Makes the complexity more manageable sub-layers

Uses standard interfaces to increase interoperability

Developers can change one feature in a layer without changing all the code

Allows for specialization which helps industry growth

Eases troubleshooting

Application- layer 7- checking availability of com partner and if resources are available

Presentation-layer 6-encryption- format- handles data compression, decompression, encryption and decryption- some standards are ANSI, PICT,MPEG, JPEG, MIDI, TIFF

Session – layer 5-coordinates comm (synchronizes) w) other nodes. Three modes. Simplex-like telegraph, Half-duplex-takes tunes tran and rec like speaker phone and full-duplex-transmits both ways same time. Has three phases: connection establishment-contact is secured and devices agree upon com parameters and protocols, data transmission and connection release.

Examples of session layer protocols are: NFS, SQL, RPC, Xwindows, ASP, DNA SCP

Transport- layer 4-segment and reassemble data. Provide end-to-end transport services and establish a logical connection. Provide mechanisms for muxing, session establishment ,and tear down of virtual circuit. Data integrity is ensured at this layer by maintaining flow control and letting users request reliable transport between systems- FLOW CONTROL- prevents buffer overflow from too much data too fast.

Delivered segments get and ACK, Non received segments are re-quested. Segments are re-sequenced. Data flow is managed

Network- layer 3- routing-path finding-finding the best path helps reduce traffic thus improving network performance. it examines the packet header to determine destination address (DA) after it picks the path- it re-encapsulates adding next hp info. It reads datagrams from local PC and forwards packet to next DA. When the router at the destination receives the packet it puts it in a FRAME with the MAC address and sends.

Datalink- layer 2- ensures deliver to proper device. Translates to bits. Formats in FRAMES with customized header with hardware destination and source address. Encapsulates:

1)Preamble or Start indicator is special bit pattern which alerts devices of beginning data frame.

2)The DA, 3) then SA

4) Ethernet_II then have 2bit type field which reports which upper layer is to receive the data

or 4) 802.3 frames also have a 2 bot field- but it is a Length field which reports how many bits are in the message before the FCS (frame check sequence) then sometimes 5)optionally there could be an 802.2 LLC header which specifies which upper layer gets the info (cause 802.3 doesn’t have this info)

6)The DATA is the actual message

7) FCS which houses CRC (Cyclic Redundancy Check) checksum

LLC-makes sure the mach and physical layers are doing their jobs. It is a buffer between the upper and lower layers. It uses SSAP’s (Source Service Access Points) and DSAP’s (Destination Service Access Points) to help lower layers communicate with the Network layer. Gives MAC layer instructions on what to do with the data- act as pointers to upper layers. 802.3 can not handle SSAPs or DSAPs- this is what the 802.2 field does.

LLC is responsible for timing, flow control and some protocol stacks.

MAC- Is responsible for framing builds frames from 1’s and 0’s It checks CRC It determines if the hardware address matches or not. If it does it sends it to LLC.

Also responsible for MEDIA ACCESS interacts between NIC and NIC driver)

WAN Datalink Protocols (encapsulation methods) layers describe how frames are carried over single datalink- including protocols

Synchronous Encapsulation includes:

Physical- layer 1- 2 responsibilities- sends bits receives bits.

State Transitions = changes in voltage. This is where the DCE is the (Data Circuit -Terminating Equipment ) is located at the provider on physical layer and DTE (data terminal equipment) is accessed is an attached device. And accessed thru a modem or CSU/DSU

Flow control- sends message when receiving entities buffers are full

Acknowledgement- confirms receipt ACK

Windowing- the number of data segments can be sent before an ack is received

Each layer encapsulates the layer above

1. user information converted to data (application to presentation)
2. data converted to segments (presentation to session/transport) (transpot layer handles segments)
3. segments converted to packets or datagrams (session/transport to network)
4. packets or datagrams are converted to frames (network to datalink)
5. frames are converted to bits (data link to physical)

Bridge: regenerate signal like repeater but can read and filter Mac address. Can cause broadcast storms.

Hubs: are concentrators. They are multiple port repeaters

Switch: can run in full duplex (hubs cant) the switch is a hub with a brain – it keeps a routing table of mac addresses.

Routers: are badder bridges. Read and filter IP and Mac addresses (network ids).

Gateways: are software interpreters.

CSU/DSU channel servie units/data service units: customer premise equipment (CPE) terminate the digital signal at the CP. They connect to the CO – central office – which is the switch at the telco.

Communication Servers: dial in servers like as5200

Multiplexors: allows more than one signal to be sent simultaneously over one line or circuit (channelizer?) called mux

OSI= Open Systems Interconnection ISO= International Standards Org

Connection orientated transmissions: 1)connection agreement segment is a request for synchronization 2) 2^nd and 3^rd segment ach the request and establish a connection parameter between hosts 3) final segment is ack also. It notifies the other host the connection agreement is accepted and a connection has been created. Data begins to flow now.

