How Protocols Work
• Protocols are how computers on a network
communicate.
• Protocols may determine packet size, information
in the headers, and how data is stored in the packet.
• Both sides of the conversation must understand
these rules for a successful transmission.
• Most protocols actually consist of several
protocols grouped together in a suite.
Lecture 5
Network Protocols
Kuang-hua Chen
Department of Library and Information Science
National Taiwan University
Language & Information Processing System, LIS, NTU
Routable Protocols
Nonroutable Protocols
• Many networks today consist of connected LANs.
• Some protocols cannot be routed and are
limited to smaller LANs.
• Besides being simpler than routable
protocols, nonroutable protocols are also
usually faster and provide better transfer
speeds, due to less overhead.
– These LANs are often connected using routers.
– One consideration of connecting LANs is the ability of
protocols to work properly across the router to the
different networks.
• A protocol with the ability to communicate across
the router is known as a routable protocol.
• This type of protocol has become increasingly
important.
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Connectionless Protocols
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Connection-Oriented Protocols
• Connectionless protocols have no feedback to
know whether it arrived safely or not.
• Connectionless protocols are faster than
connection-oriented ones due to less overhead.
• They are used mainly
• If you need to ensure that certain data
arrives at its destination, then a connectionoriented protocol can be used.
• The protocols send acknowledgments to
show that data was received successfully.
– when there is a need to send data to multiple computers
at once
– when high speed is needed, such as in video or audio.
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Popular Protocol Suites
TCP/IP Protocol Suite
• The Transmission Control Protocol/Internet
Protocol (TCP/IP) protocol suite is a suite of
industry-standard protocols.
• Today it is the main protocol used on the
worldwide Internet.
• TCPIP is routable, which enables you to connect
multiple LANs into one large internetwork.
• For more information on TCP/IP, you can visit
http://www.internic.net.
• A protocol suite is a collection of protocols
that work together to form a single system
to handle networking devices
• The purpose of a protocol suite is to handle
the underlying network functions
• The protocol suites normally have many
protocols with different capabilities, so the
needs of the user’s applications are met
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應用層
(Application Layer)
傳輸層
(Transport Layer)
傳輸層
(Transport Layer)
網際網路層
(Internet Layer)
網際網路層
(Internet Layer)
網路介面層
(Network Interface Layer)
LLC
實體層
(Physical Layer)
網路存取層
(Network Access Layer)
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TCP/IP and OSI Model
TCP/IP Model – de facto Standard
應用層
(Application Layer)
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• Network Access layer
– This layer corresponds to the Physical and Data Link
layers of the OSI model.
– TCP/IP has been shown to run over almost any type of
network connection from FDDI to radio wave.
• Internet layer
– This layer roughly matches up with the Network layer
of the OSI model.
– Both of these layers are responsible for moving data to
other devices on the network.
LAN
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TCP/IP and OSI Model (Continued)
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TCP/IP and OSI Model (Continued)
• Host-to-Host layer
– This one is similar to the Transport layer of the OSI
model.
– The job of both of these layers is to communicate
between peers on the network.
– Almost all devices on a TCP/IP network are considered
hosts.
RIP
OSPF
• Process/Application layer
– This fourth layer does the same job as the top three
layers of the OSI model.
– Provide network services
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The Internet
TCP/IP Addressing
• Every host on a TCP/IP network is given an IP
address.
• IP address is a unique 4-byte address in dotted
notation
– 140.112.198.254, 140.112.254.4
• IP addresses are handed out by interNIC
• IP addresses are divided into classes.
• IP address classes are used to segment the pool of
addresses into sizes corresponding to various
organization sizes.
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TCP/IP Addressing (Continued)
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TCP/IP Addressing (Continued)
– With this arrangement each Class B network can have
more than 65,000 hosts.
– The first byte of Class B addresses is always from 128
to 191.
• Class A: Class A addresses have one byte for the
network and three bytes for the host.
– For example, the address 56.88.1.231 has a network
number of 56, and the remaining numbers signify the
host.
– The first byte of Class A network addresses is always
from 1 and 127.
