic management into three levels: packet level, flow level and flow-aggregated level.
  • Packet level is concerned with packet queueing and packet scheduling at switches, routers & multiplexers to provide differentiated treatment for packets belonging to different QoS classes.

END-TO-END DELAY

  • This is the sum of the individual delays experienced at each system.
  • If we can guarantee that the delay at each system can be kept below some upper bound, then the end-to-end delay can be kept below the sum of the upper bounds.

JITTER

  • This measures the variability in the packet delays.
  • This is typically measured in terms of the difference of the minimum delay and maximum delay.

QUEUE SCHEDULING

  • This is concerned with strategies for controlling the transmission bit rates that are provided to the various information flows.

FIFO QUEUEING

  • Packets are transmitted in order of their arrival (Figure 7.41a).
  • Packets are discarded when they arrive at a full buffer.
  • Packet-delay depends on the packet inter-arrival time. Packet-loss depends on the packet lengths.
  • Disadvantage: 1) This is not possible to provide different information flows with different QoS.
    1. hogging occurs when a user sends packets at a high rate and fills the buffers in the system,thus depriving other users of access to the buffer.

FIFO QUEUEING WITH DISCARD POLICY

  • Provide different characteristics of packet-loss performance to different classes of traffic.
  • Higher priority packets(Class 1) are discarded when they arrive at a full buffer(Figure 7.41b).
  • Lower priority packets(Class 2) are discarded when buffer reaches a certain threshold.
  • Disadvantage: Lower priority packets will experience a higher packet-loss probability.

Figure 7.41:a)FIFO queueing b)FIFO queueing with discard policy

HEAD-OF-LINE(HOL) PRIORITY QUEUEING

  • Number of priority classes are defined (Figure 7.42).
  • A separate buffer is maintained for each priority class.
  • Each time the transmission link becomes available, the next packet for transmission is selected from the head of the line(HOL) of the highest priority queue that is not empty.
  • The size of the buffers for the different priority classes can be selected to meet different loss probability requirements.
  • Disadvantage: 1) This does not discriminate among users of the same priority
    1. This does not allow for providing some degree of guaranteed access to transmission bandwidth to the lower priority classes.
    2. Fairness problem arises when a certain user hogs the bandwidth by sending an excessive number of packets.

Figure 7.42: HOL Priority Queueing

SORTING PACKETS BASED ON PRIORITY TAG

  • Packets are sorted in the buffer based on priority tag (Figure 7.43).
  • Priority tag reflects the urgency with which each packet needs to be transmitted.
  • Advantage: This system is very flexible because the method for defining priority is open and can even be defined dynamically.

Figure 7.43:Sorting packets according to priority tag

WEIGHTED FAIR QUEUEING

  • Each user flow has its own buffer, but each user flow also has a weight that determines its relative share of the bandwidth (Figure 7.47).
  • If buffer 1 has weight 1 and buffer 2 has weight 3,then buffer 1 will receive 1/4 of the bandwidth and buffer 2 will receive 3/4 of the bandwidth.
  • This is also easily approximated in ATM. In each round, each non-empty buffer would transmit a number of packets proportional to its weight.
  • Packet by packet weighted fair queueing is also easily generalized from fair queueing.
  • Weighted fair-queueing systems are means for providing QoS guarantees.

Figure 7.47: fluid flow and packet-to-packet weighted fair queuing

RANDOM EARLY DETECTION

  • This is a buffer management technique that attempts to provide equitable access to a FIFO system by randomly dropping arriving packets before the buffer overflows (Figure 7.48).
  • A dropped packet provides feedback information to the source and informs the source to reduce its transmission rate.
  • This algorithm uses an average queue length rather than instantaneous queue length to decide how to drop packets.
  • Specifically, two thresholds are defined: minth and maxth.
  • When the average queue length is below minth, RED does not drop any arriving packets.
  • When the average queue length exceeds maxth, RED drops any arriving packets.
  • When the average queue length is between minth and maxth, RED drops an arriving packet with an increasing probability as the average queue length increases.

Figure 7.48: Packet drop profile in RED

TRAFFIC MANAGEMENT AT THE FLOW LEVEL

  • At flow level, traffic-management is concerned with managing individual flow to ensure that QoS requested by the user is satisfied.
  • Purpose of traffic-management: 1) To control flows of traffic &
    1. To maintain performance even in the presence of traffic-overload.
  • When too many packets compete for same resource, the network-performance degrades and this situation is called as congestion.
  • For example, consider the packet-switching network(Figure 7.50). Suppose that nodes 1, 2 and 5 continuously transmit packets to their respective destinations via node 4. If the aggregate incoming-rate of the packet flows to node 4 is greater than the rate the packets can be transmitted out, the buffer in node 4 will build up. If this situation persists, the buffer eventually becomes full and starts discarding packets. The net result is that the throughput at the destination will be very low.
  • The process of managing traffic-flow in order to control congestion is called congestion-control.
  • Congestion control algorithms can be classified into two types: open-loop control and closed-loop control.

Figure 7.50: Congestion arises when incoming rate exceeds outgoing rate

OPEN-LOOP CONTROL

  • This prevents congestion from occurring by making sure that the flow generated by source will not degrade network-performance to a level below the specified QoS.
  • If QoS cannot be guaranteed, network rejects flow before it enters the network.
  • The function that makes the decision to accept or reject a new traffic-flow is called an admission-control. Closed-Loop Control
  • This reacts to congestion when it → is already happening or → is about to happen.
  • This regulates traffic-flow according to state of network.
  • This does not use any reservation.