CCNP Advance EIGRP Features

Route summarization
EIGRP has the ability to auto summarize networks. However, if the networks are limited, you may want to disable automatic summarization. In order to do this enter the following command:
Router(config) # no auto-summary.
The limitation with auto summarization is that EIGRP is only capable of summarizing networks which are part of the network. Therefore, for these cases you have to input an auto summarization which the following command:

ip summary-address eigrp 100
subnet

Load balancing in Equal Cost Path

In an equal cost path, the links in the network have are symmetric which means they use the same circuit type and the same same bandwidth capacity, so the same cost is assigned to the each link.
Since both link have the same distance as well, the metrics for its destination is available, through these links which are equal. When EIGRP chooses the successor route, it wants to choose a link which is at the lowest cost. When it sees that the 2 path ways have the same metric then it chooses them as its successors. After this EIGRP will then be able to share the traffic loads across the multiple links, which is known as load balancing.

Load Balancing in Unequal Cost Path
Unequal cost load balancing is when traffic across multiple routes is balanced withing different metric routes. This load balance is done through the variance command.

Router(config-router) #
variance multiplier
In load balancing, the multiplier parameter the values from 1-128 are used. 1 is the default value where there is an equal cost for load balancing


Suppose we have a network with 3 path way
Path 1 has a metric of 10
Path 2 has a metric of 15
Path 3 has a metric of 30
The path which will be selected will be the first path since the metric is lowest in path 1. With EIGRP you have to select that path, and configure it with a variance of 2.
Once you multiply by path and variance then you will get a minimum variance of 20.
10 metric * 2 variance value = 20 minimum metric
EIGRP will includes all routes that have a metric of less than 20 and satisfy the workable condition. EIGRP will take both path one and two since their metric distance is less than 20. The 3rd path will not be taken since 20< 25.
Therefore, the load balancing will occur between path one and path two.
Bandwidth Utilization

Bandwidth needs to saved within networks, so the network performance can be enhanced. By default EIGRP is set to use up to 50 % of bandwidth within an interface for routing traffic. However, this can be changed by using the following command:
ip bandwidth-percent eigrp as-number percentage the as number is AS number and percent is percentage you want to input.

When configuring multipoint interfacess such as Frame Relay it is important to to set the bandwidth to equal to share it across the neighbors.

CCNP Basic EIGRP commands

The EIGRP process is identified by an autonomous system number. If the autonomous system numbers are the same within the routing domain, the routers will be able to exchange information. Otherwise, if the autonomous system numbers do not match then the routers will not be able to exchange information.

To Enable EIGRP the following command needs to be entered

Router (config) #
router eigrp autonomous-system-number

ie router eigrp 10

Next the network need to inputted

Router (config) #
network network number [wildcard mask]
i.e network 172.16.0.0 0.0.0.255
network 172.16.1.0 0.0.0.255

*A wildcard mask is used to connect a router to external router which is outside the autonomous system.



Next the bandwidth need to be set up. By default it is set at the speed of T1
If there are serial links then the bandwidth needs to be set up. The bandwidth is measure in kbps.


Router (config) #
bandwidth kilobytes


EIGRP default route can be enabled with the following command.

ip default-network ip address



Troubleshooting.

show – the show command can be used to trouble shoot

show ip eigrp neighbors

This command shows you if the neighbors within the routers are recognized



show ip route eigrp

shows all EIGRP routes


show ip protocols
shows all dynamic routing protocols enabled on the router

show ip eigrp interfaces
Thie command shows all the interfaces configured for EIGRP.

Fast Ethernet
Fa0/0
Serial
S0/0


show ip eigrp topology

This shows the status of the network.
P (passive) – Network is available
A(active) - Network is not available
U(update) Network is being updated
Q(Query) Requesting information from a neighbor
R(reply) Got a reply or needs a reply
S(struck in active status) There is a problem with the network


show ip eigrp traffic
To see if the packets are sent or received



For more options you can put a question mark after the show command

show ?

CCNP EIGRP Components

EIGRP Tables
DUAL uses the EIGRP tables, which are provided. Within the EIGRP tables you will find a neighbor table, a topology table and a routing table.

