TDC561 Network Programming

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TDC561 Network Programming
Review Network Terminology Internet-work
Architecture Network Protocols for the Internet

• Camelia Zlatea, PhD
• Email czlatea_at_cs.depaul.edu

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Communication Network

• Set of services and features (from End system
  view or Application programmer view)
• Ex. guaranteed message delivery between
  origination and termination points
• Type of service differentiates the type of
  networks
• Ex. voice/PSTN vs. data networks
• Network Services distinguished by a set of
  properties (mainly from Network Designer view)
• Latency, bandwidth, number of end-points, service
  interface, reliability resource utilization and
  fair allocation.
• Network Services easy-to-manage and to operate
  (from Network Provider view)
• Easy provisioning of network devices
• Rapid isolation and correlation of faults, alarms

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Network Performance

• Bandwidth (Throughput)
• of bits transmitted over the network in a
  certain interval of time
• Ex. 10 mil bits per sec (Mbps)
• Latency (Delay)
• How long it takes a message to travel from one
  end to other of a network
• Ex. One-way delay (latency)
• Round-Trip Delay
• LatencyPropagationTransmitQueue
• PropagationDistance/SpeedOfLight
• TransmitSize/Bandwidth

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Type of Networks

• Distance
• LAN (Local Area Networks)
• Ethernet, Token Ring, FDDI
• WAN (Wide Area Networks)
• X.25, ATM, Frame Relay
• Information Type
• Data Networks, telephony network (PSTN)
• Application Type
• General purpose (Internet) vs. special purpose
  (banking network)
• Security level
• Private enterprise networks
• Public PSTN, Internet
• Ownership of Protocols
• Proprietary SNA, IPX
• Open IP
• Protocol
• IP, IPX, AppleTalk, SNA

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The Internet

• Global scale, general purpose, heterogeneous
  technologies, public, computer network
• Internet Protocol (IP)
• Open system IETF (Internet Task Force) as
  standard body
• Intranet enterprise IP network
• IETF the protocol engineering and development
  arm of the Internet. Subdivided into many groups,
  which specify RFCs (Request For Comments)
• A Typical Internet Standardization Process
• Internet Drafts
• RFC
• Proposed Standard
• Draft Standard (requires 2 working
  implementations)
• Internet Standard (declared by Internet
  Architecture Board IAB, which is responsible for
  defining the overall architecture of the
  Internet, providing guidance and broad directions

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Connectivity

• Links physical medium connecting directly two
  or more computers
• Nodes computers connected by links
• Nodes attached at least two links run software
  that forwards data received on one link out on
  another
• Switched Network forwarding nodes
  systematically organized
• Circuit-switched network
• Common for telephony network
• Strategy (1) establishes a dedicated circuit
  across a sequence of links (2) source node sends
  a stream of bits across this circuit to a
  destination node.
• Packet-switched network
• Network nodes send discrete blocks of data to
  each other (packets/messages)
• Store-and-forward strategy each node (1)
  receives a packet, (2) stores packet in its
  internal memory buffer, and (3) forward packet to
  the next node.

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Connectivity

• Circuit-switched network
• Common for telephony network
• Strategy (1) establishes a dedicated circuit
  across a sequence of links (2) source node sends
  a stream of bits across this circuit to a
  destination node (3) Circuit Termination
• Busy signal if capacity for a circuit not
  available
• ExamplesPSTN Telephone networks, ISDN
  (Integrated Service Digital Network)
• Incoming links Node Outgoing links

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Circuit-switched network

• Timing

Host1 Node2 Node3 Host4
Processing Delay
(1)
(2)
DATA
(3)