• Class C: Class C addresses are the most common.
They use the first 3 bytes of the address for the
network portion and the final byte for the host.
– This allows for a great number of network addresses
given out, with more than 250 hosts on each network.
– Class C addresses always have the first byte from 192
to 223.
• Class B: Class B addresses have 2 bytes for the
network address and the remaining two for the
host address.
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TCP/IP Addressing (Continued)
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TCP/IP addressing(Continued)
• The network addresses of 128 and 224 and
up are used for special purposes and
experimentation.
• Besides the IP address, the subnet mask
completes a computer’s address on a
TCP/IP network, and thus is required.
• The subnet mask is responsible for
separating the IP address into the host
portion and the network portion.
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3
IP Address Format
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Special IP Address
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What’s in the TCP/IP suite?
•
•
•
•
•
•
•
•
•
•
•
•
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File Transfer Protocol
Simple Mail Transfer Protocol
Dynamic Host Configuration Protocol
Telnet
Network File System
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RIP and OSPF
Address Resolution Protocol
• Routing Information Protocol (RIP) and Open
Shortest Path First (OSPF) are two routing
protocols in the Internet Protocol suite.
• RIP uses the number of routers (hops) between the
originating computer and the destination to decide
the best way to route a packet.
• OSPF uses much more information to calculate
the best way to route packets.
• Address Resolution Protocol (ARP) handles
the conversion of the address by sending out
a discovery packet.
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– To find out the MAC address of a particular IP
address
• ARP maintains a list of IP and MAC
addresses so a discovery packet is not
needed every time communication takes
place.
– The hop count.
– the speed of the connection between the hops,
– the load balancing
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What’s in TCP/IP Suite? (Continued)
Internet Protocol
Internet Control Message Protocol
RIP and OSPF
Transmission Control Protocol
User Datagram Protocol
Address Resolution Protocol
Domain Name System
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Domain Name System
ARP訊息交換
• DNS (not to be confused with Microsoft domains), is the
system that converts user-friendly names such as
www.lis.ntu.edu.tw to the correct IP address 140.112.180.250.
• A client first goes to one of the main DNS servers, which
tells the client which the server to contact for the domain.
• The client then goes to that server to resolve the full name to
an IP. This way the main servers only need to point a client to
a closer server.
• Administrators can then make changes to their computer
names any time they want without having to constantly
update a main server.
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File Transfer Protocol
• Simple Mail Transfer Protocol (SMTP) is
responsible for making sure that e-mail is
delivered.
• SMTP only handles the delivery of mail to
servers and between servers. It does not
handle the delivery to the final e-mail client
application.
– There are FTP servers and clients for almost every
operating system on the market.
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Dynamic Host Configuration Protocol
Dynamic Host Configuration Protocol
(Continued)
• When a computer comes online to the network, it
sends out a DHCP request.
• The nearest DHCP server responds with all the
information to set up TCP/IP on the new client.
• DHCP is responsible for automatic IP addressing.
DHCP can provide all configuration settings —
not just an IP address, but also a subnet mask,
default gateway, and so on.
• Once your network becomes large, keeping up with
IP addresses and settings can become an ordeal.
• Dynamic Host Configuration Protocol (DHCP) takes
over the job of assigning addresses and configuring
computers on the network.
• The DHCP server is given a range of IP addresses to
hand out to network devices.
• The range of IP addresses is also configured for the
network they will be given out on.
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Simple Mail Transfer Protocol
• File Transfer Protocol (FTP) is the file-sharing
protocol most commonly used in a TCP/IP
environment.
• This protocol allows users to remotely log on to
other computers on a network and browse,
download, and upload files.
• FTP is still very popular is that it is platform
independent.
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5
Telnet
Network File System
• Telnet allows a user to remotely log in to
another computer and run applications.
• The computer at which the user is
physically working effectively becomes a
dumb terminal — no processing is done on
that computer; it is only used for display.
• Telnet clients are available for almost every
operating system on the market.
• Network File System (NFS) is a more
advanced way to share files and disk drives
than FTP and Telnet.