Here are functions each table performs.
Neighbours Table - shows all neighbours adjacent to router
Topology Table - shows all route entries learned by the router
Routing Table – shows the best route to get to other points on the network


EIGRP Packets

Uses Five Packet Types

Hello
Check if the neighbor is up
Update
Used to send routing updates
Query
Finds out information from neighbors regarding routing updates
Reply
This is where the neighbors give a response
Acknowledgement
If you send a message, it must be acknowledged by the person who receives it. This packet is used to acknowledge a reliable packet.
The above are five main packets EIGRP uses. However, EIGRP can also use a packet called request.

Request – This packet is used to get information for a specific route. The information is received from one or more neighbors. Therefore the methods to send a request can either be through a unicast or a multicast process.




EIGRP Metric
EIGRP uses the metric component.
Metric is a Calculation done by the Routing protocol to determine the best path through a network. Since EIGRP uses 32 bits for its calculation it is metric is multiplied by 256. Metric consists of 5 components which are bandwidth, delay, reliability, loading, MTU.

EIGRP Metric Calculation
Metric = bandwidth + delay

EIGRP uses two of the components of metric which are bandwidth and delay. In the bandwidth, the measurement is based on the smallest amount of consumed data between the source and destination. In delay the delays in the path is measured.

CCNP EIGRP Fundamentals

Enhanced Interior Gateway Routing Protocol (EIGRP) is an advanced distance vector protocol. However, it also has a hybrid routing protocol capability since it combines the best of a distance vector protocol with link state algorithms by using partial updates and neighbor discovery. From other distance vector protocols it offers improvements such as reduction of bandwidth use, fast convergence, support for classless subnets which use CIDR and VLSM, and support for multiple routed protocols like Apple Talk, IP and IPX.


Among the key feature of EIGRP the following are included:
1)Fast Convergence
2)VLSM Subnetting
3)Partial Update
4)Multiple Network Layer Protocol Support

Fast Convergence: EIGRP stores its neighbours routing table so it can take alternatives routes if it original route is gone. Also, it has the ability to ask its neighbours for alternative routes if needed.

VLSM Support: EIGRP uses classless subnets within it routing network. For classful major networks it automatically summarizes routes on the attached interfaces. EIGRP also support manual summarization, and for this it uses VLSM to force a summary route from an interface.

Partial Updates: Partial Updates contain information about the change routes, and they are sent when route need a change in its metric or path. They are handled by multicast or unicast packet instead of broadcast packets since it reduces the use of bandwidth.

Multiple Network Layer Protocol: EIGRP can support IP, IPX, and AppleTalk routed protocols which enable EIGRP to have good stability and high performance networks.


EIGRP has four unique key components.

1. Protocol-dependent modules: Responsible for requirements within the network layer protocols.
2. Reliable Transport Protocol (RTP) : Support Unicast and Multicast transmission. RTP's main role is to guarantee a a timely, reliable and efficiently. EIGRP reliable transport protocol (RTP) guarantees timely, reliable, and efficient exchange of routing data between EIGRP neighbours.
3. Neighbor Discovery and Recovery: Discovery and Recovery allow routers about the other routers that are attached on the network neighbor discovery and recovery enables routers to dynamically learn about other routers on their directly attached network . It does this by allowing EIGRP to build a neighbor table which shows all neighbors adjacent to the router, to a topology table which discovers routes and routing table which choses the best path.
   

4. Diffusing Update Algorithm (DUAL): DUAL is the heart of EIGRP. It relies on
protocols and data structures to provide all the routers in a network to lead up to the final route.

Reported Distance & Feasible Distance

Feasible Distance: The total path between a router and the next closest router + Sum of all cost.

Reported Distance is the distance (metric) towards a destination as advertised by an upstream neighbour.
Reported distance is the distance reported in the queries, the replies and the updates.
Reported Distance: The total path between a router and the next closest router

OSPF

• Dynamic Routing Protocol for IP Networks
• Link State Protocol
• Group of Interior Gateway Protocol
• Operates withing a single Autonomous System
• Conifgured with Wildcard Mask
• Process ID - Uses Dijkstra’s algorithm
• Network Types – point to point, and routers that are directly connected

RIPv2

• Distance Vector Protocol
• Supports classless routing protocol
• Authentication option available
• Uses multicast addresses in sending updates
• Sends subnet information in RIP header
• Supports authentication

Router Memory

RAM: The RAM stores the OS, running config file, IP routing table, Arp cache and packet buffer

ROM: Permanent storage – Scaled down version of IOS, Basic software

Flash Memory: Permanent storage of for OS, Cisco IOS

NVRAM: Used as permanent storage for startup config files.

