networks i chapter 15. chapter objectives understand basic network terminology. understand the...

Networks I

Chapter 15

Chapter Objectives• Understand basic network terminology.• Understand the basics of the TCP/IP protocol suite.• Understand the basics of IP addresses.• Understand basic IP routing.

– Understand the basics of ARP, and DNS.– Understand the basics of layer 2 and layer 3 “routing”.

• Understand common network hardware.

Network Protocols

• Internetworking - the process of connecting two computer networks together.– The interconnected networks may or may not use the

same network technology.– The interconnected networks may or may not be in the

same location.– The interconnected networks may or may not encompass

the same hardware.– The interconnected networks may or may not employ the

same software.– The Internet is one example of internetworking.

Network Protocols

WARNING:Networking seems to encompass every two,

three, four, five, and six character combination of letters into an acronym.

Network Protocols (ISO)– The International Standards Organization adopted a

networking model called the Open System Interconnect.

– This network model breaks the task of networking down into seven layers (then arranged them like a top-ten list):

• 7) Application layer - Provide end-user services• 6) Presentation Layer - Deal with problems & compression• 5) Session Layer - Authentication and Authorization• 4) Transport Layer - Guarantee end-to-end (correct) delivery• 3) Network Layer - Routing and Accounting• 2) Data Link Layer - Transmit/receive packets & addressing• 1) Physical Layer - The cable or media itself

Network Protocols (ISO)• The ISO/OSI model was the result of design by committee.• The layers had little base in reality: They did not match real-

world protocol stacks.• The ISO/OSI model suffered a horrible “death” (nobody

could make it work).• Network theory courses still hold the ISO model up as the

“right way to do things.”

Network Protocols (TCP/IP)• Internet Protocol (TCP/IP model)

– The TCP Protocol is designed around a simplified four layer approach:

• Link Layer - Network hardware and device drivers• Network Layer - Basic Communications, addressing, routing

– The network layer protocol is the Internet Protocol (IP).• Transport Layer - Communication among programs on a net.

– There are two data Transport protocols In TCP/IP:» User Datagram Protocol (UDP)

» Transmission Control Protocol (TCP)

• Application Layer - End user application programs– Utilities like ftp, ssh, rlogin, rsh, DNS, NFS, CIFS, …

Network Protocols (TCP/IP)

Network Protocols (TCP/IP)• In order for all of the computers on the Internet to communicate, we

have to:– Ensure that the computers speak the same language.

• The language used on the Internet is TCP/IP.– IP is the Internet Protocol

» IP provides a communication channel, including addressing, and routing.

– TCP is the Transmission Control Protocol.– UDP is the User Datagram Protocol..

» TCP and UDP provide data delivery over the IP channel.

– Ensure that each network device has a unique address.– Ensure that the computers have access to some form of

bridging hardware in order to connect dissimilar network technologies.

Network Protocols (TCP/IP)• Internet Protocol (Packets)

– As a packet travels through the levels of the TCP/IP protocol, each layer adds it’s own header information to the datagram.

• This process of each layer encoding it’s own management information into the existing datagram is called nesting, or encapsulation.

– Various headers contain the source and destination address, checksum, protocol specific information, and other handling instructions.

– At the receiving end the headers are stripped off by the appropriate level, the header contents are examined for special handling information, and the datagram is delivered to the appropriate application.


• Internet Protocol Version 4 (IPv4)– An IP address consists of four byte values separated by

periods. For Example: 123.45.67.89

– This notation is also known as the dotted quad format.

– Each of the values must be in the range of 0 - 255 (8 bits).

– An IPv4 address is therefore 32 bits (4 bytes * 8 bits/byte).• There are five classes of IP Addresses in IPv4:

– Class A, B, and C addresses are used for single host addressing. – Class D addresses are used for multicast connections.– Class E addresses are experimental.

Network Protocols (TCP/IP)• Internet Protocol (IPv4)

• Class A Networks - The first byte is in the range of 1 - 127.– The first four bits of the address are Binary 0 X X X– There are 127 Class A networks. – The first byte of a class A address is the network

number.– The remaining three bytes are the host address on that

network.

110 .32.4.18

network host address

– Each Class A network can address up to 16 million hosts.

– All Class A networks are currently assigned and in use. (lie)!

