Protocols and Protocol Suit Review

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Protocols and Protocol SuitReview

• Lecture 14

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Overview

• Network Access Layer
• Transport Layer
• Protocols
• Protocol Data Unit
• Protocol Architecture
• TCP/IP Stack
• Layered Approach and its Advantages
• Router

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What is a Protocol ?

• Q- What is a protocol?

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Communication Protocols

• Definition
• Protocol is a set of rules that govern all aspect
  of data communication between computers on a
  network.
• These rules include guidelines that regulate the
  following characteristics of a network access
  method, allowed physical topologies, types of
  cabling, and speed of data transfer.
• A protocol defines what, how, when it
  communicated.
• The key elements of a protocol are syntax,
  semantics and timing.
• Protocols are to computers what language is to
  humans. Since this article is in English, to
  understand it you must be able to read English.
  Similarly, for two devices on a network to
  successfully communicate, they must both
  understand the same protocols.

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Key Elements of protocol

• Syntax
• The structure or format of the data.
• Eg. A simple protocol

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Elements of protocol

• ii) Semantics
• - Refers to the meaning of each section of
  bits.
• - how is a particular pattern to be interpreted,
  and what action is to be taken based on that
  interpretation.
• Eg. Does an address identify the route to be
  taken or the final of the message?

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Elements of protocol

• iii) Timing
• Refers to two characteristics
• When data to be sent
• How fast it can be sent
• Eg. If a sender produces data at 100 Mbps but the
  receiver can process data at only 1 Mbps, the
  transmission will overload the receiver and data
  will be largely lost.

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Characteristics of protocol

• Direct / indirect
• communication between two entities maybe direct
  or indirect.
• i) point-to-point link
• - connection provides a dedicated link between
  two devices
• - the entities in these systems may
• communicate directly that is data and
• control information pass directly
• between entities with no intervening
• active agent.

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Characteristics of protocol
ii) multipoint link - connection more than two
devices can share a single link - The entities
must be concerned with the issue of access
control and making the protocol more complex.
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Common protocol used
Protocol Acronym Remarks
Point To Point PPP Used to manage network communication over a modem
Transfer/Transmission Control Protocol TCP / IP Backbone protocol. The most widely used protocol.
Internetwork package exchange IPX Standard protocol for Novell NOS
NetBIOS extended user interface NetBEUI Microsoft protocol that doesnt support routing to other network. Running only Windows-based clients.
File transfer Protocol FTP used to send and received file from a remote host
Simple mail Transfer protocol SMTP Used to send Email over a network
Hyper text transfer protocol HTTP Used for Internet to send document that encoded in HTML
Apple Talk Apple Talk Protocol suite to network Macintosh computer and a peer-to-peer network protocol
OSI Model OSI Layers A way of illustrating how information functions travels through network of its 7 layers.
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What is a Protocol ?

• Q- What is a protocol?

Protocols are a set of rules and conventions. By
enforcing that communicating parties adhere to a
common protocol, communication is made possible.
Protocol Architecture The Common Language
Ans- A protocol is the set of rules or
conventions governing the way in which two
entities cooperate to exchange data.
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PDU

• What is a protocol data unit (PDU)?

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Protocol Data Units (PDU)

• At each layer, protocols are used to communicate
• Control information is added to user data at each
  layer (PDU Control Data)
• Transport layer may fragment user data
• Each fragment has a transport header added
• Destination SAP (port)
• Sequence number
• Error detection code
• This gives a transport protocol data unit

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Protocol Data Units
Network PDU Adds network header, network address
for destination computer and Facilities requests
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PDU

• What is a protocol data unit (PDU)?

Ans- A PDU is the combination of data from the
next higher communications layer and control
information.
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Protocol Architecture

• Q- What is a protocol architecture?

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Need For Protocol Architecture

• There are lots of network applications
• Building each application from scratch is very
  time-consuming and challenging
• What commands should be supported?
• How to respond to each command?
• How to identify the two peer applications?
• Each computer may run multiple applications!
• How to identify the two computers?
• How to convert the data into bit stream?
• How to convert the bit stream into signals?
• How to detect and handle data loss and data
  error?
• The network is not perfect!
• Etc.

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Need For Protocol Architecture

• Data exchange can involve complex procedures, cf.
  file transfer example
• Better if task broken into subtasks
• Implemented separately in layers in stack
• each layer provides functions needed to perform
  communication for layers above
• using functions provided by layers below
• Peer layers communicate with a protocol

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Key Elements of a Protocol

• Syntax data block format
• Semantics - control info. error handling
• Timing - speed matching sequencing

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(Cont.)

