BGP attribute for North-Bound Distribution of Traffic Engineering (TE) performance Metric
draft-wu-idr-te-pm-bgp-01

Abstract

In order to populate network performance information like link latency, latency variation and packet loss into Traffic Engineering Database(TED) and ALTO server, this document describes extensions to BGP protocol, that can be used to distribute network performance information (such as link delay, delay variation, packet loss, residual bandwidth, and available bandwidth, link utilization, channel throughput).

Status of This Memo

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Copyright Notice

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Table of Contents

• 1. Introduction
• 2. Conventions used in this document
• 3. Use Cases
• 3.1. MPLS-TE with PCE
• 3.2. ALTO Server Network API
• 4. Carrying TE Performance information in BGP
• 5. Attribute TLV Details
• 5.1. Link Utilization TLV
• 5.2. Channel Throughput TLV
• 6. Security Considerations
• 7. IANA Considerations
• 8. References
• 8.1. Normative References
• 8.2. Informative References
• Authors' Addresses

1. Introduction

As specified in [RFC4655],a Path Computation Element (PCE) is an entity that is capable of computing a network path or route based on a network graph, and of applying computational constraints during the computation In order to compute an end to end path, the PCE needs to have a unified view of the overall topology[I-D.ietf-pce-pcep-service-aware]. [I.D-ietf-idr-ls- distribution] describes a mechanism by which links state and traffic engineering information can be collected from networks and shared with external components using the BGP routing protocol. This mechanism can be used by both PCE and ALTO server to gather information about the topologies and capabilities of the network.

With the growth of network virtualization technology, the needs for inter-connection between various overlay technologies (e.g. Enterprise BGP/MPLS IP VPNs) in the Wide Area Network (WAN) become important. The Network performance or QoS requirements such as latency, limited bandwidth, packet loss, and jitter, are all critical factors that must be taken into account in the end to end path computation ([I-D.ietf-pce-pcep-service-aware])and selection to establish segment overlay tunnel between overlay nodes and stitch them together to compute end to end path.

In order to populate network performance information like link latency, latency variation and packet loss into TED and ALTO server, this document describes extensions to BGP protocol, that can be used to distribute network performance information (such as link delay, delay variation, packet loss, residual bandwidth, and available bandwidth,link utilization, channel throughput).

2. Conventions used in this document

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC2119 [RFC2119].

3. Use Cases

3.1. MPLS-TE with PCE

The following figure shows how a PCE can get its TE performance information beyond that contained in the LINK_STATE attributes [I.D-ietf-idr-ls-distribution] using the mechanism described in this document.

                +----------+                           +---------+        
                |  -----   |                           |   BGP   |        
                | | TED |<-+-------------------------->| Speaker |        
                |  -----   |   TED synchronization     |         |        
                |    |     |        mechanism:         +---------+        
                |    |     | BGP with TE performance                      
                |    v     |        NLRI                                  
                |  -----   |                                              
                | | PCE |  |                                              
                |  -----   |                                              
                +----------+                                              
                     ^                                                    
                     | Request/                                           
                     | Response                                           
                     v                                                    
       Service  +----------+   Signaling  +----------+                    
       Request  | Head-End |   Protocol   | Adjacent |                    
       -------->|  Node    |<------------>|   Node   |                    
                +----------+              +----------+                    
                                                                          
     Figure 1: External PCE node using a TED synchronization mechanism    

3.2. ALTO Server Network API

The following figure shows how an ALTO Server can get TE performance information from the underlying network beyond that contained in the LINK_STATE attributes [I.D-ietf-idr-ls-distribution] using the mechanism described in this document.

+--------+
| Client |<--+
+--------+   |
             |    ALTO    +--------+     BGP with    +---------+
+--------+   |  Protocol  |  ALTO  |  TE Performance |   BGP   |
| Client |<--+------------| Server |<----------------| Speaker |
+--------+   |            |        |      NLR        |         |
             |            +--------+                 +---------+
+--------+   |
| Client |<--+
+--------+
  Figure 2: ALTO Server using network performance information

4. Carrying TE Performance information in BGP

This document proposes new BGP TE performance TLVs that can be announced as attribute in the BGP-LS attribute (defined in [I.D-ietf-idr- ls-distribution]) to distribute network performance information. The extensions in this document build on the ones provided in BGP-LS [I.D -ietf-idr-ls-distribution] and BGP-4 [RFC4271].

BGP-LS attribute defined in [I.D-ietf-idr-ls-distribution] has nested TLVs which allow the BGP-LS attribute to be readily extended. This document proposes seven additional TLVs as its attributes:

   Type            Value

   TBD1        Unidirectional Link Delay

   TBD2        Unidirectional Delay Variation

   TBD3        Unidirectional Packet Loss

   TBD4        Unidirectional Residual Bandwidth

   TBD5        Unidirectional Available Bandwidth

   TBD6        Link Utilization 
      
   TBD7        Channel Throughput

As can be seen in the list above, the TLVs described in this document carry different types of network performance information. Many (but not all) of the TLVs include a bit called the Anomalous (or "A") bit. When the A bit is clear (or when the TLV does not include an A bit), the TLV describes steady state link performance. This information could conceivably be used to construct a steady state performance topology for initial tunnel path computation, or to verify alternative failover paths.

When network performance downgrades and falls below configurable link-local thresholds a TLV with the A bit set is advertised. These TLVs could be used by the receiving node to determine whether to redirect failing traffic to a backup path, or whether to calculate an entirely new path. If link performance improves later and exceeds a configurable minimum value (i.e.,threshold), that TLV can be re-advertised with the Anomalous bit cleared. In this case, a receiving node can conceivably do whatever re-optimization (or failback) it wishes to do (including nothing).