• Circuit establishment
• Data Transmission
• Circuit Termination

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Connectivity

• Packet Switching
• Network nodes send discrete blocks of data to
  each other (packets/messages)
• Store-and-forward strategy each node (1)
  receives a packet, (2) stores packet in its
  internal memory buffer, and (3) forward packet to
  the next node.
• Packet/Message Structure
• Header, Data, Trailer
• Each packet is passed through the network from
  node to node along some path (Routing)
• At each node the entire packet is received,
  stored briefly, and then forwarded to the next
  node (Store-and-Forward)
• No capacity is allocated for the packets

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Packet-switching network

• Timing

Host1 Node2 Node3 Host4
Processing Delay
Pk1 Pk2 Pk3
Pk1 Pk2 Pk3
Pk1 Pk2 Pk3
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Connectivity

• Virtual-Circuit Packet Switching
• Hybrid of circuit switching and packet switching
• All data is transmitted as packets
• All packets from one stream are sent along a
  pre-established path (virtual circuit VC)
• Guarantees in-sequence delivery of packets
• Packets from different virtual circuits can be
  interleaved
• Strategy
• VC establishment
• Data Transfer
• VC Disconnect

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Virtual Circuit Packet-switching network

• Timing

Host1 Node2 Node3 Host4
Processing Delay
(1) (2) (3)
Pk1 Pk2 Pk3
Pk1 Pk2 Pk3
Pk1 Pk2 Pk3
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Protocol Architecture

• Protocol agreement between communication
  entities on how to interpret meta-data or headers
• Different layers put in different layers

NANetwork Access
Application protocol
App
App
TCP protocol
TCP
TCP
IP protocol
IP
IP
IP
IP
NA
NA
NA
NA
NA
NA
Data Links
Host Router
Router Host
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Layering

• Organization of a network system into a
  successive logically distinct entities, such that
  the service provided by one entity is determined
  based on the service provided by the previous
  (lower level) entity
• Advantages
• Abstraction ( an intermediate layer that provides
  an unique abstraction for applications regarding
  various network technologies
• Lower layers can be changed without affecting the
  upper layers
• Modularity protocol easy to manage and maintain
• Reuse upper layers can reuse the functionality
  provided by lower layers
• Disadvantages
• Information hiding can cause inefficient
  implementations

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ISO OSI Reference Model

• ISO International Standard Organization
• OSI Open System Interconnection
• Goal A general OPEN standard

Physical Medium
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OSI Model Concepts

• Service what a layer does
• Interface how to access the service
• Protocol how is the service implemented
• Set of rules and formats that govern the
  communication between two peers

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Physical Layer

• Service - move info between two systems connected
  by physical link
• Interface how to send bits
• Protocol coding scheme used to represent a bit,
  voltage levels, duration of a bit
• Examples cable coax, fiber optic links
  transmitters receivers

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Data Link Layer

• Service
• Send data frames between peers
• Framing, i.e. attach frame separators
• Arbitrate access to common media, ensure
  reliability of transmission, provide flow control
• Interface send a data unit (packet) to a node
  connected to the same physical media
• Protocol layer addresses, MAC (Medium Access
  Control)
• Examples CSMA/CD

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Network Layer

• Service
• Deliver a packet to a specified destination
• Perform segmentation/reassemble
• Packet scheduling
• Buffer management
• Interface send a packet to a specified
  destination
• Protocol define global unique addresses
  construct routing tables
• Example Routing
• Bearer/Data Plane uses forwarding table to
  forward packets
• Control Plane construct and maintain Forwarding
  Tables (distance vectors, link state protocols)

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Transport Layer

• Service
• Error-free and flow-controlled end-to-end
  connection
• Interface send a packet to specify destination
• Protocol implement reliability and flow
  control
• Example TCP and UDP

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Session Layer

• Service
• Full-Duplex
• Access management (ex. token control)
• Synchronization (ex. Check points fro long
  transfers)
• Interface depends on service
• Protocol token management, checkpoints, for
  long transfers, roll-back functions
• Presentation Layer
• Service
• Data conversions
• Interface depends on service
• Protocol define data formats, and rules to
  convert from one format to another

