(protocols and architecture (chapter 2

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William Stallings Data and Computer Communications Chapter 2 Protocols and Architecture 

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Characteristics I Direct or indirect 0 Monolithic or structured 0 Symmetric or asymmetric 0 Standard or nonstandard 

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Direct or Indirect 0 Direct I Systems share a point to point link or I Systems share a multi-point link ! Data can pass without intervening active agent O Indirect I Switched networks or I Internetworks or internets | Data transfer depend on other entities 

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Monolithic or Structured 0 Communications is a complex task 1 To complex for single unit 0 Structured design breaks down problem into smaller units 0 Layered structure 

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Symmetric or Asymmetric 0 Symmetric 1 Communication between peer entities 0 Asymmetric ! Client/server 

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Standard or Nonstandard Nonstandard protocols built for specific computers and tasks K sources and L receivers leads to K*L protocols and 2*K*L implementations If common protocol used, K + L implementations needed ص ص ص 

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Use of Standard Protocols 

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Functions Encapsulation Segmentation and reassmebly Connection control Ordered delivery Flow control Error control Addressing Multiplexing Transmission services SS Se oS eyo ea 

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Encapsulation 0 Addition of control information to data I Address information I Error-detecting code I Protocol control 

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Segmentation (Fragmentation) I Data blocks are of bounded size 0 Application layer messages may be large 0 Network packets may be smaller 0 Splitting larger blocks into smaller ones is segmentation (or fragmentation in TCP/IP) 1 ATM blocks (cells) are 53 octets long ! Ethernet blocks (frames) are up to 1526 octets long 0 Checkpoints and restart/recovery 

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Why Fragment? 0 Advantages | More efficient error control I More equitable access to network facilities I Shorter delays 1 Smaller buffers needed 0 Disadvantages ! Overheads I Increased interrupts at receiver I More processing time 

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Connection Control 0 Connection Establishment 0 Data transfer 0 Connection termination 0 May be connection interruption and recovery 0 Sequence numbers used for ! Ordered delivery | Flow control ! Error control 

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Connection Oriented Data Transfer Connection request 4 Connection accept Data Acknowledgement Tertainia Stminate-connection request 4 ‘Terminate-connection, accept Multiple exchanges Time 

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Ordered Delivery 0 PDUs may traverse different paths through network PDUs may arrive out of order Sequentially number PDUs to allow for ordering oo 

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Flow Control Done by receiving entity Limit amount or rate of data Stop and wait Credit systems I Sliding window Needed at application as well as network layers Sy mo eis ص 

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Error Control 0 Guard against loss or damage 0 Error detection I Sender inserts error detecting bits I Receiver checks these bits I If OK, acknowledge I If error, discard packet 0 Retransmission I If no acknowledge in given time, re-transmit 0 Performed at various levels 

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Addressing 0 Addressing level 0 Addressing scope 0 Connection identifiers 0 Addressing mode 

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Addressing level 0 Level in architecture at which entity is named 0 Unique address for each end system (computer) and router 0 Network level address I IP or internet address (TCP/IP) I Network service access point or NSAP (OSI) 0 Process within the system Port number (TCP/IP) I Service access point or SAP (OSI) 

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Host B Physical Network 2 Logical comseetion ‏ب‎ Address Concepts Host A Porto Logical connection ton) Gobat network, IP ge aires Network Access Protocol #1 Physical Ce vital ee point adres Router J ۳ Network 1 NaP1| NAP2 

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Addressing Scope 0 Global nonambiguity ! Global address identifies unique system I There is only one system with address X 0 Global applicability I It is possible at any system (any address) to identify any other system (address) by the global address of the other system I Address X identifies that system from anywhere on the network 0 e.g. MAC address on IEEE 802 networks 

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Connection Identifiers 0 Connection oriented data transfer (virtual circuits) J Allocate a connection name during the transfer phase | Reduced overhead as connection identifiers are shorter than global addresses I Routing may be fixed and identified by connection name I Entities may want multiple connections - multiplexing I State information 

