13 Network Layer
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Solutions to Chapter 2
CS413 Computer Networks ASN 4 Solutions Solutions to Assignment #4 3. What difference does it make to the network layer if the underlying data link layer provides a connection-oriented service versus a connectionless service? [4 marks] Solution: If the data link layer provides a connection-oriented service to the network layer, then the network layer must precede all transfer of information with a connection setup procedure (2). If the connection-oriented service includes assurances that frames of information are transferred correctly and in sequence by the data link layer, the network layer can then assume that the packets it sends to its neighbor traverse an error-free pipe. On the other hand, if the data link layer is connectionless, then each frame is sent independently through the data link, probably in unconfirmed manner (without acknowledgments or retransmissions). In this case the network layer cannot make assumptions about the sequencing or correctness of the packets it exchanges with its neighbors (2). The Ethernet local area network provides an example of connectionless transfer of data link frames. The transfer of frames using "Type 2" service in Logical Link Control (discussed in Chapter 6) provides a connection-oriented data link control example. 4. Suppose transmission channels become virtually error-free. Is the data link layer still needed? [2 marks – 1 for the answer and 1 for explanation] Solution: The data link layer is still needed(1) for framing the data and for flow control over the transmission channel. In a multiple access medium such as a LAN, the data link layer is required to coordinate access to the shared medium among the multiple users (1). -
OSI Model and Network Protocols
CHAPTER4 FOUR OSI Model and Network Protocols Objectives 1.1 Explain the function of common networking protocols . TCP . FTP . UDP . TCP/IP suite . DHCP . TFTP . DNS . HTTP(S) . ARP . SIP (VoIP) . RTP (VoIP) . SSH . POP3 . NTP . IMAP4 . Telnet . SMTP . SNMP2/3 . ICMP . IGMP . TLS 134 Chapter 4: OSI Model and Network Protocols 4.1 Explain the function of each layer of the OSI model . Layer 1 – physical . Layer 2 – data link . Layer 3 – network . Layer 4 – transport . Layer 5 – session . Layer 6 – presentation . Layer 7 – application What You Need To Know . Identify the seven layers of the OSI model. Identify the function of each layer of the OSI model. Identify the layer at which networking devices function. Identify the function of various networking protocols. Introduction One of the most important networking concepts to understand is the Open Systems Interconnect (OSI) reference model. This conceptual model, created by the International Organization for Standardization (ISO) in 1978 and revised in 1984, describes a network architecture that allows data to be passed between computer systems. This chapter looks at the OSI model and describes how it relates to real-world networking. It also examines how common network devices relate to the OSI model. Even though the OSI model is conceptual, an appreciation of its purpose and function can help you better understand how protocol suites and network architectures work in practical applications. The OSI Seven-Layer Model As shown in Figure 4.1, the OSI reference model is built, bottom to top, in the following order: physical, data link, network, transport, session, presentation, and application. -
Medium Access Control Layer
Telematics Chapter 5: Medium Access Control Sublayer User Server watching with video Beispielbildvideo clip clips Application Layer Application Layer Presentation Layer Presentation Layer Session Layer Session Layer Transport Layer Transport Layer Network Layer Network Layer Network Layer Univ.-Prof. Dr.-Ing. Jochen H. Schiller Data Link Layer Data Link Layer Data Link Layer Computer Systems and Telematics (CST) Physical Layer Physical Layer Physical Layer Institute of Computer Science Freie Universität Berlin http://cst.mi.fu-berlin.de Contents ● Design Issues ● Metropolitan Area Networks ● Network Topologies (MAN) ● The Channel Allocation Problem ● Wide Area Networks (WAN) ● Multiple Access Protocols ● Frame Relay (historical) ● Ethernet ● ATM ● IEEE 802.2 – Logical Link Control ● SDH ● Token Bus (historical) ● Network Infrastructure ● Token Ring (historical) ● Virtual LANs ● Fiber Distributed Data Interface ● Structured Cabling Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.2 Design Issues Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.3 Design Issues ● Two kinds of connections in networks ● Point-to-point connections OSI Reference Model ● Broadcast (Multi-access channel, Application Layer Random access channel) Presentation Layer ● In a network with broadcast Session Layer connections ● Who gets the channel? Transport Layer Network Layer ● Protocols used to determine who gets next access to the channel Data Link Layer ● Medium Access Control (MAC) sublayer Physical Layer Univ.-Prof. Dr.-Ing. Jochen H. Schiller ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.4 Network Types for the Local Range ● LLC layer: uniform interface and same frame format to upper layers ● MAC layer: defines medium access .. -