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Application Layer

• Service End-User type of Service
• Interface depends on application
• Protocol depends on application
• Examples FTP, Telnet, HTTP, H323

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Internet Reference Model

• OSI vs. TCP/IP Architecture

Internet
Host-to-Network
Physical Medium
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(No Transcript)
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IP is a Network Layer Protocol
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Encapsulation Example
Ethernet Header
IP Header
An Ethernet segment transmitting HTTP data.
TCP Header
HTTP Header
. HTTP Data .
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IP Hour Glass
Networking Applications
Remote Access
Voice
HOST
email
Multimedia
file transfer
Web
VPN
TCP
IP
Router
Frame
ATM
Ethernet
DWDM
SONET
FDDI
Link
X.25
Networking Technologies
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IP - Simple, Stupid, Flexible

• In the Internet, intelligence is in Hosts
• IP is connectionless, best effort.
• Routing protocols today provide only connectivity
  and supports only one type of service best
  effort datagram

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Typical Members of the IP Protocol Family
Telnet
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Routing Protocols, part of the IP Protocol Family
BGP
RIP
TCP
UDP
OSPF
IP
Routing protocols exchange network reachability
information between routers.
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Packet Delivery Model

• Connectionless (datagram-based)
• Best-effort delivery (unreliable service)
• packets are lost
• packets are delivered out of order
• duplicate copies of a packet are delivered
• packets can be delayed for a long time

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IP Routing Basics

• Routing is the process for deciding where to send
  each packet.
• There are a number of routing algorithms that
  provide rules for how routers
• Communicate with each other about router and link
  status.
• Maintain lists of reachable networks.
• Select between alternate paths.

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IP Datagram

• IP Datagram format
• Version (4) currently 4
• Hlen (4) number of 32-bit words in header
• TOS (8) type of service (used for QoS)
• Length (16) number of bytes in this datagram
• Ident (16) used by fragmentation
• Flags/Offset (16) used by fragmentation
• TTL (8) number of hops this datagram has
  traveled
• Protocol (8) demux key (TCP6, UDP17)
• Checksum (16) of the header only
• DestAddr SrcAddr (32)

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IP Datagram
0
4
8
16
19
31
TOS
Length
V
ersion
HLen
Ident
Flags
Fragment Offset
TTL
Protocol
Checksum
SourceAddr
DestinationAddr
Pad
Options (variable)
(variable)
Data
1981, RFC 791
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IP Header Format
1981, RFC 791
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Example IP Packets
TCP Packet
UDP Packet
IP Header
IP Header
UDP Header
TCP Header
UDP Payload
TCP Payload
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Fragmentation and Reassembly

• Each network has some MTU (Maximum Transfer Unit)
• Strategy
• fragment when necessary (MTU lt Datagram)
• try to avoid fragmentation at source host
• refragmentation is possible
• fragments are self-contained datagrams
• delay reassembly until destination host
• do not recover from lost fragments

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IP Fragmentation

• A main function of IP is to fragment and
  reassemble packets on the fly
• each network in a heterogeneous collection of
  networks has a Maximum Transmission Unit (MTU)
• maximum size of IP packet (datagram) that can be
  carried on network
• Packets must be fragmented if entering a network
  with a smaller MTU
• packets remain fragmented until the reach
  destination host
• packet headers remain mostly unchanged
• packets are then reassembled

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Ethernet Frame Format

• Link Layer Address Formats (802 headers - 8 bytes
  long)
• Addresses
• Unique, 48-bit unicast address assigned to each
  adaptor
• Example 802be4b12
• Broadcast all 1s
• Multicast first bit is 1

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TCP/IP Protocol Stack
HOST B Application
HOST B Application
Transport TCP, UDP
Transport TCP, UDP
Message
H
Message
H
Internet/Network
Internet/Network
Message
H
H
Message
H
H
Network Access
Network Access
Message
H
H
H
Message
H
H
H
Physical Link
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Client-Server Communication
WAN
ISP
OSPF
ISP
ISP
BGP
OSPF
OSPF
External Router
External Router
Ethernet Switch
Ethernet Hub
WWW Server
Client PC
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Network Entities

