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ECE 526 – Network ECE 526 – Network Processing Systems Processing Systems
DesignDesignNetworking: protocols and packet
formatChapter 3: D. E. Comer
Fall 2008
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Ning Weng ECE 526 2
GoalsGoals
• Review important protocols and packet formats
• Understand packet formats in different layers
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Ning Weng ECE 526 3
OutlineOutline
• Internet reference model• Linker layer• Network layer• Transportation layer
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Ning Weng ECE 526 4
Internet Reference ModelInternet Reference Model
• Five layer Internet reference model
• Multiple protocol can occur at each layer
• Question: example protocols in each layer?
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Ning Weng ECE 526 5
Example Network ProtocolsExample Network Protocols
• Linker layer: Ethernet• Network layer: IP• Transport layer: TCP,
UDP• We are not interested in
physical layer: CSMA …
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Ning Weng ECE 526 6
Data Link LayerData 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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Ning Weng ECE 526 7
Ethernet Frame ProcessingEthernet 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
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Ning Weng ECE 526 8
Network Layer: Internet Network Layer: Internet ProtocolProtocol
• 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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Ning Weng ECE 526 9
IP Datagram FieldsIP Datagram Fields
• Which field changed between hops?
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Ning Weng ECE 526 10
IP AddressingIP 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: 192.168.0.0/16,
172.16.0.0/12 and 10.*
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Ning Weng ECE 526 11
Addressing QuestionAddressing 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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Ning Weng ECE 526 12
IP ForwardingIP Forwarding• Routing Table
─ Found in both hosts and routers─ Stores destination, mask, next hop
• Example Routing Table network destination netmask gateway/next hop
131.230.0.0 255.255.0 131.230.193.66 131.230.194.0 255.255.255.0
131.230.194.66 Default 131.230.195.
• Route lookup─ Takes destination address as arguments─ Finds next hop─ Uses longest-prefix match
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Ning Weng ECE 526 13
IP Related ProtocolsIP Related Protocols• Several other protocols support IP:
• We’ll cover routing tables with packet processing later
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Ning Weng ECE 526 14
Transport LayerTransport 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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Ning Weng ECE 526 15
UDP Datagram FormatUDP Datagram Format
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Ning Weng ECE 526 16
Transport Control ProtocolTransport 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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Ning Weng ECE 526 17
TCP HeaderTCP Header• Checksum, source and destination ports similar to
UDP• Sequence and Acknowledgement is byte count
(not packet)
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Ning Weng ECE 526 18
TCP QuestionsTCP 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
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Ning Weng ECE 526 19
Protocol EncapsulationProtocol Encapsulation• Protocols are encapsulated when sent out• Example
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Ning Weng ECE 526 20
Address Resolution ProtocolAddress 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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Ning Weng ECE 526 21
QuestionsQuestions• 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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Ning Weng ECE 526 22
SummarySummary• 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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Ning Weng ECE 526 23
For Next ClassFor Next Class
• Read Comer Chapter 4─ Computer Architecture: traditional network processing
systems implementation