• Most of the network apps share some common modules

Application A
Application B
Application C
Module A
Module B
Module C
Module T
Module T
Module T
Module I
Module I
Module I
Common modules
Module N
Module N
Module N
Module P
Module P
Module P
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(Cont.)

• A complex task is broken into subtasks modular
  design
• Each subtask is implemented separately as a
  layer, arranged in a vertical stack
• Each layer performs a related subset of the
  functions required to communicate with another
  system.
• It relies on the next lower layer to perform more
  primitive functions and to conceal the details of
  those functions.
• It provides services to the next higher layer.
• Layers should be defined so that changes in one
  layer do not require changes in other layers.
• So, instead of using a single complex protocol,
  its more flexible to implement a stack of
  protocols!
• Reduce the design and development workload
  significantly!

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Vertical Stack
Application A
Application B
Application C
Module A
Module B
Module C
Module T
Module I
Module N
Module P
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Example

• E.g., A can only speak Chinese, B can only speak
  Spanish, how can A communicate with B?
• A finds a translator C, who can speak Chinese and
  English
• B finds a translator D, who can speak Spanish and
  English
• Two layers
• Higher layer A and B
• Lower layer C and D

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A Two-layer example
How to communicate?
B
Higher Layer
A
messages in Spanish
messages in Chinese
Lower Layer
messages in English
D
C
Lower layer provides services to the next higher
layer.
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Protocol Architecture

• Tasks of communications are broken up into
  modules
• Each module (or layer) can have its own protocol
• In very general terms, communications can be said
  to involve three components applications,
  computers, and networks.
• For example, file transfer could use three
  modules (or layers)
• File transfer application
• Communications service module
• Network access module
• The stack of protocols is called Protocol Stack
• Or Protocol Architecture

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TCP/IP Protocol Architecture

• Developed by the US Defense Advanced Research
  Project Agency (DARPA) for its packet switched
  network (ARPANET)
• Used by the global Internet
• It consists of a large collection of protocols
  that have been issued as Internet standard by the
  Internet Architecture Board (IAB).
• Check http//www.ietf.org/rfc/rfc2026.txt
• The TCP/IP protocol architecture organizes the
  communication task into five relatively
  independent layers
• Layer 5 Application layer
• Layer 4 Transport layer, or Host to host (TCP
  belongs to this layer)
• Layer 3 Internet layer, or Network layer (IP
  belongs to this layer)
• Layer 2 Network access layer, or Link layer
• Layer 1 Physical layer
• Remark Each layer can have lots of different
  protocols!

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Example

• World Wide Web
• Replies on the HTTP protocol

Web browser
Web server
HTTP
HTTP
Layer 5
TCP
TCP
Layer 4
IP
IP
Layer 3
IEEE 802.11
IEEE 802.3
Layer 2
IEEE 802.11g
IEEE 802.3 1000BASE-SX
Layer 1
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Standardized Protocol Architectures

• Required for devices to communicate
• Vendors have more marketable products
• Customers can insist on standards based equipment
• Two standards
• OSI Reference model
• Never lived up to early promises
• TCP/IP protocol suite
• Most widely used

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Protocol Architecture

• Q- What is a protocol architecture?

Ans- The software structure that implements the
communications function. Typically, the protocol
architecture consists of a layered set of
protocols, with one or more protocols at each
layer.
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TCP/IP

• Q- What is TCP/IP?

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Postal System
To Mr. Jacky Chan No. 123, XX Road, XXX, USA
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Inside Postal System
Central Post Office (Beijing)
Central Post Office (New York)
The delivery of your package depends on the
postal address.
Central Post Office (Hong Kong)
Local Post Office (Tseung Kwan O)
Local Post Office (Kowloon Tong)
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TCP/IP Protocol Architecture

• Developed by US Defense Advanced Research Project
  Agency (DARPA)
• ARPANET packet switched network reuired
• Now popular all over the world used by the global
  Internet
• Protocol suite comprises a large collection of
  standardized protocols

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TCP/IP
Q- What is TCP/IP?

• Ans- Transmission Control Protocol/Internet
  Protocol (TCP/IP) are two protocols originally
  designed to provide low level support for
  internetworking. The term is also used
  generically to refer to a more comprehensive
  collection of protocols developed by the U.S.
  Department of Defense and the Internet community.

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Layers

• Q- What are some advantages to layering as seen
  in the TCP/IP architecture?