Note that when a TLV does not include the A bit, that sub-TLV cannot be used for failover purposes. The A bit was intentionally omitted from some TLVs to help mitigate oscillations.

Consistent with existing ISIS TE specifications [RFC5305][ISIS-TE-METRIC], the bandwidth advertisements defined in this document MUST be encoded as IEEE floating point values. The delay and delay variation advertisements defined in this draft MUST be encoded as integer values. Delay values MUST be quantified in units of microseconds, packet loss MUST be quantified as a percentage of packets sent, and bandwidth MUST be sent as bytes per second. All values (except residual bandwidth) MUST be calculated as rolling averages where the averaging period MUST be a configurable period of time.

5. Attribute TLV Details

Link attribute TLVs defined in section 3.2.2 of [I-D. ietf-idr-ls-distribution]are TLVs that may be encoded in the BGP-LS attribute with a link NLRI. Each 'Link Attribute' is a Type/Length/ Value (TLV) triplet formatted as defined in Section 3.1 of [I-D.ietf- idr-ls-distribution]. The format and semantics of the 'value' fields in some 'Link Attribute' TLVs correspond to the format and semantics of value fields in IS-IS Extended IS Reachability sub-TLVs, defined in [RFC5305]. Although the encodings for 'Link Attribute' TLVs were originally defined for IS-IS, the TLVs can carry data sourced either by IS-IS or OSPF.

   +------------+---------------------+--------------+-----------------+
   |  TLV Code  | Description         |     IS-IS    | Defined in:     |
   |    Point   |                     |  TLV/Sub-TLV |                 |
   +------------+---------------------+--------------+-----------------+
   |    xxxx    | Unidirectional      |    22/xx     | [ISIS-TE]/4.1   |
   |            | Link Delay          |              |                 |
   |            |                     |              |                 |
   |    xxxx    | Min/Max Unidirection|    22/xx     | [ISIS-TE]/4.2   |
   |            | Link Delay          |              |                 |
   |            |                     |              |                 |
   |    xxxx    | Unidirectional      |    22/xx     | [ISIS-TE]/4.3   |
   |            | Delay Variation     |              |                 |
   |            |                     |              |                 |
   |    xxxx    | Unidirectional      |    22/xx     | [ISIS-TE]/4.4   |
   |            | Link Loss           |              |                 |
   |            |                     |              |                 |
   |    xxxx    | Unidirectional      |    22/xx     | [ISIS-TE]/4.5   |
   |            |Residual Bandwidth   |              |                 |
   |            |                     |              |                 |
   |    xxxx    | Unidirectional      |    22/xx     | [ISIS-TE]/4.6   |
   |            |Available Bandwidth  |              |                 |
   |            |                     |              |                 |
   |    xxxx    | Link Utilization    |    ----      |  section 5.1    |
   |            |                     |              |                 |
   |    xxxx    | Channel Throughput  |    ----      |  section 5.2    |
   +------------+---------------------+--------------+-----------------+

                       Table 1: Link Attribute TLVs

The following 'Link Attribute' TLVs are valid in the LINK_STATE attribute:

5.1. Link Utilization TLV

This TLV advertises the average link utilization between two directly connected IS-IS neighbors. The link utilization advertised by this sub-TLV MUST be the utilization percentage per interval from the local neighbor to the remote one. The format of this sub-TLV is shown in the following diagram:

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                Type              |                  Length    | 
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
 |                          Link Utilization                     |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

     where:

   Type: TBA

   Length: 4

   Link Utilization.  This 24-bit field carries the average
   link untilization over a configurable interval. A commonly 
   used time interval is 5 minutes, and this interval has been
   sufficient to support network operations and design for some 
   time. link utilization can be calculated by counting the 
   IP-layer (or other layer) octets received over a time interval
   and dividing by the theoretical maximum number of octets that
   could have been delivered in the same interval(see section6.4
   of [RFC6703]). If there is no value to send (unmeasured and 
   not statically specified), then the sub-TLV should not be sent 
   or be withdrawn.

5.2. Channel Throughput TLV

This TLV advertises the average Channel Throughput between two directly connected IS-IS neighbors. The channel throughput advertised by this sub-TLV MUST be the throughput between the local neighbor and the remote one. The format of this sub-TLV is shown in the following diagram:

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                Type              |            Length          | 
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
 |                          Throughput Offered                   |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                          Throughput Delivered                 |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   where:

   Type: TBA

   Length: 8

   Throughput offered:  This 24-bit field carries the average 
   throughput offered over a configurable interval. Throughput 
   offered can be calculated by counting the number of
   units successfully transmitted in the interval 
   (See section 2.3 of [RFC6374)). If there is no value to 
   send (unmeasured and not statically specified), then 
   the sub-TLV should not be sent or be withdrawn.

Throughput delivered:  This 24-bit field carries the average 
   throughput delivered over a configurable interval. 
   Throughput delivered can be calculated by counting the 
   number of units successfully received in the interval
   (See section 2.3 of [RFC6374)). If there is no value 
   to send (unmeasured and not statically specified), 
   then the sub-TLV should not be sent or be withdrawn.

6. Security Considerations

This document does not introduce security issues beyond those discussed in [I.D-ietf-idr-ls-distribution] and [RFC4271].

7. IANA Considerations

IANA maintains the registry for the TLVs. BGP TE Performance TLV will require one new type code per TLV defined in this document.

8. References

8.1. Normative References

8.2. Informative References

Authors' Addresses