Network Protocols (TCP/IP)• Internet Protocol (IPv4)

• Class B Networks - The first byte in the range of 128 - 191.– The first four bits of the address are BINARY 1 0 X X– There are 16,384 Class B networks. – The first two bytes of a class B address are the network

number.– The remaining two bytes are the host address on that

network.

129.74. 25.98network host address– Each Class B network can address up to 65,000 hosts.– Notre Dame holds a Class B license (129.74.X.Y)– All Class B networks are currently assigned and in use. (lie)!


• Internet Protocol (IPv4)• Class C Networks - The first byte in the range of 192 - 223.

– The first four bits of the address are 1 1 0 X– There are 2,097,152 Class C networks. – The first three bytes of a class C address is the network

number.– The remaining byte is the host address on that network.

210.43.2 .8

network host address

– Each Class C network can address up to 254 hosts.

– Most of the Class C networks are assigned and in use.


• Internet Protocol (IPv4)• Class D Networks - The first byte in the range of 224 - 239.

– The first four bits of the address are 1 1 1 0– These addresses are used for “one to many”

communications (multicasting). • Class E Networks - The first byte in the range of 240 - 254.

– The first four bits of the address are 1 1 1 1– These addresses are reserved for experimental use by

the IANA/IETF.

Network Protocols (TCP/IP)• The numbers 0, and 255 have special meaning in some

fields of IP addresses. – A Zero host address refers to “this network”

• For example 129.74.0.0 refers to the Class B network 129.74.

– A host address of all ones is called the broadcast address.

• For example 129.74.255.255 refers to all hosts on the 129.74 Class B network.

• The address 127.0.0.1 is the loopback address. – This address is used for inter-process communications, and

for network testing.– All of the 127 network is reserved (127.0.0.0 -

127.255.255.255).

Network Protocols (TCP/IP)• Subnets and Supernets

– Subnets provide a way of chopping up large networks into smaller entities:

– Networks might be split up to segment traffic.– Networks might be split up to facilitate better use of an

assigned IP address space.• A class A could be made to look like several class B/C networks.• A class B could be made to look like several Class C networks.• Even a Class C network can be sub-networked.

– To subnet a network, we apply a netmask.• Standard netmask for Class A is 255.0.0.0• Standard netmask for Class B is 255.255.0.0• Standard netmask for Class C is 255.255.255.0

– By logically ANDING the address and the netmask, we can determine the NETWORK portion of the address.

Network Protocols (TCP/IP)• Subnets• Network routers look at the destination IP address, and the netmask for

the address to make delivery (routing) decisions. – Once the router determines the class of the destination address, it

consults a table to find the appropriate netmask.• Class A netmask is 255.0.0.0

• Class B netmask is 255.255.0.0

• Class C netmask is 255.255.255.0

• For example, a packet bound from a random host on the Internet, to my office host would generate the following operation:– 129.74.25.98 = 10000001 . 01001010 . 00011001 . 01100010– 255.255.0.0 = 11111111 . 11111111 . 00000000 . 00000000

10000001 . 01001010 . 00000000 . 00000000

== 129.74.0.0 or 129.74/16

Network Protocols (TCP/IP)• The lab 129.74.46 network is subnetted into several

smaller networks.– By “stealing” bits from the host number, we can make the network

number larger. This allows us to make a class B or C network look like many smaller (classless) networks.

• These networks are denoted by the formula N.S.H (network.subnet.host)

– By using a 27 bit netmask we can divide a network up into several “32” host networks. 11111111 . 11111111 . 11111111 . 11100000

• 27 bits of network address, 5 bits of host address.– 129.74.46.0 through 129.74.46.31 is one such network.– 129.74.46.32 through 129.74.46.63 is one such network.– 129.74.46.64 through 129.74.46.95 is one such network.

• 129.74.46.32/27 denotes a host on a classless network which employs a 27 bit netmask.

• This is referred to as Classless InterDomain Routing (CIDR)

Network Protocols (TCP/IP)• Subnets and Supernets

– Supernets allow us to aggregate several smaller networks into one larger routing entity:

• This is the opposite of subnetting.– Supernetting is employed to minimize routing table

entries.» If an ISP has a customer who needs addresses for 400

hosts, a single class C address will not suffice.» By combining two class C networks, the ISP can make a

single routing entity:» 203.14.7.0 = 11001011 00001110 00000111 00000000» 203.14.6.0 = 11001011 00001110 00000110 00000000» The first 23 bits are the same for both addresses so the ISP

can advertise a single external route:» 203.14.6/23» This only works if the ISP also owns 203.14.4.0 and

203.14.5.0.