802.3 – created by DIX- uses CSMA/CD datalink and physical layers

Ethernet II has 2 bit type id – total of 8 bit header

802.2 has 2 bit type- bus – total of 8 bit header

802.3 has 2 bit length – bus – tota of 8 bit header

802.5 has 4 bit – star – 8 bit header. Uses Letters

ATM has 53 bit fixed length – ITU-I

FDDI – has 12 4bit symbols to designate the MAC address

Describe advantages of LAN segmentation- fewer users on a segment equla less traffic=better performance

Describe LAN segmentation using Bridge- bridges keep host addreses in their table if a message is received destined for an unknown host it broadcasts on all

Describe LAN segmentation with Routers- routers work at the network layer and keep routing tables of best paths to destination based on network address- higher overhead – filtering available

Describe benefits of network segmentation using routers- can filter

Describe LAN segmentation using Switches- faster full duplex available- smaller number of users per segment and faster forwarding increase perfomrance- keep a table of mac addresses

Cut through- reads the header and begins to send

Store - and – Forward- waits for entire frame and then sends

Describe full and half duplex Ethernet operation- full duplex allows for simultaneous transmission between receiver and transmitter doubling the amount of data that can be transferred- half duplex is like a speaker phone only one host can talk at a time

Describe network congestion and problems in Ethernet networks- broadcasts and high traffic create latency – or slowing of network

100BaseT Fast Ethernet- defines the Physical and Data Link Layers. Uses CSMA?CD- 10 times faster that 10BaseT. Use same time slots at 10mbps – meaning a station must transmit all data before another station can transmit. The distance is reduced. Regular Ethernet has 5-4-3 rule 5segments, 4 repeaters and 3 populated segments. With fats Ethernet you can use only two repeaters. The max frame size is 1518bytes (which is also the time slot) round trip can not exceed 512 which is why distance is reduced.

Can use traditional repeater at 140 bit times

Class 2 repeater has 92 bit times.

100BaseTX CAT 5 with RJ45 can go 100Meters

100BaseFX 50/125 or 62.5/125 with connector SC/ST/MIC can fo 412 meters

Medium UTP can go 200 meters with a repeater

Advantages-can migrate gradually. While migrating can use existing cabling and equipment. Can use 10Mbps and100Mbps together, uses tried and true CSMD/CD, migration is easy.

100BaseFX – fiber over 100Mbps-802.3 spec. uses two strand 50/125 or 62/125 micron multimode fiber.

100BaseT4-802.3 spec. 100Mbps over cat 3,4,5 w) standard rj45connecotr

100BaseTX- cat 5 uses two pair STP (shielded twisted pair) or type 1STP

100BaseX- refers to 100BaseTX or 100BaseFX approved compatible with Ethernet csma/cd and ANSI x3t9.5

100VGAnylan- for fast Ethernet or token ring- Cisco does not support.

Cut through – sends as soon as header is read.

Store and forward- waits for entire packet- holds in buffer then sends- higher latency

Describe the operation of Spanning tree Protocol and it benefits. Spanning tree protocols reduces looping by finding duplicate paths and blocking the least desirable

Describe the benefits of VLAN- allows for greater flexibility in creation of work groups- adds security and micro segments workgroups.

LLC uses Source Service Access points (SSAPs) – it points to the higher layer requesting the info

Destination Service Access Points – helps lower layers communicate with the network layer

802.3 can not handle DSAP and SSAP

802.2 frame handles DSAP AND SSAP

LLC is responsible for timing flow control and some

protocol stacks

MAC – uses FRAMES- builds them from 1 and 0’s

Presentation-

Session-

Transport-

Network-

DataLink

Physical-

Connection oriented services receive ack- connectionless let upper layer protocols worry about

what information has been received.

Data Link addresses are physical addresses or hardware addresses and network addresses are logical addresses.

1.a change to one layer does not effect all the others

2.defines the needs of what should happen- not the how

3.helps with troubleshooting.

1. user information converted to data

2. data is converted to segments

3. segments are converted to packets or datagrams

4. packets or datagrams are converted to frames (data link)

5. frames are converted to bits.

Flow control is keeping the receiving device from being overwhelmed by data-the reciver sends a message saying its buffer is full

Tcp – transport layer handles-Acknowledgement- confirms receipt ACK

Windowing- the number of data segments can be sent before an ack is received

For routers – they use ICMP (Internet Control Message Protocol) quench messages asking for info to be throttled back this works on the network layer

8) Differentiate between the following WAN services: Frame Relay, ISDN/LAPD, HDLC, & Synchronous Encapsulation includes:

PPP-successor of SLIP- provides router to router and host to network connection via synchronous and asynchronous communications. Works with IO, IPX ARA. It has built in security like CHAP and PAP. It relies on LCP and NCP

LCP-Link Control Protocol- establishes, configures and tests data link connections- compression of data.