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Addressing Mode [| Usually an address refers to a single system I Unicast address I Sent to one machine or person 0 May address all entities within a domain I Broadcast I Sent to all machines or users U May address a subset of the entities in a domain I Multicast I Sent to some machines or a group of users 

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Multiplexing 0 Supporting multiple connections on one machine 0 Mapping of multiple connections at one level to a single connection at another ! Carrying a number of connections on one fiber optic cable ۱ Aggregating or bonding ISDN lines to gain bandwidth 

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Transmission Services 0 Priority ! e.g. control messages 0 Quality of service ۱ Minimum acceptable throughput I Maximum acceptable delay 0 Security I Access restrictions 

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OSI - The Model 0 A layer model 0 Each layer performs a subset of the required communication functions 0 Each layer relies on the next lower layer to perform more primitive functions 0 Each layer provides services to the next higher layer 0 Changes in one layer should not require changes in other layers 

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The OSI Environment 

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OSI as Framework for Standardization 

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Layer Specific Standards 

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Elements of Standardization I Protocol specification | Operates between the same layer on two systems I May involve different operating system I Protocol specification must be precise | Format of data units Semantics of all fields 5 allowable sequence of PCUs U Service definition I Functional description of what is provided 0 Addressing I Referenced by SAPs 

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OSI Layers (1) 0 Physical I Physical interface between devices ۲ Mechanical 5 Electrical Functional Procedural 0 Data Link 1 Means of activating, maintaining and deactivating a reliable link ! Error detection and control I Higher layers may assume error free transmission 

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OSI Layers (2) I Network | Transport of information I Higher layers do not need to know about underlying technology ! Not needed on direct links 0 Transport Exchange of data between end systems Error free In sequence No losses No duplicates Quality of service 

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OSI Layers (3) I Session ! Control of dialogues between applications ! Dialogue discipline 1 Grouping 1 Recovery 0 Presentation 1 Data formats and coding ! Data compression ! Encryption 0 Application | Means for applications to access OSI environment 

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Use of a Relay END. RELAY END. sysTEM SYSTEM system 

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TCP/IP Protocol Suite Dominant commercial protocol architecture Specified and extensively used before OSI Developed by research funded US Department of Defense Used by the Internet ص oo ص 

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TCP/IP Protocol Architecture(1) 0 Application Layer 1 Communication between processes or applications 0 End to end or transport layer (TCP/UDP/...) I End to end transfer of data I May include reliability mechanism (TCP) | Hides detail of underlying network 0 Internet Layer (IP) I Routing of data 

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TCP/IP Protocol Architecture(2) 0 Network Layer I Logical interface between end system and network 0 Physical Layer ! Transmission medium I Signal rate and encoding 

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PDUs in TCP/IP Application User data byte stream TCP TCP header segment 2 IP header datagram Network Network-level header packet 

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RSVP Some Protocols in TCP/IP Suite OSPF ICMP | | IGMP. OSPF = Open Shortest Path Fest RSVP = Resource ReSerVation Protocol SMTP = Simple Mail Transfer Pro SNMP = Simple Network Manegenca TCP. = Transmision Control Protoce UDP) = User Datagram Protocol MIME FTP | | HTTP] |SMTP| |reinet| | SNMP} TCP Border Gateway Protocol File Transfer Protocol Hypertext Transfer Pratocal act Control Message Protoeal ernet Group Management Provocol fact Protocol Multi-Purpose Internet Mail Extension BGP 

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Required Reading I Stallings chapter 2 Comer,D. Internetworking with TCP/IP volume | Comer,D. and Stevens,D. Internetworking with TCP/IP volume II and volume III, Prentice Hall Halsall, F> Data Communications, Computer Networks and Open Systems, Addison Wesley RFCs a a a oa