• Client PC
• Ethernet Hub
• Fan-out a single 10Mbs connection to several end
  points (ex. PC, IP phone)
• Ethernet Switch (Layer2 switch)
• Bridges the data across multiple 10Mbs
  connections
• External Router
• Connects a LAN to the Internet (ISP network, for
  example, with frame relay link over fiber cable)
  router protected by Firewall(s)
• Clouds
• ISPs networks running OSPF (Open Shortest Path
  First) and interconnected by BGP (Border Gateway
  Protocol)

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Internet-work
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Internet-work
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Internet-work
H1
R1
R2
R3
H8
ETH
IP
(1400)
ETH
IP
(1400)
PPP
IP
(512)
ETH
IP
(512)
PPP
IP
(512)
ETH
IP
(512)
PPP
IP
(376)
ETH
IP
(376)
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IP Node
Routing Protocols
UDP
TCP
yes yes no
Local Address?
Routing Table
Errors?
Output Operations
Queue
Queue
incoming datagram
outgoing datagram
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Addressing

• Addresses need to be globally unique, so they are
  also hierarchical
• Another reason for hierarchy route aggregation
• reduces size of routing tables
• geographical distribution constraints

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Addressing in the Internet

• Addressing tied to reachability
• Every host interface has its own IP address
• Router interfaces usually have their own IP
  addresses
• Current version of IP is version 4 (IPv4
  addresses)
• 4 bytes long
• two part hierarchy
• network number and host number
• different types of boundary indicator
• class, subnet mask, prefix
• Goal of boundaries is address aggregation

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Address classes

• Historical first choice
• fixed network-host partition, with 8 bits of
  network number
• Generalization
• Class A addresses have 8 bits of network number
• Class B addresses have 16 bits of network number
• Class C addresses have 24 bits of network number
• Distinguished by leading bits of address
• leading 0 gt class A (first byte lt 128)
• leading 10 gt class B (first byte in the range
  128-191)
• leading 110 gt class C (first byte in the range
  192-223)
• leading 1110 gt class D (multicast)
• leading 1111 gt Class E (reserved)

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Address evolution

• Class based scheme was too inflexible
• Two problems
• Too many routes
• Too few addresses
• Four extensions
• Subnetting (flexible boundaries within network)
• CIDR (flexible grouping of networks)
• Dynamic host configuration (reuse of addresses)
• A bigger address (IPv6)
• One issue
• Network address translation

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Subnetting

• Allows administrator to cluster IP addresses
  within its network (mostly applicable to class B
  addresses)
• Route aggregation by maintaining routes only to
  subnets (mostly within your own network)

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IPv6 - Addressing

• No matter how much reuse, 32-bit IPv4 addresses
  are likely to eventually run out
• IPv6 extends address size to 128 bits
• Classless and supports aggregation (prefixes)
  subnetting
• Flow label of (faster) lookup
• Unicast, and multicast addresses
• Interoperability with IPv4 through encapsulation
• But deployment has been slow
• Need is less urgent than anticipated
• Impact to host software
• Complexity of routing in mixed IPv4/IPv6
  environment

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IP Addressing

• Two special addresses on each network
• Network address identifies the network
• An example is 10.1.2.0
• Broadcast address identifies all hosts on the
  network
• An example is 10.1.2.255
• These cannot be used for hosts

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TCP/UDP

• Transmission Control Protocol - reliable,
  session-based service for delivery of sequenced
  packets across an internet
• User Datagram Protocol (UDP) provides fast /
  unreliable datagram service.