Network Protocols (TCP/IP)• Classless Inter Domain Routing (CIDR)

– CIDR is the result of incorporating subnetting and supernetting into the classful IP address structure.

• We are no longer limited to class A, B, and C addresses.• By passing the netmask along with the address we can

make arbitrarily large/small networks, as we see fit, to simplify routing and network design.

– CIDR allows simplified routing tables.– CIDR is the basis of IPv6.– You may also hear the term Variable Length Subnet

Mask (VLSM). • This is the practice of using various length subnet masks

within a single network domain.


• Internet Protocol (IPv4 trivia)– We are running out of addresses under the current (IPv4)

addressing scheme.– If every class A, Class B, and Class C network address was in

use using classful addresses, there would be ((127 * 16,000,000) + (16384 * 65,000) + (2,097,152 * 254)) (or 3,629,636,608) hosts on the Internet. (3.6 gigahosts)

• The remainder of the addresses are the “zero”, and “broadcast hosts (overhead).

• If subnetworking is in use, even more of the address space is lost to “overhead”.

– Real Soon Now a new version of IP will be released. This version is known as IPV6 (Internet Protocol version 6).

Network Protocols (TCP/IP)• IPv6

– Addresses go from 32 bit to 128 bit.– Addresses will be colon separated hexadecimal quads:

• 0xFEDC:BA98:7654:3210:0123:4567:89AB:CDEF• 0x0000:0000:0000:0000:0000:FFFF:222.33.44.55

– Shorthand ::FFFF:222.33.44.55– IPv6 will not contain address classes – but prefix ranges

will have meaning (geographic regions).– IPv6 will use multicasts instead of broadcasting.– IPv6 will use CIDR routing– IPv6 will facilitate data encryption– IPv6 contains provisions for new services (bandwidth

reservation, guaranteed signal quality, more multicasting)– IPv6 will provide 340 undecillion addresses

• 340 with 24 zero’s after it

Network Protocols (TCP/IP)• Internet Protocol (packet delivery)

– The Internet protocol actually uses multiple layers of addressing to deliver packets.

• Protocol addressed packet delivery is referred to as ISO Layer 3 (Network layer) routing.

• In addition to the IP address, each network adapter card is assigned a unique hardware address (Media Access Controller or MAC address).

• Ethernet MAC addresses are 6 bytes long.• MAC addresses of other network technologies vary from 2 bytes

to 20 bytes in length.

– The mapping between the MAC address and the IP address is handled at the Link Layer of the TCP/IP stack by the Address Resolution Protocol (ARP).


• Address Resolution Protocol– By design, the network interface (the board in the host) wants

to communicate with another network interface board.• Network interface boards work with multiple protocols.• This means that they must have a way of addressing other NICs

that is independent of the software protocol address.• All packets on the media are addressed to another MAC

address.

– If the packet is bound for a host not known to the local host what happens?

• One way to resolve such a MAC address is for the host to send out a broadcast packet saying “Hi, I’m at MAC address x:y:z:a:b:c, how do I get to MAC address f:g:h:i:j:k?”.

– If the host with address f:g:h:i:j:k is on the same network, it will reply and the address is resolved.

Network Protocols (TCP/IP)• Otherwise an intermediate can be programmed to reply “send the

packet to me, and I will forward it for you.” – In this case the packet is sent from the host’s MAC address

to the MAC address of the intermediate!

• source addr = host MAC, • destination addr = intermediate MAC

– The intermediate then forwards the packet on the way to the final destination.

• source addr = intermediate MAC, • destination addr = next hop MAC

– The host software maintains a table (the ARP cache) of these MAC addresses.