The OSI Model: Understanding the Seven Layers of Computer Networks
Expert Reference Series of White Papers The OSI Model: Understanding the Seven Layers of Computer Networks 1-800-COURSES www.globalknowledge.com The OSI Model: Understanding the Seven Layers of Computer Networks Paul Simoneau, Global Knowledge Course Director, Network+, CCNA, CTP Introduction The Open Systems Interconnection (OSI) model is a reference tool for understanding data communications between any two networked systems. It divides the communications processes into seven layers. Each layer both performs specific functions to support the layers above it and offers services to the layers below it. The three lowest layers focus on passing traffic through the network to an end system. The top four layers come into play in the end system to complete the process. This white paper will provide you with an understanding of each of the seven layers, including their functions and their relationships to each other. This will provide you with an overview of the network process, which can then act as a framework for understanding the details of computer networking. Since the discussion of networking often includes talk of “extra layers”, this paper will address these unofficial layers as well. Finally, this paper will draw comparisons between the theoretical OSI model and the functional TCP/IP model. Although TCP/IP has been used for network communications before the adoption of the OSI model, it supports the same functions and features in a differently layered arrangement. An Overview of the OSI Model Copyright ©2006 Global Knowledge Training LLC. All rights reserved. Page 2 A networking model offers a generic means to separate computer networking functions into multiple layers. -
Af-Saa-Api-Dlpi-0091.000
Technical Committee Native ATM Services Data Link Provider Interface (DLPI) Addendum Version 1.0 AF-SAA-API-DLPI-0091.000 February, 1998 af-saa-api-dlpi-0091.000 Native ATM Services DLPI Addendum Version 1.0 © 1998 by The ATM Forum. The ATM Forum hereby grants its members the limited right to reproduce in whole, but not in part, this specification for its members internal use only and not for further distribution. This right shall not be, and is not, transferable. All other rights reserved. Except as expressly stated in this notice, no part of this document may be reproduced or transmitted in any form or by any means, or stored in any information storage and retrieval system, without the prior written permission of The ATM Forum. The information in this publication is believed to be accurate as of its publication date. Such information is subject to change without notice and The ATM Forum is not responsible for any errors. The ATM Forum does not assume any responsibility to update or correct any information in this publication. Notwithstanding anything to the contrary, neither The ATM Forum nor the publisher make any representation or warranty, expressed or implied, concerning the completeness, accuracy, or applicability of any information contained in this publication. No liability of any kind shall be assumed by The ATM Forum or the publisher as a result of reliance upon any information contained in this publication. The receipt or any use of this document or its contents does not in any way create by implication or otherwise: • Any -
Security Protocols Overview an RSA Data Security Brief SSL &
Security Protocols Overview An RSA Data Security Brief SSL & TLS Secure Socket Layer & Transport Layer Security Secure Sockets Layer (SSL) is the that do not necessarily need to be Internet security protocol for on the same secure network. point-to-point connections. It pro- Where SSL secures two applica- vides protection against eaves- tions, IPSec secures an entire net- dropping, tampering, and forgery. work. Clients and servers are able to au- thenticate each other and to estab- Applications lish a secure link, or “pipe,” across SSL can be used in any situation the Internet or Intranets to protect where a link between two comput- the information transmitted. ers or applications needs to be pro- tected. The following are just a few The Need for SSL of the real-world, practical appli- With the growth of the Internet cations of SSL & TLS: and digital data transmission, many applications need to se- curely transmit data to remote applications and computers. • Client/Server Systems SSL was designed to solve this problem in an open standard. SSL in the browser is not enough to secure most systems. Systems such as secure database access, or remote object SSL is analogous to a secure “telephone call” between two systems such as CORBA, can all be securely improved computers on any network including the Internet. In SSL, a using SSL. Other applications include redirection of se- connection is made, parties authenticated, and data securely cure connections such as proxy servers, secure Webserver exchanged. The latest enhancement of SSL is called Trans- plug-ins, and Java “Servlets.” port Layer Security (TLS). -