NCP-Network Control Program-in SNA routes and controls flow of data between controller and other resources. In PPP a series of protocols for establishing and configuring Network layer protocols – like AppleTalk

Frame Relay-industry standard- switched Data Link layer protocol that handles multiple virtual circuits using HDLC encapsulation

ISDN-integrated services digital network- BRI, PRI, BISDN, N-ISDN

HDLC-High Level Data Link Control. Bit oriented synchronous Data Link Protocol. Developped by ISO- uses frame characters and checksums

Most popular-bandwitdht on demand. Operates at the physical and data link layers.

CIR- Committed Information Rate- buying a pre-designated amt of bandwidth

It interfaces between DTEs (Data Terminal Equipment) connect user end devices thru DCEs

(Like modems ) includes computers, protocol translators, and muliplexors

DCE=Data communications equipment- or data terminating equipment (depending on the standard)- provides a physical connection to the network. Forwards traffic and provides clocking signal used to synch dte and dce

Frame relay is connection oriented at data link layer by using virtual circuits.- it is a logical circuit between two DTE across a PSN (public switched network)

DLCI-is a data link identifier assigned by telco. Can be mulitpoint – ip addresses are mapped to dlci’s the dlci’s have global and local meanings – so two sites can refer to the same circuit with a different id

TO Configure:

This configuration would selct the default cisco config – if you want to use IETF you would need to type it at the end. Can only use cisco is connecting two cisco devices.

To add the DLCI

LMI-designed by gang of 4= Local Management Interface - tells info about dlci values- global or local significance- and status of circuit. Is an enhancement of CCIT- there are 3 kinds Cisco is default- check with provider to see which one is best- ANSI, ITU_T or CISCO

Subinterfaces-you can have multiple virtual circuits on single interface- you can assign different network layer characterisitics to different subinterfaces. Like routing ipx on one and ip on another.

There are two kinds

Point-to_Point and Multi-Point- use multipoint when the router is the center of a star.

To configure

Mapping- for IP or IPX to recognize the devices and communicate across wan the addresses must be mapped to the DLCI’s- there are two ways to do this:

1 use frame relay map command

2. use inverse-arp function

to configure using map command:

frame-relay map ip 172.16.30.17 30 cisco broadcast (cisco encapsulation)

frame-relay map ip 172.16.30.18 50 broadcast (says forward brdcsts to virtual circuit)

(the 30, 50 and 40 are dlci numbers) mapping is the only way to mix encapsulation types between cisco and ietf

to use inverse-arp:

this is easier but not reliable.

Monitoring-

Shows staus if interfaces and pvc at one time

Will show lmi traffic.

To configure

Two b channels and a d – the d channel sends control messages

< ^ > v CTL +

Mdod #

First octet in hex is network id- the last part of the

net number is a unique node number sometimes based on

hardware address

Solves congestion problems- better allocation of bandwidth.

Breaks up collision domains by decreasing the number of workstations on same physical segment.

Builds dynamic forward table of mac addresses

Work at Network layer- makes more manageable, increased functionality, multiple active paths, more complex

49) Describe LAN segmentation using switches. Provide dedicated ppp packet switched connections – allows for simulations switching increases amount of bandwidth to each client

Cut through – sends as soon as header is read.

Store and forward- waits for entire packet- holds in buffer then sends- higher latency

Full duplex is when there is or can be a simultaneous exchange of data- a half duplex is like a speaker phone- one at a time.

Bridges work at the MAC layer creating physical and

logical network segments. – assures reliability,

scalability, and manageability

Up to 10 times as fast as regular ethernet

Dynamically works around loops. Bridges exchange BPDU (bridge protocol data unit)-

protocol sends hello packets at configurable intervals) information to find multiple paths to same

destination and shut down bridge interfaces. Stops looping

Group of devices on one or more LAN using management software so they can interact and communicate as if they were on the same wire segment. They are based on Logical connections instead of Physical. This is a switch technology.

Simplify moves, adds and changes-

Reduce admin costs-

Better control of broadcasts-

Tighetn network security-

Micro-segment with scalability-

Distribute traffic load-

Reloacate server into secured locations-

Data link layer address required for every device on a LAN. Used to locate ports on the network- create and update routing tables and data structures. They are 6 bits long and controlled by IEEE. Known as hardware address. Mac Address and physical address

Bit sync is handled at physical layer

The Data Link Layer organizes the 1 and 0 into logical groups

Transport layer hides the network dependent calls from upper layers. It is also responsible for multiplexing, session establishment and tear down of virtual circuits

Application layer identifies ad establishes availability of intended comm partners. Sync’s sending and receiving applications.- checks for sufficient resources