CSIS 4823 Data Communications Networking – Frame Relay and MPLS
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Transcript of CSIS 4823 Data Communications Networking – Frame Relay and MPLS
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CSIS 4823Data Communications
Networking – Frame Relay and MPLS
Mr. Mark Welton
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WAN transportation method that formats data into frames and sent over a network controlled by a service provider
Frame Relay is often represented in network diagrams with a cloud depiction, representing an unknown environment
Frame Relay uses VC (virtual circuits) through the cloud to allow delivery to endpoints
The endpoints appear as directly connected circuits
Frame Relay
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Two types of VCs◦ Permanent (PVC)
Circuit is always up Path is “hard coded” through the provider’s system
◦ Switched (SVC) Are on-demand circuits Path is created through the provider’s system when
used
Frame Relay
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Simple Frame Relay Network
Frame Relay
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Actual equipment involved in a frame relay network
Frame Relay
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Each VC is given a Layer-2 address called a Data Link Control Identifier (DLCI)
DLCIs are only visible to the customer and the service provider
Other customers of the service provider do not see the DLCIs or other customer data even though the Frame Relay network is shared
Frame Relay
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The primary benefits of Frame Relay are cost and flexibility
Dedicated point-to-point circuits (like T1s) are priced based on distance between the locations
Frame Relay is priced based on the components of the Frame Relay circuit
Frame Relay
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In order to provision a Frame Relay circuit four items are needed
These four items will impact the cost of the curcuit
Frame Relay
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Location for the circuit Port speed – is the physical size of the
circuit, such as a T1 or T3 CIR – Committed Information Rate
◦This is the guaranteed bandwidth allocated by the service provider in bps
Burst Rate – is the amount of additional bandwidth available on the port
Frame Relay
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Burst Rate – is the amount of additional bandwidth available on the port◦ Typically this is ordered at 2 times the CIR or
the full port speed◦ If the CIR is exceeded but not the burst rate the
frames are marked as Discard Eligible (DE)◦ This means that if the frame relay switch
becomes congested they will be dropped◦ If the frames exceed the burst rate they are
automatically dropped
Frame Relay
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Frame Relay
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Frame Relay allows for multiple links to multiple locations to terminate on the same physical circuit and router interface
common designs for frame relay◦ Hub and spoke◦ Partial mesh◦ Fully mesh
Frame Relay
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All circuits are terminated to a central location (usual the data center)
Branch sites can not communicate with each other without going through the central router
Design is commonly used when branches to not need to communication directly
Hub and Spoke
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Similar to spoke and hub but some branch site will also have circuits to each other
If two or more branch sites need to communicate to each other often a frame relay circuit is added directly between them
Partial mesh
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If an addition router was added to the right design and only had a circuit to router A I would consider it a partial mesh not spoke and hub
Spoke and Hub and Partial Mesh Design
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In a fully meshed design frame relay reduces the number of physical connections needed vs. connections like T1s
Fully Meshed Design
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To determine the number of links needed for a fully meshed network the formula N(N-1)/2 is used where N is the number of nodes (routers) in the network
How many links are needs for a network with three router for a fully meshed design?
Fully Meshed Design
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How many links are needs for a network with three router for a fully meshed design?
3(3-1)/2 = 3
Fully Meshed Design
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How many links are needs for a network with six router for a fully meshed design? 6(6-1)/2 = 15
Using T1s you would need 15 T1 In Frame Relay you would need 6 Frame
Relay circuits with 15 DLCIs
Fully Meshed Design
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Since multiple locations can terminate on the same physical circuit, oversubscription is possible
Oversubscription occurs when the amount of bandwidth provisioned in all the CIRs exceeds the port speed of the circuit
CIR cannot be guaranteed if it exceeds the amount of bandwidth physically available
Oversubscription
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LMI – (Local Management Interface) provides communication between the
Data Terminal Equipment (DTE) – or customer equipment like routers, and the
Data Communication Equipment (DCE) – or service provider equipment
LMI provides an exchange of status messages regarding the VCs
Frame Relay
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Three forms of LMI are available on Cisco equipment◦ Cisco◦ Ansi◦ Q933a
The DCE device determines the type of LMI used
Frame Relay
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Three statuses of PVCs◦ Active – normal good status for PVC◦ Inactive – indicates the service provider has
configured a PVC, but the customer equipment is not configured for that DLCI
◦ Deleted – indicates the customer equipment is configured for a DLCI, but the PVC does not exist from the service provider
Frame Relay
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Frame Relay networks will detect congestion and mark frames with Forward Explicit Congestion Notification (FECNs) and Backward Explicit Congestion Notifications (BECNs)
They are sent to the DTE equipment DTE equipment can adjust the flow of traffic
to reduce congestion on the network The DCE equipment does not perform flow
control for customers
Frame Relay
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The FECN bits are marked when congestion occurs
When FECN bits are seen in the frames, the BECN bits get marked
Now traffic leaving and coming from a Frame Relay switch is notified of the congestion
Frame Relay
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MPLS – Multi-Protocol Label Switching networks are another common WAN network
Like Frame Relay network diagrams represent them as a cloud
packets in an MPLS network are prefixed with an MPLS header (called a label stack)
The header contains one or more labels, a traffic-class field (used for quality of service [QoS]), a bottom-of-stack flag, and
an 8-bit time-to-live (TTL) field
MPLS
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The label stack is the only thing examined by the MPLS switches
no traditional routing table lookups are required, which in theory makes this a much faster solution than more traditional IP-based solutions
The MPLS header allows MPLS networks to be shared among multiple customers, without the customers seeing each other’s traffic
MPLS
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Multisite Frame Relay Design
Frame Relay follows the designed path of the PVC to each site
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MPLS Design
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From the telecom view MPLS uses switching in the cloud to move the data to the next hop
For the customer view an IP routing protocol provides a next hop for the destination IP address
traditional Interior Gateway Protocols (IGPs) like RIP, OSPF, and EIGRP do not work well over MPLS networks
BGP is the most common protocol in use to communicate to customer endpoints
How Does it Work?
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So MPLS is then a Layer-3 protocol, not really
So it must be Layer-2 protocol, not completely
It is like layer-2.5 If you could make Layer-2 that had routing
intelligence without the table overhead and processing delay and fixed problems small fixed cell size ATM adds you would be closer to MPLS
How Does it Work?