• This is ISO layer 2 (Data Link Layer) routing (switching)

Network Protocols (TCP/IP)Net to Media TableDevice IP Address Mask Flags Phys Addr------ -------------------- --------------- ----- ---------------hme0 morticia.cse.nd.edu 255.255.255.255 00:05:02:20:dd:bahme0 wizard.cse.nd.edu 255.255.255.255 08:00:20:10:0c:6ahme0 penny.helios.nd.edu 255.255.255.255 00:60:2f:88:da:63hme0 banzai.helios.nd.edu 255.255.255.255 00:60:2f:88:da:63hme0 bind.nd.edu 255.255.255.255 00:60:2f:88:da:63hme0 buckaroo.helios.nd 255.255.255.255 00:60:2f:88:da:63hme0 john.helios.nd.edu 255.255.255.255 00:60:2f:88:da:63hme0 authors.helios.nd.ed 255.255.255.255 00:60:2f:88:da:63hme0 lizardo.helios.nd.ed 255.255.255.255 00:60:2f:88:da:63hme0 hub25-1a.hub.nd.edu 255.255.255.255 08:00:44:0c:17:7dhme0 grumpy.cse.nd.edu 255.255.255.255 SP 08:00:20:7e:80:69hme0 BASE-ADDRESS.MCAST.NET 240.0.0.0 SM 01:00:5e:00:00:00

Network Protocols (TCP/IP)• Internet Protocol (packet addressing)

– IP addresses identify machines. • This allows us to get a datagram from one host to another.

– How do we deliver data to programs and services on these hosts?

• The TCP and UDP protocols extend the IP addressing concept through the use of “ports”.

– A port is a two byte number that identifies a particular service.

– These port numbers are mapped to services through the /etc/services file.

– Ports with numbers less than 1024 are called privileged ports.

» These ports are (supposed to be) only accessible by root, in an attempt to prevent impostors.

Network Protocols (TCP/IP)• Internet Protocol (packet addressing)

– Because humans have a difficult time dealing with all of these numbers (MAC address / IP address / Port number), the computers/services are also allowed symbolic names.

– Computers do not understand these names…the computer wants to work with numbers.

• The names are mapped to numbers by a variety of means.

– The most commons means of mapping system names to IP addresses are the /etc/hosts file, Network Information Services (NIS), and the Domain Name Service (DNS).

– I will talk more about how these name services work in a few days.

Other Protocols• NetBEUI

– Net Bios Extended User Interface• An extension of NetBIOS.• Not a routable protocol, as it has no network layer.• Can have bridged networks, but not routers.• Relies on broadcasts for many functions.• Connection Oriented - Connectionless

communications• Self configuration - self tuning• Error protection• Small memory overhead• Active Directory cannot use NetBEUI.

Other Protocols

• NetBIOS over TCP/IP (NBT)– Replaces NetBEUI, allows applications to use TCP/IP

• Winsock– Interface between socket based applications and TCP/IP.

• Server Message Block (SMB) networking.– Used in previous versions of Windows.– Basis for Windows file and print sharing.– Uses NetBEUI - not routable.– Relies on Windows Internet Naming Services (WINS).– Being replaced by Common Internet File Service (CIFS).

• TCP/IP based networking for Windows!• Both SMB and WINS are unpublished protocols.

– Can change on a whim!

Other Protocols• AppleTalk

– Originally developed by Apple as a printer sharing protocol. – Later expanded to allow more complete network services.– Very little administration required.

• Hardware address is used, no IP address required.• Plug in a new machine, and it works!

– The new node sends a broadcast packet that says “Hi!, I’m Joe. I want to use address X. Does anyone object?”

– If there is no objection, Joe is now at address X.– If there is an objection, the node with the lowest address

sends back a message stating “Hello Joe. I’m sorry, but you will have to use Y as your address, as X is already in use.”

– Routers are very complex.– Works with a variety of hardware and media.

• Twisted pair, coaxial cable, Ethernet, PC’s UNIX hosts.

Other Protocols

• EtherTalk– Actually AppleTalk over Ethernet.– Two flavors are available:

• Phase 1 was Apple’s first Ethernet network. It was very buggy, and tended to flood the network with broadcast packets. Phase 1 also had it’s own packet types which were not known by TCP/IP.

• Phase 2 changed the broadcast packets to Multicast packets, and encapsulated their odd packets as acceptable packets.

Other Protocols• LocalTalk

– Is actually Apple’s AppleTalk protocol implemented on twisted pair cabling.

• AppleTalk was originally implemented with an odd coaxial cable.

– Network speed reaches a blazing 230 Kilobits/second!– LocalTalk allows star topology with active or passive

hubs and multiple hosts on a leg.– Ethernet to LocalTalk bridges are very common.– MacIP is used to encapsulate Ethernet packets in

LocalTalk packets.