3 Configuration Registry

0 * 2142 For password recovery.
0 * 2102 The default. Router looks for config file in NVRAM and for a valid IOS image.
0 * 2100 Router boots into ROM monitor mode.

4 types of Timers

Update timer: 90 seconds

Invalid timer: 270 seconds

Hold down timer: 180 seconds

Flush timer: 630 seconds

Feasible Distance & Successors

Feasible Distance: The total path between a router and the next closest router + Cost.
Successors is a neighboring router that has a least cost path to a destination.

5 types of LSP packets

1)hello (checks if neighbour is up)
2)Database Description (synchronize databases in the beginning)
3)Link State Request (Request Specific LSA)
4) Link State Update (LSA flooded)
5) Link State Acknowledgement (flooded LSA’s are exploited acknowledged reliable flooding)

Difference Between Reported Distance and Administrative Distance

Reported Distance is the distance (metric) towards a destination as advertised by an upstream neighbour. Reported distance is the distance reported in the queries, the replies and the updates.
Reported Distance → The total path between a router and the next closest router.

Admistrative Distance is a measure of the trustworthiness of the source of the routing information.

Roles Of A Router

DR – reduces the number of adjacencies required on a multi-access network, which in turn reduces the amongst of routing traffic and the size of the topological database.

BDR - A router that becomes the designated router if the designated router fails

DROther - The router with the highest priority becomes the designated router (DR). If the priorities are the same, then the router with the highest router ID becomes the DR. By default, priorities are set to 1. A router with a priority of 0 never becomes a DR or a backup designated router (BDR); it is always a DROTHER, meaning a router that is neither the DR or the BDR.

How is a router id assigned ?

The router-id is chosen based on the highest IP address present on the router. If a loopback interface is present, the loopback IP will be used. If more than one loopback interface is present, the highest loopback IP will be used.

What are Hello Packets used for ?

• To discover OSPF neighbours and establish neighbour adjacency.
• Advertise parameters on which two routers must agree to become neighbours.
• Elect DR and BDR on multi access networks

Difference between Metric and Administrative Distance ?

Administrative Distance determines what priority will be given to each Routing protocol redirected through a router.
Metric is a Calculation done by the Routing protocol to determine the best path through a network.

EIGRP Tables

Neighbours Table - shows all neighbours adjacent to router

Topology Table - shows all route entries learned by the router

Routing Table – shows the best route to get to other points on the network

OSPF Tables

Neighbours Table - shows all neighbours adjacent to router.

Topology Table - shows all route entries learned by the router.

Routing Table – shows the best route to get to other points on the network.

What makes EIGRP unique ?

• Uses Diffused Update algorithm (DUAL) for all route computation
• Uses multicast and unicast for sending packets
• Administrative Distance for Internal router is 90
• Administrative Distance for External router is 170

Link State vs Distance Vector Protocol

Link state transmits data based on the speed of the WAN link.
Distance Vector transmits data based on the cost of the link (usually based on hop count).

If start up config is not found in the RAM memory what does it do ?

It searches the NVRAM where all the it is permanently stored!

DR Selection Process

OSPF chooses the designated router (DR) on a LAN as the device that has the highest IP address. If routers are added or removed from the LAN, or if a router gains an interface with a higher address than that of the existing DR, the DR likely will change if the DR or backup designated router (BDR) fails.

Routing Table

A routing table contains the information necessary to forward a packet along the best path toward its destination. Each packet contains information about its origin and destination. When a packet is received, a network device examines the packet and matches it to the routing table entry providing the best match for its destination. The table then provides the device with instructions for sending the packet to the next hop on its route across the network.

A basic routing table includes the following information:

Destination: The IP address of the packet's final destination
Next hop: The IP address to which the packet is forwarded
Interface: The outgoing network interface the device should use when forwarding the packet to the next hop or final destination

Metric: Assigns a cost to each available route so that the most cost-effective path can be chosen

Routes: Includes directly-attached subnets, indirect subnets that are not attached to the device but can be accessed through one or more hops, and default routes to use for certain types of traffic or when information is lacking.

If the IOS fails what does it do ?

