Lecture-10 - Lecture#10 Network Layer Objectives...

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Lecture #10
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Network Layer Objectives “Best-Effort Delivery End-to-End” Functions – robust delivery of packets end-to-end • packet routing • routing past failures • scalability – globally unique addressing adherence to layering abstraction (where possible) • independent of data link layer • hide details from transport layer Protocols – Most common example is IP – There are others but not worth covering
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Two Types of Networks • Datagram (connectionless) – Packets may follow separate paths • just send the packets • routing is based on packet header (complete info in the header) – Non-Internet example: post office – Internet example: IP Virtual Circuit – Packets follow the same path (a virtual circuit) • requires connection setup before send • establishes a path and per-flow state – Non-Internet example: telephone – Internet example: Asynchronous Transfer Mode (ATM)
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Two Types of Networks Services (Transport Layer) • Connectionless – No setup, just send packets – Ex: UDP • Connection-Oriented stablish state between sender and receiver – Establish state between sender and receiver – Ex: TCP • Important note: one is not necessarily reliable versus the other
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IP Packet Format ver length 32 bits 16-bit identifier Internet checksum time to live 32 bit source IP address head. len type of service flgs fragment offset upper layer data (variable length, typically a TCP or UDP segment) 32 bit destination IP address Options (if any)
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IP Packet Format ver length 32 bits 16-bit identifier Internet checksum time to live 32 bit source IP address IP protocol version number header length (bytes) max number remaining hops (decremented at ach router) for fragmentation/ reassembly total datagram length (bytes) head. len type of service “type” of data flgs fragment offset upper layer data (variable length, typically a TCP or UDP segment) each router) upper layer protocol to deliver payload to 32 bit destination IP address Options (if any) E.g. timestamp, record route taken, specify list of routers to visit.
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IP Header Version: in IPv4 is 0100 IHL: measures number of 32 bit words Service: 3 bits for precedence, prioritization bits for delay, throughput, reliability, and two unused Total Length: measures size in bytes (8 bit words) ID: used to uniquely identify fragments that go together Flags: unused, “don’t fragment”, “more fragments” rag Offset: place that the piece goes Frag Offset: TTL: time-to-live Protocol: identifies which protocol is encapsulated Checksum: 1s complement of header (16 bit words) Src/Dest Addr: IP addresses Options: strict source routing, loose source routing, record route
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network links have MTU (max.transfer size) - largest possible link-level frame. – different link types,
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This note was uploaded on 02/19/2012 for the course ENGR 361 taught by Professor Drexel during the Spring '12 term at Bloomsburg.

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Lecture-10 - Lecture#10 Network Layer Objectives...

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