Part I: Introduction

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Final Review CS1652/Telcom2310
KyoungSoo Park University of Pittsburgh
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Chapter 4 Network Layer

• Network layer service model
• Forwarding vs. Routing
• IP addressing, NAT DHCP
• Router architecture
• Routing algorithms
• Handling scale - CIDR and BGP
• ICMP, IPv6

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Network layer service model

• Unreliable, connectionless data delivery
• Q is UDP more reliable than IP?
• Q do TCP packets receive special treatment than
  UDP packets?
• Host-to-host packet delivery
• Q Transport layer?
• All systems implement network layer
• End systems routers
• Q Why not routers implement transport layer?

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Forwarding vs. Routing

• Definition?
• Switch vs. router?
• How routing affects forwarding?
• Routing algorithms
• Intradomain routing algorithms
• Distance vector, Link state
• Interdomain routing algorithms
• BGP
• Longest prefix match

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IP addressing, DHCP and NAT

• 32-bit IPv4 address
• Subnet part host part
• Subnet part is used for forwarding decision
• CIDR
• Subnet portion can be an arbitrary size
• Why CIDR?
• IP allocation efficiency supernetting
• DHCP
• How it works? Where is it useful?
• NAT
• Pros. and Cons.

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IP datagram format

• how much overhead with TCP?
• 20 bytes of TCP
• 20 bytes of IP
• 40 bytes app layer overhead

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Router Architecture

• Two key router functions
• Run routing algorithms/protocol (RIP, OSPF, BGP)
• Forwarding datagrams from incoming to outgoing
  link

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Routers

• Input ports (line cards)
• Forwarding table lookup line speed
• Queuing packets if switching fabric is busy
• Head-of-line blocking?
• Switching fabric
• Via memory, bus, special interconnection
• Output ports
• Buffering scheduling
• How much buffering?
• C x RTT/sqrt(N)

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Link state algorithm

• Broadcast local link info to all routers
• Dijkstras algorithm
• Greedy algorithm
• Compute the least cost path to every node
• Each loop finds at least one node whose least
  cost path is found
• Algorithm complexity? O(nlogn)
• Oscillation problem

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Distance vector algorithm

• Distribute ones view of network to neighbors
• Bellman-ford algorithm
• Dynamic programming
• Asynchronous update
• Problem?
• Count-to-infinity routing loops
• Possible solution?

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Border Gateway Protocol (BGP)

• Autonomous System (AS)
• AS number 16 bit id
• BGP contains full path from src to dest AS
• AS PATH list of AS numbers
• How to prevent routing loops?
• Hot potato routing?
• One reason for routing path asymmetry
• How to deliver a packet from one AS to another?
• Intradomain (Intra-AS) routing
• Interdomain routing
• Forwarding table (FIB)

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Chapter 5 Link Layer

• Delivering frames to a direct neighbor
• Error detection and correction
• Sharing a broadcasting channel
• Reliable data transfer flow control
• Hop-by-hop vs. end-to-end

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Error detection correction

• Parity checking
• Single bit vs. two-dimentional bit parity
• Odd/even parity
• Internet checksum IP/TCP layer
• Why is error checking needed in the upper layer?
• Cyclic Redunancy Check (CRC)
• Make sure to know how it works!
• CRC32 is widely used (e.g., Ethernet)

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Multiple Access Protocol

• How to share a broadcasting media
• Medium Acccess Control (MAC) protocol
• Channel Partitioning
• Random Access
• Taking turns

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Random Access Protocol

• Slotted ALOHA
• Fixed time slot synchronized
• If collision, the retransmit with a probability
  of p for each slot
• ALOHA
• No slot synchronization
• CSMA, CSMA/CD, CSMA/CA
• CSMA sense carrier before sending
• CD detect collision while sending and cancel it
• CA avoid collision by getting the permission
  first
• Ethernet and Wi-Fi?

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MAC addresses

• Ethernet 48-bit MAC addresses
• Burned into hardware
• Globally uniquely assigned
• Why not use MAC address instead of IP?
• Address Resolution Protocol (ARP)
• Determining MAC address with IP address
• ARP table ltIP address, MAC address, TTLgt
• Broadcasting mechanism (make sure to know!)