If the IOS fails what does it do ?

IOS is stored in flash memory or TFTP. It is then loaded into the RAM. If a full IOS image cannot be located, a scaled down version of the IOS is copied from ROM into Ram.

Routers

Layer 3 Routing

• Single broadcast domain per interface
• Every router is its own broadcast domain
• ACLs can be applied between segments

Issues

• High per-port cost
• Layer 3 processing required
• High latency over layer 2 switching
• Layers 3 processing happens in software

Nonhierchical Networks Issues

What wrong with Nonhierchical Networks ?

They have:

• Large collision domain
• Large broadcast domain
• High Latency- There is high latency because everyone of the repeaters is repeating the same packet

• Difficult to troubleshoot

Intelligent Information Network CCNP Module 1

IIN (Intelligent Information Network)

Integrates Network resources and information assets

Three phases in building in IIN are

1) Integrated Transport- All traffic which includes voice, data and video is put together into one IP address, so data which is sent can be secured on the network.

2) Integrated Services- After all the network resources have been gathered, the resources can be shared across the network.

3) Integrated Applications-In the third phase, the networks make the application active, so network capablities such load balancing, application level security, content caching makes the delievery and performnce more efficient for the users.

Network Topologies

BUS - All devices are connected to a central cable. Bus networks are relatively inexpensive and easy to install for small networks. Ethernet systems use a bus topology.
RING - All devices are connected to one another in the shape of a closed loop, so that each device is connected directly to two other devices, one on either side of it. Ring topologies are relatively expensive and difficult to install, but they offer high bandwidth and can span large distances.
STAR - All All devices are connected to a central hub. Star networks are relatively easy to install and manage, but bottlenecks can occur because all data must pass through the hub.
MESH - Devices are connected with many redundant interconnections between network nodes. In a true mesh topology every node has a connection to every other node in the network.
TREE TOPOLOGY - A tree topology combines characteristics of linear bus and star topologies. It consists of groups of star-configured workstations connected to a linear bus backbone cable.

Switch

A switch is a device that channels incoming data from any of multiple input ports to a specific output port. It then takes the data and sends it toward its destination. A switch operates at layer 2 or Data Link layer of the OSI model. At layers 2 it looks at each packet, and from the MAC address it determines which device the data unit is intended for. Then with this information the switch sends data it towards the devide's destination.

Layers 2 switching

• Hardware based bridging
• Wire-speed performance
• Collision domain per port
• Traffic containment based on Mac Address

Issues

• No traffic based on Mac address
• Can’t restrict where traffic can go
• No traffic between VLANs
• Unbounded Broadcast domain
• Servers are not centrally located

Bridges

A Bridge is a device that connects two local-area networks (LANs), or two segments of the same LAN. Unlike a router, bridges are protocol independent. They simply forward packets without analyzing and re-routing messages. Bridging occurs at layer 2 of the OSI model which is the data link layer. This means a bridge cannot read IP addresses, but only the outermost hardware address of a packet.

Hubs

A hub is a basic networking device that connects multiple computers and/or devices together. They work at the physical layer (layer 1) of the OSI model.

Repeaters

Repeaters are used to increase the signal's strength so it can be transmitted and received over a greater distance without a loss in quality. These devices are used with networks to help the lines running between network devices to reach greater distances. Repeaters operate at the first layer of the OSI model which is the physical layer.

Packet switching vs Circuit Switching

There are two ways you can transfer videos:
a)Packet Switching
Where content is streamed through packets.
The transfer rate of data differs depending on your location.
b) Circuit Switching
The transfer of a video is done through a voice path. You cannot store it, or tap it like you can do with packet.
The rate of transfer is constant which is at 64kb.

VTP Modes Summarized

Here is an excellent clip which summarizes the VTP modes which are server, client and transparent.

PPP, PAP and CHAP

PPP
PPP is common encapsulation type, which supports TCP/IP, AppleTalk and IPX.
It works at the data link layer of the OSI model to encapsulate data over a point-to-point connection.
PPP breaks down into three primary pieces:
NCP (Network Control Protocol)
THE NCP identifies which network layer protocol the data pertains to.
LCP (Link Control Protocol)
Used for establishing, authenticating and maintaining a connection
HDLC Used to encapsulate information


At the Physical layer, the PPP configure a range of interfaces, including:

• Asynchronous serial
• Synchronous serial
• HSSI
• ISDN

PPP operates across any DTE/DCE interface (RS-232-C, RS-422, RS-423, or V.35)

PAP and CHAP are authentication methods of PPP.