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TCP/IP Layers

• Because TCP/IP was developed earlier than the OSI
  7-layer mode, it does not have 7 layers but only
  4 layers

OSI 7-layer
TCP/IP Protocol Suite
FTP, SMTP, Telnet, HTTP,
TCP, UDP
IP, ARP, ICMP
Network Interface
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Benefit of layering

• The most challenging problem how to provide a
  reliable data transfer service on top of an
  unreliable data network?
• This problem is so important that todays
  Operating Systems all provide such reliable
  service.
• The burden of network application developers has
  been reduced significantly!
• Hence the application developers can simply focus
  on the application layer issues.
• We can easily develop thousands of network
  applications.

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TCP/IP Layers

• Q- What are some advantages to layering as seen
  in the TCP/IP architecture?
• Ans- Layering decomposes the overall
  communications problem into a number of more
  manageable subproblems

OSI 7-layer
TCP/IP Protocol Suite
FTP, SMTP, Telnet, HTTP,
TCP, UDP
IP, ARP, ICMP
Network Interface
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Router

• Q- What is a router?
• Router Functions
• Linking WANs and LANs
• Interconnecting communication lines
• Path determination and packet switching
• Application of security rules (ACLs)
• Protocol conversion (encapsulation)
• E.g. HDLC, PPP etc.

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Routers

• Internetworking among dissimilar subnetworks is
  achieved by using routers to interconnect the
  subnetworks. Essential functions that the router
  must perform include the following
• Provide a link between networks.
• Provide for the routing and delivery of data
  between processes on end systems attached to
  different networks.
• Provide these functions in such a way as not to
  require modifications of the networking
  architecture of any of the attached subnetworks.

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Routers

• Addressing schemes The networks may use
  different schemes for assigning addresses to
  devices. For example, an IEEE 802 LAN uses 48-bit
  binary addresses for each attached device an ATM
  network typically uses 15-digit decimal addresses
  (encoded as 4 bits per digit for a 60-bit
  address). Some form of global network addressing
  must be provided, as well as a directory service.
• Maximum packet sizes Packets from one network
  may have to be broken into smaller pieces to be
  transmitted on another network, a process known
  as segmentation or fragmentation. For example,
  Ethernet imposes a maximum packet size of 1500
  bytes a maximum packet size of 1000 bytes is
  common on X.25 packet-switching networks. A
  packet that is transmitted on an Ethernet system
  and picked up by a router for retransmission on
  an X.25 network may have to be fragmented into
  two smaller ones.

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Router
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TCP/IP (Sender)

• Preparing the data. The application protocol
  prepares a block of data for transmission. For
  example, an email message (SMTP), a file (FTP),
  or a block of user input (TELNET)
• Using a common syntax. If necessary, the data are
  converted to a form expected by the destination.
  This may include a different character code, the
  use of encryption, and/or compression.
• Segmenting the data. TCP may break the data block
  into a number of segments, keeping track of their
  sequence. Each TCP segment includes a header
  containing a sequence number and a frame check
  sequence to detect errors.
• Duplicating segments. A copy is made of each TCP
  segment, in case the loss or damage of a segment
  necessitates retransmission. When an
  acknowledgment is received from the other TCP
  entity, a segment is erased.

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Operation of TCP/IP(Action at Router)

• Arriving at router. The incoming signal is
  received over the transmission medium and
  interpreted as a cell of bits.
• Processing the cell. The ATM layer removes the
  cell header and processes it. The header error
  control is used for error detection. The
  connection number identifies the source.
• Routing the packet. IP examines the IP header and
  makes a routing decision. It determines which
  outgoing link is to be used and then passes the
  datagram back to the link layer for transmission
  on that link
• Forming LLC PDU. An LLC header is added to each
  IP datagram to form an LLC PDU. The header
  contains sequence number and address information.
• Framing. A MAC header and trailer is added to
  each LLC PDU, forming a MAC frame. The header
  contains address information and the trailer
  contains a frame check sequence.
• Transmission. Each frame is transmitted over the
  medium as a sequence of bits.

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Router Components

• Hardware components of a router
• Network interfaces
• Interconnection network
• Processor with a memory and CPU
• PC router
• interconnection network is the (PCI) bus and
  interface cards are NICs
• All forwarding and routing is done on central
  processor
• Commercial routers
• Interconnection network and interface cards are
  sophisticated
• Processor is only responsible for control
  functions (route processor)
• Almost all forwarding is done on interface cards

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Functional Components
Control
Datapath per-packet processing
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Routing and Forwarding

• Routing functions include
• route calculation
• maintenance of the routing table
• execution of routing protocols
• On commercial routers handled by a single
  general purpose processor, called route processor
• IP forwarding is per-packet processing
• On high-end commercial routers, IP forwarding is
  distributed
• Most work is done on the interface cards