Other Protocols• AppleTalk

– AppleTalk addressing uses a multi-layer address system like IP.

– The MAC address is hardware based. – The Node number is dynamically assigned by AppleTalk

Address Resolution Protocol (AARP).– AppleTalk networks are grouped into zones.– Each AppleTalk entity has an object name (Billy Bob’s

Office Printer), an object type (LaserWriter) as well as the zone name.

– The zone entities are bound to network and node numbers by the AppleTalk Name Binding Protocol (ANBP).

Other Protocols• IPX

– IPX is the Internet Packet Exchange Protocol.– IPX was developed by Novell for the NetWare product.

Novell is the most common network protocol in use for PC’s.

– Novell is in the process of converting the Novell Network to use TCP/IP protocol.

– Current IPX implementations use standard Ethernet packet headers.

– Older versions of IPX used non-standard Ethernet packet headers, and would not co-exist on a network with non-IPX Ethernet packets.

Other Protocols

• IPX– IPX was derived from The Xerox Network System

Internet Datagram Protocol (XNS IDP).– IPX uses a UDP like packet type. Headers have an

unused checksum field, a packet length, packet type, a hop count, and the network, node, and socket numbers of the source and destination machines.

– IPX packets are thrown away after 15 hops!– IPX is not a standardized protocol! It is a proprietary

protocol and is subject to frequent unannounced changes.

– Novell Loadable Modules (NLM’s) are available to add functionality to Novell IPX based networks.

Other Protocols• IPX

• The IPX protocol has many “helper” protocols:

– Routing Information Protocol (RIP)

– Sequenced Packet Exchanger : reliable delivery (SPX)

– ECHO (a packet echo facility)

– ERRORS (an error reporting facility)

– Packet Exchange Protocol (PEP)» VERY inefficient, as it requires an ACK for each packet

before the next packet is sent!

» On top of PEP are the Network Core Products which provide authentication, file service, RPC, print spooling, accounting).

– Service Advertisement Protocol (SAP) (address broker)

Other Protocols• DECnet

– DECnet is an implementation of the Digital Network Architecture (DNA)

– DECnet first appeared in 1974. The first version to support Ethernet was DECnet phase IV released in 1984.

– DECnet Phase V was released in 1991 and is referred to as DECnet/OSI. It supports TCP/IP, OSI, and Digital’s Network Services Protocol (NSP).

Other Protocols

• DECnet– DECnet Addressing is somewhat different from the other

protocols:– DECnet addresses are independent of the transport

media.– A DECnet address is a one byte “area” and a two-byte

node number. • An area is a logical grouping.

– One area may equate to one or more networks. – One network may contain one or more areas.

• The machine’s address is derived from the area and node number, not the hardware MAC address.

• All interfaces on the system use the same address!

Other Protocols

– DECnet• Until DECnet Phase V all routing tables were static. • Static routing limited DECnet to small network

configurations.– DECnet Phase V implemented dynamic routing via

DECdns which is actually a distributed routing protocol.• The routing is performed by DECnet routers.• A level one router routes information within one area.• A level two router routes information between two

areas.

Protocol Translators• As you may have guessed by now, there are ways to make systems

running these “other” protocols talk to a TCP/IP network. – Some of these protocols include TCP/IP modules.– Other protocols use a trick called “tunneling” to allow them to “talk

on” TCP/IP networks. Tunneling is a form of packet encapsulation.• In order for tunneling to work, the source and destination

machines have to be on the same type of network. – There may be one (or many) other types of networks

between these two hosts and their networks.– Another method of interconnecting dissimilar networks requires

special hardware/software which acts as a translator (bridges).

Network Hardware• Working With Current Network Hardware

– So far all we’ve talked about is the software side of networking.

• We saw that there are many different protocols in use on current communications networks.

– There is also a hardware component to networking. • Unfortunately, there are almost as many hardware standards as

there are protocols.• We will talk about four types of network hardware:

– Ethernet– Token Ring– FDDI (token ring in disguise)– ATM


• Network hardware has to take proximity into account. – Local Area Networks (LANs) consist of machines in close

proximity to each other. Example: Notre Dame campus, or networking within a small company building.

