Multi Protocol Label Switching (MPLS) Lecture 9: Multi Protocol Label Switching (MPLS)

Forwarding Equivalence Classes FEC - group of IP packets forwarded over same path, with same forwarding treatment FEC may correspond to destination IP subnet source, destination IP subnet QoS class

Example Each FEC is associated with different label

Routing in MPLS Hop-by-hop routing: IP router learns about the topology of its domain by exchanging information with the other IP routers. It then calculates the next hop IP router for each destination using the shortest path algorithm. This next hop is stored in its FIB. MPLS uses the same next hop information in order to set up an LSP. Explicit routing: LSP that follows an explicit route through a network which might not necessarily correspond to the hop-by-hop path. An explicit route might be set up to satisfy a QoS criterion, such as minimizing the total end-to-end delay and maximizing throughput. Also, explicit routing can be used to provide load-balancing, by forcing some of the traffic to follow different paths through a network, so that the utilization of the network links is as even as possible. Finally, explicit routing can be used to set up MPLS-based tunnels and virtual private networks (VPN).

Label Distribution Protocols LDP: A new signaling protocol. It is used to distribute label bindings for an LSP associated with a FEC. RSVP: Extending of an existing IP control protocol, so that it can carry label bindings.

LDP LDP is used to establish and maintain label bindings for an LSP associated with a FEC. Two LSRs that use LDP to exchange label bindings are known as LDP peers. LDP provides several LDP messages: Discovery: to announce and maintain the presence of an LSR in the network. Session: in order for two LDP peers to exchange information, they have to first establish an LDP session. The session messages are used to establish, maintain, and terminate LDP sessions between LDP peers. Advertisement: to create, change, and delete label bindings to FECs. Notification: to provide advisory information and to signal error information. LDP runs on top of TCP for reliability, with the exception of the LDP discovery messages that run over UDP.

LDP label distribution always done from downstream to upstream downstream-unsolicited: new route => send new label downstream-on-demand: upstream LSR asks for label

LDP Label mapping message: An LSR uses the message to advertise a mapping (i.e., a binding) of a label to a FEC to its LDP peers. A FEC element could be either a prefix or a full IP address of a destination host The FEC element identifies a set of packets that can be mapped to the corresponding LSP. The message contains the label associated with the FEC.

LDP Label request message: LSR sends this message to an LPD peer to request a mapping to particular FEC under the following conditions: The LSR recognizes a new FEC via its forwarding routing table; the next hop is an LDP peer; and the LSR does not already have a mapping from the next hop for the given FEC. The next hop to the FEC changes, and the LSR does not already have a mapping from the next hop for the given FEC. The LSR receives a label request for a FEC from an upstream LDP peer; the FEC next hop is an LDP peer; and the LSR does not already have a mapping from the next hop. Label release message: Sent to an LDP peer LSR B to signal to LSR B that LSR A no longer needs a specific FEC-label mapping that was previously requested of and/or advertised by the peer.

Constraint-based Routing LDP It is used to set up a unidirectional point-to-point explicitly routed LSP. An LSP is set up as a result of the routing information in an IP network using the shortest path algorithm. A CR-LSP is calculated at the source LSR based on criteria not limited to routing information, such as explicit routing and QoS-based routing. The route then signaled to the other nodes along the path which obey the source’s routing instructions. CR-LDP is based on LDP, and runs on top of TCP for reliability.

CR-LSP Setup Procedure A CR-LSP is set up using downstream on demand allocation with ordered control. An upstream LSR obtains the label mapping by issuing a request. In the ordered control scheme, the allocation of labels proceeds backwards from the egress LSR towards the ingress LSR. Specifically, an LSR only binds a label to a FEC if it is the egress LSR for that FEC, or if it has already received a label binding for that FEC from its next hop LSR.

IntServ architecture The following two service classes were defined in IntServ: 1. Guaranteed service: firm bounds on the end-to-end queueing delay with no packet loss for all conforming packets. 2. Controlled-load service: provides the user with a QoS that closely approximates the QoS of the best effort service that the user would receive from an unloaded network. Specifically, a user might assume the following: a. A very high percentage of transmitted packets will be successfully delivered by the network to the receiver. The percentage of packets not successfully delivered must closely approximate the basic packet error rate of the transmission links. b. The end-to-end delay experienced by a very high percentage of the delivered packets will not greatly exceed the minimum end-to-end delay experienced by any successfully delivered packet.

IntServ architecture In intserv, the sender specifies how much traffic it will transmit to its receiver(s), and a receiver specifies how much traffic it can receive and the required QoS, expressed in terms of packet loss and end-to-end delay. This information permits each IP router along the path followed by the sender’s packets to perform the following functions: 1. Policing: This is used to verify that the traffic transmitted by the sender conforms to the sender’s Tspec, a set of traffic descriptors that characterize the traffic transmitted by the sender. 2. Admission control: decide whether an IP router has adequate resources to meet the requested QoS. 3. Classification: decide which IP packets should be considered as part of the sender’s traffic and be given the requested QoS. 4. Queueing and scheduling: in order for an IP router to provide different QoS to different receivers, it has to be able to queue packets into different queues and to transmit packets out of these queues according to a scheduler. The intserv architecture requires a signaling protocol for the reliable establishment and maintenance of resource reservations. RSVP is the most popular one.

Color Blind Policer There are two buckets. The size of the first one is CBS and the received packets in CIR and lower rate are stored in it. These packets are “green”. The size of the second one is PBS-CBS and the received packets greater than CIR rate are stored in it. These packets are “yellow”. If packet arrives and current rate is above PIR, then this is “red” packet and is typically dropped. Yellow packets are discard eligible: if there is no place in the queue they are dropped, while the green are not dropped.

Color Aware Policer The packets may arrive already colored. Then yellow packets will directly arrive to yellow bucket. The marking of color of the packet from hop to hop can be done using Differentiated Services Code Points Protocol (DSCP) or VLAN Discard Eligible bit (csf bit).

RSVP-Traffic Engineering is used in MPLS to set up LSPs using either the next hop information in the routing table or an explicit route. RSVP-TE uses downstream-on-demand label allocation to set up an LSP. RSVP-TE enables the reservation of resources along the LSP. For example, bandwidth can be allocated to an LSP using standard RSVP reservations.

Traffic Engineering configuring routes to traffic demands so as to improve user performance use network resources more efficiently operates at coarse timescales not for failures, sudden traffic changes uses shortest path computations OSPF, MPLS

The traffic parameters peak data rate (PDR) and peak burst size (PBS): PDR is the maximum rate at which traffic is sent to the CR-LDP. The peak rate in CR-LDP is specified in terms of token bucket P. The maximum token bucket size of P is set equal to the peak burst size (PBS), expressed in bytes, and the token bucket is replenished at the peak data rate (PDR), expressed in bytes/sec. committed data rate (CDR) and committed burst size (CBS): Same as above for token bucket. The output of this token bucket is referred to as the committed rate which is the amount of bandwidth the network should allocate for the CR-LSP. excess burst size (EBS): The max. token bucket can be EBS and replenishing rate is CDR.

Class of Service Packets that violate token bucket can either be dropped or marked.

Q: how to set link weights? Effect of link weights unit link weights local change to congested link global optimization to balance link utilizations

Generalized MPLS GMPLS is an extension of MPLS, and was designed to apply MPLS label-switching techniques to time-division multiplexing (TDM) networks and wavelength routing networks.