Ece 526 network processing systems design
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ECE 526 – Network Processing Systems Design. Networking: protocols and packet format Chapter 3: D. E. Comer Fall 2008. Goals. Review important protocols and packet formats Understand packet formats in different layers. Internet reference model Linker layer Network layer

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Ece 526 network processing systems design

ECE 526 – Network Processing Systems Design

Networking: protocols and packet format

Chapter 3: D. E. Comer

Fall 2008


  • Review important protocols and packet formats

  • Understand packet formats in different layers

ECE 526


Internet reference model

Linker layer

Network layer

Transportation layer


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Internet reference model
Internet Reference Model

  • Five layer Internet reference model

  • Multiple protocol can occur at each layer

  • Question: example protocols in each layer?

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Example network protocols
Example Network Protocols

  • Linker layer: Ethernet

  • Network layer: IP

  • Transport layer: TCP, UDP

  • We are not interested in physical layer: CSMA …

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Data link layer
Data Link Layer

  • Providing communication between adjacent systems

    • Point-to-point or shared media communication

    • Specification of media access (e.g., CSMA)

  • Three types of communication

    • Unicast: frame destined for single station

    • Multicast: frame destined for a subset of stations

    • Broadcast: frame destined for all stations in broadcast domain

  • Two protocols are important

    • Ethernet

    • ATM

  • We will concentrate on Ethernet

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Ethernet frame processing
Ethernet Frame Processing

  • Machine access control address (MAC)

    • Hardware address

    • 48-bit

    • Globally unique

    • Not assigned to computer but Network Interface Card (NIC)

  • 16-bit frame type: indicating the next layer protocol

    • 0800 (IP), 0806 (ARP)

  • Additionally: 64-bit preamble, 32-bit CRC trailer

ECE 526

Network layer internet protocol
Network Layer: Internet Protocol

  • Internet Protocol (IP) functionality

    • Defines basic delivery service throughout the Internet

    • Provides end-to-end connectivity

  • Processing by IP routers

  • Internet packet header:

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Ip datagram fields
IP Datagram Fields

  • Which field changed between hops?

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Ip addressing
IP Addressing

  • 32-bit Internet address assigned to each computer

  • Virtual, hardware independent value

  • Prefix identifies network; suffix identifies host

    • Hosts within a subnet have same address prefix

    • Example: ECE 131.230.194.*, SIUC 131.230.*

    • Network address mask to specify boundary between prefix and suffix

  • Who assigns the prefix?

    • Internet Assigned Numbers Authority (IANA) sign it to Regional Internet Registries (RIR)

  • Are IP addresses globally unique?

    • No, network address translator allow private subnets

    • Private subnet address space:, and 10.*

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Addressing question
Addressing Question

  • What is the difference between Ethernet and IP address?

    • Software (reconfigurable) vs. hardware (hard coded)

    • Globally unique or not

    • IP: prefix and suffix

  • Why need another address (IP), if Ethernet address is globally unique?

    • mobility moving the hosts or routers from one network to another

    • easiness to construct a subnet: prefix and suffix

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Ip forwarding
IP Forwarding

  • Routing Table

    • Found in both hosts and routers

    • Stores destination, mask, next hop

  • Example Routing Table

    network destination netmask gateway/next hop 255.255.0

    Default 131.230.195.

  • Route lookup

    • Takes destination address as arguments

    • Finds next hop

    • Uses longest-prefix match

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Ip related protocols
IP Related Protocols

  • Several other protocols support IP:

  • We’ll cover routing tables with packet processing later

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Transport layer
Transport Layer

  • End-to-end protocols for communication between applications

    • Transport layer is not changed inside the network

  • How are applications identified?

    • Port number used for de-multiplexing

  • Two transport layer protocols

    • UDP (user datagram protocol)

    • TCP (transport control protocol)

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Transport control protocol
Transport Control Protocol

  • UDP shortcomings

    • Unreliable (packet loss)

    • Packet reordering

    • No congestion control

    • No flow control

  • TCP addresses these problems

    • Acknowledgements and retransmission timers

    • Sequence numbers

    • Congestion and flow control windows

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Tcp header
TCP Header

  • Checksum, source and destination ports similar to UDP

  • Sequence and Acknowledgement is byte count (not packet)

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Tcp questions
TCP Questions

  • How is a connection between two hosts established?

    • Three-way handshake

  • How is reliability ensured when packet is lost?

    • Packet is not acknowledged, timeout occurs, retransmission.

  • How is congestion control achieved?

    • Congestion window is continually increased to use available bandwidth

    • Congestion window is reduced when packet loss occurs

ECE 526

Protocol encapsulation
Protocol Encapsulation

  • Protocols are encapsulated when sent out

  • Example

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Address resolution protocol
Address Resolution Protocol

  • Used to map IP address of a computer to an Ethernet address

  • Used only within one network

  • ARP header

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  • Why not one protocol instead of many ones?

    • different applications need a different functionalities

    • different protocols solve different problems

    • easy to debug and design: concentrate one layer only

    • many protocols is connected by common protocol (IP)

  • Any cons for layered structure?

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  • Protocols standards

    • Defines semantics of computer communication

    • Specify packet formats

    • Addressing, forwarding

  • Internet protocols are divided into fiver conceptual layers

    • Layer 2: ethernet, ARP

    • Layer 3: IP

    • Layer 4: TCP, UDP

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For next class
For Next Class

  • Read Comer Chapter 4

    • Computer Architecture: traditional network processing systems implementation

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