• NFS allows users to connect to network
drives and use them as if they were local
hard drives.
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IPX/SPX Protocol Suite
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IPX/SPX Protocol Suite(Continued)
• While TCP/IP has many peer-to-peer functions,
IPX/SPX has none, as Novell did not need this
ability because their networks use the servercentric NetWare operating system.
• A main goal of the NetWare and IPX/SPX
development was user friendliness. The IPX/SPX
protocols and network applications are written so
the network environment is comfortable for users.
• IPX/SPX was created around the time the OSI
model was conceived,
• The Internetwork packet exchange/ sequenced
packet exchange (IPX/SPX) protocol suite was
developed and maintained by Novell, inc.
• The IPX/SPX protocol suite handles everything
from file and disk sharing to message and
application services.
• Most of the IPX/SPX functionality is aimed
toward requesting and receiving services from a
large server.
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IPX/SPX Protocol Suite(Continued)
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IPX/SPX Protocol Suite(Continued)
• The IPX/SPX suite is also very functional because
it is modular. That is, pieces can be removed and
replaced by protocols from other suites.
– As an example, you could remove the main IPX/SPX
protocols and replace them with User Datagram
Protocol (UDP) and TCP.
• The IPX/SPX protocol suite is its ease of use and
administration.
– The only real addressing needed is on the NetWare
server, and that is just to pick a network address not
found on any other connected network.
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Lower-layer protocols in the
IPX/SPX suite
Multiple Link Interface Driver
• Corresponding to the MAC sublayer function of
the Data Link layer, the Multiple Link Interface
Driver (MLID) protocol is concerned with media
access.
• Media access is the arbitration method devices use
to decide who can transmit on the media.For
Example:
• There are no protocols in the Physical layer
of the IPX/SPX suite because it can utilize
any popular physical network type.
• The protocols that work at the Data Link
layer are responsible for media access and
interfacing to the network card.
• There are two protocols in this layer:
– Token passing
– Polling
– Contention
– Multiple Link Interface Driver protocol
– Link Support Layer protocol.
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Multiple Link Interface
Driver(Continued)
• The other piece that makes up the IPX/SPX protocol
suite’s Data Link layer is the Link Support Layer (LSL)
software.
• It functions as the interface between MLID and the
upper-layer protocols.
• The Link Support Layer is responsible for making sure
data goes to the correct upper-layer protocols, should
multiple protocol stacks be loaded.
– Such drivers are written to a certain specification called
the Open Datalink Interface (ODI) specification.
• The MLID piece software driver is usually named
after the network card it supports.
– Examples:3Com 3C509 network card has the MS-DOS
MLID driver of 3C509.COM.
• Neither the MLID nor the LSL software are tied to a
specific proto-col.You could load TCP/IP or IPX/SPX
protocol stacks using these software drivers.
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Middle IPX/SPX suite
protocols
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• The Internetwork Pack Exchange (IPX) protocol
corresponds to the Network layer of the OSI model.
• IPX is responsible for connectionless data service. It
handles the routing of data across an internetwork, as
well as the logical network addressing.
• An IPX address is a combination of the physical MAC
address on the network card and a logically assigned
network address.
• IPX also uses socket numbers to successfully deliver
data to the correct upper-layer process on the
destination device. Socket numbers are the IPX/SPX
equivalent of TCP/IP port numbers.
IPX
SPX
NLSP
RIP
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Internetwork Packet Exchange
• The middle protocols in the IPX/SPX suite map to
the Network and Transport layers of the OSI
model, and are responsible for transferring data
between devices on the network, as well as
carrying some routing functionality.
• The protocols in this section are
–
–
–
–
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Link Support Layer
• MLID is a network interface board driver
specification — the piece of soft-ware that makes
the network card in a computer work.
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Sequenced Packet Exchange
Sequenced Packet
Exchange(Continued)
• Sequenced Packet Exchange (SPX) makes
up for the inherent unreliability of IPX.
• SPX is connection oriented,with sequencing
and error control.
• SPX rides on top of IPX to add this extra
functionality in a similar way that TCP rides
on top of IP in the TCP/IP suite.
