Assignment Hint: Centralized Binary Tree of Routers

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Assignment Hint Centralized Binary Tree of
Routers
Assume full, balanced tree. n 4 N 2n - 1
j
i
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Interfaces and Services

• Each layer provides a service to the layer above
  it.
• A service is a set of primitive operations.
• Under UNIX, primitives are implemented as C
  function calls (the entities are processes)
• e.g. Socket wrapper functions
• bind(), listen(), connect(), accept(), send(),
  recv(), ...
• e.g. TCP services to the application layer
• tcp_connect(), tcp_rcv(), tcp_sendmsg(),
  tcp_close(), ...
• e.g. UDP services to the application layer
• udp_sendmsg(), udp_recvmsg(),
• e.g. IP services to the transport layer
• ip_send_check(), ip_check_route(), ...

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Types of Services

• Two flavors
• Connection-oriented service
• Connectionless service (datagram service)
• Quality of Service
• reliable, unreliable
• Reliable connection-oriented services
• message sequences (message boundaries preserved)
• byte streams (just a stream of bytes)

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Classes of Service Primitives

• Request
• An entity wants the service to do some work.
• Indication
• An entity is to be informed about an event.
• Response
• An entity wants to respond to an event.
• Confirm
• The response to an earlier request has come back.

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Services vs. Protocols

• Service Set of primitive operations.
• Protocol Rules governing the format and the
  meaning of messages exchanged by peer entities.
• e.g. Negotiation

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TCP as an example

• TCP is a reliable, connection-oriented,
  byte-stream protocol.
• Reliability provided by mechanism call Positive
  Acknowledgement with Re-transmission (PAR).
• A system using PAR sends the data again, unless
  it hears from the remote system that the data
  arrived okay.
• Unit exchanged segment.
• Provides checksum to verify that the data is
  undamaged.
• If a data segment arrives damaged, then it is
  discarded.
• Sender will timeout and retransmit segment.
• If the data segment is undamaged, a positive
  acknowledgement is sent back to the sender.

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TCP example continued

• Logical end-to-end connection is established via
  handshake.
• Handshake control info is exchanged to establish
  a dialogue before data is transmitted.
• Segment header contains flags specifying control
  information.
• TCP uses a three-way handshake.

Host A
Host B
SYN
SYN, ACK
ACK, data
Data xfer begun
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TCP 3-way handshake

• Host A begins connection by sending host B a
  segment with SYN bit set.
• SYN synchronize sequence numbers.
• Host B responds to A with a segment that has the
  ACK and SYN bits set. B informs A of the starting
  sequence number.
• Host A replies with ACK along with the first
  actual data to be transferred.

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More TCP

• When data transfer has concluded a three way
  handshake containing segments with the FIN bit
  set is used to close the connection.
• FIN No more data from sender.
• TCP views the data as a continuous stream of
  bytes.
• ACK performs both positive acknowledgement and
  flow control.
• Not every packet is acknowledged (sequence number
  informs sender how many packets are
  acknowledged).
• Window field informs remote end of the number of
  bytes that it is able to accept.

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Server Side of Communication Setup

• Server calls listen() function.
• Process blocks, kernel handles communication
  requests.
• Receives SYN segment. SYN/ACK is returned to the
  sender. Wait for final ACK.
• ACK is received. Connection is now established.

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Client Side of Communication Setup

• Client used the connect() function to set up a
  connection with the server. This function sends a
  SYN segment to the server.
• Process is blocked until SYN/ACK is received from
  the server.
• When the SYN/ACK is received, client sends back
  the concluding ACK. The client now considers the
  connection setup complete.

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Hybrid Tanenbaum Reference Model
Application Layer
5
Transport Layer
4
Network Layer
3
Data Link Layer
2
Physical Layer
1
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Example Networks and Communication Services

• Novell NetWare
• X.25
• Frame Relay
• ISDN
• ATM

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Novell NetWare

• NetWare network operating system (NOS)
  related support services.
• Novell, Inc., early 1980s
• Transition from mainframes to PC LANs.
• Client/Server model
• clients desktop PCs.
• servers PC dedicated as servers.
• Early 1990s, NOS market share between 50 and 75
  percent.

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Technology Basics

• NetWare NOS environment specifies the upper five
  layers of the OSI reference model.
• Provides
• file/printer sharing
• email
• DBMS
• etc..
• Clients now run on a variety of systems.
• Remote procedure calls
• transparent remote access

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Media Access Layer

• Physical Data Link
• NetWare runs on
• Ethernet (IEEE 802.3)
• Token Ring (IEEE 802.5)
• FDDI
• ARCnet
• PPP

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Network Layer

• Internet Packet Exchange (IPX)
• Analogous to IP
• Encapsulation The process of packaging
  upper-layer protocol information and data into a
  frame.
• IPX uses RIP (Routing info Protocol)

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Transport Layer

• Sequence Packet Exchange (SPX)
• like TCP
• reliable, connection-oriented
• Offers IP support using UDP encapsulation of
  Novell packets (e.g. IPS,IPX packets).
• NetWare Core Protocol (NCP) services application
  requests (e.g. NetWare shell).
• More of an application layer protocol.
• Provides Network Transparency to Apps.

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Communication Services

• X.25
• older public networks (60 Kbs?)
• Connection-oriented, proved virtual circuits.
• Frame Relay
• bare bones virtual leased lines (1.5 Mbps)
• ISDN
• digital data over separate channels.