PAP
Provides a simple method for a remote node to establish its by using a two way handshake.
When the authentication is used to login the information is send as one LCP package. After the authentication is received the server either allows or denies it entry. PAP’s authentication method is vulnerable to eavesdroppers, since they can obtain the password by listening in on the serial line, and by using repeated trial and error attacks.

CHAP
In CHAP authentication , the server sends a randomly generated “challenge” string to the client, along with its hostname. The client uses the hostname to look up the appropriate secret, combines it with the challenge, and encrypts the string using a one-way hashing function. The result is returned to the server along with the client's hostname. The server now performs the same computation, and acknowledges the client if it arrives at the same result.

Hierarchical Network Design

Hierarchical Network Design
Involves dividing the network into separate layers. This way the network design becomes modular and it improves its performance and scalability. The hierarchical network design is broken down into 3 layers which are access, distribution and core layer.

Access Layer
The access layer purpose is provide a way to connect devices to the network and also control which of these devices should have control on a network. The access layer deals with end devices such PCs, printers, and IP phones to enable them to access the network. It can also include devices such as routers, switches, and hubs and wireless access points.


Distribution Layer

The Distribution Layer deals with the connection point between the core and access layers. It includes LAN-based routers and Layer 3 switches. The layer ensures that packets are properly routed between
Subnets and VLANs.

Core Layer
is the high-speed backbone of the internetwork. This layers main concern is speed. It might also do QoS on if its required on the Network.


There are many benefits associated with Network designs
Scalability
Hierarchical network can be expanded easily

Redundancy
At the core and distribution layers path availability is ensured

Performance
Performance is enhanced since the transmission of data low performing devices is avoided.

Security
Security is improved because of the port security set up at the access level and the policies which are enabled at the distribution level.

Manageability
Consistency between switches at each level management more simple.

Maintainability
The modularity of hierarchical design allows for network to scale without becoming Overly complicated.

What is VTP ?

VTP
VTP stands for vlan trunking protocol, and its used to automatically update and configure swtiches on VLAN configuration. VTP maintains a VLAN configuration consistency by managing the addition, deletion, and renaming of VLANs across multiple Cisco switches in a network.

VTP has three modes. These mode are:

1)VTP mode server
2)VTP mode client
3)VTP mode transparent

VTP Mode (server/client/mode)

Server
VTP server transits all configurations to other switches in the network. In this mode you can create, modify, and delete VLANs. Server advertise their VLAN configuration to other switches in the same VTP domain.

Client
VTP mode client cannot create, modify, of delete vlans from the network. You can only receive VLAN information and advertise to others.

Transparent
Transparent is used for local VLAN that other switches do not have access to. The Transparent switches forward VTP advertisements to VTP clients and VTP servers.

Other VTP components

VTP Domain-Consists of one or more interconnected switches. VTP allows you to separate your network into smaller management domains to help reduce VLAN management. On top of that it limits the extent to which configuration changes are propagated in the network if an error occurs.

VTP Advertisements-VTP uses a hierarchy of advertisements to distribute and synchronize VLAN configurations across the network.

VTP Frame
A VTP frame consists of a header field and a message field. The information is inserted into
a header field and an Ethernet frame. The Ethernet frame is then encapsulated as 802.1Q trunk.

In the VTP header field the following information is found
Domain name – identifies the domain in the switch
Version – What VTP are set (ex.. VTP 1, VTP 2, VTP 3
Configuration Revision Number – The current configuration revision number on the swtich.

VTP Pruning
VTP Pruning works by restricting broadcast traffic to only those trunks links that must carry the traffic. Remember, by default, VTP pruning is disabled.
VTP version 2 features support for Token Rig, consistency check, unrecognized TLV support, version-independent and transparent mode.

Switching

Switching
Circuit Switching

Circuit Switching involves three different phases. These phases are known as circuit establishment, data transfer and Circuit disconnect.

Circuit Establishment
The circuit establishment is used to establish an end to end connection before the transfer of data. For the circuits segments there are two option. It can be dedicated link or it can be a shared link.