• SPX is mainly used when a connection is made
across an internetwork device such as a router, or
to a print server to service a printing request. SPX
use acknowledgments to ensure delivery, where
IPX does not.
• SPX also establishes virtual circuits, called
connections, between devices. Each connection
has its own connection ID to distinguish it.
Connection IDs can be tied to upper-layer
processes.
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Routing Information Protocol
Network Link Services Protocol
• One protocol that IPX can use to decide the best route
through an internetwork is the Routing Information
Protocol (RIP).
• RIP is a very simple routing protocol that uses the
distance vector method to calculate hop count and then
chooses the route with the least number of hops.
• Network Link Services Protocol (NLSP) is a more
advanced routing protocol than RIP.It uses a link
state routing mechanism to choose the best route.
• In a link state routing protocol, the best route is
chosen using more information than just hop count.
Things such as latency and speed of the links
between the internetwork devices come into the
picture.
• Only broadcasts routing information when a
change occurs, not at a preset interval.
– No consideration is given for the speed of the links over
which the data would travel, just the number of hops.
• Another problem is that devices using this method
occasionally (every 30 or 60 seconds) broadcast their
routing information.
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Upper-layer IPX/SPX protocols
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NetWare Core Protocol
• NetWare Core Protocol (NCP) is the “language”
spoken between a NetWare client and a server.
• This protocol handles most network services,
including file services, printing, file locking,
resource access, and synchronization.
• NCP is a high-level language built into NetWare and
is used inside any lower-level protocol that accesses
the server.
• The two upper-layer protocols in the IPX/SPX
suite for use with NetWare are
– Netware Core Protocol
– Service Access Protocol.
• They cover multiple layers of the OSI model:
Netware Core Protocol corresponds to the
Transport, Session, Presentation, and Application
layers, and Service Access Protocol corresponds
to the Session and Application layers.
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– The commands are grouped into requests and replies. The
NCP commands are mainly concerned with file, directory,
and printer access.
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NetWare Core Protocol(Continued)
Service Access Protocol
• Servers using the IPX/SPX protocol are easy to set up
and maintain, thanks to the Service Access Protocol
(SAP).
• At a set interval, each computer sharing a resource on
the network sends out a SAP packet containing
information about the resource and where it is located.
• SAP can also become a problem. While allowing
clients to find servers without having to manually
configure every client for each server, the SAP
packets can quickly overrun a large network.
• NCP functions at the following four layers
of the OSI model:
– Transport layer: Connection services with
segment sequencing, error control, and flow
control
– Session layer: Session control
– Presentation layer: Character translation
– Application layer: Application and service
interface to the end-user application
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– Steps must be taken to filter out the excessive SAP packets
and keep them down to a manageable level.
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Microsoft protocols
NetBIOS
• NetBIOS was originally developed by IBM and
acts as an interface for applications to the network.
• It was made so that developers could easily use
this interface to write network-aware applications.
• NetBIOS is still very prominent today. Most
Microsoft systems use NetBIOS commands for
communications.
• Most file sharing and administration done on
Microsoft networks use the NetBIOS interface on
top of TCP/IP or IPX/SPX.
• Though Microsoft can use many standard
protocol suites, there are some protocols
that Microsoft uses almost exclusively.
• These are
– NetBIOS
– NetBEUI
– Server Message Block
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NetBEUI
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Windows Network Model
• NetBIOS Extended User Interface or NetBEUI
(pronounced net-buoy) is a small, very fast protocol
used in Microsoft networks.
• The main advantages of NetBEUI are
應用層
表達層
商議層
– speed
– ease of configuration.
傳輸層
• NetBEUI is one of the fastest protocols you can use
to share files.
• Configuration is simple because all that is needed is
a computer name — no network or logical addresses
are required.
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網路層
資料鏈結層
實體層
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Server Message Block
Wide Area Network Protocols
• The Server Message Block (SMB) protocol is a
Presentation layer protocol used by Microsoft
networking software to communicate.