» LANs typically employ high speed technologies ( 1Mb - 10 Gb / second throughput).

– Metropolitan Area Networks (MANs) - consist of machines within a metropolitan area. Notre Dame could also be considered a Metropolitan Area Network.

» MANs typically operate at lower speeds (56 Kb - 622 Mb / second throughput).

Network Hardware

• Working With Current Network Hardware–Wide Area Networks (WANs) consist of

machines separated by large distances. Example the Internet.

» WANs typically operate at rates of 56 Kb to 622 Mb / second throughput.

• The type of hardware selected for a network must be capable of working within the boundaries of the particular network.


– Ethernet - developed by Xerox in the 1970’s.

• Still has bugs!• Ethernet is the most common network technology.• Ethernet employs Carrier Sense Multiple Access with Collision

Detect to determine who gets to talk at any given time.• Ethernet does not include built-in error detection/correction. That

is left to the software!• Most of the protocols we discussed run on Ethernet hardware.• Ethernet is a LAN technology that the users wanted (desperately)

to become a WAN technology.

Network Hardware

• Working With Current Network Hardware• There are many flavors of Ethernet available:

– 802.5 - Thicknet - 10Base-5 - Screaming Yellow 50 Ohm Coaxial cable.

» Attachment Unit Interface (AUI) connectors (DB15).

» This is the oldest form of Ethernet. » Length Limit 500 Meters / segment. » Up to three segments connected via repeaters.» 10 Mb/s shared bandwidth


–802.2 - Thinnet - 10Base-2 - cheapernet,

»Cheap coaxial cable»cheap BNC style connectors. »length limit: 200 Meters/segment. »Up to two segments connected via

repeater.»Multiport repeaters allowed.»10 Mb/s shared bandwidth

Network Hardware

• Working With Current Network Hardware• 10Broad36 - Broadband Ethernet.

–Not used very often

–EXPENSIVE

–Multiplex Ethernet packets onto a broadband carrier system.

–36 Kilometer length limit

–Cable modems use similar technology.


• 10BaseF - Fiber based Ethernet. –Two fibers required (one for transmit, one for

receive)–Optical to copper repeaters handle the collision

detection.–Typical segments 2.2 Km maximum.–Multiple segments may be connected via

repeaters–Two repeaters/route maximum–10 Mb/s shared bandwidth


• 10 BaseT - Twisted pair Ethernet – Category 4 or Category 5 twisted pair wiring, or fiber.

– Star topology - all hosts connect to hubs/routers/switches.

– Length limit: 100 meters per connection, 500 meters between the two most distant hosts (if shared bandwidth).

– Cheap RJ45 connectors (telco style)

– 10 Mb/s shared or switched bandwidth» Switched connections allow full 10Mb/s to the host

instead of shared bandwidth.» Connections can be “full duplex”


• 100BaseT - Twisted pair Ethernet

– Category 4 or category 5 twisted pair wiring, or fiber.

– Star topology - all hosts connect to hubs/routers/switches.

– Length limit: 100 meters per connection

– Cheap RJ45 connectors (telco style)

– 100 Mb/s switched bandwidth» Switched connections allow full 100Mb/s to the host

instead of shared bandwidth. Half, or Full Duplex connections.

Network Hardware

• Working With Current Network Hardware– Token Ring Networks

• Token Rings utilize a special data structure called a token to determine who gets to talk.

• Token Rings are typically built on a copper based media.

• Token Rings are very common on PC systems, but not found very often on UNIX systems (with the exception of FDDI/CDDI).

• Token Ring systems have two modes of operation: receive and transmit.

• Typical Token Rings run at 1, 4, 10, or 16 Mbit/second.

Network Hardware

• Working With Current Network Hardware– Fiber Distributed Data Interconnect (FDDI)

• FDDI is a token ring in disguise.• FDDI uses fiber optical cabling instead of copper. Copper

Distributed Data Interconnect (CDDI) is FDDI over copper.• FDDI is capable of 100 Mbit/second data rates.• Single Attachment Stations (SAS) require a pair of fibers and

have little fault tolerance.

– SAS FDDI networks are star-topology networks.• Dual Attachment Stations (DAS) provide for fault tolerance and

require two pairs of fibers.

– DAS FDDI networks are ring topology networks.


– Automatic Teller Machines (ATM)

• ATM networks have been in use for many years by the banking industry.