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End-to-End (Transport) Protocols

• Underlying best-effort network
• drops messages
• re-orders messages
• delivers duplicate copies of a given message
• limits messages to some finite size
• delivers messages after an arbitrarily long delay
• Common end-to-end services
• guarantee message delivery
• deliver messages in the same order they are sent
• deliver at most one copy of each message
• support arbitrarily large messages
• support synchronization
• allow the receiver to apply flow control to the
  sender
• support multiple application processes on each
  host

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UDP

• Simple Demultiplexor
• Unreliable and unordered datagram service
• Adds multiplexing
• No flow control
• Endpoints identified by ports
• servers have well-known ports
• see /etc/services on Unix
• Optional checksum
• pseudo header udp header data
• Header format

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UDP Packet Format
0
16
32
Source Port Address
Destination Port Address
Header
Checksum
Length
DATA
Checksum -- Numeric calculation to ensure packet
is not corrupt. Length -- Length of the data
portion of the packet, in bytes.
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UDP
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TCP

• Reliable Byte-Stream
• Connection-oriented
• Byte-stream
• sending process writes some number of bytes
• TCP breaks into segments and sends via IP
• receiving process reads some number of bytes
• Full duplex
• Flow control keep sender from overrunning
  receiver
• Congestion control keep sender from overrunning
  network

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TCP

• Connection-oriented protocol
• logical connection created between two
  communicating processes
• connection is managed at TCP protocol layer
• provides reliable and sequential delivery of data
• receiver acknowledgements sender that data has
  arrived safely
• sender resends data that has not been
  acknowledged
• packets contain sequence numbers so they may be
  ordered
• Bi-directional byte stream
• both sender and receiver write and read bytes
• acknowledgements identify received bytes
• buffers hold data until there is a sent
• multiple bytes are packaged into a segment when
  sent

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TCP Packet Format
0
16
31
Source Port Number
Destination Port Number
Sequence Number
Acknowledgement
0
Flags
Window
Hdr Len
Checksum
Urgent Pointer
Options/Padding
Data
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End-to-End Issues

• Based on sliding window protocol used at data
  link
• level, but the situation is very different.
• Potentially connects many different hosts
• need explicit connection establishment and
  termination
• Potentially different RTT
• need adaptive timeout mechanism
• Potentially long delay in network
• need to be prepared for arrival of very old
  packets
• Potentially different capacity at destination
• need to accommodate different amounts of
  buffering
• Potentially different network capacity
• need to be prepared for network congestion

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Client Server Communication

• The transport protocols TCP and UDP were designed
  to enable communication between network
  applications
• Internet host can have several servers running.
• usually has only one physical link to the rest
  of the world
• When packets arrive how does the host identify
  which packets should go to which server?
• Ports
• ports are used as logical connections between
  network applications
• 16 bit number (65536 possible ports)
• demultiplexing key
• identify the application/process to receive the
  packet
• TCP connection
• source IP address and source port number
• destination IP address and destination port
  number
• the combination IP Address Port Number pair is
  called a Socket

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Client Server Communication
Port
IP
Network Host
Network
122.34.45.67
Network Host
123.45.67.89
SOCKETS
122.34.45.6780
123.45.67.8965533
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Client Server Communication
Port
HTTP Server with three active connections
(sockets).
IP Network
Active
Active
Active
Listening
IP Host/ Server
The HTTP server listens for future connections.
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Common Ports

• Port numbers divided into three categories
• Well Known Ports 0-1023
• Registered Ports 1024-49151
• Dynamic/Private Ports 49152-65535
• Well Known Ports
• 1 TCP Port Service Multiplexor
• 20 File Transfer Protocol (FTP) Data
• 21 FTP Control
• 23 Telnet
• 25 Simple Mail Transfer (SMT)
• 43 Who Is
• 69 Trivial File Transfer Protocol (TFTP)
• 80 HTTP

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TCP/IP protocol suite

• File Transfer
• Remote Login
• Electronic Mail
• Network File Systems
• Remote Printing
• Remote Execution
• Name Terminal Servers
• Network-Oriented Windows Systems