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Ethernet Switch

• Access protocol CSMA/CD
• Old Ethernet hub used to share the access
• Understand the exponential back-off algorithm
• Most current devices are swtiches
• Connectionless, unreliable
• Frame format
• Preamble, 2 MAC address, type, data, CRC32
• Switch
• Make sure to understand self-learning algorithm

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Chapter 6 Wireless

• 802.11/802.15/802.16
• Difference from wired enviroment
• Signal attenuation
• Hidden terminal problem
• Interference from other sources (phone,microwave)
• Multi-path propagation
• SNR (Signal-to-Noise raitio)
• The larger, the better
• BER (Bit error rate)
• CDMA

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Wi-Fi

• Access protocol CSMA/CA
• Reserve the channel first before sending
• No collision detection why?
• Understand the sending protocol
• Access Point(AP)
• Link layer device (may run DHCP)
• Passive/Active scanning for association
• 802.11 frame format
• Why we need three MAC addresses?
• Encryption - WEP

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Chapter 7 Multimedia

• Quality of service guarantee
• Provding performance guarantee required by app
• Current Internet does not directly support it
• Delay sensitive, loss tolerant application
• Video streaming vs. Email?
• What is jitter?
• MM application
• Stored streaming
• Live streaming
• Real-time interactive

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Internet Phone, CDN

• Internet phone
• Network loss vs. delay loss
• Adaptive playout delay how to estimate delay?
• Forward Error Correction (FEC)
• N1 chunks with 1 redundant data (XOR)
• Piggyback lower-quality stream
• Interleaving
• Content distribution networks (CDNs)
• Definition?
• DNS redirection for finding the near server?

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RTP/RTCP, SIP

• Real-Time Protocl (RTP)
• General packet structure to deliver audio, video
• Runs in end sytems (using UDP)
• Real-Time Control Protocol (RTCP)
• Periodically sent by the participants
• Receiver report sender report
• Feedback mechanism to control performance
• Session Initiation Protocol (SIP)
• Provide email address like ID for Internet phone
• Protocol format similar to HTTP and SMTP
• Typically run on RTP/UDP (but no requirement)

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QoS Principles

• QoS principles
• Packet marking to classify the flows
• Protection for one class from another
• Efficient resource usage
• Packet scheduling
• FIFO
• Priority Queuing
• Round Robin
• Weighted Fair Queuing
• Policing mechanism
• Token bucket - r tokens/sec, b bucket size

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DiffServ Integreated Services

• Differentiated Services
• Use IPs ToS field (DSCP) to mark each packet
• PHB on each router
• Expedited forwarding assured forwarding
• Integrated Services
• Signalling (RSVP) used for resource
  reservation, receiver oritened protocol
• Soft state can expire if not renewed
• Per-flow QoS enforcement (scalability problem)
• Guaranteed service controlled load service

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Chapter8 Network security

• What do want to achieve?
• Confientiality
• Authentication
• Message Integrity
• Access and Availability
• Firewall, IDS not covered in the class
• Cryptography used beyond confidentiality
• Symmetric crypto
• Public crypto (asymmetric)
• One-way hash function

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Symmetric/Asymmetric cyphers

• Shared secret between parties
• Stream cipher RC4
• Block cipher 3DES, AES
• Cipher Block Chaining (CBC)
• Why is it needed?
• How does it work?
• Public cryptography
• RSA algorithm?
• K(K-(m)) K-(K(m)) ?

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Integrity, signature, certificate

• Message Intergrity
• Use a hash function (MD5, SHA-1) - digest
• Hash function property?
• MAC Hash (shared secret data)
• MAC provides both Integrity and Authentication
• How HMAC is calculated?
• Digital signature
• Provides MAC functionality with public key crypto
• Digital certificate
• CA attests the ownership of a public key

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Email security SSL

• Secure Email
• Make sure to understand how you provide
  confidentiality, message integrity, and
  authentication using a public key scheme
• Secure Sockets Layer (SSL)
• Transport-layer security (TLS)
• Handshake
• Key Derivation
• Data transfer
• Connection Clousre

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VPN, IPsec, and Wireless security

• Virtual Private Network
• Private network too expensive
• Coupled with IPsec
• IPsec
• AH and ESP
• Security Association (SA)
• How ESP encodes and decodes IP packet?
• Internet Key Exchange
• Wirelss security
• Understand WEP
• Understand WEP vulnerability