Chapter 4 Network Layer
Chapter 4 Network Layer A note on the use of these ppt slides: We’re making these slides freely available to all (faculty, students, readers). Computer They’re in PowerPoint form so you see the animations; and can add, modify, and delete slides (including this one) and slide content to suit your needs. Networking: A Top They obviously represent a lot of work on our part. In return for use, we only ask the following: Down Approach v If you use these slides (e.g., in a class) that you mention their source th (after all, we’d like people to use our book!) 6 edition v If you post any slides on a www site, that you note that they are adapted Jim Kurose, Keith Ross from (or perhaps identical to) our slides, and note our copyright of this Addison-Wesley material. March 2012 Thanks and enjoy! JFK/KWR All material copyright 1996-2012 J.F Kurose and K.W. Ross, All Rights Reserved Network Layer 4-1 Chapter 4: outline 4.1 introduction 4.5 routing algorithms 4.2 virtual circuit and § link state datagram networks § distance vector 4.3 what’s inside a router § hierarchical routing 4.4 IP: Internet Protocol 4.6 routing in the Internet § datagram format § RIP § IPv4 addressing § OSPF § BGP § ICMP § IPv6 4.7 broadcast and multicast routing Network Layer 4-2 Interplay between routing, forwarding routing algorithm determines routing algorithm end-end-path through network forwarding table determines local forwarding table local forwarding at this router dest address output link address-range 1 3 address-range 2 2 address-range 3 2 address-range 4 1 IP destination -
CSCI-1680 Network Layer: Wrapup
CSCI-1680 Network Layer: Wrapup Rodrigo Fonseca Based partly on lecture notes by Jennifer Rexford, Rob Sherwood, David Mazières, Phil Levis, John JannoA Administrivia • Homework 2 is due tomorrow – So we can post solutions before the midterm! • Exam on Tuesday – All content up to today – Questions similar to the homework – Book has some exercises, samples on the course web page (from previous years) Today: IP Wrap-up • IP Service models – Unicast, Broadcast, Anycast, Multicast • IPv6 – Tunnels Different IP Service Models • Broadcast: send a packet to all nodes in some subnet. “One to all” – 255.255.255.255 : all hosts within a subnet, never forwarded by a router – “All ones host part”: broadcast address • Host address | (255.255.255.255 & ~subnet mask) • E.g.: 128.148.32.143 mask 255.255.255.128 • ~mask = 0.0.0.127 => Bcast = 128.148.32.255 • Example use: DHCP • Not present in IPv6 – Use multicast to link local all nodes group Anycast • Multiple hosts may share the same IP address • “One to one of many” routing • Example uses: load balancing, nearby servers – DNS Root Servers (e.g. f.root-servers.net) – Google Public DNS (8.8.8.8) – IPv6 6-to-4 Gateway (192.88.99.1) Anycast Implementation • Anycast addresses are /32s • At the BGP level – Multiple ASs can advertise the same prefxes – Normal BGP rules choose one route • At the Router level – Router can have multiple entries for the same prefx – Can choose among many • Each packet can go to a different server – Best for services that are fne with that (connectionless, stateless) Multicast -
Data Link Layer Design Issues • Error Detection and Correction • Elementary Data Link Protocols • Sliding Window Protocols • Example Data Link Protocols
The Data Link Layer Chapter 3 • Data Link Layer Design Issues • Error Detection and Correction • Elementary Data Link Protocols • Sliding Window Protocols • Example Data Link Protocols Revised: August 2011 CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011 The Data Link Layer Application Responsible for delivering frames of information over a single link Transport Network • Handles transmission errors and Link regulates the flow of data Physical CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011 Data Link Layer Design Issues • Frames » • Possible services » • Framing methods » • Error control » • Flow control » CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011 Frames Link layer accepts packets from the network layer, and encapsulates them into frames that it sends using the physical layer; reception is the opposite process Network Link Virtual data path Physical Actual data path CN5E by Tanenbaum & Wetherall, © Pearson Education-Prentice Hall and D. Wetherall, 2011 Possible Services Unacknowledged connectionless service • Frame is sent with no connection / error recovery • Ethernet is example Acknowledged connectionless service • Frame is sent with retransmissions if needed • Very unreliable channels; Example is 802.11 • NOTE: DL acknowledgement is an optimization to improve performance for unreliable channels, ACKs can also be done at higher layers Acknowledged connection-oriented service • Connection is set up; rare • Long -
Medium Access Control Sublayer
