CSIS 4823 Data Communications Networking – Frame Relay and MPLS

1. CSIS 4823Data Communications Networking – Frame Relay and MPLS Mr. Mark Welton

2. Frame Relay • 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

3. Frame Relay • 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

4. Frame Relay • Simple Frame Relay Network

5. Frame Relay • Actual equipment involved in a frame relay network

6. Frame Relay • 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

7. Frame Relay • 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

8. Frame Relay • In order to provision a Frame Relay circuit four items are needed • These four items will impact the cost of the curcuit

9. Frame Relay • 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

10. Frame Relay • 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

11. Frame Relay

12. Frame Relay • 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

13. Hub and Spoke • 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

14. Partial mesh • 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

15. Spoke and Hub and Partial Mesh Design • 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

16. Fully Meshed Design • In a fully meshed design frame relay reduces the number of physical connections needed vs. connections like T1s

17. Fully Meshed Design • 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?

18. Fully Meshed Design • How many links are needs for a network with three router for a fully meshed design? • 3(3-1)/2 = 3

19. Fully Meshed Design • 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

20. Oversubscription • 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

21. Frame Relay • 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

22. Frame Relay • Three forms of LMI are available on Cisco equipment • Cisco • Ansi • Q933a • The DCE device determines the type of LMI used

23. Frame Relay • 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

24. Frame Relay • 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

25. Frame Relay • 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

26. MPLS • 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

27. MPLS • 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

28. Multisite Frame Relay Design Frame Relay follows the designed path of the PVC to each site

29. MPLS Design

30. How Does it Work? • 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

31. How Does it Work? • 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