Data Transfer
Data is transferred from the source to the destination. The data can be either analog or digital, and the connection is a full duplex connection for the two stations that are connected.

Circuit Disconnect
Once the data transfer is complete and the circuit is disconnected which terminates the connection at data transfer.

PSTN and ISDN are two types of circuit-switching technology that may be used to implement a WAN in an enterprise setting.

Access Control List

An ACL is a sequential list of permit or deny statements that apply to addresses or upper-layer protocols. They provide a powerful way to control traffic into and out of your network. This control can be as simple as permitting or denying network hosts or addresses.

However, ACLs can also be configured to control network traffic based on the TCP port being used. The ACL extracts the information from the packet header, test it against its rules, and make "allow" or "deny" decisions based on:

1.) Source IP address

2.) Destination IP address

3) ICMP message type

The ACL can also extract upper layer information and test it against its rules. Upper layer information includes:

TCP/UDP source port and TCP/UDP destination port

Routers

An ACL is a router configuration script that uses packet filtering to control whether a router permits or denies packets to pass based on criteria found in the packet header. ACLs are also used for selecting types of traffic to be analyzed, forwarded, or processed in other ways. ACLs are among the most commonly used objects in Cisco IOS software.

ACLs perform the following tasks:

Limit network traffic to increase network performance. Any network which uses excessive bandwidth can be controled.

Provide traffic flow control. ACLs can restrict the delivery of routing updates. If updates are not required because of network conditions, bandwidth is preserved.

Provide a basic level of security for network access. ACLs can allow one host to access a part of the network and prevent another host from accessing the same area. For example, access to the Human Resources network can be restricted to select users.

Decide which types of traffic to forward or block at the router interfaces. For example, an ACL can permit e-mail traffic, but block all Telnet traffic.

Control which areas a client can access on a network.

ACLs define the set of rules that give added control for packets that enter inbound interfaces, packets that relay through the router, and packets that exit outbound interfaces of the router.

Configuration

ACLs are configured either to apply to inbound traffic or to apply to outbound traffic.

Inbound ACLs-Incoming packets are processed before they are routed to the outbound interface. An inbound ACL is efficient because it saves the overhead of routing lookups if the packet is discarded. If the packet is permitted by the tests, it is then processed for routing.

Outbound ACLs-Incoming packets are routed to the outbound interface, and then they are processed through the outbound ACL.

ACL statements operate in sequential order. They evaluate packets against the ACL, from the top down, one statement at a time.

There are different types of ACLs - standard, extended, named and numbered.

Standard ACLs

A standard ACL is a sequential collection of permit and deny conditions that apply to IP addresses.

It IP packets are filted based on source address only

ie access-list 10 permit 192.168.30. 0 0.0.0.255

Extended ACLs

Extended ACLs filter IP packets based on several attributes which are:

Source and destination IP address,

Source and destination TCP or UDP ports

Protocol type (IP, ICMP, UDP, TCP or protocol number)

access-list 103 permit tcp 192.168.30.0 0.0.0.255 any eq 80

List of ACL types and their ranges

ACL TYPE Range

Standard IP 1-99

Extended IP 100-199

Standard IPX 800-899

Extend IPX 900-999

SAP IPX 1000-1099

Time Division Multiplexing

TDM was invented so voice traffic that is carried over a medium can be maximized. For multiple signals to share a medium, the medium must be somehow divided. In TDM the users take turns, where each has a turn to have an exclusive use of the medium in a round robin fashion. TDM works under the physical layer, and it divides the bandwidth of a single link by separating channels or time slots. TDM transmits two or more channels over the same link by allocating a different time interval (time slot) for the transmission of each channel. The channels are each given a regular time slot in which they send a PCM signal. TDM increases the capacity of the transmission link by slicing time into smaller intervals so that the link carries the bits from multiple input sources, effectively increasing the number of bits transmitted per second. With TDM, the transmitter and the receiver both know exactly which signal is being sent.

TDM is used for digital signals or analog signals to carry digital data. The Data Rate of the transmission media has to exceeds the data rate of the signals for the TDM system to work. It also uses a frame where numbers of bits and bytes are put together to form one particular unit at in order to send data over.

An example of a technology that uses synchronous TDM is ISDN & SONET

Just like many technology out there TDM has its disadvantage. The disadvantage is that is a lot of bandwidth is wasted the TDM system is used.