• Once a communication channel has been established
with a protocol such as TCP/IP, a NetBIOS session
is made between the devices. The SMB commands
flow over this NetBIOS session.
• It provides the communication and commands
between the client and server to handle resource
requests and replies.
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• Suppose your company just merged with
another that had a remote office in another
state. We need to engineer a way to connect
your network to their network.
• We need technology to handle the
movement of data across these WAN
connections.
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Connection Types
Switched Connections
• Dedicated connections
• Packet switching
– In a dedicated connection, you have full use of the
connection as if it were a physical cable.
– The difference is that the service provider owns and
manages the “cable.”
– Packet switching takes the total message and divides it
into smaller chunks.
– These chunks are then routed through the network the
best way possible to reach the destination.
– Packet switching can also use virtual circuits
• Switched connections
– Switched connections take special hardware to manage
the connections, allow several people to use a connection
at once.
– You are only charged for the bandwidth used.
– Bandwidth could be limited
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• Circuit switching
– A “virtual” circuit between you and the other end is set
up dynamically for you to use.
– The advantage of circuit switching is you get the
features of a dedicated service without the price.
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Popular WAN Protocols
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• The local telephone company is responsible for all
communications between you and their local central
office (CO).
– The connection between the CO and you is known as the local
loop. This local loop is usually made up of UTP cable or, fiber
optic.
– Public switched telephone network
• ISDN
• SLIP and PPP
• xDSL
• Using the PSTN, several different connection types:
–
–
–
–
–
ATM
Switched Multimegabit Data Service
X.25
Frame relay
Synchronous Optical Network
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Public Switched Telephone Network
• WAN protocols allow you to route data over a large
internetwork.
• They carry TCP/IP and IPX/SPX through the internetwork
so they may deliver the data.
• The protocols covered are:
–
–
–
–
–
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Dial-up connections
Dedicated leased line
Switched-56
T-carrier System
Integrated Services Digital Network (ISDN)
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Dial-up connections
• The simplest and most common connection
over the PSTN
• You make one of these connections each
time you call up your Internet provider.
• Using a normal modem, speeds can reach
up to 56Kbps.
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Dedicated leased lines
Digital Leased Lines
• Leased lines are either analog or digital.
• Analog leased lines are basically just a dialup connection that is connected all the time.
• Faster than analog lines
• Not as error prone as analog lines
• Digital leased lines are usually called Digital Data
Service (DDS) lines.
• They require special digital equipment to be used,
which is called Channel Service Unit/Data Service
Unit (CSU/DSU).
• The CSU/DSU is connected to the digital line and
to your LAN.
– They use standard modems at each end.
– They have the same speed-limiting problems as
normal dial-up connections.
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T-carrier system
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T-carrier system (Continued)
• Originally designed in the 1960s to handle multiple
voice calls at once, the T-carrier system is now used
in data communications.
• The T-carrier system uses devices called
multiplexers, or MUXes, to combine multiple
communications into one. At the other end, another
MUX separates the different communications.
• The basic T-carrier system is a T1. A T1 is composed
of twenty-four 64Kbps channels that can be
combined for a total bandwidth of 1.544Mbps.
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T-carrier system (Continued)
T-carrier system (Continued)
• One big feature of T-carrier is that the channels can
be split so that some are used for voice traffic and
some for data.
• These 64Kbps channels are called Digital Signal
Level 0 (DS-0) signals. A full T1 line is also known
as a DS-1, or in European an E-1.
• T1 lines use standard copper cable, whereas the T3
and T4 lines use fiber optic. (T2s are not offered to
the public.)
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• Fractional T1 (or Fractional T3 if you need
more than a T1).
– With this line, you can get as many of the DS-0
lines as you need without getting all twentyfour in a DS-1.
– A special CSU/DSU and a router or bridge is
required on both sides of the connection.
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SLIP
PPP
• Serial Line Internet Protocol (SLIP) is an older
protocol used to handle TCP/IP traffic over a dialup or other serial connection.
• SLIP is a Physical layer protocol that doesn’t
provide error checking, relying on the hardware to
handle this.