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Basic Architectural ComponentsPer-packet
processing
Output Scheduling
Routing Table
Switch Fabric
Routing Decision
Routing Table
Forwarding Decision
Routing Table
Forwarding Decision
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Router Components

• On a PC router
• interconnection network is the (PCI) bus
• Interface cards are NICs (e.g., Ethernet cards)
• All forwarding and routing is done on central
  processor
• On Commercial routers
• Interconnection network and interface cards can
  be sophisticated
• Central processor is the route processor (only
  responsible for control functions)

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Router

• Q- What is a router?
• Router Operations
• Layer 3 device
• Accepts PDUs on incoming network
• Examines PDU data
• Makes decision(s) for next stage of PDU journey
• May modify PDU contents (not payload)
• Passes PDU on to outgoing network

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Router

• Q- What is a router?
• Ans-A router is a device that operates at the
  Network layer of the OSI model to connect
  dissimilar networks.

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Summary

• Network Layer Functionality
• Task performed _at_ Transport Layer
• Protocol and Protocol Stack
• Protocol Data Unit
• Protocol Architecture
• TCP/IP Stack
• Layering Advantages in TCP/IP
• Router Architecture and Functionality

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Question

• Q- A broadcast network is one in which a
  transmission from any one attached station is
  received by all other attached stations over a
  shared medium. Examples are a bustopology local
  area network, such as Ethernet, and a wireless
  radio network. Discuss the need or lack of need
  for a network layer (OSI layer 3) in a broadcast
  network.

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Routing in Case of Broadcast

• A case could be made either way. First, look at
  the functions performed at the network layer to
  deal with the communications network (hiding the
  details from the upper layers). The network layer
  is responsible for routing data through the
  network, but with a broadcast network, routing is
  not needed. Other functions, such as sequencing,
  flow control, error control between end systems,
  can be accomplished at layer 2, because the link
  layer will be a protocol directly between the two
  end systems, with no intervening switches. So it
  would seem that a network layer is not needed.
  Second, consider the network layer from the point
  of view of the upper layer using it. The upper
  layer sees itself attached to an access point
  into a network supporting communication with
  multiple devices. The layer for assuring that
  data sent across a network is delivered to one of
  a number of other end systems is the network
  layer. This argues for inclusion of a network
  layer. In fact, the OSI layer 2 is split into two
  sublayers. The lower sublayer is concerned with
  medium access control (MAC), assuring that only
  one end system at a time transmits the MAC
  sublayer is also responsible for addressing other
  end systems across the LAN. The upper sublayer is
  called Logical Link Control (LLC). LLC performs
  traditional link control functions. With the
  MAC/LLC combination, no network layer is needed
  (but an internet layer may be needed).

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Question

• Q- A TCP segment consisting of 1500 bits of data
  and 160 bits of header is sent to the IP layer,
  which appends another 160 bits of header. This is
  then transmitted through two networks, each of
  which uses a 24-bit packet header. The
  destination network has a maximum packet size of
  800 bits. How many bits, including headers, are
  delivered to the network layer protocol at the
  destination?
• Sol- Data plus transport header plus internet
  header equals 1820 bits. This data is delivered
  in a sequence of packets, each of which contains
  24 bits of network header and up to 776 bits of
  higher-layer headers and/or data. Three network
  packets are needed. Total bits delivered 1820
  (3 x 24) 1892 bits.

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UDP Requirement

• Q- Why is UDP needed? Why can't a user program
  directly access IP?
• Ans- UDP provides the source and destination
  port addresses and a checksum that covers the
  data field. These functions would not normally be
  performed by protocols above the transport layer.
  Thus UDP provides a useful, though limited,
  service.

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IP, TCP and UDP Error Checksum

• Q- IP, TCP, and UDP all discard a packet that
  arrives with a checksum error and do not attempt
  to notify the source. Why?
• Ans- In the case of IP and UDP, these are
  unreliable protocols that do not guarantee
  delivery, so they do not notify the source. TCP
  does guarantee delivery. However, the technique
  that is used is a timeout. If the source does not
  receive an acknowledgment to data within a given
  period of time, the source retransmits.

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TCP UDP Header Length

• Q- Why does the TCP header have a header length
  field while the UDP header does not?
• Ans- UDP has a fixed-sized header. The header in
  TCP is of variable length.

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Summary

• Network Layer Functionality
• Task performed _at_ Transport Layer
• Protocol and Protocol Stack
• Protocol Data Unit
• Protocol Architecture
• TCP/IP Stack
• Layering Advantages in TCP/IP
• Router Architecture and Functionality