Telematics Chapter 5: Medium Access Control Sublayer User Server watching with video Beispielbildvideo clip clips Application Layer Application Layer Presentation Layer Presentation Layer Session Layer Session Layer Transport Layer Transport Layer Network Layer Network Layer Network Layer Prof. Dr. Mesut Güneş Data Link Layer Data Link Layer Data Link Layer Computer Systems and Telematics (CST) Physical Layer Physical Layer Physical Layer Distributed, embedded Systems Institute of Computer Science Freie Universität Berlin http://cst.mi.fu-berlin.de Contents ● Design Issues ● Metropolitan Area Networks ● Network Topologies (()MAN) ● The Channel Allocation Problem ● Wide Area Networks (WAN) ● Multiple Access Protocols ● Frame Relay ● Ethernet ● ATM ● IEEE 802.2 – Logical Link Control ● SDH ● Token Bus ● Network Infrastructure ● Token Ring ● Virtual LANs ● Fiber Distributed Data Interface ● Structured Cabling Prof. Dr. Mesut Güneş ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.2 Design Issues Prof. Dr. Mesut Güneş ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.3 Design Issues ● Two kinds of connections in networks ● Point-to-point connections OSI Reference Model ● Broadcast (Multi-access channel, Application Layer Random access channel) Presentation Layer ● In a network with broadcast Session Layer connections ● Who gets the channel? Transport Layer Network Layer ● PtProtoco ls use dtdtd to determ ine w ho gets next access to the channel Data Link Layer ● Medium Access Control (()MAC) sublay er Phy sical Laye r Prof. Dr. Mesut Güneş ▪ cst.mi.fu-berlin.de ▪ Telematics ▪ Chapter 5: Medium Access Control Sublayer 5.4 Network Types for the Local Rang e ● LLC layer: uniform interface and same frame format to upper layers ● MAC layer: defines medium access - LLC IEEE 802.2 Logical Link Control .. -
Network Layer/Internet Protocols Ip
04 2080 CH03 8/16/01 1:34 PM Page 61 CHAPTER 3 NETWORK LAYER/INTERNET PROTOCOLS You will learn about the following in this chapter: • IP operation, fields and functions • ICMP messages and meanings • Fragmentation and reassembly of datagrams IP IP (Internet Protocol) does most of the work in the TCP/IP protocol suite. All protocols and applications within the TCP/IP suite run on top of IP and utilize it for logical Network layer addressing and transmission of datagrams between internet hosts. IP maps to the Internet layer of the DoD and to the Network layer of the OSI models. ICMP (Internet Control Message Protocol) is considered an integral part of IP and uses IP for its datagram delivery; we will dis- cuss ICMP later in this chapter. Figure 3.1 shows how IP maps to the DoD and OSI models. How Do I Buy a Ticket on the IP Train? The phrase ”runs on top of” might sound as if an application or protocol is buying a ticket to ride on an IP train. This term is not restricted to IP. In reality, it is industry jargon used to describe any upper- layer protocol or application coming down the OSI model and utilizes another lower-layer protocol’s features (in this case IP at the Network layer). IP provides an unreliable, connectionless datagram delivery service, which means that IP does not guarantee that an IP datagram successfully reaches its destination; rather it provides best effort of delivery, which means it sends it out and hopes it gets there. -
The Network Layer
TheThe NetworkNetwork LayerLayer • Concerned with getting packets from the source all the way to the destination: Routing through the subnet, load balancing, congestion control. • Protocol Data Unit (PDU) for network layer protocols = packet • Types of network services to the transport layer: – Connectionless: Each packet carries full destination address. – Connection-oriented: • Connection is set up between network layer processes on the sending and receiving sides. • The connection is given a special identifier until all data has been sent. • Internal organization of the network layer (in the subnet): – Datagram: Packets are sent and routed independently with each carrying the full destination address (TCP/IP) – Virtual circuit: A virtual circuit is set up to the destination using a circuit number stored in tables in routers along the way. Packets only carry the virtual circuit number. All packets follow the same route (ATM). EECC694 - Shaaban #1 Final Review Spring2000 5-11-2000 RoutingRouting AlgorithmsAlgorithms To decide which output line an incoming packet should be transmitted on. • Static Routing (Nonadaptive algorithms): – Shortest path routing: • Build a graph of the subnet with each node representing a router and each arc representing a communication link. • The weight on the arcs represents: a function of distance, bandwidth, communication costs mean queue length and other performance factors. • Several algorithms exist including Dijkstra’s shortest path algorithm. – Selective flooding: Send the packet on all output lines going in the right direction to the destination. – Flow-based routing: Based on known capacity and link loads. EECC694 - Shaaban #2 Final Review Spring2000 5-11-2000 StaticStatic Routing:Routing: ShortestShortest PathPath RoutingRouting • First five steps of an example using Dijktra’s algorithm EECC694 - Shaaban #3 Final Review Spring2000 5-11-2000 StaticStatic Routing:Routing: Flow-BasedFlow-Based RoutingRouting • A routing matrix is constructed; used when the mean data flow in network links is known and stable.