• It also only supports the transmission of one
protocol, TCP/IP.
• CSLIP--the protocol actually just reduces the
amount of information in the headers, and does
not compress the transmission.
• PPP provides a Physical and Data Link
layer functionality that fixes many problems
with SLIP.
• Basically, your modem is transformed into a
network card, as far as upper-level protocols
are concerned.
• At the Data Link layer, PPP provides error
checking to ensure the accurate delivery of
the frames that it sends and receives.
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ADSL
(Asymmetric Digital Subscriber Line)
PPP(Continued)
• 非對稱數位用戶迴路
• 利用調變技術，藉由普通電話用的雙絞
銅線傳輸，將現有的電話線上加裝ADSL
數據機，利用ADSL寬頻技術，以高於
512 Kbps以上的速率上網或進行資料的
傳輸。
• ADSL用戶上網時並不佔用傳統電話的頻
帶，亦即上網與打電話可同時進行，不
會互相干擾。
• PPP also keeps a Logical Link Control
communication between the two connect devices
by using the Link Control Protocol (LCP).
• PPP also lets you use almost any protocol you
want over the link.
• PPP also supports the dynamic configuration of
the dialed-in computer.
• Most Internet dial-up connections today are made
using PPP over modem or ISDN.
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Frame relay
ADSL (Continued)
• Frame relay took the features of X.25 and stripped
out the error control and accounting.
• Frame relay uses Permanent Virtual Circuits (PVC)
to establish connections ahead of time.
• ADSL的上行與下行的頻寬是不對稱的，
下載速率為1.5Mbps～9Mbps，上傳速率
為64Kbps～到640Kbps，由於上傳與下載
速率不同因而稱為非對稱。
• 從網路提供者到用戶家中的頻寬是比較
高的，符合了一般使用網際網路的使用
習慣與特性，也就是說使用者接收的資
料量遠比其送出的資料量來得多。
Language & Information Processing System, LIS, NTU
– Packets can now just have the PVC number attached to
them and be sent through the frame relay network.
– Frame relay can reach speeds of 1.544Mbps.
• A nice feature of frame relay is its ability to
guarantee bandwidth and then occasionally exceed
that amount when needed.
• The physical connection requires a frame relay
CSU/DSU and a bridge or router.
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• There are two types of ISDN:
• ISDN allows you to send voice, data, and
video over normal copper telephone lines
by sending digital signals instead of analog.
• ISDN uses 64Kbps channels, called B
channels, for data transfer. It also has a 16K
channel, called the D channel, for call setup
and control information. It is also possible
to send X.25 data over the D channel.
– Basic Rate Interface (BRI): BRI is intended at home
users and small offices. It consists of two B channels and
one D channel for a total data bandwidth of 128Kbps.
Each B channel can be used separately.
– Primary Rate Interface (PRI): PRI is mainly for larger
organizations that need high bandwidth connections. It
provides twenty-three B channels and one D channel for a
capacity of 1.544Mbps, the same as a T1 line. B channels
can either be used for voice or data.
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Asynchronous Transfer Mode
ATM (Continued)
• ATM is a new packet-switching technology
aimed at real-time applications, such as
voice and video over data lines.
• ATM uses a different type of switching
called cell switching.
• ATM uses switches to quickly move the
cells across a network. When a connection
needs to be made to a distant device over
ATM, a virtual connection is set up through
the switches.
• For the duration of the virtual connection,
the cells only need this connection number
in the header to designate their path through
the network.
– It uses a fixed packet size of only 53bytes, 5 of
which are header information.
– Each of these 53-byte packets are called cells.
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ISDN (Continued)
Integrated Services Digital Network
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Synchronous Optical Network
• Synchronous Optical Network (SONET) specifies
how to deliver voice, data, and video over WAN
connections at speeds in excess of 2Gbps.
• It is a Physical layer standard that defines the
transfer of data over fiber-optic media.
• SONET links are rated in what are called optical
carrier levels (OC).
– The base OC-1 is rated at 51.8Mbps.
– Each additional OC level is calculated by taking the level
and multiplying it by the OC-1 speed.
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