• Users put a card in a slot and can magically get money out of the ATM machine.

– OOPS. Sorry. Wrong ATM!

Network Hardware• ATM is part of a larger network:

– SONET (Synchronous Optical Network) is used for (extremely) high speed connections between telephone switches.

• Current Telco operations can handle 100 Gigabit/second over SONET.

• Test frames currently running at 350+ Gb/second!

– Computer network hardware is available which allows you to use SONET connections between systems.

– SONET is VERY expensive!


– Asynchronous Transfer Mode (ATM)• The basic foundations for ATM were developed by people who

know about wide area networks and packet switching: Long Distance Telephone carriers.

• ATM is the underlying technology behind the Broadband Integrated Services Digital Network (B-ISDN).

– B-ISDN is part of the “send a fax from the beach, tuck your kids into bed from around the world” technology.

• ATM is currently running with 622Mbit/second links.

– High-end Internet links are running at 155 Mbit/second.– NOTE: Most hosts cannot drive such links at speeds over

350 Mbit/second.


• ATM comes in a variety of speeds. For example:

– 25 Mbit/second IBM standard

– 45 Mbit/second Digital Service-3 (DS3) (T-3)

– 51 Mbit/second SONET(OC-1)

– 100 Mbit/second Taxi interface

– 155 Mbit/second Optical Carrier-3 (OC-3)

– 622 Mbit/second Optical Carrier-12 (OC-12)

– 1.2 Gbit/second Optical Carrier-24 (OC-24)

– 2.4 Gbit/second Optical Carrier-48 (OC-48)

• Speeds are based on Telco transmission rates.


– ATM encompasses the Integrated Services Digital Network (ISDN), • ISDN is used for (relatively) high speed connections to homes

and businesses. A typical ISDN connection is actually a multiple-channel connection over telephone wire.

– ISDN uses two B channels, and a D channel.

– The B channels are 64 Kb/second data channels.

– The D channel is a 9.6 Kb/second signaling channel.

– Current technology allows you to “bond” the two B channels together and use 4x data compression to get throughput up to 512 Kb/second.

Network Hardware

• Working With Current Network Hardware– xDSL technology (new) is similar to ISDN.

• ADSL (Asymmetric Digital Subscriber Loop) has one channel running at high speed, and one running at low speed (for example 512Kb/sec one direction, and 128 Kb/sec the other direction).

• ADSL has been tested at rates up to 1.544 Mbit/second (same speed as a T1 link).

• ADSL runs over standard telco wiring (ISDN and DSL require some tweaks to run over telco infrastructure).


– Because ATM is a telephone protocol, it has some odd “features” when used for data networking.

• ATM is a connection oriented service. No packets can be sent until a channel is opened.

– Ethernet/FDDI/Token Rings are all “connectionless”. – IP is also connectionless.

• ATM sends/receives fixed length data cells, as opposed to the other technologies we discussed which send/receive variable length packets.

– Ethernet exchanges 64 - 1500 byte packets– FDDI exchanges 64 - 4500 byte packets– ATM exchanges 53 byte “cells”

» Each cell has a 5 byte header and 48 data bytes.


– ATM

• Fun with International Standards:– The European telephone industry wanted ATM to use

16 byte cells for voice traffic, but would compromise up to 32 bytes.

– The United States telephone industry wanted 128 byte cells for data, but would compromise down to 64 bytes.

– The CCITT split the difference, and ATM cells were defined to be 48 bytes.

» Because headers were already defined as no more that 10% of the cell, headers became 5 bytes.

Network Hardware– ATM

• Result:– The ATM cell size is a poor choice for voice

(packets are too big; bandwidth is wasted) – The ATM cell size is a poor choice for data

(packets are too small; bandwidth is wasted with excessive overhead).

– Welcome to the fascinating world of International Standards!

Summary

• Configuration, management, and troubleshooting network connections is a major portion of any system administrator’s job. The system administrator needs to:

• Understand basic network terminology.• Understand the basics of the TCP/IP protocol suite.• Understand the basics of IP addresses.• Understand basic IP routing.

– Understand the basics of ARP, and DNS.– Understand the basics of layer 2 and layer 3 “routing”.

• Understand common network hardware.

networks i chapter 15. chapter objectives understand basic network terminology. understand the...

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